LBBB with left axis differs mechanistically from LBBB with normal axis

 A paper by L. Sciarra et al  (1) presents evidence that LBBB with left axis deviation ( frontal plane axis between -30 and -90 degrees) differs in terms of the conduction sequence  and regional left ventricular contraction patterns. They argue that patterns differs from what is observed in LBBB with a normal axis and suggest that a different approach to CRT is indicated.

Normally, with intact left bundle branch conduction the interventricular septum is activated from left to right. In LBBB the septum is activated from right to left  In typical LBBB there is early activation and contraction of the septum with bulging of the left basal portion of the left ventricle which then contracts late causing a bulging of the septum. Because the lateral LV wall is the last segment to contract it has been thought best to place the coronary sinus lead in a vein draining that area of the heart to optimize CRT.

However, in LBBB with LAD the last segment to contract is the anterior wall of the LV suggesting optimal  CRT might be obtained by positioning the CS lead more anteriorly .

A sub analysis from the MADIT CRT trial found that LBBB plus LAD has an increase risk of Heart failure and death and a trend ( not stat significant ) toward less benefit from CRT.

Speculation - maybe CS leads were not in optimal location.

1) Sciarra, L et al Patients with left bundle branch block and left axis deviation show a specific left ventricular asynchrony pattern Implications for lft ventricular lead placement during CRT implantation.J Electrocardiology Mar-Apr 2018:51,(2) 175 

What does chronaxie have to do with His Bundle pacing?

 What does chronaxie have to do with His Bundle Pacing (HBP), for that matter what does chronaxie have to do with anything?

The minimal voltage amplitude that can capture a nerve or muscle at an infinitely long pulse duration is called the rheobase.More simply rheobase is the minimal voltage necessary to stimulate the tissue. The chronaxie is defined as the pulse duration required for capture with a voltage of twice the rheobase. 

The chronaxie is important in regard to programing pulse generators. The chronaxie approximates the point on the strength duration curve at which there is minimal energy expended. The strength duration curve intersects the energy curve at the chronaxie, where energy equals V2/r X I .

Quoting Ellenbogen, fifth edition " As a practical point when programming the pulse duration of a  pulse generator,chronaxie is an excellent choice to minimize energy,limit charge drained from the battery... 

That sentence was written at a time before there was clinical application of His Bundle pacing. Is there any reason to believe that that rule of thumb would be no longer applicable? Is the chronaxie an excellent choice to minimize energy and limit battery depletion in patients with His Pacing? If so does that apply to both selective and non-selective His pacing?

Dr. Marek Jastrzebski and his colleagues in Krakow along with Dr. Pugazhendi  Vijayaraman from Geisinger Commonwealth School of Medicine (1)have studied the strength duration curves of the His bundle and the adjacent right ventricular muscle and make suggestions regarding programming .

They determined the HB and adjacent Right ventricular muscle chronaxies in 127 patients finding that in patients with selective HB pacing that the His bundle had a shorter chronaxie than the adjacent RV muscle while in non selective HBP patients the RV and HBP chronaxies did not differ.

The authors say that it is their practice to promote selective HB capture by empirically programming the pulse duration  (pd) to 0.2 -0.3 ms.However,for non selective , particularly in cases of distal AV block a longer pd ( i.e. 1.0 ms) would offer greater safety. They suggest that sometimes (often ?) the default setting from the factory is often 1.0 ms, which is far from optimal. 

 

1) Jastrzebski,M et al His bundle has a shorter chronaxie that does the adjacent ventricular myocardium:Implications for pacemaker programming. Heart Rhythm 2019;16:1808-1810.

2) Clinical Cardiac pacing,defibrillation,and resynchronization therapy, Ellenbogen,Wilkoff,Kay,Lau and Auricchio FifthEdition  

Is it safe to do MRI in pacemaker patients with abandoned leads?

 Is it safe to perform an MR in a Pacemaker patient who has one or more abandoned leads? It seems that the conventional wisdom has been that it is not safe.

This article from RD Schaller et al (1) at the University of Pennsylvania  provides reassuring data. They present data on 139 patients in whom 200 MRs were performed without serious events. There were 5 instances of transient decrease in lead sensing and one patient complained of subjective sternal heating.

There were  no changes in battery voltage,or changes in pacing rate. Quoting the authors:

"The growing aggregate of data questions the absolute contraindication for MRI in patients with abandoned CIED leads." The authors also point out that CMS will typically  not reimburse such cases.

(1) Schaller,RD et al, Magnetic resonance imaging in patients with cardiac implantable electronic devices with abandoned leads. JAMA Cardiol. published online Feb 17, 2021. doi:10/1001/jamacardiol.2020.7572

Another battery related recall for Medtronic implantable electronic devices

 

Has Medtronic had more battery related problems than other pacemaker manufacturers or does it just seem that way because of the number of recalls and battery life estimation issues reported in the last 2 -3 years and the fact that Medtronic makes more units than any other company? Medtronic is not alone. both Guidant and St. Jude have had major recalls .

Premature battery failure lead to St Jude's recall of ICDs and CRT-D units involving over 300 thousand world wide with 250000 in the US.Reports indicate that St. Jude knew of the problem for years before the recall. One death was reported in 2014 and a second death in 2016 before the October 2016 recall was issued.St Jude was purchased by Abbott.

A similar narrative can be told about Guidant who became aware of a shorting issue in their Prize II IC which did not allow the unit to deliver a shock while also destroying the  shocking system . Guidant informed the FDA and fixed the problem but did not warn physicians nor patients and continued to sell some units that had not been modified.The Prize was introduced into the market in 2000,  the flaw discovered in 2003 but it was not until  2005 that the company disclosed the problem. Finally in  October 2013 Boston Scientific who had purchased  Guidant pleaded guilty to a false claims act litigation and agreed to pay 296 million dollar fine. 

There were problems with  Medtronic CIED programmers in units made between October 2018 and January 2019 that resulted in erroneous estimate of battery life.These were ultimately corrected and in the end seemed to be really more of an anxiety producing nuisance than a threat. 

Also in 2019 there were three reports of pacemaker batteries being completely drained resulting in one death.This problems involved five different Medtronic models and 131000 units and involved a potential capacitor damage. This situation was troublesome to both EP cardiologists and the patients as there was no way to determine which specific units were likely to fail and pacemaker replacement is not a risk free minor procedure. Having a complicated device under your chest wall skin is anxiety producing enough without the added worry that the type unit you have had been known to suddenly fail. It seems to be a recurrent situation with CIED recalls that there is no way to determine if a particular unit within a class of units subject to the recall is in fact one that is doomed to fail.

On 2/3/2021 Medtronic send an "Urgent Medical Device Correction" letter to all affected physicians.  On 4/12/2021 The FDA announced a recall of about 240,00 Medtronic CIEDS.These are seven models of  CRT-ICDs and pacemaker ICDs. see here for link  This is a class I recall which means a potential risk for serious  injury or  death.

When a Medtronic pacemaker reaches a certain predetermined battery life remaining signal  the device is said to go to a RRT  setting or condition (Recommended replacement time) which sets a 3 month clock ticking before it goes to the next condition which is called ERT (elective replacement time).This condition, which I understand is unique to Medtronic PMs involves a Mode switch  to a VVI mode at a heart rate of 65.

Some devices involved in this latest recall may move from the RRT warning to full battery depletion in as little as 24 hours.There have been over 400 complaints with these devices and 18 "injuries" also reported. Generally PMS do not have a system feature that notifies patient or physician when RRT is reached. I will not know if my PM has reached RRT until a remote  ( or office ) interrogation designates that.(I have a five year old Medtronic model "Consulta"

 Questions come to mind-

Has Medtronic contacted the approximate quarter million patients who have these units or does the letter send to the physicians put the onus on the docs to spread the word?

Does the typical PM clinic have computerized records of which PM each of their patients have? 

A 2017 report from office of the inspector general estimated that 1.5 billion dollars had been paid by Medicare for replacement of 7 different models of CIED in 73,000 patients during the time period 2005-2013.According to the report manufacturers do not typically pay for replacement costs, 

Medtronic has also had recalls recently for its HVAD units (see here) and its blood pump (see here)

Complications from Left Bundle Branch area pacing

 Chen et al (1) report their experience in 612 LBBA implantations from 2018 to  2020 .Mean time of followup was 12.5 months.

Complication rate was low. and consisted of:

2 post operative septal perforations,2 post operative lead displacements ,4 intra operative septal injuries and 2 intra operative lead fractures,none of which had serious consequences.

1) Chen, X. Procedures-related complications of Left Bundle pacing: A single center experience. 

frontiers of Cardiovascular Medicine,24 March 2021. Full text is available on line. 

What is the mechanism of left axis deviation in some cases of Left bundle branch block?

 Dr. Saer Abu-Alrub et al (1) offer one explanation for  the occurrence of left axis deviation (LAD) in some cases of left bundle branch block (LBBB).

Twenty nine patients with non-ischemic cardiomyopathy were studied with non invasive cardiac mapping, CT and MR imaging .Sixteen had a normal QRS axis while 13 had LAD .The LAD group demonstrated delayed activation of the basal anterolateral region.The LAD group demonstrated an apex to base activation pattern versus a circumferential pattern observed in the normal axis group.

 Imaging studies demonstrated no differences in cardiac structure between the two groups so the investigators concluded that LBBB with LAD was a "purely electrical phenomenon".

Some LBBB patients with LAD  treated with CRT ( either by BIV or conduction system pacing)have normalization of the QRS duration and of the electrical axis while others have only the QRS normalized with the left axis unchanged. I have been unable to find any explanation of that. 

1) Abu-Alrub,S et al Left axis deviation in patients with non ischemic heart failure and left bundle branch block is a purely electrical phenomenon. Heart Rhythm, 2021 April  33831543

Do some patients with idiopathic left bundle branch block have an underlying cardiomyopathy?

Janek Salatzki and co workers (1) present evidence that there may more at work in idiopathic LBBB (ILBBB) than simply dysynchrony. It is generally accepted than LBBB alone can cause heart failure (HF) and myocardial remodeling. Salazki present data using an innovative technique,determination of septal flash volume, which they believe suggests that a contractile impairment is a necessary condition for remodeling while dysynchrony alone may induce heart failure.

The authors state that another explanation for their data is that the LBBB group with remodeling were simply patients who had the LBBB longer. The retrospective nature of their data does not enable them to exclude that alternative.

The first description of ILBBB causing heart failure was in 2005 and one of the speculations at that time was that there was an underlying cardiomyopathy , i.e. it just was not simply the dysynchrony operative in causing HF to develop but a disease process affecting both muscle and conduction fibers.The various case series demonstrating a favorable and often super respond in lone LBBB patients treated with either  BiV or conduction system pacing  suggests that desynchrony is the dominant problem.  

1)Salatski,J et al Presence of contractile impairment appears crucial for structural remodeling in idiopathic left bundle branch block Journal of cardiovascular resonance.2021 april 23 

2). Blanc J et al. Evaluation of left bundle branch block as a reversible cause of non-ischemic dilated cardiomyopathy with severe heart failure. A new concept of left ventricular dyssynchrony-induced cardiomyopathy. Europace 2005;7,604

Left bundle branch area pacing as alternative for bi-ventricular pacing for refractory heart failure

 Should cardiac conduction system pacing replace bi-ventricular pacing for patients with refractory heart failure (HF)? The two forms of conduction system pacing are His bundle pacing and left bundle branch area pacing.

Vijayaraman et al(1)have  published the results of a retrospective multi center study to asses the feasibility and outcomes of left bundle branch area pacing (LBBAP) in patients as an alternative to bi-ventricular  pacing (Bi-V). See herehttps://www.jacc.org/doi/pdf/10.1016/j.jacep.2020.08.015

LBBAP pacing was attempted in 325 patients and was successful in 277 or 85%.LBBAP resulted in significant shortening of the QRS,clinical and echocardiographic improvement, and was achieved with low thresholds and adequately high R waves. In short, LBBAP seemed feasible and safe. No mention was made in the abstract regarding septal wall perforation an event that had been reported in some earlier case series. 

Among clinical indications for pacemaker implantation none equal the randomized clinic trial data supporting CRT using BIV.

There are observational data supporting the value of both His Bundle pacing and now LBBAP as an alternative to Bi V pacing. I think  a large RCT would be necessary to demonstrate superiority or more likely non-inferiority  of cardiac conduction pacing versus BiV.Where would funding for that be found?

1)Vijayaraman,p et al Left bundle branch area pacing for cardiac resynchronization therapy:Results from  the International LBBAP collaborative study. JACC Clin EP archives, vol 7 no. 2 135-137. 

  

Implantation of both His Lead and LBBA lead in atrial fibrillation patients

 In the early days of His bundle pacing (HBP) there was a issue of whether or not a backup lead should also be implanted.This controversy has apparently not been completely resolved and may have regained some steam as reports have appeared indicating  that some not insignificant number of His  leads develop high thresholds over time  even though the initial threshold was appropriate.

Yand Ye et al (1) describe an interesting variation of using a backup in conjunction with a His Lead.They studied 16  AF patients who were pacemaker dependent in whom they attempted to place both a His lead and a left bundle branch area lead.(LBBA).The His lead was the primary pacing lead and the LBBA lead was considered the backup lead. Thirteen of the sixteen were successfully implanted. Although the results section of the paper is somewhat unclear apparently at least one patient had a increase in the capture threshold leading to switching to the LBBA lead. During the six month follow-up there were no lead dislodgments or ventricular perforations.There have been a few reports of late perforations of the  LBBA pacing lead.

The authors conclude that the technique is doable and safe and may offer an approach at least for PM dependent patients with AF.In this group of patients the rivalry between HBP and LBBA pacing could be avoided.Maybe not a either or but a both.

1) Yand Ye, Feasibility and safety of both His Bundle Pacing and left bundle branch area pacing in atrial fibrillation patients: intermediate term follow-up.Journal of interventional cardiac electrophysiology. 2021 March 15 33723691

Does location of His lead (above or below the tricuspid valve) matter?

 A study of fifty patients by Y. Hu et al (1)  indicates that it does matter. Two problems with His pacing are higher capture threshold voltage are needed and lower R waves . Hu's data indicate that in the 25 patients who were implanted below the TV there were lower ventricular capture thresholds and higher R waves.Echo studies showed no tricuspid regurgitation.

 Somewhat different results were reported by Tang et al (2) in that they found capture voltage to be no different in the atrial leads  compared to the ventricular lead placement in a study of 13 atrial placed His leads and 16 ventricular placed leads. However, they also found that the R wave sensing values were higher in the ventricular lead group with values at implant being 1.87 V for the atrial lead and 4.53 V for the ventricular group. 

Also it is generally thought  in cases of AV block that a sub valvular implantation may be preferred  and that non-selective His pacing may to preferable to selective because it can be its own back up. 

 1)Hu,Y Electrical characteristics of pacing different portion of the His bundle in bradycardia patients 

Europace,2020 December 26, supplement ii 27

2)Tang, C Effect of implantation site of the His bundle pacing leads on pacing parameters a single center experience BMC Cardiovascular disorders. 2021 Feb 24 2021 (1) 112, 

His Bundle pacing can normalize ventricular activation but can it also actually reconstitute native intrinsic conduction ?

His Bundle pacing  (HBP) has been known for years to be capable of normalizing bundle branch blocks. By normalizing I mean that the QRS while the patient is being paced becomes normal with Selective HBP and nearly so with non selective HBP. By reconstitution I mean that the QRS remains normal after HBP is turned off.  Reconstitution  is what authors of 2 case reports document in a article in Heart Rhythm Case Reports.

Dr FM Ezzeddine at al  (1) report two case in which patients with long standing conduction defects were implanted with His leads and after several months of treatment with His bundle CRT  were noted on routine testing  to have resolution of their conduction defects.One patient who had an av block and LBBB had resolution of the AV block while the LBBB continued and the second patient had restoration of normal ventricular conduction no longer having an LBBB pattern. Both patients experienced a significant resolution of their heart failure symptoms when His bundle paced CRT was begun.

Quoting the authors with my underlining.

"His Bundle pacing can restore native intrinsic conduction in some cases after years of chronic conduction block". ..    this demonstrates new theoretical benefits of HBP , the ability to promote conduction down the native pathways that were previously non-conducting." 

 What I  believe  the authors are proposing is that  His bundle pacing had somehow brought about  electrical remodeling  leading to a condition in which pacing was no longer needed to bypass or override whatever specific type of conduction defect the patient had experienced. They consider mechanisms such as Wedensky facilitation which refers to an impulse arriving at a blocked zone and increasing the excitability of tissue beyond the block. Other electrophysiologic speculations are offered.

There have reports of exercise induced LBBB and intermittent rate related LBBB but the authors believe these are the first reports of long standing conduction defects that recovered native conduction following continuous His bundle pacing.

On page 412 of Serge Barold's illustrated guide to pacemakers and resynchronizatio (2)n  the authors suggest there is value to periodically "expose " the underlying spontaneous EKG. This was said in the context of followup on bi-ventricular pacing but perhaps Ezzeddine's paper offers a reason to do that for patients with LBBB who are being His bundle paced.   

 

1) Ezzeddine, FM et al Reconstitution of native intrinsic conduction in patients with chronic conduction block with His bundle pacing. Heart Rhythm Case Reports.2021 1-5,  https;//doi/org/10.1016/j.hrcr,2021.03.006

note: The same cases were presented as a poster, at the JACC meting march 20,2018 by Dr. Ezzeddine

2) Cardiac Pacemakers and Resynchronization , step by step  An Illustrated guide. Second Edition,

Bakrold,SS, Stroobandt, RX adn Sinnaeve, AF 

Some Pacemaker program features do not work well with His Bundle Pacing

 Some pacemaker programming features do not work well with His Bundle pacing and may cause some  problems raising the question of why have pacemaker manufacturers  not developed programs and algorithms specific to His Pacing . 

In particular the automatic  capture threshold determination(ACM for automatic capture management) program may give falsely high thresholds leading to  setting the capture voltage safety factor too high leading to premature battery depletion as illustrated in a case report referenced later in this article.

If the His lead is placed in the ventricular port (pulse generators used with CRT have three ports) the ACM  which is based on the evoked potential will indicate the RV capture threshold , i.e. not the His threshold. If the RV threshold is higher than the His threshold then the ACM determination will be falsely high. If ,by chance the right ventricular evoked potential is approximately the same as the His potential then ACM works just fine , except you don't know if it working right or not. 

If the His lead is in the LV port, since it is based on the LVP-RVS conduction times the threshold will be that with lowest value either RV myocardial or His. 

The ventricular capture program is activated nightly at 1:am and if unsuccessful another attempt is made every half hour.

Articles by Vijayaraman and Burri has explicated the problems with automatic capture algorithms and HBP and the basic recommendation is that those features be turned off or at most turned to monitor. 

Quoting Vijayaraman, 2018 JACC ;" Utility of automatic threshold testing feature is limited in HBP. In patients with selective HBP  due to lack of evoked potential,this feature may fail to detect the true  His capture threshold. On the contrary in patients with nonselective HBP this feature will detect myocardial capture threshold rather than His bundle capture. " 

Quoting Starr and Burri (Heart Rhythm 2019)

"The RV capture management algorithm of Medtronic devices considers an RVS event that occurs in the 110 ms window following pacing to be V capture ( i.e. it does not specifically detect the evoked  potential)." The authors  then explain that in cases of RBBB selective His Pacing  may have the erroneous diagnosis of non capture  could if the pace capture interval falls outside of the 110 ms window.

Quoting Burri,(2019) ;

"RV capture management algorithms are based on detection of the evoked potential which is absent in case of selective his bundle capture.Even in the case of non-selective capture, the algorithm seldom yields accurate results and the feature should either be inactivated to switched to  "monitor"

The following case report illustrates one undesirable clinical outcome when the ACM is set to "program" but fortunately the problem was quickly corrected.

Wu et al ( 1) report a case in Clinical Case reports in 2020 in which the Medtronic capture management algorithm caused a large and inappropriate increase in the voltage setting.The patient was a 72 year old man with a second degree heart block who was implanted with a His Lead resulting in selective His pacing with an initial Voltage of < 1.5 volts at 0.4 ms.However the next day the EKG now showed nonselective His pacing pattern and the Voltage was set at 5.00V at 1 ms.

 The authors believe that the automatic capture management system which was set on  the factory default setting of adaptive repeatedly noted "pacing capture loss" and reputedly increased the RV voltage. The treating physicians recognized the problem and changed the ACM setting to monitor before significant battery depletion had occurred.

It is not possible from the case report to know  when this event occurred .There were two articles published in 2019 that called attention to problems with the adaptive setting for automatic capture management systems such that the adaptive setting should not be considered the default position. 

As of this writing there seems to be no IPG (PM) specifically designed for His pacing nor is there an automatic capture threshold program designed for HBP. I wonder how often various pacing settings are just left to the factory settings when a PM is implanted with His pacing  even though there is information available in the literature indicating  that  a device features that worked well for right apical ventricular pacing  will not work in His-bundle pacing. 

1) Wu, Jung-Pin et al Automatic capture management may cause   unnecessary battery depletion in selective His Bundle Pacing Clinical Case Reports 2020. DOI 10.1002/ccr3.3168

Take home messages for "lone " Left bundle branch block

Introductory and personal note

Five  plus years ago I experienced a sudden decrease in my exercise ability.As a long time marathon runner I was well aware of running times and perceived exertional sensation for various speeds. My running times decreased by about 15% (comparing times for a one mile run at a comfortable pace).

My EKG at my  internist's office show an LBBB pattern. Neither he nor I were aware of the significant exercise impairment that can be caused by LBBB. A number of web sites even now offer misinformation about LBBB.  Over the past five years there has been much learned about LBBB,His Bundle Pacing,and the potentially harmful effects of pacing the heart from the right apex, and the entity of LBBB induced cardiomyopathy. 

 I also had developed an exercise induced high grade second degree heart block for which I received a pacemaker ( PM) importantly with a Bundle of His lead  (HB)  After recovery from the implantation  procedure I was able to return to running with an apparent recovery to my pre LBBB level. A number of blog readers have contacted me about exercise problems similar to mine and their frustration with the medical advice from their cardiologists. I was evaluated for coronary artery disease and none was found.(see endnote 1)

The following is a recap of what I have learned about LBBB and related  matters which may be of interest at least to folks with that condition. It is not offered as specific medical advice and is just my take on a subject of obvious great personal  importance from a non-cardiologist who over the last five years has enjoyed a non-sanctioned,personal,perhaps quiky ,self directed mini fellowship in electrophysiology. 
____
All LBBBs are not created equal. Even the subset of lone LBBB is not homogenous.

About half of patients whose EKGs meet standard  criteria for LBBB are shown to have a particular pattern on echocardiography.This seems to be the case whether the standard criteria are used or the more stringent Strauss criteria.(see end note 2)

This echo  pattern describes an abnormal,out- of -sync contraction pattern of the left ventricule (LV)
It begins with a electrical activation of the interventricular septum from right to left  (opposite to the normal direction of septal activation) and then a swift leftward movement of the septum and a bulging out of the left lateral ventricular wall,followed by a delayed LV wall contraction and rightward bulging of the septum.The septal movement occurs before the aortic valve opens (in the isovolemic contraction phase when mitral and aortic valves are closed as pressure builds up to snap open the aortic valve).Some ,but not all, patients with an EKG pattern of LBBB demonstrate this pattern on echocardiography or Cardiac MRI studies

This same pattern has been observed in  at least some cases of RV apical pacing.


Cramer and De Boeck (1)et al describe this mechanism by which abnormal electrical activation leads to abnormal contraction-a dyscoordination of contraction in at least many cases of LBBB.

 " This discoordination encompasses regional differences in timing,duration and amplitudes of contraction.When the differences are large enough,part of the contractile energy of the early contracting segments will be dissipated into abnormal stretching of remote areas during early systole and vice versa at end systole...The decreased global pump function will activate neurohormonal response mechanisms in an attempt to maintain normal cardiac output,favouring ventricular dilatation and remodeling. "




In some patients, LBBB is not associated with this pattern and in these it may be that electrical signals are merely delayed but occur in the normal left to right pattern .Several patterns of septal motion have been described.

The resting echo typically demonstrates no problem other than an ejection fraction (EF) that might be at the lower limits of normal and in the absence of a earlier higher value carries little diagnostic value.However some work indicates that the ejection fraction is not  accurately measured in LBBB using the Simpson method and that the "true" EF is lower than measured.

It should be noted that it may be possible to recognize the early left ward motion of the septal on echo and has been named "septal flash".Patients with this septal flash pattern generally respond well and sometimes exceptionally well with CRT-either with traditional bi-ventricular CRT or with His Bundle pacing.

With exercise, stroke volume fails to increase ,diastolic pressures rise and the patient may become short of breath. Human and animal work have demonstrated that   increased afterload (as with increased blood pressure) and increased heart rate cardiac function decreases significantly including decrease in EF.

A patient presenting to a cardiology clinic with LBBB,no symptoms and a negative evaluation for coronary artery disease would likely be reassured and followed.

A symptomatic patient poses a more difficult problem.If he had a normal echo some docs  would just follow the patient , a management plan not likely to be well received by an endurance athlete.If the patient had reached  a phase of cardiomyopathy with evidence of heart failure, the usual medications would likely be prescribed .However reports indicate that the usual goal directed therapy GRT) is not effective in LBBB induced cardiomyopathy.Some authors have suggested that earlier  (that is less than the standard three month  trial of GDT) pacemaker therapy should be used.

Five years ago His Bundle pacing was not a routine  procedure for PM implantation- now it has become the default procedure in a number of centers for AV block and for sinus node disease and for pacing after A-V node ablation and in some centers the preferred approach for CRT instead of Left ventricular pacing through a lead in the coronary sinus.

Although by 2000 there was great interest and enthusiasm for HBP  and had become a II A AHA/ACC/HRS guideline recommendation, more recent analysis of data from HBP follow up has revealed perhaps as many as a quarter of  successful His bundle  implantation with adequately capture voltages  over time increase voltage requirements to levels which likely will lead to premature battery replacements.This in part has lead to increasing acceptance of another,newer form of conduction system pacing namely pacing the left bundle  directly by advancing a lead further into the RV apex and screwing in a lead deep into the septum. As of this writing bundle branch area pacing has become popular in China, it s country of origin, and also apparently used a a primary means of pacing  in place of HBP at Virginia Commonwealth Medical School according to a recent article by Padala and Ellenbogen (2). As best I can tell as an outsider, some form of conduction system pacing has largely replaced the traditional pacing from the right ventricular apex. 



1 Cramer,MMJ and De Boeck, BW Three dimensional echocardiography and left bundle branch block:Prime time in cardiology. Neth Heart J 2007 Mar 15(3) 87

2) Padala, S and Ellenbogen KA  Left bundle branch pacing is the best approach to physiological pacing. Heart rhythm ,2020 


end note 1

As was the party line recommendation at the time,coronary disease was evaluated by a stress echo in a patient with LBBB.Abnormal movement of the interventricular septum,decreased septal blood flow not caused by obstructive disease and abnormal changes on the ekg generally make various testing methods less than optimally reliable, eg.regular treadmill exercise  and some isotope tests. The SPECT myocardial perfusion imaging is a problem because of septal perfusion defects occurring in patients who do not have obstructive lesions in the Left anterior descending artery. The stress echo test is popular in some centers but a recent review from the Cleveland Clinic discredits the stress echo considering it unreliable and favors CT angiography if patients  less than 65 and the pharmacologic nuclear imaging or dobutamine stress echocardiography if over 65 years of age.Older patients are more likely to have coronary calcification making the CT  angio less useful. (.https://consultqd.clevelandclinic.org/in-patients-with-left-bundle-branch-block-whats-the-best-test-for-cad/)

end note 2

Strauss criteria for EKG diagnosis of LBBB- QRS greater than 140 msec in males,and greater than 130 msec in women and mid QRS notching in 2 contiguous leads.(Strauss,D Defining Left bundle branch block in the era of Cardiac Resynchronization Therapy. Am J Cardiology 107 (6)2011

So maybe Bundle of His pacing (HBP) is not the holy grail of pacing after all.

 To understand why EP cardiologists might have considered  His Bundle Pacing (HBP) the holy grail it might help to have a brief survey of some of the history of pacing the heart and then look at why HBP , thought  to be the most physiological may not now be considered to be the best-at least by some EP cardiologists.

By the early 2000s EP cardiologists had not yet determined the best way to pace the heart even though the dual chamber pacemaker had been employed widely since the mid 1980s .

For example, in a patient with sinus node disease and bradycardia should the patient be implanted with a single lead in the  right ventricle or be given dual chamber pacing with a lead in the right atrium as well. At that time right ventricular pacing meant pacing in the apex of the right ventricle as opposed to pacing in the right ventricular septal wall or the right ventricular outflow path or actually accessing the His Purkinje system also now referred to a conduction system pacing. 

While it was known that pacing the ventricle alone could at times lead to something called pacemaker syndrome and it seems that synergy of the atria and ventricles made much more physiologic sense,there had been no clinical trial demonstrating the best approach.Looking back from the vantage of an outsider it seems that as recently as 20 years ago the EP cardiology community was not in agreement about how many leads did a patient with sick sinus syndrome need/

The MOST trial  was designed to settle that issue and results were published in 2002.That trial and the DAVID trial provided less than slam dunk evidence favoring the dual chamber (DDD) mode  ( 20% fewer instances of atrial fibrillation) but subsequent analysis of the data gave another important answer related to the harmful effect of pacing the heart from the right ventricle. That and subsequent analysis indicated that there was a significant risk of heart failure if the right ventricle were pacing more than 20-40% of the time. Consider that-the treatment that could be live saving for irreversible bradycardia could over time cause the patient to develop heart failure. Some EP cardiologists must have thought that there must be a better way. 

It gets worse -patients with pacing induced heart failure respond poorly to the usual heart failure battery of medications and the only fix was another pacemaker, which while  potentially very  helpful, implanting a pacemaker should be considered a big deal . Infection and other complications may occur more frequently when PM are revised or replaced.

The patient would  have to undergo another PM implantation procedure with the attendant risks of infection,pocket hematoma,pericardial  effusion,pneumothorax,etc. This time a lead would be placed from the right atrium through the coronary sinus into  a vein on the epicardial surface of the left ventricle. Then the PM would be programmed to attempt to optimize the timing of the right ventricle (still paced at the apex) with the left ventricle which is now depolarized from epicardium to endocardium  which is the  opposite of the usual route.Two wavefronts would be generated, one from the endocardium of the right ventricle and the other from the epicardium of the LV and the two would  hopefully fuse so as to improve  cardiac output and  even bring about often beneficial remodeling of the heart.

This Rube Goldberg arrangement worked quite well for these cases of pacemaker induced cardiomyopathy as it does for about 70% of patients with medication refractory heart failure   It seemed that those cases whose EKG showed a left bundle branch pattern were most likely to have a good and often impressive improvement, sometimes referred to as "super responders".

By 2013 the value of CRT was firmly established. CRT means cardiac resynchronization therapy and  at that time  was synonymous with biventricular pacing (Bi-V) and randomized clinical trials had proven its value in symptomatic relief,reduction in hospitalizations and  increased survival.As best I can tell, as a non cardiologist looking in, the randomized controlled trial evidence supporting pace maker implantation for CRT is more robust and convincing that for any other pacemaker indication.

A look at the time line regarding recognition and acceptance of  the role of loss of interventricular and intraventricular synchrony as exemplified by left bundle branch block (LBBB) is of interest juxtaposed to the evolution of thought concerning right ventricular apical pacing .

Blanc et al 2005 and Vaillant et al 2013 described cases of heart failure caused by left bundle branch block and treated successfully with CRT. Blanc's cases seem to be the first recognition that lone LBBB could cause heart failure and that this desynchrony  could be fixed by CRT often with dramatic resolution of the heart failure.

The abnormal depolarization and sequence of ventricular contraction in RV apical pacing and that induced by LBBB are very similar as are the EKGs and it should not be a surprise that CRT worked well for both, at least in many cases

The first clinical series of His Bundle pacing was done  in 2000 by Desmuhk  in patients with rate control recalcitrant atrial fibrillation patients who needed an av node ablation but its use did not become widespread due to the complexity of the implantation and lack of tools designed for the task.   

For the next decade there was little clinical application of His Bundle pacing in the US although  work was progressing in Spain and Italy.

Two important papers in 2015 contributed to a growing interest and application of HBP. A case series by Dandimundi and Vijayaramen from the Geisinger Clinic  demonstrated that HBP was not overly difficult after all and that results seemed good. Daniel Lustgarten from Vermont published a proof of concept cross over study  study that compared HBP with BiV pacing .

By 2017 at the Heart Rhythm Society meeting there was considerable enthusiasm regarding HBP and one prominent EP cardiologist referred to HBP as the Holy Grail of pacing and it seemed that   finally physiologic pacing was practical. The alternative, namely right ventricular apical pacing and Bi V pacing could hardly be considered physiologic.By 2020 the same EP cardiologist wondered in left bundle branch area pacing would be the new holy grail. 

In 2019 Dr. Kenneth Ellenbogen gave a presentation that was very optimistic regarding the future of His pacing in part based on a small ( n=20) group with five year followup.

However, by 2020 the bloom was less well fixed on the  His Bundle pacing rose. Though physiologically beautiful HBP had some negatives such as: High initial capture threshold, adequately initial low capture thresholds that subsequently rose to unacceptable levels in some cases,low R waves which may lead to sensing problems and  the technical difficulty of the procedure. Earlier  than anticipated pulse generator replacements were occurring because of the high thresholds. Padala and Ellenbogen claim that 25% of HBP patients will have an increase in capture threshold to 2.V at 1 ms. over time. In Zanon's report of 844 HBP patients the median battery replacement time was 5.8 years .

So When Dr. W Huang  published results of left bundle branch area pacing (LBBAP) which was technically easier,resulted in lower thresholds and higher r waves hence less programming problems  LBBAP seemed to be  very quickly accepted in China and in some US centers.

LBBP may not be quite as physiologic as HBP after all it in effect may cause a right bundle branch block ( it does not always though it should theoretically ). The LBBAP technique is now considered by at least one prominent EP cardiologist as the best even though at this point long term followup is lacking. 

In a YouTube presentation  given on  Feb 2010, by Dr. Santosh Padala from VCU  who  discussed his results with LBBAP and indicated they they now proceed with that modality without trying  His capture first. The reason for this seemed to be that they had seen some cases where the initial His capture threshold was acceptable but within a few months the threshold increased to unacceptable levels. He mentioned they had two out of 59 LBBAP cases with a LV penetration complication but the lead was withdrawn and apparently no significant consequences resulted.

I believe a good  argument can be made for saying that such a move is premature, We now  have fairly robust data on followup on HBP patients.In 2019 Zanon published a multicenter  experience of 844 patients with HBP who were implanted from 2004 to 2014 with a median followup of 3 years. (91.6 % were free of complications. Mean pacing threshold at implant was  1.6  V. and  2.0 at followup. In the second group of 476 in whom the fixed curve sheath was used the complication rate was 4.2 % versus 11.9 in the earlier group of 368 patients in whom a deflectable sheath was used. 

However, LBBAP is relatively new and the medium and long term results have yet to play out.How well a pacing lead inserted 1.5 cm  into the septal will perform  over time remains to be determined. There has been at least one case of a delayed migration of the lead through the septum penetrating into the left ventricle.

Venkatesh, and Sharma from Rush reported their experience with LBBAP regarding 59 patients done from June 2018 to April 2020 most of which were attempted because of unsatisfactory His implantation or unacceptably high His capture voltage.

There were 7 "lead related "complications during the short follow up period of about 6 months with 3 requiring lead revisions.In one patient an interventricular septal perforation occurred two weeks after the initial implantation.Penetratiion during the procedure apparently can be quickly recognized and at least so far  it seems  that no significant harm was done.Late penetration is a different matter. but it seems rare. Capture voltages were low(average 0.62 Volts at 0.4ms)and stable over the short followup period which should predict a longer battery life than is seen with HBP. Improvement was noted in left ventricular performance  in HF patients during the follow up as has typically been the case with HBP.

1) Venkatesh,R et al Pros and Cons of Left Bundle Branch pacing.A single center experience.Cikrculation,arrhythmias and electrophysiology 2020 13 12 

Battery problems with Medtronic Pacemakers, actual battery drainage and battery life estimation error

 The leads in a pacemaker (PM) is said to be the Achilles heel of those systems.A close runner up in the Achilles heel competition is the PM battery.

In 2019 Medtronic reported problems involving batteries.

In one case the problem did not  pose an imminent threat to patients as the issue was that some of their units (manufactured between October 2018 and January 2019 ) were displaying erroneous estimates  of battery life. The problem was said to be in the "programmers" and not in the units themselves and battery life was not altered. The term programmer here refers to the computers that are used to communicate with the PM in the doctor's office and to make programming changes and to make updates to firmware.

A much more serious battery issue also was reported in 2019.There were three reports of pacemaker batteries being completely drained resulting  in one death.The devices involved with this problem were the following models: Astra,Azure,Percepta,Serena,and Solara.Damage to a capacitor in the units was said to be the cause of the battery drainage. Unfortunately there was no way to determined if a given Pacemaker was likely to have a battery failure. The FDA was not recommending  replacing all of the units.Some 131,000 units were potentially affected.

PMs can be "interrogated" by bedside monitors providing various parameters of PM function including a value for battery life estimation.

In theory battery life determination seems  simple.It is the battery drain rate divided into the battery capacity which is measured in ampere hours. The devil is in the denominator of the equation. How accurate are these estimations.

My own PM was  implanted in October 2015.I am writing this in January 2021 .

An interrogation done on October 2016 gave an estimate of 2-2.5 years which corresponds to October 2018 to June 2019. An interrogation done October 2017 gave a estimation of 1.5 to 2.5 years which corresponds to June 2018 to June 2019.IN January 2021 the estimate was 4 to 10 months. By May the estimate was still 4 to 10 months.

So at least as regards my PM the estimations of battery life do not instill confidence. 

Addendum 5/17/2021 undated battery estimates were added to the next to last paragraph. 

    

Longevity in athletes -good genes,exercise levels or both

 There are several reports suggesting that endurance athletes enjoy good longevity .These studies have involved professional cyclsits,Ski racers,French oarsmen and Harvard rowers. 

Do the  genetic endowments that world class endurance athletes possess that facilitate their athletic ability also either alone or with other genetic contributions enable to live longer? Alternatively is it the long hours and perhaps years of exercise that lead to a long life? Maybe both.

A key, perhaps the key,to be a world class endurance athlete is a high maximum oxygen uptake (02Max).Although intense aerobic training can increase one's 02 max a moderate amount  (maybe 10-15%),world class endurance athletes inherit high 02 max values. A typical 25 year old man may have a value of 40-45 ml/kilo/minute while a budding world class marathon runner typically has a value of 80 or higher with few exceptions.Values as high as 90 have been recorded in some world champion cross country skiers. 

The prodigious exercise capacity of elite endurance athletes is characterized by a slightly larger than normal ventricular size with great capacity to fill quickly.

The maximal oxygen capacity of humans inexorably decreases over time.Whether continuing moderate or even high levels of aerobic exercise will mitigate that rate of loss is the topic of an ongoing debate.

 What is clear,however, is that if you have for example a 02Max of 60 or 70 when you are thirty years old you are more likely to have a 02 max in the high 20s or low 30's when you are 75 or eighty.

A  80 year old with a 02 max of 28 is more likely to come out the other side of a serious illness or accident than an 80 years with an 02 max of 18 or 20. 

 Practice,practice practice arguably may get you to Carnegie Hall but someone with a 02 max of 45 will not win the Olympic marathon regardless of how much training he endures and you will not have a 02 max of 50 when you are 80 years ( Ed Whitlock had an 02 Max of 52 at age 82))  unless you  had a very high  02 max in your youth.

For more on Ed Whitlock and how he slowed down marathon time wise during his 70's while his O2 Max seemingly was unchanged, see here.

Late gadolinium enhancement at Right Ventricular insertion points in highly trained endurance athletes

 A study from Spain (1)demonstrated late gadolinium enhancement in 37 % of highly trained young endurance athletes, all of which occurred at the insertion points of the right ventricle into the inter ventricular septum.See here for full text of article.

All of the athletes trained at least 7 hours per week for the previous five years.Compared to controls the study group had a 10 fold increase in late gadolinium enhancement (LGE) .

LGE is seen in patients with coronary artery disease with  a post myocardial infarction scar and in cardiomyopathy patients in whom the LGE may be considered a negative prognostic sign.

Early reports of LGE in older , long time endurance athletes were confusing and in one study confounded by a significant number of cigarettes smokers. Some of the cases demonstrated a coronary artery pattern ( i.e. LGE along the distribution pattern of the coronary arteries ) and some did not and some were noted in the insertion point of the right ventricle.

The authors described the LGE as a possible "matrix remodeling" and along with bi-atrial and bi-ventricular chamber size increase and superior diastolic function characterizes  the pattern of  the so-called athlete's heart.

1)Domenech-Ximenos,  Prevalence and pattern of cardiac magnetic resonance in highly trained endurance athletes Journal of cardiovascular Magnetic Resonance 2020 Sept 3, 22,(1) 62 

Normal pacemaker function near battery depletion can pose clinical problems

 Can normal pacemaker behavior near battery depletion cause alarming symptoms and clinical diagnostic difficultly?

To put the topic in context we need to describe normal PM functioning as the battery nears depletion.

My PM is a Consulta CRT-P model and according to the Medtronic manual, here is the sequence, which we can use as an example of PM behavior at near battery depletion. 

When the battery reading reaches a value equal to or less than 2.77 volts a replacement indicator named RRT or Recommended Replacement time is displayed on the interrogation.  More precisely, there has to be a reading of 2.77 V or less for three consecutive daily readings A "clock" is  then set to run for  3 months and when it is timed out ,another replacement indicator named ERI or Elective Replacement Indicator is displayed. 

At this point the PM is switched to a VVI Mode at 65bpm. If a magnet is paced on the PM ,the rate will read 65 indicating that the unit is in the RRI mode.If battery life is adequate this power saving mode will continue for three months and then the unit reaches EOS or end of service.

VVI mode works in the following way.The right  ventricles is  paced unless a spontaneous ventricular activation occurs first and then the lower limit for ventricular activation is reset.If a spontaneous ventricular activation does not occur first then the ventricle is paced.Atrial activity and ventricular activity are independent.

According to reference 1 and 2 (see below ) only Medtronic PMs exhibit this near end of service behavior.

A PM in the VVI  mode is in an asynchronous mode meaning that there is loss of synchrony between the atrium and ventricle possibly resulting in a clinical scenario called pacemaker syndrome .Symptoms can include chest pain,shortness of breath, fatigue.palpitations  and neck pulsation among others.The heart was not designed to have the atria contract against closed AV valves nor to have the ventricles contract with the AV valves open.

A 2020  case report (which seems to be very similar to a case referenced in 2010 (ref 2)) of a 70 year old man with a Medtronic  Adapta PM presented to ER with palpitations and dyspnea. Physicians were unable to do a PM interrogation ( another feature of the ERI mode in some . ( but not all) Medtronic models is  that the interrogation feature is disabled ) . The clinical problem was solved and a replacement PM was implanted with resolution all symptoms .

It should be noted the the device was not malfunctioning. At manufacture it was programmed to shift into an asynchronous mode when it reached ERI status. To the manufactures of the PM this was a feature not a bug. However, as a pacemaker patient, I consider this a bug-one in which "normal" behavior of the unit can cause serious symptoms and to add insult to injury have the interrogation function disabled making the diagnosis of the problems difficult even to cardiologists. 

The authors of both referenced  articles were critical of ERI management  in Medtronic PMs. Dr. John Mandrola (ref 2) stated in 2010  he has personally seen 4 cases in which this type of syndrome occurred in a patient with a PM whose unit shifted into a VVI mode with resultant pacemaker syndrome, a situation  in which the diagnosis may not be apparent potentially  leading to further  further diagnostic tests with missed diagnosis even by cardiologists.Mandrola mentions two patients who were subjected  to unnecessary  coronary angiograms before the diagnosis was finally made.Here failure to warn by the patient's EP doc and/or by the PM manufacturer lead to possible harm.Coronary angio is not a zero risk procedure. Siroky made his criticism obvious in the title to the case report ,"bad device behavior or malfunction".

 An obvious comment is -should not EP cardiologists and PM manufacturers inform patients of the untoward events that may  occur  as their battery approaches depletion. In my limited experience patient education before and after the PM implantation has much room for improvement .

 

1)Siroky,GP et al Shortness of breath and palpitation in an elderly man:Bad device behavior or malfunction .Journal of Arrhythmia,2010:36,1109 -1111

2) Madrola, J. https://www.drjohn.org/2010/09/answer-to-this-weeks-clinical-vignette/

Dealing with the covid pandemic is not science all the way down

Ross Douthat,writing in the WSJ on 12/19/2020 entitled his opinion piece "Why you can't just trust the science." I think he was not saying to distrust science but rather he was saying all decisions regarding how the human enterprise copes with the pandemic is not science all the way down. Logistical questions,ethical and moral decisions have to be  made and sometimes those decisions get camouflaged as a scientific decision . 

A key paragraph:

"Last month their Advisory Committee on Immunization Practices produced a working document that’s a masterpiece of para-scientific effort, in which questions that are legitimately medical and scientific (who will the vaccine help the most), questions that are more logistical and sociological (which pattern of distribution will be easier to put in place) and moral questions about who deserves a vaccine are all jumbled up, assessed with a form of pseudo-rigor that resembles someone bluffing the way through a McKinsey job interview and then used to justify the conclusion that we should vaccinate essential workers before seniors … because seniors are more likely to be privileged and white."

Software glitches and Pacemaker problems

 To discuss software problems and their effect on pacemakers  an overview of their "ecosystem" might be helpful.

The ecosystem of  Cardiovascular implantable electronic devices(CIEDs) consists of the device ,  which is a pacemaker (PM) or Implantable cardioverter  defibrillator,ICD),a programmer in the doctor's office,a home monitor,a cloud server and central achieving  unit ,and proprietary software in the physician's office and often with a third party vendor who interprets interrogation reports for the physician. 

More details: The CIED communicates with the monitor with an inductive coil telemetry (ICT) method or a radiofreqency  (RF) at 402 -405 band, which is known as the MICS ( Medical implant communication service).The data received by the monitor is then transmitted by VPN to the PM company server where it can be accessed by the physician's office or a third party service vendor which include among others :Rhythm 360,Ambucor and  Cardiac RMS solutions,

An important aspect of the ecosystem is that the CIED cannot be reprogrammed remotely. The patient has to have an in office doctor visit and have programming change or firmware update done by the programmer. This may be considered more of a feature than a bug as it provides an important level of security.In the doctor's office the programmers uses ICT to retrieve a token key which is then used to generate a session key. Importantly only the programmer can terminate the session so a careless tech could leave the channel open leading to CIED battery drainage or a pathway for hacking.

In the last few years software problems have affected hundreds of thousands of CIEDs manufactured by Abbott ( formerly St. Jude) and Medtronic.

On August 29,2017 the FDA issued a safety communication for 6 models of Abbott pacemakers (Accent,Anthem,Accent MRI, Accent ST,Assurity,Allure). Dr. Subrat Das and co authors in their 2020 article (see reference (1),full text on line) graphically  (see their figure 3)  illustrate the time lag between the FDA communication  of a cyberattack vulnerability and the actions by the pacemaker manufacturers.

A firmware update was required to fix a cybersecurity vulnerability that could allow an hacker to access the devices potentially harming the patients by causing rapid battery depletion or pacing problems.Patients would need to go to their physician/s office for the update as CIEDs cannot be programmed remotely.

At that time and as far as I determine by internet search no harm has occurred to a CIED patient by hacking into the units. However 3 instances of software malfunction was reported by one group of physicians  from Mayo Clinic (2) in one week in their effort to upload the firmware (version 23.1.1.) fix.So the fix itself possibly was a threat to patients in the course of the updating  particularly those who were PM dependent .In one case there was a 4 second pause in pacing and and increase in the battery current .In another the pacemaker mode was changed from the DDDR setting to DOO and assistance from the company engineering team was needed to restore the original mode setting. In patients who were pacemaker dependent it was a choice between eliminating a very remote risk (a cyberattack harming  the patient) and the risk of a problem encountered during the process of updating the  firmware.

Later,(April 2018) Abbott issued wider application of the security patch, this time involving 350,000 ICDs and CRT units. 

In 2018 a cybersecurity vulnerability was discovered in Medtronic's method for their Carelink programmers  receiving updates over the internet.The vulnerabilities was linked to use of a outdated operating system (Windows XP) and lack of digital code signing during the updates. Medtronic solution at that time was not to fix their internet communication system but rather the more hands on  and  arguably more hacking resistant method of insertion of a jump drive into the USB port on the programmers to supply the update.

In 2019 Medtronic notified physicians that some of their PM and ICD models  (manufactured between October 2018 and April 2019) were reporting erroneously short battery life estimates. This involved approximately 53,000 units .Apparently there no serious event because of this and a software patch was said to be available sometime  in 2020. The error resided in the programmers and the computational programs on Medtronic's Carelink system and not in the CIED and there was no actual effect on battery life.

Also in January 2019 150,00 of Medtronic models Adapta,Versa and Sensia ( manufactured between March 2017 and Jan 2019) were recalled because of a software error to an integrated circuit.See here for Medtronic Urgent recall notice)

This problem was said by Medtronic to be due to "a design change in an integrated circuit , i.e. another programming error. This glitch under certain pacing setting could lead to pausing in pacing in when in a dual pacing mode. Medtronic said they estimated a software fix could be sent to FDA  for approval by the second half of 2019.So help was on the way but not quickly and in some circumstances (patient with no ventricular escape rhythm and  who did not tolerate an asynchronous mode) PM replacement was the only option. In this case a programming error would lead to PM replacement, an example of extreme downstream effect of a programing error.

The  Medtronic  battery life estimation error  mentioned above should not be confused with a actual premature  serious battery drainage problem experienced by Medtronic  pacemakers also in 2019 leading to at least one death. A report in 2019 indicated there had been three medical reports in which the pacemaker was completely drained as a result of damage to the  unit's capacitor.  The devices potentially affected were 131,000 units of the following models; Astra,Azure,Percepta,Serena Solara.

This poses a vexing problem to patients with those units and their EP cardiologists. There was/is no way to know which devices have damaged capacitors only that certain models were vulnerable to that problem. Pacemaker replacement is far from a risk free procedure and the FDA was not recommending prophylactic replacement. Medtronic began using a different capacitor and a better method to detect capacitor failure.The psychological impact on a patient knowing that they have a pacemaker model that might suddenly loose battery power should not be underestimated.

Medtronic pacemakers have a feature not shared by other PM manufacturers.When the PM reaches ERT , a mode shift occurs and the PM is shifted into  VVI mode at a fixed rate of 65.This is an asynchronous mode and may result in a syndrome called pacemaker syndrome.See here for details about this situation in which a programmed feature may cause serious symptoms while the PM is functioning as it was designed to do. What some would consider a bug is actually a feature in the eys of the pace maker manufacturer.

1)Das S et al Cybersecurity:The need for data and patient safety with cardiac implantable electronic devices, Heart Rhythm 2020 1-9 , (full text on line) 

2)Lee,JZ et al Pacemaker firmware  update and interrogation malfunction.Heart Rhythm case reports, vol5,#4, 213-216,April2019 

addendum 12/24/20. Additional paragraph added with link.