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.

EP cardiologists farm out monitoring of pacemaker remote interrogations to third party companies

 There are  an estimated 200,000 pacemaker implantations per year in the U.S and only about 2,000 board certified EP cardiologists. I believe many PM implantation must be done by cardiac cath cardiologists with the on-site technical assistance of a PM company rep.There are an estimated 1.5 million patients in the U.S. with pacemakers as well as many patient with ICDs  (defibrillators)

In 2015, the Heart Rhythm Society consensus statement stated that remote interrogations (RI) are the standard of care with one annual in office examination. Typically remote interrogations are done every three months. At least in the US and Germany  government health care programs will pay for RIs.

Medicare ( a high percent of PM patients are Medicare eligible) will pay for a RI every 91 days and the CPT code of a professional interpretation is  typically less than 50 dollars ( as of data from 2019)

So if you look at the math and the economics with several million RIs per year it is not surprising that a number of companies are now offering management services for RI for pacemaker  and ICD patients which  include a screening interpretation as well as follow-up for patients who miss their scheduled RI and reminders for scheduled RIs and perhaps other services as well.

For personal experience I can relate that the first year after my pacemaker was implanted the device clinic at the hospital where my EP practices provided good patient service, answering the phone and giving me a report on the results of my remote interrogation typically within a day or two. Over the next year or so service deteriorated significantly , never answering the  phone and only  getting a call back no soon than 4-5  business days.  

One interrogation report indicated that my PM had recorded 8 episodes of " AT/AF" which stands for atrial tachycardia/atrial fibrillation. The PM did not differentiate between the two. Actually what was being recorded was "far field R wave sensing, which should have been apparent to a trained technician viewing the recorded tracings in the printout but was not.It is not clear if the  EP doc reviewed the details of the report even after I sent a email asking about the "atrial fibrillation"

3 months later I had an in office interrogation and visit with the EP doc. The pacemaker company tech doing the interrogation said that the earlier report of AF was not correct but rather the tracings clearly demonstrated a PM pseudo arrhythmia  issue known as "far field R wave sensing. The atria channel senses R waves and double counts them. The  "fix" was simple.The tech lowered the sensitivity of the atrial channel and no such events occurred again. 

I learned that my PM has a program feature than is supposed to detect Far field sensing  ( aka far field R wave sensing) and not misdiagnose Far field sensing as AF. I contacted the Pace maker company and after several phone calls and emails exchanges I was told that the reason their algorithm missed the correct diagnosis was that my runs of far field  were  slightly too short  for the  algorithm  to detect them. I do not now if the company saw fit to alter their algorithm to be more accurate.

After my written complaints to my cardiologists I have been able to obtain my  RI reports  soon after they are transmitted. As a non cardiologist it took me no small amount of time  (and buying 2 books on PMs and electrophysiology) to learn how to read the reports at least on a basic level arguably with a degree of knowledge approximating the work  quality done by the original clinic. At least in regard to PMs , ICD interrogation reports are a different level of complexity and detail. 

After my complaints about the poor patient service delivered by the hospital device clinic the EP department of which my EP doc is the section head stopped using that device clinic and contracted with an outside proprietary firm to manage the interrogation reports. I am not claiming  my complaints played any role in the  change of procedure for interrogation report review but there is a temporal relationship.

A quick internet search yielded several companies that review PM and ICD interrogations including the following -Ambucor,Iron Rod Health and Cardiac RMS.

Are bradyarrhythmias more common in long time endurance athletes?

 The relationship between the volume of aerobic exercise and health benefits has been described alternatively as curvilinear or U shaped with the current consensus favoring the former .

The curvilinear relationship between aerobic exercise volume and cardiovascular and all cause mortality is firmly founded in multiple large epidemiologic studies. The suggestion that the curve turns upward at some range of exercise volume and becomes U shaped  has not been actually  demonstrated in large epidemiologic studies. and is conjectural. 

.A reported increase in atrial fibrillation, foci of myocardial fibrosis and increased coronary artery calcification may  provide mechanisms for this proposed  ascending portion of the proposed U shaped curve which is the graphic representation of the "Extreme exercise hypothesis".

Is it possible or likely that  there may be other deleterious effects of too much of a good thing in regard to aerobic exercise.?Sinus node disease and cardiac conduction defects might also represent long term deleterious effects of long time aerobic exercise.I say "might" because there is suggestive but not conclusive data to that effect. 

 My personal experience ( 35 years of marathon running  and  development  of  a left bundle branch block (LBBB) and an exercise induced,high grade second degree AV block requiring a pacemaker) and  personal knowledge of two other long time, local runners also needing  a pacemaker) peaked my interest.

 But so much for numerator based reasoning what is the evidence for long time aerobic exercise contributing to the development of  clinically relevant bradycardia induced by sinus node  disease and/or A-V blocks. Case series and some epidemiologic studies provide some insight.

Andersen et al (1) published a  widely quoted cohort study of 52.755 cross  country skiers who participated in the Vasaloppet,a 90 kilometer cross country ski race,said to be the oldest and largest cross country event in the world. 

Outcomes of interest were hospitalizations for atrial fibrillation (AF) or bradyarrhythmias( BA) as documented in Swedish national registries. When comparison were made between those who skied the race more times ( five or more)  with those who skied only once there was a statistically significant  increase in the hazard ratios for both AF and BA.For AF the HR was 1.29 (1.04 -1.61,for BA the HR was 2.10 (1.28-3.47).

A similar trend for AF and BA was noted when the faster skiers were compared with slower skiers but failed to reach statistical significance.

The bradyarrhythmias were mainly second degree heart blocks but the hospital codes did not distinguish between type 1 and 2 which is an important distinction as type1 (Wenckeback) is recognized in endurance athletes and is not usually considered an indication for pace maker implantation.

This was very coarse grain study and such important data such as history of elevated blood pressure,diabetes,obesity,alcohol abuse,habitual level of exercise, etc were not available ..

 Baldesberger at al (2)  studied 62 former professional cyclists who had long since retired from competition . and compared them to 62 age matched golfers for controls. Two had pacemakers.None had bundle branch blocks or second degree AV blocks while six were said to have sinus node disease based on heart rates less than 40 per minute. A question that the authors wanted to answer was -does the slow heart rate , first degree heart block and type 1 second degree block said to be  common in competitive racers persist in later years after their period  of  heavy training has ended. Their persistence would suggest that vagal tone which is usually  the proposed mechanism for those cardiac finding is not correct and that electrical remodeling of the SA node and AV node might be responsible.  Though a small study these data suggesting increased risk of sinus node disease  seem to be the best evidence so far since a comparison was made with age matched controls 

The remaining data are simply case reports.

 Dr R Northcote (3)  published a study of the bradycardias seen in 20 long time, older endurance athletes in Scotland.Nine of the twenty had heart rates less than 35,six had a prolonged P-R interval and four had Mobitz type 2 heart block which disappeared with exercise..One of the 20 had a pacemaker implanted. A follow-up publication in 1999 (4) indicated that 2 more of the original group has been implanted with a pacemaker. 

Doutreleau et al (3) published a report of 2 active  endurance athletes with type 2 second degree heart block that occurred during exercise. The authors claimed erroneously that their publication was the first to report a high degree AV block either at rest or with  exercise, somehow  having missed Northcote 's2 reports. Exercise induced heart block is uncommon.

The athlete's bradycardia has traditionally been attributed to high vagal tone but an alternative proposed mechanism is electrical remodeling, specifically downregulation of the so called funny channel AKA HCN4. In older endurance athletes "fibrosis" of the SA noted is often proposed as the culprit but remodeling is an alternative explanation. The sparse data so far available suggest that SA node disease may be more common in endurance athletes while there is less compelling data implicating AV blocks. 

In a comprehensive review of the "extreme exercise hypothesis" by Eijsvogels in 2018 (6) there is no discussion of the issue of bradyarrhythmias but perhaps  clinically significant BA should at least be considered candidates for still another consequence of too much of a good thing. 

In 1964 writing in the same journal Dr. Lev and Dr. Lenegre  separately  described age related fibrosis of the conduction system as a cause of heart block in the elderly. In 1999 ,JJ Schott (7) identified two families with progressive cardiac conduction defects related to a mutation in the gene encoding for the sodium channel SCN5A.

How could one know given  for example an older endurance athlete  with a heart block if Lev/Lenegre disease  were responsible or if the block was somehow induced by excessive aerobic activity? 

1) Andersen K et al  Risk of arrhythmias in 52,755 long-distance cross-country skiers: a cohort study.Eur Heart J. 2013 3624 31, Dec 34 (47)

2)Baldesberger,S et al Sinus node disease and arrhythmias in the long term follow-up of former professional cyclists.Euro Heart Journal 2008, 29, 71-78

3)Northcote, R et al Electrocardiographic findings in male veteran endurance athletes. British Heart J. 1989,61,155-160

4)Hood,A and Northcote, R of Cardiac assessment of veteran endurance athletes, a 12 year follow up study. British J Sports Med. 1999, 33, 239-243

5)D'Souza, A,Cross talk opposing view: Bradycardia in the trained athlete is attributable to a downregulation of a pacemaker channel in the sinus node. J Physiol 2015 Apr 15 593 (pt 8)1749-1741

(6) Eijsvogels T. et al The "extreme exercise  hypothesis":Recent findings and cardiovascular health implications Current Threat Options Cardio Med (2018)20:84

(7) Schott, JJ et al Cardiac conduction defects associated with mutations in  SCN5A .Nature Genetics 23:20-21 1999

Addendum : 12/12/20 In the original posting the section of Lev/Lenegre and SCN5A was inadvertently  omitted,