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Sunday, March 28, 2021

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

Thursday, March 25, 2021

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

Tuesday, March 16, 2021

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