Physiologic Pacing

Podcast Transcript

Announcer:
Welcome to Cleveland Clinic Cardiac Consult, brought to you by the Sydell and Arnold Miller Family Heart, Vascular and Thoracic Institute at Cleveland Clinic.

Oussama Wazni, MD, MBA:
Hello, everybody. Welcome once more to a podcast from the Cleveland Clinic, Electrophysiology. As you know, I'm Oussama Wazni. I'm the Section Head of Electrophysiology here at the Clinic, and today it's my honor and pleasure to have with me, Dr. Roy Chung, who is the Director of Physiologic Pacing Center and leading our effort in physiologic pacing. So, Roy, could you please tell us why physiologic pace and how is it different from the usual pacing we've been practicing for many decades now?

Roy Chung, MD:
Good morning, everyone. Thank you, Dr. Wazni, for the kind introduction. So, about five years ago, Dr. Vijayaraman from Geisinger published his experience comparing right ventricular pacing versus His bundle pacing in patients who has greater than 40% RV pacing burden. What they demonstrated was, there was a higher percentage of patients presenting with recurrent heart failure hospitalization due to RV pacing-induced cardiomyopathy. In view of that result, and also even from our own publications from Dr. Cantillon, when you have a threshold of 20% or more RV pacing burden, we start seeing patients with cardiomyopathy. They did not notice this in patients who has conduction system pacing, namely RV pacing. This is five years ago.

Oussama Wazni, MD, MBA:
So, just to clarify then, we're talking about patients who have probably complete heart block, and they need a pacemaker. In the usual pacemaker, we have a lead in the right atrium and in the right ventricle. In these patients, there's a high percentage of right ventricular pacing, and that is associated with heart failure.

Roy Chung, MD:
That's correct. When you have-

Oussama Wazni, MD, MBA:
To negate that, we are doing His bundle pacing. So could you explain to us then what is physiologic pacing and why do we think physiologic pacing is probably better for patients than the regular RV pacing?

Roy Chung, MD:
So every patient, every individual has a innate, conduction His Purkinje system. Even in the setting of high grade AV block, if we can implant elite along the His bundle site and engage the activation of the natural conduction system, then we will generate a very narrow QRS, activating both ventricles simultaneously. So when you have simultaneous bi-ventricle activation, it's almost mimicking bi-ventricle pacing or CRT, if you will.

Oussama Wazni, MD, MBA:
Or even normal conduction.

Roy Chung, MD:
Yes. So be because of that, you really avoid the traditional asymmetrical, right ventricle activation prior to left ventricular. Which is through basis of pacing-induced cardiomyopathy.

Oussama Wazni, MD, MBA:
So basically what RV pacing does is actually asynchrony where the RV is stimulated before the right ventricle is stimulated before the left ventricle. That is a cause of heart failure and it's like giving a patient a left bundle branch block because now we're pacing the right ventricle before the left vent. Which we know now can cause heart failure. So, that's great. Could you tell us about our experience here at the Clinic?

Roy Chung, MD:
We have a manuscript and under revision in our own observation, we have actually done both. There's two different type of physiologic pacing. We have His bundle pacing and then we have left bundle branch pacing. The fundamental difference really is in His bundle pacing. You have elite implanted along the His bundle, which is an insulated fiber compared to left bundle branch pacing, where you have a lead traversing across the right ventricle septum into the left bundle branch along these left sub endocardium.

Roy Chung, MD:
So our experience is that like most centers have, who has high volume of conduction system pacing is His bundle pacing in general has a much higher capture threshold compared to left bundle branch pacing. In the short term, it's not an issue; but we are implanting these for patients who has AV block or even CRT indications. They're going to be pacing a lot. And with the higher capture thresholds, we are going to run into a problem with premature battery depletion and as a result of that, a very premature battery changes and subsequent risk of infections.

Oussama Wazni, MD, MBA:
That's great. Just to summarize quickly, the field has moved now and you and your own experience have moved for His bundle pacing, which is protected by a sheath basically, and the results in high thresholds. Which depletes the battery much sooner than if you're able to just place the lead in the septum. The pace the left bundle, or recruit the left bundle with a lower threshold and therefore, the device will last longer.

Roy Chung, MD:
That's correct.

Oussama Wazni, MD, MBA:
Very good. Could you share with us some examples of what this has accomplished in a patient?

Roy Chung, MD:
In our own experience, both His bundle pacing and left bundle branch pacing population, none of our patients has had worsening pacing induced cardiomyopathy, and none of our patients has presented with recurrent half hospitalization, or more importantly for CRT, traditional CRT upgrade. That is the fundamental difference compared to a regular right ventricular pacing populations.

Oussama Wazni, MD, MBA:
Do you think you would recommend now, any patient who comes to you, would you recommend physiologic pacing? Are there any barriers to physiologic pacing? Are there any cases where you will not be able to, or it's not advisable to perform physiologic pacing?

Roy Chung, MD:
At our center, our primary approach for pacing now is left bundle branch pacing. Especially in patients with high grade AV block. Now, if you have interventricular conduction delay, physiologic pacing will not work because the delay is due to a pathological left ventricular issue really, rather than a conduction issue. So physiologic pacing would not work in that in patients who has failed traditional CRTs because of elevated left CS lead threshold or diaphragmatic simulations, those are excellent candidates for physiologic pacing. Finally patients who has uncontrolled refractory atrial fibrillation and right rapid response and cardiomyopathy who are elderly, those are also excellent patients for this therapy in conjunction with AV node ablation.

Oussama Wazni, MD, MBA:
That sounds great. Thank you very much. In summary, it looks like a majority of our patients who have heart block or will develop heart block, are better served with left bundle branch pacing to decrease their risk of heart failure and recurrent hospitalizations. Thank you very much, Dr. Chung, and please join us for another podcast at some other time. We will keep you updated. Thank you so much.

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