Sunday, May 14, 2017

Is his bundle pacing (HBP) a feasible alternative to RV pacing now or to CRT in future?

Dr. Nabil Paktin

The answer is, the Time and Market will prove it, NOT the Knowledge and Scholars!

Estimated that worldwide, about 1-3 million patients die annually due to a Lack of a Pacemaker.
 - By comparison, about 30.000 persons die annually from influenza, 1.6 million people died of HIV/AIDS in 2012.
Death from bradycardia is entirely preventable.

Right ventricular RV apical pacing has been the standard practice for patients requiring permanent ventricular pacing however long term RV apical pacing has its drawbacks.
 A prolonged PR interval results in reduced left ventricular filling, abnormal filling pattern, presystolic mitral regurgitation due to delayed and ineffective closure of the mitral valve. Prolongation of the PR interval results from cardiac conduction disease but may also be a marker of advanced structural heart disease associated with atrial electrical and structural remodeling of a long-standing RV apical or septal pacing.
 Prolongation of PR interval by itself independently associated with an increased risk of AF, increased mortality and heart failure hospitalization in the general population, in patients with CAD and in patients with left ventricular dysfunction.

Isolated RV pacing activates the interventricular septum before the LV lateral wall, seen as LBBB pattern on the ECG due to propagation of the electrical wave front away from the sternum result in LV dyssynchrony and mismatched timing between chamber walls, with deleterious effects on LV function and adverse clinical outcomes. Including heart failure and mortality. RV pacing-induced cardiomyopathy rates of up to 20% with frequent RV pacing among patients with preserved EF is reported.
RV apical pacing deleterious effects are as follows:

1,Altered left ventricular electrical and mechanical activation
2, Altered ventricular function
3, Remodeling
4, Cellular disarray
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The outflow tract has been used as the alternative to the apex; however, the results have been discouraging.

The reduction of QRS duration obtained with right ventricular septal pacing correlated with homogenization of left ventricular contraction and improved systolic performance, albeit with minor differences in ejection fraction.

Bifocal right ventricular (apical and outflow tract) pacing has been proposed for patients with heart failure where the coronary sinus approach to effect biventricular pacing turns out to be unsuccessful due to various reasons, such as failure to cannulate the os or to advance the lead. in the ROVA study, there was partial improvement reported with right ventricular bifocal pacing.

However, preliminary data have indicated that there were no significant differences between single-site left ventricular pacing and biventricular pacing for cardiac resynchronization therapy suggesting that RV pacing may be redundant and left ventricular pacing alone might suffice.
A few studies have compared RV apical pacing with LV or BiV pacing, which has now become the standard method to apply cardiac resynchronization therapy in patients with refractory heart failure. Overall, patients treated with BiV pacing had significantly greater improvement in QRS duration, 6-minute walk test, and quality-of life scores compared to RV pacing therapy.
Because His-bundle pacing (HBP) produces ventricular contraction via the specific conduction system, it does not induce interventricular or intraventricular asynchrony or trigger the myocardial perfusion disorders described with RV apical pacing. It is reported that 73% of AV conduction disturbances which required permanent pacing, regardless of location, were corrected with HBP. 

However, the HBP is encouraging for narrow-QRS block, where success is considerable ( 67%) , but even in patient who have a block with wide QRS complex success is about 57%.
In the case of blocks with a wide QRS complex, HBP is known to be capable of correcting bundle-branch blocks, and obtain a normal QRS complex in the presence of complete AV block considered “infra-hisian”. 
The theory of the longitudinal dissociation of the His bundle explains these phenomena. Functional longitudinal dissociation of the His-bundle was first proposed by Kaufman and Rothberger in 1919. Predestined fibers within the His bundle selectively conducted to the individual bundle branches, and these fibers originated within the proximal portions of the common bundle. 
This concept was demonstrated in humans by Narula in 1977. According to this theory, the fibers ascribed to the right and left branches are histologically differentiated and isolated inside the trunk. Injury to the trunk may damage these fibers, showing up in the ECG as a bundle-branch block or complete block. 
Stimulation of the portion distal to the injury normalize the QRS complex. Patients with LBBB and baseline prolonged HV intervals were paced slightly distal to the proximal His-bundle, resulting in a narrowing of the QRS. 

HBP’s Limitations : His-bundle pacing does entail greater energy consumption due to the higher stimulation threshold. A higher degree of fibrosis that causes a thicker layer of unexcitable tissue between lead and excitable myocardium, or calcification of this region, could explain this phenomenon. However, new types of batteries that are able to withstand higher energy consumption without significant shortening of their lifespan be an advantage.
The loss of capture and dislodgement occurred in about 5% of patients, higher than conventional RV apical pacing is another disadvantage of HBP.

Final Message:
Significant improvement in left ventricular performance has been reported with HBP use.
His bundle pacing has been shown to result in the same QRS duration and pressure development as sinus rhythm and atrial pacing and better hemodynamics than RV apex pacing.

   1-  About 10-20% of patients who get ventricular pacers ( lots) develop pacing induced heart failure
- Many of these patients go on to upgrade to a more expensive CRT device. (Second Device)
- HB prevents pacing induced heart failure. Scaled worldwide this is massive.
2 2-     HBP can reverse LBBB and that is exactly what CRT devices do.
3 3-     These two features reduce market demand for CRT devices. 

References :
  1- Narula OS . Longitudinal dissociation in the His bundle. Bundle branch block due to asynchronous conduction within the His bundle in man. Circulation. 1977l.
2-Barsheshet A., Moss AJ, Mcnitt S, et al. long-term implication of cumulative right ventricular   acing among patients with an implantatble cardioverter defibrillator, heart rhythm. 2011
3-Permanet His-bundle pacing: seeing physiological ventricular pacing. Europace 2010
4-His bundle pacing , A new promise in Heart failure therapy? 2015 JACC
5-Cheng S, keyes MJ Larson MG, et al. long-term outcomes in individuals with rologed PR interval or first-degree AV block , JAMA 2009
6-DAVID Trial investigaors, Dual-chamebr pacing or vnetriular backup pacing in patients with an implandtable defibrillator: the dual chamber and VVI Implantable Defibrillator ( DAVID) Trial.JAMA 2002
7-Khurshid S, Epstien AR, Verdino RJ, E al. incidence and predictors of Right Ventricular Pacing induced cardiomyopathy. Heart Rhythm 2014
8-Hear Rhythm Society 2017 meeting.

The outflow tract has been used as the alternative to the apex; however, the results have been discouraging. 

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