Honing in on optimal ventricular pacing sites: an argument for his bundle pacing

Recent approaches to His-Purkinje system pacing

OBJECTIVE

Physiologic cardiac pacing is a novel technique which has been largely popularized in recent decades. His bundle pacing (HBP) has been long considered the most physiologic pacing method; however, with the widespread implementation of this method, its disadvantages have become apparent. In this context, left bundle branch pacing (LBBP)-directly engaged in the His-Purkinje system-has been foreseen as the best pacing method to mimic physiologic activation patterns. This review aimed to summarize recent approaches to physiologic cardiac pacing.

DATA SOURCES

This review included fully peer reviewed publications up to July 2018, found in the PubMed database using the keywords "His bundle branch pacing," "right ventricular pacing," and "physiologic pacing."

STUDY SELECTION

All selected articles were in English, with no restriction on study design.

RESULTS

The HBP has been studied worldwide, and is currently considered the most physiologic pacing method. However, it has disadvantages, such as high pacing threshold, unsatisfactory sensing and long procedure times, among others. Although LBBP is theoretically superior to HBP, the clinical relevance of this difference remains under debate, as few large randomized clinical trials with LBBP have been published.

CONCLUSIONS

Although HBP indeed appears to be the most physiologic pacing method, it has certain shortcomings, such as high pacing threshold, difficult implantation due to specific anatomic features, and others. Further studies are required to clarify the clinical significance of LBBP.

Conduction abnormalities after transcatheter aortic valve implantation

In the last few years, transcatheter aortic valve implantation (TAVI) has become an alternative procedure in patients with severe aortic stenosis and high risk for surgical aortic replacement. Due to the anatomic correlation between aortic valve structure and conduction system of the heart, one of the most common complications after TAVI is conduction system disturbances which including bundle branch block, complete heart block and need for permanent pacemaker implantation. Although these disturbances are usually not lethal, they may have a great influence on patients' state and long term-survival. Several risk factors for conduction disturbances have been identified which including age, anatomy of the heart, periprocedural factors, type of implanted valve, preexisting abnormalities and comorbidities. As this technique becomes more familiar to physicians, patients should be carefully screened for risk factors for the development of conduction abnormalities after TAVI in order to provide effective prevention and proper treatment.

His Bundle Pacing Or Biventricular Pacing For Cardiac Resynchronization Therapy In Heart Failure: Discovering New Methods For An Old Problem

Heart failure (HF) is one of the biggest epidemics of modern cardiovascular medicine. Cardiac resynchronization therapy (CRT) with biventricular (BiV) pacing has proven to have an integral role in the management of patients with reduced left ventricular (LV) function and left bundle branch blocks (LBBB). However, CRT with BiV pacing is not always feasible and even when it is, the percentage of non-responders remains high. Limitations in LV lead implantation due to anatomical or other constraints; non response to BiV pacing due to lead position or patient related factors and lack of benefit in patients with RBBB and patients with AV block and low normal LV function limit the use of BiV pacing. Permanent His Bundle pacing (HBP) is now a feasible alternative to BiV pacing for CRT therapy. This allows for recruitment of BBB disease and ventricular activation in a more physiological fashion. In this paper we review the physiology of HBP, available data on HBP for CRT and highlight how HBP can be a potential alternative in patients in whom BiV pacing did not provide clinical response or was unsuccessful.

Physiological mechanisms of QRS narrowing in bundle branch block patients undergoing permanent His bundle pacing

His bundle pacing is increasingly used to avoid chronic right ventricular pacing, and electrically resynchronize ventricular activation by narrowing or normalizing the QRS interval in left and right bundle branch block. The mechanisms by which this occurs remain poorly understood. In this review, the proposed mechanisms and evidence supporting them are discussed. Also discussed are aspects of mechanisms that are not completely supported by the evidence. We also review the differences and physiological bases for direct vs. indirect His bundle capture, and the physiological mechanisms for QRS narrowing vs. normalization following His bundle pacing.

Mechanisms of Heart Block after Transcatheter Aortic Valve Replacement - Cardiac Anatomy, Clinical Predictors and Mechanical Factors that Contribute to Permanent Pacemaker Implantation

Transcatheter aortic valve replacement (TAVR) has emerged as a valuable, minimally invasive treatment option in patients with symptomatic severe aortic stenosis at prohibitive or increased risk for conventional surgical replacement. Consequently, patients undergoing TAVR are prone to peri-procedural complications including cardiac conduction disturbances, which is the focus of this review. Atrioventricular conduction disturbances and arrhythmias before, during or after TAVR remain a matter of concern for this high-risk group of patients, as they have important consequences on hospital duration, short- and long-term medical management and finally on decisions of device-based treatment strategies (pacemaker or defibrillator implantation). We discuss the mechanisms of atrioventricular disturbances and characterise predisposing factors. Using validated clinical predictors, we discuss strategies to minimise the likelihood of creating permanent high-grade heart block, and identify factors to expedite the decision to implant a permanent pacemaker when the latter is unavoidable. We also discuss optimal pacing strategies to mitigate the possibility of pacing-induced cardiomyopathy.