His Bundle Pacing: A New Strategy for Physiological Ventricular Activation

T he specialized fibers of the His-Purkinje system are essential for the maintenance of the coordinated, synchronous ventricular contraction via endocardial to epicardial and apical to basal electrical activation. The right ventricle has been the most commonly used site to deliver artificial pacemaker stimuli since the 1950s, although pacing from both right ventricular (RV) apical and septal positions causes ventricular dyssynchrony, which is in turn associated with deleterious consequences including impaired myocardial perfusion, mitral and tricuspid regurgitation, an increased risk of atrial fibrillation, and systolic contractile dysfunction. As a result, the risk of hospitalization for heart failure was strikingly increased in patients receiving a higher proportion of ventricular pacing in the DAVID (Dual Chamber and VVI Implantable Defibrillator) trial 4,5 and MOST (Mode Selection Trial) alongside an increased risk of ventricular tachycardia/ fibrillation. Current guidelines and pacemaker algorithms therefore promote the minimization of right ventricular pacing wherever possible; however, excessive restriction of RV pacing with, for example, long atrioventricular delays impairs atrioventricular synchrony, increasing the risk of atrioventricular block at higher atrial rates and predisposing to mitral regurgitation. Furthermore, current strategies for the reduction of RV pacing have not improved clinical outcomes. In patients with impairment of left ventricular (LV) systolic function and dyssynchrony attributable to left bundle branch block with a broad QRS duration, the benefits of at least partial restoration of ventricular synchrony with cardiac resynchronization therapy (CRT) from RV and coronary venous approaches are well established. However, there remain patient groups for whom the indication for CRT is contentious, including those with right bundle branch block, while 30% of patients meeting criteria for CRT implantation have a suboptimal clinical response. The benefits of CRT are also less clear cut in patients with left bundle branch block and a relatively narrow QRS complex, and in a further group of patients it is not possible to achieve satisfactory placement of an left ventricular lead because of unfavorable anatomy of the coronary venous system. There exists a need for new pacing techniques that could reduce intraventricular and atrioventricular dyssynchrony by providing a more physiological pattern of ventricular electrical activation, with the aim of maintaining contractile function, optimizing atrioventricular synchrony and reducing the clinical complications of a high burden of RV pacing (RVP). His bundle pacing (HBP) is an alternative approach to RV and biventricular pacing and is performed with the aim of maintaining a physiological pattern of ventricular activation via the native His-Purkinje system. One further potential advantage of HBP compared with RVP is a theoretical reduction in the risk of functional tricuspid regurgitation when the lead position lies on the atrial side of the tricuspid valve (as is the case in proximal His bundle implants). A reduction in tricuspid regurgitation has yet to be proven clinically with His bundle pacing, however, and would not be expected when His pacing is combined with transvalvular lead systems such as implantable cardioverter-defibrillator leads or with including RVP and distal His/conducting system implants. The conceptual benefits of HBP compared with RVP in terms of improved QRS durations and ventricular activation patterns are increasingly recognized, while the feasibility of permanent HBP in patients was demonstrated in 2000. The development of new leads and delivery catheters has From the Department of Cardiology, Great Western Hospitals NHS Foundation Trust, Swindon, United Kingdom (A.J.M.L., P.F., B.C.); Radcliffe Department of Medicine and British Heart Centre for Research Excellence, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom (A.J.M.L.); Imperial College London, Hammersmith Hospital, London, United Kingdom (Z.W., D.K.). Correspondence to: Andrew J. M. Lewis, DPhil, MBBS, Department of Cardiology, Great Western Hospitals NHS Foundation Trust, Marlborough Rd, Swindon SN3 6BB, United Kingdom. E-mail: andrew.lewis@cardiov.ox. ac.uk J Am Heart Assoc. 2019;8:e010972. DOI: 10.1161/JAHA.118. 010972. a 2019 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.