Abstract
Purpose of ReviewThe aim of cardiac resynchronization therapy (CRT) is to improve cardiac function by delivering more physiological cardiac activation to patients with heart failure and conduction abnormalities. Biventricular pacing (BVP) is the most commonly used method for delivering CRT; it has been shown in large randomized controlled trials to significantly improve morbidity and mortality in patients with heart failure. However, BVP delivers only modest reductions in ventricular activation time and is only beneficial in patients with prolonged QRS duration. In this review, we explore conduction system pacing as a method for delivering more effective ventricular resynchronization and to extend pacing therapy for heart failure to patients without left bundle branch block (LBBB).Recent FindingsThe aim of conduction system pacing is to provide physiological ventricular activation by directly stimulating the conduction system. Current modalities include His bundle and left conduction system pacing. His bundle pacing is the most established method; it has the potential to correct left bundle branch block and deliver more effective ventricular resynchronization than BVP. This translates into greater acute haemodynamic improvements and observational data suggests that His-CRT results in improvements in cardiac function and symptoms. AV-optimized His bundle pacing is being investigated in patients with heart failure and long PR interval without LBBB, to see if this improves exercise capacity. More recently, a technique for pacing the left bundle branch has been developed. Early studies show potential advantages including low and stable capture thresholds.SummaryConduction system pacing can deliver more effective ventricular resynchronization than BVP, which has the potential to deliver greater improvements in cardiac function. It may also provide the opportunity to extend pacing therapy for heart failure to patients who do not have LBBB. Further data is required from randomized trials to assess these promising pacing techniques.
Highlights
Cardiac resynchronization therapy (CRT) is as an important treatment for patients with heart failure and cardiacThis article is part of the Topical Collection on Clinical Heart Failure conduction system disease
We found that AV delay optimization improved acute haemodynamics in this group with a mean increase in systolic blood pressure of 4 mmHg, which is around 60% of the effect size of biventricular pacing when it is delivered to patients with heart failure and left bundle branch block
Biventricular pacing may not be the optimal method for delivering cardiac resynchronization to patients with RBBB, since left ventricular activation may be preserved during intrinsic conduction, in which case LV pacing via the coronary sinus may produce more dyssynchronous left activation that occurs during intrinsic conduction, some patients with a RBBB ECG morphology may have left conduction system disease and delayed left ventricular activation [41], which may account for the benefits observed in some studies in this group with BVP
Summary
Cardiac resynchronization therapy (CRT) is as an important treatment for patients with heart failure and cardiac. Biventricular pacing is the most established method for delivering cardiac resynchronization therapy, and its use is supported by the findings from several large randomized controlled trials [1, 2]. When delivered to patients with heart failure and QRS prolongation, BVP reduces the risk of death and improves symptoms [1, 3]. Despite the success of BVP as a treatment, there are potential reasons to explore alternative methods for delivering CRT which include the following: 1. More effective ventricular resynchronization: Despite biventricular pacing, morbidity and mortality remains. Biventricular pacing delivers only modest reductions in QRS duration, and there appears to be potential to deliver greater improvements in cardiac function if more effective ventricular resynchronization can be delivered
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