Pacing for Cardiac Resynchronisation Using the Intrinsic Conduction System to Maintain Physiologic Ventricular Activation

Background:

Conventional ectopic myocardial right ventricular pacing (RVP) causes ventricular dyssynchrony and may be associated with reverse ventricular remodeling, reduced ejection fraction (EF), left ventricular dilatation, functional mitral valve regurgitation, heart failure and an increased rate of new onset atrial fibrillation.

Dependent on individual patient's characteristics, several strategies are established to prevent and to overcome the potential drawbacks of chronic RVP. In general, unnecessary ectopic RVP should be avoided. For example, in patients with sinus node disease and intact atrioventricular (AV) conduction, atrial pacing, AV (search) hysteresis or AAI-DDD/ADI pacing may be used. In patients with impaired cardiac function and an expected higher percentage of RVP, pacing strategies for cardiac resynchronization are indicated. Conventional cardiac resynchronization therapy (CRT) uses an additional transvenous left ventricular lead for synchronous ventricular stimulation and was shown to shorten QRS duration and to reduce morbidity and mortality in patients with chronic heart failure, left bundle branch block (LBBB) and reduced EF. Due to the non-physiological left ventricular epicardial stimulation, however, conventional CRT is associated with 30% of non-responders and may even prolong ventricular activation in patients with narrower QRS complex. First described in 1968, His bundle pacing (HBP) has evolved to an increasingly used alternative for cardiac pacing. Currently, HBP is regarded the most physiologic approach for ventricular stimulation because it prevents ventricular dyssynchrony and its potential fatal long-term consequences by preserving normal electrical activation of the ventricles. Clinical benefit of HBP has been shown compared with conventional permanent RVP and CRT. Recent studies documented restoration of normal electrical and mechanical left ventricular synchrony for both selective and non-selective HBP. However, compared with conventional RVP the implantation procedure for HBP is much more demanding requiring exact placement of the pacing lead within the anatomically variable His bundle area. Alternatively, the correction of bundle branch conduction disorders has been demonstrated for left bundle branch area (LBBA) pacing. As a consequence, current guidelines recommend pacing methods that maintain physiologic ventricular activation in patients with atrioventricular block who have an indication for permanent pacing with a LVEF between 36% and 50% and are expected to require ventricular pacing more than 40% of the time (class IIa indication).

In summary, there is increasing evidence showing the benefits of the different strategies for physiologic pacing but the appropriate use of these approaches may be challenging in the individual case. Therefore, appropriate patient selection, implantation approaches, device programming and follow-up require further intensive evaluation.

Objective: