Evaluation of Left Bundle Branch Area Pacing As A Rescue Strategy for Cardiac Resynchronization Therapy Non-Response

Heart failure is one of the leading causes of death, hospitalization and poor quality of life among Veterans. For many Veterans despite receiving maximal medical therapy for heart failure with reduced ejection fraction (HFrEF), their cardiac function and functional capacity markedly decreases and they develop delays and blocks in their intrinsic conduction system (i.e. left bundle branch block). These patients then meet criteria for cardiac resynchronization therapy (CRT), which has been shown to improve cardiac function. However, up to 40% of patients who undergo CRT do not experience the expected improvement in cardiac function or clinical improvement, and this is termed "non-response".

A critical limitation of traditional CRT is that the leads do not directly utilize the heart's intrinsic conduction tissue, called the His-Purkinje system. An extensive web of conduction tissue capable of transmitting the electrical signals all over the ventricles within milliseconds, the His-Purkinje system conducts electrical stimuli much faster than conduction through a usual myocardial cell. The left bundle branch is a component of the His-Purkinje system. As such, electrophysiologic therapies that directly activate the left bundle branch area (LBBAP) have emerged as possible solutions to the problem of non-response to CRT. Although data suggests that in patients with complete LBBB, LBBAP can better optimize electrical synchrony and improve cardiac function compared to traditional bi-ventricular CRT, the efficacy has not been studied in CRT non-responders.

Currently, the most frequently used technique for assessment of the left ventricle is echocardiography because it is widely available. However, several studies have demonstrated that cardiac MRI (CMR) is superior to echocardiography in measuring left ventricle ejection fraction, particularly in terms of interstudy reproducibility. Recent studies have also demonstrated CMR imaging to be safe even in patients with non-MRI-conditional pacemakers and defibrillators. Studies have also observed that patients undergoing MRI with non-MRI-conditional pacemakers or ICDs neither experienced device/lead failure nor were they at increased risk by undergoing MRI. Despite established safety of CMR in patients with cardiac devices, it is not being routinely performed because there are concerns that the devices will cause field inhomogeneity resulting in magnetic susceptibility artifacts and non-diagnostic image quality. However, these concerns are overcome by utilizing contemporary imaging protocols with gradient echo sequences as opposed to standard steady-state free precession. By using these new protocols for CMR in this study, the investigators aim to establish the feasibility of CMR to prospectively assess cardiac function at baseline and during follow-up in patients with cardiac devices (i.e. that the image quality in subjects with implantable devices is adequate and not undermined by image artifact).