The evolution of cardiac resynchronization therapy and an introduction to conduction system pacing: a conceptual review

Abstract

In chronic systolic heart failure and conduction system disease, cardiac resynchronization therapy (CRT) is the only known non-pharmacologic heart failure therapy that improves cardiac function, functional capacity, and survival while decreasing cardiac workload and hospitalization rates. While conventional bi-ventricular pacing has been shown to benefit patients with heart failure and conduction system disease, there are limitations to its therapeutic success, resulting in widely variable clinical response. Limitations of conventional CRT evolve around myocardial scar, fibrosis, and inability to effectively simulate diseased tissue. Studies have shown endocardial stimulation in closer proximity to the specialized conduction system is more effective when compared with epicardial stimulation. Several observational and acute haemodynamic studies have demonstrated improved electrical resynchronization and echocardiographic response with conduction system pacing (CSP). Our objective is to provide a systematic review of the evolution of CRT, and an introduction to CSP as an intriguing, though experimental physiologic alternative to conventional CRT.

Left Bundle Branch Area Pacing vs. Biventricular Pacing for Cardiac Resynchronization Therapy: A Meta-Analysis

“…Previous studies with epicardial activation mapping indicated that electrical dyssynchrony remained despite the use of BVP, suggesting that activation time and pattern could not be corrected to a physiological level by BVP delivered CRT ( 21 ). Among new strategies of conduction system pacing, although LBBAP could not achieve normal physiological activation maintained via the right bundle as HBP ( 22 , 23 ), compared with BVP, LBBAP is associated with a significantly further decreased QRSd of −29.2 ms, as evidenced in our meta-analysis. In this meta-analysis, greater improvement of LVEF was achieved by LBBAP delivered CRT compared with BVP delivered CRT, which is paralleled with the more remarkable shortened QRSd in patients after LBBAP delivered CRT.…”

QUARTO III. Response rate in cardiac resynchronization therapy patients implanted with a left ventricular quadripolar lead and the MultiPoint TM Pacing feature activated.

“…CRT by biventricular pacing is the only heart failure therapy that improves cardiac function, functional capacity and survival while decreasing hospitalizations 14 . Nevertheless, the response to BiV pacing is variable, ranging from complete normalization of cardiac function to lack of benefit.…”

His-bundle Pacing as a Bailout Therapy for a Patient with Subclavian Stenosis and No Suitable Coronary Sinus Branch: A Double Whammy

“…We know that CRT is the only known non-pharmacologic HF therapy that improves cardiac function, functional capacity, and survival while decreasing cardiac workload and hospitalization rates in chronic systolic HF and conduction system disease. 6 , 7 However, CRT is not without its limitations. One major limitation of BiV pacing in CRT is the failure of LV lead deployment due to limitations in CS anatomy, 8 and the standard of care suggests epicardial LV lead insertion as the next alternative.…”

“…Presently, CSP serves as an attractive bailout strategy in patients with a lack of coronary venous access, diaphragmatic pacing, and/or failure to respond to classic CRT. 7 The 2021 European Society of Cardiology guidelines 11 recommend HBP as a treatment option together with other techniques such as surgical epicardial lead (class IIa level of evidence B indication) in CRT candidates in whom CS lead implantation is unsuccessful.…”