Cardiac resynchronization therapy (CRT) with biventricular pacing (BVP) is a well-established therapy in patients with reduced left ventricular ejection fraction (LVEF) and bundle branch block or indication for pacing.[1,2] However, BVP achieves CRT through non-physiological fusion of paced wave fronts from the right ventricular endocardium and left ventricular epicardium. Up to one third of patients treated with BVP may not derive clinical or echocardiographic benefit, and some may worsen. Conduction system pacing (CSP) utilizing His bundle pacing (HBP), or left bundle branch area pacing (LBBAP) has been shown to be a feasible and more physiologic alternative to BVP.[4,5,6,7,8] Whether CRT through CSP results in better patient outcomes than conventional BVP was the scope of Vijayaraman et al.'s publication in Heart Rhythm.
In their multi-center observational study, the investigators published the findings from 477 consecutive patients with LVEF ≥35% and Class I or II indications for CRT. Patients underwent BVP (n = 219) or CSP (n = 258, which included HBP, n = 91, and LBBAP, n = 167) based on operator's preference and/or institutional practice. Both groups' baseline characteristics were similar. Procedural characteristics were slightly different. More patients received defibrillators in BVP group (93% vs. 85% respectively, P = 0.06), whereas longer procedural duration with similar fluoroscopy times were required for CSP group. LVEF improved in both groups during a mean follow-up duration of 27±12 months but significantly greater in the CSP group (39.7% vs. 33.1%, P<0.001). The primary outcome of death or heart failure hospitalization (HFH) was significantly lower in CSP versus BVP (28.3% vs. 38.4%; hazard ratio [HR] 1.52; confidence interval [CI] 1.082-2.087; P=0.013). Within the CSP group, no significant differences in the primary endpoint of death or HFH were observed among HBP versus LBBAP (33% vs. 27%; HR 1.095, 95% CI 0.677-1.769, p=0.712). Paced QRS duration was significantly narrower in the CSP group than in the BVP group (133±21ms vs. 152±24 ms, respectively; p<0.001).
BVP to improve electrical resynchronization is very effective in reducing death and HFH but the non-physiological fusion of paced wavefronts does not always result in complete electrical resynchronization. Previous studies have well demonstrated the higher success rates of electrical resynchronization with HBP or LBBAP.[6,11] For the first time, the long-term clinical outcomes of death or HFH among the CRT population undergoing BVP versus CSP was addressed and was shown to achieve better outcomes with CSP.
As acknowledged by the study investigators, this is an observational study leaving room for selection bias. Patients underwent CSP or BVP based on operator/institutional preference and were not randomized to either strategy. Echocardiographic evaluations were not blinded or performed in a core-lab. Furthermore, although the baseline characteristics were similar due to its non-randomized nature, this study does not ensure homogeneity between the study groups.
In conclusion, this study establishes a major constituent in the literature of CRT in heart failure patients and inspires researchers to look meticulously into the use of CSP to achieve CRT. Moreover, it also illustrates the previously demonstrated success rate of greater electrical synchronization with CSP. Large, prospective, randomized trials with a longer-term follow-up, comparing BVP and CSP are needed to confirm the clinical outcomes superiority of CSP as noted in this study.
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