6.1. Pacing for bradycardia
Several small studies have demonstrated the superiority of HBP over RV pacing in avoiding Pacing-Induced Cardiomyopathy. Even though upgrading simple RV to biventricular pacing could be a highly effective solution in patients with post-implant LVEF <35%, nevertheless, it is significantly underutilized even in those with lower preimplant LVEF.28 The echocardiographically estimated LVEF is used as a study indicator of Pacing-Induced Cardiomyopathy, knowing, of course, the limitations of this indicator in terms of the impact of clinical endpoints and mortality in patients with heart failure.29 The older studies by Zanon et al. (2008), Barba-Pichardo et al. (2010), and Kronborg et al. (2014) recorded an LVEF improvement in 12, 59, and 32 patients, respectively, mainly with atrioventricular block, with relatively short follow-up of 3-12 months, in single-center trials.30-32 Sharma et al. (2015) and Vijayaraman et al. (2018) included 75 patients in each study, recording less heart failure hospitalization and a trend in lower mortality in patients with >40% ventricular pacing, as well as no difference in patients with atrial fibrillation, in HBP group.27, 33
The largest study is that of Abdelrahman et al. (2018), a two-center study that included 304 consecutive patients with HBP and 433 patients with RV pacing at a sister hospital. In a 2-year follow-up, the study showed the superiority of HBP in terms of the combined endpoint of all-cause mortality, heart failure hospitalization, or upgrade to biventricular pacing. The HBP superiority was even great in patients with ventricular pacing >20% (HR 0.71 and 0.65, respectively).34 Additionally, two recently published studies with a small number of patients with bradycardia have documented the adequacy of HBP in maintaining LVEF after transcatheter aortic valve implantation, as well as in comparison with LBBAP.35, 36 The commonality of all the above studies is that the data came from observational, single, or two-center studies, with few patients, with short follow-up periods. For that reason, most authors emphasize the need to conduct large, prospective, randomized control trials (RCTs) comparing HBP to RV pacing to prove beneficial clinical endpoints, such as reduction in hospitalizations and mortality attributable to HBP in patients with bradycardia.