Invited commentary: Necessary first steps

This editorial refers to ‘Efficacy on resynchronization and longitudinal contractile function comparing His-bundle pacing with conventional biventricular pacing: a substudy to the His-alternative study’, by E.V. Højgaard et al., https://doi.org/10.1093/ehjci/jead181. Cardiac resynchronization therapy (CRT) is an established treatment for patients with heart failure with reduced ejection fraction (HFrEF) and wide QRS complexes. However, in recent years, the advent of His-bundle pacing and left bundle branch area pacing (LBBaP) has introduced promising alternatives. These innovative pacing techniques aim to maintain the physiological activation of the ventricles by directly stimulating the conduction system. His-bundle pacing, in that regard, allows for the rapid conduction of electrical stimuli through the bundle branches and Purkinje fibres to the myocardium, ultimately resulting in narrow QRS complexes. Moreover, His-bundle pacing is able to correct proximally located bundle branch blocks (LBBBs) in some patients, suggesting a potential alternative to traditional CRT.1 However, His-bundle pacing is not without challenges, including the occurrence of high and escalating pacing thresholds in certain patients during follow-up, alongside limitations in addressing distally located blocks. So far, there are only very few prospective randomized studies comparing His-bundle pacing with CRT, one of them being the His-alternative study2 where 50 patients with HFrEF and LBBB were randomized to receive either a His-bundle electrode (HIS-CRT) or an LV electrode (BiV-CRT). In the current issue of the European Heart Journal—Cardiovascular Imaging, Højgaard et al.3 present an in-depth echocardiographic analysis of myocardial mechanics and restoration of synchronous contraction pattern in both groups of the HIS-Alternative study. The assessment of mechanical dyssynchrony was conducted through the standard deviation of time-to-peak strain and the calculation of the septal-to-lateral myocardial work ratio. Further characterization of LBBB contraction patterns involved visual assessments of septal flash and apical rocking, all signs that have been previously shown to be predictive for CRT response.4 Following implantation, overall improvement in mechanical dyssynchrony was observed with no significant differences between the HIS-CRT and BiV-CRT groups, across any of the analysed parameters. This study demonstrates that His-pacing can be an efficient treatment for dyssynchrony. It also highlights, however, the challenges that come with this type of treatment. It is striking that the cross-over rate was close to 30% (7 out of 25), mainly due to a high threshold for capturing or a lacking His-signal. Furthermore, this study does not demonstrate, whether His-pacing is as efficient as CRT. For this, the patient cohort is far too small to reach sufficient statistical power for a non-inferiority proof. A longer follow-up may have also helped to better distinguish between groups. In addition, strict electrocardiogram criteria were used to select patients with LBBB, potentially leading to the over-representation of patients with non-ischaemic cardiomyopathy and a more proximally localized electrical block. This study is, therefore, a necessary first step towards objectifying the benefits of His-pacing. Nevertheless, larger prospective multi-centre studies with clinical endpoints are warranted to further elucidate the role of HIS-bundle pacing in CRT. In the meantime, LBBaP emerges as a potentially stronger alternative owing to its higher success rates, stable and low pacing thresholds, and a more distal position of the pacing electrode, facilitating correction of more distally located electrical blocks. Theoretically, LBBaP also holds promise for correcting LBBB and may offer an alternative to CRT in HFrEF patients.5 But also here, it is not yet known whether the method can achieve the same benefit for the patient as classical CRT. First steps are taken, but there is still a way to go. None declared. No original data have been used in the preparation of this manuscript.