Introduction: Biventricular pacing is currently recognized as an effective therapy for cardiac resynchronization, indicated for symptomatic patients with left ventricular systolic dysfunction and left bundle branch block (LBBB). However, the percentage of non-responders can be up to 30%. This lack of response could be explained by the many variables derived from the fact that biventricular pacing is not physiological, combining an epicardial stimulation of the left ventricle (LV) with the endocardial stimulation of the right ventricle. On the other hand, retrospective studies showed that pacing the distal His bundle can correct the left bundle branch block.

Objective: This observational study evaluated the effectiveness of permanent His bundle pacing in correcting the electrical and mechanical parameters in patients with non-ischemic dilated cardiomyopathy, an ejection fraction of less than 35% and LBBB.

Methods: 12 patients with non-ischemic etiology and conventional indications for cardiac resynchronization were included. The procedure went as follows: after ga-ining venous access, a lead delivery system including a C315 His sheath and a 3830 Select Secure lead (Medtronic, Minneapolis) was placed at the septal atrioventri-cular junction. Careful mapping was performed until a distal His bundle signal was recorded. At that site, the pacing response was evaluated at variable pacing outputs. The procedural criteria for success was narrowing of the QRS complex to less than 130 ms with an amplitude of less than 3V/1ms. If the criteria was met, the lead was fixed, then an atrial lead was placed and both connected to a dual-chamber pacemaker. If the criteria was not met, then a biventricular pacemaker was implanted instead. Procedural characteristics and clinical and echocardiography parameters were recorded at ba-seline and 3 months follow-up.

Results: The mean age of the patients was 64.7 ± 10.6 years, with a prevalence of male sex (58.3%). Proce-dural success was recorded in 9 patients (75%) with a fluoroscopy time of 6.2 ± 1.1 min. The QRS detection threshold was 3.5 ± 1.2 mv, and the acute His bundle pacing threshold was 1.55 ± 0.74 V at 1 ms with nonselective capture in 78 % of cases. A significant narrowing of the QRS was observed, from 160 ± 16 ms to 91 ± 8.75 ms (p< 0.001). The three months follow-up showed a significant improvement in clinical and echocardiogra-phy parameters. The NYHA functional class improved from 2.66 ± 0.47 to 1.22 ± 0.41 (p< 0.001). The end-diastolic LV volume decreased from 200 ± 60 ml to 166 ± 55 ml (p< 0.001), the end-systolic LV volume decreased from 142 ± 42 ml to 94 ± 30 ml (p< 0.001), and the ejec-tion fraction increased from 28.2 ± 4.7 % to 47.2 ± 6.5 (p< 0.001). At three months, the His bundle pacing threshold remained practically the same, without any complications noted.

Conclusions: Permanent His bundle pacing is a much more physiological option for cardiac electrical and mechanical resynchronization in patients with left ventricular systolic dysfunction, left bundle branch block and non-ischemic etiology, achieving a near-complete correction of the intra and interventricular conduction abnormalities and a significant improvement in clinical and echocardiography parameters.