To the Editor:
We have read with interest the article by Dr. Moriña et al1 describing their initial experience with implantation of active fixation electrodes in the His bundle for permanent ventricular stimulation following ablation of the AV node. Their results are interesting as they establish stimulation threshold parameters and stable echocardiography measures after only a few months followup. Nevertheless, it must be noted that the failure rate with electrode implantation was considerable (33%) and the procedure was significantly long (approximately 3 hours). Their data are important because they open a potential treatment path for patients who require long-term ventricular stimulation with the aim of avoiding some of the serious complications that can result from stimulation of the RV apex.2-4
The authors point out that stimulation of the His bundle could be the most appropriate technique in patients with an intact His-Purkinje system (normal HV, normal surface ECG). Nevertheless, we would like to point out that the theoretically ideal candidates for the implantation of this system must be patients with an intact His-Purkinje and structural cardiopathy (prior ventricular dilatation or mitral insufficiency), which are the subgroups identified as being at greatest risk for developing hemodynamic deterioration or worsening of mitral insufficiency after ablation of the AV node.2
It is well known that stimulation from the apex of the right ventricle (RV) interferes with the closure of the mitral valve due to changes in the activation sequence of the mitral valve apparatus and the tension generated in the papillary muscles, or both. The function of the mitral valve depends on the integrity of the veils, the tendon cords, the mitral ring, the papillary muscles, and all these structures as a whole during ventricular systole in order to occlude the mitral orifice. The dimensions of the ventricles and the valve ring vary during the cardiac cycle, so that the position of the papillary muscles and their interaction with the mitral valve area can produce changes in regurgitation during the cardiac cycle. The anomalous activation of the papillary muscles during right ventricular stimulation will change the tension of the valve veils in a way that could cause a coaptation fault and an increase in the regurgitation orifice. In these patients, stimulation from the His bundle could be an excellent alternative in the hands of an expert, although this has not been proven in intermediate and long-term studies. In patients without structural heart disease and AV block at the suprahisian level, permanent stimulation of the His bundle is technically possible, as shown by Moriña et al; nevertheless, this patient population is not the one that a priori appears would benefit most in terms of mortality and morbidity. Biventricular stimulation could be an interesting option in patients with possible hemodynamic deterioration, although this would also be subject to various technical limitations.