ABC | Volume 112, Nº4, April 2019

Original Article Philbois et al Isolated left ventricular pacing in bradyarrhythmias Arq Bras Cardiol. 2019; 112(4):410-421 Figure 4 – Behavior of Functional Classification of Heart Failure (NYHA) during assessment in the clinical follow-up phase. FC: functional class; LV: left ventricle; RV: right ventricle. 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% RV LV 1m RV LV 6m RV LV 12m RV LV 18m RV LV 24m FC I FC II FC III 13.9 86.1 86.1 8.6 88.6 11.1 17.1 82.9 69.4 30.6 22.9 77.1 77.1 75.0 18.7 20.0 91.4 5.7 14.3 85.7 Patients (%) 2.8 2.8 6.3 2.9 2.9 According to the criteria defined for the present study, tissue Doppler analysis showed that 55.9% of the individuals in the RV Group and 43.7% of those in the LV Group had left ventricular intraventricular dyssynchrony (p = 0.324). This method also detected that 91.2% and 68.7% of patients in the RV and LV groups, respectively, had interventricular dyssynchrony (p = 0.022). Discussion The present study was the first designed with the specific purpose of comparing the clinical and functional effects of left ventricular pacing to those of right ventricular pacing in patients with advanced atrioventricular conduction block, as well as evaluating the feasibility of using coronary sinus as a safe alternative for the artificial pacemaker dependent patients on this type of therapy. Considering the evidence that there are deleterious effects related to right ventricular pacing in patients with advanced atrioventricular blocks who have preserved ventricular function at the time of first PM implantation 7-14 and the fact that new transvenous techniques for implanting leads in the LV are being developed, we judge that it is important to evaluate whether there are clinical and functional differences that justify changing from the classic form of endocardial right ventricular pacing to LV pacing, as well as whether the routine use of left ventricular pacing through the coronary sinus is technically feasible in patients with atrioventricular blocks. There were difficulties in patient inclusion in the study, mainly due to the high rate of chronic renal dysfunction in individuals with acquired atrioventricular block and due to the urgency of treating bradycardia, which made it difficult to perform fundamental tests for selection and inclusion of patients into the study. The main reason why only 91 patients were included was the monitoring committee’s decision to interrupt the study, owing to problems related to the safety of the Medtronic Attain StarFix ® Model 4195 OTW lead in the present study project. In more than a third of individuals allocated for LV implant, it was not possible to obtain safe conditions for artificial pacing of patients who were dependent on this type of therapy. In this manner, in 20 of the 55 patients allocated into the LV Group, after unsuccessfully attempting the left ventricular implant through the coronary sinus, the surgical team decided to perform the implant in the RV. Despite the fact that, at the end of the operation, these 20 patients received the lead in the RV, they were excluded from the phase which compared results regarding pacing effectiveness and clinical and functional effects. On the other hand, regarding safety analysis, the failure to obtain safe conditions for LV pacing in 36.4% of cases was decisive to the conclusion that the Medtronic Attain StarFix ® Model 4195 OTW lead, notwithstanding its utility in patients undergoing biventricular implantation for cardiac resynchronization, is not an adequate option for unifocal ventricular pacing in patients dependent on PM. The most frequent reason that left ventricular pacing failed in the patients of the present study was phrenic nerve stimulation. Although this complication is reported in 2–37% of patients with severe left ventricular dysfunction, 31-33,36 in the present study it occurred in 12 patients, which represents the main cause of failure to implant in the LV. Nevertheless, 25.7% of patients presented phrenic nerve stimulation in the postoperative period. We believe that the small epicardial surface of the LV lateral wall, in patients with preserved ventricular function, when compared to the epicardial area of patients with severe dysfunction, caused the regions where the left ventricular lead was implanted to be very close to the phrenic nerve. The association of this condition with the unipolar configuration of the StarFix. lead implicated an absence of alternatives for correcting the 417