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 3 – Composition of the study population. LV: left ventricle; RV: right ventricle. Period: June 2012 to January 2014 Potential candidates for the study (n = 417) 326 individuals were not included • Did not meet study eligibility criteria (n = 289) • Did not agree to participate (n = 37) Randomization (n = 91) RV Group (n = 36) LV Group (n = 55) Excluded from the study Impossibility of LV implant (n = 20) Loss of follow-up (n = 0) Loss of follow-up (n = 0) RV Implant (n = 36) LV Implant (n = 35) Inclusion Composition of study population Intervention Final analysis Primary study outcomes Success of the proposed surgical procedure In all patients in the RV Group, PM implantation was successfully performed without any intercurrences. In the LV Group, on the other hand, it was not possible to implant the lead in coronary veins in 20 (36.4%) of the of the 55 patients initially allocated. The most frequent cause of failure to implant the LV lead was undesired phrenic nerve stimulation in regions that could be stimulated through the LV free wall. This problem occurred in 12 patients, representing 60% of all causes of LV implant failure. Coronary sinus cannulation difficulties (n = 3), inability to access coronary veins (n = 5), and unstable positioning (n = 2) prevented the use of left ventricular pacing in the other cases of failure to use the coronary sinus. Surgical procedure safety Postoperative complications were detected only in the LV Group. The most frequent complication was phrenic stimulation, observed in 9 (25.7%) patients. During the clinical follow-up period, 4 (11.4%) patients in the LV Group underwent reoperation. There were 1 case of LV lead fracture (358 days after the initial implant) and 3 (8.6%) cases of phrenic stimulation which could not be resolved by reprogramming (42, 55, and 70 days after the initial procedure). In all 4 cases, the surgical procedure was performed successfully and without complications. The surgical team, however, decided to perform new lead implants in the RV, leading to a crossover of patients from the LV Group to the RV Group. Surgical procedure efficacy Once the previously mentioned complications were corrected, stimulation and sensitivity were considered adequate in all phases of the study in 100% of the patients in the RV Group and 31 (88.6%) patients in the LV Group (Table 3). Of the 4 patients who presented ventricular stimulation thresholds above those considered adequate in this study, 2 cases occurred intraoperatively (acute phase); 1 patient presented alterations in the stimulation threshold during months 6, 12, 18, and 24 of clinical follow-up and 1 presented alterations in months 18 and 24 of clinical follow-up. Secondary study outcomes Clinical outcomes There were two deaths in the study, both in patients in the RV Group. The declared causes were acute myocardial infarction, 13.2 months after implantation, and septic shock due to pneumonia, 20.9 months after implantation. 414