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 phrenic nerve stimulation, with the exception of reducing the stimulation energy. Reducing the stimulation energy, in turn, prevented an adequate safety margin from being maintained in patients pacemaker dependent patients. Notwithstanding the premature interruption of the study, the results observed regarding ventricular pacing safety and effectiveness assessments were sufficient to reach strong conclusions. Analysis of the intraoperative parameters of ventricular leads showed that the stimulation threshold, impedance, and sensitivity for QRS complexes showed significant differences between the groups. With the exception of two cases in the LV Group, the values obtained for both RV and LV stimulation were within the range considered ideal for safe ventricular pacing. Even though the postoperative complication rate was expressively higher in the LV Group, undesired phrenic nerve stimulation was the most common complication, occurring in 9 of the 35 patients in this group. Of these, 3 cases required surgical correction due to the impossibility of resolving the problem by reprogramming the energy. A fourth patient required reoperation due to a fracture of the StarFix lead conductor. In these 4 cases, the medical team decided to implant a new lead in the RV, which resulted in 4 cases of crossover in the study. Based on the criteria established in the study, efficacy, stimulation and sensitivity parameters were considered adequate in all evaluations perfomed for all patients of the RV group. In the LV Group, however, only 31 of the 35 patients studied presented adequate ventricular pacing conditions in all phases of the study. In 2 patients, the parameters did not meet the conditions established as adequate by the study during the intraoperative phase, but there was improvement in the stimulation conditions during the postoperative period. In 2 other cases, failure began to occur in month from the 6th and 18th months of follow-up. The premature interruption of the study compromised the analysis of secondary results, as the sample size calculation had defined that 282 research subjects would be included in the study, 188 patients in the LV Group and 94 in the RV Group. During the study’s follow-up period, there were no hospitalizations owing to heart failure. On the other hand, we observed the occurrence of left ventricular remodeling and reduction of left ventricular ejection fraction when comparing the echocardiogram performed at the baseline with that obtained at month 24 of follow-up. Although the rate of patients whose LV ejection fraction worsened was higher in patients in the RV Group (23.5% vs. 20.6%), the number of individuals included in the study did not allow the sample to be analyzed regarding this result. The rate of ventricular remodeling was slightly higher in patients in the LV Group (29.4% vs. 27.3%). Analysis of cardiac synchrony showed that there was an important difference between LV wall activation time in patients in the RV Group more frequently than in the LV Group (55.9% vs. 43.8%). Similarly, patients in the RV Group more frequently showed delays in activation between the RV and LV (91.2% vs. 68.8%). Notwithstanding the small number of patients evaluated, the difference in the occurrence rate of interventricular dyssynchrony between groups was statistically significant (p = 0.022). Study limitations Although the study met its primary objectives, there are some inevitable limitations. The main limitation is related to the premature interruption of the study which made it impossible to reach the sample size necessary for evaluating clinical and echocardiographic outcomes. Additionally, a small number of individuals with LV ejection fraction between 0.40 and 0.50 were included; these individuals would possibly have had greater chances of suffering the deleterious effects of RV pacing. This notwithstanding, the safety and efficacy results refer exclusively to the use of unipolar leads, which no longer represent state-of-the-art LV pacing through the coronary sinus, given that the last 3 years have seen the development of quadripolar leads that facilitate positioning with ideal stimulation in a location far from the phrenic nerve. 36,37 Regardless of the methodological problems occurred, it was possible to observe that interventricular synchrony was shown to be significantly better in patients with LV pacing. This perspective opens doors for future studies to be conducted using quadripolar leads with the aim of preventing the deleterious effects of conventional ventricular pacing. Conclusions The routine use of isolated left ventricular pacing pacemaker dependent patients with the use of a Medtronic Attain StarFix® Model 4195 OTW lead through the coronary sinus was shown to be impractical given the low rates of procedural success, safety, and efficacy. The comparison of the clinical and echocardiographic effects of left ventricular pacing with those of right ventricular pacing was not possible owing to the low level of cases studied, even though interventricular synchrony was shown to be significantly better in patients with LV pacing. Author contributions Conception and design of the research, analysis and interpretation of the data and writing of the manuscript: Crevelari ES, da Silva KR, Costa R; acquisition of data: Crevelari ES, Albertini CMM, Vieira MLC; obtaining funding: Costa R; critical revision of the manuscript for intellectual content: Crevelari ES, da Silva KR, Albertini CMM, Vieira MLC, Martinelli Filho M, Costa R. Potential Conflict of Interest No potential conflict of interest relevant to this article was reported. Sources of Funding This study was funded by Medtronic. Study Association This article is part of the thesis of Doctoral submitted by Elizabeth Sartori Crevelari, from Instituto do Coração do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo. 418