BackgroundCardiac resynchronization therapy (CRT) is associated with challenges such as elevated capture thresholds, diaphragmatic stimulation, and lead instability. ObjectiveAssess the chronic safety and efficacy of the quadripolar CRT-D device system with the Quartet 1458Q Left Ventricular (LV) lead in a CRT-indicated population followed for 5 years and evaluate all-cause mortality and impact of baseline characteristics on survival through 5 years. MethodsPatients indicated for a CRT-D system were followed every 6 months post-implant for 5 years and assessed device performance and adverse events at each visit. The three primary endpoints were freedom from quadripolar CRT-D system-related complications through 5 years, freedom from Quartet 1458Q LV lead-related complications through 5 years, and the mean programmed pacing capture threshold at 5 years. ResultsThe study enrolled 1,970 subjects at 71 sites. The quadripolar CRT-D system was successfully implanted in 97.2% of subjects. Freedom from quadripolar CRT-D device system-related complications through 5 years was 89.7% and freedom from Quartet 1458Q LV lead-related complications through 5 years was 95.7%. 3.49 % of subjects had LV lead-related complications and an overall LV lead complication rate was 0.0122 events per subject-year. A mean LV pacing capture threshold was 1.52 ± 1.01 V at 5 years. The 5-year survival rate was 67.4%. ConclusionThe quadripolar CRT-D system with the Quartet 1458Q LV lead exhibited low rates of complications and stable electrical performance through 5 years of follow-up and suggested a higher 5-year survival rate compared to traditional CRT systems.