Introduction on Update on Cardiac Resynchronisation Therapy for Heart Failure
Interventricular conduction delay is common in patients with systolic heart failure (HF) and has been associated with a poor prognosis amongst these patients.1 Abnormal ventricular depolarization results in prolonged ventricular activation time and increased myocardial tension thus increasing myocardial oxygen consumption and decreasing ventricular diastolic filling time. In addition, asynchronous ventricular contraction caused by conduction delay induces ventricular remodeling and has been shown to increase the duration of mitral regurgitation.2,3 Cardiac resynchronisation therapy (CRT) has been investigated as a therapy to reverse the deleterious effects of conduction delay by improving electrical and mechanical synchrony.
The first attempt CRT was performed over thirty years ago by placing an epicardial lead on the left ventricular lateral wall in patients with a left bundle branch block undergoing aortic valve replacement.4 Subsequently, Bakker, Gold and others assessed the role of epicaridal pacing in HF. Later, Daubert et al. reported the first case series of patients undergoing left ventricular pacing by transvenous lead placement into the coronary sinus.5 During the early years of CRT, a haemodynamic benefit of improved interventricular synchrony was shown setting the stage for future study. Since that time, multiple large, randomised clinical trials have been performed and demonstrated that CRT improves mortality and clinical outcomes in severe HF patients who are symptomatic despite optimal medical therapy.6–9