Ventricular Resynchronization: Current State of the Art

In summary, CRT is an extremely promising and effective strategy to improve hemodynamic performance in patients with HF and bundle-branch blocks. Numerous elegant studies have demonstrated that CRT can restore synchrony and improve cardiac performance without the cost of increased myocardial oxygen consumption. This hemodynamic benefit rapidly translates into improved patient well-]being as evidenced by enhanced exercise capacity and reduced utilization of inpatient care. As-yet unpublished studies and meta-analyses suggest that CRT has a mortality benefit, particularly when combined with a defibrillator. Enthusiasm must be balanced by the high cost of the procedure, the relative dearth of clinical trial data (notably long-term follow-up studies powered for mortality endpoints), and very limited pathophysiological/mechanistic studies that support the idea that CRT addresses a fundamental biological process in the failing heart not otherwise addressed by conventional medical therapies. As with all new treatment strategies, the continuing conduct of new clinical trials remains a critical means by which practitioners clarify the appropriate use of the new therapy. Our current recommendation is that CRT is appropriate in the exact scenario addressed by the MUSTIC, MIRACLE, and COMPANION trials, ie, in patients with wide QRS complexes who remain symptomatic despite optimal medical therapy. Attempts should be made to ensure that the latter is achieved, and patients should be referred for participation in HF clinics or other disease management programs. There are multiple additional scenarios in which CRT could have a potential role-less symptomatic patients, patients with atrial fibrillation, or patients with narrow QRS complexes who are given iatrogenic LBBBs as a result of right ventricular pacing for conventional reasons. To date, evidence-based medicine criteria for dyssynchrony are based on QRS duration, but we can expect that in the near future, the assessment of mechanical dyssynchrony using sophisticated imaging techniques might play an important role in the selection and follow-up of patients and the optimization of the therapy. Although we endorse the conduct of clinical trials to test these scenarios, we do not currently recommend CRT for these indications.