Cardiac Resynchronization Therapy: A Review and Future Directions

Abstract

In millennia past, descriptions of congestive heart failure (CHF) often included ancient remedies. The earliest Egyptian papyri translated in the last century reveal a remarkably sophisticated understanding of heart ailments being the prime culprit in conditions of generalized edema (also called dropsy) and CHF.1 Starting in medieval times and continuing until the late 19th century, treatment for CHF included bloodletting to restore balance among the four humors.2 Writings as early as 1250 A.D. described using adjunctive pharmacologic therapy such as cardiac glycoside-containing herbal extracts to treat CHF.3 Several centuries ago, William Withering, a physician and botanist, wrote about the clinical effects of a foxglove plant extract in treating CHF. As a result, digitalis and its derivatives became one of the earliest medicines used in heart failure therapy. Rather than bloodletting, medical management of CHF has progressed in the last century to include diuretics to reduce pulmonary congestion; vasodilators of differing stripes; and, in the last 15 years, the initially counterintuitive use of beta-blockers as therapeutic mainstays. Other therapies are directed at treating the underlying cause of CHF, such as revascularization or valve replacement. Ultimate destination therapies include cardiac transplantation or the implantation of mechanical assist devices (e.g., left ventricular assist devices), while new strategies such as immunomodulation or stem cell therapy remain in various stages of investigation. In the late 1990s, the important role of electrical conduction disease was recognized in a significant number of patients with moderate to severe CHF; these patients demonstrated electrocardiac evidence of ventricular dyssynchrony (VD), Small clinical studies subsequently demonstrated that restoration of ventricular-ventricular synchrony could acutely improve parameters of cardiac performance.4-6 This concept of electromechanical therapy led to the initial trials of cardiac resynchronization therapy (CRT) as an important adjunctive treatment for patients with moderate to severe CHF. CRT is now a well-established adjunctive therapy for drug-refractory CHF in patients with moderate to severe diminishment in functional capacity.7-12