The American Heart Association has published a science advisory on selecting patients for cardiac resynchronization therapy (CRT). The advisory, “Patient Selection for Cardiac Resynchronization Therapy,” appears in the April 26, 2005 issue of Circulation.
CRT is a somewhat new therapy that can be added to the treatment regimen of patients with symptomatic heart failure caused by systolic dysfunction. CRT is accomplished by simultaneously pacing the left and right ventricles, which resynchronizes the timing of global left ventricular depolarization and consequently improves mechanical contractility and mitral regurgitation.
CRT has been shown in trials to improve functional status and quality of life for patients with symptomatic heart failure. It also has been shown to significantly reduce the combined endpoint of all-cause mortality and hospitalization.
The best candidates for CRT are patients with dilated cardiomyopathy on an ischemic or nonischemic basis, a left ventricular ejection fraction of 0.35 or less, a QRS complex of more than 120 milliseconds, sinus rhythm, and New York Heart Association (NYHA) functional class III or IV symptoms despite maximal medical therapy for heart failure.
The use of CRT for patients with minimal heart failure has not been studied widely and is not recommended at this time. Most patients in the CRT trials had a wide QRS complex on the basis of a left bundle branch block. The benefit for patients with a left versus a right bundle branch block is unclear; however, the current recommendation for CRT is based on QRS duration, not QRS morphology. Other unresolved issues regarding CRT include the risks and benefits of left ventricular pacing without a right ventricular lead, the risks and benefits of surgical placement of a left ventricular pacing lead versus a nonthoracotomy approach, and the use of CRT for patients with NYHA class IV symptoms who are nonambulatory and dependent on intravenous inotropes for hemodynamic support.
The risks associated with implanting a CRT device are small and similar to those associated with the transvenous implantation of a conventional permanent pacemaker or implantable defibrillator. These risks include bleeding, infection, hematoma, pneumothorax, pericardial effusion, myocardial infarction, stroke, and death.