Rationale for and mechanisms of benefit of cardiac resynchronization therapy
- Leslie A Saxon, MD
Leslie A Saxon, MD
- Professor of Medicine
- University of Southern California
- Teresa DeMarco, MD
Teresa DeMarco, MD
- Professor of Medicine
- University of California, San Francisco
Medical therapies, such as angiotensin converting enzyme inhibitors, beta blockers, and spironolactone, have led to marked improvements in both symptom control and overall survival in patients with heart failure (HF). (See "Overview of the therapy of heart failure with reduced ejection fraction".)
Implanted devices, such as cardioverter-defibrillators (ICDs) and pacemakers, can also be beneficial. In particular, ICDs are now recommended for primary prevention of sudden cardiac death in selected patients with ischemic and nonischemic cardiomyopathy.
In addition, some patients with HF and bundle branch block benefit from simultaneous pacing of both ventricles (biventricular or BiV pacing) or of one ventricle. This approach is referred to as cardiac resynchronization therapy (CRT) [1-6]. CRT can be achieved with a device designed only for pacing or can be incorporated into a combination device with an ICD (figure 1).
CRT is now recommended across a spectrum of patients with HF due to systolic dysfunction in association with QRS delay [7,8]. Initial studies of CRT therapy resulted in United States Food and Drug Administration (FDA) approval for patients with advanced HF (usually New York Heart Association [NYHA] class III or IV), severe systolic dysfunction (eg, left ventricular ejection fraction ≤35 percent) and intraventricular conduction delay (eg, QRS >120 msec). Based on the positive results of the MADIT-CRT trial, which evaluated CRT in the setting of Class I-II HF with QRS delay, the FDA has approved CRT to this class of patients . (See "Cardiac resynchronization therapy in heart failure: Indications" and "Cardiac resynchronization therapy in heart failure: Indications", section on 'Clinical trials'.)
The rationale for CRT is that ventricular dyssynchrony can further impair the pump function of a failing ventricle. Resynchronization may improve pump performance and reverse the deleterious process of ventricular remodeling.
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