Role of echocardiography in selection of patients for biventricular pacing therapy.

Cardiac resynchronization therapy (CRT) has demonstrated improved quality of life, New York Heart Association class, left ventricular ejection fraction, and survival in patients with moderate to severe heart failure, left ventricular ejection fraction less than or equal to 35%, and a prolonged QRS duration. QRS duration remains the primary surrogate for mechanical dyssynchrony, defining the pathophysiology of abnormal regional mechanical activation. Studies have demonstrated that 30% to 40% of patients who meet current criteria for CRT are nonresponders. Therefore, there is great interest in the relationship between electrical and mechanical dyssynchrony, and the ability of each alone or together to predict response remains unknown. Echocardiographic approaches have emerged to quantify mechanical dyssynchrony with greater specificity than QRS duration alone. Although these methods are complex, exciting, and highly accurate for predicting response to CRT in single-center studies, they lack widespread applicability and validation to replace current criteria for device implantation. Use of echocardiography to define dyssynchrony and the impact of promising imaging methods for future patient selection for CRT are discussed.