Role of echocardiography to determine candidacy for cardiac resynchronization therapy

Cardiac resynchronization therapy is a great benefit to many patients with severe symptomatic heart failure, wide QRS duration, and depressed left ventricular ejection fraction. Although the widened QRS is a surrogate for delayed mechanical activation, known as dyssynchrony, imaging techniques have identified a subset of patients with widened QRS who do not have dyssynchrony and accordingly do not respond to cardiac resynchronization therapy.

Many echocardiographic techniques have emerged to quantify regional dyssynchrony, in hopes of improving patient selection and response rate to cardiac resynchronization therapy. Principal methods include M-mode septal to posterior wall motion delay, pulsed Doppler measures of left ventricular ejection in relation to right ventricular ejection, diastolic filling time as a ratio of cycle length, and several tissue Doppler imaging techniques to assess intraventricular opposing wall delay or dispersion of time to peak velocities. Although the simple and straightforward methods are easy to reproduce, they are modest in predictive value. In contrast, tissue Doppler imaging and other more recent techniques have higher predictive value, but are technically much more complex and require training and experience.

This field continues to evolve and further data are needed to precisely define the appropriate role of echocardiographic dyssynchrony information in patient selection for cardiac resynchronization therapy.