Patient Selection and Echocardiographic Assessment of Dyssynchrony in Cardiac Resynchronization Therapy

Appropriate cardiac resynchronization therapy (CRT) enhances quality of life and improves survival in patients with refractory heart failure due to systolic dysfunction and mechanical dyssynchrony. On the assumption that the main therapeutic mechanism of CRT is the correction of dyssynchronous myocardial contraction, imaging-based measures of dyssynchrony have been intensely investigated with the aim of predicting response to therapy. Numerous echocardiographic dyssynchrony parameters have been proposed, but no large prospective trial have been published to prove the clinical utility of any of these indexes. Moreover, the methodology to derive the proposed dyssynchrony indexes has not been standardized. Therefore, the purpose of this article is to critically review the current status of proposed dyssynchrony indexes by echocardiography for patient selection and to recommend future investigations in this area. The adverse effects of dyssychronous activation1 and the ability to correct these abnormalities with biventricular stimulation2 were described long ago, but the potential therapeutic application was not realized until an unprecedented study in 1990 reported recovery from intractable heart failure in 16 patients implanted with conventional dual-chamber pacemakers programmed to a short atrioventricular (AV) delay.3 Although these results could not be reproduced in prospective studies4,5 and improvements could only be demonstrated short-term in highly selected patients,6 the race to find a pacing therapy for heart failure had begun. On the hypothesis that the disappointing results of dual-chamber pacing in prospective studies were due to cancelling or overcoming the beneficial effects of AV synchronisation by the adverse effect of RV pacing-induced dyssynchrony,7,8 Cazeau and colleagues proposed a 4-chamber pacing mode and reported the first successful permanent implant in 1994.9 Early randomized controlled trials confirmed short-term improvements in functional capacity and quality of life for patients.10–13 However it was the Comparison of Medical Therapy, Pacing, and Defibrillation in …