Identification of wasted energy is a key to predict positive response to cardiac resynchronization therapy: Is strain imaging the answer?

The introduction of cardiac resynchronization therapy (CRT) more than 10 years ago has been a major progress in heart failure therapy,1 and it has been shown clearly that CRT is beneficial to patients with intraventricular conduction delay in terms of reduced hospitalization and mortality.2 On the basis of clinical and ECG criteria alone, up to 70% of the patients with nonischemic cardiomyopathy respond positively to CRT, but only about 50% of the patients with ischemic cardiomyopathy respond.3–5 Recently, clinical and ECG criteria have been revised to limit the class 1 indication to QRS ≥150 ms and left bundle branch block (LBBB), but to include those with NYHA class II.6 Although echocardiography seemed to be an ideal tool to identify patients who would benefit positively from CRT, the 2012 device-based therapy guideline does not include echocardiography as one of selection criteria. Article see p 177 Initial results using different tissue Doppler imaging velocity-derived dyssynchrony indices from single-center studies were encouraging.7,8 However, the results of the multicenter study, PROSPECT,4 were disappointing as they demonstrated that all previously promising dyssynchrony indices had at best moderate predictive value for CRT response, if any.4 Although a substantial interobserver variability in PROSPECT was blamed for its poor result, our CRT working group confirmed that none of temporal dyssynchrony measures determined by M-mode, 3-dimensional volumetric, tissue Doppler, or strain echocardiography imaging was able to predict CRT response satisfactorily.3 A major reason for the failure of temporal dyssynchrony by echocardiography is that even if dyssynchronous activation can be corrected by CRT, mechanical dyssynchrony or discoordination may not be satisfactorily improved or corrected, especially when there are few viable myopcardium or none.9 Therefore, an ideal parameter that predicts CRT response should be able to identify the …