Assessment of Systolic Dyssynchrony for Cardiac Resynchronization Therapy Is Clinically Useful

The beneficial effects of cardiac resynchronization therapy (CRT) on morbidity and mortality of heart failure patients with wide QRS complex have been demonstrated extensively. Various single-center and multicenter randomized, clinical trials have shown that CRT improves heart failure symptoms and left ventricular (LV) function and induces a significant reduction in LV volumes and mitral regurgitation.1,–,4 In addition, CRT reduces the number of heart failure hospitalizations and improves long-term survival.5,–,8 More important, unlike other heart failure medical therapies that may lose their effects over time, CRT is a long-term effective therapy.9 Accordingly, current American Heart Association/American College of Cardiology/Heart and Rhythm Society guidelines consider CRT a class I indication for patients with drug-refractory heart failure symptoms, LV ejection fraction 120 ms).10Response by Sung and Foster on p 655Despite these encouraging results, cumulative evidence shows that only 60% to 80% of patients exhibit a favorable clinical or echocardiographic response to CRT.1 For example, in the MIRACLE (Multicenter InSync Randomized Clinical Evaluation) and the MIRACLE-ICD (Multicenter InSync Implantable Cardioverter Defibrillator) trials, more than 30% of the patients fulfilling the aforementioned inclusion criteria did not show a favorable clinical response to CRT.5,8 Several single-center studies have reported similar nonresponse rates and have questioned the accuracy of these inclusion criteria to identify patients who will respond to CRT, which has encouraged the research of novel indices and strategies that can reliably predict response to CRT.One of these indices is LV mechanical dyssynchrony. In the last decade, multiple single-center trials and the Cardiac Resynchronization in Heart Failure (CARE-HF) trial have demonstrated that LV mechanical dyssynchrony indices (most of which are based on echocardiographic measures) have superior accuracy compared with LV electric dyssynchrony …