Assessment of Systolic Dyssynchrony for Cardiac Resynchronization Therapy Is Not Clinically Useful

Cardiac resynchronization therapy (CRT) is an effective treatment in patients with medically refractory heart failure. Several clinical trials have shown improvement in both left ventricular (LV) function and symptoms with CRT compared with controls,1,–,4 with the 2 largest trials showing a reduction in rates of hospitalization and death.5,6 On the basis of data from these studies, most international guidelines agree on the standard indications for CRT: impaired functional status with New York Heart Association functional class III or IV, LV ejection fraction (LVEF) ≤35%, and prolonged QRS duration ≥120 ms in the setting of optimal medical therapy.7,–,9 However, not all patients experienced improvement in symptoms or LV function, and numerous studies have focused on improving the selection criteria for CRT in the hopes of excluding these “nonresponders.”1,–,4 One of the most frequently studied modalities for patient selection is echocardiographic measurement of LV systolic dyssynchrony based on the supposition that there is a threshold for mechanical dyssynchrony below which there is no therapeutic benefit. Despite these studies, we argue that current echocardiographic methods of measuring dyssynchrony should not be used to exclude patients who are otherwise candidates for CRT. Conversely, in patients with narrow QRS, echocardiographic evidence of dyssynchrony is insufficient to warrant CRT on the basis of current data.Response by Delgado and Bax on p 663There are important unresolved issues regarding the use of mechanical dyssynchrony measurements for determining CRT eligibility in an individual patient. Let us examine the case of a 60-year-old man with ischemic cardiomyopathy, recurrent hospitalizations, and New York Heart Association functional class III despite an excellent heart failure drug regimen. He inquires about additional therapy to help improve his symptoms and keep him out of the …