QRS Duration Criteria to Select Patients for Cardiac Resynchronization Therapy

Cardiac resynchronization therapy (CRT) is now a major therapeutic tool in the management of patients with systolic heart failure. In several small- and large-scale studies, CRT led to statistically significant improvements in cardiac performance, promoted reverse remodeling, and reduced adverse clinical events, including death in patient populations with heart failure and prolonged QRS durations.1–4 However, soon after these studies were completed and guidelines were written, it was recognized that these statistically very significant benefits, observed at the level of study cohorts, did not translate into clinical improvement in many individual patients receiving CRT according to the enrollment criteria of these previous studies, that is, symptomatic systolic heart failure with a QRS duration usually greater than 120 ms. Postapproval studies showed that one third to one half of patients receiving this treatment based on the guidelines do not respond to this treatment.5,6 Response by Guglin and Curtis on p 442 Treatment guidelines initially recommended CRT in patients with systolic heart failure with New York Heart Association (NYHA) III or IV symptoms and a QRS duration >120 ms7–10 and were extrapolated from the patient enrollment criteria of the 2 early major CRT trials.11,12 Given the well-documented lack of response in a sizable fraction of patients who met these guideline criteria for CRT, cardiologists had to contend with a large group of CRT nonresponders, which led to the creation of special nonresponder clinics in some institutions.13 This type of approach primarily focused on an attempt to optimize the device settings echocardiographically after device implant when there was lack of a clinical improvement. However, lack of benefit from CRT has other causes, including a lack of a suitable electromechanical substrate. Therefore, patients may not derive any benefit no matter what type …