Selection for Cardiac Resynchronization Therapy

SEE PAGE 969 C ardiac resynchronization therapy (CRT) is a highly effective treatment for some patients with heart failure. Current guidelines recommend the implantation of CRT devices in patients with left ventricular (LV) dysfunction and electrical dyssynchrony, evidenced by a left bundle branch block (1). Unfortunately, not all patients suitable for CRT derive symptomatic benefit—an unsatisfactory situation, because device implantation is costly and carries a small risk. Despite the failure of previous CRT selection strategies involving echocardiographic techniques (2), there have been continued efforts to predict those most likely to benefit. Because device implantation itself provides a placebo effect, responsiveness has been defined on the basis of imaging changes or survival benefit. There are problems with this approach (3). The use of imaging to identify reverse remodeling or improvement in ejection fraction is limited by the test–retest reliability of the reference measurement. The statistical challenges of using echocardiography for identifying CRT response have been previously emphasized in iJACC (4). Moreover, the additional problem of using reverse remodeling as an endpoint is that a 15% change of a severely remodeled LV is substantially different biologically from that in a small ventricle. Unfortunately, arguing for CRT responsiveness based on survival is also problematic. In the absence of a control group, it is impossible to discern whether treated patients would have survived for a shorter time frame had a device not been implanted.