Cardiac-resynchronization therapy (CRT) does not improve peak oxygen consumption in patients with moderate-to-severe heart failure, providing evidence that patients with heart failure and narrow ventricular depolarizing (QRS) may not benefit from CRT, according to a study published in the Dec. 13 issue of the New England Journal of Medicine.
The indications for CRT in patients with heart failure include a prolonged QRS interval (of greater than, or equal to120 msec), in addition to other functional criteria. Some patients with narrow QRS complexes have echocardiographic evidence of left ventricular mechanical dyssynchrony and may also benefit from CRT.
In order to investigate the phenomena, John F. Beshai, MD, of the University of Chicago in Chicago, and colleagues, enrolled 172 patients who had a standard indication for an implantable cardioverter–defibrillator. In the study, the patients received the CRT device and were randomly assigned to the CRT group or to a control group (no CRT) for six months. The primary endpoint was the proportion of patients with an increase in peak oxygen consumption of at least one ml per kilogram of body weight per minute during cardiopulmonary exercise testing at six months.
At six months, the authors observed that the CRT group and the control group did not differ significantly in the proportion of patients with the primary endpoint (46 percent and 41 percent, respectively). In a prespecified subgroup with a QRS interval of 120 msec or more, the peak oxygen consumption increased in the CRT group, but it was unchanged in a subgroup with a QRS interval of less than 120 msec.
The researchers also reported that there were 24 heart-failure events requiring intravenous therapy in 14 patients in the CRT group (16.1 percent) and 41 events in 19 patients in the control group (22.3 percent), but the difference was not significant.
The study was a government clinical trial, sponsored by St. Jude Medical.