Resynchronization Therapy in Patients with Narrow QRS - RethinQ - Presented at AHA 2007


The goal of the trial was to evaluate cardiac resynchronization therapy (CRT) among patients with heart failure with narrow QRS complexes who were implanted with an implantable cardioverter defibrillator (ICD).

Study Design

Study Design:

Patients Enrolled: 172
Mean Follow Up: 6 months
Mean Patient Age: Mean age 58 years
Female: 35

Patient Populations:

Approved indication for implantation of an ICD; advanced HF with New York Heart Association (NYHA) Class III, despite receiving optimal pharmacological therapy; stable heart failure medical regimen; LVEF ≤35%; evidence of mechanical dyssynchrony as measured by echocardiography using tissue Doppler imaging or M-mode; QRS duration < 130 ms (present in all ECG leads); ability to complete exercise stress testing and 6-minute hall walk test, with the only limiting factors being related to cardiac fitness.


Standard bradycardic indication for pacing; previously treated with CRT; continuous atrial fibrillation within 1 year prior to enrollment or have undergone cardioversion for AF in the past month; ability to walk > 450 meters during the 6-minute walk test; symptomatic chronic obstructive pulmonary disease (COPD); classification of Status 1 for cardiac transplantation or consideration for transplantation over the next 6 months; recent MI, unstable angina or cardiac revascularization within prior 40 days; recent cerebrovascular accident or transient ischemic attack within prior 3 months ; severe musculoskeletal disorder.

Primary Endpoints:

Proportion of patients with increased peak oxygen consumption ≥1.0 ml/kg of body weight per minute during cardiopulmonary exercise testing at 6 months

Secondary Endpoints:

Quality of Life Questionnaire at 6 months; New York Heart Association (NYHA) Classification at 6 months

Drug/Procedures Used:

Approximately 14 days after implantation of ICD, patients were randomized in a double-blind manner to receive cardiac resynchronization treatment (CRT ON; n = 85) or not to receive cardiac resynchronization treatment (CRT OFF; n = 87). At baseline and 6 months, cardiopulmonary exercise stress testing, an ECG, and a quality of life questionnaire were performed.

Principal Findings:

At baseline, the mean QRS interval was 107 msec, with 27% of patients having a QRS ≥120 msec. Indication for ICD was primary prevention in the majority of patients (85%) and secondary prevention in 15%. Heart disease etiology was ischemic in 52% of patients. Mean ejection fraction was 25%. Approximately one-quarter had moderate mitral regurgitation. Peak oxygen consumption averaged 12 ml/kg/min and exercise duration was 9 minutes.

The primary endpoint of increase in peak oxygen consumption ≥1.0 ml/kg of body weight per minute did not differ between the CRT group and the control group (46% vs. 41%, p = NS). There was also no difference in change in quality of life scores (median -8 vs -7, p = 0.91), change in 6-minute walking test (median 26 vs. 6, p = 0.23), or change in ejection fraction (median 1.2 vs. 2.0, p = 0.83). Improvement in NYHA class of ≥1 class was more common in the CRT group than the control group (54% vs. 29%, p = 0.006). Among the subgroup of patients with a QRS interval ≥120 msec, peak oxygen consumption increased in the CRT group compared with the control group (p = 0.02), but did not differ in the subgroup of patients with a QRS interval <120 msec (p = 0.45). By 6 months, there were 5 deaths in the CRT group and 1 in the control group (p = 0.11).


Among patients with heart failure with narrow QRS complexes who were implanted with an ICD, cardiac resynchronization therapy was not associated with a difference in the primary endpoint of peak oxygen consumption at 6 months compared with no CRT.

While CRT has shown benefit in patients with heart failure with a normal QRS ≥120 msec, no benefit was observed in the present study of patients with moderate and severe heart failure (predominantly NYHA class III) with narrow QRS complexes. The authors had hypothesized that CRT would improve LVEF and functional status by minimizing regional left ventricular delay caused by prolonged ventricular conduction, reducing mitral regurgitation and left ventricular reverse remodeling, and normalizing neurohormonal factors. Patients with a QRS interval ≥120 msec did show improved peak oxygen consumption with CRT compared to control, but these data should be interpreted with care given the overall negative findings of the trial.


Beshai JF, et al. Cardiac-Resynchronization Therapy in Heart Failure with Narrow QRS Complexes. N Engl J Med 2007;357:epub before print.

Presented by Dr. John F. Beshai at the American Heart Association Annual Scientific Session, Orlando, FL, November 2007.

Clinical Topics: Arrhythmias and Clinical EP, Diabetes and Cardiometabolic Disease, Heart Failure and Cardiomyopathies, Prevention, Valvular Heart Disease, Implantable Devices, SCD/Ventricular Arrhythmias, Acute Heart Failure, Exercise, Mitral Regurgitation

Keywords: Pyridinolcarbamate, Mitral Valve Insufficiency, Body Weight, Electrocardiography, Primary Prevention, Cardiac Resynchronization Therapy, Walking, Secondary Prevention, Oxygen Consumption, Quality of Life, Ventricular Remodeling, Heart Failure, Questionnaires, Heart Ventricles, Defibrillators, Implantable, Exercise Test

< Back to Listings