Cardiac Resynchronization Therapy: Who Responds?
Abstract & Commentary
By John P. DiMarco, MD, PhD
Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville
Source: Hsu JC, et al. Predictors of super-response to cardiac resynchronization therapy and associated improvement in clinical cutcome: The MADIT-CRT study. J Am Coll Cardiol 2012;59:2366-2373.
This study examines the patterns of response to cardiac resynchronization therapy (CRT) among patients enrolled in the MADIT-CRT (Multicenter Automatic Defibrillator Implantation Trial With Cardiac Resynchronization Therapy) trial. MADIT-CRT was a study that looked at the effects of CRT among defibrillator candidates who had QRS durations over 130 msec and less severe heart failure symptoms (NYHA class I or II) as part of the protocol. 2-D echocardiograms were obtained prior to study enrollment and at 1 year. This study reports an analysis of the 752 patients randomized to the CRT-D therapy group who had complete clinical and electrocardiographic data collected both at baseline and at the 12-month follow-up. Patients with baseline and 12-month echocardiograms were divided into quartiles of left ventricular ejection fraction (LVEF) response. Patients in the highest quartile were termed “super responders,” patients in the second and third quartiles were termed “responders,” and patients in the lowest quartile were “hypo-responders.” Echocardiographic response was then associated with the primary endpoints in the study, which were nonfatal heart failure events or all-cause death, whichever came first, and the secondary endpoints of all-cause death or appropriate ICD therapy.
Super responders experienced a mean absolute LVEF increase of 17.5 ± 2.7%. The cutoff for entry into the super responder cutoff quartile was an LVEF improvement ≥ 14.5%. The mean LVEF increase in the responder group was 11.1 ± 1.8% with a range of 7.9 to 14.4%. The mean absolute LVEF increase among hypo-responders was 4.4 ± 3.2%. More than 70% of the super responders had an increase in LVEF to ≥ 45% at 12 months. Super responders were more often female and had a nonischemic heart failure etiology, baseline left bundle branch block, and longer QRS durations. Super responders were less likely to have histories of revascularization, myocardial infarction, smoking, or ventricular arrhythmias. Cox regression analysis showed that female gender, absence of prior myocardial infarction, QRS duration > 150 msec, left bundle branch block conduction pattern, body mass index less than 30 kg/m2, and smaller baseline left atrial volume index were independent predictors of super responder status. The primary endpoint of heart failure admission or death also correlated with responder status. The primary endpoint occurred in 2.6% in the super responder group, 7.8% in the responder group, and 19% of the hypo-responder group. A similar pattern was seen for the secondary endpoint of all-cause death: 1.6% among super responders, 2.7% among responders, and 6.3% among hypo-responders.
The authors conclude that dramatic responses to CRT can be predicted by clinical variables easily ascertained at baseline.
Commentary
Cardiac resynchronization therapy can improve outcomes in many patients, but we must remember that it has several potential disadvantages. The implant procedure is longer and has an increased complication risk compared to simple single- or dual-chamber ICD implantations. CRT-D devices are more expensive and the battery longevity is shorter. Therefore, it would be of considerable clinical value to be able to estimate accurately the potential benefit to individual patients with mild heart failure symptoms before committing them to the more complex device. In this paper, the authors identify six easily identified clinical or echocardiographic characteristics (female gender, QRS duration ≥ 150 ms, LBBB, body mass index ≤ 30, no history of myocardial infarction, and left atrial volume index) that can be used to predict potential long-term benefit from CRT. In patients with these characteristics, the risk-benefit ratio appears to favor CRT strongly. In patients with milder grades of heart failure without these characteristics and with predictors of a poor response (ischemic heart disease with revascularization or prior MI, a smoking history or established ventricular arrhythmia), the risk-benefit ratio may not be as favorable. In the latter group of patients, it may be wise to use a simpler ICD wait until heart failure worsens or QRS duration increases before attempting CRT.
This study examines the patterns of response to cardiac resynchronization therapy (CRT) among patients enrolled in the MADIT-CRT (Multicenter Automatic Defibrillator Implantation Trial With Cardiac Resynchronization Therapy) trial.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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