Six-Minute-Walk Predicted ICD Mortality: New SCD-HeFT Analysis

April 14, 2014

WASHINGTON, DC — A follow-up analysis to the 2005 SCD-HeFT trial, an important milestone on the road to implantable cardioverter-defibrillator (ICD) therapy for primary prevention, has found that baseline performance on the six-minute-walk test (6MWT) predicted how much survival benefit patients would reap from the devices[1].

In SCD-HeFT, 2521 patients in NYHA class 2-3 with an LVEF <35% had been randomized to receive an ICD, amiodarone, or an amiodarone placebo (the latter two on a double-blind basis). Of those, 2397 had performed a baseline 6MWT.

Three-Year Mortality Hazard Ratios* (95% CI), ICD v Placebo, in SCD-HeFT by Six-Minute-Walk-Distance Tertiles

6MWT distance (m) HR (95% CI) p
<288 1.02 (0.75–1.39) 0.90
288-386 0.57 (0.39–0.83) 0.0035
>386 0.42 (0.26–0.66) 0.0002

*Adjusted for age, sex, HF etiology, NYHA class, LVEF, time since HF diagnosis, diabetes, mitral regurgitation, substance abuse, renal insufficiency, systolic BP, PR interval, QTc, intraventricular conduction delay, and use of an ACE inhibitor or digoxin

The trial's primary analysis, as heartwire reported on its preliminary presentation at a 2004 meeting, had shown that mortality reductions with ICD therapy were concentrated in patients who enrolled in NYHA class 2 heart failure but largely absent among those in NYHA class 3. The trial's leadership and independent observers have downplayed the clinical importance of the finding, one who wasn't involved in the trial calling it a "fluke."

Nonetheless, the current analysis, from Dr Daniel P Fishbein (University of Washington, Seattle) and colleagues, "confirms and extends previous findings from the SCD-HeFT trial showing that the survival benefit of primary-prevention ICD therapy varies importantly depending upon baseline functional capacity." It suggests that the 6MWT, a more objective measure of functional status compared with NYHA class, may be able to stratify patients according to whether they are likely to benefit from ICD therapy with longer survival.

But the two potential prognosticators don't necessarily sort out the same patients as either higher or lower risk, they note. Whether any individual patient with advanced heart failure is suitable for an ICD remains a judgment call, "recognizing that sicker patients are much less likely to benefit," the group writes in their report published online April 9, 2014 in the Journal of the American College of Cardiology. Where to draw the line in individual cases "can reasonably take account of both the NYHA class and the six-minute-walk distance."

The authors declare they have no conflicts to disclose.

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