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Author Block:
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Bryan J. Har, MD, Ryan T. Mitchel,
BSc, Mariko
A. Shibata, BSc, Katherine M. Kavanagh, MD, Darlene Ramadan, RN, Derek V. Exner, MD, MPH, REFINE Investigators.
Libin Cardiovascular Institute of Alberta, Calgary, AB, Canada
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Introduction: Noninvasive tests have been developed to evaluate the
risk of death in patients surviving a myocardial infarction (MI). The use of
a single test to assess multiple measures of risk is desirable in terms of
time and resource utilization. We sought to assess if spectral repolarization alternans (TWA)
assessment provides additive prognostic value to heart rate (HR) recovery
evaluation early post-MI.
Methods: HR recovery and TWA were assessed from a single modified Bruce
exercise stress test performed 10 to 14 weeks post-MI. All patients received
standard, appropriate medical therapy.
HR recovery and TWA were assessed and interpreted in a blinded fashion. The
primary outcome was death from any cause. Cox models were used to assess the
utility of the noninvasive tests.
Results: The median age of the 228 patients was 61 years, 86% were male and
median ejection fraction was 0.47.
During a median follow-up of 51 months, 23 patients (10%) died.
A total of 96 (42%) patients had a non-negative TWA result, 163 patients
(71%) had abnormal HR recovery, and both tests were abnormal in 97 patients
(43%).
Individually, attenuated HR recovery and a non-negative TWA test each
predicted a higher risk of death. The addition of TWA to HR recovery was
associated with improved predictive accuracy, as evidenced by a significantly
larger area under the receiver operating characteristic curve (0.59 for HR
recovery alone vs. 0.67 for HR recovery plus TWA; p = 0.03).
The combination of abnormal HR recovery plus a non-negative TWA result was
associated with a 3.4-fold (95% confidence interval [CI] 1.3, 8.8) higher
risk of death after adjustment for history of previous MI, history of
diabetes, and ejection fraction (p = 0.01). This combination of tests
resulted in 18% positive (95% CI 13%, 23%) and 95% negative predictive
accuracy (95% CI 93%, 98%).
Conclusions: The combination of a non-negative TWA test and impaired HR
recovery predict a higher independent risk of death with good diagnostic
accuracy. This combination of parameters can be readily assessed from a
single exercise test.
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