Design of clinical cardioprotection trials using CMR: impact of myocardial salvage index and a narrow inclusion window on sample size
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KeywordsCardiac Magnetic Resonance Late Gadolinium Enhancement Sufficient Statistical Power Fixed Time Point Cardiac Magnetic Resonance Examination
Cardiac magnetic resonance imaging (CMR) can be used to determine both myocardial infarct (MI) size and myocardium at risk (MaR), enabling assessment of myocardial salvage index (MSI). MI size as assessed by hyperenhancement on late gadolinium enhancement (LGE) has been shown to decrease approximately 25% during the first week after infarction. The aim of this study was to determine to what extent assessment of MSI and a narrow inclusion window affect the number of patients needed to reach sufficient statistical power in a clinical CMR cardioprotection trial.
Control subjects (n=91) from the recent CHILL-MI1 and MITOCARE2 cardioprotection trials, examined by CMR 2-6 days after acute reperfusion therapy, were used to assess the difference in sample size required to reach sufficient statistical power when using MI size alone compared to MSI as outcome variable. In addition, 22 patients undergoing CMR at day 1 and 7 after acute reperfused infarction from a previous follow-up study3 were included to assess to what extent sample size is affected by the decrease in hyperenhancement seen during the first week after infarction. The variability of MI size by LGE, MaR by contrast-enhanced SSFP and MSI was used to simulate 100.000 clinical trials for different assumed treatment effects to determine the number of patients needed to reach sufficient statistical power.
There is a significant reduction in sample size needed to reach sufficient statistical power in CMR cardioprotection trials when using MSI instead of MI size alone as outcome variable. In addition, sample size can be further reduced by narrowing the inclusion window during the first week after the acute event.
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