Impact of Natural Mild Hypothermia in the Early Phase of ST-Elevation Myocardial Infarction: Cardiac Magnetic Resonance Imaging Study

BACKGROUND: Mild hypothermia (32–35°C) during acute myocardial ischemia has been considered cardioprotective in animal studies. We sought to determine the association of between natural mild hypothermia and myocardial salvage as assessed by cardiac magnetic resonance imaging (CMR) in ST-elevation myocardial infarction (STEMI) patients undergoing primary percutaneous coronary intervention (PCI). METHODS: In 291 patients with STEMI, CMR was performed a median of 3 days after the index event. Body temperature was collected for 24 hours after PCI. Fifty-one patients (17.5%) had natural mild hypothermia (less than 35°C) during the day after PCI, and 240 (82.5%) did not. RESULTS: The primary endpoint, the myocardial salvage index, was significantly higher in the natural mild hypothermia group than in the normothermia group (median [IQR], 50 [37–64] vs. 43 [30–56], p = 0.013). The myocardial area at risk between the 2 groups did not differ (39 [22–51] vs. 35 [24–44], p = 0.361), nor did the infarct size (16 [10–28] vs. 20 [12–27], p = 0.301), presence of microvascular obstruction (57% vs. 60%, p=0.641), or hemorrhagic infarction (43% vs. 46%, p = 0.760). A multivariable linear regression showed a significant association between the lowest body temperature and myocardial salvage index (β = -0.191, p = 0.001). CONCLUSIONS: In patients with STEMI undergoing primary PCI, natural mild hypothermia within 24 hours is associated with greater salvaged myocardium.