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Updated: Feb 15, 2026
Acute Myocardial Infarction in Rats
Published on: February 16, 2011
Dose-Dependent Cardioprotection of Moderate (32°C) Versus Mild (35°C) Therapeutic Hypothermia in Porcine
Rajesh Dash1, Yoshiaki Mitsutake2, Wook Bum Pyun3
1Division of Cardiovascular Medicine, Stanford University, Stanford, California; Cardiovascular Institute, Stanford University, Stanford, California.
Objectives:
The study investigated whether a dose response exists between myocardial salvage and the depth of therapeutic hypothermia.
Background:
Cardiac protection from mild hypothermia during acute myocardial infarction (AMI) has yielded equivocal clinical trial results. Rapid, deeper hypothermia may improve myocardial salvage.
Methods:
Swine (n = 24) undergoing AMI were assigned to 3 reperfusion groups: normothermia (38°C) and mild (35°C) and moderate (32°C) hypothermia. One-hour anterior myocardial ischemia was followed by rapid endovascular cooling to target reperfusion temperature. Cooling began 30 min before reperfusion. Target temperature was reached before reperfusion and was maintained for 60 min. Infarct size (IS) was assessed on day 6 using cardiac magnetic resonance, triphenyl tetrazolium chloride, and histopathology.
Results:
Triphenyl tetrazolium chloride area at risk (AAR) was equivalent in all groups (p = 0.2), but 32°C exhibited 77% and 91% reductions in IS size per AAR compared with 35°C and 38°C, respectively (AAR: 38°C, 45 ± 12%; 35°C, 17 ± 10%; 32°C, 4 ± 4%; p < 0.001) and comparable reductions per LV mass (LV mass: 38°C, 14 ± 5%; 35°C, 5 ± 3%; 32°C 1 ± 1%; p < 0.001). Importantly, 32°C showed a lower IS AAR (p = 0.013) and increased immunohistochemical granulation tissue versus 35°C, indicating higher tissue salvage. Delayed-enhancement cardiac magnetic resonance IS LV also showed marked reduction at 32°C (38°C: 10 ± 4%, p < 0.001; 35°C: 8 ± 3%; 32°C: 3 ± 2%, p < 0.001). Cardiac output on day 6 was only preserved at 32°C (reduction in cardiac output: 38°C, -29 ± 19%, p = 0.041; 35°C: -17 ± 33%; 32°C: -1 ± 28%, p = 0.041). Using linear regression, the predicted IS reduction was 6.7% (AAR) and 2.1% (LV) per every 1°C reperfusion temperature decrease.
Conclusions:
Moderate (32°C) therapeutic hypothermia demonstrated superior and near-complete cardioprotection compared with 35°C and control, warranting further investigation into clinical applications.
Insights
Moderate therapeutic hypothermia (32°C) significantly improved myocardial salvage and cardiac output after acute myocardial infarction (AMI) compared to mild hypothermia (35°C) or normothermia. Deeper cooling offers superior cardioprotection.
Area of Science:
- Cardiology
- Cardiovascular Research
- Therapeutic Hypothermia
Background:
- Clinical trial results for mild hypothermia in acute myocardial infarction (AMI) are equivocal.
- Rapid, deeper hypothermia may enhance myocardial salvage during AMI.
Purpose of the Study:
- To investigate the dose-response relationship between myocardial salvage and therapeutic hypothermia depth.
- To determine if deeper hypothermia improves cardiac protection during AMI.
Main Methods:
- Swine models of AMI were subjected to normothermia (38°C), mild hypothermia (35°C), or moderate hypothermia (32°C).
- Rapid endovascular cooling to target temperatures commenced 30 minutes before reperfusion and was maintained for 60 minutes.
- Infarct size was assessed using cardiac magnetic resonance, triphenyl tetrazolium chloride, and histopathology.
Main Results:
- Moderate hypothermia (32°C) reduced infarct size by 77% and 91% compared to mild hypothermia (35°C) and normothermia (38°C), respectively.
- Cardiac output was preserved only in the 32°C group.
- A dose-response was observed, with a predicted 6.7% infarct size reduction per 1°C decrease in reperfusion temperature.
Conclusions:
- Moderate therapeutic hypothermia (32°C) provides superior cardioprotection compared to mild hypothermia or normothermia.
- These findings support further investigation into the clinical application of moderate hypothermia for AMI treatment.
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