Very mild hypothermia during ischemia and reperfusion improves postinfarction ventricular remodeling.
BACKGROUND
Mild hypothermia (< 4 degrees C) improves myocardial salvage after infarct reperfusion in animals and in early clinical studies. In this experiment the effect of mild hypothermia during ischemia and early reperfusion on long-term postinfarction left ventricular (LV) remodeling was assessed in an ovine infarct model.


METHODS
In the initial phase of the experiment the effect of progressive degrees of hypothermia on infarct size was quantified. Thirty-eight male sheep were subjected to 1 hour of ischemia using a standardized anteroapical infarct followed by 3 hours of reperfusion. Temperature was maintained at either 39.5 degrees C (n = 11), 38.5 degrees C (n = 7), 37.5 degrees C (n = 7), 36.5 degrees C (n = 7), or 35.5 degrees C (n = 6) for the entire period of ischemia and reperfusion. The area at risk (AR) and infarct size as a percentage of AR (I/AR) were determined with a double staining and planimetry technique. In the second phase of the study, chronic post-infarction remodeling was assessed in animals with nonreperfused infarcts (n = 6), 1 hour of ischemia followed by reperfusion at 39.5 degrees C (n = 6) and 1 hour of ischemia followed by reperfusion at 37.5 degrees C (n = 6). Remodeling was determined at 8 weeks after infarction using echocardiography.


RESULTS
The I/AR in the 39.5 degrees C, 38.5 degrees C, 37.5 degrees C, 36.5 degrees C, and the 35.5 degrees C groups was 71.8 +/- 3.0%, 63.1 +/- 1.9%, 49.4 +/- 1.4%, 38.7 +/- 1.4%, and 21.7 +/- 2.2%, respectively (p < 0.05 between all groups). In the chronic study LV end systolic volume at 8 weeks after infarction was 81 +/- 8 mL in the nonreperfused group, 57 +/- 4 mL in the 39.5 degrees C reperfusion group, and 41 +/- 3 mL in the 37.5 degrees C reperfusion group (p < 0.05 for between group differences).


CONCLUSIONS
Subtle degrees of hypothermia can significantly improve immediate myocardial salvage and long-term LV remodeling after infarct reperfusion.
Hamamoto
Hirotsugu
H
Harrison Department of Surgical Research, Glenolden Research Laboratory, Glenolden, Pennsylvania 19036, USA.
Sakamoto
Hiroaki
H
Leshnower
Bradley G
BG
Parish
Landi M
LM
Kanemoto
Shinya
S
Hinmon
Robin
R
Plappert
Theodore
T
Miyamoto
Shinji
S
St John-Sutton
Martin G
MG
Gorman
Joseph H
JH
Gorman
Robert C
RC
D000704:Analysis of Variance; D000818:Animals; D003326:Coronary Circulation / Q000502:physiology; D004195:Disease Models, Animal; D006439:Hemodynamics / Q000502:physiology; D007036:Hypothermia, Induced / Q000379:methods*; D007150:Immunohistochemistry; D019157:Ischemic Preconditioning, Myocardial / Q000379:methods*; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology; D009203:Myocardial Infarction / Q000473:pathology* / Q000628:therapy*; D015425:Myocardial Reperfusion / Q000379:methods; D015428:Myocardial Reperfusion Injury / Q000473:pathology / Q000517:prevention & control*; D011336:Probability; D011897:Random Allocation; D012016:Reference Values; D012680:Sensitivity and Specificity; D013696:Temperature; D020257:Ventricular Remodeling / Q000502:physiology*