Left ventricular diastolic dysfunction during acute myocardial infarction: effect of mild hypothermia.
BACKGROUND
Mild hypothermia (MH) decreases infarct size and mortality in experimental reperfused myocardial infarction, but may potentiate ischaemia-induced left ventricular (LV) diastolic dysfunction.


METHODS
In anaesthetized pigs (70 ± 2 kg), polystyrol microspheres (45 μm) were infused repeatedly into the left circumflex artery until cardiac power output decreased >40%. Then, pigs were assigned to normothermia (NT, 38.0°C, n=8) or MH (33.0°C, n=8, intravascular cooling) and followed for 6h (CME 6h). p<0.05 vs baseline, †p<0.05 vs NT.


RESULTS
In NT, cardiac output (CO) decreased from 6.2 ± 0.3 to 3.4 ± 0.2 l/min, and heart rate increased from 89 ± 4 to 101 ± 6 bpm. LV end-diastolic volume fell from 139 ± 8 to 64 ± 4 ml, while LV ejection fraction remained constant (49 ± 1 vs 53 ± 4%). The corresponding end-diastolic pressure-volume relationship was progressively shifted leftwards, reflecting severe LV diastolic dysfunction. In MH, CO fell to a similar degree. Spontaneous bradycardia compensated for slowed LV relaxation, and the leftward shift of the end-diastolic pressure-volume relationship was less pronounced during MH. MH increased systemic vascular resistance, such that mean aortic pressure remained higher in MH vs NT (69 ± 2† vs 54 ± 4 mm Hg). Mixed venous oxygen saturation at CME 6h was higher in MH than in NT (59 ± 4† vs 42 ± 2%) due to lowered systemic oxygen demand during cooling.


CONCLUSIONS
We conclude that (i) an acute loss of end-diastolic LV compliance is a major component of acute cardiac pump failure during experimental myocardial infarction, and that (ii) MH does not potentiate this diastolic LV failure, but stabilizes haemodynamics and improves systemic oxygen supply/demand imbalance by reducing demand.
Department of Cardiology, Medical University of Graz, Auenbruggerplatz 15, 8036 Graz, Austria.
Michael
M
Schwarzl
Stefan
S
Huber
Heinrich
H
Maechler
Paul
P
Steendijk
Sebastian
S
Seiler
Martie
M
Truschnig-Wilders
Thomas
T
Nestelberger
Burkert M
BM
Pieske
Heiner
H
Post
D000818:Animals; D003971:Diastole; D007036:Hypothermia, Induced; D009203:Myocardial Infarction / Q000150:complications* / Q000628:therapy*; D013552:Swine; D018487:Ventricular Dysfunction, Left / Q000209:etiology*