Background: Despite advances in reperfusion times, patients presenting with acute myocardial infarction carry an unacceptably high rate of mortality and morbidity. Mechanical unloading of the left ventricle (LV) has been suggested to reduce infarct size after acute myocardial infarction. Although prior studies have investigated LV unloading during ischemia with a delay in reperfusion, little is known about the optimal timing for LV unloading in the setting of acute myocardial infarction.
Methods: Studies were conducted in 17 adult Yorkshire swine weighing 67±5 kg. A coronary balloon was inflated in the mid left anterior descending for 60 minutes to induce a myocardial infarction. The coronary balloon was then deflated for 120 minutes (reperfusion). The animals were stratified into 3 groups: group 1 (control, reperfusion with no LV unloading, n=5), group 2 (LV unloading during ischemia with delayed reperfusion, n=6), and group 3 (simultaneous LV unloading and reperfusion, n=6). Staining the hearts with Evans blue and 2,3,5-triphenyltetrazolium chloride was used to identify the area at risk and the infarct area respectively. Infarct percent size was defined as the area of infarcted myocardium divided by the area at risk.
Results: Of the 3 groups, group 3 demonstrated significantly smaller infarct percent size compared with controls (54.7±20.3% versus 22.2±13.4%; P=0.03). Comparison between group 1 and group 2 did not reveal significant difference (54.7±20.3% versus 43.3±24.6%; P=0.19).
Conclusions: In our large animal experimental model, simultaneous reperfusion and mechanical LV unloading yielded the smallest infarct size compared with no LV unloading or LV unloading with delayed reperfusion. In the context of prior studies showing benefit to unloading before reperfusion, these findings raise questions about how this strategy may be translated to humans.
Keywords: heart; myocardial infarction; myocardium; staining; triphenyltetrazolium.