High frequency of spontaneous acute myocardial infarction due to small coronary artery disease in dead (NZWxBXSB)F1 male mice.

To determine whether or not male (NZWXBXSB)F1 [WXB)F1) mice exhibiting a lupus-like syndrome died of acute myocardial infarction (MI), and whether acute MI is directly related to small coronary artery disease, acute and old MIs were examined histologically in 55 dead (WXB)F1 male mice and 30 age-matched, surviving (WXB)F1 male mice used as a control group. In each heart from the 15 dead mice with MI and the five surviving mice without MI, 300 to 400 5-microns-thick serial sections were made; every fourth section was stained. Acute MI was found in 35 (64%) dead mice and in one (3%) survivors, whereas old MI was found in 50 (91%) dead mice and 17 (57%) survivors: a significant difference between the dead and surviving mice. The MIs were numerous, scattered, and small in most mice. Quantitative analysis revealed that the percentage of acute MI and old MI in the left ventricular (LV) wall was 6% +/- 11% and 3% +/- 3% in the dead group, and 0.4% and 2% +/- 3% in the control group. This indicated that recurrent acute MI is a major factor in the death of the mice. Although all the epicardial major coronary arteries of the (WXB)F1 male mice were intact, significant stenoses were noted in the intramyocardial small arteries. The serial sections in the 15 dead mice with MI revealed 1) segmental occlusive thrombi in the infarct-related small coronary artery in 14 of the 20 foci of acute anemic MIs, two of the 18 foci of acute hemorrhagic MIs, and four of the 58 foci of old MIs; and 2) segmental intimal thickenings in the infarct-related small artery in six of the 20 foci of acute anemic MIs, two of the 18 foci of acute hemorrhagic MIs, and 56 of the 58 foci of old MIs. There was no evidence of small coronary artery disease in the surviving mice without MI. The thrombus would result in thickened intima as MI progresses from the acute to the old stage. Because it was established that acute MI of hemorrhagic type follows reperfusion after transient occlusion of the coronary artery, hemorrhagic acute MI with rare incidence of thrombi in this mouse suggests that thrombolysis occurs after occlusion due to thrombus formation. Thus, the pathogenesis of multiple MIs is occlusive thrombi, recanalization in small coronary arteries or both. Some of the mice had dilated cardiomyopathy (DCM)-like features (marked LV dilatation).(ABSTRACT TRUNCATED AT 400 WORDS)