Background Patients with acute coronary artery thrombosis often develo
p primary malignant ventricular arrhythmias (MVA) early after coronary
occlusion. In contrast, acute ischemia induced by nonthrombotic ballo
on occlusion during routine coronary angioplasty rarely elicits such a
rrhythmias. This study was designed to assess the role of intracoronar
y thrombosis in arrhythmogenesis during acute ischemia. Methods and Re
sults We compared the incidence of MVA associated with acute left ante
rior descending coronary artery (LAD) thrombosis elicited in open-ches
t anesthetized dogs by electrical injury (n=10) or intracoronary stent
(n=9) versus LAD balloon occlusion (n=15). Compared with animals subj
ected to balloon occlusion, those with thrombotic occlusion had a sign
ificantly greater incidence of MVA, defined as nonsustained ventricula
r tachycardia (total duration >10 seconds), sustained ventricular tach
ycardia, or ventricular fibrillation developing within the first 30 mi
nutes of occlusion. In the combined thrombosis groups, MVA developed i
n 11 of 19 animals (58%) (6 of 10 dogs with electrical injury and 5 of
9 stent animals). In contrast, MVA occurred in only 1 of 15 animals (
7%) subjected to balloon occlusion. This striking and significant diff
erence in arrhythmias occurred despite the fact that radioactive micro
sphere perfusion analysis documented that the extent of left ventricul
ar myocardium rendered ischemic was equal in all groups (percent of le
ft ventricular myocardium with occlusion flow less than or equal to 50
% of baseline: electrical injury, 25.2+/-5.3%; stent, 27.1+/-3.6%; bal
loon, 34.3+/-11.6%; P=NS). Furthermore, there were no differences betw
een the animals with thrombosis or balloon occlusion with respect to c
hanges in echocardiographic parameters of left ventricular function, a
ortic pressure, or heart rate after occlusion. Conclusions These data
provide evidence that despite equal magnitudes of jeopardized myocardi
al mass, acute ischemia induced by thrombotic coronary occlusion resul
ts in a greater incidence of MVA than does nonthrombotic balloon occlu
sion. These findings suggest that the process of intracoronary thrombo
sis itself exerts arrhythmogenic effects above and beyond the impact o
f ischemia on myocardium induced by coronary occlusion.