It is well known that collateral circulation has important roles in ischemic heart diseases. The method most commonly used at present to evaluate collateral flow is coronary angiography. However, there are debates about the functional significance of angiographically visible collaterals because angiography visualizes only vessels that are larger than 100um in diameter. Recent studies suggest that myocardial contrast echocardiography (MCE) is a useful method in assessing collateral flow because it uses small microvascular tracers (4-12um) as a contrast agent. By using MCE, this study evaluates the role of angiographically visible collaterals in patients with acute myocardial infarction (AMI) and chronic ischemic heart disease.

Forty-one patients who underwent coronary angiography and MCE were included in this study (22 patients with acute myocardial infarction and 19 patients with chronic ischemic heart disease). Antegrade coronary flow was less than TIMI 3 flow in all patients. Myocardial perfusion through collaterals with MCE was evaluated by injecting sonicated Hexabrix into nonobstructing coronary arteries. Angiographically visualized collateral vessels were analysed as four grades and compared with the degree of myocardial opacification by MCE through collateral vessels.

Angiographic collaterals were frequently observed in patients with AMI and chronic ischemic heart disease with≤ TIMI 2 flow . There was poor correlation between TIMI grade and the grade of collaterals by angiography in AMI (r--0.29, p-0.20) and chronic ischemic heart disease (r--0.31, p-0.19). There was no correlation between collateral grades and myocardial opacification by MCE through collateral vessels in AMI (r-0.07, p-NS) and chronic ischemic heart disease (r-0.10, p-NS). In patients with relatively well developed collaterals (Grade II or III), the ischemic zone was perfused better through collateral flow in the chronic ischemic heart disease group than in the AMI group (Mean Retrograde Opacification Index 0.84±0.23 vs 0.32±0.22, p<0A65A>0.05).

The study suggests that the role of angiographically visible collaterals is different in chronic ischemic heart disease and acute myocardial infarction. The grade of angiographically visible collaterals does not imply the extent of perfusion to myocardum at risk through collateral vessels.