THE INFLUENCE OF CORONARY COLLATERAL FLOW ON THE ASSESSMENT OF MYOCARDIAL PERFUSION BY VIDEODENSITOMETRY

Objectives: Coronary collateral flow often mitigates the effects of co ronary artery obstruction and has a significant impact on the prognosi s of patients with coronary artery disease. In the presence of variabl e degrees of coronary collateral flow, digital radiographic assessment of myocardial blood flow has not been quantitatively validated. Metho ds: A distal coronary arterial collateral path was created into the le ft anterior descending coronary artery (LAD) bed in 8 anesthetized pig s. Both LAD and collateral paths were pump-perfused and corresponding flows measured. A number of commonly used digital indices and parametr ic images of myocardial perfusion were then extracted from the sequenc e of images filmed before and during the injection of contrast. Data w ere acquired at 5 levels of total flow (LAD flow + collateral flow): 1 00, 85, 70, 55 and 40% of maximally vasodilated, baseline flow. At eac h level of total flow, data were acquired at 4 levels of collateral fl ow ratios (collateral flow/total flow): 0, 10; 25 and 50%. Results: Re gional percent segment shortening, reflecting myocardial blood flow, d ecreased as total flow fell, and remained unaltered when coronary coll ateral ratio alone was altered without change in total flow. On the ot her hand, linear regression between total flow and digital indices at 10, 25 and 50% coronary collateral flow ratios, compared with 0%, show ed a successive and significant downward displacement, documenting an underestimation of flow by all digital indices in the presence of coll ateral flow. Conclusions: In the absence of a collateral pathway and d uring maximal coronary vasodilation with adenosine, digital radiograph ic indices of myocardial perfusion, based upon indicator dilution theo ry, show a relatively good correlation with regional transmural myocar dial blood flow. However, due to underestimation of total transmural b lood flow, these indices have limited utility when myocardial perfusio n is provided in part by a collateral pathway. The effect is probably related to an alteration in the regional vascular volume into which io dinated contrast is injected.