Coronary clearance frame count:: A new index of microvascular perfusion

Background: The angiographic data of myocardial perfusion obtained following direct angioplasty in acute myocardial infarction (AMI) can be evaluated only by qualitative methods: the myocardial blush grade (MBG) or the TIMI myocardial perfusion grade (TMPG). To minimize the subjective nature of this evaluation, we describe a quantitative index, the "coronary clearance frame count" (CCFC); and have tested it against known indices. Methods: All patients with AMI treated with direct angioplasty in a single center over 2 years were prospectively analyzed. All films were assessed off-line to determine the traditional indices of TIMI flow grade, TIMI frame count, MBG and TMPG. To define CCFC, we used the first frame in which the contrast is cleared from the ostium of the artery as "frame 0" and that in which contrast begins to wash-in into the same coronary artery distal landmark proposed by TIMI Group, as the "last frame". Results: Of the 147 patients studied, 110 had films that were technically adequate for measuring qualitative and quantitative indices of myocardial perfusion. CCFC showed a good correlation with MBG (p = 0.045) and with TMPG (p < 0.001). CCFC was strongly related to the presence of TMPG 2 or 3 (p < 0.001). A cut-off value of 45 frames has a sensitivity of 75% and specificity of 70% to predict a TMPG 2 or 3. Conclusion: Coronary clearance frame count has a good correlation with known indices of reperfusion and has the advantage of being an objective, quantitative index that is efficient even in inexperienced hands.