OBJECTIVESWe evaluated the relation between pressure-derived fractional collateral flow (PDCF) and left ventricular (LV) recovery after reperfused acute myocardial infarction (AMI).BACKGROUNDThe functional significance of collateral flow remains uncertain in AMI.METHODSThe PDCF was measured in 70 patients with first AMI (pain onset <12 h) treated with primary angioplasty (PA), being determined by simultaneous measurement of mean aorta pressure (Pa), distal coronary pressure during the balloon occlusion (Poc), and central venous pressure (CVP): (Poc − CVP)/(Pa − CVP)∗100. Sufficient collateral (group I) was defined as PDCF index >24% and insufficient collateral (group II) as PDCF index <24%. Echocardiography was performed before, and on day 3, day 7, and day 30 after PA. Wall-motion recovery index (RI) was obtained by dividing the number of improved wall-motion segments (>grade 1) at follow-up by the number of abnormal wall-motion segments within the infarct zone at baseline.RESULTSBaseline characteristics were similar between both groups. Peak levels of creatine kinase were lower in group I than in group II (2,600 ± 1,900 U/liter vs. 4,100 ± 3,000, p < 0.05). At one month, infarct zone wall-motion score index (1.65 ± 0.54 vs. 2.31 ± 0.46, p < 0.01) and LV volume indexes were smaller in group I than in group II, whereas, LV ejection fraction was higher in group I than in group II (52.8 ± 8.3 vs. 45.9 ± 9.0, p < 0.01). The PDCF index was the strongest predictor of RI at one month (r = 0.61, p < 0.01). Time to reperfusion was not related to RI at one month. However, it was significantly related to RI in group II (r = −0.34, p < 0.05).CONCLUSIONSThe LV recovery after reperfused AMI is primarily determined by PDCF and is less dependent on time to reperfusion in patients with sufficient collaterals.