Residual flow to the infarct zone as a determinant of infarct size after direct angioplasty.

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Abstract
BACKGROUND In acute myocardial infarction, residual flow to the infarct zone either through antegrade flow in the infarct-related coronary artery or collateral flow from the non-infarct-related arteries is often present before reperfusion therapy. The purpose of this study was to assess the influence of antegrade flow in the infarct-related artery and/or collateral flow to the infarct zone before successful direct angioplasty on infarct size and myocardial salvage in patients with acute evolving myocardial infarction. METHODS AND RESULTS Sixty patients with acute evolving myocardial infarction underwent direct successful angioplasty without prior thrombolytic therapy. The myocardium at risk of infarction, the final infarct size, and myocardial salvage were measured by tomographic perfusion imaging with 99mTc sestamibi. Antegrade flow in the infarct-related artery before intervention was graded according to the Thrombolysis in Myocardial Infarction (TIMI) study group classification. Collateral flow to the infarct zone before angioplasty was also graded (0 through 3, 0 being no collateral flow). The presence of even minimal antegrade flow before angioplasty (TIMI grade 1) in the infarct-related artery compared with absent flow was associated with a significant reduction in final infarct size (9 +/- 17% versus 23 +/- 19% of left ventricle, P = .02) and a significant increase in myocardial salvage (23 +/- 16% versus 14 +/- 13% of left ventricle, P = .05) after angioplasty. When antegrade flow in the infarct-related artery was absent before angioplasty, the presence of collateral flow before angioplasty resulted in a significantly smaller final infarct size (P = .01) and more myocardial salvage (P = .05) after angioplasty. Both antegrade infarct-related artery flow and collateral flow to the infarct zone had significant independent ability to predict infarct size after angioplasty. When collateral grade and TIMI grade were added to provide an estimate of residual flow, a model including residual flow, myocardium at risk, and the interaction of residual flow and infarct site explained 83% of the variability in infarct size after angioplasty. CONCLUSIONS The presence of antegrade flow in the infarct-related artery and/or collateral flow to the infarct zone before direct angioplasty in acute evolving infarction results in a smaller infarct size after direct successful angioplasty.

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