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Figure 1 Determination of collateral flow index (CFI) in a patient receiving placebo before (left) and after treatment (right). Surface (III, avF) and intracoronary (i.c.) electrocardiogram (ECG) lead recordings are shown in the upper part of the panels. After 1 min of vessel occlusion before and after treatment, there are ST-segment elevations on the i.c. ECG lead, indicating coronary collaterals insufficient to prevent myocardial ischemia. Collateral flow index is calculated by dividing distal mean coronary occlusive pressure (P_occl, mm Hg) minus central venous pressure (CVP, mm Hg) by mean aortic pressure (P_ao, mm Hg) minus CVP.