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Figure 3 Coronary collaterals assessed by angiography (squares and circles, thick short lines: standard deviation) and intracoronary (IC) ECG (triangles and diamonds) compared with the IC velocity- and pressure-derived collateral flow index (CFI, vertical axis). Well-developed collaterals were defined as those with an angiographic collateral degree 2 (0 to 3). Patients with sufficient collaterals were defined as those without ST-segment changes (>1 mm) on IC or surface ECG during balloon occlusion (IC guidewire distal to the stenosis). Velocity- and pressure-derived collateral flow indices do not accurately differentiate between well and poorly developed collaterals, whereas they accurately predict sufficient and insufficient collaterals at a threshold of 0.30 (broken line).