When collateral supply is accounted for epicardial stenosis does not increase microvascular resistance

Background-The relationship between epicardial stenosis and microvascular resistance remains controversial. Exploring the relationship is critical, as many tools used in interventional cardiology imply minimal and constant resistance. However, variable collateralization may impact well on these measures. We hypothesized that when collateral supply was accounted for, microvascular resistance would be independent of epicardial stenosis. Methods and Results-Forty patients with stable angina were studied before and following percutaneous intervention. A temperature and pressure sensing guide wire was used to derive microvascular resistance using the index of microcirculatory resistance (IMR), defined as the hyperemic distal pressure multiplied by the hyperemic mean transit time. Lesion severity was assessed using fractional flow reserve. For comparison, evaluation of an angiographically normal reference vessel from the same subject also was undertaken. Both simple IMR (sIMR) and IMR corrected for collateral flow (cIMR) were calculated. When collateral supply was not accounted for, there was a significant difference in IMR values between the culprit, the post PCI, and nonculprit values (culprit sIMR 26.68<±2.06, nonculprit sIMR 18.37±1.89, PP=0.002; post percutaneous intervention sIMR 18.5±<1.94 versus culprit sIMR 26.68±<2.06, P±0.0001). However, when collateral supply was accounted for there was no difference observed (cIMR 16.96<1.78 versus nonculprit sIMR 18.37<±1.89, PP=0.52; post percutaneous intervention sIMR 18.5±<1.94 versus cIMR 16.96<1.78, PP=0.42). Conclusions-When collateral supply is accounted for, epicardial stenosis does not increase microvascular resistance in patients with stable angina.