Abnormal epicardial coronary resistance in patients with diffuse atherosclerosis but "normal" coronary angiography

Background-Coronary arteries without focal stenosis at angiography are gene rally considered non-flow-limiting. However, atherosclerosis is a diffuse p rocess that often remains invisible at angiography. Accordingly, we hypothe sized that in patients with coronary artery disease, nonstenotic coronary a rteries induce a decrease in pressure along their length due to diffuse cor onary atherosclerosis. Methods and Results-Coronary pressure and fractional flow reserve (FFR), as indices of coronary conductance, were obtained from 37 arteries in 10 indi viduals without atherosclerosis (group I) and from 106 nonstenotic arteries in 62 patients with arteriographic stenoses in another coronary artery (gr oup II). In group I, the pressure gradient between aorta and distal coronar y artery was minimal at rest (1 +/-1 mm Hg) and during maximal hyperemia (3 +/-3 mm Hg). Corresponding values were significantly larger in group II (5 +/-4 mm Hg and 10 +/-8 mm Hg, respectively; both P <0.001). The FFR was ne ar unity (0.97 +/-0.02; range, 0.92 to 1) in group I, indicating no resista nce to flow in truly normal coronary arteries, but it was significantly low er (0.89 +/-0.08; range, 0.69 to 1) in group II, indicating a higher resist ance to flow. In 57% of arteries in group II, FFR was lower than the lowest value in group I. In 8% of arteries in group II, FFR was <0.75, the thresh old for inducible ischemia. Conclusion-Diffuse coronary atherosclerosis without focal stenosis at angio graphy causes a graded, continuous pressure fall along arterial length. Thi s resistance to flow contributes to myocardial ischemia and has consequence s for decision-making during percutaneous coronary interventions.