Effect of myocardial contractility on hemodynamic end points under concomitant microvascular disease in a porcine model

In this study, coronary diagnostic parameters, pressure drop coefficient (CDP: ratio of trans-stenotic pressure drop to distal dynamic pressure), and lesion flow coefficient (LFC: ratio of % area stenosis (%AS) to the CDP at throat region), were evaluated to distinguish levels of %AS under varying contractility conditions, in the presence of microvascular disease (MVD). In 10 pigs, %AS and MVD were created using angioplasty balloons and 90-mu m microspheres, respectively. Simultaneous measurements of pressure drop, left ventricular pressure (p), and velocity were obtained. Contractility was calculated as (dp/dt)(max), categorized into low contractility < 900 mmHg/s and high contractility > 900 mmHg/s, and in each group, compared between %AS < 50 and > 50 using analysis of variance. In the presence of MVD, between the %AS < 50 and > 50 groups, values of CDP (71 +/- 1.4 and 121 +/- 1.3) and LFC (0.10 +/- 0.04 and 0.19 +/- 0.04) were significantly different (P < 0.05), under low-contractility conditions. A similar %AS trend was observed under high-contractility conditions (CDP: 18 +/- 1.4 and 91 +/- 1.4; LFC: 0.08 +/- 0.04 and 0.25 +/- 0.04). Under MVD conditions, similar to fractional flow reserve, CDP and LFC were not influenced by contractility.