Coronary Circulatory Indexes Before and After Percutaneous Coronary Intervention in a Porcine Tandem Stenoses Model

Background In tandem stenoses, nonhyperemic pressure ratio pullback is the preferred method to fractional flow reserve (FFR), based on the assumption of stable resting coronary flow. This study aimed to evaluate temporal changes of coronary circulatory indexes in tandem stenoses before and after angioplasty for proximal stenosis. Methods and Results Coronary tandem stenoses were created by porcine restenosis model with 2 bare metal stents in the left anterior descending artery. Four weeks later, changes in distal coronary pressure (Pd), averaged peak velocity, microvascular resistance, transstenotic pressure gradient across distal stenosis, resting Pd/aortic pressure, and FFR were measured before and 1, 5, 10, 15, and 20 minutes after balloon angioplasty for proximal stenosis. After angioplasty, there were significant changes in both resting and hyperemic Pd, averaged peak velocity, microvascular resistance, and transstenotic pressure gradient across distal stenosis (all P values <0.01). After initial acute changes, hyperemic averaged peak velocity and microvascular resistance did not show significant difference from the baseline values (P=0.712 and 0.972, respectively). Conversely, resting averaged peak velocity remained increased (10.1±0.7 to 17.8±0.7; P<0.001) and resting microvascular resistance decreased (6.0±0.1 to 2.2±0.7; P<0.001). Transstenotic pressure gradient across distal stenosis was significantly increased in both resting (13.1±7.6 to 25.3±4.2; P=0.040) and hyperemic conditions (11.0±3.0 to 27.4±3.3 mm Hg; P<0.001). Actual post-percutaneous coronary intervention Pd/aortic pressure and FFR were significantly lower than predicted values (Pd/aortic pressure, 0.68±0.22 versus 0.85±0.14; P<0.001; FFR, 0.63±0.08 versus 0.81±0.08; P<0.001). Conclusions After angioplasty for proximal stenosis, transstenotic pressure gradient across distal stenosis showed similar changes between resting and hyperemic conditions. Both actual post-percutaneous coronary intervention resting Pd/aortic pressure and FFR were significantly lower than predicted values.