Effects of microvascular dysfunction on myocardial fractional flow reserve after percutaneous coronary intervention in patients with acute myocardial infarction.

Fractional flow reserve (FFR) has emerged as a lesion-specific index of the functional severity of coronary stenosis in patients with chronic coronary artery disease. As the coronary blood flow in acute myocardial infarction (AMI) patients with microvascular damage is restricted, the pressure drop across the stenosis during hyperemia may be smaller than expected. However, the effects of microvascular dysfunction on FFR in AMI patients remain undetermined. The study comprised 33 AMI patients who underwent coronary stenting within 12 hr of onset, and 15 patients with stable angina pectoris who underwent elective stenting. Assessment of the 48 lesions by means of intravascular ultrasound and pressure measurements after stenting showed that postinterventional FFR was higher in AMI than angina pectoris patients (0.95 +/- 0.04 vs. 0.90 +/- 0.04; P = 0.002), although there were no significant differences in intravascular ultrasound parameters. AMI patients were divided into two subgroups based on their postprocedural Thrombolysis on Myocardial Infarction (TIMI) flow grade (23 patients with TIMI 3 and 10 with TIMI 2). There were no differences in intravascular ultrasound parameters between the AMI subgroups, while FFR was greater in the patients with TIMI 2 than in those with TIMI 3 (0.98 +/- 0.02 vs. 0.93 +/- 0.05; P = 0.017). No significant correlation was found between FFR and intravascular ultrasound parameters in either AMI subgroup, while FFR of more than 0.94 was observed in all TIMI 2 cases independent of residual stenosis severity. We conclude that in patients with marked microvascular dysfunction, FFR may not be reliable for the assessment of coronary lesion severity and may underestimate coronary lesion severity.