A post hoc analysis of the placebo-controlled ORBITA (Objective Randomised Blinded Investigation With Optimal Medical Therapy of Angioplasty in Stable Angina) trial published in the JACC: Cardiovascular Interventions examined the relationship between microvascular resistance (MVR) and clinical response to percutaneous coronary intervention (PCI). 

The analysis included patients with single-vessel coronary artery disease receiving optimal medical therapy and randomized to PCI or placebo. Hyperemic MVR was derived using computational fluid dynamics (MVR_CFD), and its association with placebo-controlled changes in exercise capacity, symptom burden, and stress imaging outcomes was assessed at 6-week follow-up.

MVR_CFD was successfully calculated in 131 participants (66 PCI; 65 placebo), with a median value of 1.38 mm Hg·min/mL (interquartile range 0.89–2.09). Baseline exercise duration showed a modest positive correlation with MVR_CFD (correlation coefficient 0.20; 95% credible interval [CrI] 0.18–0.22). Among patients with low MVR_CFD (20th percentile), PCI increased treadmill exercise time by 48 seconds compared with placebo (95% CrI 6–92 seconds; probability 98.5%).

In contrast, patients with high MVR_CFD (80th percentile) showed no clear improvement (16 seconds; 95% CrI −29 to 61; probability 75.2%), with modest evidence for interaction (interaction probability 83.1%). Lower MVR_CFD was also associated with higher likelihood of complete angina relief (probability 98.8%), reduced angina frequency (97.8%), and improved stress echocardiography scores (99.9%).

Lower MVR_CFD was associated with greater placebo-controlled benefit from PCI. Microvascular dysfunction may attenuate symptomatic and functional gains following PCI.