Determining the Physiological Threshold for Angina (ORBITA-FIRE): A Double-Blind, Randomized, Placebo-Controlled...

In stable coronary artery disease, the primary goal of percutaneous coronary intervention (PCI) is symptom relief. Fractional flow reserve (FFR) and nonhyperemic pressure ratios such as resting full-cycle ratio (RFR) are used to guide revascularization. Although these indices correlate with myocardial ischemia, they have never been validated against the onset of angina. The physiological thresholds for angina, FFR_angina and RFR_angina, angina (FFR_angina at rest and during exercise remain undefined.

ORBITA-FIRE (Finding the Invasive Threshold for Symptom Relief in Exertional Angina) was a multicenter, double-blind, randomized, placebo-controlled study in patients with stable angina and single-vessel coronary artery disease. After imaging-guided PCI, an in-stent balloon was incrementally inflated until angina occurred at rest. This angina threshold was verified against placebo inflation, and corresponding FFR_angina and RFR_angina values were recorded at symptom onset. The protocol was repeated during low- and high-intensity exercise to assess changes in angina thresholds with increasing cardiac workload.

Sixty-five patients were enrolled (mean age, 63.9±8.7 years; 74% male; 69% hypertensive; 23% diabetic; 91% with Canadian Cardiovascular Society class II-III angina). Median pre-PCI FFR was 0.59 (interquartile range [IQR], 0.46-0.70) and RFR was 0.61 (IQR, 0.40-0.82). Median FFR_angina at rest was 0.29 (IQR, 0.23-0.35), increasing to 0.38 (IQR, 0.30-0.48) during low-intensity exercise and 0.45 (IQR, 0.36-0.55) during high-intensity exercise. RFR_angina similarly increased from 0.22 (IQR, 0.16-0.30) at rest to 0.26 (IQR, 0.18-0.36) and 0.32 (IQR, 0.23-0.46) during low- and high-intensity exercise. All thresholds were significantly lower than clinical diagnostic cut points (P<0.001). Lower FFR_angina and RFR_angina thresholds were associated with greater symptom reproducibility across rest, low- and high-intensity exercise conditions (FFR_angina: P=0.008, P<0.001, P<0.001, respectively; RFR_angina: P=0.015, P<0.001, P=0.002, respectively). Lower angina thresholds across all conditions predicted higher baseline angina burden and greater symptom relief with PCI (probability of interaction >0.999).

Physiological thresholds for angina, FFR_angina and RFR_angina, are highly individualized, vary with cardiac workload, and are consistently lower than the universal ischemia-based thresholds used to guide revascularization. These findings support integrating personalized, symptom-linked physiology to refine patient selection and to improve symptomatic response to PCI.