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

Clinical Snapshot

Key Findings

• P Value: P<0.001 for all threshold comparisons vs clinical cut-points

• Effect Size: All angina thresholds significantly lower than clinical diagnostic cut-points

• Primary Outcome: FFRangina thresholds: 0.29 (rest), 0.38 (low exercise), 0.45 (high exercise); RFRangina thresholds: 0.22 (rest), 0.26 (low exercise), 0.32 (high exercise)

• Nnt Or Sensitivity: Lower thresholds predicted greater symptom relief with PCI (probability of interaction >0.999)

• Confidence Interval: Interquartile ranges provided for all measurements

Clinical Application

Requires specialized catheter laboratory equipment and expertise for in-stent balloon inflation procedures Relevant to Australian interventional cardiology practice; may influence PBS criteria for PCI if validated in larger trials; aligns with CSANZ guidelines emphasizing symptom-driven revascularization Patients with stable angina and single-vessel coronary artery disease undergoing consideration for PCI

Abstract

BACKGROUND: 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, FFRangina and RFRangina, angina (FFRangina at rest and during exercise remain undefined. METHODS: 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 FFRangina and RFRangina 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. RESULTS: 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 FFRangina 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. RFRangina 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 FFRangina and RFRangina thresholds were associated with greater symptom reproducibility across rest, low- and high-intensity exercise conditions (FFRangina: P=0.008, P<0.001, P<0.001, respectively; RFRangina: 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). CONCLUSIONS: Physiological thresholds for angina, FFRangina and RFRangina, 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.