Some individuals with significant coronary narrowing experience only mild or no chest discomfort, a paradox that has long intrigued cardiologists. The placebo-controlled Objective Randomized Blinded Investigation With Optimal Medical Therapy of Angioplasty in Stable Angina (ORBITA) study, published in Circulation, provides fresh insight into this clinical puzzle.

The analysis included 51 participants with stable single-vessel CAD (mean age 63 years; 78% men). All discontinued antianginal therapy and recorded daily angina using a smartphone application. Each underwent invasive pressure-wire evaluation and four 60-second balloon occlusions paired with identical placebo inflations. Pain scores were recorded after each episode, and collateral flow was measured from simultaneous aortic, right atrial, and distal wedge pressures.

Angina frequency showed little association with ischemic severity as measured by fractional flow reserve (median 0.68) or instantaneous wave-free ratio (median 0.80). In contrast, higher collateral flow index values correlated strongly with lower pain intensity during occlusion. Pain and collateral measurements remained stable across repeated occlusions, indicating no evidence of ischemic preconditioning.
These findings suggest that well-developed coronary collateral vessels can lessen ischemic chest pain and help explain the limited relationship between stenosis, ischemia, and angina severity in stable CAD.