A 49-year-old white man with tobacco dependence and COPD presented with exertional dyspnea and a centrally located dull, aching chest pressure that was non-radiating, triggered by exercise, and relieved by rest — a textbook description of stable exertional angina (CCS Class I–II). Vital signs and cardiovascular and respiratory examinations were benign. High-sensitivity troponin I was negative at presentation and at three hours. EKG showed sinus bradycardia with right bundle branch block without new ST-T changes. Transthoracic echo demonstrated preserved LVEF without regional wall motion abnormality.
A nuclear stress test with regadenoson was abnormal — borderline apical ischemia — with calculated LVEF of 49%. This prompted coronary angiography and aortography, which revealed the pivotal finding: the RCA and left main (LM) arose from a single ostium at the right coronary sinus. The left coronary cusp contained no ostium and showed no flow after contrast injection.
Coronary CT angiography (CCTA) provided the critical anatomical detail: the anomalous left coronary artery arose from the right coronary sinus and coursed with an acute angle at its origin through the interventricular septum — between the right ventricular outflow tract and the aorta — before bifurcating into LAD and LCX. Subtle calcification at the LAD origin caused mild focal stenosis. This anatomy is classified as RII-S by the modified Lipton classification — a high-risk category due to the intraseptal (intramural) course.
Given the RII-S classification (intraseptal course from the right sinus), positive stress imaging, and typical anginal symptoms — meeting both ESC Class I and AHA Class I surgical indications — the patient underwent surgical correction. The main pulmonary artery was separated from the aorta, the interventricular septal muscle overlying the left main was divided (unroofing) until the LM merged with the epicardial arteries, and the PA was reanastomosed. This simple unroofing of the LM from the interventricular septum without pulmonary artery relocation was performed with an excellent outcome. The patient was discharged in five days, symptoms resolved, and follow-up echo showed normal ejection fraction.
Single coronary artery disease is one of the rarest congenital coronary anomalies, classified by the modified Lipton system into three groups based on the origin and course of the dominant vessel. The RII-S subcategory — in which a single artery arises from the right sinus and the anomalous left coronary takes an intraseptal (intramuscular) course through the ventricular septum before bifurcating — is considered high-risk because the artery is sandwiched within muscle that contracts during systole, creating dynamic compression. During exertion, as cardiac output rises and the aortic root and PA dilate, this compression intensifies. The proposed mechanism of ischemia-triggering and sudden cardiac death risk involves this exertional dynamic compression squeezing the intramural segment, reducing coronary flow precisely when demand peaks. A slit-like or fish-mouth-shaped orifice at the anomalous origin and an acute angle takeoff compound the hemodynamic challenge.
Management decisions in SCA with RII-S classification require confirmation of ischemia by non-invasive functional imaging before recommending surgery, as stipulated by both ESC 2020 and AHA guidelines. In this case, the nuclear stress test with regadenoson confirmed perfusion abnormality in the anomalous vessel territory, crossing the threshold for surgical recommendation. The choice of operative technique remains individualized — CABG is avoided in the absence of significant stenosis because competitive native flow causes graft failure. Unroofing, supraarterial myotomy, and modified Lecompte maneuver are all described; this case demonstrates that simple unroofing of the intraseptal LCA without pulmonary artery relocation can achieve complete symptom resolution. As cardiac CT becomes more widely used in ischemia workups, the incidence of detected coronary anomalies will rise, making familiarity with Lipton classification and referral pathways increasingly important for general cardiologists.
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