Discussion

Coronary arteries form with migration of the proepicardium to envelop the myocardium. The proepicardium thickens, preferentially over the atria and atrioventricular groove. As cells lose contact with the epicardial epithelium, they transition into mesenchymal cells and form channels that become the endothelium of coronary arteries. ^{Reference Reese, Mikawa and Bader1} Coronary ostia are formed by capillary penetration of the aortic root. Anomalous coronary arteries occur due to failure of the capillary plexus surrounding the aorta and main pulmonary artery to penetrate the appropriate sites on the aorta. ^{Reference Tomanek and Angelini2} For example, in anomalous left coronary artery from pulmonary artery, the capillary penetration occurs ectopically at the main pulmonary artery. ^{Reference Reese, Mikawa and Bader1,Reference Tomanek and Angelini2}

In one retrospective study of patients who underwent coronary angiography, coronary anomalies were present in 0.9% of paediatric patients. ^{Reference Tuo3} However, in those with CHD, the risk of having coronary anomalies is higher, with some studies reporting up to 36% of patients with CHD having anomalous coronaries. ^{Reference Taylor4} Moreover, variation in coronary artery anatomy is more common in patients who have left coronary dominance. ^{Reference Eren5} Anomalous origin of coronary arteries can be fatal if unrecognised. Anomalous left coronary artery from pulmonary artery occurs in 1 in 300,000 live births, comprising 0.24–0.46% of infants with CHD. ^{Reference George6} Anomalous left circumflex artery from pulmonary artery is furthermore rare, with very few cases reported in the literature.

The anomalous left circumflex artery in this case likely experienced a steal phenomenon from the main pulmonary artery with closure of the ventricular septal defect. Closure of the ventricular septal defect led to decreased pressure transmitted to the main pulmonary artery with removal of the left to right intracardiac shunt. Without forward driving pressure, there was no longer prograde flow from the left circumflex artery to the posterior wall of the heart. In addition, the myocardial bed was likely not adequately protected during cardiac arrest in the operating room. A single 20 mL/kg dose of cold blood Del Nido cardioplegia was injected into the aortic root, which is standard for low-risk, routine ventricular septal defect repairs. Ideally, it would flow through the left and right coronary arteries, reaching the left circumflex artery and offering protection to the posterior heart. ^{Reference Carvajal7} However, given this patient’s unanticipated anatomy, cardioplegia may not have reached her left circumflex artery and thus her posterior wall was likely ischaemic for the duration of the repair once the ventricular septal defect patch was completed.

While isolated new right bundle branch block is not uncommon after surgical closure of ventricular septal defect, it is unusual to have new superior right axis deviation with right bundle branch block after a perimembranous ventricular septal defect closure if no other CHD lesions are present. This suggested injury to the left inferior/ and posterior fascicles of left and right bundle of the cardiac conduction system in our patient. Due to her left-dominant coronary system, this patient lost perfusion not only to her postero-lateral walls but also her inferior wall and posterior/inferior fascicle, showing what we now know was posterior myocardial infarction on electrocardiogram.

This case adds to the sparse literature on anomalous left circumflex artery from pulmonary artery. In the case of post-operative CHD repair with ventricular dysfunction out of proportion to the expected course, it is important to consider undiagnosed anomalous coronary anatomy in the differential diagnosis. Early recognition may be amenable to intervention and preclude an adverse outcome.