Anomalous Left Coronary Artery from the Pulmonary Artery

Anomalous left coronary artery from the pulmonary artery (ALCAPA, Bland-White-Garland syndrome) is a congenital anomaly in which the left coronary artery arises from the main pulmonary trunk, usually from the left posterior sinus, instead of the aorta.

It affects about 1 in 300,000 live births (0.25 to 0.5% of congenital heart disease) and is usually isolated. The infantile form presents at 1 to 3 months of age with left ventricular failure and mitral regurgitation.

When abundant collaterals develop from the right coronary artery, patients can survive to adolescence or adulthood and present with angina, arrhythmia, heart failure, sudden death or an incidental murmur. About 90% of untreated infants die in the first year.

Pathophysiology. In foetal life and the first days after birth, pulmonary artery pressure is high and the left coronary artery is perfused antegrade with desaturated blood. As pulmonary vascular resistance falls, perfusion pressure in the left coronary artery falls and flow reverses.

Blood passes from the right coronary artery through collaterals into the left coronary system and then drains retrograde into the pulmonary artery (coronary steal, a left-to-right shunt).

The left ventricular free wall, septum and papillary muscles become ischaemic, producing infarction, papillary muscle dysfunction with mitral regurgitation, ventricular dilatation and endocardial fibroelastosis. Feeding and crying raise oxygen demand and cause ischaemic episodes.

• Infants (1 to 3 months, up to 6 months): paroxysms of irritability, pallor and sweating during feeds or crying (anginal equivalent), tachypnoea, poor feeding, failure to thrive, heart failure, gallop rhythm and an apical holosystolic murmur of mitral regurgitation. Cardiac arrest can be the first event.
• Adult form: exertional dyspnoea, angina, palpitations, syncope, ventricular arrhythmia and sudden death. The patient may be asymptomatic, with a continuous murmur from collateral flow at the left sternal border.
• ECG: pathological Q waves in I, aVL and V4 to V6 with ST-T changes (anterolateral infarct pattern).

Red flags.

• Infant with heart failure, cardiomegaly and an infarct pattern on ECG
• Episodic distress with feeding
• Ventricular tachycardia or cardiac arrest
• Mitral regurgitation with reduced ejection fraction in an infant or young adult
• Rising troponin

• Chest X-ray: cardiomegaly and pulmonary venous congestion.
• Echocardiography: dilated, poorly contracting left ventricle, mitral regurgitation, bright papillary muscles and endocardial fibroelastosis, a dilated right coronary artery, septal collaterals on colour Doppler, no left coronary ostium on the aortic root, and left coronary flow entering the pulmonary artery (diastolic jet). Normal appearing echocardiography does not exclude the diagnosis.
• CT angiography: the best test for origin, course, collaterals and associated anomalies.
• Cardiac MRI: left ventricular function, scar on late gadolinium enhancement and viability.
• Cardiac catheterisation with aortography: reserved for unclear imaging. It shows a dilated right coronary artery filling the left system retrogradely with contrast entering the pulmonary artery.
• Blood tests: troponin and NT-proBNP.

Differential diagnosis.

• Dilated cardiomyopathy
• Acute myocarditis
• Primary endocardial fibroelastosis
• Left ventricular non-compaction
• Metabolic cardiomyopathy (Pompe disease, carnitine deficiency)
• Kawasaki disease with coronary aneurysm
• Coronary arteriovenous fistula
• Aortopulmonary window
• Anomalous aortic origin of the left coronary artery from the right sinus
• Primary mitral valve disease
• Neonatal myocardial infarction

Diagnosis alone is an indication for urgent surgery, whatever the age or ventricular function.

• Operation: direct reimplantation of the left coronary artery into the aorta by button transfer (preferred), restoring a two coronary system. When the origin is too far from the aorta, an intrapulmonary tunnel (Takeuchi repair) creates an aortopulmonary window with a baffle, at the cost of late baffle leak and supravalvular pulmonary stenosis. In older patients, ligation of the anomalous origin with bypass grafting (left internal mammary artery) is an alternative. Mitral valve repair is done only for severe regurgitation with structural valve disease, because regurgitation often falls as the ventricle recovers.
• Mechanical support: early ECMO or a ventricular assist device for refractory shock, severe ventricular dysfunction or arrhythmia, before or after surgery. Left ventricular function recovers over weeks to months in most survivors.
• Preoperative stabilisation: furosemide in infants and children: 0.5 to 1 mg/kg intravenously every 6 to 12 hours, or 1 to 2 mg/kg orally every 6 to 12 hours, maximum 6 mg/kg daily; monitor sodium, potassium, creatinine and weight. In low output states use inotropes sparingly because they increase myocardial oxygen demand. Milrinone 0.25 to 0.75 microgram/kg/min intravenously (loading dose 50 microgram/kg over 15 minutes, omitted if hypotensive), reduced in renal impairment, monitoring blood pressure and rhythm. Avoid measures that lower pulmonary vascular resistance and worsen steal: unneeded supplemental oxygen, hyperventilation and pulmonary vasodilators. Avoid agents that reduce diastolic blood pressure.
• Outcome: early surgical mortality is under 10% in most series and higher with severe preoperative dysfunction.
• Ventricular arrhythmia or cardiac arrest in adults: an implantable cardioverter defibrillator is considered when arrhythmia persists after revascularisation, because scar remains.

Special groups. Pregnancy is contraindicated with unrepaired ALCAPA. After repair with normal ventricular function it is generally tolerated.

Monitoring. Echocardiography at discharge, 3 and 6 months, then yearly for ventricular recovery, mitral regurgitation and coronary patency. CT angiography or MRI perfusion and viability at 6 to 12 months and when symptomatic. Ambulatory ECG yearly. Exercise testing in older children and adults.

Referral and escalation. Immediate transfer to a paediatric cardiac surgical centre for any infant with suspected ALCAPA. Adults go to an adult congenital heart disease centre. Escalate urgently for ventricular arrhythmia, falling ejection fraction or rising troponin.