Anomalous Left Coronary Artery from the Pulmonary Artery (ALCAPA) is a rare, life-threatening congenital heart defect present from birth. It involves a malformation where the primary artery supplying blood to the left side of the heart is incorrectly connected. ALCAPA is one of the most severe congenital coronary artery anomalies, accounting for less than one percent of all congenital heart diseases. If left uncorrected, the defect carries a very high mortality rate, particularly in infancy, making early detection and surgical intervention necessary for survival.
The Abnormal Heart Structure
The heart muscle receives its blood supply through the right coronary artery (RCA) and the left coronary artery (LCA). Normally, both arteries originate from the high-pressure aorta. In ALCAPA, the LCA mistakenly arises from the pulmonary artery (PA), which is a much lower-pressure system than the aorta after the first few weeks of life.
This misplacement means the LCA receives blood at a much lower pressure than the heart muscle requires. The most damaging effect is the “coronary steal” phenomenon. As pulmonary artery pressure drops after birth, blood flows from the high-pressure RCA, through collateral vessels, into the low-pressure LCA.
Instead of supplying the left ventricular muscle, the blood flows backward (retrogrades) from the LCA directly into the pulmonary artery, stealing oxygenated blood away from the heart muscle. This reversal of flow starves the left ventricle of oxygen, leading to myocardial ischemia, which is effectively a heart attack in the infant. Chronic lack of oxygen causes the left ventricle muscle to weaken and dilate, often resulting in significant mitral valve regurgitation.
Signs and Age of Presentation
The clinical presentation of ALCAPA depends on the degree of collateral blood flow that develops between the coronary systems. The most common and severe form is the Infantile Type, where symptoms typically appear within the first one to two months of life. Initially, the infant may be asymptomatic while pulmonary artery pressure is high. Once the pressure drops, the coronary steal phenomenon begins, and the child quickly develops signs of severe heart failure.
Infants often present with nonspecific signs such as profuse sweating during feeding, persistent irritability suggesting chest pain, poor feeding, failure to thrive, and rapid breathing. Without immediate intervention, the mortality rate for infants with the Infantile Type is high within the first year of life.
A smaller percentage (10 to 15%) develop sufficient collateral circulation to survive into childhood or adulthood, sometimes referred to as the Adult Type. These patients may remain asymptomatic or experience delayed symptoms like exercise intolerance, shortness of breath, chest pain, or palpitations from heart rhythm abnormalities. ALCAPA is a known cause of sudden cardiac death in adults, often found incidentally during a workup for unexplained cardiac events.
Identifying the Condition
Diagnosis of ALCAPA is often prompted by severe symptoms of heart failure in an infant. Initial screening may involve an electrocardiogram (ECG), which can show patterns suggestive of myocardial damage, and a chest X-ray, which may reveal an enlarged heart.
The primary non-invasive diagnostic tool is a transthoracic echocardiogram. This ultrasound imaging allows the cardiologist to visualize the heart’s structure and function in real-time. Echocardiography definitively confirms the diagnosis by showing the absence of the LCA originating from the aorta and confirming its abnormal origin from the pulmonary artery. It also provides information on the extent of left ventricular dysfunction and associated mitral valve regurgitation.
Before surgical correction, detailed anatomical mapping is necessary to guide the procedure. Cardiac Computed Tomography (CT) angiography or Cardiac Catheterization/Angiography can precisely delineate the course of the anomalous LCA and the extent of the collateral circulation. CT angiography provides excellent three-dimensional detail of the coronary arteries, often eliminating the need for more invasive catheterization.
Treatment Methods
Treatment for ALCAPA requires immediate surgical intervention to establish a normal, two-coronary system supplied by the high-pressure aorta. The standard and preferred surgical technique is coronary artery relocation, also known as the direct implantation or “button transfer” technique.
This procedure involves carefully excising the origin of the left coronary artery from the pulmonary artery. The excised LCA is then reimplanted directly into the wall of the aorta, ensuring high-pressure, oxygenated blood flow. This repair restores normal coronary perfusion and halts the damaging coronary steal phenomenon.
If direct transfer is not feasible due to distance, surgeons may use techniques to lengthen the artery or create a tunnel within the pulmonary artery to redirect flow. While other techniques like the Takeuchi repair exist, the current standard focuses on establishing a dual coronary system. Post-operatively, left ventricular function is expected to progressively improve. Long-term follow-up with a cardiologist specializing in congenital heart disease is necessary to monitor heart function.