Department of Cardiology
St. Luke's Episcopal Hospital
Texas Heart Institute
6624 Fannin, Suite 2780
Houston, TX 77030, USA
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The accompanying publication by Talwar and colleagues of a relatively large series of cases of ALCAPA provides an occasion for a few additional comments on this rare defect. This unique anomaly of coronary origination gives rise to a series of different functional states during the life of the patient, and has recently attracted great clinical interest. Anatomically, this anomaly is well known not only in humans but also in the experimental model of the hamster, where it has been described as occurring in association with bicuspid aortic valve.1 Most likely, this anomaly is related to a defect in the cardiac neural crest cell that normally contribute to the septation of the aortic pulmonary septum and this may lead to ectopic migration of the primitive coronary vessels.2,3
Anomalous origin of a coronary artery from the pulmonary artery has been observed in a spectrum of cases: it may affect the left coronary artery (most common case), or both right and left coronary arteries, only the circumflex branch, only the left anterior descending artery, or only the right coronary artery.3 Whereas the origin of both coronary arteries from the pulmonary artery leads to immediate postnatal death, all other forms may be compatible with survival. Anomalous origin of a coronary artery from the pulmonary artery leads not only to an anatomic variant but to critical hemodynamic alterations that vary during the early life of the patient. During embryonic and fetal life, the anomalous artery supplies blood flow to the dependent myocardium that is essentially normal in flow but in the context of a low oxygen content. In a highly oxygen-avid parenchyma (myocardial oxygen extraction is the highest in the human body) and under the limited hemodynamic loading conditions of the developing heart, such a pathophysiologic change is well tolerated. At the same time, no hemodynamic gradient between neighboring coronary territories is established to stimulate the formation of collateral circulation at this stage (both the aorta and pulmonary artery have the same pressure before birth).
Such a benign fetal situation precipitates into critical decompensation early after birth when the pulmonary resistances fall quickly to one fifth of systemic resistance, leading to obligatory interruption of the prograde flow into the ectopic vessel. Critical ischemia usually occurs with a clinical pattern of neonatal myocardial infarction. The highest phase of mortality is consequently concen-trated in the first month of life (low cardiac output, pulmonary edema, ventricular fibrillation). The entity of the ischemic event is mainly dependent on the territory at risk; a normal (dominant) left coronary artery supplies approximately 70% of the left ventricular myocardium, the left anterior descending artery supplies 45%, and the circumflex supplies 25%.4 If the patient survives this early critical stage, this is mainly because either the territory at risk is smaller than in a typical case of ALCAPA, or some coexisting conditions lead to persistent pulmonary hypertension (pulmonary banding beyond the anomalous origin could be an effective palliative inter-vention). The presence of severe mitral insufficiency could also be favorable in this sense.
Critical ischemia in the newborn myocardium is notably different from the adult case because the window of opportunity for recovery on reperfusion is much longer. Whereas akinesia or dyskinesia usually occurs shortly after birth (with creatine kinase leakage), the reversibility of myocardial dysfunction is amazingly better than in adult myocardial infarction. The degree of myocardial recovery on reperfusion is critically dependent on timing: up to one year of extrauterine life, recovery to normal systolic function is possible (even though histologically a scar can still be found); afterwards, potential recovery becomes gradually less, becoming close to zero in late adulthood. Such observations are nicely confirmed by the current report and have led to the statement that ALCAPA realizes the best clinical example of hibernating myo-cardium.5 The All India Institute series presents a preoperative mean ejection fraction of 35.8% with a postoperative ejection fraction of 58.6%: a dramatic but not unusual finding in a population composed mainly of infants (median age, 6 months).
The adult onset of myocardial hibernation is caused by chronic critical ischemia leading to a slow partial recovery at 2 to 6 weeks after reperfusion.5 In contrast, ALCAPA-related hibernation is usually caused by critical ischemia in the newborn stage, followed by spontaneous reperfusion although with limited flow (by collateral circulation). Myocardial recovery may involve myo-cardial regeneration in the infant, just as cardiac chamber remodeling can be enhanced during the following years of growth, unlike the adult case of ALCAPA. In the adult patient with acute myocardial infarction, clearly "time is myocardium," whereas in the case of ALCAPA, the first priority is to assure survival throughout the initial crisis, the second less urgent priority is to plan physiologic repair during infancy in the best center for such an unusual intervention.
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References
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Sans-Coma V, Duran AC, Fernandez B, Fernandez MC, Lopez D, Arque JM. Coronary artery anomalies and bicuspid aortic valve. In: Angelini P, editor. Coronary artery anomalies. Philadelphia: Lippincott, Williams and Wilkins, 1999:17–27.
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DelaCruz MV, Moreno-Rodriguez R, Angelini P. Ontogeny of the coronary vessels. In: Angelini P, editor. Coronary artery anomalies. Philadelphia: Lippincott, Williams and Wilkins, 1999:11–7.
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Angelini P, Villason S, Chan AV, Diez JG. Normal and anomalous coronary arteries in humans. In: Angelini P, editor. Coronary artery anomalies. Philadelphia: Lippincott, Williams and Wilkins, 1999:27–151.
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Angelini P. Preventing ischemia during angioplasty via mechanical hemoperfusion. J Myocard Isch 1990; 2:81–100.
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Shivalkar B, Borgers M, Daenen W, Gewillig M, Flameng W. ALCAPA syndrome: an example of chronic myocardial hypoperfusion? J Am Coll Cardol 1994;23:772–8.[Abstract]
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Fagan TE, Palacios-Macedo A, Nihill MR, Fraser CD Jr, Cooley D. Coronary anomalies in pediatric patients. In: Angelini P, editor. Coronary artery anomalies. Philadelphia: Lippincott, Williams and Wilkins, 1999:151–72.
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