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a Department of Cardiac Surgery, Imam Hospital, Children's Medical Center, Tehran University of Medical Sciences, Tehran, Iran
b Department of Pediatric Cardiology, Children's Medical Center, Tehran University of Medical Sciences, Tehran, Iran
Accepted for publication August 13, 2008.
* Address correspondence to Dr Shabanian, Children's Medical Center, 62 Gharib St, Tehran, 14194, Iran (Email: rshabanian{at}gmail.com).
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A nondysmorphic 2-month-old boy (3.5 kg) was referred to us for surgical intervention because of little improvement in his growth and intractable cardiac failure despite optimal medical management. At age 3 weeks he was evaluated for cardiac anomaly because of tachypnea and poor feeding. The echocardiography demonstrated a complete AVSD (Rastelli type C) with unbalanced ventricles (the right ventricular type), a left-sided superior caval vein draining through an enlarged coronary sinus, and a right aortic arch. Although a retrograde review of echocardiographic video images confirmed an AP window, it was not diagnosed preoperatively. The infant also had a midline liver with equally sized lobes.
The operation was initiated through a midsternotomy, but cardiac arrest suddenly occurred while the sternotomy was being performed. We rapidly completed the sternotomy, and open cardiac massage was begun. The external cardiac anatomy was evaluated, and a type I AP window (Richardson classification) of about 5 mm in diameter was noted. To have the highest cardiac output during cardiopulmonary resuscitation, we clamped the right pulmonary artery.
Cardiopulmonary resuscitative measures were not successful, and cardiopulmonary bypass was initiated. The patient was cooled to 20°C. The aorta and pulmonary arteries were separated, and the resultant aortic and pulmonary arterial defects were each closed with two separate pericardial patches. The pulmonary artery was banded.
Unfortunately, the patient could not be weaned from bypass by either a tight or loose band because of very poor contractility. The autopsy confirmed all echocardiographic findings and also bilateral trilobed lungs with eparterial bronchi, asplenia, and a symmetrical liver.
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Partitioning of the AV canal begins about the middle of the fourth week of gestation and is essentially complete by the end of the fifth week. Concurrent with atrial septation, thickenings of subendocardial tissue, called endocardial cushions, develop in the dorsal and ventral walls of the heart in the region of the AV canal. Therefore, abnormal growth in this region produces a deficiency in the lowermost part of the atrial septum and also a VSD.
Because the dextrodorsal conus cushion contributes to the development of the right AV valve and the outflow tracts lie adjacent to their respective inflow tracts, AVSDs may be associated with conotruncal anomalies, such as tetralogy of Fallot and double-outlet right ventricle. Like in patients with AP window, neural crest ablation in embryonic avian models almost never results in anomalies of the AV junction [6].
AVSDs are also associated with other cardiac defects, including heterotaxy syndromes, total anomalous pulmonary venous return, transposition of great arteries, patent ductus arteriosus, small secundum ASD, and mitral valve abnormalities [7]. The nature of any potential relationship between anomalies of the AV junction, outflow tracts, and laterality defect could be explained neither by the neural crest ablation nor deletions of chromosome 22q11 [6]. Hence, the neural crest axis was not central to the development of the cardiac lesions in our patient.
In the human embryo, the growth of endocardial cushions, lobation of the lungs, the development of the spleen, and the connections between the left atrium and pulmonary venous plexus all occur between the fourth and fifth weeks of gestation. Recent human genetic studies have implicated several genes and mutations, such as submicroscopic deletion of ZIC3, as a cause of laterality defect in both X-linked and sporadic cases [8].
The direct apposition of the AV junction to the conotruncal region may be a hypothetic reason that the developmental anomalies of one area may affect the other. Some authors have suggested that any association between anomalies of the AV junction and the outflow tracts is most likely to involve impaired rotation/alignment of the conotruncal region [1].
It seems that something such as an expression of a gene (paracrine and growth-related factors), an exogenous insult, or an altered flow pattern (local mechanical effect) happens in the fifth week of gestation that will affect the embryologic maturation in the formation of these associated anomalies at the same time.
The importance of reporting a patient with combination of these cardiac anomalies is for interrogation and perioperative management for pediatric cardiologists and cardiac surgeons, respectively. The foundation for anesthesia and perioperative management in AP window must achieve the best balance between pulmonary and systemic blood flow that preserves systemic flow and minimizes pulmonary shunt. The balance may be so precarious that simply opening the chest could disrupt the balance of flow and cause the heart to fail, as occurred in our patient. So, diagnosis of AP window is crucial for perioperative anesthetic technique and preservation of myocardium.
Finally, little evidence exists to support genetic, flow-related, or other mechanisms that might explain the association of AVSD, AP window, and heterotaxy syndrome.
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