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in those with a ventricular septal defect according to the most recent data from The Society of Thoracic Surgeons Congenital Heart Surgery Database.63 Survival approaches 100% in some series, which include patients with a ventricular septal defect.64 Factors associated with an increased risk of mortality include the presence of a ventricular septal defect, the requirement for prolonged cardiopulmonary bypass, early gestational age, institutional volume, and some coronary anomalies.65–68 Timing of the Arterial Switch Operation In most neonates with an intact ventricular septum, the arterial switch is undertaken in the first week of life As discussed, the principal reason for carrying out surgery early in the neonatal period in such infants is to avoid the deconditioning of the left ventricle It is known that the left ventricular mass begins to regress within a few days of birth, and if this continues, the left ventricle will lose its ability to support the systemic circulation subsequent to the arterial switch operation Deconditioning may be arrested, or slowed, by the presence of a ventricular septal defect, a large patent arterial duct, or obstruction to the left ventricular outflow tract By allowing a few days before operating, the newborn achieves more complete transition of circulation, maturation of organ function, decrease in pulmonary vascular resistance, and initiation of enteral nutrition Recent evidence suggests that outcomes (mortality and morbidity) may be best when surgery takes place at 3 to 4 days of life (in the absence of surgical, medical, or other contraindications).43,69,70 Many centers are currently moving the timing of surgery to earlier and earlier, which is also affecting the decision analysis of whether to perform a septostomy and/or continue to infuse prostaglandin.70 The age beyond which a primary arterial switch operation cannot safely be undertaken is ill defined Recent data from the developing world are illustrative In a retrospective study of 778 infants undergoing surgery for transposition in resource-limited countries, 80% underwent a single-stage arterial switch operation Only 11% of all operations were performed within the first week, and most of the remainder were performed beyond the first month of life The mortality rate was high at 15%, but age at the time of surgery was not a predictor of risk.71 In a different cohort of patients ranging in age from 1 to almost 7 months who were considered to have favorable left ventricular geometry, early and late mortality after single-stage arterial switch operation was 2.6% and 2.7%, respectively.72 There has been significant interest in the preoperative echocardiographic assessment of the ability of the left ventricle to support the systemic circulation in the postoperative state The position of the interventricular septum has traditionally been used (Fig 37.19) However, in one study, compression of the ventricle to a banana shape was shown not to be predictive of the duration of postoperative ventilation, the subsequent need for extracorporeal support, or mortality in patients undergoing an arterial switch operation at greater than 3 weeks of age.73 Several quantitative criterions have subsequently been proposed to identify the patient in whom training of the left ventricle may be required These include a left ventricular end-diastolic volume of less than 90% of predicted, a left ventricular ejection fraction of less than 0.5, a left ventricular mural thickness at end-diastole of less than 4 mm, a predicted left ventricular mural stress of less than 120 × 103 dynes/cm2,74 a left ventricular mass of less than 60% of predicted,75 or, when indexed to the surface area of the body, of less than 35 G/m2.76 FIG 37.19 Echocardiographic image from a 9-month-old patient with an intact ventricular septum The ventricular septum can be seen bulging into the left ventricle (LV) RV, Right ventricle Two-Stage Repair In patients for whom it is considered that the left ventricle may not support the systemic circulation, a two-stage approach may be considered First, the pulmonary artery is banded, and the arterial switch operation is performed after a period of left ventricular “training.” When the two-stage approach was first introduced, an interval of between 5 and 8 months was allowed to elapse after the pulmonary arterial banding It has since become clear that the immature ventricle has the capacity for rapid hypertrophy,77 so that adequate preparation can be achieved within days With better preoperative and postoperative management, this strategy is less commonly used currently, instead proceeding with a primary arterial switch operation in these patients, anticipating and managing the hemodynamic consequences of that decision Coronary Arterial Anatomy A decade before the arterial switch became routine, Yacoub and Radley-Smith78 described their classification of the most common coronary arterial patterns, as well as methods for their transfer Once the arterial switch had become routine, Brawn and Mee described a variety of techniques for coronary arterial transfer in those patients with more complex arrangements.79 In an analysis of the outcomes for a large cohort, it was shown that an arrangement in which one or both of the major coronary arteries passed between the arterial trunks was associated with an increased risk of mortality.80 The effect of coronary artery origin on outcome likely varies between institutions with no effect demonstrated in some series.64 An extensive multiinstitutional analysis undertaken by the Congenital Heart Surgeons Society has been reviewed on a regular basis Although earlier reviews81,82 suggested that the arrangement of the coronary arteries did not impact on outcome, in retrospect, the relatively high overall mortality at this time may have masked the subtle contribution of coronary arterial anatomy In a later analysis,83 which included more than 500 patients, the anatomy of the coronary arteries was shown to be a risk factor In this series, there were a number of arrangements that were associated with reduced survival These included the main stem of the left coronary artery, the left anterior interventricular or the circumflex artery arising from sinus 2, or the presence of an intramural coronary artery A meta-analysis,68 which included almost 2000 patients, showed that mortality for those with any variant coronary arterial