Transitional atrioventricular septal defect: diagnostic variability and its clinical significance.

INTRODUCTION: Discrepancies between preoperative echocardiographic diagnosis and intraoperative surgical findings for incomplete atrioventricular septal defects are frequently encountered. We assess the frequency of diagnostic discordance and its impact, focusing on subtype-specific predictors of the postoperative course. METHODS: We reviewed 172 patients post repair of incomplete atrioventricular septal defects at a single institution between November 2000-February 2025, including transitional atrioventricular septal defects (n = 74), partial atrioventricular septal defects (n = 71), and primum atrial septal defect with isolated left atrioventricular valve cleft (n = 27). Preoperative echocardiographic diagnoses were compared with intraoperative surgical diagnoses to determine diagnostic discordance and assess impact. RESULTS: Baseline characteristics were similar across subtypes. Transitional atrioventricular septal defects were associated with a higher prevalence of syndromic diagnoses (52.7% versus 33.8% versus 22.2%, p = 0.008) and greater preoperative ventricular dilation (LVIDd Z-score -0.88 versus -1.70 versus -1.70, p = 0.031). Diagnostic discordance occurred most frequently in partial atrioventricular septal defects (74.6%), followed by primum atrial septal defect with isolated left atrioventricular valve cleft (37.0%) and transitional atrioventricular septal defects (13.5%) (p < 0.001). Transitional atrioventricular septal defect repairs were associated with longer cardiopulmonary bypass and cross-clamp times, prolonged ventilation, and longer hospital stays (all p < 0.05). Residual shunt was more frequent in transitional atrioventricular septal defects early postoperatively and at the last follow-up (p < 0.001). One death was observed in the partial atrioventricular septal defects group, reintervention rates were similar across subtypes (p = 0.643), and follow-up duration differed modestly between groups (p = 0.047). CONCLUSION: The high rate of diagnostic discordance reflects inherent challenges in preoperative classification and suggests that a simplified, clinically oriented nomenclature may improve communication, surgical planning, and outcome prediction.