Applicability of Guideline-Based Aortic Intervention Thresholds in the Indian Population

Clinical guidelines for thoracic aortopathy rely on absolute diameter thresholds to guide surveillance and prophylactic intervention. These thresholds, derived largely from Western cohorts, are applied globally, including in populations with smaller baseline vascular dimensions. We performed a counterfactual, denominator-based analysis comparing the distribution of ascending aortic diameter and its body surface area (BSA)-indexed equivalent in a South Asian general population (n = 2,000) with diameters at presentation in a cohort of acute Stanford type A aortic dissection (ATAAD) patients (n = 71), with Bayesian 95% credible intervals around exposure ratios. The general population showed a narrow distribution (median 30.2 mm; 95th percentile 37.6 mm; mean indexed diameter 18.5 ± 3.1 mm/m2), with under 1% reaching the 45 mm guideline threshold. Dissections occurred across a broad diameter range (median 52 mm; indexed median 28.0 mm/m2, interquartile range [IQR] 22.1–34.0 mm/m2) and were disproportionately concentrated in the extreme right tail of both distributions. Guideline-based absolute diameter thresholds correspond to an extremely small fraction of this South Asian population, yet dissections remain concentrated in the extreme right tail, a pattern preserved and amplified after BSA indexing. These findings support population-aware interpretation of aortic size thresholds.