The aortic paradox: a nationwide analysis of 523,994 individual echocardiograms exploring aortic dissection

Abstract Background Increasing aortic dilation increases risk of aortic dissection. Nevertheless, dissection occurs below guideline-directed cut-offs for prophylactic surgery. There is no current large-scale population imaging data assessing aortic dimensions before dissection. Purpose To examine the proportion of aortic dissections occurring in people with aortic diameters below guidelines for prophylactic intervention. Methods Patients within the National Echo Database of Australia (NEDA) were stratified according to absolute, height-indexed and body surface area (BSA)-indexed aortic dimensions. Fatal thoracic aortic dissections (ICD-10-AM code I79) were identified via linkage with the National Death Index. Results 524,994 individuals were assessed, comprising patients with normal aortic dimensions (n=460,992), mild dilation (n=53,402), moderate dilation (n=10,029) and severe dilation (n=572). 274,992 (52.4%) were male, with median age 64 years and median follow-up time 6.9 years. 899 fatal aortic dissections occurred (normal diameter=610, mildly-dilated aorta=215, moderately-dilated =53 and severely-dilated=21). Using normal aortas as the reference population, odds of fatal dissection increased with aortic diameter (mild=OR 3.05, 95% confidence interval (CI) 2.61-3.56; moderate=OR 4.0, 95% CI 3.02-5.30; severe=OR 28.72, 95% CI 18.44-44.72). Due to the much larger number of patients without severe aortic dilation, 97.7% of fatal aortic dissections occurred in non-severely dilated aortas. Following sensitivity analysis, severe aortic dilation was responsible for at most 24.4% of fatal aortic dissections. Results were robust for absolute, height-indexed or BSA-indexed aortic measurements. Conclusion Although severe aortic dilatation is associated with a thirty-fold increase in fatal dissection, severely dilated aortas are implicated in only 2.3-24.4% of fatal dissections. This highlights the ‘aortic paradox’ and limitations of current guidelines. Future studies should seek to refine risk predictors in patients without severe aortic dilation.