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

Aims: Increasing aortic dilation increases the risk of aortic dissection. Nevertheless, dissection occurs at dimensions below guideline-directed cut-offs for prophylactic surgery. Currently, there are no large-scale population imaging data assessing aortic dimensions before dissection.

Methods and results: Patients within the National Echo Database of Australia were stratified according to absolute, height-indexed, and body surface area (BSA)-indexed aortic dimensions. Fatal thoracic aortic dissections (ICD-10-AM Code I71) were identified via linkage with the National Death Index. A total of 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). A total of 274 992 (52.4%) were males, with a median age of 64 years and a median follow-up time of 6.9 years. Eight hundred and ninety-nine 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 = odds ratio (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. The results were robust for absolute, height-indexed, or BSA-indexed aortic measurements.

Conclusion: Although severe aortic dilatation is associated with a near-30-fold increase in fatal dissections, 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.