Interval changes in four-dimensional flow-derived in vivo hemodynamics stratify aortic growth in type B aortic dissection patients

Background: Aortic diameter growth in type B aortic dissection (TBAD) is associated with progressive aortic dilation, resulting in increased mortality in patients with both de novo TBAD (dnTBAD) and residual dissection after type A dissection repair (rTAAD). Preemptive thoracic endovascular aortic repair may improve mortality in patients with TBAD, although it is unclear which patients may benefit most from early intervention. In vivo hemodynamic assessment using four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has been used to characterize TBAD patients with growing aortas. In this longitudinal study, we investigated whether changes over time in 4D flow-derived true and false lumen (TL and FL) hemodynamic parameters correlate with aortic growth rate, which is a marker of increased risk. Methods: We retrospectively identified TBAD patients with baseline and follow-up 4D flow CMR at least 120 days apart. Patients with TBAD intervention before baseline or between scans were excluded. 4D flow CMR data analysis included segmentation of the TL and FL, followed by voxel-wise calculation of TL and FL total kinetic energy (KE), maximum velocity (MV), mean forward flow (FF), and mean reverse flow (RF). Changes over time (A) were calculated for all hemodynamic parameters. Maximal diameter in the descending aorta was measured from magnetic resonance angiogram images acquired at the time of 4D flow. Aortic growth rate was defined as the change in diameter divided by baseline diameter and standardized to scan interval. Results: Thirty-two patients met inclusion criteria (age: 56.9 +/- 14.1 years, female: 13, n = 19 rTAAD, n = 13 dnTBAD). Mean follow-up time was 538 days (range: 135-1689). Baseline aortic diameter did not correlate with growth rate. In the entire cohort, A FL MV (Spearman's rho [rho] = 0.37, p = 0.04) and A FL RF (rho = 0.45, p = 0.01) correlated with growth rate. In rTAAD only, A FL MV (rho = 0.48, p = 0.04) and A FL RF (rho = 0.51, p = 0.03) correlated with growth rate, while in dnTBAD only, A TL KE (rho = 0.63, p = 0.02) and A TL MV (rho = 0.69, p = 0.01) correlated with growth rate. Conclusion: 4D flow-derived longitudinal hemodynamic changes correlate with aortic growth rate in TBAD and may provide additional prognostic value for risk stratification. 4D flow MRI could be integrated into existing imaging protocols to allow for the identification of TBAD patients who would benefit from preemptive surgical or endovascular intervention.