False lumen flow dynamics and partial thrombosis in patients with chronic aortic dissection of the descending aorta: a 4D flow CMR study

Abstract

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Spanish Ministry of Science, Innovation, and Universities Background Partial thrombosis of the false lumen (FL) in patients with chronic aortic dissection (AD) of the descending aorta has recently been associated with poor outcomes (1). However, four-dimensional phase-contrast cardiovascular magnetic resonance (4D flow CMR) studies analyzing flow dynamics and biomechanics in the FL and their relationship with partial thrombosis are lacking. Purpose This study aimed to compare FL flow dynamics and biomechanics between patients with non- and partially-thrombosed FL. Methods Patients with a chronic (>3 months after the acute event), non-thrombosed or partially-thrombosed FL in the descending aorta after an AD underwent an imaging follow-up including a magnetic resonance angiography (MRA) and a 4D flow CMR study. FL thrombosis was quantified as the ratio of thrombus volume and FL volume on MRA. Forward systolic and diastolic flow, and wall shear stress (WSS) were calculated at 8 equidistant planes covering the FL descending aorta from the pulmonary bifurcation to the diaphragmatic level, and averaged values were used (1,2). Maximum kinetic energy (KE), maximum acceleration and flow stasis were quantified in a volume covering the same region of the descending aorta (1). Aortic stiffness in the FL was assessed in terms of pulse wave velocity (PWV), which was calculated from the third supraortic trunk to the diaphragmatic level (3). Results Sixty-five patients with a complete imaging protocol were included in the study. The FL was non thrombosed in 34 patients and partially thrombosed in 31 patients, which presented with the 21 ± 13 % of the FL volume occupied by thrombus. Demographics and clinical data, and flow dynamic and biomechanical parameters of these patients are shown in Table 1. Partial thrombosis of the false lumen was associated with a reduction in the amount and energy of flow in the FL (reduced forward systolic flow, KE and acceleration (Figure 1B-D, respectively)), and a more stagnated flow in the FL (increased flow stasis (Figure 1E)). Axial WSS showed a tendency to be lower in the partial-thrombosis group compared to the no-thrombosis group (Figure 1F), while PWV were similar in both of them. Conclusion In patients with chronic AD of the descending aorta, false lumen axial wall shear stress, kinetic energy, and flow acceleration and stasis proved to be the main discriminators between no and partial thrombosis of the false lumen.