Impact of aortic dimensions and pulse pressure on late aneurysm formation in operated type A aortic dissection. A magnetic resonance imaging study

Use of multi-velocity encoding 4D flow MRI to improve quantification of flow patterns in the aorta

PURPOSE

To show that the use of a multi-velocity encoding (VENC) 4D-flow approach offers significant improvements in the characterization of complex flow in the aorta. Four-dimensional flow magnetic resonance imaging (MRI) (4D-flow) can be used to measure complex flow patterns and dynamics in the heart and major vessels. The quality of the information derived from these measures is dependent on the accuracy of the vector field, which is limited by the vector-to-noise ratio.

MATERIALS AND METHODS

A 4D-flow protocol involving three different VENC values of 150, 60, and 20 cm/s was performed on six control subjects and nine patients with type-B chronic aortic dissection at 3T MRI. Data were processed using a single VENC value (150 cm/s) or using a fused dataset that selected the lowest appropriate VENC for each voxel. Performance was analyzed by measuring spatial vector angular correlation, magnitude correlation, temporal vector conservation, and "real-world" streamline tracing performance.

RESULTS

The multi-VENC approach provided a 31% improvement in spatial and 53% improvement in temporal precision of velocity vector measurements during the mid-late diastolic period, where 99% of the flow vectors in the normal aorta are below 20 cm/s. In low-flow conditions this resulted in practical improvements of greater than 50% in pathline tracking and streamline tracing quantified by streamline curvature measurements.

CONCLUSION

A multi-VENC 4D-flow approach provides accurate vector data across normal physiological velocities observed in the aorta, dramatically improving outputs such as pathline tracking, streamline estimation, and further advanced analyses.

MRI in Chronic Aortic Dissection: A Systematic Review and Future Directions

The acute event of thoracic aortic dissection carries with it high mortality and morbidity. Despite optimal initial surgical or medical management strategies, the risk of further complications in the long-term, including aneurysmal dilatation and false lumen (FL) expansion, are not insignificant. Adequate follow-up of such conditions requires dedicated imaging where relevant prognostic indicators are accurately assessed. We perform a systematic review of the literature and report the current evidence for the use of magnetic resonance imaging (MRI) in assessment of chronic aortic dissection. We then make a comparison with traditional imaging modalities including computed tomography and echocardiography. We discuss new ways in which MRI may extend existing aortic assessment, including identification of blood-flow dynamics within the TL and FL using phase-contrast imaging.

Hybrid repair of type A acute aortic dissections with the Lupiae technique: ten-year results

OBJECTIVES

Replacing the ascending aorta and the arch in patients with type A acute aortic dissection achieves good short-term results, but several patients are left with distal intimal tears or a patent false lumen in the descending aorta. In this series, we report the 10-year experience with the Lupiae technique, a hybrid aortic repair technique for patients with type A acute aortic dissection.

METHODS

From 2003 to 2013, 89 patients with type A acute aortic dissections underwent replacement of the ascending aorta, the arch, and the rerouting of the neck vessels on the ascending aorta, creating a proximal Dacron landing zone for a completion with thoracic endovascular aortic repair if necessary.

RESULTS

In-hospital mortality was 8.9%. In 16 patients, the false lumen healed spontaneously, whereas the remaining 65 patients underwent thoracic endovascular aortic repair. One patient died after thoracic endovascular aortic repair. Eighty patients were followed up. Complete thrombosis of the false lumen was obtained in 93.8% of patients. The median follow-up was 46 ± 35 months. Overall 8-year survival was 93.7% ± 5%, 100% for patients with spontaneously healed residual false lumen after just type A acute aortic dissection repair and 92.3% ± 7.7% for patients who underwent thoracic endovascular aortic repair after type A acute aortic dissection repair. In 10 years, 1 patient underwent a reoperation on the distal aorta (1.25%).

CONCLUSIONS

The availability of a Dacron landing zone on the distal ascending aorta after type A acute aortic dissection repair allows the exclusion, with a thoracic endovascular aortic repair, of any residual intimal tear refilling a patent false lumen. This approach seems to be associated with a high probability of false lumen thrombosis and low rates of reoperations on the distal aorta.

Acute aortic dissection: an update

The aorta, which has a complex intrinsic biology and sophisticated mechanical properties for conducting the blood ejected from the left ventricle to the rest of the systemic arterial bed, is the largest and strongest artery in the body. It carries roughly 200 million liters of blood in an average lifetime. Any process that undermines the architecture threatens the structure, stability, and functionality of the aorta. In this regard, acute aortic dissection (AAD) requires special attention because it is the most catastrophic acute illness of the aorta; it has high morbidity and mortality because of potentially fatal complications. AAD has, therefore, become an important topic of recent research, and knowledge about this disease has improved during the past few years. Up-to-date knowledge about the natural history, epidemiology, presentation, physiopathology, evolution, management, follow-up, and long-term outcomes of AAD are summarized in this review.