Large-scale computed tomography study of aortic arch and supra-aortic artery morphology: Variations and potential implications for arterial extracorporeal life support access

Abstract

Background

The anatomy and morphology of the aortic arch and its supra-aortic arteries can vary significantly among individual patients. This variability may have a particular relevance in cardiovascular procedures or interventions, and specifically during the use of mechanical circulatory support. This importance accounts for a specific influence on hemodynamics in veno-arterial extracorporeal membrane oxygenation (V-A ECMO) through an axillary/subclavian artery access. The related hemodynamic effects and interplay with native cardiac blood flow dynamics have been poorly investigated.

Methods

To assess the existing patterns of aortic arch and related supra-aortic artery morphology, thoracic computed tomography (CT) scans of patients undergoing pre-procedural (trans-catheter aortic valve or aortic or other cardiovascular surgery) assessment were investigated. All CT scans clearly showing the thoracic aorta in all its anatomical parts were selected and evaluated in terms of anatomical features (aortic arch type, position of the supra-aortic arteries along the aortic arch or ascending aorta, length and disposition of the ascendent aorta and aortic valve plane, and descending thoracic aorta). Aortic arch morphology was classified according to the Madhwal description, ¹ namely Type I, II, and III based on the exit point of the left subclavian artery along the aortic arch, with Type III configuration with all the three supra-aortic arteries departing leftwards the aortic arch peak, and Type I presenting the left subclavian artery departing from the peak of the aortic arch.

Results

The CT scans of 1228 patients were analyzed and categorized. Overall, 70% (860 cases) of the aortic arch were Type III, 16.9% (208 cases) Type II, and 8.4% (103 cases) Type I. No difference was found between male and female patients. Type III aortic arch morphology presents a potentially unfavorable relationship due to a retrograde flow from the right axillary or subclavian artery, in case of such a V-A ECMO perfusion access, allegedly towards/against the aortic valve and left ventricular ejection. Type I and II aortic arch morphology showed patterns potentially more favorable from a mechanistic point of view, with an apparent more favorable anatomical disposition for a blood flow mainly directed towards the descending aorta.

Conclusions

Aortic arch and supra-aortic artery morphology vary markedly among patients. However, in this large patient population, the majority of aortic arch morphology was Type III which has a potentially unfavorable interaction between the native blood flow and V-A ECMO retrograde flow from the right axillary/subclavian artery compared to the left-sided access. Dedicated fluid-dynamic studies investigating the actual right or left axillary artery-generated retrograde flow direction and distribution along the ascending aorta, aortic arch and descending aorta deserves further investigation. Indeed, the interplay of blood flows generated by the left ventricle and that of V-A ECMO perfusion from right or left axillary/subclavian arteries and the consequence of this interplay on oxygen mixing, delivery and LV afterload, are warranted due to the increased use of such an approach.