Aortic valve replacement : anatomical considerations in a narrow aortic root.

Abstract

Coronary artery ostial stenosis is a life threatening complication of aortic valve replacement (AVR) surgery. It occurs in 3-5% of all AVR operations. Most cases occur 1 to 6 months following AVR. However, some cases have been recorded during and immediately after operation and these have been attributed to embolization of calcium debris, coronary artery spasm, occlusion by the prosthetic valve and distortion of the anatomy of the aortic root. AVR is a standard procedure routinely performed to alleviate the symptoms of aortic valve stenosis and regurgitation. The standard procedure involves removing the diseased, poorly functioning valve cusps and implanting a mechanical or biological prosthesis whose size allows it to perform almost like a normal aortic valve. The size of the prosthesis may be determined through pre-operative echocardiographic assessment of the aortic root correlated to the body surface area of the patient. Intra-operative “sizing” of the aortic annulus is also performed using graduated obturators. The required size may not fit well in patients who have narrow aortic roots forcing the implantation of a smaller size prosthesis, a situation that is termed patient-prosthesis mismatch. To prevent patient-prosthesis mismatch surgeons have developed techniques to enlarge the aortic annulus and place larger prostheses. However, the operating surgeon may elect not to surgically enlarge the aortic annulus but forcibly implant or “shoe-horn” a larger prosthesis. The aim of this study was to investigate and document anatomical changes on the aortic root when a large size valve is implanted in a simulated AVR operation where the aortic root is considered to be narrow. The study also aimed to report the size of the aortic root and the influence of sex, race, body height and age. Additionally, the study demonstrates the difference between the pliability of the aortic annulus and sino-tubular junction. The study was conducted at Gale Street State Mortuary in Durban, KwaZulu-Natal, South Africa. A total number of 60 unfixed cadaveric heart specimens were selected for the investigations. For investigation of morphometry of the aortic root, 30 heart samples were selected for this study. The other 30 specimens were selected for the experimental study to investigate the effect of placing a large size valve. Ethics approval for the study was obtained from the University of KwaZulu-Natal Biomedical Research Ethics Committee (Ethics number 307/15). Of the 30 normal hearts, the mean aortic annulus diameter was 20.2mm and the mean sinotubular junction diameter was 21.8mm. There was a significant correlation between aortic root diameters and age but no association with sex, race or body height. The mean diameter of the left coronary ostium (LCO) was 6.1mm. The most common shapes of the LCO were circular (96.7%) and ellipsoidal (3.3%). The mean distance of LCO from the aortic annulus was 12.6mm. The LCO was located below, on and above the sino-tubular junction in 73.3%, 23.3% and 3.3%, respectively. The study showed clearly that when an oversized prosthesis is implanted into a normal aortic root, the LCO is distorted and displaced caudally towards the aortic annulus. A transverse ridge of aortic tissue, in the form of a tight bar was created above the LCO extending from the adjacent commissures. The sino-tubular junction was more pliable than the aortic annulus by a factor of 1.5.