Aortic valve replacement : anatomical considerations in a narrow aortic root.
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Date
2015
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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.
Description
Master of Medical Science in Clinical Anatomy. University of KwaZulu-Natal, Westville 2015.
Keywords
Aortic valve--Surgery., Heart valves--Surgery., Theses--Clinical anatomy., Aortic root., Aortic valve replacement.