Imaging of the distal ascending aorta using modified transesophageal echocardiography in cardiac surgery

Abstract

Epiaortic ultrasound scanning of the ascending aorta is a safe and useful method to detect atherosclerosis in patients undergoing cardiac surgery. The use of epiaortic ultrasound can lead to modifications of the surgical technique, which effectively reduces the post-operative incidence of stroke in case of severe ascending aorta atherosclerosis. Epiaortic ultrasound scanning is considered the ‘gold’ standard for detecting atherosclerosis in the ascending aorta. However, epiaortic ultrasound scanning can only be applied after sternotomy. If then atherosclerosis appears more severe than anticipated, decisions regarding changes in surgical strategy have to be made at a relatively late stage. Transesophageal echocardiography is a widely used imaging modality permitting evaluation of the extent of atherosclerosis in the thoracic aorta. However, assessment of the distal ascending aorta using transesophageal echocardiography is disturbed by the interposition of the air-filled trachea between the oesophagus and the ascending aorta. Recently the A-View method was introduced as a modification of conventional transesophageal echocardiography with the aim to overcome this limitation. An intra-tracheal balloon filled with saline replaces the air in the trachea. Hence, it becomes possible to assess the distal ascending aorta for the presence and severity of atherosclerosis before cardiac surgery. It is widely acknowledged that in the scientific evaluation of a diagnostic device a phased approach should be followed. After technical development and safety evaluation, but before investigating whether the test may replace current diagnostic techniques and actually improves the (cost)-effectiveness in terms of patient outcome, the test’s reproducibility and potential discriminative accuracy must be quantified. This thesis describes the scientific evaluation process of the A-View method. In a cross-sectional diagnostic study in patients undergoing cardiac surgery we showed that with the A-View method the distal ascending aorta was visible in all patients. There were no clinical important side effects associated with use of the A-View catheter. In a subsequent performed larger study we showed that the positive predictive value of the A-View method was 67%, and negative predictive value was 97%. Sensitivity was 95% and specificity was 79%. Therefore the A-View method yields adequate diagnostic accuracy to detect ascending aorta atherosclerosis. To study the reproducibility of the A-View method images, obtained with the A-View method, were reviewed by 4 different observers at two moments. The agreement across observers was slight to moderate and the agreement within observers was moderate to substantial. We have to further investigate how to improve this agreement to enhance the applicability of the A-View method. Finally we showed in a cost-effectiveness modeling study that the A-view method and subsequent adjustment of the surgical procedure based on it findings is likely to reduce health care costs and increase health benefits as compared to the current strategy. The A-View method offers a minimally invasive method to image the distal ascending aorta and guide surgical strategy. Future research is needed to investigate whether the use of the A-View method indeed leads to changes in therapeutic management and a reduction of embolic events and subsequent stroke.