Novel applications of transoesophageal echocardiography

Transoesophageal echocardiography has become a widely used diagnostic imaging technique by virtue of its ability to yield high quality images of the heart and great vessels. This thesis is based on work performed between January 1991 and July 1992 during which novel applications of transoesophageal echocardiography were investigated in the intraoperative and critical care settings. The mechanism by which closed chest cardiopulmonary resuscitation (CPR) generates forward blood flow has long been debated. Use of transoesophageal echocardiography allowed the physiology of CPR to be elucidated in 18 human subjects with cardiac arrest. These observations supported the cardiac pump theory of CPR and suggested that transoesophageal echocardiography might be utilised to monitor the efficacy of CPR. A preliminary investigation of CPR performed with the active compression-decompression device is described. The pathophysiology of the fat embolism syndrome (FES) is poorly understood. Transoesophageal echocardiography detected intraoperative fat embolism in 24 patients with traumatic injuries, three of whom subsequently developed clinical evidence of FES. Paradoxical embolism through a patent foramen ovale occurred in one subject with fulminating fat embolism. These results support the mechanical theory of the aetiology of fat emboli, and suggest that transoesophageal echocardiography might be used to identify patients at greatest risk of FES. The role of transoesophageal echocardiography in monitoring regional and global myocardial function was explored in a study of the cardioprotective properties of acadesine in patients undergoing coronary artery bypass surgery. No differences were observed between the acadesine and control groups in the incidence of new regional wall motion abnormalities or in changes in the area ejection fraction. The strengths and limitations of transoesophageal echocardiography are discusssed. Transoesophageal echocardiography was used to examine the role of transgastric imaging in the assessment of cardiac haemodynamics. This novel imaging plane facilitates assessment of aortic stenosis and estimation of cardiac output. Use of transoesophageal echocardiography for estimation of pulmonary artery systolic pressure was also examined. The role of transoesophageal echocardiography in cardiac surgical intensive care was explored. Important clinical information was obtained in the majority of patients when used for emergency diagnosis. Elective monitoring of cardiac function was shown to be feasible and gave valuable information in 12 out of 33 patients. In conclusion, transoesophageal echocardiography is a valuable imaging technique that has useful applications in a variety of clinical settings. It can provide new insights into long-recognised conditions and might provide new avenues for future research.