Direct visualisation of the beating heart in vivo in an ovine model
John F Fraser, John Keys, Kimble Dunster,Bruce Garlick, Charles McDonald, Graeme Hart,Andrew Clarke, Eric Janes, Kathy Wilson, Greg Scalia
Critical Care Research Group, Prince Charles Hospital, Brisbane, QLD
Introduction
Mitral valve disease is a major cause of premature death. Indications for surgical correction are based on clinical progress and echocardiographic assessment. There is minimal knowledge of the mitral valve as it functions under direct vision. We created a model of direct visualisation of the mitral valve, as a precursor to a model of mitral regurgitation with assessment of flow dynamics by echocardiography versus true visual images.
Methods
Five Merino sheep were selected. Autologous blood was obtained by preoperative phlebotomy and administration of supplemental iron. After induction of anaesthesia and sterile preparation, an arterial cannula was placed in the right pulmonary artery, and a second cannula was placed proximally in the aortic root, leaving room for an aortic cross clamp to be placed between the two cannula. Systemic perfusion was achieved using standard cardiopulmonary bypass (CPB). The circuit was primed with 1 L plasma-lyte P148, and 2 units of autologous sheep blood. CPB was established using a twostage venous drainage and ascending aortic return. Physiological monitoring was conducted using a Tramscope 12C monitor(GE, Chicago,USA). Systemic pressures were maintained using pump flows of 2.5–3.5 L/min.
Following left ventriculotomy, a bronchoscope was inserted into the cavity of the left ventricle. Crystalloid solution was then sucked from a reservoir and infused into the right pulmonary artery. The pulmonary circulation, left atrium and left ventricle were then perfused by crystalloid solution at a left atrial pressure of about 10 mmHg, and a videorecording of the left atrium, mitral and aortic valves was obtained in bursts of 1–2 minutes. As the ischaemic time progressed, ventricular function deteriorated, and blood perfusion was then reinitiated to rest the heart.
Results and discussion
This is the first successful attempt to obtain in-vivo images of the beating heart. Future plans include creation and correction of mitral regurgitation with computer-gated imaging. This may assist in future design of devices to treat mitral valve regurgitation.
