Description
A Left Ventricular Assist Device (LVAD) is a mechanical pump which is surgically implanted in the cardiovascular system. It reduces the work load of the heart by pumping the blood from the left ventricle to the aorta, bypassing the regular circulatory pathway. LVADs have been successfully used to support the function of the heart in heart failure patients as a bridge to transplant, bridge to recovery, or destination therapy. However, previous studies report that an abnormal aortic valve pathology, called commissural fusion, was found in LVAD patients. The fusion of the valve commissures, where the valve leaflets meet when the valve is closed, results from increased collagen deposition at the commissures which, we hypothesize, is due to the alteration of valve biomechanics. The fusion narrows the area of valve opening, which leads to a condition known as aortic stenosis which results in a reduction in the amount of blood sent to the body. The purpose of this study is to evaluate the effect of leaflet fusion in the LVAD assisted heart on the biomechanics of the aortic valve. Experiments were performed using the SDSU cardiac simulator with a MicroMed Debakey continuous flow LVAD to test different LVAD speeds and levels of cardiac contraction. Hemodynamic parameters, including the left ventricular pressure, aortic pressure, aortic flow and the LVAD flow were measured before and after simulated fusion. A high speed camera was used to take images of valve opening and closing. Porcine bioprosthetic valves were used as test samples. Three conditions of the valves were observed, including unfused valves, one-commissural fused valves, and twocommissural fused valves. The results show that the LVAD causes alterations in hemodynamics. Increasing LVAD speed produces a reduction in the area of valve opening, even in the valve with no fusion, creating a condition of functional aortic stenosis. Fusion of the valve leaflets causes a decrease in the area of valve opening and may lead to a condition of structural aortic stenosis . Such a decrease in the valve opening area corresponds to a decrease in flow through the aortic valve. Also, LVAD and fusion cause an increase in leaflet strain. Strain gradients across the valve leaflet are also found, showing non-homogenous strain distribution. These results support the hypothesis that LVAD and fusion of aortic valve leaflets change the nature of the aortic valve leading to valvular dysfunction, such as aortic stenosis and regurgitation.
