Narrowed valves do not rupture. The aorta distal to the valve may be dilated in some people with bicuspid valve predisposing to rupture. There may have been an infection on the valve causing back leak, leading to fluid in the lungs. I am unaware of EECP (Enhanced External Counter Pulsation) predisposing to rupture and I don’t think it contributed to your father’s demise. The commonest causes of sudden death are silent heart attacks and very fast rates due to electric problems of the heart (especially in people with heart failure for which your father might have been using the EECP).