Can you explain how the heart valves opening/closing is synchronized with the heart's pacemaker firing?
Passive valves. The heart valves are passive mechanisms. They open as blood flows through them. When blood starts to backflow, they slam shut, causing the sounds you hear when you listen to your heart. So long as the valves are functioning properly, the synchronization is all done by the four chambers, with the valves just opening and closing automatically.
One causes the other. The pacemaker of the heart initiates an electrical impulse that spreads across the upper chambers and causes them to contract. Contraction of the atria pushes the atrioventricular valves open. Subsequently, the electrical impulse is transmitted to the lower chambers of the heart. The contraction of the ventricles opens the semilunar valves; at the same time the atrioventricular valves close.
Not recommended. Mri is contraindicated in this situation. A ct of the brain is recommended.
Valves. The two main types are tissue and mechanical. Tissue valves can come from cows, pigs or humans. Mechanical valves are tilting disc or ball, the ball valves are rarely seen now.
Many. Essentially any mobile valve has been used. Mechanical: ball valve tilting disc bivalve tilting biologic: pig valves sewn to a sewing ring bovine tissue - pericardium sewn to a sewing ring homografts.