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I have a friend who's father died suddenly, and the coroner described the cause as his prosthetic heart valve "bursting." Can someone illustrate in words what that means, and would heart valve thrombosis have any influence on that outcome?

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There are a number of different heart valve prostheses, and the age and type of the valve in question would make answering the question somewhat easier and more specific. Prosthetic heart valves are implanted to replace a failing or failed natural valve (or in some congenital cases, a missing or malformed one) to prevent backflow into the heart and in the most general terms, prevent congestive heart failure and improve overall circulatory performance. Atrio-ventricular valves are subject to relatively low opening pressures and higher closing pressures. Ventricular outflow valves are subjected to higher opening pressures and lower closing pressures.

Today, most valve prostheses are biological in origin, based often on porcine heart valves supported on a ring to support suturing to the heart and vessel, or on a flexible and expandable ring that can be manipulated and implanted in a cath-lab procedure and without open surgery. There is still a small space for mechanical valves, and several types remain available. ALL types of prosthetic valve can fail catastrophically.

Mechanical valves can fragment and lose a piece of the valve mechanism, either leaflet or ball, or can lose a portion of the mechanical supporting structure. Most of these failure modes result in down-steam impairment of blood flow with what can only be called bad outcomes, but they may also result in sudden incompetence of the valve causing an immediate increase in pressure to the heart muscle (if you were able to identify the location of the valve I could be more specific). I have also seen structural failure where the valve failed closed, another catastrophic event for a valve where emergent surgery and cardiopulmonary bypass are required to remediate the problem and attempt to salvage the heart muscle.

Bioprostheses are generally made of porcine valves attached to some form of ring, as previously mentioned, or are hand-manufactured using pieces of bovine pericardium. In both cases, the tissue has been denatured to remove foreign protein and preclude an immune response. Bioprostheses are subject to stress from the pressures they encounter as well as bacterial infection (why some dentists want to see you pretreat with an antibiotic before dental work), and damage to the valve seen as striations subject to calcium buildup. The less flexible the leaflets are, the more prone they are to several failure modes including poor opening dynamics, leading to flow restrictions, poor closing leading to elevated pressures in the upstream chamber, or outright failure. As with mechanical valves, fractured leaflets can lead to downstream occlusion of smaller vessels and organ or tissue damage or death. Similarly, a catastrophic bioprosthesis failure can lead to heart failure and death but primarily through sudden increases in upstream pressure, known as "afterload". The physiology of cardiac function is pretty fascinating, and doesn't lend itself to a short post like this (I've several texts on the subject). If you have further, specific questions, I can try to answer those.

So, a "burst" valve, at least to me, suggests a fracture of a portion of the valve mechanism (mechanical or bioprosthetic) causing an increase in pressure on the side of the valve normally thought of that on the upstream side. It could also result from a catheter-implanted valve losing its "lock" on the implant site and moving downstream, but this is less likely. I'm also inferring from the coroner's comment this was likely an aortic valve, and the failure caused sudden heart failure in the left ventricle, as well as decreasing blood flow into the coronary arteries, leading to what we call "ischemia" and a classic heart attack. Note these are inferences based on what I've seen.

The article below is a good overview of the types of prostheses available. The article is somewhat dated, but still worthwhile. The debate still rages over mechanical or biologic and there are some few clear indications remaining for mechanical valves.

https://www.ahajournals.org/doi/full/10.1161/circulationaha.108.778886

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