Porcine heart valves are a type of bioprosthetic valve used to replace a diseased human heart valve. These replacements restore the proper, one-way direction of blood flow through the heart’s chambers and into the major arteries. Unlike mechanical valves, which require lifelong blood-thinning medication, bioprosthetic valves function without chronic drug therapy. However, the biological material has a finite lifespan in the high-stress environment of the heart. After a period of years, the replacement valve tissue inevitably begins to deteriorate, leading to a malfunction that requires re-intervention.
Understanding Porcine Valve Deterioration
The primary mechanism of long-term bioprosthetic valve failure is structural valve deterioration (SVD), an expected consequence of placing biological tissue under constant mechanical stress. The most common form of SVD is calcification, where calcium phosphate crystals accumulate within the valve leaflets. This buildup is not a passive process of simple mineral deposit but an active, regulated process similar to bone formation, often linked to factors like inflammation and lipid deposition.
Calcification causes the once-flexible valve leaflets to stiffen and harden, preventing them from fully opening or closing with each heartbeat. Over time, the constant movement also leads to mechanical wear and tear, causing the tissue structure to break down. This stress can result in small tears, perforations, or disruption of the valve’s cusps. Less common forms of failure, known as non-structural deterioration, can also occur, such as the growth of scar tissue (pannus) on the valve that impedes movement. Valve failure is typically a gradual process.
Symptoms Indicating Valve Malfunction
A failing porcine valve often causes symptoms that mirror the signs of the original valve disease. One of the earliest and most common signs is shortness of breath (dyspnea), which may initially occur only during physical exertion. As the condition progresses, breathing difficulty can happen even when the person is resting or lying flat.
Patients often report fatigue and weakness, noticing a reduction in their capacity to exercise or perform daily activities. The heart may struggle to maintain adequate blood flow, leading to lightheadedness or dizziness. In severe cases, a person may experience syncope (fainting). Fluid retention (edema) is another common indicator, manifesting as swelling in the ankles, feet, or abdomen. These symptoms signal that the heart is straining and should prompt immediate medical evaluation.
Physiological Impact of a Failed Valve
When a bioprosthetic valve fails, it typically results in one of two major problems: stenosis or regurgitation. Stenosis occurs when the valve leaflets stiffen and narrow the opening, which is often a result of calcification. This narrowing forces the left ventricle to pump blood out against high resistance.
The heart muscle responds to this increased workload by thickening, a process called hypertrophy, which temporarily maintains the heart’s function. However, this chronic strain leads to an increased demand for oxygen in the muscle, sometimes causing chest pain. Over time, the muscle cannot sustain this effort, and the ventricle begins to stretch and weaken.
Alternatively, the valve may experience regurgitation, where tears or perforations prevent the leaflets from closing completely. This failure allows blood to leak backward into the chamber it just left. Regurgitation lowers the effective cardiac output and causes a volume overload, as the ventricle must handle both the blood coming from the atrium and the blood leaking backward. Whether the failure is due to stenosis, regurgitation, or a combination of both, the physiological consequence is a progressive decline in the heart’s pumping ability. The chronic strain and volume overload ultimately weaken the heart muscle, leading to congestive heart failure. This is the stage where the heart can no longer meet the body’s demands for oxygenated blood.
Interventions After Valve Failure
Once a porcine valve has failed to the point of causing severe symptoms, replacement is the only treatment, as no medication can reverse the structural deterioration. The traditional approach is Surgical Valve Replacement (SVR), which is open-heart surgery to remove the failed bioprosthesis and implant a new valve, either mechanical or bioprosthetic. SVR has historically been the standard of care, especially for patients with a low or intermediate surgical risk.
A less invasive option is the Transcatheter Aortic Valve Replacement (TAVR) procedure, specifically performed as a “valve-in-valve” (ViV) intervention for a failed bioprosthesis. This technique involves threading a new collapsible valve through a catheter and expanding it within the frame of the old, failed valve. ViV-TAVR avoids the need for a second open-heart surgery and is often preferred for patients who are at a high or prohibitive risk for a traditional operation.
The choice between redo SVR and ViV-TAVR is complex and depends on factors such as the patient’s age, overall health, and the size of the original implanted valve. While ViV-TAVR offers quicker recovery and lower short-term complications, it can sometimes be associated with a higher risk of late heart failure or a residual blockage if the original valve was small. A comprehensive evaluation by a multidisciplinary heart team determines the most appropriate strategy for re-intervention.