Prosthetic Heart Valves

Identification & Potential Complications of Heart Valve Replacement

Patients with significant native heart valve disease (HVD) often experience valvular stenosis, incompetence, or both, leading to progressive cardiac changes as well as secondary organ involvement.^[1] In cases where native valve repair is not possible, patients must be treated by valve replacement.^[1,2] Prosthetic heart valves (PHVs) have been in use for over 50 years^[2] and have undergone many changes since their inception. Today, patients with a replacement valve have a better quality of life when compared to those HVD patients with significant disease who are medically managed.^[1]

PHVs are broadly categorized as mechanical heart valves (MHVs), composed entirely of synthetic or nonbiological materials, or bioprosthetic heart valves (BHVs), composed of synthetic and biological materials (Figure 1).^[2] Bioprostheses are of two kinds: xenografts, which are taken from different species than the recipient, and homografts, which are donor valves taken from the same species as the recipient.^[3] Over 250,000 PHVs are implanted worldwide each year, of which 55% are MHV and 45% are BHV (the reverse is true in developed countries).^[1,2] Prosthetic valve implantation is increasing at a rate of 5-7% per year, with BHVs gaining favour at a slightly faster pace than MHVs (8-11% increase per year vs. 3-5% increase per year, respectively).^[2]

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Marketed Prosthetic Valves

Mechanical valves are divided into two types based on their flow patterns: lateral flow (i.e., ball and cage valves) and central flow (i.e., tilting disc and bileaflet valves).^[2] In contrast to MHVs, the most essential component of a BHV is the biological tissue. This tissue is either an intact porcine aortic valve or segments of bovine or equine pericardium fashioned into three valve cusps.^[1] These materials are fixed in low concentrations of glutaraldehyde and often treated with antimineralization agents.^[1]

BHVs more closely imitate the functional properties of native valves than do MHVs. Namely, BHVs have good thrombo-resistance and hemodynamics.^[1] Some stented BHVs have functioned effectively for up to 24 years, and some stentless valves have now been in place for over 10 years with good results.^[1] In young patients, MHVs are preferred as the valves are not prone to structural valve deterioration (SVD).^[5] However, MHV components are thrombogenic, requiring life-long anticoagulant therapy, which increases a patient's susceptibility to hemorrhage.^[2] Patients with a single bioprosthetic heart valve do not require anticoagulant therapy,^[1] and bioprostheses are therefore favoured for use in older patients.^[5] Although BHVs are prone to SVD at up to 15 years postimplantation, they are suitable for use in older patients as the valves often outlive the patient. Nevertheless, some authors report that there is no advantage in either survival or quality of life for patients 65-75 years of age receiving a bioprosthetic or mechanical valve.^[5]

Complications frequently occur in both mechanical and biological heart valves, significantly affecting the postoperative success of a patient ( Table 1 ). Complications are usually prosthesis-related, such as device failure or SVD due to materials and/or design, or host-related factors, such as infection and/or host tissue overgrowth (pannus).^[2,6] In BHVs, SVD most commonly manifests as collagen degeneration and mineralization of the cuspal tissue.^[1] Mineralization continues to be a problem with all BHVs and is likely related to a number of factors, including the aldehyde fixation process. Ultimately, significant complications necessitate removal and replacement of the prosthesis.^[2]

The following sections present information about the most commonly implanted (contemporary) mechanical and bioprosthetic heart valves. The intent is to familiarize the reader with the important features of these valves, including materials, design, and common potential complications.

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