Surgical considerations for avoiding disc interference based on a ten-year experience with the Medtronic Hall heart valve

Research approaches for studying flow-induced thromboembolic complications in blood recirculating devices

The advent of implantable blood recirculating devices has provided life-saving solutions to patients with severe cardiovascular diseases. Recently it has been reported that ventricular assist devices are superior to drug therapy. The implantable total artificial heart is showing promise as a potential solution to the chronic shortage of available heart transplants. Prosthetic heart valves are routinely used for replacing diseased heart valves. However, all of these devices share a common problem--significant complications such as hemolysis and thromboembolism often arise after their implantation. Elevated flow stresses that are present in the nonphysiologic geometries of blood recirculating devices, enhance their propensity to initiate thromboembolism by chronically activating the blood platelets. This, rather than hemolysis, appears to be the salient aspect of blood trauma in devices. Limitations in characterizing and controlling relevant aspects of the flow-induced mechanical stimuli and the platelet response, hampers our ability to achieve design optimization for these devices. The main objective of this article is to describe state-of-the-art numerical, experimental, and in vivo tools, that facilitate elucidation of flow-induced mechanisms leading to thromboembolism in prosthetic devices. Such techniques are giving rise to an accountable model for flow-induced thrombogenicity, and to a methodology that has the potential to transform current device design and testing practices. It might lead to substantial time and cost savings during the research and development phase, and has the potential to reduce the risks that patients implanted with these devices face, lower the ensuing healthcare costs, and offer viable long-term solutions for these patients.

Modern cardiac valve devices--bioprostheses and mechanical prostheses: state of the art

The choice of bioprostheses and mechanical prostheses as valvular substitutes for cardiac valve replacement surgery has existed for over 20 years. The extensive developments over the past three decades have been introduced to reduce or eliminate valve related complications, namely thromboembolism, anticoagulant related hemorrhage, and structural failure, as well as to optimize hemodynamic performance. The biological valvular prostheses, namely porcine aortic or bovine pericardium, have been developed with tissue preservation, together with stent designs, that contribute to preservation of anatomical characteristics and biomechanical properties of the leaflets. The mechanical prostheses have been developed to eliminate structural failure, to facilitate prevention of blood status and thrombus formation, to facilitate radiopacity for evaluation of prosthesis function, and to facilitate intraoperative leaflet positioning. The implantation of the various present generation bioprostheses and mechanical prostheses requires special considerations to avoid technical complications and support ventricular performance. The studies of biological and mechanical prostheses, both randomized and nonrandomized, as well as specific prosthesis assessments, have contributed to the establishment of indications for types of prostheses. Bioprostheses have a high risk of structural failure and reoperation, while mechanical prostheses have a high risk of thromboembolism and anticoagulant hemorrhage. Within the bioprostheses population, the risk factors for structural valve deterioration are younger age and mitral prosthesis. Older patients (> 65 years of age) have a greater risk of valve related complications with mechanical prostheses, while younger patients (< 40 years of age) are at greater risk with bioprostheses. Comparison of large bioprostheses and mechanical prostheses populations by age groups revealed that regardless of the differences in the freedom from structural valve deterioration, the freedom from treatment failure (valve related mortality and permanent impairment from thromboembolism, anticoagulant hemorrhage, and septal emboli from prosthetic valve endocarditis) is essentially the same for mechanical prostheses and bioprostheses at 10 years. The quality of life is superior with bioprostheses, while patient survival and total valve related morbidity/mortality are similar with both types of prostheses.

Preservation of all chordae tendineae and papillary muscle during mitral valve replacement with a tilting disc valve

Mitral valve replacement was performed in 21 patients using a surgical technique that preserves the entire papillary muscle and chordal apparatus. With this technique, the anterior mitral leaflet is split from the center of the free edge toward the annulus. Bilateral incisions are made from the proximal end of this split to the two mitral commissures, detaching the anterior leaflet from the annulus. These two halves of the leaflet, with all chordae intact (corresponding to the anterolateral and posteromedial papillary muscles), are judiciously trimmed to remove areas of leaflet untethered by chordae tendineae and (when necessary) fibrous thickening; then swung posteriorly and sutured to the posterior mitral annulus using mattress sutures with pledgets. This surgical technique is expected to favor the preservation of left ventricular function and avoid occurrence of irreversible left ventricular dilation/dysfunction, and has been used successfully for calcific and degenerative etiologies, using both tilting disc valves and porcine bioprostheses. It is especially useful in the implantation of tilting disc and bileaflet mechanical prostheses because anterior subvalvular chordae tissue may interfere with the disc excursion and relocated to the posterior leaflet annulus.

Technique of implantation of the Medtronic-Hall valve and other modern tilting-disc prostheses

Modern tilting-disc prostheses (Medtronic-Hall, Björk-Shiley Monostrut, and Omniscience) have distinctive mechanical characteristics, including wide-angle disc opening, that require special care about the implantation technique. Proper sizing, suturing, and orientation of the prosthesis are essential if problems of nonstructural valve dysfunction are to be avoided. A number of complications of this type, reported recently, appear to be related to a mismatch between the size of the disc and that of the cavities, whether ventricular or aortic. Based on an institutional experience of over 2,000 Medtronic-Hall valve replacements, described are the technical details of the implantation, centered on the sizing and orientation of the prostheses, including the technique of continuous suture used in mitral valve replacement.

Implantation techniques: a primary consideration in valve surgery

Clean site preparation for a prosthesis is mandatory to avoid tissue interference with the prosthesis. Oversizing of a prosthesis is fraught with peril. In all types of prostheses, orientation has importance. A prosthesis is designed with consideration for axial flow. Tilting the valve in implantation will likely result in a dysfunctional valve. The sewing ring serves not as a gasket but as an additional factor that increases the possibilities of success of a properly implanted valve by taking advantage of its naturally compliant features.