Elevation of plasma beta-thromboglobulin in patients with prosthetic cardiac valves

Modern management of prosthetic valve anticoagulation

Prosthetic heart valves have been effectively used for many years. Nonetheless, they are associated with risks of thrombosis and thromboembolic events, as well as anticoagulation-induced bleeding. Substantial changes in anticoagulation measurement and dosing have occurred during the past several years. In this review, the rationale for anticoagulation in patients with prosthetic heart valves, the changes in monitoring and dosing, and the comparison of relevant anticoagulation trials are discussed. On the basis of the existing data, new recommendations regarding lower anticoagulation levels are offered, utilizing a single value goal rather than the traditional therapeutic range. Perioperative management of anticoagulation is discussed in light of the available literature, and major drug interactions are reviewed.

Cardiac valve prostheses: pathological and bioengineering considerations

Cardiac valve replacement with mechanical prosthetic or bioprosthetic devices enhances patient survival and quality of life. Nevertheless, prosthesis-associated complications are frequent and contribute significantly to outcome. Thromboembolic complications are the most important problems in patients with mechanical valves, necessitating chronic anticoagulation in all patients receiving them. In contrast, patients with bioprosthetic valves, composed of chemically treated animal tissues, generally do not require anticoagulants. However, bioprostheses fail frequently by degeneration, especially that involving cuspal calcification. This paper reviews the pathological and bioengineering considerations in the selection of cardiac prosthetic valves and the management of patients who have received these devices. The significance, morphology, and pathogenesis of the observed major complications and other alterations during function are described in detail. Contemporary investigative trends are summarized, including studies of inhibition of mineralization and other degenerative changes in bioprostheses, improved design rigid mechanical valves with pyrolytic carbon occluders and the development of central-flow, flexible polymeric leaflet valves.

Are platelet factor 4 and beta-thromboglobulin markers of cardiovascular disorders?

Beta-thromboglobulin and platelet factor 4 are the two best characterized platelet-specific proteins. They are stored in the platelet alpha-granules and released during platelet activation. Their physiological function is unknown. PF4 has high anti-heparin activity, whilst beta-TG does not. Certain factors can affect the plasma level of one or both of these two proteins and these must be borne in mind whenever the evaluation of beta-TG and PF4 are thought to represent true in vivo platelet activation: their artificial release due to sample collection and processing, the in vivo release of PF4 induced by heparin, and the elevation of beta-TG due to renal failure. What really represents an abnormal level of beta-TG and PF4 is unknown, since we do not know their pathophysiology. At present, however, the platelet-specific proteins, even if they are considered as 'markers' of platelet activation, do not necessarily reflect the severity of the cardiovascular disorders nor do they signal thrombus formation, as thrombosis is a consequence of several interacting factors.

Platelet alpha granule depletion: findings in patients with prosthetic heart valves and following cardiopulmonary bypass surgery

The alpha granule content of platelets, as indicated by the amount of beta-thromboglobulin (beta-TG) in lysed platelet rich plasma was measured to determine whether platelet stimulation resulted in a circulating population of granule-depleted platelets. In 101 normal controls, with a mean platelet count of 242.6 +/- 6.5 X 10(9)/1, the mean platelet beta-TG content was 55.9 +/- 1.2 ng/10(6) platelets. There was a significant reduction in both these parameters (mean platelet count 195.5 +/- 5.8 X 10(9)/1 (P less than 0.001), mean platelet beta-TG 50.0 +/- 1.2 ng/10(6) platelets (P less than 0.01)) in 74 patients with prosthetic cardiac valves. In 24 patients, cardiopulmonary bypass surgery caused a much greater reduction in median platelet count from 210 X 10(9)/1 to 11.1 X 10(9)/1, two hours after surgery (P less than 0.001) but no overall change in platelet beta-TG. However, five patients who experienced diffuse haemorrhage in the postoperative period had a lower median platelet beta-TG (35.5 ng/10(6) platelets) than the other 19 patients (51.0 ng/10(6) platelets) (P less than 0.05).

Bioengineering aspects of heart valve replacement

Biomedical engineering inputs have been important in the design, development and testing of substitute heart valves as well as in the pre- and post-operative management of patients with cardiac valve disease. This paper is a review of heart valve replacement whose goal is the enhancement of future bioengineering contributions. We review the approach to the patient with valvular heart disease, and the sources of early and late postoperative pathology with emphasis on complications of the prostheses used. Major significant problem areas relate to the noninvasive evaluation of cardiovascular function (both before and after surgery), device design, hemodynamics, and the need for thromboresistant and durable materials.