Choosing a prosthetic heart valve

Cost-Effectiveness of the Combined Use of Warfarin and Low-Dose Aspirin versus Warfarin Alone in Egyptian Patients with Aortic Valve Replacements: A Markov Model

BACKGROUND

The combination of antiplatelet and anticoagulant therapy significantly reduces the rate of thromboembolic events in patients with heart valves compared with anticoagulant therapy alone. Cost-effectiveness of this therapy in Egypt, however, has not yet been established.

OBJECTIVE

The aim of the present study was to evaluate the cost-effectiveness of the combined use of warfarin and low-dose aspirin (100 mg) versus warfarin alone in patients with mechanical aortic heart valve prostheses who began therapy at the age of 50 to 60 years over a 5-year period from the perspective of the medical providers.

METHODS

A cohort Markov process model with five health states (recovery, reoperation, bleeding, thromboembolism, and death) based on Egyptian clinical practice was derived from published sources. The clinical parameters were derived from meta-analyses of randomized controlled trials of patients with mechanical valve prostheses. The quality of life of the health states was derived using the available published data. Direct medical costs were obtained from four top-rated governmental cardiology hospitals in Egypt. All costs and effects were discounted at 3.5% annually. All costs were converted using the purchasing power parity rate and are reported in US $ for the financial year of 2013.

RESULTS

The total quality-adjusted life-years (QALYs) were estimated to be 1.1616 and 1.1199 for the warfarin plus aspirin group and the warfarin group, respectively, which resulted in a difference of 0.0416 QALYs. The total costs for the warfarin plus aspirin group and the warfarin group were US $307.33 and US $315.25, respectively (the difference was US $7.92), which yielded an incremental cost-effectiveness ratio of -190.38 for the warfarin plus aspirin group. Thus, the combined therapy was dominant. Various one-way sensitivity analyses indicated that probabilities of reoperation and bleeding in the recovery state had the greatest effects on incremental costs. The model parameters that had the greatest effects on incremental QALYs were the relative risk reduction of death and the utility value in the recovery state.

CONCLUSIONS

The present study is the first cost-utility analysis to conclude that, from the perspective of Egyptian medical providers, combined therapy is more effective and less costly than warfarin alone for patients with mechanical aortic valve prostheses. For clinicians and patients who choose to focus on minimizing thromboembolic risk, these results suggest that combined therapy offers the best protection. This study helps to inform decisions about the allocation of health care system resources and to achieve better health in the Egyptian population.

Aortic Root Compliance Influences Hemolysis in Mechanical Heart Valve Prostheses: An In-Vitro Study

Mechanical heart valve prostheses are known to activate coagulation and cause hemolysis. Both are particularly dependent on the leaflet dynamics, which in turn depends on the flow field in the aortic root influenced by the aortic root geometry and its compliance. Compliance reduction of large vessels occurs in aging patients, both in those who have atherosclerotic diseases and those who do not. In this study we investigated the correlation between hemolysis and the compliance of the proximal aorta in a novel, pulsatile in vitro blood tester using porcine blood. Two mechanical heart valves, the St Jude Medical (SJM) bileaflet valve and a trileaflet valve prototype (Triflo) were tested for hemolysis under physiological conditions (120/80 mm Hg, 4.5 l/min, 70 bpm) and using two different tester setups: with a stiff aorta and with a compliant aorta. Valve dynamics were subsequently analyzed via high-speed videos. In the tests with the Triflo valve, the free plasma hemoglobin increased by 13.4 mg/dl for the flexible and by 19.3 mg/dl for the stiff setup during the 3-hour test. The FFT spectra and closing speed showed slight differences for both setups. Free plasma hemoglobin for the SJM valve was up by 22.2 mg/dl in the flexible and 42.7 mg/dl in the stiff setup. Cavitation induced by the higher closing speed might be responsible for this, which is also indicated by the sound spectrum elevation above 16 kHz.

Newer concepts in the surgical treatment of valvular heart disease

The search for the ideal therapy for valve replacement continues. The major options include mechanical or tissue valves, with an increasing variety of tissue valves becoming available. The key factor continues to be thrombogenicity versus durability. Aortic valve surgery primarily consists of replacement. This is aided by the increased variety of options allowing tailoring of the procedure to the patient's native valve disease. Mitral valve surgery has greater potential for repair, which affords preservation of the native valve, optimizing function and reducing long-term complications. An increasingly popular concept is treatment of secondary or functional mitral valve regurgitation in the setting of depressed left ventricular function. The routine use of intraoperative transesophageal echocardiography and a trend toward the use of minimally invasive procedures are altering the conduct of valve operations.

Prosthetic valve type for patients undergoing aortic valve replacement: a decision analysis

BACKGROUND

In two large, randomized, clinical trials long-term survival after aortic valve replacement (AVR) was similar for patients receiving tissue and mechanical aortic heart valve prostheses. Higher bleeding rates among patients with mechanical valves, who must receive permanent oral anticoagulation to prevent thromboembolism, were offset by higher reoperation rates for valve degeneration among patients with tissue valves. Because the average age of patients undergoing AVR and clinical practices have changed considerably since the randomized clinical trials were conducted, we performed a decision analysis to reassess the optimal valve type for patients undergoing AVR.

METHODS

We used a Markov state-transition model to simulate the occurrence of valve-related events and life expectancy for patients undergoing AVR. Probabilities of clinical events and mortality were derived from the randomized clinical trials and large follow-up studies.

RESULTS

Although the two valve types were associated with similar life expectancy in 60-year-old patients (mean age of patients in the randomized clinical trials), tissue valves were associated with greater life expectancy than mechanical valves (10.7 versus 11.1 years) in 70-year-old patients (currently mean age of AVR patients). For 70-year-old patients, the effects of major bleeding complications (24%) with mechanical valves substantially outweighed those of reoperation for valve failure (12%) with tissue valves at 12 years. Of the clinical practice changes assessed, the recommended valve type was most sensitive to changes in bleeding rates with anticoagulation. However, bleeding rates would have to be 68% lower than those reported in the European randomized clinical trial to affect the recommended valve type for 70-year-old patients. Reoperation rates would have to be five times higher, and mortality rates at reoperation would have to be four times higher to affect the recommended valve type for 70-year-old patients.

CONCLUSIONS

Although mechanical valves are preferred for AVR patients less than 60 years old, most patients currently undergoing AVR are elderly and would benefit more from tissue valves.

New developments in the treatment of infective endocarditis infective cardiovasculitis

The natural history of infective endocarditis has undergone remarkable changes over the past 100 years as regards both the demographic characteristics of the disease and changes in the incidence of the so-called diagnostic signs. Alongside these changes and the development of new and better diagnostic tools and criteria, we are also facing new problems with the precise definition of cardiovascular infections and calculation of the incidence of the disease. Nosocomial endocarditis presents an emerging problem of diagnosis and treatment after heart valve surgery, with pace-maker catheters, defibrillators and a very large variety of foreign materials used in connection with heart valve surgery. New technological progress including new types of prosthetic valves and use of homografts or the Ross operation will give a greater possibility of choosing the best solution in a particular case. Antimicrobial chemotherapy is mainly based on our understanding of the pathophysiology of the disease and efficacy of the antibiotics achieved in an experimental animal model of endocarditis. Important recommendations of single or combined drug therapy or the dosing regimens of antibiotics are still an expression of expert opinion not always supported by experimental or clinical proof. A typical example is the recommendation of two divided doses of gentamicin for treatment of streptococcal endocarditis. Nevertheless, it is the author's opinion that the development of uncomplicated, easy to handle diagnostic and treatment regimens are justified in order to achieve better compliance with these recommendations.