Ann Thorac Surg 2001;71:1187-1188
© 2001 The Society of Thoracic Surgeons
Invited commentary
Eric G. Butchart, FRCSa
a Department of Cardiothoracic Surgery, University Hospital, Cardiff, UK
According to Dr Li and colleagues, this article represents the largest number of Carbomedics aortic valves implanted in a single institution yet reported. However, the potential value of this study is somewhat diminished by methodologic deficiencies. First, data collection was entirely retrospective, with patients or their relatives being contacted by telephone only at the end of the study period. As the authors acknowledge, it has been shown that this method of data collection considerably underestimates the true number of adverse events, as one is relying on the memory of patients or (worse) their relatives over a long period of time. Second, in an article that concentrates heavily on thromboembolic performance, the lack of information on anticoagulation intensity is a serious omission. Neither the target range, nor the achieved international normalization ratio levels are stated, making it difficult to evaluate the thromboembolic and bleeding complications reported.
Thromboembolic rates in isolation are notoriously unreliable as a means of comparing one prosthesis with another, as they are heavily influenced by the prevalence of stroke risk factors in the patient population under investigation, by antithrombotic management, and by the method of data collection. Valve thrombosis rates give a better, although less than perfect, indication of the thrombogenicity of a prosthesis, but are still influenced by anticoagulation management and methods of data collection, for example, the percentage of patients with heart failure subjected to echocardiography and the percentage of patients dying of heart failure who received autopsies. It is acknowledged that the mitral position is a much more challenging test of prosthesis thrombogenicity. For example, the Medtronic Parallel bileaflet valve, which was withdrawn from the market before the completion of clinical trials, had acceptable performance after aortic valve replacement but a very high incidence of valve thrombosis after mitral valve replacement. Other series of Carbomedics valves have reported higher rates of valve thrombosis in mitrals than aortics. From the present article, one can conclude that the Carbomedics valve appears to have satisfactory performance in the aortic position, given the reservations about data collection, but it would have been more interesting to know how it performed in the mitral position, as that would have given a much better indication of its thrombogenicity. The ideal level of anticoagulation for the Carbomedics valve remains to be determined by prospective studies comparing dif-ferent international normalization ratio ranges. As the Medtronic Parallel valve experience has demonstrated, all bileaflet designs are not of equal thrombogenicity and it is insufficient to assume that an international normalization ratio range that gives satisfactory long-term results with a bileaflet valve of one design will achieve the same outcome with other bileaflet valves of different design.
