TO THE EDITOR:
I refer to the article "Prevention of Deep-Vein Thrombosis after Total Hip Arthroplasty. Comparison of Warfarin and Dalteparin" (79-A: 1365—1372, Sept. 1997), by Francis et al.
When low-molecular-weight heparin or warfarin is administered prophylactically after total joint arthroplasty, the ultimate goal is to prevent a fatal pulmonary embolism. Our literature does not support the contention that a higher prevalence of thrombosis in the veins of the calf is associated with a higher prevalence of fatal pulmonary embolism among patients receiving prophylaxis. Thrombi continue to develop in a certain percentage of patients no matter what form of prophylaxis is used, but it appears that both warfarin and low-molecular-weight heparin effectively prevent fatal pulmonary embolism. The incidence of pulmonary embolism (fatal or non-fatal) was not mentioned in this article.
Also, since the incidence of fatal pulmonary emboli in patients who do not receive any prophylaxis at all is only in the range of 1 per cent, studies regarding prophylaxis need to contain thousands of patients before they become meaningful. Small studies such as this one are of very little help in our decision-making. I realize that deep-vein thrombosis and non-fatal pulmonary embolism have morbidities of their own, but those morbidities in-and-of themselves are probably not sufficient reasons to treat prophylactically.
Kenneth J. Hoek, M.D.: 236-B Hospital Drive, Ukiah, California 95482
Dr. Francis, Dr. Pellegrini, Dr. Totterman, Dr. Boyd, Dr. Marder, Ms. Liebert, Dr. Stulberg, Dr. Ayers, Dr. Rosenberg, Dr. Kessler, and Dr. Johanson reply:
We agree with Dr. Hoek that the prevention of fatal pulmonary embolism is an important goal of prophylaxis after total hip replacement. The size of our study was chosen to allow for the identification of a clinically important difference between the groups with regard to the prevalence of deep-vein thrombosis as diagnosed with use of venography at the time of discharge from the hospital. There were too few patients to expect any difference between the two groups with regard to the prevalence of fatal pulmonary embolism, and, fortunately, no such events occurred. A very large study would be required in order to use fatal pulmonary embolism as an end point for efficacy, considering that the rates in two recent large studies were 0 per cent (zero of 1024 patients3) and 0.1 per cent (one of 1162 patients4). However, we had good reasons for using venographically-defined deep-vein thrombosis as the end point in our study. First, venography is accurate and represents the so-called gold standard for diagnosis. Second, venous thromboembolic disease can be viewed as representing a continuous spectrum of increasing severity ranging from thrombosis in the veins of the calf and the proximal veins to non-fatal pulmonary embolism to fatal pulmonary embolism. Thrombosis in the proximal veins is the most frequent predecessor of pulmonary embolism, and patients who have thrombosis in the veins of the calf are also at risk1. The ability to prevent deep-vein thrombosis is, therefore, an indirect indicator of the ability to prevent pulmonary embolism. Third, deep-vein thrombosis and non-fatal pulmonary embolism cause morbidity by themselves and can lead to the later development of chronic venous insufficiency2. Prophylaxis against these complications is, therefore, clinically important.
Charles W. Francis, M.D.; Saara Totterman, M.D.; Allen D. Boyd, Jr., M.D.; Victor J. Marder, M.D.; Kristin M. Liebert, M.A.: Vascular Medicine Unit, P.O. Box 610 (C. W. F., V. J. M., and K. M. L.) and Departments of Radiology, P. O. Box 6944 (S. T.) and Orthopaedics, P.O. Box 665 (A. D. B., Jr.), University of Rochester Medical Center, 601 Elmwood Avenue, Rochester, New York 14642
Vincent D. Pellegrini, Jr., M.D.: Department of Orthopaedics and Rehabilitation, The Milton S. Hershey Medical Center, P.O. Box 850, Hershey, Pennsylvania 17033
Bernard N. Stulberg, M.D.: Cleveland Center for Joint Reconstruction, St. Vincent Charity Hospital, 2322 East 22nd Street, Suite 102, Cleveland, Ohio 44115
David C. Ayers, M.D.: Department of Orthopedic Surgery, State University of New York Health Science Center at Syracuse, 550 Harrison Center, Suite 100, Syracuse, New York 13202
Aaron Rosenberg, M.D.: Department of Orthopaedic Surgery, Rush-Presbyterian-St. Luke's Medical Center, 1725 West Harrison Street, Suite 1063, Chicago, Illinois 60612
Craig Kessler, M.D.: Lombardi Cancer Center, Georgetown University Medical Center, 3800 Reservoir Road, N.W., Washington, D.C. 20007
Norman A. Johanson, M.D.: Department of Orthopaedic Surgery, Temple University School of Medicine, 3401 North Broad Street, Philadelphia, Pennsylvania 191401