Anticoagulants and the Björk-Shiley prosthesis.

Sir, We read this paper with great interest (British Heart Journal, 1978, 40, 558-562). Long-term anticoagulation is associated with the risk of bleeding and to an extent enforces restriction on the quality of life of the patient (British Medical Journal, 1978). In addition there is a risk, though small, of thrombosis in spite of adequate anticoagulation. In view of this we feel that it is important to look for alternatives to long-term oral anticoagulants. However, there are several important points in your study that require careful consideration before drawing any conclusions. Dipyridamole has been started on day 3; it is well documented that platelets become 'stickier' in the immediate postoperative period, and by day 3 platelets may have already become attached to the valves. In the absence of anticoagulation the platelet plugs may be stabilised by thrombin generation and clot formation. We have shown that dipyridamole when used clinically has to attain an optimum blood level of 3.5 sumol/l (range 2 to 5 V±mol/l) to produce an adequate antiplatelet effect (Rajah et al., 1977). There is no indication in the study that any blood level or platelet functions had been done on any of the patients in the dipyridamole group before discharge from hospital. It has been our experience that on a dose of 150 mg daily most patients did not attain optimum blood levels and platelet functions were not inhibited. This implies that in your study most of the patients in the dipyridamole group were in no way protected after valve replacement. Before embarking on the use of antiplatelet drugs alone in this clinical situation we feel that it is necessary to extend the findings of Sullivan et al. (1971). Here it was clearly shown that the dipyridamole and warfarin group combined was superior to warfarin alone, but the limitation of that trial was that a number of patients dropped out of the trial because of the side-effects of dipyridamole. We have been conducting a similar trial to that of Sullivan et al. for the past 4 years; the dose of dipyridamole is determined by its blood level and/or platelet functions routinely. We confirm the superiority of dipyridamole and warfarin over warfarin in patients with the Starr-Edwards, BjorkShiley, and Lillehei-Kaster valves, and in addition the drop-out of patients because of the side-effects of dipyridamole is negligible. If dipyridamole alone is to be used in a trial, we we suggest starting it before operation, giving it intravenously in the immediate postoperative period, and orally when the patient can swallow. It may be relevant to point out that dipyridamole has been shown not to prolong bleeding time and hence increase the risk of bleeding; however, intravenous dipyridamole is to be used with caution in patients with hypotension. We also suggest that the dosage be titrated against either blood level or platelets function or both. Further, it may be more reasonable to consider a combination of platelet inhibitory drugs like dipyridamole and acetyl salicylic acid, than a single agent in the prophylaxis of arterial thrombosis especially with disc valve prosthesis in the mitral position. S. M. Rajah, Suba Rao, and D. A. Watson, Leeds Area Health Authority (Teaching), Eastern District, Leeds Regional Thoracic Surgical Centre, Killingbeck Hospital, Leeds.