Rebound Phenomena after Anticoagulant Therapy

T HE occurrence of inyocardial inifaretion and embolic incidents in patients with ischemic heart disease after cessation of anticoagulant therapy is well recognized.1-6 Likewise, the recurrence of intermittent ischemic attacks in the carotid and vertebro-basilar territory when anticoagulant treatment has been stopped has been described.7 These experiences have led to the suggestion that following the cessation of anticoagulant therapy there is a "rebound phenomenon" during which further clinical ineidents are more likely to occur. Ascertaining whether such a phenomenon exists meets with two difficulties. The first is that if anticoagulant therapy is effectively suppressing a continuing tendency to thromboembolism, stopping therapy allows the tendency to reassert itself; hence there is likely to be a recurrence of clinical incidents. It has indeed been snggested that the "rebound phenomenon " is simply "'a return to the status quo ante" and not a rebound in the usual sense.8 But others have envisaged "a rebound hypercoagulable state, " at least when therapy is stopped because of hemorrhage.9 Evidence for a state of hypercoagulability following cessation of heparin therapy in dogs has been found,10 but attempts to find hematologic evidence of a similar state in man have not yet been successful.1 The second difficulty is that atherosclerosis is a progressive condition, hence the disease must of necessity be more advanced after a period of therapy that is suppressive and not curative, than it was before. An apparent increase in thrombo-embolic incidents after cessation of anticoagulant therapy might well be due to the more advanced stage of the disease.