On 169 occasions anticoagulant therapy for thromboembolic disease was stopped electively and patients were followed for 16 subsequent weeks. The records of those who remained well and those who suffered a relapse were compared in an attempt to identify factors that might affect liability to thromboembolic relapse.
During the follow-up period there were 37 thromboembolic recurrences, an incidence of 22 per cent. None occurred among the patients in whom the original diagnosis of thromboembolic disease was discarded or when a predisposing cause had ceased to be present. There was an inverse relation between liability to relapse and degree of prothrombin time prolongation.
No significant relation could be shown between liability to relapse and any of the following: sex and age; type and severity of the initiating thromboembolic episode; history of earlier thromboembolic disease or relapse after stopping earlier anticoagulant courses; presence of hypertension, hypercholesterolaemia, or diabetes mellitus; type of anticoagulant drug used, duration of therapy, and method of stopping treatment.
Patients with overt occlusive arterial disease at more than one site had a significantly increased liability to relapse when compared with patients with symptomatic disease at a single site. In the group of 134 subjects receiving anticoagulant therapy for coronary arterial disease, occurrence of a thromboembolic episode during the course of treatment and the presence of angina of effort in the months before it was discontinued were both associated with a significant increase in liability to relapse. It is suggested that, ideally, anticoagulant therapy should be continued indefinitely in any patient whose pattern of disease thus increases the likelihood of a thromboembolic recurrence.