Paradoxical embolism and acute arterial occlusion: rare or unsuspected?

The high prevalence of clinically silent venous thrombosis and the presence of a patent foramen ovale (PFO) in up to 35% of the general population suggests that paradoxical emboli may be the cause of an ischemic stroke or a peripheral thromboembolic occlusion more often than is presently considered. This study was undertaken to review our experience with presumed paradoxical embolism.

Hospital records were reviewed for all patients diagnosed with both a documented PFO and a thromboembolic event between January 1970 and June 1993. Patients with a ventricular or an atrial septal defect or a probable pulmonary arteriovenous fistula were excluded.

The presumptive diagnosis of paradoxical embolism was made in seven patients. There were five men and two women, with a median age of 43 years. Four patients were admitted with an acute cerebral ischemic event, and in three others hospitalization was prompted by the development of an acutely ischemic limb (two upper extremity; one lower extremity). In none was there evidence of angiographically significant peripheral or extracranial atherosclerotic occlusive disease. Symptoms suggestive of pulmonary emboli were noted in two patients, and in only one patient was there evidence on physical examination of a deep venous thrombosis. Before 1988 the diagnosis of paradoxical embolism had been made in only one patient after postmortem examination. All six patients who were discharged were available for follow-up (mean 20 months; range 6 to 60 months). There was one late death from lung cancer. Recurrent paradoxical emboli have not been documented during the follow-up period.

The incidence of presumed paradoxical embolism has increased dramatically in the recent past as a consequence of our improved ability to unequivocally detect PFO with associated physiologic shunting. The suspicion of this heretofore "rare" event should be raised, particularly in the young or middle-aged adult diagnosed with an acute thromboembolic event. Until the risk of recurrent ischemic events in the presence of a PFO is better defined, we currently recommend closure of the foramen ovale after a significant or recurrent paradoxical embolus. Otherwise, the selective use of intracaval filters, antiplatelet therapy, and oral anticoagulation remain undefined.