Paradoxical Embolism Parth B. Amin, Timothy F. Kresowik and Rachel Nicholson Paradoxical embolism describes an event in which embolic material originates in the venous system or right heart, passes through any right-to-left shunt, and ends in the arterial system. Although this sequence of events usually is thought to occur with venous thrombus migrating through a patent foramen ovale (PFO), any material (e.g., air, tumor, fat, foreign body) migrating through any right-to-left shunt (e.g., ventricular septal defect, pulmonary arteriovenous fistula, patent ductus arteriosus) is also correctly referred to as paradoxical embolism. Paradoxical embolization should be considered as part of the differential diagnosis in any patient who comes to the hospital with simultaneous pulmonary embolism or deep vein thrombosis (DVT) and acute ischemia in any arterial bed. Since the turn of the century, considerable attention has been placed on the role of PFO closure in treating and preventing cerebrovascular events. The widespread use of echocardiography, the relatively high incidence of PFO in the normal population, and financial interest has created a milieu in which enthusiasm in treating this entity continues. Case reports and case-control studies make up the bulk of published literature, although larger, well-designed studies have not shown any benefit to closing a PFO. Still, the mainstay of treatment is the same as for any embolic event and consists of evaluating the source, treating arterial bed ischemia, and instituting anticoagulation. Pathophysiology The pulmonary system develops late in fetal life and thus cannot accommodate all the blood returning to the right atrium. The normal embryologic compensation exists in the form of a right-to-left shunt. The two major pathways are from the right atrium to the left atrium through a PFO and from the pulmonary artery to the aorta through the ductus arteriosus. After birth, the left atrial pressure rises substantially from right-sided pressure, causing physiologic closure of a PFO. The ductus arteriosus also closes and leaves its remnant, the ligamentum arteriosum. Autopsy studies have demonstrated that a PFO persists in 25% to 30% of normal adults, with a decreasing incidence with age. Any pathologic condition leading to pulmonary hypertension or right heart failure could cause enough elevation in right atrial pressure to allow shunting of blood and thus the potential for embolization through a PFO. Pulmonary embolism can be the cause of elevated right heart pressures and is commonly present in reported cases of paradoxical embolism. In addition to pathologic states, echocardiographic studies have documented that transient right-to-left shunting can occur through a PFO in association with a Valsalva maneuver, with coughing, or even as a normal part of the cardiac cycle. Diagnosis Paradoxical embolization is part of the differential diagnosis of any patient who comes to the hospital with acute arterial ischemia suggesting an embolic etiology without a history that indicates a left heart or arterial source. Theoretically, the presence of DVT or pulmonary embolus, along with an arterial embolus, should increase the index of suspicion for a paradoxical embolus; evaluation for a right-to-left shunt may then be appropriate. The presence of an impending paradoxical embolus (IPDE), or an embolus visualized in both the right and left atria in transit through a PFO, is definitive in the diagnosis of paradoxical embolus. When IPDE is not seen, more common causes that can explain both arterial and venous thromboembolic phenomenon should be sought. Certainly, a hypercoagulable state, myocardial infarction, and cardiomyopathy all predispose patients to both DVT and arterial emboli. Nevertheless, imaging to evaluate for a right-to-left shunt is often performed as part of the workup for any arterial embolus. A transthoracic study is less sensitive and less invasive than a transesophageal study, but it can preclude the need for a transesophageal examination. Color Doppler studies can document shunting. In addition, echocardiographic contrast studies with microbubbles can be performed. Contrast is obtained by agitating saline or another intravenous solution between two syringes connected by a stopcock and then rapidly injecting the solution into a peripheral vein. The injected solution fills the right atrium with echo-reflecting microbubbles. Early appearance of the bubbles in the left atrium suggests a right-to-left communication. These studies can be combined with provocative maneuvers such as Valsalva or coughing to increase the sensitivity in detecting a PFO. Contrast transesophageal echocardiography studies with provocative maneuvers done in normal volunteers document an incidence of PFO similar to the autopsy incidence, suggesting a high sensitivity for this study. Similar microbubble studies have also been done with a transcranial Doppler to detect microbubbles entering the cerebral circulation after venous injection. The transcranial Doppler microbubble examination documents the presence of any right-to-left shunt, including noncardiac shunts such as pulmonary arteriovenous fistulas, but it cannot identify the location of the shunt. Transcranial Doppler assessment may be more sensitive for evaluating a right-to-left shunt than transthoracic echocardiography, but data are inconsistent when it is compared to transesophageal echocardiography. The preponderance of data points makes contrast evaluation in combination with color Doppler using transesophageal echocardiography the best test for diagnosing right-to-left shunt. The presence of positive echocardiography or the less often used transcranial Doppler yields a diagnostic dilemma, particularly in young patients with cerebrovascular events without predisposing risk factors. This group of patients with cryptogenic strokes has an estimated 15% to 50% incidence of PFO, although without any documented IPDE or venous embolic source. Attempts to evaluate PFO characteristics (size, location, hemodynamic parameters) and to stratify patients’ characteristics (age and sex) to achieve clinical relevance of these often incidental echocardiography findings has yielded conflicting results. Several authors have also indicated atrial septal aneurysm has a high correlation with symptomatic PFO. Although study continues, the small number of patients and lack of reproducible data warrant seeking IPDE or at least a concomitant venous thrombotic source before establishing a confirmed diagnosis of parodoxical embolus in the setting of a cerebrovascular event. Only gold members can continue reading. 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Paradoxical Embolism Parth B. Amin, Timothy F. Kresowik and Rachel Nicholson Paradoxical embolism describes an event in which embolic material originates in the venous system or right heart, passes through any right-to-left shunt, and ends in the arterial system. Although this sequence of events usually is thought to occur with venous thrombus migrating through a patent foramen ovale (PFO), any material (e.g., air, tumor, fat, foreign body) migrating through any right-to-left shunt (e.g., ventricular septal defect, pulmonary arteriovenous fistula, patent ductus arteriosus) is also correctly referred to as paradoxical embolism. Paradoxical embolization should be considered as part of the differential diagnosis in any patient who comes to the hospital with simultaneous pulmonary embolism or deep vein thrombosis (DVT) and acute ischemia in any arterial bed. Since the turn of the century, considerable attention has been placed on the role of PFO closure in treating and preventing cerebrovascular events. The widespread use of echocardiography, the relatively high incidence of PFO in the normal population, and financial interest has created a milieu in which enthusiasm in treating this entity continues. Case reports and case-control studies make up the bulk of published literature, although larger, well-designed studies have not shown any benefit to closing a PFO. Still, the mainstay of treatment is the same as for any embolic event and consists of evaluating the source, treating arterial bed ischemia, and instituting anticoagulation. Pathophysiology The pulmonary system develops late in fetal life and thus cannot accommodate all the blood returning to the right atrium. The normal embryologic compensation exists in the form of a right-to-left shunt. The two major pathways are from the right atrium to the left atrium through a PFO and from the pulmonary artery to the aorta through the ductus arteriosus. After birth, the left atrial pressure rises substantially from right-sided pressure, causing physiologic closure of a PFO. The ductus arteriosus also closes and leaves its remnant, the ligamentum arteriosum. Autopsy studies have demonstrated that a PFO persists in 25% to 30% of normal adults, with a decreasing incidence with age. Any pathologic condition leading to pulmonary hypertension or right heart failure could cause enough elevation in right atrial pressure to allow shunting of blood and thus the potential for embolization through a PFO. Pulmonary embolism can be the cause of elevated right heart pressures and is commonly present in reported cases of paradoxical embolism. In addition to pathologic states, echocardiographic studies have documented that transient right-to-left shunting can occur through a PFO in association with a Valsalva maneuver, with coughing, or even as a normal part of the cardiac cycle. Diagnosis Paradoxical embolization is part of the differential diagnosis of any patient who comes to the hospital with acute arterial ischemia suggesting an embolic etiology without a history that indicates a left heart or arterial source. Theoretically, the presence of DVT or pulmonary embolus, along with an arterial embolus, should increase the index of suspicion for a paradoxical embolus; evaluation for a right-to-left shunt may then be appropriate. The presence of an impending paradoxical embolus (IPDE), or an embolus visualized in both the right and left atria in transit through a PFO, is definitive in the diagnosis of paradoxical embolus. When IPDE is not seen, more common causes that can explain both arterial and venous thromboembolic phenomenon should be sought. Certainly, a hypercoagulable state, myocardial infarction, and cardiomyopathy all predispose patients to both DVT and arterial emboli. Nevertheless, imaging to evaluate for a right-to-left shunt is often performed as part of the workup for any arterial embolus. A transthoracic study is less sensitive and less invasive than a transesophageal study, but it can preclude the need for a transesophageal examination. Color Doppler studies can document shunting. In addition, echocardiographic contrast studies with microbubbles can be performed. Contrast is obtained by agitating saline or another intravenous solution between two syringes connected by a stopcock and then rapidly injecting the solution into a peripheral vein. The injected solution fills the right atrium with echo-reflecting microbubbles. Early appearance of the bubbles in the left atrium suggests a right-to-left communication. These studies can be combined with provocative maneuvers such as Valsalva or coughing to increase the sensitivity in detecting a PFO. Contrast transesophageal echocardiography studies with provocative maneuvers done in normal volunteers document an incidence of PFO similar to the autopsy incidence, suggesting a high sensitivity for this study. Similar microbubble studies have also been done with a transcranial Doppler to detect microbubbles entering the cerebral circulation after venous injection. The transcranial Doppler microbubble examination documents the presence of any right-to-left shunt, including noncardiac shunts such as pulmonary arteriovenous fistulas, but it cannot identify the location of the shunt. Transcranial Doppler assessment may be more sensitive for evaluating a right-to-left shunt than transthoracic echocardiography, but data are inconsistent when it is compared to transesophageal echocardiography. The preponderance of data points makes contrast evaluation in combination with color Doppler using transesophageal echocardiography the best test for diagnosing right-to-left shunt. The presence of positive echocardiography or the less often used transcranial Doppler yields a diagnostic dilemma, particularly in young patients with cerebrovascular events without predisposing risk factors. This group of patients with cryptogenic strokes has an estimated 15% to 50% incidence of PFO, although without any documented IPDE or venous embolic source. Attempts to evaluate PFO characteristics (size, location, hemodynamic parameters) and to stratify patients’ characteristics (age and sex) to achieve clinical relevance of these often incidental echocardiography findings has yielded conflicting results. Several authors have also indicated atrial septal aneurysm has a high correlation with symptomatic PFO. Although study continues, the small number of patients and lack of reproducible data warrant seeking IPDE or at least a concomitant venous thrombotic source before establishing a confirmed diagnosis of parodoxical embolus in the setting of a cerebrovascular event. Only gold members can continue reading. Log In or Register to continue Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related Related posts: Technical Aspects of Percutaneous Carotid Angioplasty and Stenting for Arteriosclerotic Disease In-Situ Treatment of Aortic Graft Infection with Prosthetic Grafts and Allografts Treatment of Dyslipidemia and Hypertriglyceridemia Intraoperative Assessment of the Technical Adequacy of Carotid Endarterectomy Stay updated, free articles. Join our Telegram channel Join
