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A pregnant patient with bilateral ischaemic limbs

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Q1: What is the diagnosis?

The patient has paradoxical embolism and patent foramen ovale.

Q2: Describe the pathogenesis of this clinical condition?

A favourable right to left pressure gradient, secondary to raised right atrial pressure (RAP), must exist to promote shunting of venous thrombi through the intracardiac defect. Pulmonary thromboembolism is the most common cause of acute elevation of RAP. Occlusion of left pulmonary artery causes a rise in mean pulmonary arterial pressures with a simultaneous fall in systemic arterial pressure. Favourable pressure gradient only exists when at least one third of the pulmonary arterial tree is occluded or when the mean pulmonary arterial for right to left shunting at least 30 mm Hg.1

Q3: How should the diagnosis be made?

Four criteria have to be met for diagnosis: (1) deep vein thrombosis and/or pulmonary thromboembolism, (2) an abnormal communication between the venous systemic circulation, (3) clinical, angiographic, and pathological evidence for systemic embolism, and (4) pressure gradient allowing right to left shunting at some point in the cardiac cycle.1 Clinically, the diagnosis of paradoxical embolism is presumptive, relying on circumstantial evidence as well as a high index of suspicion. Premorbid diagnosis of patent foramen ovale is usually made by transthoracic or transoesophageal colour Doppler echocardiography (TTE or TOE). Studies as well as our case confirm the superiority of TOE over TTE in detecting patent foramen ovale.1 2 For the diagnosis, Chen et al reported that TOE had a sensitivity of 100% and a specificity of 97%, while they were 63% and 78% respectively for TTE.2

In this case, postoperative TOE revealed a large atrial septal defect with a free left to right flow and thrombus in the right middle pulmonary artery.

Q4: Describe the most recent development in the diagnosis of this condition?

It was suggested that contrast echocardiography is a useful and probably more effective manoeuvre to exclude patent foramen ovale.1 It involves high pressure injection into the venous circulation of a saline solution containing microbubbles in suspension. A valsalva manoeuvre can increase the sensitivity of the contrast study. However, it was also reported that the cough test is superior to the valsalva manoeuvre in the contrast study.

Recently, contrast transcranial Doppler (TCD) was shown to have a sensitivity and specificity of 100% in comparison with contrast TOE.1 Therefore, contrast TCD can be an alternative method for detection of right to left shunting.

Q5: What is the treatment?

Our patient was started on intravenous heparin infusion. She was taken to theatre for an emergency caesarean section and bilateral femoral embolectomies. The baby was delivered uneventfully. Anticoagulation was continued postoperatively and the mother made an uncomplicated recovery. It is planned to close the atrial septal defect in the near future.

As part of acute management,3 most authors agree that immediate anticoagulation should be started in the absence of any contradiction. Thrombolysis or embolectomy is indicated to treat peripheral embolism which threatens limb viability. In suspected cases of paradoxical embolism, thrombolysis is indicated in the presence of both pulmonary thromboembolism and acute cor pulmonale.

Thrombolysis can reduce RAP and minimise recurrence of paradoxical embolism.1 As for the patient who is haemodynamically compromised, pulmonary embolectomy should be performed if indicated and feasible. Rarely, impending paradoxical embolism is best managed with intracardiac embolectomy and closure of patent foramen ovale.1

Current long term therapeutic options are: (1) long term anticoagulation therapy, (2) long term antithrombotic therapy, (3) surgical closure of patent foramen ovale either open heart surgery or transcatheter placement of the double umbrella device, or (4) inferior vena cava (Greenfield) filter. Until now, there has been little information regarding the long term outcome of any particular treatment modality.1

Discussion

For venous thromboses to travel into the systemic circulation the clot has to bypass the pulmonary bed by passage through an abnormal communication. This may be a fixed atrial septal defect or a patent foramen ovale which allows right to left shunting when the right atrial pressure RAP is raised by a pulmonary thromboembolism.1 It was first diagnosed in 1877 by Cohnheim,4 and although cases are not infrequently reported, it was rarely described in pregnancy.5

Aburahma reported that 56% of cases of emboli had probable or possible paradoxical embolism,3 while Caplan et al reported that 36% of embolic strokes had an unidentifiable cardiac source.6 Importantly, Lechatet al showed that patent foramen ovale was found in 40% of patients with unexplained embolic stroke compared with 10% in a control group.7 Patent foramen ovale occurs in 11% to 35% of the normal population and grows larger with age.8

In our case, the clinical features were strongly suggestive of a large pulmonary thromboembolism in association with acute peripheral arterial ischaemia, giving a strong suspicion of the diagnosis of paradoxical embolism. It is interesting that the TTE did not suggest paradoxical embolism but the postoperative TOE did show the atrial septal defect and clot in the pulmonary artery. This is in keeping with studies which have shown the superiority of TOE against TTE in detecting patent foramen ovale.2

Learning points

  • Prevalence of paradoxical embolism as the cause of peripheral or cerebral embolic events has been under-estimated

  • There is right to left shunting through atrial septal defect or patent ductus arteriosus when right atrial pressure is elevated by pulmonary thromboembolism

  • Transoesophageal echocardiogram is superior to transthoracic echocardiogram in detecting patent foramen ovale

  • Angiography is safe in the third trimester and magnetic resonance arteriography is less invasive

  • Thrombolysis reduces right atrial pressure and prevents recurrence of patent ductus arteriosus

  • In pregnancy, surgical embolectomy is a safer option

  • Acute management requires a high index of suspicion, early diagnosis, and timely intervention with a multidisciplinary approach

The contrast echocardiogram, especially with the valsalva manoeuvre and cough test, is useful for excluding patent foramen ovale.1Contrast transcranial Doppler can be an alternative method for detection of right to left shunting. We showed the extent of the peripheral clot in our patient by angiography, which is safe for the fetus in the third trimester, but we had considered magnetic resonance angiography, which is less invasive and also safe in pregnancy.9

Normally, management of patients with paradoxical embolism would be determined by the need to re-establish peripheral flow, if possible; to prevent further arterial embolisation; and to reduce the haemodynamic threat from the pulmonary embolus. This may require that, in addition to immediate anticoagulation, both venous and peripheral thrombolysis should be considered. We felt that thrombolysis, which has been advocated to reduce RAP and minimise recurrence of paradoxical embolism, would threaten the pregnancy,10 and that surgical embolectomy and caesarean delivery would offer the safest solution. Placement of an inferior vena cava filter before section to prevent further pulmonary emboli was considered but as the pelvic veins were patent on ultrasound, it was considered unnecessary. After successful delivery, the TOE confirmed atrial septal defect and the patient is awaiting surgical closure at present. The complexity of this case—which requires specialist obstetric, imaging, surgical, intensive care, and anaesthetic expertise—could be used as an argument for locating obstetric units within general hospital centres.

It is interesting to speculate about the outcome if the peripheral embolus had lodged in the right internal iliac as well as the left. The uterine artery supplying the placenta would have been occluded with a probable intrauterine death. Fortunately, however, this was not the case and both the mother and baby have done well.

The high prevalence of clinically occult deep vein thrombosis and the presence of patent foramen ovale in up to 35% of the population highlights the fact that paradoxical embolism may be the cause of a peripheral or cerebral embolic event more often than is currently suggested.

The key points of management are the need for high index of suspicion, early diagnosis, and timely intervention with a multidisciplinary approach. The long term treatment of paradoxical embolism is less well defined. More studies are needed to assess the risk of recurrent arterial ischaemic events in the presence of patent foramen ovale as well as to examine the long term outcome of the respective treatment strategies.

Final diagnosis

Paradoxical embolism and patent foramen ovale.

References

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