What does a positive saline contrast echocardiogram (Echo) of the left atrium indicate in a stroke workup?

From the Guidelines

A positive saline echo test in the left atrium during a stroke workup indicates the presence of a right-to-left cardiac shunt, most commonly a patent foramen ovale (PFO), which can be a potential cause of cryptogenic stroke. This test involves injecting agitated saline (a mixture of saline and air) into a peripheral vein while performing an echocardiogram. Normally, the microbubbles in the saline would be filtered by the lungs, but if bubbles appear in the left atrium within 3-5 cardiac cycles after right atrial opacification, it suggests a direct pathway between the right and left sides of the heart 1.

Significance in Stroke Evaluation

This finding is significant in stroke evaluation because it can explain cryptogenic strokes (strokes with no identifiable cause) through paradoxical embolism, where a blood clot passes from the venous system through the shunt into the arterial circulation and reaches the brain. The sensitivity of saline contrast for detection of a PFO is increased by asking the patient to perform a Valsalva manoeuvre, which transiently increases right atrial pressure 1.

Management Options

Management options for patients with PFO-related strokes typically include antiplatelet therapy (aspirin 81-325 mg daily or clopidogrel 75 mg daily) or consideration of PFO closure in selected patients, particularly those under 60 years with cryptogenic stroke and high-risk PFO features 1. The decision between medical therapy and closure should be individualized based on patient characteristics, stroke recurrence risk, and other risk factors. Not all PFOs require treatment, as they are present in approximately 25% of the general population, but their discovery during stroke workup warrants careful evaluation of their potential causative role.

Diagnostic Evaluation

According to the 2021 guideline for the prevention of stroke in patients with stroke and transient ischemic attack, echocardiography with or without contrast is reasonable to evaluate for possible cardiac sources of or transcardiac pathways for cerebral embolism in patients with cryptogenic stroke 1. Transesophageal echocardiography (TEE) can provide more detailed visualization of the atrial septal anatomy when PFO closure is planned 1.

Right-to-Left Shunting Detection

TCD (transcranial Doppler) with embolus detection might be reasonable to screen for right-to-left shunt in patients with ischemic stroke or TIA in whom patent foramen ovale (PFO) closure would be contemplated 1. A pooled analysis of the OXVASC (Oxford Vascular Study) data found an association between right-to-left shunting and cryptogenic TIA or nondisabling stroke 1.

Conclusion is not allowed, so the response ends here.

From the Research

Left Atrium Positive Saline Echo Test

The left atrium positive saline Echo test is used to detect the presence of a right-to-left shunt, which can be a cause of stroke.

• A right-to-left shunt occurs when blood flows from the right side of the heart to the left side, bypassing the lungs and potentially carrying clots or other debris to the brain, leading to a stroke.
• The saline Echo test, also known as a bubble study, involves injecting saline solution into a vein while performing an echocardiogram to visualize the flow of blood through the heart 2.
• If the saline solution appears in the left side of the heart, it indicates a right-to-left shunt, which can be caused by a patent foramen ovale (PFO) or other cardiac anomalies.

Patent Foramen Ovale (PFO)

A PFO is a hole in the wall between the upper chambers of the heart, which can allow blood to flow from the right side to the left side.

• Studies have shown that PFO is a common cause of cryptogenic stroke, which is a stroke with no known cause 3, 4.
• The presence of a PFO can increase the risk of paradoxical embolism, which occurs when a clot forms in the veins and travels to the brain through the PFO 5, 6.

Diagnosis and Treatment

The diagnosis of a PFO and right-to-left shunt is typically made using a combination of echocardiography, transesophageal echocardiography, and saline contrast transthoracic echocardiography 2.

• Treatment for PFO and right-to-left shunt may involve transcatheter closure of the PFO, which has been shown to be effective in preventing recurrent stroke in certain patient populations 3, 4, 2.
• The decision to close a PFO should be based on the severity of the right-to-left shunt and the presence of other risk factors for stroke 2, 6.