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Robot-Assisted Transcranial Doppler Versus Transthoracic Echocardiography for Right to Left Shunt Detection

October 13, 2023

A prospective clinical trial compared two methods, robot-assisted transcranial Doppler (raTCD) and transthoracic echocardiography (TTE), to see which one is better at diagnosing right-to-left shunt (RLS), a risk factor for stroke especially in young patients.

The study found that raTCD was three times more likely to diagnose RLS than TTE, with a higher sensitivity, especially for large shunts. RaTCD was deemed safe and could be performed by health professionals without extensive TCD training, potentially making it a superior screening method for RLS compared to TTE.

As a result, raTCD should become part of the cryptogenic stroke workup.

Read The Full Study Here

What is a cryptogenic stroke?

A “cryptogenic stroke” is a term used to describe a stroke that doesn’t have a clear cause after initial testing and evaluation. In other words, doctors have tried to figure out why the stroke happened but haven’t identified a definite reason.

The “workup” for a cryptogenic stroke involves a series of tests and evaluations to try to find the cause. The goal is to identify any underlying conditions or risks so that targeted treatments can be applied to prevent another stroke in the future.

The workup can include a range of tests such as:

  • Imaging: This might include MRI or CT scans of the brain to get detailed pictures of the areas affected by the stroke.
  • Heart Monitoring: Devices like Holter monitors or event recorders might be used to monitor heart rhythms over a period of time. This can help identify irregular heart rhythms, like atrial fibrillation, which can lead to strokes.
  • Blood Tests: These can help identify clotting disorders or other blood conditions that might increase stroke risk.
  • Ultrasounds: These might be done of the heart (echocardiography) or of the blood vessels in the neck (carotid ultrasound) to look for potential sources of clots that could cause a stroke.
  • Cerebral Angiography: This is a more invasive test where a dye is injected into the blood vessels of the brain to look for any abnormalities.
  • Other Tests: Depending on the patient’s situation, other tests might be conducted to look for less common causes.

Once all these tests are done, if a clear cause is still not found, the stroke remains classified as “cryptogenic.” However, even if a specific cause isn’t identified, treatment to reduce the risk of another stroke, such as blood thinners or blood pressure medications, may still be recommended.

What is a robot-assisted transcranial Doppler (raTCD)

Transcranial Doppler (TCD) is a non-invasive ultrasound method used to measure the flow velocity of cerebral blood vessels. It helps in assessing various neurological conditions, like detecting emboli, vasospasm after a subarachnoid hemorrhage, and assessing blood flow in conditions like sickle cell disease.

Robotically assisted TCD system provides an alternative to manual TCD for assessment, expanding the availability of TCD to settings in which specialized clinicians are not available.

What is right-to-left shunt (RLS)?

A right-to-left shunt (RLS) refers to a condition where blood moves directly from the right side to the left side of the heart, bypassing the lungs. This can result in deoxygenated blood (blood that hasn’t been enriched with oxygen from the lungs) being pumped out to the body, which can lead to a variety of health issues.

There are a few different ways that a right-to-left shunt can happen:

  • Congenital Heart Defects: These are structural problems with the heart that are present at birth. Examples include:
    • Atrial Septal Defect (ASD): A hole in the wall between the two upper chambers of the heart.
    • Ventricular Septal Defect (VSD): A hole in the wall between the two lower chambers of the heart.
    • Patent Foramen Ovale (PFO): A hole between the two upper chambers of the heart that fails to close after birth.
    • Eisenmenger Syndrome: A condition where a long-standing left-to-right cardiac shunt causes pulmonary hypertension and eventually reverses to a right-to-left shunt.
  • Pulmonary Hypertension: Increased pressure in the pulmonary arteries can cause blood to flow from the right to the left side of the heart.
  • Pulmonary AVMs (Arteriovenous Malformations): Abnormal connections between arteries and veins in the lungs can also cause a right-to-left shunt.

When there’s a right-to-left shunt, it increases the risk of certain complications. For example, clots or particles in the bloodstream that would normally be filtered out by the lungs can bypass this filtering system and travel directly to the brain or other organs. This can increase the risk of stroke or systemic embolism.

It’s important to diagnose and treat right-to-left shunts, as management strategies can reduce the risk of associated complications.

Why would a neurologist find it important to study right-to-left shunt (RLS)?

A neurologist would find it important to study right-to-left shunts (RLS) for several reasons, primarily because of the neurological implications and potential complications associated with such shunts:

  • Risk of Stroke: One of the most significant concerns with a right-to-left shunt is the potential for paradoxical embolism. Normally, any small clots or debris in the venous system would be filtered out by the lungs. However, with a right-to-left shunt, these can bypass the lungs, entering the arterial system, and potentially travel to the brain, causing a stroke.
  • Migraine Connection: Some studies have suggested a link between patent foramen ovale (PFO), a type of right-to-left shunt, and migraine headaches, especially migraines with aura. The exact mechanism is not entirely clear, but closing the PFO has been shown in some studies to reduce the frequency and severity of migraines in certain patients.
  • Transient Ischemic Attacks (TIAs): Similar to the risk of stroke, smaller emboli that don’t necessarily cause permanent damage can lead to transient ischemic attacks, which are brief episodes of neurological dysfunction.
  • Cryptogenic Stroke: In cases where a stroke has occurred and the cause is unclear (termed “cryptogenic”), the presence of a right-to-left shunt, like a PFO, might be considered as a potential source. A neurologist might then be involved in the evaluation and management of such cases.
  • Detection during Neurological Imaging: During procedures like transcranial Doppler (TCD) with a bubble study, right-to-left shunts can be detected. A neurologist may be involved in ordering or interpreting such tests, especially if there’s a suspicion of an RLS based on a patient’s clinical presentation.
  • Overall Patient Management: Recognizing the presence of a right-to-left shunt can influence a neurologist’s recommendations on treatments, preventive strategies, and potential referrals for intervention.

Given these potential neurological consequences and the importance of early detection and appropriate management, studying right-to-left shunts becomes crucial for neurologists.

Study Contributions

In recognition of this monumental work, we want to extend our heartfelt congratulations and appreciation to our very own Dr. Ruchir Shah, Director of Clinical Service Lines & Implementations.

Enrolling the highest number of patients in the USA for the study is no small feat, and it underscores Dr. Shah’s passion and dedication to advancing medical research. His contributions to this study have undoubtedly brought us closer to enhancing the diagnostic methods for RLS, a critical step forward in stroke prevention.

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