What is the role of an echo with bubble study in evaluating and managing patients with stroke, particularly cryptogenic stroke?

Role of Echocardiography with Bubble Study in Stroke Evaluation

Transesophageal echocardiography with bubble study is essential for detecting patent foramen ovale in patients with cryptogenic stroke, particularly in younger patients (≤60 years) without traditional stroke risk factors, and should be performed to guide decisions about PFO closure for secondary stroke prevention. 1

Diagnostic Role in Cryptogenic Stroke

Cryptogenic stroke accounts for approximately one-third of all ischemic strokes, defined as strokes without an identifiable cause after standard diagnostic evaluation. Patients with cryptogenic stroke:

• Are less likely to have traditional risk factors (hypertension, hyperlipidemia, diabetes)
• Have higher prevalence of PFO compared to the general population 1

Echocardiographic Evaluation Process

1. Initial Screening:

   • Transthoracic echocardiography (TTE) with bubble study
   • Transesophageal echocardiography (TEE) has higher sensitivity for PFO detection 1

2. Bubble Study Technique:

   • Agitated saline (microbubbles) injected intravenously
   • Bubbles enter right atrium
   • If PFO present, bubbles pass into left atrium within a few cardiac cycles
   • Valsalva maneuver increases sensitivity by transiently raising right atrial pressure 1

3. Findings to Document:

   • Presence of right-to-left shunting
   • Associated atrial septal aneurysm (excessive bulging of atrial septal fossa ovalis)
   • Other potential embolic sources:
     • Atrial septal defects
     • Cardiac tumors (myxoma, papillary fibroelastoma)
     • Valve vegetations
     • Atrial thrombi 1

Patient Selection for Bubble Study

Not all stroke patients benefit from bubble studies. Appropriate selection criteria include:

• Young patients (≤60 years) 2, 3
• Absence of traditional stroke risk factors
• No other identified stroke etiology after standard workup
• Higher RoPE (Risk of Paradoxical Embolism) scores (>5) 4, 5

Caution in Patient Selection

Research shows bubble studies are frequently overused:

• 8.7% of patients referred had atrial fibrillation
• 9.2% had significant carotid stenosis (≥70%)
• 39.3% had ≥3 traditional stroke risk factors
• Only 47.1% had modified RoPE scores >5 4

Clinical Decision Algorithm

1. Initial Stroke Workup:

   • Rule out common causes (atrial fibrillation, carotid stenosis, large vessel disease)
   • Calculate RoPE score to estimate likelihood of PFO-attributable stroke

2. Consider Bubble Study When:

   • Age ≤60 years
   • Cryptogenic stroke after comprehensive evaluation
   • RoPE score >5
   • No significant atherosclerosis on carotid ultrasound 3

3. TEE Indications After Positive Bubble Study:

   • Confirm PFO presence
   • Assess PFO characteristics (size, associated atrial septal aneurysm)
   • Evaluate for other cardiac sources of embolism
   • Plan for potential PFO closure 1, 3

Management Implications

Detection of PFO in cryptogenic stroke patients may lead to:

1. PFO Closure Consideration:

   • Particularly beneficial in patients ≤60 years
   • Higher RoPE scores (>6) suggest greater benefit 5
   • Presence of atrial septal aneurysm increases embolic risk 1

2. Medical Therapy Options:

   • Antiplatelet therapy is standard for most cryptogenic strokes
   • Anticoagulation may be considered with concurrent venous thromboembolism 1

Important Caveats

1. Incidental PFO vs. Causative PFO:

   • PFO is common in general population
   • Low RoPE scores suggest PFO may be incidental rather than causative 5
   • Management changes occurred in only 31% of patients with detected PFO 4

2. Alternative Shunt Sources:

   • Positive bubble study after PFO closure may indicate:
     • Pulmonary arteriovenous malformations
     • Residual leak through device
     • These alternative sources were identified in 1.8% of cases 6

3. Safety Considerations:

   • Bubble studies are generally safe
   • Complication rate is approximately 0.1% (primarily TIAs) 4
   • Informed consent should be obtained

4. Combined Approach:

   • Transcranial Doppler bubble test plus carotid ultrasound has 97.1% negative predictive value for therapy-relevant TEE findings 3
   • This combined approach can help determine which patients truly need TEE

By following these guidelines, clinicians can optimize the use of echocardiography with bubble study in stroke evaluation, focusing on patients most likely to benefit from PFO detection and potential closure.