What is the role of cardiac MRI (Magnetic Resonance Imaging) in evaluating a patent foramen ovale (PFO)?

Role of Cardiac MRI in Evaluating Patent Foramen Ovale (PFO)

Cardiac MRI is rated as "Appropriate" for assessment of atrial septal anatomy in PFO evaluation, but is inferior to transesophageal echocardiography (TEE) for detecting right-to-left shunting and identifying atrial septal aneurysms. 1

Primary Diagnostic Modalities for PFO Evaluation

• Transesophageal echocardiography (TEE) remains the gold standard for PFO diagnosis due to its superior ability to detect right-to-left shunting and identify atrial septal aneurysms 1
• Transthoracic echocardiography (TTE) with contrast is rated "Appropriate" for initial evaluation and is more sensitive than previously thought 1, 2
• Transcranial Doppler (TCD) with contrast has high sensitivity (91.3%) and specificity (93.8%) for detecting right-to-left shunts 3

Cardiac MRI Applications in PFO Assessment

• Cardiac MRI is rated "Appropriate" specifically for assessment of atrial septal anatomy in preprocedural evaluation for PFO closure 1
• Contrast-enhanced cardiac MRI can detect right-to-left shunting but has limitations compared to TEE 4
• Cardiac MRI detects only 66.6% of moderate-to-severe shunts and 18.8% of mild shunts that are visible on TEE 4
• High-resolution cine imaging in cardiac MRI can identify atrial septal aneurysms but with lower sensitivity than TEE (37.3% vs 62.7%) 4

Diagnostic Algorithm for PFO Evaluation

1. Initial Screening: TTE with contrast should be performed first due to its non-invasive nature and improved sensitivity 1, 2
2. Definitive Diagnosis: TEE with contrast remains the reference standard for confirming PFO and assessing anatomical features 1, 5
3. Complementary Testing: TCD can be used as a highly sensitive screening tool, especially when TEE is contraindicated 3
4. Role of Cardiac MRI:
   • Best used for comprehensive assessment of atrial septal anatomy when planning PFO closure 1
   • Valuable for excluding other structural cardiac abnormalities 4
   • Can identify additional relevant findings such as coronary anomalies 4

PFO Diagnostic Criteria

• PFO is diagnosed by demonstrating an interatrial communication with right-to-left transit of contrast microbubbles within 3-4 cardiac cycles of right atrial opacification 6
• Color Doppler TEE showing turbulent flow within the atrial septum has 100% sensitivity and specificity for PFO detection 5
• The color Doppler jet width correlates well with the PFO diameter determined at autopsy (r=0.99) 5

Clinical Significance and Indications for PFO Evaluation

• PFO evaluation is particularly important in patients with cryptogenic stroke, especially those younger than 55 years 1, 6
• In patients with cryptogenic stroke in whom PFO closure would be contemplated, TCD with embolus detection might be reasonable to screen for right-to-left shunt (Class 2b, Level C-LD) 1
• In patients with embolic stroke of undetermined source (ESUS), cardiac MRI might be reasonable to identify possible cardioaortic sources or transcardiac pathways for cerebral embolism (Class 2b, Level C-LD) 1

Limitations and Pitfalls

• Cardiac MRI is inferior to TEE for detection of contrast-enhanced right-to-left shunting and identification of atrial septal aneurysms 4
• TEE may underestimate shunt severity compared to TTE in some cases 2
• The Valsalva maneuver significantly improves detection of right-to-left shunting with all imaging modalities (26-28% improvement) and should be incorporated into protocols 2, 7
• Routine surveillance of asymptomatic patients with PFO using TTE or TEE is rated "Rarely Appropriate" 1