How is Left Ventricular Ejection Fraction (LVEF) quantification performed in patients who are candidates for a wearable defibrillator like LifeVest?

Left Ventricular Ejection Fraction Quantification for LifeVest Candidates

Two-dimensional echocardiography with Doppler is the standard first-line method for LVEF quantification in patients being evaluated for wearable defibrillators like LifeVest. 1

Primary Methods for LVEF Assessment

Echocardiography (First-Line)

• 2D echocardiography with Doppler is recommended during initial evaluation to assess:
  • LVEF quantitative value (single value or numerical range)
  • Left ventricular size
  • Wall thickness
  • Valve function 1

Alternative Methods (When Echocardiography is Inadequate)

• Radionuclide ventriculography can be used to assess LVEF and volumes 1
• Cardiac MRI provides excellent reproducibility and is considered the gold standard for volume measurements 2

Technical Considerations for LVEF Measurement

Echocardiographic Methods

• Calculated LVEF uses the formula: LVEF = ([EDV-ESV]/EDV) × 100 1
• Visual estimation is commonly reported as a percentage or midpoint of a range 1
• 3D echocardiography shows better agreement with CMR than 2D non-contrast echo 3
• Contrast echocardiography improves endocardial border definition and accuracy 3

Measurement Variability

• LVEF measurements can vary between imaging modalities with relatively wide limits of agreement (-12.1% to 11.4% between CMR and radionuclide methods) 2
• Choice of imaging modality may reclassify approximately 21% of patients for device therapy eligibility 2

Clinical Application for LifeVest Candidates

Patient Selection Criteria

• LifeVest is typically prescribed for patients with:
  • LVEF ≤35% following cardiac surgery 4
  • Following ICD explantation 4
  • Patients at transient risk of sudden cardiac death 4

Follow-up Assessment

• LVEF should be reassessed to determine if improvement occurs
• In a large cardiac surgery cohort, median LVEF improved from 28% to 35% during WCD use 4
• Approximately 37% of non-ICD explant patients ultimately required permanent ICD implantation 4

Important Considerations and Pitfalls

Technical Limitations

• Image quality significantly impacts measurement accuracy
• Loading conditions affect LVEF independent of myocardial contractility
• Cavity geometry can influence volume calculations 5

Clinical Interpretation Challenges

• LVEF may be normal despite impaired myofibril systolic function
• Subendocardial dysfunction may be compensated by circumferential fibers, maintaining overall LVEF 5
• LVEF is a marker of global ejection performance rather than direct myocardial contractile function 5

Documentation Requirements

• The quantitative result of LVEF assessment must be available in the medical record 1
• Documentation should include the specific imaging modality used
• Serial measurements should use consistent techniques when possible 1

Conclusion

When evaluating patients for LifeVest therapy, 2D echocardiography with Doppler remains the primary method for LVEF quantification, with radionuclide ventriculography or cardiac MRI as acceptable alternatives when echocardiography is inadequate or inconclusive. The specific value of LVEF is critical for determining eligibility for wearable defibrillator therapy, with LVEF ≤35% typically being the threshold for consideration.