What is annulus paradoxus in echocardiography (echo)?

Annulus Paradoxus in Echocardiography

Definition and Mechanism

Annulus paradoxus is a phenomenon where the expected relationship between mitral annular tissue Doppler velocities (e') and left ventricular filling pressures is disrupted, causing the E/e' ratio to remain normal or only mildly elevated despite elevated left ventricular filling pressures. 1

• Normally, as left ventricular filling pressures increase, the E/e' ratio increases proportionally, making it a useful marker for estimating filling pressures 1
• In annulus paradoxus, this relationship is disrupted, leading to potential underestimation of elevated filling pressures 1
• This phenomenon is most commonly observed in patients with advanced diastolic dysfunction and restrictive filling patterns 1

Clinical Significance

• Recognition of annulus paradoxus is crucial to avoid underestimating left ventricular filling pressures in patients with heart failure 1
• When annulus paradoxus is suspected, additional parameters should be assessed to accurately evaluate diastolic function: 1
  • Left atrial size
  • Pulmonary vein flow patterns
  • Tricuspid regurgitation velocity
  • Color M-mode flow propagation velocity

Diagnostic Implications

• The 2016 ASE/EACVI diastolic function guidelines recommend using multiple parameters rather than E/e' alone in cases where annulus paradoxus may be present 1, 2
• In patients with restrictive cardiomyopathy, the E/e' ratio may not accurately reflect the elevated left ventricular filling pressures 2
• For accurate assessment of diastolic function in these cases, evaluation should include: 2
  • Mitral inflow patterns (E/A ratio >2.5 in restrictive physiology)
  • Deceleration time (<150 msec in restrictive physiology)
  • Isovolumic relaxation time (<50 msec in restrictive physiology)

Physiological Context

• In normal hearts, the mitral annulus undergoes approximately 25% reduction in area during systole 3
• The mitral annular motion is an important component of left ventricular function 4
• Real-time 3D echocardiography has demonstrated that the saddle shape of the mitral annulus becomes enlarged and less nonplanar mainly in the anteroposterior direction during systole 4
• These geometric changes are proportional to global left ventricular systolic function 4

Differentiation from Other Paradoxical Findings

• Annulus paradoxus should not be confused with "annulus reversus," which is a finding in constrictive pericarditis where the septal e' velocity is higher than the lateral e' velocity (opposite to the normal pattern) 5, 2
• It is also distinct from "pulsus paradoxus," which refers to an exaggerated decrease in systolic blood pressure during inspiration 6

Clinical Application

• When evaluating patients with suspected heart failure with preserved ejection fraction (HFpEF), awareness of annulus paradoxus can prevent misdiagnosis 2
• For accurate assessment of diastolic function in patients with advanced heart disease, the ASE/EACVI guidelines recommend: 2
  • Evaluating multiple echocardiographic parameters
  • Considering the clinical context
  • Using an integrated approach to diastolic function assessment

Conclusion

• Annulus paradoxus represents an important echocardiographic concept that highlights the limitations of using E/e' ratio alone for estimating left ventricular filling pressures 1
• Recognition of this phenomenon is essential for accurate assessment of diastolic function and appropriate clinical decision-making in patients with advanced heart disease 1, 2