Is a PR end diastolic velocity of 2.1 m/s significant in a patient with hypertrophic cardiomyopathy (HCM) and diastolic dysfunction?

Significance of PR End Diastolic Velocity of 2.1 m/s in HCM with Diastolic Dysfunction

A PR end diastolic velocity of 2.1 m/s is clinically significant in a 15-year-old with hypertrophic cardiomyopathy (HCM) and diastolic dysfunction, as it exceeds the threshold of 2.0 m/s that indicates elevated left atrial pressure and advanced diastolic dysfunction. 1

Interpretation of PR End Diastolic Velocity in HCM

• PR end diastolic velocity >2.0 m/s is one of the key parameters used to evaluate diastolic function in patients with HCM, indicating elevated left atrial pressure (LAP) and at least grade II diastolic dysfunction 1
• This finding is particularly significant in the context of HCM with diastolic dysfunction, as it reflects increased right ventricular systolic pressure secondary to elevated left-sided filling pressures 1
• The American Society of Echocardiography guidelines specifically identify peak velocity of tricuspid regurgitation jet by CW Doppler >2.8 m/s as a cutoff value for elevated LAP in HCM patients 1

Clinical Significance in HCM Pathophysiology

• Diastolic dysfunction is a major pathophysiologic abnormality in HCM that affects both ventricular relaxation and chamber stiffness 1
• The elevated PR end diastolic velocity reflects impaired ventricular relaxation resulting from:
  • Systolic contraction load caused by outflow tract obstruction 1
  • Nonuniformity of ventricular contraction and relaxation 1
  • Delayed inactivation due to abnormal intracellular calcium reuptake 1
• In HCM patients, severe hypertrophy leads to increased chamber stiffness, which further contributes to elevated filling pressures 1

Correlation with Symptoms and Prognosis

• Elevated PR end diastolic velocity correlates with worse clinical outcomes in HCM patients 1, 2
• This finding is associated with:
  • Increased risk of heart failure symptoms 1
  • Reduced exercise tolerance 1
  • Worse functional status 2
• Left atrial volume typically increases in parallel with worsening symptoms and diastolic dysfunction in these patients 2

Assessment Algorithm for Diastolic Dysfunction in HCM

When evaluating diastolic function in a young patient with HCM:

1. Assess multiple parameters including:

   • Average E/e' ratio (>14 indicates elevated LAP) 1
   • LA volume index (>34 mL/m²) 1
   • Pulmonary vein atrial reversal velocity (Ar-A duration ≥30 msec) 1
   • Peak velocity of TR jet by CW Doppler (>2.8 m/s) 1

2. Determine grade of diastolic dysfunction:

   • If more than half of available variables meet cutoff values, LAP is elevated and grade II diastolic dysfunction is present 1
   • If <50% of variables meet cutoff values, LAP is normal and grade I diastolic dysfunction is present 1
   • Grade III diastolic dysfunction is present with restrictive filling pattern and abnormally reduced mitral annular e' velocity 1

Management Implications

• The finding of elevated PR end diastolic velocity should prompt consideration of preload management strategies 3
• Patients with HCM are preload dependent, and management should focus on:
  • Avoiding dehydration and ensuring adequate fluid intake 3
  • Avoiding arterial and venous dilators that can worsen LVOT obstruction 3
  • Using non-vasodilating beta-blockers as first-line therapy 3, 4
  • Considering calcium channel blockers (particularly verapamil) to improve diastolic filling characteristics 4

Important Caveats

• While PR end diastolic velocity is valuable, it should not be used in isolation; multiple parameters should be evaluated together for accurate assessment 1
• Doppler echocardiographic estimates of LV filling pressure correlate only modestly with direct measurements of left atrial pressure in HCM patients 5
• The complex nature of diastolic dysfunction in HCM means that precise characterization of LV filling pressure in an individual patient requires comprehensive assessment 5
• Conventional treatment approaches for heart failure (diuretics and inotropic agents) can potentially worsen the clinical picture in HCM patients with diastolic dysfunction 6