What are filling pressures?

Understanding Filling Pressures in Cardiac Assessment

Filling pressures refer to the pressures that drive blood into the ventricles during diastole, including mean pulmonary capillary wedge pressure (PCWP), mean left atrial pressure (LAP), LV pre-A pressure, mean LV diastolic pressure, and LV end-diastolic pressure (LVEDP). 1

Types of Filling Pressures

Filling pressures can be categorized into several specific measurements:

1. Left Ventricular End-Diastolic Pressure (LVEDP)

   • Occurs at the end of diastole just before contraction
   • Normal value: <12 mmHg
   • Best pressure to use when evaluating left ventricular function 2
   • In LV failure, LVEDP is usually elevated over 18 mmHg 1

2. Mean Left Atrial Pressure (LAP)

   • Reflects the average pressure in the left atrium
   • Normal value: 8-12 mmHg
   • Most relevant when considering tendency for pulmonary congestion 2
   • Most relevant for determining if pulmonary hypertension has a left heart component 2

3. Pulmonary Capillary Wedge Pressure (PCWP)

   • An indirect estimate of LV diastolic pressures
   • Measured via right heart catheterization
   • Normal value: 8-12 mmHg
   • In LV failure, PCWP is usually elevated over 18 mmHg 1

4. LV Pre-A Pressure

   • Pressure just before atrial contraction
   • Reflects the early filling phase of diastole

5. Mean LV Diastolic Pressure

   • Average pressure throughout diastole
   • Best option for estimating mean LAP when only LV pressure tracing is available 2

Clinical Significance

Filling pressures are crucial for:

• Diagnosing diastolic dysfunction: Elevated LV diastolic pressure in the absence of increased LV end-diastolic volume is strong evidence of diastolic dysfunction 1

• Assessing heart failure severity: In decompensated heart failure, right atrial pressure is usually >12 mmHg, and cardiac index is usually <2.2 L/min/m² 1

• Guiding treatment decisions: Monitoring filling pressures helps determine the need for diuretics or vasodilators

• Evaluating response to therapy: Changes in filling pressures can indicate effectiveness of heart failure treatment

Measurement Methods

Invasive Methods

• Right heart catheterization: Measures PCWP, right atrial pressure, and cardiac output 1
• Left heart catheterization: Directly measures LVEDP 1

Non-invasive Echocardiographic Parameters

Several echocardiographic parameters correlate with filling pressures:

1. E/e' ratio:

   • Values <8 usually indicate normal filling pressures
   • Values >14 have high specificity for increased filling pressures 1
   • Pooled correlation coefficient with invasive measurements: r=0.56 1

2. E/A ratio:

   • 2 suggests restrictive filling with high pressures

   • <1 suggests delayed LV relaxation with normal filling pressures 1

3. Deceleration time (DT):

   • Short DT (<150 ms) in patients with reduced EF indicates increased LVEDP 1

4. Isovolumic relaxation time (IVRT):

   • Shortened IVRT (<50 ms) suggests elevated filling pressures 3

5. Tricuspid regurgitation velocity:

   • 3.4 m/s suggests increased right ventricular systolic pressures 1

Clinical Pitfalls and Caveats

1. Terminology confusion: LVEDP and mean LAP are not interchangeable and often differ in magnitude in cardiac disease 2

2. E/A fusion: With tachycardia or first-degree AV block, E and A waves may fuse, making interpretation difficult 1

3. Gray zone measurements: E/e' ratios between 8-14 may be indeterminate for filling pressures 1

4. Limited accuracy in specific conditions: E/e' ratio is not accurate in normal subjects, patients with heavy annular calcification, mitral valve disease, or pericardial disease 1

5. Estimating LVEDP from right heart pressures: Only reliable when heart and pulmonary circulation are normal; inaccurate with mitral valve disease, LV disease, or pulmonary hypertension 2

Clinical Application

When evaluating a patient for possible elevated filling pressures:

1. Assess multiple echocardiographic parameters rather than relying on a single measurement
2. Consider the clinical context, including symptoms of dyspnea or heart failure
3. Look for structural evidence such as left atrial enlargement (volume >34 mL/m²) 1
4. Evaluate for diastolic dysfunction patterns (impaired relaxation, pseudonormal, or restrictive)
5. Consider invasive measurement when non-invasive assessment is inconclusive or when precise values are needed for management decisions

Understanding filling pressures is essential for proper diagnosis and management of cardiac conditions, particularly heart failure with preserved ejection fraction and diastolic dysfunction.