What causes a diastolic gradient between Pulmonary Capillary Wedge Pressure (PCWP) and Left Ventricular (LV) end-diastolic pressure?

Understanding the Diastolic Gradient Between PCWP and LV

The diastolic gradient between Pulmonary Capillary Wedge Pressure (PCWP) and Left Ventricular (LV) end-diastolic pressure primarily occurs in early stages of diastolic dysfunction when LVEDP is elevated while mean PCWP remains normal due to a large atrial pressure wave. 1

Physiological Basis of the Gradient

• LV diastolic pressures and left atrial pressures are not identical throughout the cardiac cycle, creating natural gradients during different phases of diastole 1
• The term "LV filling pressures" can refer to several distinct measurements: mean PCWP, mean left atrial pressure (LAP), LV pre-A pressure, mean LV diastolic pressure, and LV end-diastolic pressure (LVEDP) 1
• These different pressure measurements correlate with different Doppler echocardiographic parameters and have different clinical significance 1

Early Diastolic Phase

• During early diastole, after mitral valve opening, blood flows from the left atrium to the left ventricle due to a pressure gradient 2
• This phase is represented by the LV rapid filling wave (RFW) on pressure tracings 2
• The early diastolic gradient is influenced by LV relaxation (lusitropy) and LV compliance 2

Late Diastolic Phase

• During late diastole, atrial contraction creates another pressure gradient that contributes to LV filling 1
• The LA "A wave" pressure precedes the late diastolic rise (LV A wave) in LV pressure 1
• In early stages of diastolic dysfunction, LVEDP may be the only abnormally elevated pressure due to a large atrial pressure wave, while mean PCWP and LAP remain normal 1

Measurement and Assessment

• PCWP is obtained by inflating a balloon at the tip of a pulmonary artery catheter, creating a static column of blood between the catheter tip and the left atrium 3
• PCWP correlates best with earlier occurring LV diastolic pressures such as mean PCWP, pre-A pressure, and mean LV diastolic pressure 3
• Doppler signals that occur at end-diastole correlate best with LVEDP, including mitral peak A velocity, A-wave duration, pulmonary vein peak Ar velocity, and tissue Doppler-derived mitral annular a' velocity 1
• Simultaneous pressure measurements in the left ventricle and left atrium via transseptal catheterization provide the most accurate assessment of the gradient 4

Clinical Significance

• The presence of a diastolic gradient between PCWP and LVEDP is important for accurate diagnosis and management of heart failure, particularly heart failure with preserved ejection fraction (HFpEF) 3
• In patients with mitral valve disease, the time interval between the onset of early diastolic mitral inflow velocity (E) and annular early diastolic velocity (Ea) can help estimate mean PCWP 5
• The ratio of isovolumic relaxation time (IVRT) to this time interval (T(E-Ea)) has shown excellent correlation with PCWP in patients with mitral valve disease 5
• During exercise, sympathetic stimulation can cause a downward shift of the early diastolic portion of the LV pressure-volume loop, increasing the maximum mitral valve pressure gradient 6

Clinical Pitfalls and Considerations

• PCWP and LVEDP cannot be used interchangeably as they often differ in magnitude in the presence of cardiac disease and have different clinical significance 7
• LVEDP is the best pressure to use when considering left ventricular function, whereas mean LAP is most relevant when considering the tendency to pulmonary congestion 7
• In patients on mechanical ventilation, positive pressure ventilation affects the relationship between PCWP and LVEDP 4
• Heart rate and rhythm abnormalities can significantly affect the assessment of diastolic gradients 2
• Age-related changes in diastolic function must be considered when interpreting pressure gradients 2

Conclusion

Understanding the diastolic gradient between PCWP and LV pressure is essential for accurate assessment of diastolic function and filling pressures. This gradient exists naturally during different phases of diastole but becomes particularly significant in early stages of diastolic dysfunction when LVEDP may be elevated while mean PCWP remains normal.