Is the right ventricular (RV) preload dependent on volume status?

Right Ventricular Preload Dependence

Yes, the right ventricle (RV) is preload dependent, but it is more sensitive to changes in afterload than to variations in preload. 1

RV Physiological Characteristics

The RV has distinct physiological characteristics that influence its preload dependence:

• Anatomical structure: The RV has a funnel-like configuration with a heavily trabeculated structure, making it more compliant than the LV 1
• Energy expenditure: The RV requires one-sixth the energy expenditure of the LV due to the low-resistance pulmonary circulation 1
• Pressure-volume relationship: The RV pressure-volume loop lacks isovolumic phases of contraction and relaxation, has lower peak systolic pressure, and exists at a higher steady-state volume compared to the LV 1

Preload vs. Afterload Sensitivity

• The RV is highly sensitive to changes in afterload, with minor increases in afterload causing large decreases in stroke volume 1
• The RV has a shallower end-systolic pressure-volume slope than the LV, resulting in greater changes in end-systolic volume with changes in pressure 1
• When pulmonary artery systolic pressure increases acutely, RV stroke volume decreases significantly and arterial elastance increases out of proportion to end-systolic elastance 1

Clinical Implications of RV Preload Dependence

Volume Management

• Traditional misconception: The mantra that "the RV is preload dependent" often leads to inappropriate volume loading in RV dysfunction 1
• Optimal approach: The RV prefers euvolemia with a central venous pressure of 8-12 mmHg 1
• Risks of volume overload: Excessive volume loading can worsen RV dilation and tricuspid regurgitation 1

Hemodynamic Monitoring

• Right ventricular end-diastolic volume index (RVEDVI) correlates better with cardiac index (r=0.61) than pulmonary artery wedge pressure (r=0.42) 2
• RVEDVI more accurately predicts preload-recruitable increases in cardiac output compared to pressure-based measurements 2, 3
• Stroke volume variation (SVV) has better correlation with RVEDVI (R²=0.48) than central venous pressure (R²=0.19) or pulmonary artery diastolic pressure (R²=0.33) 4

Special Considerations in RV Failure

Mechanical Ventilation Effects

• Positive pressure ventilation increases pleural pressure (Ppl), which decreases venous return to the RV 1
• When positive end-expiratory pressure (PEEP) is present, the gradient for venous return is decreased throughout the ventilatory cycle 1
• Increased mean airway pressure can increase pulmonary vascular resistance, further compromising RV function 1

Ventricular Interdependence

• RV dilation causes leftward interventricular septal shift, compromising LV filling and reducing cardiac output 1
• Diuresis reduces ventricular dilation and improves biventricular coupling 1
• In acute RV failure, mechanical flattening with leftward shift of the interventricular septum increases LV end-diastolic pressure and impedes LV diastolic filling 1

Management Principles

1. Maintain euvolemia: Target central venous pressure of 8-12 mmHg rather than aggressive volume loading 1
2. Consider volume status carefully: In RV infarction, maintain RV preload but avoid excessive volume loading 1
3. Avoid factors that reduce preload: Volume depletion, diuretics, and nitrates can have profoundly adverse hemodynamic effects in RV failure 1
4. Monitor using volumetric parameters: RVEDVI provides better assessment of preload status than pressure-based measurements 2, 3
5. Address afterload: The RV is particularly sensitive to increases in afterload, so managing pulmonary vascular resistance is crucial 1

Pitfalls to Avoid

• Excessive volume loading: Can worsen RV dilation, tricuspid regurgitation, and interventricular dependence 1
• Relying solely on pressure measurements: CVP and PAWP correlate poorly with cardiac output compared to volumetric measurements 2, 5, 3
• Ignoring ventricular interdependence: RV dilation affects LV filling and function 1
• Overlooking afterload: The RV is more sensitive to changes in afterload than preload 1

In summary, while the RV is preload dependent, it is more sensitive to changes in afterload. Optimal management requires careful assessment of volume status using volumetric parameters rather than pressure-based measurements, and maintaining euvolemia rather than aggressive volume loading.