Expansion
Equalisation of diastolic pressures with impaired filling and pulsus paradoxus
Expansion
Fluid in the inelastic pericardium raises intrapericardial pressure until it exceeds chamber diastolic pressures, limiting filling.
Consequences:
- Equalisation of diastolic pressures across all four chambers
- Reduced end-diastolic volume, so low stroke volume, with compensatory tachycardia and vasoconstriction
- Raised jugular venous pressure with a preserved x descent but an absent y descent, since the ventricle cannot accept blood in early diastole
- Pulsus paradoxus: an inspiratory fall in systolic pressure exceeding 10 mmHg
Pulsus paradoxus arises from ventricular interdependence. Within a fixed total volume, inspiratory filling of the right ventricle pushes the septum leftwards and reduces left ventricular filling, so left-sided output falls.
The patient is preload dependent, so fluids may help temporarily, while diuretics and vasodilators are dangerous. Definitive treatment is pericardial drainage.