Background: In the normal heart, pericardial pressure is greater than previously believed.
Objectives: To explore the contribution of pericardial constraint to the elevated left ventricular (LV) end-diastolic pressure in chronic heart failure (CHF).
Animals and methods: Pericardial pressure was measured directly in 11 dogs with CHF. Seven dogs were instrumented with LV and right ventricular micromanometers and epicardial pacing leads, and paced at 240 to 260 beats/min for four to seven weeks. After the development of CHF, a left thoracotomy was performed and a flat pericardial balloon was positioned over the LV free wall through a slit in the pericardium.
Results: LV end-diastolic pressure was 31+/-9 mmHg, and pericardial pressure only 7+/-2 mmHg. Nitroglycerin in six dogs decreased LV end-diastolic pressure from 33+/-8 to 28+/-7 and pericardial pressure from 7+/-2 to 6+/-3 mmHg (both P<0.05). Calculated transmural LV end-diastolic pressure also decreased (26+/-8 to 22+/-7 mmHg, P<0.05). Volume loading in five dogs increased LV end-diastolic pressure from 29+/-8 to 42+/-10 mmHg (P<0.05), pericardial pressure from 6+/-3 to 12+/-6 mmHg (not significant) and transmural LV end-diastolic pressure from 23+/-7 to 30+/-7 mmHg (not significant). When the pericardium was opened in three dogs, the LV end-diastolic pressure decreased by 5 mmHg. Four previously uninstrumented dogs were studied to exclude the effects of epicardial scarring; LV end-diastolic pressure was 42+/-6 mmHg and pericardial pressure was 10+/-6 mmHg.
Conclusion: Pericardial constraint, a prerequisite for pericardially mediated ventricular interaction, was not present to the same extent in this model of CHF as in acute models, probably reflecting the importance of pericardial remodelling.