Fluid retention is a classical sign of cardiac failure . (Elevated JVP, hepatomegaly , edema legs ) The mechanism of fluid retention are many .But, traditionally we have given importance to venous back pressure (Hydrostatic pressure) . Equally important (if not more !) is the renal sodium and fluid conservation in response to reduced effective renal blood flow.
How common is ascites in cardiac failure ?
While we see hydrothorax little more frequently it is rare to get ascites in cardiac failure .However ascites often manifests late in the pre terminal phase of cardiac failure *. This is due to congestive hepatomegaly, secondary hyperaldosteronism and renal dysfunction .
When does ascites come early before edema of extremities in cardiac failure ?
It is classically reported in in constrictive pericarditis. The reason why ascites precedes edema legs is long been speculative . Now we have evidence , the pericardial pathology , has a direct effect on the hepatic venous morphology. There can be a selective , partial constrictor effect on at least one of the hepatic vein as it enters the right atrium .In fact , the entry point of hepatic vein is delicately close to IVC/RA junction.
*It should be remembered in the current era we are expected to diagnose cardiac failure even before the onset of edema !
Anatomical constriction has a mechanical effect on the hepatic venous drainage and subsequently alters the hepatic function . Segmental hepatic dysfunction is thought to ooze out the ascitic fluid from the surface of liver .Ultimately severe raise of hepatic venous pressure results in congestive hepatomegaly and could result in now obsolete , cardiac cirrhosis.
Other mechanisms of ascites in constrictive pericarditis , include
Common infection of peritoneum and pericardium( like tueberculosis)
Is ascites precox an exclusive feature of constrictive pericarditis ?
Not necessarily so . Even though , it was first described in this condition ,clinical experience suggest, any congestive cardiac failure with predominate right sided pathology like organic tricuspid valve stenosis or regurgitation, right ventricular endomyocardial fibrosis , all can result in significant ascites which may precede edema legs.
What is effect of of severe TR on hepatic venous hydrodynamics ?
TR like MR can be eccentric and some times hits upon the hepatic veins directly
and result in disproportionate elevation of hepatic venaous presure than even IVC pressure
which may contribute to early ascites in organic tricuspid valve disease.