Pericardial Knock

[g8orlife]

Hey guys!

I'm a PA-C and will be MD/DO next year, and have a question concerning pericardial knocks in constrictive pericarditis:

I don't understand why I could auscultate a pericardial knock in constrictive pericarditis but not in cardiac tamponade?

I understand that pericardial effusion will not have a pericardial knock if the level of fluid does not compromise chamber filling; but since the pericardial sac fluid in cardiac tamponade does compromise ventricular diastolic filling, wouldn't the constricted pericardium also cause a pericardial knock in cardiac tamponade???

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[f1re11]

A pericardial knock is due to abrupt cessation of early diastolic filling due to a thickened inelastic pericardium. There is nothing that impedes early diastolic filling of the ventricle. Once the ventricle reaches the maximum size the pericardial sac allows it to, filling stops.

In tamponade you do not get the rapid early diastolic filling with sudden cessation. Instead, there is decreased overall venous return due to compression of the chambers by the surrounding fluid. Also, due to pericardial effusion, heart sounds will be muffled.

 

[g8orlife]

A pericardial knock is due to abrupt cessation of early diastolic filling due to a thickened inelastic pericardium. There is nothing that impedes early diastolic filling of the ventricle. Once the ventricle reaches the maximum size the pericardial sac allows it to, filling stops.

In tamponade you do not get the rapid early diastolic filling with sudden cessation. Instead, there is decreased overall venous return due to compression of the chambers by the surrounding fluid. Also, due to pericardial effusion, heart sounds will be muffled.

Hey! I never thanked you for this answer... I couldn't picture the slower diastolic filling due to the compression of the chambers. This was exactly what I was searching for.

Thanks, f1re11!