Cardiac Tamponade Hemodynamics

Tamponade is a hemodynamic emergency with a classic signature. Learn the pressure findings, the waveform clues, and how to separate it from constriction.

What is cardiac tamponade?

Cardiac tamponade occurs when fluid in the pericardial sac raises intrapericardial pressure enough to compress the heart and impair filling. Because the ventricles cannot fill normally, stroke volume and cardiac output fall — a potentially fatal, treatable emergency.

The hemodynamic findings

• Equalisation of diastolic pressures — RA, RV diastole, PA diastole, and PCWP converge (typically within ~5 mmHg).
• Elevated right atrial pressure with a blunted y descent — the hallmark waveform clue.
• Preserved x descent — the atrial pressure shows a prominent x but attenuated y.
• Pulsus paradoxus — an exaggerated (>10 mmHg) fall in systolic pressure on inspiration.
• Low output with tachycardia as compensation.

Why the y descent is blunted

Normally the y descent reflects rapid early-diastolic ventricular filling when the AV valve opens. In tamponade the surrounding pericardial pressure prevents that rapid filling, so the y descent is blunted or absent. This is the single most useful waveform feature — and the key contrast with constriction.

Tamponade vs constrictive pericarditis

Feature	Tamponade	Constriction
y descent	Blunted	Prominent
Diastolic pressures	Equalised	Equalised
Pulsus paradoxus	Present	Sometimes
Kussmaul sign	Absent	Present
Square-root sign	Absent	Present

More detail in the hemodynamics study guide.

Summary

• Tamponade compresses the heart and impairs diastolic filling.
• Findings: equalised diastolic pressures, blunted y descent, pulsus paradoxus.
• The blunted y descent separates it from constriction (prominent y).
• It is a treatable emergency — recognise it fast.

Frequently asked questions

What are the hemodynamics of cardiac tamponade?

Equalisation of diastolic pressures across the chambers, an elevated right atrial pressure with a blunted y descent, pulsus paradoxus, and a low cardiac output with compensatory tachycardia.

Why is the y descent blunted in tamponade?

Pericardial pressure prevents rapid early-diastolic ventricular filling, so the y descent — which normally reflects that filling — is blunted or absent.

How do you distinguish tamponade from constrictive pericarditis?

Both equalise diastolic pressures, but tamponade has a blunted y descent and no Kussmaul sign, whereas constriction has a prominent y descent, a square-root sign, and Kussmaul sign.

What is Beck's triad?

The clinical triad of tamponade: hypotension, muffled heart sounds, and distended neck veins.