Welcome back to MasterUSMLE, where we break down high-yield Step 2 CK topics in a way that makes sense. Today, we’re talking about cardiac tamponade, a rapidly fatal emergency that you must recognize and manage quickly.

Case Scenario

You’re working the night shift in the ER when a 50-year-old woman arrives after a minor car accident. She was stable initially but now looks pale, diaphoretic, and short of breath. Her blood pressure is 78/40, pulse is 135, and her jugular veins are distended. Heart sounds are distant, but her lungs are clear.

This isn’t just shock—it’s cardiac tamponade from traumatic pericardial bleeding.

Pathophysiology & Hemodynamic Changes

In tamponade, fluid rapidly accumulates in the pericardium, preventing normal cardiac filling. The key to understanding tamponade is that all four chambers experience increased diastolic pressures until they equalize with pericardial pressure.

Let’s break it down:

Right Atrial Pressure (RAP) ↑

Increased due to restricted venous return and chamber compression.

Leads to jugular venous distension (JVD).

Pulmonary Capillary Wedge Pressure (PCWP) ↑

Normally reflects left atrial pressure but increases because the left atrium is compressed.

Unlike other shock states (e.g., pulmonary embolism), PCWP remains high despite low cardiac output.

Cardiac Index (CI) ↓

Represents cardiac output per body surface area.

Decreases because the heart can’t fill properly, reducing stroke volume and cardiac output.

Leads to hypotension and obstructive shock.

Systemic Vascular Resistance (SVR) ↑

Reflex vasoconstriction occurs to maintain perfusion in response to low cardiac output.

This is why extremities may be cold and clammy.

Right Ventricular End-Diastolic Pressure (RVEDP) ↑

Right ventricle is compressed first because it’s a low-pressure chamber.

Leads to pulsus paradoxus—a drop in systolic BP >10 mmHg during inspiration due to further RV filling restriction.

How Does This Show Up on USMLE?

Classic Triad (Beck’s Triad)

Hypotension (low cardiac output)

JVD (high right atrial pressure)

Muffled heart sounds (fluid-insulated heart)

ECG Findings

Low-voltage QRS from pericardial fluid.

Electrical alternans (varying QRS amplitude) due to heart swinging in fluid.

Pulsus Paradoxus

Blood pressure drops >10 mmHg during inspiration due to further RV restriction.

Key Differentiator from Other Shock Types

Tamponade = High PCWP, High RAP, Low CI, High SVR.

Pulmonary Embolism = High RAP, Low PCWP, Low CI, High SVR.

Septic Shock = Low SVR, High CI, Low PCWP.

Management

🚨 Pericardiocentesis → Immediate drainage to relieve pressure.

🚨 IV Fluids → Temporarily increases preload and maintains right-sided filling.

🚨 Pericardial Window → If recurrent or post-surgical.

Key Takeaway

If you see sudden hypotension, JVD, and clear lungs, think cardiac tamponade. The key is recognizing high PCWP, high RAP, low CI, and high SVR—a unique shock state that demands urgent intervention.

That’s it for today. Keep studying, stay sharp, and master the USMLE.