Pericardial Effusion ECG Case: Low Voltage Misdiagnosed as Pulmonary Embolism “Small, Yet Dangerous"

21.10.25 07:47 AM - By Hesham Ibrahim

Case Presentation:

A 52-year-old male with metastatic cancer undergoing chemotherapy presented to the Emergency Department with:

● Acute chest pain

● Shortness of breath

Vital signs:

● Respiratory Rate: 26

● O₂ Saturation: 94% (on room air)

● Blood Pressure: 100/65 mmHg

● Heart Rate: 111 bpm

His chest X-ray (AP view) showed enlarged mediastinal lymph nodes, which were known.
His chest X-ray (AP view) showed enlarged mediastinal lymph nodes, which were known.

This was the ECG of the patient,

Then came the ECG — and the diagnosis.
Then came the ECG — and the diagnosis.

What is your diagnosis?

Let’s walk through the case as it unfolded in real time.

First Impression: Suspected Pulmonary Embolism

The initial clinical picture strongly suggested PE:

● Active cancer

● Ongoing chemotherapy

● Sudden chest pain + SOB

● Tachypnea and tachycardia

He fit every box for anticoagulation and admission with planned CT Pulmonary Angiogram (CTPA)

But one key detail almost derailed everything…


Chest X-Ray Clue

Although the CXR was AP view, cardiomegaly was evident.

This raised concern — and led to a closer look at the ECG.

    • ECG Findings

The ECG showed two critical abnormalities:

      1. Prolonged QTc

      2. Low voltage ECG

      • About the Long QT 

    ● Likely related to chemotherapy

    ● Electrolytes were not severely abnormal

    ● Will be covered in detail in another blog

      • Focus: Low Voltage ECG

Definition:

● Limb leads (I + II + III) total height < 15 small squares, and/or

● Precordial leads (V1–V3) total height < 30 small squares

Causes fall into two categories:

1) Poor signal generation by the heart:

● Cardiomyopathy

● Hypothyroidism

● Myocardial infiltration (e.g. sarcoidosis)

2) Barriers between the heart and leads:

● Fat (obesity)

● Air (COPD)

● Fluid (pericardial/pleural effusion)

    • Pattern Recognition: Tachycardia + Low Voltage

💡 This combination strongly suggests:

Pericardial Effusion

Classic ECG Triad of Massive Pericardial Effusion:

● Low Voltage ECG

● Tachycardia

● Electrical Alternans(not seen in this case)

    • Why This Matters?

If this patient had been anticoagulated for presumed PE, he may have deteriorated due to hemorrhagic tamponade from undiagnosed pericardial effusion.

    • What Was Done?

● Immediate bedside echo was performed → Confirmed pericardial effusion

● CTPA was expedited (to rule out PE before anticoagulating)

● CTPA showed no pulmonary embolism

🟢 Patient was safely admitted to CCU and did well.

    • Key Learning Points:

● Low-voltage ECG is a powerful early clue

● Tachycardia + Low Voltage = Think pericardial effusion

● Don’t treat presumed PE blindly — stop and confirm

● CTPA + Echo combo is crucial when the diagnosis is unclear

    • 🔗 Further Learning

● LITFL ECG Library: Low Voltage Patterns

✅ FAQ – Small, Yet Dangerous

Q1: What are the ECG criteria for diagnosing low voltage?

A1: Limb leads I + II + III < 15 mm combined, or V1–V3 < 30 mm combined.

Q2: What are the most likely causes of low voltage with tachycardia?

A2: Pericardial effusion is the most likely cause, especially in cancer patients or those with inflammatory conditions.

Q3: Why is anticoagulating blindly in suspected PE dangerous?

A3: In cases like pericardial effusion, anticoagulation may lead to hemorrhagic tamponade and death.

Hesham Ibrahim

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