What are the characteristic ECG (electrocardiogram) findings in cardiac tamponade?

ECG Findings in Cardiac Tamponade

The most characteristic ECG findings in cardiac tamponade are low QRS voltage and electrical alternans, though these findings have limited sensitivity and specificity. 1, 2

Key ECG Findings

Primary Findings

• Low QRS voltage:

  • Present in only about 29% of tamponade cases 2
  • May persist in approximately 18% of patients even after pericardiocentesis 2
  • More common in large effusions that cause significant cardiac compression

• Electrical alternans:

  • Seen in approximately 23% of tamponade cases 2
  • Characterized by beat-to-beat variation in QRS amplitude
  • Results from the swinging motion of the heart within a large effusion
  • May persist in about 10% of patients after pericardiocentesis 2

Secondary Findings

• Sinus tachycardia (compensatory mechanism for decreased stroke volume)
• Non-specific ST-T wave changes
• PR segment depression (if associated with pericarditis)

Clinical Correlation

ECG findings should always be interpreted in the context of the clinical presentation. The diagnosis of cardiac tamponade is primarily clinical, supported by imaging findings, particularly echocardiography 1, 3.

Beck's Triad

When evaluating a patient with suspected tamponade, look for Beck's triad:

• Hypotension
• Elevated jugular venous pressure
• Muffled heart sounds 4, 1

Additional Clinical Signs

• Pulsus paradoxus (>10 mmHg drop in systolic BP during inspiration)
• Tachycardia
• Dyspnea progressing to orthopnea

Diagnostic Approach

1. ECG: While useful as an initial screening tool, ECG has limited sensitivity and specificity for tamponade 2

2. Echocardiography: Gold standard for diagnosis showing:

   • Pericardial effusion
   • Right ventricular diastolic collapse (high specificity)
   • Right atrial systolic collapse (earliest sign)
   • Plethoric inferior vena cava with minimal respiratory variation
   • Exaggerated respiratory variations in mitral and tricuspid inflow 1, 5

Important Considerations

• ECG changes alone are insufficient to diagnose or rule out cardiac tamponade 2
• Low voltage on ECG may be caused by other conditions including obesity, emphysema, hypothyroidism, and infiltrative cardiomyopathies 6
• In pulmonary arterial hypertension with pericardial effusion, typical tamponade findings may be masked due to elevated right-sided pressures 4
• B-mode ultrasound significantly improves diagnostic accuracy compared to ECG alone 4

Management Implications

When ECG suggests possible tamponade (low voltage or electrical alternans):

• Obtain immediate echocardiography
• Prepare for potential pericardiocentesis if hemodynamic compromise is present
• Identify and treat the underlying cause

Remember that cardiac tamponade is a clinical diagnosis that requires prompt recognition and treatment, as it can rapidly progress to circulatory collapse and death if left untreated 3, 7.