What ECG (electrocardiogram) changes are associated with pulmonary embolism?

ECG Changes in Pulmonary Embolism

The most common ECG finding in pulmonary embolism is sinus tachycardia (present in about 28% of cases), while the S1Q3T3 pattern, though classically associated with PE, occurs infrequently and has limited diagnostic value on its own. 1, 2

Common ECG Findings in Pulmonary Embolism

ECG changes in pulmonary embolism primarily reflect right ventricular strain and hemodynamic consequences of pulmonary arterial obstruction:

1. Sinus tachycardia (most frequent finding, present in 28-40% of cases) 1, 2, 3
2. T-wave inversions in leads V1-V4 (indicating right ventricular overload) 1, 4
3. Non-specific ST-segment and T-wave changes (common but non-specific) 1, 5
4. Right bundle branch block (complete or incomplete, present in ~9% of cases) 1, 2
5. Right ventricular strain pattern (sensitivity 11.1%, specificity 97.4%) 2
6. S1Q3T3 pattern (S wave in lead I, Q wave and inverted T wave in lead III) - occurs in only 3.7-8.5% of PE cases despite being classically associated with PE 2, 3
7. QR pattern in V1 (associated with more severe cases) 1, 4
8. Atrial dysrhythmias (particularly atrial fibrillation, in ~10% of cases) 4, 2
9. Clockwise rotation (in ~20% of cases) 2

Diagnostic Value and Clinical Significance

The diagnostic value of ECG in PE is limited:

• 20-25% of patients with PE, including those with large clot burden, have completely normal ECGs 2
• ECG findings have modest diagnostic accuracy when used alone 5
• The presence of RV strain pattern is highly specific (97.4%) but not sensitive (11.1%) for PE 2
• The S1Q3T3 pattern has a positive likelihood ratio of only 2.07-3.7 5, 3

However, certain ECG patterns have important prognostic value:

• The presence and number of RV strain signs correlate with worse outcomes 1
• ECG findings of RV overload are associated with higher risk of adverse events 1
• More extensive ECG abnormalities correlate with larger perfusion defects and higher pulmonary arterial pressures 6

Clinical Application

When evaluating a patient with suspected PE:

1. Do not use ECG alone to rule in or rule out PE - ECG has insufficient standalone accuracy 5
2. Look for RV strain pattern - this finding is highly suggestive of PE when present (specificity 97.4%) 2
3. Pay special attention to T-wave inversions in V1-V4 - these indicate RV overload and are more common in severe cases 1, 4
4. Consider the "Zurkurnai ECG pattern" - a recently described pattern combining right axis deviation, deep symmetrical T wave inversions in V1-V5, II, III, and aVF (maximal at V3-V4), and poor R wave progression - which may indicate high-risk PE 7

Important Caveats

• Similar ECG patterns can be seen in other conditions causing right heart strain (COPD exacerbation, right ventricular infarction) 1
• The absence of ECG signs of RV overload practically excludes massive PE as the cause of hemodynamic instability 1
• ECG findings tend to normalize over time, with T-wave inversions being the most persistent abnormality 6
• Atrial flutter or fibrillation is more typical in patients with PE who have pre-existing cardiac disease 6

Remember that while ECG changes can support a diagnosis of PE, definitive diagnosis requires appropriate imaging (typically CT pulmonary angiography) based on clinical probability assessment and D-dimer testing when indicated 4, 1.