ECG Changes Associated with Pulmonary Embolism
The most common ECG changes in pulmonary embolism include sinus tachycardia, T wave inversions in precordial leads V1-V4, S1Q3T3 pattern, and right ventricular strain pattern, though many patients with PE may have normal ECGs. 1, 2
Common ECG Findings in Pulmonary Embolism
Right Ventricular Strain Patterns
- T wave inversions in right precordial leads (V1-V4) - most specific finding, especially in massive PE 1, 2
- QR pattern in V1 - indicates acute right ventricular overload 2
- S1Q3T3 pattern (deep S wave in lead I, Q wave and inverted T wave in lead III) - classic but present in only 8.5% of PE cases 3
- Right bundle branch block (complete or incomplete) - seen in approximately 9% of PE cases 4
Rhythm Abnormalities
- Sinus tachycardia (heart rate >100 beats/min) - most common ECG finding, present in approximately 28% of patients with PE 4, 3
- Atrial dysrhythmias (atrial fibrillation, atrial flutter) - occur in about 10% of cases 4
Other Findings
- Clockwise rotation - present in approximately 20% of PE cases 4
- Right axis deviation - relatively uncommon, seen in only about 4% of cases 4
- ST segment changes (elevation or depression) over left precordial leads - associated with worse outcomes 5
- Low voltage in peripheral leads - associated with worse prognosis 5
Diagnostic Value
- Right ventricular strain pattern has high specificity (97.4%) but low sensitivity (11.1%) for PE diagnosis 4
- Sensitivity increases to 17.1% in patients with large clot burden 4
- S1Q3T3 pattern has a positive likelihood ratio of 3.7 but is present in only a small percentage of cases 3
- T wave inversions extending from V1 to V4 have a positive likelihood ratio of 3.7 3
Clinical Significance
- ECG findings correlate with severity of pulmonary hypertension and right ventricular dysfunction 1, 2
- Presence of specific ECG abnormalities (atrial arrhythmias, complete right bundle branch block, peripheral low voltage, Q waves in III and aVF, ST changes) is associated with higher 30-day mortality 5
- 20-25% of patients with PE, including those with large clot burden, may have completely normal ECGs 4
Important Caveats
- ECG alone has insufficient accuracy for diagnosing or excluding PE 6
- ECG should be used as part of a comprehensive assessment including clinical prediction scores (Wells' rule or revised Geneva score) 1
- Continuous ECG monitoring is highly recommended in patients with suspected PE during transport/transfer 1
- ECG is also valuable for excluding other diagnoses such as acute myocardial infarction and pericardial disease 1
Clinical Application
- In patients with high-risk suspected PE (with shock or hypotension), the absence of echocardiographic signs of right ventricular overload virtually excludes PE as the cause of hemodynamic instability 2
- Recognition of PE-associated ECG patterns in patients with appropriate symptoms should prompt further diagnostic workup 7
- ECG findings of right ventricular strain in a breathless patient should raise suspicion for PE 4