In a patient being evaluated for suspected pulmonary embolism, should an electrocardiogram be obtained and what ECG findings indicate right‑ventricular strain suggestive of PE?

ECG in Suspected Pulmonary Embolism

An electrocardiogram should be obtained in all patients with suspected pulmonary embolism, primarily to exclude alternative diagnoses such as acute myocardial infarction and pericarditis, and secondarily to assess disease severity through detection of right ventricular strain patterns. 1, 2

Primary Role of ECG

• The ECG cannot definitively diagnose or exclude PE, but serves as an essential screening tool in the diagnostic algorithm 2, 3
• Chest radiography, ECG, and arterial blood gas measurements should be performed in all patients with suspected PE 1
• The main utility is excluding other life-threatening conditions that present similarly, particularly acute coronary syndromes and pericardial disease 2, 3, 4

Integration with Clinical Assessment

• ECG findings must be used in conjunction with validated clinical prediction scores (Wells or revised Geneva) rather than in isolation to determine pre-test probability 1, 2, 3
• The ECG should be viewed as one component of a structured diagnostic approach that includes clinical probability assessment, D-dimer testing, and definitive imaging 2
• Continuous ECG monitoring is highly recommended during patient transport/transfer for suspected PE, particularly in hemodynamically unstable patients 1, 2, 3

ECG Findings Indicating Right Ventricular Strain

Most Clinically Significant Findings

• T wave inversions in right precordial leads (V1-V4) are the most specific finding (97.4% specificity) for RV strain and indicate more severe PE 2, 3, 5
• These inversions suggest right ventricular overload and are more frequent in massive pulmonary embolism 2, 4

Classic RV Strain Pattern (S1Q3T3)

• The S1Q3T3 pattern (prominent S wave in lead I, Q wave in lead III, inverted T wave in lead III) is a classic but insensitive finding 2, 3
• When present, it carries important prognostic implications and correlates with more severe PE 2
• This pattern is part of the broader acute cor pulmonale ECG pattern 2

Additional RV Strain Indicators

• Right bundle branch block (complete or incomplete) occurs in 4.8-9% of PE cases and is associated with RV strain 2, 3
• QR pattern in lead V1 indicates acute right ventricular overload but is uncommon 2, 3
• Right axis deviation of the QRS complex 5, 6
• P pulmonale pattern 6

Common but Non-Specific Findings

• Sinus tachycardia is the most frequent abnormality (present in approximately 40% of cases) but is entirely non-specific 2, 3, 4
• In milder cases of PE, sinus tachycardia may be the only detectable abnormality 3
• Atrial dysrhythmias including atrial fibrillation occur in 10-23.5% of patients 2, 3
• Nonspecific ST segment and T wave changes occur in 41-42% of patients 6

Diagnostic Accuracy and Limitations

• The ECG has limited diagnostic accuracy with sensitivity of 50-60% and specificity of 80-90% 2
• The ECG is abnormal in over two-thirds of patients with PE, but may be entirely normal in up to 23% of patients with submassive PE 4, 6
• Traditional manifestations of acute cor pulmonale (S1Q3T3, right bundle branch block, P pulmonale, or right axis deviation) occur in only 26% of patients 6
• Individual ECG signs are neither sensitive nor specific for PE 3

Clinical Algorithm for ECG Interpretation

1. First, exclude acute MI, pericarditis, and other cardiac emergencies using the ECG 2, 3

2. Look specifically for RV strain patterns, particularly T wave inversions in V1-V4, as this has the highest specificity and suggests more severe PE 2, 3

3. Integrate ECG findings with clinical prediction scores (Wells or revised Geneva) to determine pre-test probability 1, 2, 3

4. If hemodynamic instability is present with RV strain on ECG, obtain urgent echocardiography to assess RV function and guide reperfusion therapy decisions 1, 2

5. The presence of ≥1 classic RV strain sign is associated with higher adverse event rates and worse short-term prognosis 2, 3

Prognostic Value

• ECG findings correlate with severity of pulmonary hypertension and RV dysfunction 1, 2, 3
• The number of ECG abnormalities correlates with the probability of pulmonary trunk/main pulmonary artery embolism 7
• Serial ECG evaluation should be performed as changes and resolution of abnormalities may have prognostic implications 4
• ECG abnormalities often change over time with worsening or resolution of the embolic event 4

Common Pitfalls to Avoid

• Do not rely on ECG alone to diagnose or exclude PE - it must be part of a comprehensive diagnostic strategy 2, 3
• Do not assume a normal ECG excludes PE - up to 23% of patients with submassive PE may have normal ECGs 4, 6
• Do not use sinus tachycardia as a specific indicator of PE - it is the most common finding but lacks specificity 3, 4
• Consider pericarditis in every patient in whom fibrinolysis is considered for presumed STEMI, as ECG changes may mimic acute coronary syndrome 1