How often does pulmonary embolism (PE) occur without right ventricular (RV) strain on the electrocardiogram (ECG)?

Frequency of Pulmonary Embolism Without RV Strain on ECG

The majority of pulmonary embolism cases occur without ECG evidence of right ventricular strain—approximately 75-80% of PE patients have either normal ECGs or non-specific findings, with classic RV strain patterns appearing in only 11-17% of cases, primarily in more severe presentations. 1, 2

ECG Findings in Confirmed PE

Normal ECG Frequency

• 20-25% of patients with confirmed PE, including those with large clot burden, have completely normal ECGs 2
• This underscores that ECG cannot be used to exclude PE, even in hemodynamically significant cases 2

Classic RV Strain Pattern Prevalence

• RV strain pattern (T wave inversions in V1-V4) occurs in only 11.1% of all PE patients 2
• In patients with large clot load, this increases to 17.1%, but still represents a minority 2
• The European Society of Cardiology guidelines note that ECG signs of RV strain are "generally associated with the more severe forms of PE" 1

Other ECG Abnormalities

• Sinus tachycardia is the most common finding at 26-40%, but is entirely non-specific 1, 3, 2
• The classic S1Q3T3 pattern appears in only 3.7% of PE cases 2
• Right bundle branch block occurs in 4.8-9% 3, 2
• P pulmonale is rare at 0.5% 2
• Right axis deviation occurs in only 4.2% 2

Clinical Implications

Diagnostic Value

• ECG has limited sensitivity for PE detection but high specificity when RV strain is present (97.4%) 2
• The primary role of ECG is to exclude alternative diagnoses such as acute MI or pericarditis, not to diagnose PE 3, 2
• Individual ECG signs and symptoms are neither sensitive nor specific for PE 1

Prognostic Significance

• When RV strain patterns are present on ECG, they indicate more severe PE with greater hemodynamic compromise 1, 3
• ECG evidence of RV strain (odds ratio 1.9) is associated with increased adverse events, but is less predictive than echocardiographic or CT findings 4
• The presence of ≥1 classic RV strain sign correlates with higher adverse event rates 3

Risk Stratification Context

• Echocardiographic RV dysfunction is found in at least 25% of PE patients, which is substantially higher than the 11-17% showing ECG strain patterns 1, 5
• This discrepancy indicates that ECG is insensitive for detecting RV dysfunction compared to imaging modalities 1
• Multimodality assessment (ECG, CT, echocardiography, and troponin) provides superior risk stratification, with elevated risk only when RV strain is present on all modalities 4

Key Clinical Pitfalls

Common Misconceptions

• Do not rely on ECG to rule out PE—up to 25% of patients with confirmed PE, including large clot burden, have normal ECGs 2
• Absence of RV strain on ECG does not indicate low-risk PE, as echocardiographic RV dysfunction may still be present 1
• Sinus tachycardia, while common, is non-specific and occurs with similar frequency in patients without PE 2

Appropriate ECG Utilization

• Use ECG primarily to exclude acute MI, pericarditis, and other cardiac emergencies in the differential diagnosis 3, 2
• Integrate ECG findings with clinical prediction scores (Wells or revised Geneva) rather than interpreting in isolation 3
• When RV strain pattern is present on ECG in a breathless patient, this is highly suggestive of PE and warrants urgent imaging 2
• In hemodynamically unstable patients with ECG evidence of RV strain, obtain urgent echocardiography to assess RV function 3