Can an electrocardiogram (ECG) be used to help rule out pulmonary embolism (PE)?

ECG Has Limited Value in Ruling Out Pulmonary Embolism

ECG alone cannot reliably rule out pulmonary embolism (PE) due to its low sensitivity, despite some findings being highly specific for PE. 1, 2

Diagnostic Value of ECG in Suspected PE

ECG Findings in PE

• The most common ECG finding in PE is sinus tachycardia (28% of cases) 3
• Specific ECG signs of right ventricular overload include:
  • S1Q3T3 pattern (sensitivity 11-50%, specificity >90%) 2, 3
  • T wave inversions in leads V1-V4 1, 2
  • QR pattern in V1 1
  • Right bundle branch block (complete or incomplete) 1, 2
  • Right axis deviation 3

Limitations of ECG for PE Diagnosis

• 20-25% of patients with PE, including those with large clot burden, have completely normal ECGs 3
• Most ECG findings have poor sensitivity for PE:
  • S1Q3T3 pattern occurs in only 3.7% of PE cases 3
  • Right axis deviation is found in only 4.2% of cases 3
  • P pulmonale is extremely rare (0.5%) 3

Best Diagnostic Value

• Right ventricular strain pattern has the highest specificity (97.4%) but poor sensitivity (11.1%) for PE 3
• This specificity increases to 97.4% with sensitivity of 17.1% in patients with large clot load 3
• The most recent research confirms that classical ECG findings have minimal standalone diagnostic accuracy 4

Clinical Implications

Role of ECG in PE Diagnostic Algorithm

• ECG should be considered a first-line test in suspected PE, but primarily to:
  1. Assess for alternative diagnoses 1
  2. Evaluate for signs of right ventricular strain that may indicate severity 1, 2
  3. Support clinical probability assessment as part of validated prediction rules 1

Risk Stratification Value

• Certain ECG abnormalities have prognostic rather than diagnostic value:
  • Atrial arrhythmias, complete right bundle branch block, peripheral low voltage, pseudoinfarction pattern, and ST segment changes are associated with higher 30-day mortality 5
  • Patients with at least one pathological ECG finding had significantly higher mortality (29% vs 11%) 5

Recommended Diagnostic Approach

1. Use validated clinical prediction scores (Wells or Geneva) to assess pre-test probability 1
2. Include ECG as part of the initial evaluation, but recognize its limitations 1, 2
3. Proceed with appropriate additional testing based on clinical probability:
   • D-dimer testing in low-probability patients 1
   • CT pulmonary angiography for definitive diagnosis 1, 2
   • Consider immediate echocardiography in hemodynamically unstable patients 1, 2

Pitfalls and Caveats

• Relying solely on ECG to rule out PE is dangerous due to its poor sensitivity 3, 4
• Some PE cases can mimic acute coronary syndrome on ECG with ST-segment elevation 6
• The most recent research (2025) confirms that even when combined, classical ECG findings "lack sufficient standalone accuracy" for ruling in or ruling out PE 4
• Point-of-care echocardiography is more valuable than ECG for evaluating suspected PE in unstable patients 1, 6

In conclusion, while certain ECG patterns may increase suspicion for PE when present, the absence of these findings cannot be used to rule out the diagnosis due to their poor sensitivity.