What EKG (electrocardiogram) changes are associated with pulmonary embolism (PE)?

EKG Changes in Pulmonary Embolism

The EKG in pulmonary embolism is frequently abnormal but rarely diagnostic—its primary value lies in excluding alternative diagnoses (like acute MI or pericarditis) and identifying signs of right ventricular strain that correlate with disease severity, though 20-25% of PE patients have completely normal EKGs. 1

Most Common EKG Findings

Sinus Tachycardia

• Sinus tachycardia is the single most frequent abnormality, present in approximately 40% of PE cases, but it is entirely non-specific 1, 2
• In milder cases of PE, sinus tachycardia may be the only detectable abnormality 1

Right Ventricular Strain Pattern

• T wave inversions in the right precordial leads (V1-V4) are the most clinically significant finding, as they indicate RV strain and are typically found in more severe cases 1
• RV strain pattern has a specificity of 97.4% and occurs in 11.1% of all PE cases, but increases to 17.1% in patients with large clot burden 2
• This finding carries an odds ratio of 4.58 for PE diagnosis, and 7.55 specifically for large clot load 2

Classic PE Patterns (Less Common Than Traditionally Taught)

• S1Q3T3 pattern occurs in only 3-4% of PE cases, making it an infrequent and unreliable finding despite its classic association 2, 3
• QR pattern in lead V1 suggests acute RV overload but is uncommon 1
• Right axis deviation occurs in only 4.2% of cases 2
• P pulmonale is extremely rare (0.5% of cases) 2

Conduction Abnormalities

• Right bundle branch block (complete or incomplete) occurs in 4.8-9% of PE cases and is associated with RV strain 1, 2
• This finding is more common in severe PE but also occurs in controls, limiting its specificity 2

Atrial Arrhythmias

• Atrial fibrillation and other atrial dysrhythmias occur in 10-23.5% of PE patients 1, 2
• These arrhythmias may be associated with acute PE but lack diagnostic specificity 1

Critical Clinical Context

Diagnostic Limitations

• 20-25% of PE patients, including those with large clot burden, have completely normal EKGs 2
• The overall predictive value of any single EKG feature is less than 80%, meaning the EKG cannot rule in or rule out PE when used in isolation 4, 3
• Most EKG changes in PE are non-specific ST segment and T wave alterations that occur in numerous other conditions 5

Appropriate Use of EKG

• The primary role of EKG is to exclude alternative diagnoses such as acute myocardial infarction, pericarditis, and other cardiac conditions that may present similarly 5, 4
• EKG should be obtained immediately in suspected PE to rule out acute MI and pericardial disease 5
• EKG must be used in conjunction with clinical prediction scores (Wells or revised Geneva) rather than in isolation 1, 5

Severity Assessment

• EKG findings correlate with severity of pulmonary hypertension and RV dysfunction 5
• The presence of ≥1 classic RV strain sign is associated with higher adverse event rates 5
• In patients with hemodynamic instability, EKG may show ischemic patterns combined with RV strain, prompting urgent echocardiography 4

Rare but Important Presentations

ST Segment Elevation

• ST elevation is a rare EKG manifestation in PE but can occur, typically representing reciprocal changes from myocardial strain in the interventricular septum or RV lateral wall 6
• This presentation can mimic acute coronary syndrome and requires echocardiography for differentiation 6

Clinical Algorithm for EKG Interpretation in Suspected PE

1. First, use the EKG to exclude acute MI, pericarditis, and other cardiac emergencies 5, 4

2. Look specifically for RV strain pattern (T wave inversions in V1-V4), as this has the highest specificity (97.4%) and suggests more severe PE 2

3. Do not rely on classic findings like S1Q3T3 or right axis deviation, as these occur in <5% of cases 2, 3

4. A normal EKG does not exclude PE—proceed with clinical probability assessment and appropriate imaging 2

5. Integrate EKG findings with clinical prediction scores (Wells or revised Geneva) to determine pre-test probability 1, 5

6. If hemodynamic instability is present with RV strain on EKG, obtain urgent echocardiography to assess RV function 4

Common Pitfalls to Avoid

• Never use EKG findings alone to rule in or rule out PE—the sensitivity and specificity are insufficient for standalone diagnosis 4, 3
• Do not dismiss PE because of a normal EKG—up to 25% of PE patients have normal tracings 2
• Do not overweight the absence of S1Q3T3 pattern—this classic finding is present in <4% of cases 2, 3
• Do not confuse sinus tachycardia as diagnostic—it is the most common finding but entirely non-specific 1, 2
• Implement continuous EKG monitoring during transport/transfer for suspected PE, as arrhythmias may develop 5