What ECG findings are commonly seen in an adult with acute pulmonary embolism?

ECG Findings in Pulmonary Embolism

Sinus tachycardia is the most common ECG abnormality in pulmonary embolism, occurring in approximately 40% of cases, but the ECG is primarily used to exclude alternative diagnoses like acute myocardial infarction rather than to diagnose PE itself. 1, 2

Most Frequent ECG Abnormalities

Sinus Tachycardia

• Present in 26-40% of PE cases, making it the single most frequent finding 1, 2
• Entirely non-specific and may be the only detectable abnormality in milder cases 1
• Remains independently associated with PE on multivariable analysis 3

T Wave Inversions in Right Precordial Leads (V1-V4)

• The most clinically significant finding with highest specificity (97.4%) for right ventricular strain 1, 4
• Indicates more severe PE with greater hemodynamic compromise 1, 2
• Present in approximately 11-17% of PE patients 1, 4
• More frequent in massive pulmonary embolism 5

Normal ECG

• Occurs in 20-25% of patients with confirmed PE, including those with large clot burden 4
• In massive embolism, only 6% have normal ECG; in submassive embolism, 23% have normal ECG 6

Less Common but Specific Findings

S1Q3T3 Pattern

• Classic finding but present in only 3.7-4% of cases 4
• When present, yields a positive likelihood ratio of 2.07, modestly increasing post-test probability 3
• More common in severe PE but lacks sensitivity as a standalone finding 1, 4

Right Bundle Branch Block (Complete or Incomplete)

• Occurs in 4.8-9% of PE cases 1, 2
• Associated with right ventricular strain 1

Atrial Dysrhythmias

• Atrial fibrillation and other atrial arrhythmias occur in 10-23.5% of PE patients 1, 2
• Atrial flutter and atrial fibrillation appear more typical in patients with preexisting cardiac disease 6

QR Pattern in Lead V1

• Suggests acute right ventricular overload but is uncommon 1

Right Axis Deviation

• Infrequent finding, present in only 4.2% of cases 4

P Pulmonale

• Rare, occurring in only 0.5% of cases 4

Clinical Role and Limitations

Primary Diagnostic Purpose

• The ECG cannot diagnose or exclude PE but serves primarily to exclude alternative life-threatening diagnoses such as acute myocardial infarction and pericarditis 2, 7
• Should be obtained immediately in all patients with suspected PE 1, 2

Integration with Clinical Assessment

• ECG findings must be used in conjunction with validated clinical prediction scores (Wells or revised Geneva) rather than in isolation 1, 2
• Individual ECG signs are neither sensitive nor specific for PE 1
• Classical ECG findings lack sufficient standalone accuracy to rule in or rule out PE 3

Prognostic Value

• ECG findings correlate with severity of pulmonary hypertension and right ventricular dysfunction 1, 2
• Presence of ≥1 classic RV strain sign is associated with higher adverse event rates 1, 2
• ECG abnormalities often change over time with worsening or resolution of the embolic event 5

Clinical Algorithm for ECG Interpretation

Step 1: Exclude Cardiac Emergencies

• First use the ECG to rule out acute MI, pericarditis, and other cardiac conditions that may present similarly 1, 2

Step 2: Assess for RV Strain

• Look specifically for T wave inversions in V1-V4, as this has the highest specificity and suggests more severe PE 1, 4
• Liberal RV strain pattern (inverted/flattened T-waves in ≥2 inferior + ≥2 anterior leads) yields positive likelihood ratio of 4.75 3

Step 3: Integrate with Clinical Probability

• Combine ECG findings with Wells or revised Geneva scores to determine pre-test probability 1, 2
• Never use ECG findings in isolation for diagnostic decisions 2, 3

Step 4: Hemodynamic Assessment

• If hemodynamic instability is present with RV strain on ECG, obtain urgent echocardiography to assess RV function and guide reperfusion therapy decisions 1, 2
• Implement continuous ECG monitoring during transport/transfer for suspected PE, as arrhythmias may develop 1, 2

Important Caveats

• The most common ECG abnormalities in PE are nonspecific ST segment/T wave changes (42%) and RST segment abnormalities (41%) 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
• Left axis deviation occurs as frequently as right axis deviation (7% of cases) 6
• ECG abnormalities are more common in patients with larger clot burden and higher pulmonary arterial pressures 6