What are the ECG (electrocardiogram) findings in a patient with suspected pulmonary embolism?

ECG Findings in Pulmonary Embolism

The ECG in pulmonary embolism is most commonly abnormal but nonspecific, with sinus tachycardia being the single most frequent finding (present in ~40% of cases), while signs of right ventricular strain—particularly T-wave inversions in leads V1-V4—indicate more severe disease and correlate with worse outcomes. 1, 2

Primary Role of ECG

The ECG cannot diagnose or exclude pulmonary embolism but serves two critical functions: 3

• Exclude alternative diagnoses such as acute myocardial infarction, pericarditis, and other cardiac emergencies that may present similarly 3, 2
• Assess disease severity through detection of right ventricular strain patterns, which correlate with pulmonary hypertension severity and RV dysfunction 1, 3

Most Common ECG Abnormalities

Nonspecific Findings (Mild-to-Moderate PE)

• Sinus tachycardia (heart rate >100 bpm): Present in approximately 40% of cases but entirely nonspecific; may be the only abnormality in milder cases 1, 2, 4
• Nonspecific ST-segment and T-wave changes: Common but occur in numerous other conditions 3, 4
• Atrial dysrhythmias (atrial fibrillation, flutter, tachycardia): Occur in 10-23.5% of patients 3, 2, 4

Signs of Right Ventricular Strain (Severe PE)

These findings indicate acute RV overload and are typically seen in more severe cases: 1

• T-wave inversions in right precordial leads (V1-V4): The most clinically significant finding with highest specificity (97.4%) for RV strain; suggests more severe PE 1, 2
• S1Q3T3 pattern: Classic finding present in many cases, though sensitivity and specificity are limited (LR+ 2.07) 1, 2, 5
• QR pattern in lead V1: Indicates acute RV overload but uncommon 1, 2
• Right bundle branch block (complete or incomplete): Occurs in 4.8-9% of cases, associated with RV strain 3, 2, 4
• S1S2S3 pattern: Part of acute cor pulmonale pattern 1

ECG Patterns During Hemodynamic Instability

In patients with high-risk PE presenting with shock or hypotension, three distinct ischemic ECG patterns emerge that reflect myocardial ischemia combined with RV strain: 6

• ST-elevation in lead aVR with ST-depression in leads I and V4-V6 6
• ST-elevation in leads V1-V3/V4 6
• ST-elevation in leads III and/or V1/V2 with ST-depression in leads V4/V5-V6 6

These ischemic patterns combined with S1Q3 and/or abnormal QRS morphology in V1 are significantly more common during hemodynamic instability (90%) than at baseline (5%) 6

Diagnostic Accuracy and Limitations

Critical caveat: The ECG has limited standalone diagnostic accuracy with sensitivity of only 50-60% and specificity of 80-90% 3. Recent evidence confirms that classical ECG findings have minimal diagnostic accuracy when used in isolation, with most traditional signs being noninformative 5. The positive predictive value of any individual ECG finding is less than 80% 3.

The ECG must be used in conjunction with clinical prediction scores (Wells or revised Geneva) rather than in isolation 1, 3, 2. The Pisa model specifically incorporates ECG findings of acute cor pulmonale (S1Q3T3, S1S2S3, negative T-waves in right precordial leads, transient RBBB, pseudoinfarction) with a coefficient of 1.96 and odds ratio of 7.11 for PE diagnosis 1

Clinical Algorithm for ECG Interpretation

When evaluating a patient with suspected PE: 3, 2

1. Obtain ECG immediately to exclude acute MI and pericardial disease 3, 2

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

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

4. If hemodynamic instability is present with RV strain on ECG, obtain urgent echocardiography to assess RV function and guide reperfusion therapy decisions 1, 6

5. Implement continuous ECG monitoring during transport/transfer for suspected PE, as the clinical status is usually not complicated by major ventricular arrhythmias even in critical cases 1, 3, 7

Prognostic Value

The presence of ≥1 classic RV strain sign is associated with higher adverse event rates 3. ECG abnormalities in PE are typically transient, reflecting acute RV overload/strain, with a trend toward regression of S1Q3 and septal patterns at 48 hours after admission, while T-wave inversions in anterior leads become more evident 7

Right-sided ECG derivations can increase diagnostic sensitivity, with 88.1% of PE patients showing at least one abnormality on right-sided ECG 3