What ECG changes are associated with pulmonary embolism?

ECG Changes in Pulmonary Embolism

The ECG in pulmonary embolism is typically abnormal but non-specific, serving primarily to exclude alternative diagnoses rather than confirm PE, though certain patterns—particularly signs of right ventricular strain—correlate with disease severity and hemodynamic compromise. 1

Primary ECG Findings

Most Common Abnormalities

The most frequent ECG changes in acute PE are non-specific and include:

• Sinus tachycardia (heart rate >100 bpm) occurs in approximately 28.8% of PE patients and has a positive likelihood ratio of 1.8 2
• Non-specific ST segment and T wave changes are the most common findings, occurring in 41-42% of patients with documented PE 3
• T wave inversions in precordial leads V1-V4 suggest right ventricular overload and are more frequent in massive PE, with T wave inversions in V1-V3 having a positive likelihood ratio of 2.6 1, 2

Classic Signs of Right Ventricular Strain

Traditional manifestations of acute cor pulmonale occur in only 26% of patients, making them insensitive but relatively specific when present 3:

• S1Q3T3 pattern (S wave in lead I, Q wave and inverted T wave in lead III) occurs in 8.5% of PE patients versus 3.3% without PE, yielding a positive likelihood ratio of 3.7 2
• Right bundle branch block (complete or incomplete) is seen in 4.8% of cases and is associated with right ventricular strain 1, 2
• Right axis deviation occurs infrequently, in approximately 7% of patients 3
• P pulmonale (peaked P waves in leads II, III, aVF) is an uncommon finding 3

Atrial Dysrhythmias

• Atrial fibrillation and other atrial dysrhythmias occur in 10-23.5% of PE patients and are associated with the diagnosis, though they are more common in patients with preexisting cardiac disease 1, 2

ECG Patterns in Hemodynamically Unstable PE

During hemodynamic instability, ischemic ECG patterns combined with right ventricular strain are highly characteristic 4:

• ST-segment elevation in lead aVR with concomitant ST-segment depression in leads I and V4-V6 is a specific pattern for massive PE with hemodynamic compromise 4
• ST-segment elevation in leads V1-V3/V4 can occur during clinical deterioration 4
• ST-segment elevation in leads III and/or V1/V2 with ST-segment depression in leads V4/V5-V6 represents another ischemic pattern 4
• Ischemic ECG patterns combined with S1Q3 and/or abnormal QRS morphology in V1 occur in 90% of hemodynamically unstable PE patients versus only 5% at baseline 4

Diagnostic Limitations and Clinical Context

Sensitivity and Specificity

• The ECG has an overall sensitivity of 50-60% and specificity of 80-90% for PE diagnosis, making it inadequate as a standalone test 1
• Normal ECG occurs in 6% of massive PE and 23% of submassive PE, effectively ruling out the use of ECG to exclude the diagnosis 3
• A recent 2025 study confirmed that classical ECG findings have minimal diagnostic accuracy when used in isolation, with most traditional signs lacking sufficient standalone accuracy 5

Clinical Application

The ECG should be obtained immediately in suspected PE but used primarily to exclude acute myocardial infarction and pericardial disease as alternative diagnoses 1:

• ECG findings must be interpreted in conjunction with clinical prediction scores (Wells' criteria or revised Geneva score) rather than in isolation 1
• The presence of ≥1 classic right ventricular strain sign is associated with higher adverse event rates and helps with risk stratification 1
• Continuous ECG monitoring is recommended during transport/transfer of patients with suspected PE 1

Risk Stratification Value

ECG abnormalities correlate with severity of pulmonary hypertension and right ventricular dysfunction 1:

• Larger perfusion defects on imaging and higher pulmonary arterial mean pressures occur in patients with ECG abnormalities compared to those with normal ECGs 3
• T wave inversions in right precordial leads are more frequent in massive pulmonary thromboembolism and indicate acute right ventricular overload 1
• Most ECG abnormalities can resolve within 2 weeks, though T wave inversion tends to be the most persistent finding 3

Key Clinical Pitfalls

• Do not rely exclusively on traditional manifestations of acute cor pulmonale (S1Q3T3, right bundle branch block, P pulmonale, right axis deviation), as they occur in only 26% of cases 3
• Left axis deviation occurs as frequently as right axis deviation (7% of patients), challenging the assumption that right axis deviation is a reliable sign 3
• The ECG cannot diagnose or exclude PE definitively—it serves as one component of a structured diagnostic approach that includes clinical probability assessment, D-dimer testing, and definitive imaging 1