What are the characteristic EKG (electrocardiogram) findings in patients with pulmonary embolism?

Characteristic ECG Findings in Pulmonary Embolism

The most common ECG findings in pulmonary embolism include sinus tachycardia, non-specific ST-segment and T-wave changes, with more severe cases showing the classic S1Q3T3 pattern, right bundle branch block, and T-wave inversions in leads V1-V4. 1

Common ECG Findings in Pulmonary Embolism

Most Frequent Findings

• Sinus tachycardia - the most common ECG abnormality in PE 1
• Non-specific ST-segment and T-wave changes 2, 3
• T-wave inversions in leads V1-V4 - indicating right ventricular overload 1

Classic Signs of Right Ventricular Strain

• S1Q3T3 pattern - deep S wave in lead I, Q wave in lead III, and inverted T wave in lead III 1, 3
• Right bundle branch block (complete or incomplete) 2, 1
• Right axis deviation 3

Findings in Massive/Submassive PE

• QR pattern in lead V1 - associated with more severe cases 1
• Right ventricular strain pattern - more pronounced in hemodynamically significant PE 2
• 60/60 sign on echocardiography - acceleration time of pulmonary ejection <60 ms with midsystolic notch and mildly elevated peak systolic gradient at the tricuspid valve 2, 1

Diagnostic Value of ECG Findings

Sensitivity and Specificity

• ECG abnormalities in PE are common but usually non-specific 2
• The presence of ≥1 of the 3 classic signs of RV strain (S1Q3T3, RBBB, or T-wave inversions in V1-V4) is associated with higher risk of adverse events 4
• The number of RV strain signs present correlates with worse outcomes (odds ratio 1.35 per sign) 4

Limitations

• ECG may be entirely normal in patients with PE 3
• Individual ECG signs have variable interrater reliability (κ 0.40-0.95) 4
• ECG alone has limited value in diagnosis due to low sensitivity and specificity 5

ECG Patterns During Hemodynamic Instability

In hemodynamically unstable PE, three ischemic ECG patterns may emerge 6:

1. ST-segment elevation in lead aVR with concomitant ST-segment depression in leads I and V4-V6
2. ST-segment elevation in leads V1-V3/V4
3. ST-segment elevation in leads III and/or V1/V2 with concomitant ST-segment depression in leads V4/V5-V6

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

Clinical Application

When to Suspect PE Based on ECG

• Unexplained sinus tachycardia
• New-onset atrial arrhythmias (atrial fibrillation, atrial flutter, atrial tachycardia) 3
• Sudden appearance of right ventricular strain pattern, especially in patients with risk factors for venous thromboembolism

Important Caveats

• The absence of ECG signs of RV overload practically excludes massive PE as the cause of hemodynamic instability 1
• Similar ECG patterns can be seen in other conditions causing right heart strain, such as COPD exacerbation or right ventricular infarction 1
• ECG findings suggestive of PE may be mistaken for acute coronary syndrome, especially when ST elevations are present 5

Role in Diagnostic Algorithm

• ECG should be performed in all patients with suspected PE but cannot confirm or exclude the diagnosis 2
• When ECG shows signs of RV strain in a patient with shock or hypotension, immediate echocardiography should be performed 2, 1
• Definitive diagnosis requires imaging studies like CT pulmonary angiography 1
• In patients with suspected high-risk PE where CT is not immediately available, echocardiographic signs of RV dysfunction can support the diagnosis 2

Remember that while ECG findings can raise suspicion for PE and provide prognostic information, they should not delay appropriate diagnostic imaging or treatment when PE is strongly suspected clinically.