From the Guidelines
The typical ECG signs of pulmonary embolism include sinus tachycardia, inversion of T waves in leads V1–V4, QR pattern in V1, S1Q3 pattern, and incomplete or complete right bundle-branch block, with sinus tachycardia or atrial fibrillation being the most frequent findings. These ECG changes reflect right heart strain and pressure overload resulting from pulmonary vascular obstruction, as noted in the European Heart Journal study 1. The sudden increase in pulmonary vascular resistance leads to right ventricular dilation and dysfunction, causing these characteristic electrical changes.
Key ECG Findings
- Sinus tachycardia
- Inversion of T waves in leads V1–V4
- QR pattern in V1
- S1Q3 pattern
- Incomplete or complete right bundle-branch block
- Atrial fibrillation
It's essential to note that ECG findings may be entirely normal in some pulmonary embolism cases, so a normal ECG does not rule out the diagnosis. ECG should be used in conjunction with clinical assessment, D-dimer testing, and imaging studies like CT pulmonary angiography for accurate diagnosis of pulmonary embolism, as recommended by the Acute Cardiovascular Care Association 1. The use of clinical prediction scores and point of care echocardiography may also be considered in the pre-hospital setting for evaluation of the severity of pulmonary embolism 1.
From the Research
Typical ECG Signs of Pulmonary Embolism
The typical ECG signs of pulmonary embolism include:
- S1Q3T3 pattern 2, 3, 4, 5
- Nonsinus rhythm 2
- Inverted T waves in V1 to V2, V1 to V3, and V1 to V4 2, 6
- Incomplete right bundle branch block 2, 5
- Tachycardia (pulse rate >100 beats/min) 2, 5
- ST elevation in lead aVR 5
- Atrial fibrillation 5
ECG Findings and Pulmonary Embolism Severity
ECG findings can aid in determining the severity of pulmonary embolism. Studies have shown that certain ECG signs, such as T-wave inversion in precordial leads, are correlated with the severity of pulmonary embolism 6. The Daniel score, which includes heart rate > 100 beats/min, presence of the S1Q3T3 pattern, incomplete and complete right bundle branch block, and T-wave inversion in leads V1-V4, plus ST elevation in lead aVR and atrial fibrillation, can predict circulatory shock from pulmonary embolism 5.
Clinical Implications
Early recognition of ECG signs of pulmonary embolism can alter the estimated pretest probability of pulmonary embolism and prompt more aggressive treatment before hemodynamic instability ensues 2. The ECG can also help distinguish between pulmonary embolism and myocardial infarction, allowing for effective treatment selection 4.