From the Guidelines
S1Q3T3 is not specific for pulmonary embolism (PE), though it is associated with it. S1Q3T3 refers to an electrocardiogram (ECG) pattern consisting of an S wave in lead I, a Q wave in lead III, and an inverted T wave in lead III. While this pattern can be seen in patients with PE, particularly those with right heart strain, it has poor sensitivity (occurring in only about 10-25% of PE cases) and specificity (as it can appear in other conditions causing right heart strain) 1. The S1Q3T3 pattern was originally described as part of the McGinn-White pattern in acute cor pulmonale. Other conditions that can produce this pattern include right ventricular strain from any cause, such as chronic obstructive pulmonary disease, right ventricular infarction, or pneumothorax.
Key Points to Consider
- The S1Q3T3 pattern has poor sensitivity and specificity for PE, and therefore cannot be relied upon for diagnosis 1.
- More definitive testing such as CT pulmonary angiography or ventilation-perfusion scanning is required to confirm PE 1.
- Echocardiography may be useful in the diagnosis of PE, particularly in patients with hemodynamic instability, but it is not a definitive diagnostic tool 1.
- The presence of S1Q3T3 should raise suspicion for PE in the appropriate clinical context, but it is not a specific indicator of the condition 1.
Clinical Implications
- Clinicians should be aware of the limitations of the S1Q3T3 pattern in diagnosing PE and should not rely solely on this pattern for diagnosis.
- A comprehensive diagnostic approach, including clinical evaluation, laboratory tests, and imaging studies, is necessary to confirm the diagnosis of PE.
- The use of echocardiography and other diagnostic tools should be guided by the clinical context and the severity of the patient's symptoms.
From the Research
S1Q3T3 Pattern and Pulmonary Embolism
- The S1Q3T3 pattern on an electrocardiogram (ECG) is often associated with pulmonary embolism (PE) 2.
- However, this pattern is not specific to PE and can be seen in other conditions, such as pneumothorax 3.
- The S1Q3T3 pattern is one of several ECG findings that can be observed in patients with PE, including arrhythmias, nonspecific ST segment/T wave changes, and right bundle branch block 2.
- The diagnosis of PE should be based on a combination of clinical presentation, diagnostic algorithms, and imaging studies, rather than relying solely on ECG findings 4, 5.
- Other diagnostic modalities, such as CT pulmonary angiography, ventilation-perfusion scanning, and lower extremity ultrasound, are also important for diagnosing PE 4, 5, 6.