Incidence of S1Q3T3 Pattern in Pulmonary Embolism
The S1Q3T3 pattern (prominent S wave in lead I, Q wave in lead III, and inverted T wave in lead III) is present in a minority of acute pulmonary embolism cases and is typically found only in more severe presentations with right ventricular strain.
Frequency and Clinical Context
The 2019 ESC Guidelines explicitly state that the S1Q3T3 pattern, along with other electrocardiographic changes indicative of RV strain (such as T wave inversion in V1-V4, QR pattern in V1, and right bundle branch block), are "usually found in more severe cases of PE" 1. The guidelines emphasize that in milder cases, the only ECG abnormality may be sinus tachycardia, which is present in 40% of patients 1.
Key Clinical Points
The S1Q3T3 Pattern Indicates:
- Right ventricular strain and acute cor pulmonale 1, 2
- More severe, hemodynamically significant PE rather than small peripheral emboli 1
- Part of a broader constellation of ECG findings suggesting RV dysfunction 1
Important Caveats:
The S1Q3T3 pattern is neither sensitive nor specific for PE:
- Low sensitivity: Most PE patients do NOT have this pattern, particularly those with mild or moderate disease 1
- Low specificity: The pattern can occur in other conditions causing acute cor pulmonale, including:
The Pisa clinical prediction model includes "acute cor pulmonale" (defined as one or more ECG abnormalities including S1Q3T3, S1S2S3, negative T waves in right precordial leads, transient RBBB, or pseudoinfarction) as a predictor with an odds ratio of 7.11 for PE 2. However, this encompasses multiple ECG patterns, not S1Q3T3 alone.
Clinical Implications
Do not rely on the presence or absence of S1Q3T3 for diagnostic decision-making in suspected PE. The pattern's presence suggests more severe disease with RV involvement, but its absence does not exclude PE 1. When present, it should prompt consideration of hemodynamic assessment and risk stratification for potential advanced therapies 6.
The newer T1T2T3/III pattern (T wave inversion maximal in V1-V3 and lead III) may be a more descriptive way to recognize RV involvement in PE, though this requires further validation 7.