How helpful is S1Q3T3 for diagnosing PE?

ECG: NSR @ 90 bpm, normal axis, S1Q3T3 pattern

BACKGROUND

• S1Q3T3 was first described in 1935 in JAMA by Drs. McGinn & White
• They report a case series of 9 patients with pulmonary embolism (PE) and “acute cor pulmonale” and the ECG findings in 7 of those patients.
• 5 of these ECGs demonstrated a constellation of findings that we now term the “S1Q3T3” pattern:
  • (1) prominent S wave and low origin of the T wave in lead 1; ST segment starting slightly below the baseline
  • (2) the gradual staircase ascent of the ST interval from the S wave to the T wave in lead 2
  • (3) the Q wave and definite late inversion of the T wave in lead 3
• They concluded: “Whether or not these electrocardiographic manifestations are pathognomonic for pulmonary embolism, the consistency with which they have been demonstrated in tracings taken soon after acute attacks of extensive pulmonary embolism has been striking.”

PATHOPHYSIOLOGY

• McGinn and White thought that these ECG findings would help clinicians differentiate between a myocardial infarction and a pulmonary embolism. They attributed the ECG changes to the acute occlusion of the pulmonary artery causing “dilatation and partial failure of the chambers of the right side of the heart.”
• S1Q3T3 can be found in other states of acute cor pulmonale or right heart strain:

• • COPD and/or asthma exacerbation
  • Pneumothorax
  • Severe pneumonia
  • Upper airway obstruction

UTILITY OF S1Q3T3?

• The incidence of S1Q3T3 in patients diagnosed with PE varies from as low as 10% to as high as 50%.
• Thus, S1Q3T3 should not be thought of as being pathognomonic for acute PE

• S1Q3T3 and other ECG findings become useful when they are applied together rather than separately – for instance, in the Daniel Score:
  • Maximum score of 21
  • Correlates with severity of pulmonary hypertension
  • Score of > or = 10: specificity of 97.7% and sensitivity of 23.5%

• Shopp et al published a systematic review and meta-analysis of 10 studies (3,007 patients with acute PE) to determine the prognostic value of certain ECG findings that would help predict patients at risk for circulatory shock and death.
• The ECG findings they reviewed included components of the Daniel score as well as ST elevation in aVR and atrial fibrillation.
• In this meta-analysis, the most common ECG findings among patients with PE were tachycardia (38%) and T wave inversion in V1 (38%).
• Despite it’s lower incidence, Shopp et al found that S1Q3T3 was one of six ECG findings that predicted hemodynamic collapse and death within 30 days of acute PE:

1. Tachycardia
2. S1Q3T3
3. Complete RBBB
4. Inverted T waves in V1-V4
5. ST elevation in aVR
6. Atrial Fibrillation

• A constellation of these ECG findings or a Daniel score >5 can be used to risk stratify patients with RV failure secondary to PE who are at a higher risk for hemodynamic collapse.

TAKE HOME POINTS

• The ECG in PE is often abnormal, but these findings are neither sensitive nor specific.
• S1Q3T3 on an ECG does not automatically equal PE! It can be seen in other pathologies causing right heart strain such as pneumothorax, pneumonia, and bronchospasm.
• S1Q3T3 is more helpful when used in the appropriate clinical context with other ECG findings to identify patients at risk for shock.

Back to our patient…

• He had a work-up including D-dimer, which was negative, and he was happily discharged home.

Sources:

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