56 year old female CC: Short of Breath – Conclusion

This is the conclusion to 56 year old female CC: Short of Breath. Be sure to check out the first post for the full story!

When we left our crew they were just getting ready to leave the parking garage with a 56 year old female who was short of breath and dizzy after mild exertion. They had obtained IV access, a 3-Lead, and a 12-Lead ECG.

Let's review our patient's 3-Lead:

Breathless View - Initial Rhythm

This is a regular, narrow complex tachycardia at 120 bpm with what appear to be sinus P-waves best appreciated in leads II and aVF. Given our patient's tachypnea and dizziness, her tachycardia is likely a compensatory mechanism.

It is important that we find out what her body is compensating for!

Perhaps her 12-Lead can clue us in on her malady?

Breathless View - 12-Lead

Her 12-Lead shows a sinus tachycardia with an incomplete right bundle branch block (the QRS duration is 100ms) and some diffuse ST/T-wave changes including some T-wave inversion and ST-depression.

These changes, when taken in the context of our patient's breathlessness strongly suggest the patient is suffering from a pulmonary embolism! Given her chest pain, we should also consider acute coronary syndrome as her problems as well.

However, as Dr. Smith notes, T-wave inversions in Lead III and the anterior precordials are far more common in PE than in acute coronary syndrome.

I've marked up the 12-Lead to highlight some of the key features, including the S1Q3T3 pattern, incomplete right bundle branch block, and anterior T-wave inversions:

Breathless View - 12-Lead - Marked Up

The patient's condition remained stable throughout the transport and the crew elected to continue oxygen therapy and administer a fluid bolus.

While the surface ECG is not sensitive nor specific for pulmonary embolism, it often times can provide clues as to the diagnosis. Here is a list of changes seen in Pulmonary Embolism on the ECG adapted from Chou's Electrocardiography in Clinical Practice ordered by their prevalence:

  1. Sinus tachycardia (73%)
  2. Prominent S-wave in Lead I (73%)
  3. "Clockwise rotation" / late precordial transition (56%)
  4. T-wave inversion in 2+ precordials (50%)
  5. Incomplete or complete RBBB (20-68%)
  6. P-pulmonale (28-33%)
  7. Right axis deviation (23-30%)
  8. No significant findings (20-24%)
  9. S1Q3T3 (12-25%)
  10. Supraventricular arrhythmias (12%)

During her stay in the emergency department it was confirmed that she was experiencing multiple small pulmonary emboli, and given their size they elected to start her on low molecular weight heparin and observe the patient overnight.


  • majed says:

    what is meant by S1Q3T3

  • Christopher says:


    S1Q3T3 means:

    – There is an S-wave in Lead I
    – There is a Q-wave in Lead III
    – There is an inverted T-wave in Lead III

  • anonymous says:

    Thank you for this clarification. When we say S1Q3T3 is it inferred that the T-wave is inverted since the Q-wave is already occupying lead III or is it just uncommon to find the T-wave not inverted in lead three?

    • Christopher Watford says:

      You can find inverted T-waves in III normally. Just in this specific instance it is not simply due to the axis, rather ischemia. Inferior and anterior T-wave inversions are also fairly sensitive for pulmonary embolisms.

Leave a Reply

Your email address will not be published. Required fields are marked *