S1Q3T3 EKG Classic Pattern in Pulmonary Embolism (Example).

It's not every day you get to see a classic EKG finding for a very common medical condition. Most doctors have heard of S1Q3T3. That's the classic EKG pattern used by attendings to pimp medical students all across this country.  It is also the ECG pattern known to residents and  hospitalists all across this country as the boards type question for evidence of a pulmonary embolism. What does S1Q3T3 mean? It is the triad of an S wave in lead one (the first down slope after the first upslope in the QRS complex) a Q wave in lead 3 (first down slope in lead 3) and T3 (or T-wave inversion in lead 3). The S1Q3T3 was first described In a 1935 JAMA paper  by McGinn and White. Some things never change  despite all our great technology these days.

This finding is indicative of right sided heart strain (acute cor pulmonale) which can often be seen in patients with a pulmonary embolism.  If a young female with shortness of breath and this EKG presents on your boards, the answer is probably pulmonary embolism.  In this case, the patient had all the other signs and symptoms of right heart strain and pulmonary embolism (dyspnea on exertion, elevated d-dimer, tachycardia, enlarged right ventricle on echo,  elevated pulmonary pressures,  elevated troponin due to right heart strain and of course large central pulmonary emboli on CT scan).

Interestingly, despite all these pronounced findings of large central clot burden, this patient did not have hypoxemia. Their oxygen saturation was 97% on room air.    The human body has the amazing ability to counteract extreme physiological circumstances. That's what makes the diagnosis of pulmonary embolism so elusive at times.  If you aren't thinking about it in your differential diagnosis, you won't be able to treat it.   


Another common ECG  finding in pulmonary embolism is a transient right bundle branch block.  This suggests acute cor pulmonale as electric conduction traverses down the right bundle.    Also consider acute pulmonary embolism in patients with T-wave in versions across the anterior leads.  And of course, tachycardia including both sinus tachycardia and new onset atrial fibrillation should both raise the suspicion of pulmonary embolism. 

Pulmonary emboli can be deadly.  Always keep PE in the back of your differential diagnosis in patients with unexplained syncope, unexplained pleural effusions!  It's not every day when clinical practice presents such a classic presentation for EKG findings in pulmonary embolism.  It makes all those years of medical school education worth while.  

And then there is the case of syncope.  Chief Complaint:  I passed out.  This patient was a young female on birth control pills.  A V/Q scan confirmed the presence of bilateral pulmonary emboli.  Her EKG also showed the classic S1Q3T3 changes one can see with pulmonary emboli

S1Q3T3-EKG-Findings-Pulmonary-Embolism

I have grouped other great EKG findings here to enhance your educational experience here at The Happy Hospitalist.  In addition, you can find the two greatest books on learning how to read EKGs from Amazon by going here and here.


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