ECG —    JUNE 2021

Case presentation

EMS providers treat a 29-year-old female with syncope.  She has a history of lupus and recently returned to Los Angeles after a trip to Europe.  Her vital signs are BP 110/70 HR 148 RR 16.

Rate:                                                  ~150 bpm

Rhythm:                                          Sinus tachycardia (there are p-waves before each QRS (seen best in the lead II rhythm strip).

SST Segment Elevation >1mm
In 2 or more contiguous Leads?:
      No. Artifact is present with a wandering baseline that challenges interpretation in some leads.

Reciprocal Changes:                          N/A

This ECG demonstrates sinus tachycardia and a RBBB in a patient with a massive pulmonary embolism (PE).  Syncope can be a presenting sign for pulmonary embolism which occurs when emboli, typically from the lower extremities, propagate into the pulmonary circulation.  The clot burden in the pulmonary vasculature causes right sided strain on the heart and can lead to obstructive shock which can manifest as hypotension, poor perfusion (leading to syncope) and can progress to death.

There are many ECG changes associated with PE, with sinus tachycardia being the most common ECG finding (44% of patients)1.  Other findings include RBBB, right ventricular strain pattern, right axis deviation, right atrial enlargement (P pulmonale), S1Q3T3 pattern, clockwise rotation, and atrial tachydysrhythmia.

In this ECG, the patient is tachycardic and has a RBBB pattern as displayed by the rSR’ pattern (“rabbit ears”), in the precordial leads (V1-V3).

Right ventricular strain patterns can also be seen in patients with PE where there are simultaneous t-wave inversions in the inferior leads (II, III, aVF) and the right precordial leads (V1-V4) as demonstrated in the ECG below from another patient with PE.

Figure 2.  Right ventricular strain pattern.  T-wave inversions in the inferior (II, III, aVF) and precordial (V1 – V4) leads are underlined.

This third ECG demonstrates the S1Q3T3 pattern which is considered a “classic” pattern for PE though it is not sensitive nor specific to PE.  In a patient with a clinical story concerning for PE, this finding should further your suspicion and confirm the need for further evaluation at the hospital.

Figure 3. S1Q3T3 pattern with S wave in lead I, Q wave in lead III and t-wave inversion in lead III.

One retrospective study found that the right ventricular strain pattern in a patient suspected of PE was highly suggestive of the diagnosis because it was found to be significantly more common in patients that had PE compared to controls without PE.  Other ECG findings were thought to occur too infrequently to be of predictive value2.

The provider impression for this patient is Syncope / Near Syncope (SYNC).  She should be treated in accordance with TP-1233, Syncope / Near Syncope.  Initiate cardiac monitoring, obtain an ECG to evaluate for cardiac dysrhythmia given her tachycardia, and administer Normal Saline for orthostasis, signs of dehydration or fluid losses, or for poor perfusion.  Orthostatic vital signs provide little information and may result in harm and should not be performed.  Instead, determine orthostasis based on the patient’s symptoms.  Confirm that the patient has no trauma from her fall and transport.

This patient was transported to the Most Accessible Receiving (MAR) where a CT Angiogram of the chest demonstrated a massive pulmonary embolism.  She was started on anticoagulation medications and admitted to the hospital.


  1. Burns E, Buttner R. ECG Changes in Pulmonary Embolism. LITFL. https://litfl.com/ecg-changes-in-pulmonary-embolism/. Accessed June 7, 2021.
  2. Thomson, D et al. ECG in suspected pulmonary embolism.  Postgrad Med J 2019;95:12–17


Author:  Dr. Denise Whitfield, MD, MBA