Emergency Medical Services (EMS) Agency

ECG —    December 2019

Case presentation

Paramedics respond to a 39-year-old male with lightheadedness prior to nearly fainting.  He is currently asymptomatic.    

Vital signs are blood pressure 125/68, HR 88, RR 14, O2 saturation 99%.



Rate:                                                  ~60 bpm

Rhythm:                                            Sinus Rhythm – p waves are noted before every QR

SST Segment Elevation >1mm
In 2 or more contiguous Leads?:

Reciprocal Changes:                          N/A

Other Abnormalities:                          There is a shortened PR interval (<120 ms/3 small boxes) and a slurred                                                          upslope in the QRS complex.

This ECG pattern is consistent with Wolff-Parkinson-White syndrome which is a cardiac pre-excitation syndrome.  It is characterized by a shortened PR-interval as well as the upsloping QRS which is also known as a “delta wave”(arrow).  Pre-excitation refers to premature activation of the ventricles when electrical impulses bypass the AV node through an accessory pathway for electrical conduction.

Figure 1.  Electrical Conduction through an accessory pathway leads to early depolarization of the ventricle1.

Instead of the electrical impulse traveling through the AV node to depolarize the ventricles in the standard fashion, the ventricles are depolarized early (pre-excitation) through the accessory pathway.  This early depolarization is manifested on the ECG as a shortened PR interval (decreased time from atrial to ventricular depolarization) and an upsloping QRS.  Patients with pre-excitation syndromes are at risk for developing supraventricular tachycardias (SVT) when the accessory electrical conduction pathway leads to “re-entry” electrical conduction.

Re-entry Conduction Explained (video)


Figure 2.  ECG from a patient with SVT due to WPW syndrome.

If a patient experiences SVT transiently, as may have occurred in this case, the patient may present with a history of syncope, lightheadedness, palpitations, weakness, or other symptoms of a cardiac dysrhythmia.  At the time of evaluation, they may be in sinus rhythm, but ECG findings (shortened PR interveal and delta wave) can suggest that their transient symptoms may have been due to a cardiac dysrhythmia.

This patient presents with near syncope and should be managed in accordance with TP-1233, Syncope/Near Syncope.  He is currently in a normal sinus rhythm and asymptomatic so he requires no further treatment during transport, though a 12-lead ECG should be obtained.  He should remain on a cardiac monitor during transport since he likely experienced a cardiac dysrhythmia and is at risk for recurrence.


  1.  Image obtained from:  Pre-excitation syndromes.  LITFL. https://litfl.com/pre-excitation-syndromes-ecg-library/ accessed 11/6/2019.
  2. AVRT & AVNRT full open access video available at: https://commons.wikimedia.org/wiki/File:AVRT_%26_AVNRT.webm

Author:  Dr. Denise Whitfield, MD, MBA