Emergency Medical Services (EMS) Agency

ECG of The Month — July 2020

Paramedics respond to an 11-year-old male with a history of asthma that complains of shortness of breath and a “fast heart beat”.

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ECG obtained from LITFL.com

Rate:                                                 ~ 150 bpm

Rhythm:                                            possible p-waves, most prominent in leads I, II, III, aVF, appearing like a
“camel hump”

ST Segment Elevation >1mm
In 2 or more contiguous
Leads?:
                                             No

Reciprocal Changes:                        N/A

This ECG demonstrates sinus tachycardia.  Sinus tachycardia is a common rhythm that is defined as a rhythm that originates from the SA node but with a rate > 100 bpm in adults or above the normal range in children.  When a patient’s heart rate is fast, it may be difficult to discern p-waves on the ECG to identify the rhythm as sinus and sinus tachycardia may be mistaken for supraventricular tachycardia (SVT).  This can be a common error when evaluating children with tachycardia.

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Figure 1. This is an example of sinus tachycardia where the p-wave is “buried” with the t-wave resulting in a “camel hump” appearance. 

A few criteria can be used to distinguish sinus tachycardia from SVT:

Sinus Tachycardia

SVT

Heart Rate (bpm)

Infants: < 220

Children: < 180

Infants, > 220

Children, > 180

R-R interval

Variable

Fixed

P-waves

Present, upright

Absent or may be hidden in the QRS or ST segment

Patient History

Underlying reason (fever, dehydration, volume loss, medication, stress response)

Sudden onset

 

To distinguish sinus tachycardia from SVT one can first assess the heart rate, which is typically much faster in SVT.  In addition, the beat-to-beat heart rate can change with sinus tachycardia whereas it is fixed in SVT.  This can be seen by evaluating the R-R interval, which can be variable with sinus tachycardia but fixed with SVT.  In addition, p-waves can be discerned in sinus tachycardia, whereas there may be no p-waves or a “retrograde” p-wave that is hidden in the QRS complex or ST segment in SVT.  Lastly, the patient’s history can be very helpful as to whether they are in sinus tachycardia or SVT.  Sinus tachycardia is a normal response to stress and may be present with conditions like fever, dehydration, volume loss or administration of medications that stimulate the heart (e.g. albuterol).

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Figure 2. The R-R interval is measured between the top of sequential R waves.  In SVT, this distance is fixed throughout the ECG.

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Figure 3. A “retrograde” p-wave is present in this SVT ECG and appears with the QRS complex.  A typical p-wave prior to the QRS is not present.

This patient presented with shortness of breath.  On assessment he had wheezing consistent with his asthma and Provider Impression Respiratory Distress / Bronchospasm.  The patient should be managed in accordance with TP-1237P – Respiratory Distress.  The patient took two doses of albuterol with his metered-dose-inhaler prior to arrival which may explain the sensation of his heart racing.  To evaluate for cardiac dysrhythmia, an ECG was obtained.  Base contact should be obtained concurrently in accordance with TP-1237P – Respiratory Distress.  Since sinus tachycardia is confirmed on the ECG, and the patient’s respiratory distress improves after additional albuterol, he is transported to the MAR for further management.  The key in this case is distinguishing sinus tachycardia from SVT so that the patient is treated appropriately and does not receive adenosine when not indicated.

References

1 https://litfl.com/sinus-tachycardia-ecg-library/

2 Manole MD, Saladino RA.  Emergency Department management of the pediatric patient with supraventricular tachycardia.  Pediatric Emergency Care. 2007; 23(3): 176-185.

 

Author:  Denise Whitfield, MD, MBA