Before starting this month’s case study, I would like to ask our readers two questions to get the gray matter going. These are standard questions I ask when running my courses:

 What is the normal “pacemaker” of the heart? What rate does it normally fire at?
 How would you be able to differentiate a supraventricular beat vs a ventricular beat?

The answers will be viewed at the bottom of this case.

With those questions asked, let’s move on to the case study which was presented in Dawn Altman’s site, ECG Guru. Thank you Dawn, it’s always a pleasure to feature your cases.
Case: A 60-year-old male is brought into the Emergency Department by EMS. He was involved in a MVC, sustained no apparent injuries but is severely intoxicated. He is hemodynamically stable with a heart rate of 170/minute.

Below is the first ECG taken at 1507hrs. What do you think this rhythm is?
a. SVT b. Sinus Tachycardia c. Atrial Flutter d. VT

Rate: 170/min and regular. Intervals: P wave – even though the rate is rapid, there is evidence of a P wave prior to each QRS complex. The PR interval is the same. QRS – narrow. Rhythm: Sinus tachycardia. Discussion: The release of stress hormones combined with his intoxication put this patient into a sinus tachycardia. Many may think that any narrow complex tachycardia over 150/min is SVT. SVT can be an atrial flutter, atrial tachycardia, re-entry tachycardia. Oftentimes, we label a narrow complex tachycardia SVT because we are unable to distinguish identifiable features to specifically label the rhythm: such as P waves or flutter waves. In this ECG, there is evidence of one P wave prior to each QRS complex, making this tachycardia likely sinus in origin. 

Below is the second ECG taken at 1543hrs. What is the rhythm?

Note that all complexes are still the same; however, the rate is now 110/min. The rate has gradually decreased from the initial ECG, which supports sinus tachycardia vs. the other SVT options that were discussed.
Conclusion: a narrow complex regular tachycardia less than 150/minute is sinus tachycardia. A narrow complex regular tachycardia over 150/minute may still be sinus tachycardia and may be challenging for the health care provider to properly interpret. Is it SVT or is it Sinus Tachycardia? This is a very important question to answer properly because treatment varies greatly between the two. When deciding SVT vs Sinus Tachycardia, look at the story and presentation. And, here is a great tip: A gradual increase or gradual decrease in the rate occurs in a sinus tachycardia. Whereas for SVT, the rates suddenly increases or suddenly terminates.

Thanks again to Dawn for this great reminder.

Answers to the 2 questions above:
1. The Sinus Node is the normal pacemaker of the heart and usually fires between 60-100/minute. The hallmark of a sinus rhythm is a P wave prior to each QRS complex. Sinus rhythm can be faster than 100/minute = sinus tachycardia or slower than 60/minte = sinus bradycardia. 2. Supraventricular tachycardia originates above the ventricles; therefore, the QRS duration should be normal (unless there is also a bundle branch block). Ventricular tachycardia is always a widecomplex regular rhythm.