There is no abrupt change in rate in sinus tachycardia

No clinical history.

Image 1

What is the rhythm? What are your differential?

This is a narrow complex tachycardia at a rate of about 150 bpm. There is an ABRUPT/SUDDEN change in the rate towards the end of the strip which is from about 150 bpm to 83 bpm. This abrupt change is not seen in sinus tachycardia. Sinus tachycardia will show a gradual decrease in rate.

The differential diagnoses are: 

1. Inappropriate sinus tachycardia (IST)

2. Atrial reentry tachycardia (ART)near the sinus node

3. Sinoatrial reentry tachycardia (SART/SNRT)

IST is non-paroxysmal, elevated resting rate and gradual (excessive 

acceleration as reaction to mild exercise.However, as we  see in the strip, this is paroxysmal. Thus, IST is ruled-out.

ART - paroxysmal and difficult to differentiate from SART.

Sinus node reentry tachycardia is defined as a reentrant tachycardia involving the sinus node and perinodal tissue.  It is possible that SNRT may represent a high cristal atrial tachycardia (AT) originating near the sinus node . The features of SART/SNRT are:

The features of SART/SNRT are:

1. Abrupt onset/termination (may have gradual slowing)

2. Similar p-wave morphology compared to regular sinus beats (or may 

differ slightly)/ upright in leads II, III and aVF

3. Rate may vary from 80-140 bpm (ave apprx 100-110)

Thus, this is ART vs SART/SNRT.

References:

Das and Zipes. 2012. Electrocardiography of arrhythmias : a comprehensive review. Elsevier PA

Fisch C and Knoebel SB. 2000. Electrocardiography of Clinical  Arrhythmias. Futura Pub NY

Mohammad-Reza et al.1985 Sinus Node Reentry: Case Report and  Review of Electrocardiographic and Electrophysiologic Features. Texas Heart Institute 12(3) 249-252 

Sanders et al. 1994. Catheter Ablation of Sinus Node Reentry Tachycardia. JACC 23 (4) 926-934 

Simmers TA and Seeram N. 2003. Sinoatrial Reentry Teacycardia: A  Review. Indian Pacing and Electrophsiology 3(3):109-116 

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