March 8, 2016

Sinus node reentry

A 60 yo pt is admitted due to shortness of breath. What is ECG interpretation?

Figure 1 - ECG case

Figure 2 - ECG case marked

The initial rate  is about 90-100 bpm then suddenly drops to about 50's. There is some variability in the R to R interval. There is slight difference of the P wave morphology compared to the regular sinus beats which can be seen on the latter part of the strip.

These features  fit sinoatrial reentry tachycardia (SART or SNRT):

  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 approx 100-110)
Other differential diagnoses are (Table1):

1. Inappropriate sinus tachycardia (IST)

IST is non-paroxysmal, elevated resting rate and gradual (excessive acceleration as reaction to mild exercise. Since this case in paroxysmal, then likely this is not IST.

2. Atrial reentry tachycardia near the sinus node

In intraatrial reentrant tachycardia, the reentry circuit is confined to the atrium and consist of two functionally distinct pathways with different conduction velocities and refractory periods.
The diagnostic criteria include:

  1. regular ectopic supraventricular tachycardia 
  2. an activation sequence differing from that in sinus rhythm 
  3. tachycardia that does not require participation of the AV node
  4. a rate slower than that of atrial flutter.
Demonstration of second-degree AV block is helpful for documenting the mechanism.

Table 1 - Differentiation Between SART, IST and ART

Sinus node reentry

According to Miller and Zipes (Clinical Arrhythmology and Electrophysiology: A Comprehensive Review - A Companion to Braunwald’s Heart Disease 2nd Ed):

"Sinus node reentry is defined as a reentrant tachycardia involving the sinus node and perinodal tissue that is induced and terminated with PES and is adenosine sensitive. It is possible that sinus nodereentry tachycardia may represent a high cristal AT originating near the sinus node that is adenosine sensitive if the mechanism of the tachycardia is triggered activity. Alternatively, it is an AT owing to microreentry in tissue near the sinus node or perinodal region (superior crista termi-nalis) that is responsive to adenosine because of involvement of sinus nodal tissue. The P wave morphology during the tachycardia is identical to that seen during sinus rhythm".

In the 2015 SVTguideline  , sinus node reentry is classified as A specific type of focal AT that is due to microreentry arising from the sinus node complex, characterized by abrupt onset and termination, resulting in a P-wave morphology that is indistinguishable from sinus rhythm.


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

Issa Z, Miller J and Zipes D. 2012. Clinical Arrhythmology and Electrophysiology: A Comprehensive Review - A Companion to Braunwald’s Heart Disease 2nd Ed. PA Saunders

Surawicz B and Knilans TK. 2008. Chou’s Electrocardiography in Clinical Practice. 6th ed. PA. Saunders-Elseiver


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