Can AF be regular?

No clinical hx. What are the rhythms?

1

Can AF be regular? Yes, this can happen in AF with:

•  AV block
• AV dissociation with a junctional, subjunctional or ventricular rhythm. 

Even rare is AF that is REGULARLY IRREGULAR.

2

This is atrial fibrillation (AF). How come AF becomes a regularly irregular rhythm? AF by definition MUST be irregular. How did this happen?

The rhythm strip shows a regularly irregular rhythm with "group-beating" . The groups are 2-2-2-3-3-2-2-. In the groups of 3, there is shortening of the RR interval. The RR interval between the groups is less than 2x the preceding RR interval. Group-beating is a"footprint" of a Wenckebach. So, this is 3:2 and 4:3 Wenckebach. 

AF cannot do this precise grouping. The AF cannot penetrate the junction because there is an ENTRANCE BLOCK. Entrance block denotes failure of an impulse to reach, enter, suppress, reset, or discharge a dominant pacemaker.

How to get the junctional rate

1. Get the RR interval between the beginning of the first group to the beginning of the next group. 

45 small squares or 45 x 40 ms = 1800 ms.

2. Divide the computed RR interval in 1 by the number of expected junctional beats. In this case, we expect 4 junctional beats for every 3 QRS (with the 4th  junctional beat being the dropped beat). 

1800 / 4 = 450 or use 45 small squares / 4 = 11.25

3. Compute the rate using the small squares method. 

1500 / 11.25 small squares = ~ 133 bpm

So, this is junctional tachycardia.

The final interpretation is AF with ENTRANCE BLOCK, junctional tachycardia with Wenckebach EXIT BLOCK.

References:

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

Fisch C and Knoebel SB. 2000. Electrocardiography of Clinical Arrhythmia. New York. Futura Publishing Co.