Causes of regular RR interval in atrial fibrillation (AF)

Causes of regular RR interval in atrial fibrillation (AF)

ECG in atrial fibrillation is characterized by absent P waves, presence of fibrillary waves (f waves) and a totally irregular RR interval. But regular RR interval in atrial fibrillation can occur if there is associated:

1. Complete AV (atrioventricular) block
2. Ventricular tachycardia
3. AV junctional tachycardia
4. AV node ablation followed by permanent pacemaker implantation

In all these conditions, regular RR interval in atrial fibrillation occurs because the ventricles are controlled by a different rhythm, not dependent on the irregularly conducted atrial signals of atrial fibrillation.

AV node ablation with permanent ventricular pacemaker implantation is usually considered when the ventricular rate in AF is high despite optimal medications. In one study, significant improvement in left ventricular ejection fraction, quality of life and activity scores was documented, after discontinuing rate controlling medications, AV node ablation and pacemaker implantation [1]. The Ablate and Pace Trial also had documented similar improvements [2].

Sometimes there can be an apparent regularity when the ventricular rate in atrial fibrillation is slow as those on digoxin or beta blockers. But close scrutiny will reveal the subtle irregularity in RR intervals. Digoxin toxicity can cause complete heart block and regular RR intervals due to the subsidiary pacemaker in atrial fibrillation [3]. Atrial fibrillation with non-paroxysmal AV junctional tachycardia can also cause complete AV dissociation and regular ventricular rhythm in digoxin toxicity [3].

References

1. Natale A, Zimerman L, Tomassoni G, Newby K, Leonelli F, Fanelli R, Beheiry S, Pisano E. AV node ablation and pacemaker implantation after withdrawal of effective rate-control medications for chronic atrial fibrillation: effect on quality of life and exercise performance. Pacing Clin Electrophysiol. 1999 Nov;22(11):1634-9.
2. Kay GN, Ellenbogen KA, Giudici M, Redfield MM, Jenkins LS, Mianulli M, Wilkoff B. The Ablate and Pace Trial: a prospective study of catheter ablation of the AV conduction system and permanent pacemaker implantation for treatment of atrial fibrillation. APT Investigators. J Interv Card Electrophysiol. 1998 Jun;2(2):121-35.
3. Chung EK. Digitalis intoxication. Postgrad Med J. 1972 Mar;48(557):163-79.