Serendipitous Supernormality

Abstract

We describe a patient who underwent AV node modification to create complete heart block in the setting of incessant, ablation-and-drug-refractory, symptomatic atypical atrial flutter. His dual chamber defibrillator (previously implanted for resuscitated cardiac arrest) was programmed to the VVIR mode at a faster pacing rate of 85 bpm. Serendipitously, this rate was an almost exact factorial of his flutter rate of 250-260 bpm. This resulted in every 6th flutter wave falling in the supernormal period, resulting in fixed-coupled supraventricular bigeminy and trigeminy in the setting of complete heart block. Reprogramming the pacing rate to 75 bpm abolished bigeminy and trigeminy.

Keywords: atrioventricular node ablation; atypical atrial flutter; supernormal conduction.

FIGURE 1

12‐lead ECG rhythm strip showing creating of complete heart block within 4 s of onset of radiofrequency ablation, with emergence of VVI pacing at 35 bpm. There are 2 narrow QUS complexes (shaded in pink) that show fixed coupling to the end of the T wave. See also Figure 6.

FIGURE 2

Section of remote transmission from dual chamber Boston Scientific defibrillator within 24 h of AV node ablation. There are ventricular pacing and native QRS complexes in a pattern of fixed coupled bigeminy at a coupling interval of about 580 ms. See also Figure 6.

FIGURE 3

Heart rate trends from 7‐day Holter showing hourly burden of “ventricular” ectopy. Note the immediate reduction in ectopy burden coincident with the lowering of the base rate from 85 to 75 bpm, as marked by the arrow.

FIGURE 4

Two (non‐consecutive) Holter strips with flutter waves marked by red arrows. The top strip shows supraventricular beats in a pattern of bigeminy transitioning to trigeminy, whereas the bottom strip shows trigeminal coupling. There are 11 intervals (measured from the pacing spike to the flutter waves that are presumed to conduct within the window of supernormal conduction) shown in green. There are 5 intervals that fall within this window that do not conduct shown in red. All other flutter waves outside this window fail to conduct.

FIGURE 5

Graph of 51 intervals measured for 650 ms after each pacing spike from the 2 strips shown in Figure 4. The only coupling intervals that conduct to the ventricles are between 360 and 440 ms.

FIGURE 6

Enlarged section of Figures 1 and 2 to show measurements of coupling intervals that were conducted within the supernormal window of 480 to 540 ms. This coupling was longer than the window identified from the Holter because the QT interval was longer immediately following AV node ablation.