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Introduction Focal impulse and rotor modulation (FIRM)‐guided ablation has had mixed results of published success, and most studies have had a follow‐up for a year or less. We aimed to study a consecutive group of patients followed for at least 1.5 years, subgrouped into those with an initial FIRM ablation and those with a previous, failed ablation who now received a FIRM guided one, to evaluate for success in each group and factors that might affect success. Methods Of 181 patients, 167 were available for analysis. Group 1 (n = 122) had a first or primary ablation (paroxysmal atrial fibrillation [PAF] 51; persistent atrial fibrillation [PeAF] 71) and group 2 (n = 45) had a redo ablation (PAF 18; PeAF 27). All patients were done under general anesthesia. FIRM mapping was done in the right atrium first and then the left, and only rotors consistently seen on multiple epochs were ablated, using 15 to 30 W. Rotor ablation was discontinued when remapping showed elimination of rotational activity at the site. Wide area catheter ablation was done for pulmonary vein isolation (PVI). Routine follow‐up was at 3, 6, and 12 months of the first year, with a Holter monitor at 6 months, and then every 6 months thereafter. Event recorders were given to patients with potential arrhythmic symptoms. Results Mean follow‐up was 16 months. Nearly 40% of patients had obstructive sleep apnea; mean body mass index was 32; and average left atrial size was 39.7 mm and 46.2 mm for PAF and PeAF patients, respectively. Freedom from atrial arrhythmia recurrence was: in group 1 patients, 82.4% for PAF and 67.6% for PeAF patients; in group 2 patients, 83.3% for PAF, but only 40.7% for PeAF patients. Comparing outcomes for the first 10 patients studied to the next 20 or more done by three operators showed no difference, suggesting no learning curve affecting the ablation results. Furthermore, the univariate analysis did not show any demographic factor to have an independent significance for ablation success or failure. Spontaneous termination during rotor ablation occurred in 76.8% of PAF and 27.6% of PeAF patients but did not affect the long‐term outcomes for maintenance of sinus rhythm. Conclusions FIRM‐guided atrial ablation plus PVI in our patient population resulted in good success from a recurrence of atrial arrhythmias in patients undergoing an initial ablation procedure. For those with persistent AF undergoing a second procedure now using FIRM guidance plus PVI, the results are lower. Further research is needed to define better the appropriate population for FIRM‐guided ablation and the degree of ablation needed for success in these patients.

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A 57-year-old man with a structurally normal heart and normal baseline ECG (Figure 1) underwent pulmonary vein isolation for atrial fibrillation. An electrophysiology study was then undertaken with an octapolar catheter positioned at the His bundle and an ablation catheter at the mid-right atrium. See Editor's Perspective p 985At baseline, the sinus cycle length was 890 ms, the AH interval 48 ms, the HV interval 80 ms, and the QRS duration 80 ms. During extrastimulus atrial pacing, the HV interval shortened and the QRS complex widened with a left bundle branch block morphology (Figure 2). Atrial burst pacing at cycle length 330 ms demonstrates progressive shortening of the HV interval and widening of the QRS complex with left bundle branch block morphology ( Figure 3A and 3B). On the final 3 beats in the figure, a His bundle electrogram seems after the QRS complex. On termination of pacing, a wide QRS complex tachycardia of identical morphology is noted (Figure 4). The atrial (A), His (H), and ventricular (V) electrograms are labeled. What is the mechanism of the tachycardia? DiscussionAlthough the baseline ECG is normal, the presence of a slowly conducting accessory pathway is apparent from atrial extrastimulus pacing demonstrating HV interval shortening, QRS widening, and a long A-V interval ( Figure 2). Further inferences of the nature of the accessory pathway may also be made. The retrograde right bundle (RB) and His activation preceding the preexcited ventricular complex with left bundle branch block morphology is most consistent with an accessory pathway connection directly into the right bundle branch (atriofascicular pathway or nodofascicular pathway).Similar changes are noted at the onset of atrial burst pacing ( Figure 3A). There is evidence of a slowly conducting accessory pathway with shortening of HV interval and a long A-V interval. The His electrogram precedes the preexcited ventricular complex. Because only the distal electrode records an His electrogram, retrograde versus anterograde His activation cannot be discerned on this tracing. The H and V relationship changes further on the sixth paced beat when the His bundle electrogram occurs after the ventricular electrogram. Having established the presence of an atrio-fascicular (or nodo-fascicular) pathway, the only explanation for the late His is the development of retrograde block in the RB. Most likely, the His activation is still retrograde via transeptal activation of the left bundle branch. This is represented schematically in Figure 3B. Less likely, retrograde block in the RB allows for antegrade conduction over an AV node slow pathway and anterograde His activation.At termination of the atrial pacing, a left bundle branch block morphology wide QRS tachycardia is initiated (Figure 4). The tachycardia morphology is identical to the pre-excited QRS complex. The His activation is not seen on the first beat of tachycardia but occurs just before the onset of the QRS for the second and third beats. The His recording is seen after the ventricular s...

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