Simplified Electrophysiologically Directed Catheter Ablation of Recurrent Common Atrial Flutter
Background Despite verification of bidirectional conduction block after radiofrequency (RF) catheter ablation in the inferior vena cava (IVC)–tricuspid annulus (TA) isthmus, recurrence of common atrial flutter is relatively common. Although complete linear reablation is usually performed, we evaluated a simplified electrophysiological strategy selectively targeting recovered conducting isthmus tissue.
Methods and Results Twenty-one patients (18 men and 3 women, age, 54±10 years) with a recurrence of typical atrial flutter 6±7 months after an apparently successful catheter ablation in the IVC-TA isthmus prospectively underwent electrophysiologically targeted reablation during flutter. Sites with narrow electrograms or fractionated electrograms interposed between adjacent sites with double potentials considered to represent gaps were ablated without movement of the catheter. Mapping showed that 18 of 21 patients had a single gap. Successful ablation required a single application in 14 patients and, in the group as a whole, a median of one application (mean, 2±2; range, 1 to 11) with resultant bidirectional block in 13 of 16. A single narrow electrogram (duration, 48±6 ms; amplitude, 0.1±0.05 mV) was noted at the successful site in 11, whereas a fractionated electrogram (97±32 ms, 0.05±0.04 mV, P<.05) was noted in 9. There were four additional recurrences during a follow-up at 7±5 months; three were similarly ablated with a median of one pulse.
Conclusions Transmural ablation lesions in the isthmus can be recognized during flutter by double potentials separated by an isoelectric interval. Postablation recurrent flutter is usually due to a single discrete recovered gap; this is represented by a single or a fractionated potential spanning the isoelectric interval of adjacent double potentials, which can be selectively targeted to minimize repeat ablation.
Transcatheter energy applied to the region between the IVC-TA and the coronary sinus ostium for typical atrial flutter has achieved high success rates with low morbidity and mortality.1 2 3 4 Presently, the common practice is to interrupt conduction through the IVC-TA coronary sinus ostium isthmus, with the exact site being mostly a matter of operator preference within specified anatomic limits. However, typical atrial flutter recurs after apparently successful catheter ablation in as many as 44% of cases.1 Ablation with the use of recently described markers of isthmus conduction block as complementary end points has resulted in lower rates of recurrence, although medium-term follow-up in one series revealed recurrence in ≈9%.3 Although published experience on reablation is limited, repeat complete linear ablation within the above anatomic limits is commonly performed. This practice may not be necessary if the remnant of recovered conducting tissue could be identified and selectively ablated. In this study, we evaluate the relative extent of this conducting tissue and describe a simplified electrophysiologically directed strategy of RF catheter reablation in a consecutive prospectively enrolled cohort of patients with recurrence of common atrial flutter after previous apparently successful IVC-TA isthmus ablation.
Between December 1995 and April 1997, 21 patients underwent RF catheter reablation at our hospital (of a total of 205 typical flutter ablations) for recurrent common atrial flutter after an “index” ablation procedure. There were 18 men and 3 women (mean age, 54±10 years), and 4 had structural heart disease—1 each with coronary artery disease, valvular heart disease, postoperative atrial septal defect, and dilated cardiomyopathy.
Based on the technique initially described,1 we previously reported electrophysiologically and anatomically directed ablation in the IVC-TA isthmus with the aim of creating a linear lesion using sequential point-by-point RF application directed at sites in the isthmus with atrial electrograms centered on the surface ECG flutter wave plateau.5 Consistent targeting of sites with this timing while withdrawing the catheter from the RV to the IVC edge ensures a linear lesion perpendicular to the wave front independent of fluoroscopic orientation. In all 21 cases, the target site during the index ablation was the IVC-TA isthmus, with ablation directed during flutter at electrograms in the center of the surface ECG flutter wave plateau in 19 of 21 patients. Two patients underwent anatomic ablation: 1 during flutter and another during atrial fibrillation. Noninducibility of typical atrial flutter was demonstrated as an end point of successful ablation in all cases by programmed or incremental right atrial stimulation. Isthmus conduction was assessed in 9 cases: bidirectional isthmus conduction block was found in 7 and unidirectional block in 2.6 7
All antiarrhythmic medications were stopped 3 or 4 days before the present ablation procedure. The ablation was performed with the patient under light sedation (2 to 4 mg midazolam IV) and after 4 to 6 hours of fasting. Informed consent was obtained in all cases. Standard quadripolar catheters (Bard Inc) with 5- to 10-mm interelectrode spacing were introduced through the femoral veins for stimulation and for verification of isthmus conduction block. In 2 cases, a duodecapolar Halo catheter (Cordis-Webster Inc) was used for the latter purpose. Bipolar electrograms were filtered with a bandpass setting of 30 to 500 Hz and amplified at high gains (0.1 mV/cm) on a PPG Midas polygraph and recorded at paper speeds of 100 mm/s. RF application as well as rove mapping were performed with a 4-mm thermocouple-equipped–tip electrode, quadripolar catheter (Cordis-Webster Inc) with 2-5-2–mm interelectrode spacing. A Stockert-Cordis RF generator was used to apply closed-loop temperature-controlled RF current (as a 550-kHz unmodulated sine wave) in unipolar mode between the catheter tip electrode and an indifferent 525-cm2 electrode placed under the patient’s back. Individual applications were nominally of 90 seconds’ duration but were interrupted earlier in case of an impedance rise. The target temperature was set between 60° and 70°C. Isthmus conduction was assessed by comparing activation times between two sites low down in the lateral right atrial free wall during coronary sinus ostium pacing as well as between the His bundle–recording position and the coronary sinus ostium during low lateral right atrial pacing.6 A programmable stimulator (Cardiostimulateur Orthorythmique) with a 2-ms output pulse width and four-times-threshold amplitude was used. Procedural success was defined as interruption of flutter with noninducibility during high rate incremental atrial pacing from two right atrial sites, the region of the ostium of the coronary sinus and the low lateral right atrium, as well as evidence of at least counterclockwise isthmus block.
Electrophysiological Study and Ablation Strategy
All patients underwent RF ablation during sustained typical atrial flutter during the procedure (1 patient required rapid atrial stimulation for induction). The IVC-TA was carefully “scanned” in each case during flutter, with the ablation catheter being progressively withdrawn from the RV margin of the isthmus to its junction with the IVC during continuous recording from the distal bipole. On the basis of earlier data,8 9 10 we hypothesized that previously ablated atrial tissue within this region could be identified by relatively widely separated double potentials (with an isoelectric interval) centered around an imaginary midpoint of the surface ECG flutter wave plateau best seen in leads II, III, and aVF. This allowed exclusion of double potentials from the region of the ostium of the coronary sinus, where such potentials may be found in the absence of previous ablation attempts but coincide with the end of the plateau. Clockwise or counterclockwise torquing of the catheter recording double potentials allowed registration of large-amplitude sharp and single atrial electrograms flanking either side of the center of the surface ECG flutter wave plateau. This zone of previous ablation was traced from the RV margin to the inferior vena cava, and we considered gaps within the initial ablation line to be indicated by sites with (i) a single electrogram centered on or (ii) a fractionated or “triple” potential straddling the center of the surface ECG flutter wave plateau. During continuing atrial flutter, RF energy was applied at such sites in the above order of preference without moving the catheter (ie, if both types of potentials were encountered, the narrow higher-amplitude single potential was preferentially targeted). Continuous variables are presented as mean±SD values, and comparisons were made using Student’s t test.
The interval between the two ablations was 6±7 months, and the surface ECG morphology was identical or markedly similar.
Activation Mapping in the Isthmus
During typical atrial flutter (cycle length, 237±30 ms), the region of the previous ablation was in all cases easily located by the presence of widely separated double potentials in the appropriate anatomic context with a characteristic convergent configuration. The configuration varied according to the position of the gap, with narrower interspike intervals at one edge indicating gap proximity to this border (RV edge interspike intervals, 67±19 ms; IVC edge, 94±25 ms). Withdrawal mapping demonstrated that this zone of double potentials occupied all the isthmus except a single discrete gap in 18 patients (Figure⇓). There were 2 gaps in 2 patients and 1 large gap in 1 patient who had a small zone of double potentials and a larger zone of single potentials, suggesting only minor damage to the isthmus as a result of the initial ablation.
Atrial flutter was successfully ablated and definitively interrupted by 1 application in 14 patients, 2 applications in 2 patients, 3 applications in 4 patients, and 11 applications in the patient with a large gap, for a median of 1 and a mean of 2±2 RF applications (range, 1 to 11). Atrial flutter was terminated 12±10 seconds after application of RF energy. Bidirectional block was confirmed after flutter interruption in 13 patients, whereas 3 others were noted to have only counterclockwise isthmus block, which remained unchanged despite additional (1.6±0.9; range, 1 to 3; median, 1) applications. Isthmus conduction was not assessed in 5 patients—in 2 because of sustained atrial arrhythmias induced by atrial burst pacing. The procedure and fluoroscopic durations were 56±30 and 19±13 minutes, respectively. There were no significant side effects. For 11 of the patients, the electrogram at the successful site was a narrow single potential (48±6 ms); for 9 others, it was a fractionated/triple potential (97±32 ms). In 1 patient, a narrow double potential without an isoelectric interval was observed. The fractionated atrial electrograms had a lower amplitude than the single ones (0.05±0.04 versus 0.1±0.05 mV, P<.05). There was no specific location of the gaps along the isthmus. For sites with single electrograms, the time to interruption of flutter was longer than that for sites with fractionated electrograms (15.5±10 versus 7±7 seconds, P<.05).
After a follow-up of 7±5 months, 4 patients had a recurrence of typical flutter; 3 of these 4 had had previous unidirectional counterclockwise block, and 1 had had bidirectional counterclockwise block. Three were successfully reablated (median, 1 pulse; mean, 2±2; range, 1 to 4); 2 of these patients were ablated at discrete similar sites, and 1 at the same site as the previous ablation. This patient with previously documented complete bidirectional block was successfully reablated at the identical site, requiring 4 applications, because of rapid recovery of isthmus conduction after each of the first 3 transiently successful applications. One patient refused repeat ablation.
The present study indicates that recurrence of atrial flutter after previous ablation in the IVC-TA isthmus is usually due to a single discrete gap, and therefore repetition or creation of a new line of ablation lesions is not required. These gaps can be identified electrophysiologically and selectively ablated. This is the first attempt at prospectively studying a consecutive cohort of patients with recurrent atrial flutter after previous ablation in the IVC-TA isthmus.
Activation in the IVC-TA isthmus during common atrial flutter is unidirectional and proceeds from the lateral to the medial right atrium.11 12 Thus, a transmural lesion in this region with spared tissue on both sides will result in the activation wave front detouring around both sides of the lesion. A bipole (such as used clinically with 4-mm-tip ablation catheters) when placed astride the lesion will therefore record sequential nonsimultaneous activation from both the upstream and downstream aspects of the lesion in the form of double potentials. Movement of the bipole toward the healthy margins on either side will result in recording of a single short duration potential, the position of which is indicated by the atrioventricular ratio and a different relation to the surface ECG flutter wave. By extension, with a large lesion almost spanning the isthmus and a relatively small zone of spared tissue (the “gap”), the activation wave front during recurrent flutter would be expected to pass through the remaining conducting isthmus tissue (gap) and activate the downstream flank of the lesion antidromically. Double potentials with progressively increasing isoelectric interpotential intervals were accordingly recorded as the bipole was gradually withdrawn toward either edge but with fractionated or narrow single electrograms on the gap occupying the isoelectric interval of adjacent double potentials. The significance of single versus fractionated electrograms on the gap is unclear, but single, short-duration electrograms may indicate a rapidly and homogeneously conducting tissue, whereas fractionation indicates a more tenuous, slowly conducting tissue gap, as suggested by the shorter time to flutter interruption and lower amplitude in our study. Alternatively, the two morphologies (in cases in which both were noted) could be a function of the distance between the recording bipole and the actual gap tissue.
The most important proof of the accurate location of the gap in the lesion line/zone was successful ablation of flutter with a single punctiform RF application in most patients. It is important to emphasize that we could fill in the “gaps” with relative ease because of the similar technique used for the previous index ablation and, notably, because of the previous effort to trace a relatively straight line. This strategy therefore may not be as efficacious for previous wide and irregularly targeted ablation lesions. This is supported by the requirement of 11 applications for 1 of our patients in whom mapping demonstrated a large gap of healthy potentials, thus necessitating practically a new ablation line. Of course, such an assessment is valid only when activation through the IVC-TA isthmus is strictly unidirectional, as occurs during typical atrial flutter and presumably during inverse clockwise flutter.
Our results can also be applied to facilitate first-time ablation of typical atrial flutter to search for remnant gaps in the newly created line after previous applications of RF energy failed to terminate flutter. In a broader sense, this cohort also represents a near-perfect paradigm of an incomplete (discontinuous) linear ablation lesion that can be completed by specifically targeted “point” lesions.
Additional recurrences occurred despite the targeting of localized gaps; they were due to inaccurate ablation and/or a difficult anatomy, with both resulting in a transient conduction block. Of the 4 patients with a recurrence, 3 were noted to have a unidirectional counterclockwise isthmus block. Additional recurrences may also reflect stereotypical limitations of the similar anatomic and technical milieu at successive ablations. Successful additional reablation with stable bidirectional isthmus block was, however, accomplished with the same strategy (again, with a median of 1 application).
Most postablation recurrent typical flutters are due to a discrete gap in the ablation line permitting conduction through the isthmus. Both the transmural ablation lesion and the “gap” can be identified by on-site electrograms, permitting ablation in the majority with a single RF application and a relatively short procedure.
Selected Abbreviations and Acronyms
|IVC||=||inferior vena cava|
- Received June 12, 1997.
- Revision received August 4, 1997.
- Accepted August 7, 1997.
- Copyright © 1997 by American Heart Association
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