Bidirectional Isthmus Conduction Block Research Articles

Results From a Single-Blind, Randomized Study Comparing the Impact of Different Ablation Approaches on Long-Term Procedure Outcome in Coexistent Atrial Fibrillation and Flutter (APPROVAL)

This study examined the impact of different ablation strategies on atrial fibrillation (AF) recurrence and quality of life in coexistent AF and atrial flutter (AFL). Three-hundred sixty enrolled patients with documented AF and AFL were blinded and randomized to group 1, AF±AFL ablation (n=182), or group 2, AFL ablation only (n=178). AF recurrence was evaluated with event recording and 7-day Holter at 3, 6, 9, and 12-month follow-ups. Quality of life was assessed at baseline and at the 12-month follow-up with 4 questionnaires: the Medical Outcome Study Short Form, the Hospital Anxiety and Depression Score, the Beck Depression Inventory, and the State-Trait Anxiety Inventory. Of the 182 patients in group 1, 58 (age, 63±8 years; 78% male; left ventricular ejection fraction, 59±8%) had AF+AFL ablation and 124 (age, 61±11 years; 72% male; left ventricular ejection fraction, 59±7%) had AF ablation only. In group 2 (age, 62±9 years; 76% male; left ventricular ejection fraction, 58±10%), only AFL was ablated by achieving bidirectional isthmus conduction block. Baseline characteristics were not different across groups. At 21±9 months of follow-up, 117 in group 1 (64%) and 34 in group 2 (19%) were arrhythmia free (P<0.001). In group 1, scores on most quality-of-life subscales showed significant improvement at follow-up, whereas group 2 patients derived relatively minor benefit. In coexistent AF and AFL, lower recurrence rate and better quality of life are associated with AF ablation only or AF+AFL ablation than with lone AFL ablation. Furthermore, quality of life directly correlates with freedom from arrhythmia, as shown in this study for the first time in patients blinded to the procedure. URL: http://www.clinicaltrial.gov/. Unique identifier: NCT01439386.

A Case of Successful Ablation of Postoperative Atrial Flutter with Pouch-Like Recesses Using Irrigated Tip Catheter

A 64-year-old man was referred to our hospital in October 2009 because of atypical atrial flutter (AFL). He had received the surgical repairment of atrial septal defect at 20-year-old. Electrophysiological study revealed that the activation sequence was cavotricuspid-isthmus-dependent and indicated the clockwise rotation around tricuspid valve annulus (TVA). Electro-anatomical mapping revealed that atrial incision was by-stander. Linear ablation to cavotricuspid-isthmus was unsuccessful because of enlargement of right atrium and temperature-rising leading to thrombogenesis and stream pop. Right atrial angiography performed before the second session revealed deep pouch-like recesses in mid-isthmus lesion. Large and sharp atrial potentials were recorded on the TVA side of the pouch. Point-by-point radiofrequent application on the both sides of TVA and inferior vena cava (IVC) of the pouch was performed under the sinus rhythm using 8 mm-irrigated tip catheter (30 W, 60 sec), and the bidirectional isthmus conduction block was completed. The irrigated tip catheter may give the effectiveness to the ablation on the pouch-like recesses such as our case.

Evaluation of the Surface ECG in Detecting Isthmus Conduction Block after Ablation of Typical Atrial Flutter

To investigate the value of changes in P wave morphology and duration detected by surface electrocardiogram (ECG) during proximal coronary sinus (PCS) and low lateral right atrial (LLRA) stimulation as a marker for complete bidirectional isthmus conduction block in the procedure of typical atrial flutter ablation. Morphology, duration, and ratio of a positive terminal P wave were estimated in 52 typical atrial flutter patients before and after radiofrequency catheter ablation (RFCA). Atrial flutter ablation resulted in a complete bidirectional isthmus block in all 52 patients. The terminal portion of the P wave towards a positive morphology was detected in 90.7% (47/52) patients both during PCS and LLRA stimulation. These changes were predominantly observed in the inferior leads. Positive morphological changes of the terminal P wave portion and the measured P wave ratio (40% +/- 12%) in the inferior leads indicating bidirectional isthmus conduction block with a sensitivity of 87.5% and a specificity of 91.7% were observed. An increment of 20 ms or more in P wave duration during the PCS stimulation and 10 ms or more during the LLRA stimulation indicating the conduction block with a sensitivity of 90% and a specificity of 100%. The variation of P wave morphology and duration in inferior leads of the surface ECG is a helpful technique to assess the complete bidirectional isthmus conduction block in the procedure of typical atrial flutter ablation.

Prospective randomized comparison of a steerable versus a non-steerable sheath for typical atrial flutter ablation

Although cavotricuspid isthmus (CTI) ablation can cure typical atrial flutter (AFL), it might be difficult to achieve a bidirectional conduction block in the isthmus in some patients. We investigated the usefulness of a steerable sheath for CTI ablation in patients with typical AFL or atrial fibrillation. A total of 40 consecutive patients (36 males; mean age 55.2 +/- 10.0 years) undergoing CTI ablation were randomized to one of the following two groups: group S (using a steerable long sheath) or group NS (using a non-steerable long sheath). Ablation was performed using an 8 mm tip catheter. The anatomy of the CTI was evaluated by a dual-source computed tomography scan prior to the procedure. The procedural endpoint was the achievement of a bidirectional isthmus conduction block. Bidirectional block in the CTI was achieved in all patients with 485.3 +/- 416.4 s of radiofrequency (RF) application. The CTI anatomy, including the length, depth, and morphology, was similar between the two groups. The duration and total amount of RF energy delivery were significantly shorter and smaller in group S than in group NS (310 +/- 193 vs. 661 +/- 504 s, P = 0.006, and 12,197 +/- 7306 vs. 26,906 +/- 21,238 J, P = 0.006, respectively). The use of a steerable sheath reduced the time and amount of energy needed to achieve a bidirectional conduction block in the CTI. For patients in whom the establishment of a conduction block is difficult, a steerable sheath should be considered as a therapeutic option for typical AFL ablation.

Prospective Randomized Comparison of 8‐mm Gold‐Tip, Externally Irrigated‐Tip and 8‐mm Platinum‐Iridium Tip Catheters for Cavotricuspid Isthmus Ablation

Radiofrequency (RF) ablation of the cavotricuspid isthmus (CTI) can be performed using different types of ablation catheter. Gold tip electrodes have the theoretical advantage of creating bigger lesions than standard platinum-iridium electrode. This prospective, randomized study compares the clinical efficacy of 8-mm gold tip catheter, externally irrigated and 8-mm platinum-iridium tip (Pt tip) catheters. Sixty consecutive patients (51 men, 60 +/- 10 years) undergoing de novo CTI ablation for documented typical atrial flutter were randomized to one of the following ablation catheters: 8-mm gold tip catheter, an externally irrigated-tip (Irr. tip) catheter, or an 8-mm Pt tip catheter. The procedural endpoint was achievement of bidirectional isthmus conduction block with < or = 20 minutes of RF energy application. The latter was achieved equally with the 3 catheters (95% for gold tip, 100% for irrigated tip, 95% for Pt tip) and the durations of RF (10 +/- 6, 10 +/- 4, 13 +/- 8 minutes), fluoroscopy (12 +/- 6, 12 +/- 7, 15 +/- 12 minutes) and the procedure (34 +/- 23, 38 +/- 24, 40 +/- 30 minutes) were similar in all groups. The maximal targeted power could not be reached in at least one location in 40% of patients with gold tip and in 35% of patients with Pt tip catheters whereas it was always achieved with an Irr. tip catheter (P = 0.003, P = 0.008). The reduction in impedance during RF delivery was greater with Irr. tip (11 +/- 7 ohms) than with gold (7 +/- 4 ohms, P = 0.02) or Pt tip (5 +/- 3 ohms, P = 0.001) catheters. This study demonstrates equivalent efficacies of gold, platinum-iridium and externally Irr. tip catheters for successful de novo ablation of the CTI.

Catheter inversion: a technique to complete isthmus ablation and cure atrial flutter.

Cure of typical atrial flutter (AFL) by catheter ablation to produce bidirectional block across the tricuspid annulus-inferior vena cava isthmus (IS) is highly effective, but failures may occur. We describe a technique that may allow creation of bidirectional block where a conventional strategy has failed. AFL ablation was performed using the conventional approach with a mapping/ablation (ablation) catheter introduced via the right femoral vein (RFV) to create a line of bidirectional block across the IS. If this was not achieved after five passes of the ablation catheter from the tricuspid annulus to the inferior vena cava (IVC) a catheter inversion technique was used. This allowed stable positioning of the ablation catheter at the IVC end of the isthmus. In 11 patients, a mean of 17 (range 3 to 45) radiofrequency (RF) applications was given before the catheter inversion technique was applied. Following catheter inversion a mean of 4 (1 to 14) further RF applications achieved bidirectional isthmus block in every patient. No complications occurred. Catheter inversion provides a simple, safe, and effective means of achieving bidirectional isthmus conduction block in cases where a conventional ablation strategy might have failed.

Catheter-based cryoablation produces permanent bidirectional cavotricuspid isthmus conduction block in dogs.

Catheter-based cryoablation has been shown to produce punctate and effective cardiac lesions to treat focal targets. However, sequential applications are required to produce a continuous linear lesion needed to cure macroreentrant arrhythmias with large critical isthmuses. The purpose of this study was to compare and contrast linear cardiac lesions produced with sequential applications using a novel cryoablation system to those produced using radiofrequency (RF) energy. Seven mongrel dogs were prepared for femoral venous insertion of the ablation catheter (either a 10-French, 6-mm tipped, bipolar cryoablation catheter (N = 5, cryo group) or a 7-French, 4-mm tipped, bipolar RF ablation catheter (N = 2, RF group)). Ablation of the cavotricuspid isthmus was performed by delivering applications at sequential locations across the isthmus. The cryo group received 6 to 10 (mean 8 +/- 1.4), 5-minute applications at 3 to 5 separate sites with a mean nadir temperature of -74.5 +/- 1.6 degrees C. Each dog in the RF group received 9, 90-second applications with a mean temperature and power of 62 +/- 0 degrees C and 32 +/- 3.6 W. No acute or chronic complications were associated with either form of ablation. Immediately and six weeks after the index procedure, electroanatomical mapping showed the presence of bidirectional isthmus conduction block in all dogs. Gross and histopathologic examination revealed the presence of linear lesions, which were continuous and transmural. Similar to RF ablation, catheter-based cryoablation can produce linear, transmural lesions in the cavotricuspid isthmus resulting in permanent bidirectional isthmus conduction block.

Impact of Transisthmus Linear Ablation of Typical Atrial Flutter on Coronary Sinus Activation Time

Complete or incomplete bidirectional isthmus conduction block after linear ablation of atrial flutter is difficult to interpret without detailed multiple electrodes mapping along the tricuspid annulus and the low right atrial isthmus area. The influence of isthmus block on the intraatrial septal and coronary sinus activation has not been assessed by endocardial mapping. This study was designed to analyze the intraartial and interatrial activation times in a retrospective fashion to investigate (1) whether isthmus conduction block can change the coronary sinus activation sequence during low lateral right atrial pacing, and (2) the correlation between change of coronary sinus activation time and isthmus conduction block. Sixty-five consecutive patients (mean age, 57 +/- 18 years) with clinically documented typical atrial flutter were studied. A 20-pole "Halo" catheter was placed around the tricuspid annulus including the entire low right atrial isthmus to verify complete bidirectional isthmus block. Activation time from ostium to distal coronary sinus (OCS-->DCS), and interatrial septum and isthmus activation times during right atrial pacing were analyzed and compared before and after incomplete or complete isthmus block. Complete bidirectional isthmus block was achieved in 50 (77%) patients. During low lateral right atrial pacing, linear ablation at low right atrial isthmus results in a significant delay of activation in all coronary sinus recording sites with greater extent at the ostium area without influence on interatrial septum activation in complete and incomplete isthmus conduction block. The difference of the OCS-->DCS interval before and after ablation, delta (OCS-->DCS), was well correlated with results of isthmus conduction block and significantly longer in patients with complete than those with incomplete isthmus block (34 +/- 11 vs 11 +/- 8 ms, P < 0.001), thereby allowing a value of 20 ms as a discriminative parameter to differentiate incomplete (< 20 ms) from complete (> or = 20 ms) isthmus counterclockwise conduction block with a sensitivity of 96% and a specificity of 88%. In conclusion, creation of a line of block at the inferior vena cava-tricuspid annulus isthmus could change coronary sinus activation sequence during low lateral right atrial pacing in sinus rhythm. The change of coronary sinus activation time after linear ablation, delta (OCS-->DCS), was well correlated with isthmus conduction block by using a value > or = 20 ms to discern complete counterclockwise isthmus block.

Persistent atrial flutter in patients treated for atrial fibrillation with amiodarone and propafenone: electrophysiologic characteristics, radiofrequency catheter ablation, and risk prediction.

Antiarrhythmic drugs have been reported to promote the conversion of atrial fibrillation to atrial flutter in patients with paroxysmal atrial fibrillation. However, information about the electrophysiologic mechanism and response to radiofrequency ablation of these drug-induced atrial flutters is limited. Furthermore, the determinants of the development of persistent atrial flutter in patients treated for atrial fibrillation with antiarrhythmic drugs are still unknown. Among the 136 patients treated for atrial fibrillation with amiodarone (n = 96) or propafenone (n = 40), 15 (11%, mean age 65.5 +/- 12.3 years) were identified to have subsequent development of persistent atrial flutter based on surface ECG characteristics during antiarrhythmic drug treatment. The mean interval between the beginning of drug treatment and the onset of atrial flutter was 5.0 +/- 5.5 months. Intracardiac mapping and entrainment studies revealed that 11 patients had counterclockwise typical atrial flutter, and 4 had clockwise typical atrial flutter. All 15 patients underwent successful ablation with creation of complete bidirectional isthmus conduction block. After a mean follow-up of 12.3 +/- 4.2 months, 14 (93%) of 15 patients who underwent successful ablation and continued taking antiarrhythmic drugs have remained in sinus rhythm. Univariate analysis of clinical variables demonstrated that only atrial enlargement was significantly related to the occurrence of persistent atrial flutter. In patients with atrial fibrillation, persistent typical atrial flutter might occur during antiarrhythmic drug treatment, and atrial enlargement was a risk factor for the development of such an arrhythmia. Radiofrequency ablation and continuation of pharmacologic therapy offered a safe and effective means of achieving and maintaining sinus rhythm.

Catheter ablation of atrial flutter.

Typical atrial flutter in humans is the consequence of a stable macro-reentrant circuit produced by the unique right atrial architecture providing anatomic barriers and functional blocks to conduction. Mapping studies have indicated that the so-called isthmus between the inferior aspect of the tricuspid annulus and the ostium of the inferior caval vein is a critical zone for maintenance of atrial flutter. An anatomically guided approach with placement of a transmural and contiguous lesion line throughout the isthmus has established as curative treatment of typical atrial flutter. Electrophysical criteria indicating complete bidirectional isthmus conduction block after ablation proved to be superior with respect to redurrences of atrial flutter compared with the noninducibility criterion. The gold standard for prove of complete conduction block is the recording of double potentials along the entire isthmus ablation line. Recently, it proved possible to reduce the period of fluoroscopy during isthmus ablation by using electro-anatomical mapping.

Isoproterenol to Evaluate Resumption of Conduction After Right Atrial Isthmus Ablation in Type I Atrial Flutter

After radiofrequency (RF) ablation of atrial flutter (AFL), the demonstration of bidirectional isthmus conduction (BIC) block is considered the hallmark of a successful procedure. The purpose of our study was to test the persistence of BIC block after isoproterenol administration and to evaluate the importance of this finding with regard to AFL recurrences. RF ablation of AFL was performed in 44 consecutive patients with type I AFL by linear ablation of the posterior isthmus (n=29 patients), septal isthmus (n=4 patients), or both right atrial (RA) isthmi (n=11 patients). The procedural end point was complete BIC block and noninducibility of AFL. In case of noninducibility and apparent BIC block, the pacing protocol was repeated under isoproterenol infusion (1 to 3 microgram/min). Reversal of apparent BIC block occurred in 7 (15.9%) of 44 patients. Six patients had bidirectional and 1 had unidirectional resumption of isthmus conduction. Counterclockwise AFL could be reinduced in 4 of these patients. Two to 24 (median, 4) additional RF applications were required to achieve permanent BIC block. At a mean follow-up of 7.3+/-7.6 months (range, 2 to 31 months), 2 (4.5%) of 44 patients had AFL recurrences. Partial linear RF ablation could possibly aggravate preexisting nonuniform anisotropic conduction in the RA isthmus, resulting in profound conduction slowing and apparent BIC block. Isoproterenol can unmask apparent BIC block, thus providing an opportunity to assess the possibility of reversal of BIC block and completeness of isthmus ablation during the same procedure. The low incidence (4.5%) of AFL recurrences at follow-up suggests that noninducibility and BIC block under isoproterenol infusion may be a better end point for successful AFL ablation.