Role of bipolar electrogram polarity mapping in localizing recurrent conduction in the isthmus early and late after ablation of atrial flutter

Variable procedural strategies adapted to anatomical characteristics in catheter ablation of the cavotricuspid isthmus using a preoperative multidetector computed tomography analysis

Objectives

This study aimed to investigate the anatomical characteristics complicating cavotricuspid isthmus (CTI) ablation and the effectiveness of various procedural strategies.

Methods and Results

This study included 446 consecutive patients (362 males; mean age 60.5 ± 10.4 years) in whom CTI ablation was performed. A total of 80 consecutive patients were evaluated in a preliminary study. The anatomy of the CTI was evaluated by multidetector row-computed tomography (MDCT) prior to the procedure. A multivariate logistic regression analysis revealed that the angle and mean wall thickness of the CTI, a concave CTI morphology, and a prominent Eustachian ridge, were associated with a difficult CTI ablation (P < 0.01). In the main study, 366 consecutive patients were divided into 2 groups: a modulation group (catheter inversion technique for a concave aspect, prominent Eustachian ridge, and steep angle of the CTI or increased output for a thicker CTI) and nonmodulation group (conventional strategy). The duration and total amount of radiofrequency energy delivered were significantly shorter and smaller in the modulation group than those in the nonmodulation group (162.2 ± 153.5 vs 222.7 ± 191.9 seconds, P < 0.01, and 16,962.4 ± 11,545.6 vs 24,908.5 ± 22,804.2 J, P < 0.01, respectively). The recurrence rate of type 1 atrial flutter after the CTI ablation in the nonmodulation group was significantly higher than that in the modulation group (6.3 vs 1.7%, P = 0.02).

Conclusion

Changing the procedural strategies by adaptating them to the anatomical characteristics improved the outcomes of the CTI ablation.

Electrophysiology of a gap created on the canine atrium

OBJECTIVE

It is crucial to detect the unablated regions (="gap") in the radiofrequency linear ablation of atrial tachyarrhythmias. The purpose of this study was to examine the relationship between the electropysiological properties of the gap created in the canine atrium and its anatomicohistologic findings.

METHODS AND RESULTS

In 17 dogs, a linear epicardial radiofrequency ablation lesion was created on the right atrial wall with a gap of surviving tissue in the mid-portion of the lesion. For each gap, the local electrogram (LE) from the gap and conduction pattern through the gap were recorded using an electrode catheter and a plaque electrode during pacing from each side of the gap and the gap size was measured. The gaps >5 mm exhibited a conductive property and the gaps <3 mm had no conduction property according to 3-D mapping. The size of the conductive gaps was larger than that of the non-conductive gaps (7.1 +/- 2.6 vs. 2.6 +/- 2.5 mm, p < 0.0001). The LE configurations were categorized into single, double and continuous potentials and single potentials were demonstrated only in wide gaps >7 mm. There was a significant inversed correlation between the duration of the LE and gap size and also between the LE duration and the conduction velocity. Histological examination showed that the conduction properties through the gap depended mainly on its size.

CONCLUSIONS

The conductivity through the gap, which was affected by the size of the gap, may be evaluated by the duration and configuration of the local electrogram recorded from the gap.

Usefulness of the polarity in high-density wide range-filtered bipolar mapping to detect isthmus block during radiofrequency ablation of typical atrial flutter

BACKGROUND

The atrial activation sequence around the tricuspid annulus (TA) cannot always be used to establish whether complete block has been achieved across the cavotricuspid isthmus (CTI) during radiofrequency ablation (RFCA) for typical counterclockwise atrial flutter (CCW-AFL).

AIM

We examined whether a change in the polarity of the atrial high-density wide range-filtered bipolar electrograms recorded near the ablation line is an accurate indicator of complete CTI block.

METHODS

Nineteen patients with CCW-AFL underwent RFCA. Electrograms were recorded around the TA with duodecapolar conventional (2mm x 8mm x 2mm spacing) and high-density (2-mm spacing) Halo catheters. The bipolar electrograms on the high-density Halo catheter recorded from a series of adjacent electrode pairs positioned just lateral to the ablation line were filtered at a bandpass setting of 0.05-500 Hz. The activation sequence on the conventional Halo catheter during coronary sinus pacing (CSp) and inferolateral TA pacing, and the bipolar electrograms on the high-density Halo catheter during CSp were determined before and after RFCA. The final complete CTI block was verified by the presence of widely split double electrograms > or =100 msec along the ablation line.

RESULTS

The final complete CTI block was achieved in all the 19 patients. Before RFCA, the polarity of bipolar electrograms was predominantly negative during CCW-AFL and positive during CSp. In 18 of the 19 patients, the bipolar electrograms exhibited the CCW activation and a negative polarity during CSp only after complete CTI block. In one of those 18 patients, additional applications of RFCA changed the polarity of bipolar electrograms positive to negative although the conventional Halo electrogram activation sequence suggested complete CTI block during CSp. In seven patients, who had transverse conduction across the crista terminalis during CSp, the conventional Halo electrogram activation sequence suggested an incomplete CTI block. However, in six of those seven patients, the CCW activation had a predominantly negative polarity of the bipolar electrograms. In one of those seven patients, complete CTI block was unable to be detected even using the high-density Halo catheter.

CONCLUSIONS

These data demonstrate that the high-density wide range-filtered mapping can identify the CTI block in undetectable cases of complete CTI block or incomplete CTI block by the conventional method. The polarity of the bipolar electrograms recorded just lateral to the ablation line during CSp after RFCA of AFL may be used as a simple and an accurate indicator of complete CTI block.

Simple and efficient identification of conduction gaps in post-ablation recurring atrial flutters

AIMS

Cavo-tricuspid isthmus (CTI) radiofrequency (RF) ablation is a curative therapy for common atrial flutter (AFl), but is associated with a recurrence rate of 5-26%. Although complete bidirectional conduction block is usually achieved, the recurrence of AF is due to recovered conducting isthmus tissue through which activation wavefronts pass. We evaluated a simple and efficient electrophysiological strategy, which pinpoints the ablation target.

METHODS AND RESULTS

Twenty-five patients (19 men), mean age 61 +/- 6, with recurrent AFl required a repeat ablation, 250 +/- 160 days after a successful RF CTI procedure. Transverse CTI conduction was monitored during AFl or coronary sinus (CS) pacing by a 24-pole mapping catheter positioned in the right atrium (RA), with the distal poles in the CS, proximal poles on the lateral RA, and intermediate poles on the CTI. A slow conduction area traversing the CTI (velocity, 37 +/- 22 vs. 98 +/- 26 cm/s on either side, P < 0.05) and a lower potential amplitude than at both sides (0.2 +/- 0.15 vs. 0.5 +/- 0.5 mV, P < 0.05), defined by a bayonet-shaped depolarization sequence, were considered to represent the incomplete line of block (InLOB). An ablation catheter was progressively dragged up to this InLOB, from the tricuspid annulus to the inferior vena cava, analysing the widely separated double potentials (DPs) until these coalesced. In nine patients (35%), the target conduction gap was a coalesced fractionated atrial potential within the InLOB (duration, 77 +/- 12 ms), and in 16 patients (65%), a narrow DP toward the healthy margins of this InLOB (duration, 28 +/- 15 ms). Adopting this strategy yields 100% successful re-ablation of recurring AFl leading to bidirectional block, with a mean 2.7 +/- 1.4 RF applications.

CONCLUSION

Transverse CTI mapping precisely locates the InLOB and helps find conduction gaps along the CTI in re-ablation procedures for common AFl.

Vector Mapping in Localizing the Transverse Conduction Site of the Crista Terminalis in Patients with Typical Atrial Flutter

BACKGROUND

The difference in the conduction properties of the crista terminalis (CT) along its course, has not been fully clarified. Using the vector mapping method, we localized the transverse conduction (TC) site of the CT and elucidated its conduction capabilities in patients with typical atrial flutter (AF).

METHODS

The TC site of the CT was localized by the analysis of the polarity reversal of the double potentials recorded at 10 sites along the CT using a 20-pole deflectable catheter in 17 patients. The conduction capabilities of the TC site were analyzed during incremental pacing delivered from 100 beats/min to 2-to-1 local capture at the low anterior (LARA) and posterior (LPRA) right atrium.

RESULTS

At a pacing rate of 100 beats/min, TC at a single site was observed in 15 patients during LARA pacing and 7 patients during LPRA pacing, respectively. TC sites were distributed from superior to middle third of the CT in all patients. TC was bidirectional in 4 sites, but was unidirectional in the remaining 14 sites. Following an increase in the pacing rate, TC was blocked in all 7 sites during LPRA pacing and 11 of 15 sites during LARA pacing. Shift in the location of the TC site was not observed in any of the patients before TC block. The conduction block rate during pacing from LARA was significantly higher than that from LPRA (211 +/- 59 beats/min vs 145 +/- 66 beats/min, P < 0.01).

CONCLUSIONS

The superior to middle third of the CT provides TC capabilities. The TC across the CT was caused by a preferential conduction site and most of these TC were unidirectional, and stable in location irrespective of the change in the conduction rate.

Recurrent atrial flutter and atrial fibrillation after catheter ablation of the cavotricuspid isthmus: a very long-term follow-up of 333 patients

INTRODUCTION

Radiofrequency catheter ablation of the cavotricuspid isthmus is an effective therapy for typical atrial flutter (AFL), however, the long-term recurrence of AFL and early or late occurrence of atrial fibrillation (AF) are not well defined. This study investigated the long-term (up to 68 months) outcome of patients with typical AFL after catheter ablation of the cavotricuspid isthmus.

METHODS

This study included 380 patients with typical AFL, who received linear ablation of the cavotricuspid isthmus. They were followed up at the outpatient clinic. A questionnaire was used to evaluate the symptoms suggestive of tachyarrhythmias, and 12-lead ECG, Holter monitoring and event recorders were used to confirm the diagnosis of tachyarrhythmias.

RESULTS

At the end of study, 47 patients lost follow-up, so that 333 patients were enrolled into final analysis. Ten (3%) patients had failed ablation of typical AFL. Univariate analysis showed that left atrial dimension was the only factor related to failed ablation. During the long-term follow-up period of 29 +/- 17 months (range 7 to 68 months), 29 (9%) patients had recurrent AFL, including 15 with typical and 14 with atypical AFL. Univariate and multivariate analyses showed that incomplete isthmus block and inducible atypical AFL were the independent predictors of recurrent typical and atypical AFL, respectively. One hundred and two (31%) patients developed AF, including 48 with early occurrence of AF (within 3 months after ablation), and 54 with late occurrence of AF (greater than 3 months). Univariate and multivariate analyses showed that prior history of AF and inducible AF were independent predictors of early occurrence of AF, and prior history of AF was the only independent predictor of late occurrence of AF.

CONCLUSIONS

Linear ablation of the cavotricuspid isthmus is an effective therapy with low recurrence rate for patients with typical AFL. However, one-third patients had early or late occurrence of AF.

Identification of extremely slow conduction in the cavotricuspid isthmus during common atrial flutter ablation

INTRODUCTION

Complete isthmus block has been used as an endpoint for radiofrequency ablation for common atrial flutter (AF). We sought to systematically evaluate extremely slow conduction (ESC), which is easily misinterpreted as complete block.

METHODS AND RESULTS

We studied 107 consecutive patients (92 men, 15 women, 58 +/- 11 years) who had undergone a successful AF ablation procedure. A 24-pole catheter was positioned along the tricuspid annulus spanning the isthmus. Complete isthmus block was defined as the presence of a complete corridor of double potentials along the ablation line. Activation delay time (AT), activation difference (deltaA) between two adjacent dipoles, maximum activation difference (deltaA(max)), change in polarity (CP) and change in amplitude (CA) of the bipolar atrial electrogram were recorded and P-wave morphology in the surface electrocardiogram was analyzed. ESC was observed in 16 patients. Between ESC and complete block, differences were found on the two lateral dipoles adjacent to the ablation line (AT: 148 +/- 17 vs. 183 +/- 27 ms and 155 +/- 18 vs. 170 +/- 28 ms, P < 0.01; deltaA: -91 +/- 22 vs. -126 +/- 28 ms and -7 +/- 13 vs. 13 +/- 6 ms, P < 0.01). Statistically significant differences in CP were detected on the relevant dipoles (7/16 vs. 14/16 and 6/16 vs.13/16, P < 0.05). No significant difference was found either in CA or in terminal P wave positivity. Mean deltaA(max) were 13.8 +/- 5.0 and 27.8 +/- 9.5 ms (P < 0.001) respectively in ESC and complete block. Two types of ESC, regular and irregular, were demonstrated during the ablation procedure.

CONCLUSIONS

(1) ESC was observed in 15% of the patients during the AF ablation procedure. (2) The parameters of AT, deltaA, and CP may help to differentiate ESC from complete block. DeltaA(max) might be the most powerful indicator. (3) To verify complete block, it is essential to position the mapping catheter across the CTI in order to demonstrate the activation sequence up to the ablation line.

Electrogram polarity reversal as an additional indicator of breakthroughs from the left atrium to the pulmonary veins

OBJECTIVES

We assessed the anatomical distribution and electrogram characteristics of breakthrough from the left atrium (LA) to the pulmonary veins (PVs).

BACKGROUND

Localization of LA-PV breakthrough is an important technique for PV ablation in patients with atrial fibrillation (AF).

METHODS

A total of 157 patients with paroxysmal AF underwent PV disconnection guided by mapping with a circumferential 10-electrode catheter. Radiofrequency (RF) current was delivered ostially at the site(s) of earliest activation (113 patients) or electrogram polarity reversal defined by opposite polarity across adjacent bipoles (44 patients). Breakthrough sites were proved by changes in pulmonary vein potential activation sequence occurring as a result of localized RF delivery and were classified into four segments around the ostium (top, bottom, anterior, posterior). Results of mapping and ablation were compared between the two groups.

RESULTS

A total of 99% of 411 targeted PVs were successfully disconnected in both groups. Breakthroughs were most frequent at the bottom of superior PVs (85% prevalence) and the top of inferior PVs (75% prevalence). A wide activation front (>5 synchronous bipoles) indicating broad breakthrough was observed in 18% of PVs. Polarity reversal occurred with 88% sensitivity and 91% specificity at breakthrough sites. Polarity reversal was restricted to fewer bipoles (2.0 +/- 0.4 bipoles vs. 3.4 +/- 2.0 bipoles, p < 0.01) compared with earliest activation. Shorter RF application time was required to disconnect PVs with wide synchronous activation using polarity reversal compared with using conventional earliest activity (10.3 +/- 3.0 min vs. 12.3 +/- 3.4 min, p < 0.05).

CONCLUSIONS

Bipolar electrogram polarity reversal allows more precise localization of breakthrough compared with the earliest activation, particularly in cases of wide synchronous PV activation.

Monitoring of platelet function in the setting of glycoprotein IIb/IIIa inhibitor therapy

The role of the platelet in the pathogenesis of acute coronary syndromes is clearly established. In addition, the beneficial effects of oral and intravenous platelet inhibitor therapies were demonstrated in multiple, large, randomized clinical trials. However, despite these advances, current antiplatelet therapy fails to prevent coronary events in a substantial proportion of patients. One possible explanation for this phenomenon is that antiplatelet medications are administered without monitoring of the response to therapy. For example, oral antiplatelet therapy is administered as a standard dose for all patients, while intravenous inhibitors of the platelet glycoprotein (GP) IIb/IIIa receptor are dosed based on patient body weight. A major limitation of measuring platelet function has been that no practical test exists. The historic gold standard, bleeding time, was a very crude measure of platelet function with limited clinical utility. The current "gold standard," turbidimetric aggregometery, requires a central laboratory and is cumbersome to perform. Fortunately, a number of new tests with rapid turnaround time can be performed at the patient's bedside. This article discusses the details regarding the performance, advantages, disadvantages, and available data related to clinical use of each test in populations with coronary disease and patients treated with antiplatelet therapy.

Apparent bidirectional conduction block following radiofrequency catheter ablation of typical atrial flutter

OBJECTIVE

The purpose of this study is to determine the reliability of activation sequence mapping in assessing the presence of bidirectional conduction block (BCB) in typical atrial flutter (AFL) ablation.

INTRODUCTION

Radiofrequency ablation (RFA) can cure typical AFL by creating BCB across the right atrial isthmus. Effective conduction block across this region can prevent AFL recurrence, but accurate assessment of isthmus conduction may be flawed.

METHODS

BCB was measured before and after RFA by pacing at multiple rates on both sides of the isthmus during sinus rhythm. Pacing was performed from a low lateral tricuspid annulus site (proximal to the isthmus) and a coronary sinus Os site (distal to the isthmus), while recording simultaneously from 8-10 right atrial sites bordering the isthmus (4-5 free wall sites; 4-5 septal sites) as well as from an isthmus site. After ablation reinduction of atrial flutter was attempted from both sides of the block with rapid atrial pacing after BCB was established in all patients. In some patients lines of conduction block were evident at the isthmus (using the ablation catheter to map).

RESULTS

Of 65 patients undergoing RFA of AFL, 59 had typical AFL. In all 59 patients, BCB was demonstrated at all pacing cycle lengths 30 min after RFA applications. In 6 of these 59, AFL was inducible with atrial pacing despite apparent BCB. Further RFA resulted in non inducibility in all 6 patients. In the remaining 53/59 patients, BCB was associated with noninducibility at 30 min. A total of 8 recurrences were seen during a mean 19.3 +/- 8.3 (SD) month follow-up.

CONCLUSION

Apparent BCB as determined by activation sequence mapping outside of the isthmus is an excellent marker, but, as measured, may be a misleading method of assessing the presence or absence of conduction through the isthmus. It is necessary to attempt reinduction of AFL after apparent success. Elimination of typical AFL does not preclude other AFLs.

Resumption of right atrial isthmus conduction following atrial flutter radiofrequency ablation

Right atrial isthmus block is currently accepted as a success criterion of atrial flutter ablation. An electrophysiological study performed days after the ablation procedure may show recovery of conduction across the isthmus in some patients, followed by arrhythmia recurrence. However, few data are available on the time course of this recovery and on the monitoring of isthmus conduction at the end of the ablation procedure as a means of increasing the success rate of the procedure. Radiofrequency (RF) catheter ablation was performed in 28 men and 7 women (mean age = 65 +/- 11 years) presenting with common or clockwise atrial flutter (AFL) resistant to 2.9 +/- 1.8 antiarrhythmic drugs. Underlying heart disease was present in 13 patients. The ablation procedure was performed with an 8-mm-tip catheter, by several 45-second applications at a target temperature of 65 degrees C, directed to the isthmus between tricuspid annulus and inferior vena cava. Bidirectional isthmus block (BDB) was created with 4-24 RF applications in all but one patient. Special attention was paid to exclude incomplete block by meticulous mapping during pacing at the coronary sinus os and at the low lateral right atrium every 5 minutes for 20 minutes thereafter. Conduction recovered across the isthmus in 5 patients at 10, 10, 12, 15, and 16 minutes, respectively, and further RF applications were needed to obtain stable block. At a follow-up of 17 +/- 10 months, AFL occurred in the patient without, and in one patient with BDB. Thirty-three of the 34 patients (97%) with persistent BDB remained free of arrhythmia recurrence. This study showed that conduction resumed across the isthmus within 20 minutes, after AFL ablation in 15% of the patients. The long-term results of the procedure can be optimized by ascertaining the persistence of BDB during that period of time.

Electrogram characteristics indicative of a recurrent conduction site after ablation of the inferior vena cava-tricuspid annulus isthmus: a study in the canine blood-perfused atrioventricular preparation

Analysis of the electrograms recorded along the ablation line can identify a recurrent conduction site after ablation of the isthmus between the inferior vena cava (IVC) and tricuspid annulus (TA) for atrial flutter. The present study examined the relationship between the activation sequence and electrogram characteristics using a model of recurrent conduction in the isthmus. The canine heart was isolated (n=8) and cross-circulated with the arterial blood of a support dog. A plaque electrode was placed at the isthmus, and 42 bipolar electrograms (filtered and unfiltered) were recorded during pacing at 120beats/min from the lateral right atrium before and after creating a narrow gap by 2 discontinuous incisions from the TA to the IVC. All bipolar electrodes, with the cathode in the TA side and the anode in the IVC side, were placed perpendicular to the TA. Before creating the incisions, the wavefront (WF) from the pacing impulse traveled uniformly in the isthmus and almost in parallel to the TA, and the filtered electrogram at each site showed a single potential. After creating the incisions, the WF propagated through the gap and spread radially to the area distal to the incisions. In close proximity to the incision lines opposite to the pacing site, the WF advanced from the gap towards the TA and IVC perpendicularly to the TA. Filtered electrograms on the incision lines showed double or split potentials, whereas those on the gap showed a single or fractionated potential. In unfiltered electrograms recorded from the TA to the IVC in close proximity to the incision lines opposite the pacing site, reversal of electrogram polarity was noted at the gap. A single or fractionated potential between double potentials indicates a gap between lines of conduction block. Electrogram polarity reversal along the ablation line indicates the presence of 2 opposing WF arising from the gap.