Electrogram polarity and cavotricuspid isthmus block during ablation of typical atrial flutter

Initial negative concordance on unipolar and bipolar electrograms: a novel parameter for localizing the origin of premature ventricular contractions arising from pulmonary sinus cusps

BACKGROUND

The features of the unipolar electrogram (UEGM) and bipolar electrogram (BEGM) have been utilized to identify the site of origin of idiopathic premature ventricular contractions (PVCs) arising from pulmonary sinus cusps (PSCs), but for these PVCs, whether a negative concordance in the initial waves of both EGMs recorded above pulmonary valves can be used as a parameter to localize the origin has not been previously studied. We aimed to assess whether an initial negative concordance (INC) between the UEGM and BEGM might determine the origin of PVCs mapped and ablated within PSCs.

METHODS

Data were collected from 22 patients undergoing successful radiofrequency catheter ablation for symptomatic idiopathic PVCs within PSCs. The morphological features of both the UEGM and the BEGM recorded at all ablation sites were analyzed.

RESULTS

A total of 109 sites within PSCs were ablated in 22 patients with an age (mean ± SD) of 47.2 ± 17.2 years. Ablation resulted in procedural success in all patients. The INC was observed at 18 of 22 (81.8%) successful ablation sites, contrasted with 3 of 87 (3.4%) unsuccessful sites (P < 0.001). The INC was consistent with the outcomes of conventional mapping parameters and proved to be an additional useful predictor of ablation success, with a sensitivity, specificity, positive predictive value and negative predictive value of 81.8%, 96.6%, 85.7% and 95.5%, respectively.

CONCLUSIONS

An INC between the UEGM and the BEGM can predict the origin of PVCs arising from PSCs. An initial negative concordance between unipolar and bipolar electrograms indicates that the distal electrode of the ablation catheter is at the origin of premature ventricular contractions within pulmonary sinus cusps.

Achieving bi-directional conduction block during catheter ablation is not enough to prevent recurrence of cavo-tricuspid isthmus dependant atrial flutter: Role of subclinical conduction

BACKGROUND

Achieving bi-directional conduction block, as assessed by differential pacing and change in activation along tricuspid annulus (TA), across the cavo-tricuspid isthmus (CTI), is considered a satisfactory end point during catheter ablation of atrial flutter (AFL).

AIM

To assess role of subclinical conduction by observing polarity reversal of local bipolar signals from RS to QR pattern lateral to the line of ablation, in predicting recurrence of CTI dependant AFL after ablation in patients with bidirectional conduction block.

METHOD AND RESULTS

Of 683 patients undergoing ablation of CTI dependent AFL, 73 (10.6%) patients underwent redo flutter ablation and were evaluated further. The mean age was 60.8 years and 51% were males. Evidence of bidirectional block by differential pacing and change is activation along multipolar catheter and reversal of local bipolar signals from RS to QR pattern lateral to the line of ablation, during the 1st and subsequent procedure, were studied. 60% patients had confirmed bidirectional block of which 71% had lack of voltage reversal, at the end of 1st procedure. All patients with bidirectional block with lack of reversal of bipolar signals, after the first procedure had recurrence of AFL whereas only 3/11 (27%) people with bidirectional block and with absence of subclinical conduction had recurrence of AFL.

CONCLUSION

Achieving bidirectional conduction block is not sufficient to prevent recurrence of AFL after CTI ablation. Reversal of local bipolar signals, from RS to QR pattern along with achieving bidirectional conduction delay would reduce recurrence of AFL, post ablation.

Fundamentals of Cardiac Mapping

To characterize cardiac activity and arrhythmias, electrophysiologists can record the electrical activity of the heart in relation to its anatomy through a process called cardiac mapping (electroanatomic mapping, EAM). A solid understanding of the basic cardiac biopotentials, called electrograms, is imperative to construct and interpret the cardiac EAM correctly. There are several mapping approaches available to the electrophysiologist, each optimized for specific arrhythmia mechanisms. This article provides an overview of the fundamentals of EAM.

Impact of previous cardiac surgery on long-term outcome of cavotricuspid isthmus-dependent atrial flutter ablation

AIMS

The aim of this study was to determine the acute and long-term outcome of radiofrequency catheter ablation (RFCA) for cavotricuspid isthmus-dependent atrial flutter (CTI-AFL) in adults with and without previous cardiac surgery (PCS), and predictors of these outcomes. Structural alterations of the anatomical substrate of the CTI-AFL are observed in post-operative patients, and these may have an impact on the acute success of the ablation and in the long-term.

METHODS AND RESULTS

Clinical records of consecutive adults undergoing RFCA of CTI-AFL were analysed. Two main groups were considered: No PCS and PCS patients, who were further subdivided into acquired heart disease (AHD: ischaemic heart disease and valvular/mixed heart disease) and congenital heart disease [CHD: ostium secundum atrial septal defect (OS-ASD) and complex CHD]. Multivariate analysis identified clinical and procedural factors that predicted acute and long-term outcomes. A total of 666 patients (73% men, age 65 ± 12 years) were included: 307 of them with PCS. Ablation was successful in 647 patients (97%), 96% in the PCS group and 98% in the No PCS group (P = 0.13). Regression analysis showed that surgically corrected complex CHD was related to failure of the procedure [odds ratio 5.6; 95% confidence interval (CI) 1.6-18, P = 0.008]. After a follow-up of 45 ± 15 months, recurrences were observed in 90 patients (14%), more frequently in the PCS group: absolute risk of recurrence 18 vs. 10.5%, relative risk 1.71, 95% CI: 1.2-2.5, P = 0.006. Multivariate analysis indicated that the types of PCS [OS-ASD vs. No PCS: hazard ratio (HR) 2.57; 95% CI: 1.1-6.2, P = 0.03 and complex CHD vs. No PCS: HR 2.75; 95% CI: 1.41-5.48, P = 0.004], female gender (HR 1.55; 95% CI: 1.04-2.4, P = 0.048), and severe LV dysfunction (HR 1.36; 95% CI: 1.06-1.67, P = 0.04) were independent predictors of long-term recurrence.

CONCLUSION

Radiofrequency catheter ablation of CTI-AFL after surgical correction of AHD and CHD is associated with high acute success rates. The severity of the structural alterations of the underlying heart disease and consequently the type of surgical correction correlates with higher risk for recurrence.

Pace mapping in the atrium using bipolar electrograms from widely spaced electrodes

BACKGROUND

Pace mapping is a useful tool but is of limited utility for the atrium because of poor spatial resolution. We investigated the use of bipolar electrograms recorded from widely spaced electrodes in order to improve the resolution of pace mapping.

METHODS

This prospective study included patients undergoing a clinical electrophysiology study. Unipolar pacing from either the superior or inferior lateral right atrium was performed to simulate atrial tachycardia. Twelve-lead electrocardiograms were recorded during pacing as a template. In addition, three intracardiac bipolar electrograms from a set of widely spaced electrodes were also recorded. Subsequently, unipolar pacing was performed from electrodes at known distances from the initial pacing site, and the morphology of P waves in the electrocardiogram and bipolar electrograms were compared with that of the template. Morphological comparison was performed by a cardiologist and by automated computerized matching. Spatial resolution was calculated as the minimum distance at which there was no match.

RESULTS

Fifteen patients participated in the study. Distance at which differences in morphology were noted was smaller in the bipolar electrograms compared to that indicated by P waves in the electrocardiogram, when matched by the cardiologist (6.1±3.8 mm vs. 9.9±5.2 mm, p=0.012) or by automated analysis (4±0 mm vs. 9.9±4 mm, p<0.001).

CONCLUSIONS

Use of three bipolar electrograms recorded from a set of widely spaced electrodes in the right atrium improves the resolution of pace mapping compared to that using P waves from surface electrocardiograms alone.

Optimal Electrogram Voltage Recording Technique for Detecting the Acute Ablative Tissue Injury in the Human Right Atrium

BACKGROUND

The optimal recording technique of the electrogram voltage for detecting abnormal atrial tissue remains unclear. The aim of this study was to compare the impact of various recording techniques on the electrogram voltage after the delivery of ablation therapy in the human right atrium (RA).

MATERIAL AND METHODS

Noncontact mapping was performed in 27 patients with typical atrial flutter (mean age = 63 +/- 16, males = 20). Noncontact unipolar and bipolar electrograms were obtained before and after cavotricuspid isthmus (CTI) linear ablation. All unipolar electrograms were acquired with both wide-band filtering (0.5-300 Hz) and narrow-band filtering (32-300 Hz). The unipolar voltage measurements included both the peak-to-peak voltage and peak-negative voltage (PNV) for both filter settings.

RESULTS

A comparison of the electrogram voltage along the ablation line before and after the ablation demonstrated a greater reduction in the unipolar PNV with wide-band filtering (70 +/- 24%) than in any of the other recording modalities (P = 0.03). It was the most sensitive and specific recording technique to predict conduction block (cut-off Value 0.35 mV; sensitivity = 94.4% and specificity = 80%). A comparison of the electrogram voltage between the ablated atrial myocardium and nearby nonablated myocardium showed that the unipolar PNV with the wide-band filtering remained the most sensitive method to detect the acute ablative tissue injury, whereas the peak-to-peak bipolar voltage was the most specific method.

CONCLUSION

The noncontact unipolar electrogram using the PNV with wide-band filter settings (0.5-300 Hz) provided the most sensitive recording technique for detecting acute ablative tissue injury.

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.

Right ventricular pacing to assess transisthmus conduction in patients undergoing isthmus-dependent atrial flutter ablation: A new useful technique?

BACKGROUND

Successful radiofrequency (RF) ablation of typical, isthmus-dependent atrial flutter requires establishment and confirmation of bidirectional conduction block across the cavotricuspid isthmus. Low atrial pacing usually is performed from the bipoles of the 20-pole Halo catheter, septal and lateral to the cavotricuspid isthmus ablation line. However, occasionally this is difficult because of high pacing thresholds and/or saturation of the atrial electrograms recorded near the pacing catheter.

OBJECTIVES

The purpose of this study was to assess if right ventricular (RV) pacing and resulting retrograde atrial activation can be used to assess conduction block from the septum to the lateral wall in a clockwise direction.

METHODS

Thirty-five consecutive male patients (mean age 64 +/- 10 years; mean ejection fraction 42 +/- 13%; mean left atrial dimension 44 +/- 6 mm) with typical isthmus-dependent atrial flutter were studied. The following electrophysiology catheters were used: 20-pole catheter along the tricuspid annulus, quadripolar catheters at the His and/or RV apex, and 8-mm ablation catheter. Following RF ablation of the cavotricuspid isthmus, bidirectional conduction block was confirmed in all 35 patients by pacing at a cycle length of 600 ms from bipoles septal and lateral to the cavotricuspid isthmus ablation line. Conduction times from pacing artifact to adjacent bipolar atrial electrograms and reversal of atrial activation pattern were analyzed. RV pacing was performed and retrograde atrial activation pattern assessed. If retrograde AV nodal conduction was absent, isoproterenol was infused intravenously at 2 microg/min, and RV pacing was repeated. The conduction time between the double potentials across the cavotricuspid isthmus ablation line was measured.

RESULTS

Mean conduction times across the isthmus during septal (S), lateral (L), and RV pacing were 145 +/- 21 ms, 144 +/- 24 ms, and 129 +/- 20 ms, respectively. Retrograde AV nodal conduction was present in 34 of 35 patients (isoproterenol 8 patients). Evidence of conduction block by a clear change in activation pattern across the isthmus was seen during RV pacing in 33 of 35 patients with bidirectional conduction block.

CONCLUSION

RV pacing is a simple and easy maneuver that can be performed to assess isthmus conduction in most patients.

Recording Techniques for Clinical Electrophysiology

The precise techniques employed in the electrophysiology laboratory influence the nature of the electrograms that are recorded during mapping procedures. Unipolar recordings that are minimally filtered can be useful for mapping focal arrhythmia sources, but have substantial far-field signal that can obscure low-amplitude signals of interest in abnormal regions. Bipolar recordings are standard in most laboratories because rejection of far-field signal facilitates identification of local potentials in abnormal areas, but the signal of interest can be beneath either recording electrode and far-field signals do occur. Simultaneously obtained unipolar recordings are a useful adjunct to bipolar recordings in some situations. High pass filtering and digital sampling also influence electrogram characteristics. High pass filtering of unipolar recordings can be useful to reduce far-field components, but limits inferences from electrogram morphology.

Pattern of Isthmus Conduction Recovery Using Open Cooled and Solid Large‐Tip Catheters for Radiofrequency Ablation of Typical Atrial Flutter

INTRODUCTION

Open cooled-tip and solid 8-mm-tip catheters have demonstrated safety and effectiveness for radiofrequency current (RFC) ablation of typical atrial flutter (AFL). However, data from prospective and randomized studies in this setting are lacking.

METHODS AND RESULTS

One hundred thirty consecutive patients (104 men; 61 +/- 11 years) with AFL were randomized to undergo RFC catheter ablation either using a solid 8-mm-tip catheter (group A, 65 degrees C, 70 W, 60 s) or an open irrigated-tip catheter (group B, 65 degrees C, 50 W, 60 s, 17 mL/min flow). Endpoint was bidirectional conduction isthmus block. In cases of repeated (two times) transient isthmus block, the catheter was changed (crossed over) to the catheter used in the other randomization arm, but patients remained in the original group following intention-to-treat analysis. The selected endpoint could be achieved in all patients after 12 +/- 6 RFC pulses in group A and 10 +/- 7 RFC pulses in group B (P = 0.11). Procedure times were longer (159 +/- 38 min vs 138 +/- 37 min, P = 0.002) and x-ray exposures higher in group A (fluoroscopy time 25 +/- 17 min vs 21 +/- 10 min, P = 0.08; x-ray dosage 3,133 +/- 2,576 cGy.cm2 vs 2,326 +/- 1,405 cGy.cm2, P = 0.03). Transient isthmus block was observed in 23 group A patients and 12 group B patients (P = 0.03). Onset time of transient isthmus block ranged from 0.5 to 27 minutes. Repeated transient isthmus block occurred in 8 of the 23 patients in group A after 19 +/- 3 RFC applications. After crossover to the cooled-tip catheter, the endpoint was reached another 5 +/- 1 RFC pulses. In group B, all patients could be treated without change of ablation catheter. After a follow-up of 14 +/- 2 months, 2 patients (3%) in group A and 1 patient (1.5%) in group B presented with AFL recurrence.

CONCLUSION

Open cooled-tip catheters are more effective than solid large-tip catheters for AFL ablation. The greater effectiveness is evident in cases showing repeated conduction recovery within the cavotricuspid isthmus. Primary use of open irrigated-tip catheters should be considered for AFL ablation.

Clinical significance of inducible atrial flutter during pulmonary vein isolation in patients with atrial fibrillation

OBJECTIVES

This study was designed to determine the prevalence and clinical significance of atrial flutter (AFL) that occurs during catheter ablation for atrial fibrillation (AF).

BACKGROUND

Atrial flutter frequently occurs in patients with AF.

METHODS

Pulmonary vein isolation was performed in 133 consecutive patients (age 52 +/- 11 years) for paroxysmal (n = 112) or persistent (n = 21) AF. A clinical episode of AFL was documented in 40 of the 133 patients (30%). During the ablation procedure, AFL occurred in 86 patients (65%), either spontaneously (n = 36) or by rapid atrial pacing (n = 50), with AFL being typical in the majority (80%). Cavo-tricuspid isthmus ablation was performed in 28 of the 133 patients.

RESULTS

Among the 105 patients who did not undergo isthmus ablation, 25 patients (24%) were documented to have symptomatic AFL during a mean follow-up of 609 +/- 252 days. Among the clinical variables of age, gender, history of clinical AFL, ejection fraction, left atrial diameter, duration of AF, and occurrence of AFL during ablation, only a history of clinical AFL (p = 0.05) and occurrence of typical AFL during the ablation (p = 0.01) were independent predictors of symptomatic AFL during follow-up. The incidence of symptomatic AFL during follow-up was similar among patients who did and did not have long-term freedom from recurrent AF.

CONCLUSIONS

In patients with AF who have either a history of AFL or an episode of typical AFL during an electrophysiologic study, symptomatic AFL is common after pulmonary vein isolation. Therefore, cavo-tricuspid isthmus ablation is appropriate during pulmonary vein isolation if AFL has been observed clinically or in the electrophysiology laboratory.

Randomized comparison of anatomical versus voltage guided ablation of the cavotricuspid isthmus for atrial flutter

OBJECTIVES

The purpose of this prospective study was to compare radiofrequency catheter ablation of the cavotricuspid isthmus using a strictly anatomic approach to an approach guided by a bipolar voltage map to avoid high voltage zones in the cavotricuspid isthmus.

BACKGROUND

It is not clear whether local atrial electrogram amplitude influences the achievement of complete cavotricuspid isthmus block during radiofrequency catheter ablation for atrial flutter.

METHODS

Thirty-two patients with atrial flutter were randomized to cavotricuspid isthmus ablation using an anatomical approach (group I, 16 patients) or guided by a bipolar voltage map (group II, 16 patients). A 3-dimensional electroanatomic mapping system and an 8-mm-tip ablation catheter were used in all patients. With the anatomical approach, an ablation line was created in the cavotricuspid isthmus at a 6 o'clock position in the 45 degree left anterior oblique projection. During voltage-guided ablation, a high-density bipolar voltage map of the cavotricuspid isthmus was created, and then contiguous applications of radiofrequency energy were delivered to create an ablation line through the cavotricuspid isthmus sites with the lowest bipolar voltage.

RESULTS

Complete cavotricuspid isthmus conduction block was achieved in 100% of patients in each group. The mean maximum voltages along the line were 3.6 +/- 1.5 mV in group I, and 1.2 +/- 0.9 mV in group II (P < .01). Creating a high-density voltage map was associated with approximately 15-minute increase in the total procedure time (P = .2). During a mean follow-up of 177 +/- 40 days, there were no recurrences of atrial flutter in either group. There were no complications in either group.

CONCLUSIONS

When cavotricuspid isthmus ablation for atrial flutter is performed with an 8-mm-tip catheter, complete block can be achieved in all patients regardless of local voltage. Ablation of high voltage zones is not associated with a higher recurrence rate. Therefore, anatomic ablation without voltage mapping is the preferred initial approach for cavotricuspid isthmus ablation.

Atrial electrogram amplitude and efficacy of cavotricuspid isthmus ablation for atrial flutter

Large atrial electrogram amplitudes recorded in the cavotricuspid isthmus (CTI) may reflect thick atrial musculature. For this reason, in patients with atrial flutter, the efficacy of an application of conventional radiofrequency energy may be related to the amplitude of the local atrial electrogram. In 100 consecutive patients (mean age 59 +/- 13 years) with atrial flutter, contiguous applications of radiofrequency energy were delivered in the CTI. The criterion for complete CTI block was the presence of widely split double potentials (>110 ms) along the entire ablation line during pacing from the coronary sinus and posterolateral right atrium. The atrial electrogram amplitude was measured before and after applications of radiofrequency energy at sites of gaps in the ablation line. Complete CTI block was achieved in 90 (90%) of the 100 patients. The mean atrial electrogram amplitudes at gap sites where an application of radiofrequency energy did and did not result in complete block were 0.36 +/- 0.42 and 0.67 +/- 0.62 mV, respectively (P < 0.01). The positive and negative predictive values (for complete block) of a >/=50% decrease in electrogram amplitude after an application of radiofrequency energy were 100% and 35%, respectively. The mean atrial electrogram amplitude is larger at CTI sites where complete isthmus block cannot be achieved with conventional radiofrequency energy. The efficacy of conventional radiofrequency ablation may be improved by identifying areas in the CTI where the voltage is relatively low.

Effects of isoproterenol and amiodarone on the double potential interval after ablation of the cavotricuspid isthmus

INTRODUCTION

A corridor of double potentials along the ablation line has been recognized to be an indicator of complete cavotricuspid isthmus block. Isoproterenol is used to confirm cavotricuspid isthmus block, but the effects of isoproterenol on the double potential interval (DPI), either in the absence or presence of amiodarone, are unknown.

METHODS AND RESULTS

Thirty-two patients with isthmus-dependent atrial flutter underwent successful ablation of the cavotricuspid isthmus. The procedure was performed in the drug-free state in 23 patients, and 2 to 7 days after discontinuation of chronic amiodarone therapy in 9 patients. Electrograms recorded along the ablation line before and during isoproterenol infusion were analyzed after isthmus block was achieved. Double potentials were recorded along the entire ablation line upon achievement of complete isthmus block in all patients. The DPI in 9 patients treated with amiodarone was longer than in the other patients (147 +/- 32 msec vs 119 +/- 19 msec, P < 0.001). The DPI increased as the pacing cycle length shortened in patients treated with amiodarone, but not in the other patients. At all pacing cycle lengths, isoproterenol shortened the DPI to a greater extent in the patients treated with amiodarone than in the other patients.

CONCLUSION

Amiodarone results in rate-dependent prolongation of the DPI during coronary sinus pacing after ablation of the cavotricuspid isthmus. Isoproterenol shortens the DPI despite the presence of complete isthmus block, and this effect is accentuated in the presence of amiodarone.

Double potential interval and transisthmus conduction time for prediction of cavotricuspid isthmus block after ablation of typical atrial flutter

BACKGROUND

Complete bi-directional isthmus block is the endpoint of typical atrial flutter ablation. The purpose of this study was to investigate the feasibility of the local double potential (DP) interval and the change in transisthmus conduction time for predicting complete isthmus block after ablation of the cavotricuspid isthmus.

METHODS

The study population consisted of 32 patients with typical atrial flutter after a procedure of radiofrequency (RF) ablation of the cavotricuspid isthmus (16 had incomplete block and 16 had complete block). The transisthmus conduction time was determined during pacing from the proximal coronary sinus and low lateral right atrium before and after RF ablation. The DP interval close to the ablation line was evaluated after final RF energy application.

RESULTS

In the counterclockwise direction, transisthmus conduction time had an increase of 37 +/- 25.4% and 127.3 +/- 35.5% (P < 0.001), and the DP interval was 63.3 +/- 8.7 ms and 120 +/- 17.4 ms (P < 0.001) after achievement of incomplete and complete block, respectively. The sensitivity, specificity, positive and negative predictive values of an increase in the transisthmus conduction time > or =50% were 100%, 81%, 84% and 100%, respectively; those of DP interval > or =100 ms were 100%. In the clockwise direction, transisthmus conduction time had an increase of 38.8 +/- 28.6% and 135.7 +/- 63.6% (P < 0.001), and the DP interval was 63.6 +/- 13.8 ms and 127.7 +/- 27.1 ms (P < 0.001) after achievement of incomplete and complete block, respectively. The sensitivity, specificity, positive and negative predictive values of an increase in the transisthmus conduction time > or =50% were 100%, 67%, 83% and 100%, respectively; those of the DP interval > or =100 ms were 100%.

CONCLUSIONS

The transisthmus conduction time > or =50% increase or DP interval > or =100 ms was feasible to predict complete bi-directional isthmus block.

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.

Catheter ablation of atrial flutter and macroreentrant atrial tachycardia

Catheter ablation has evolved from an experimental technique to first-line therapy for the treatment of atrial flutter. Atrial flutter is characterized by a macroreentrant atrial tachycardia circuit. Successful ablation of atrial flutter involves (1) mapping the atrial flutter to define the conduction zones within the re-entrant circuit to determine whether the atrial flutter is isthmus-dependent, non-isthmus-dependent, or atypical; (2) interrupting the atrial flutter macroreentrant circuit with an ablation catheter by creating either focal or linear lesions within a critical zone of slow conduction that extends to anatomical borders; and (3) terminating the tachycardia and demonstrating conduction block within the atrial flutter circuit after ablation. This update discusses the classification schemes of atrial flutter and macroreentrant atrial tachycardias, reviews the technique of radiofrequency catheter ablation, and highlights recent ablation approaches for atrial flutters and macroreentrant atrial tachycardias.

Double potentials along the ablation line as a guide to radiofrequency ablation of typical atrial flutter

OBJECTIVES

The purpose of this study was to determine the characteristics of double potentials (DPs) that are helpful in guiding ablation within the cavo-tricuspid isthmus.

BACKGROUND

Double potentials have been considered a reliable criterion of cavo-tricuspid isthmus block in patients undergoing radiofrequency ablation of typical atrial flutter (AFL). However, the minimal degree of separation of the two components of DPs needed to indicate complete block has not been well defined.

METHODS

Radiofrequency ablation was performed in 30 patients with isthmus-dependent AFL. Bipolar electrograms were recorded along the ablation line during proximal coronary sinus pacing at sites at which radiofrequency ablation resulted in incomplete or complete isthmus block.

RESULTS

Double potentials were observed at 42% of recording sites when there was incomplete isthmus block, compared with 100% of recording sites when the block was complete. The mean intervals separating the two components of DPs were 65 +/- 21 ms and 135 +/- 30 ms during incomplete and complete block, respectively (p < 0.001). An interval separating the two components of DPs (DP(1-2) interval) <90 ms was always associated with a local gap, whereas a DP(1-2) interval > or =110 ms was always associated with local block. When the DP(1-2) interval was between 90 and 110 ms, an isoelectric segment within the DP and a negative polarity in the second component of the DP were helpful in indicating local isthmus block. A DP(1-2) interval > or =90 ms with a maximal variation of 15 ms along the entire ablation line was an indicator of complete block in the cavo-tricuspid isthmus.

CONCLUSIONS

Detailed analysis of DPs is helpful in identifying gaps in the ablation line and in distinguishing complete from incomplete isthmus block in patients undergoing radiofrequency ablation of typical AFL.