Tracking dynamic conduction recovery across the cavotricuspid isthmus

Interest of waiting time for spontaneous early reconnection after cavotricuspid isthmus ablation: A monocentric randomized trial

INTRODUCTION

The aim of this study was to determine the rate of recurrent atrial flutter (AFl) after isolated cavotricuspid isthmus (CTI) ablation and to evaluate the impact of a waiting period with the search for early resumption of the CTI block on the long-term outcome.

METHOD

Three hundred and nineteen consecutive patients referred for typical AFl ablation were randomly assigned to CTI ablation with continuous reevaluation of the CTI block during 30 minutes and early reablation if needed (waiting time [WT] + group, n  =  155) or to CTI ablation with no waiting period after proven bidirectional CTI block (WT - group, n  =  164). All patients were regularly followed-up.

RESULT

In the WT+ group, 10 patients (6%) presented a recovery across the CTI (time to recovery: 17 ± 7') and were reablated at the end of the waiting period. After a median follow-up of 21 months, the rate of recurrent AFl was significantly higher in the WT - group as compared to the WT+ group (11.6% [19/164] vs 2.5% [4/155], respectively; P  =  0.007). However, no significant differences in the subsequent rate of AF were observed between the two groups (29% [WT -] vs 32% [WT+], P  =  0.66). During the follow-up, 28 patients from the WT - group underwent a second ablation procedure (16 AFl redo and 12 AF ablation) versus 10 patients form the WT+ group (three AFl redo and seven AF ablation).

CONCLUSION

Waiting 30 minutes after CTI ablation to check for early resumption and early reablation allows for decreasing significantly the rate of recurrent atrial flutter.

Atrial Flutter, Typical and Atypical: A Review

Clinical electrophysiology has made the traditional classification of rapid atrial rhythms into flutter and tachycardia of little clinical use. Electrophysiological studies have defined multiple mechanisms of tachycardia, both re-entrant and focal, with varying ECG morphologies and rates, authenticated by the results of catheter ablation of the focal triggers or critical isthmuses of re-entry circuits. In patients without a history of heart disease, cardiac surgery or catheter ablation, typical flutter ECG remains predictive of a right atrial re-entry circuit dependent on the inferior vena cava-tricuspid isthmus that can be very effectively treated by ablation, although late incidence of atrial fibrillation remains a problem. Secondary prevention, based on the treatment of associated atrial fibrillation risk factors, is emerging as a therapeutic option. In patients subjected to cardiac surgery or catheter ablation for the treatment of atrial fibrillation or showing atypical ECG patterns, macro-re-entrant and focal tachycardia mechanisms can be very complex and electrophysiological studies are necessary to guide ablation treatment in poorly tolerated cases.

Usefulness of pre-procedure cavotricuspid isthmus imaging by modified transthoracic echocardiography for predicting outcome of isthmus-dependent atrial flutter ablation

BACKGROUND

Anatomic characteristics of the cavotricuspid isthmus (CTI) have been reported to be related to the outcome of atrial flutter ablation therapy. However, preprocedural evaluation of CTI anatomy using modified transthoracic echocardiography to guide atrial flutter ablation has not been well described.

METHODS

Transthoracic echocardiography was prospectively performed before atrial flutter ablation in 42 patients with typical CTI-dependent atrial flutter. A modified apical long-axis view was designed to visualize and evaluate anatomic characteristics of the CTI and Eustachian ridge (ER). A prominent ER, extending from the inferior vena cava to the interatrial septum, is defined as an extensive ER.

RESULTS

Twenty-eight patients had straightforward ablation procedures, and 14 patients had difficult ablation procedures. Two patients with difficult procedures had unsuccessful ablation. Multivariate analysis (using CTI length, the presence of a pouch or recess, ER morphology, and significant tricuspid regurgitation as variables) showed that the presence of extensive ER was the only independent predictor of a difficult ablation procedure. The ablation time in patients with extensive ER (n = 13) was significantly longer than in those patients with nonextensive ER (n = 29) (1,638.4 ± 1,548.3 vs 413.8 ± 195.5 sec, P = .015). The incidence of difficulty in achieving bidirectional isthmus block was also higher in patients with extensive ER (10 of 13 vs four of 29, P < .001).

CONCLUSION

Preprocedural transthoracic echocardiography using a modified apical long-axis view is useful to characterize the morphology of the CTI and the ER. An extensive ER is a strong predictor for difficult ablation of CTI-dependent atrial flutter.

Translesion stimulus-excitation delay indicates quality of linear lesions produced by radiofrequency ablation in rabbit hearts

Failure of cardiac antiarrhythmic ablation to block action potential conduction produces poor outcomes which lead to repeat procedures. To overcome this, an intraoperative index of the quality of an ablation lesion is needed. We hypothesized that a rise in the translesion stimulus-excitation delay (TED) can indicate a continuous, transmural, linear lesion, and that the TED is related to the path length in the viable tissue around the lesion. Rabbit hearts were isolated, perfused with a warm physiological solution and stained with transmembrane potential-sensitive fluorescent dye. Radiofrequency (RF) ablation was performed on ventricular epicardium with a vacuum-assisted coagulation device to produce either a complete or incomplete lesion. Complete lesions were both transmural and continuous. Incomplete lesions were noncontinuous or nontransmural. The TED was determined with bipolar stimulation at one side of the lesion and either a bipolar electrogram at the other side or optical mapping on both sides. Hearts were then stained with tetrazolium chloride and examined histologically to estimate minimum path lengths of viable tissue from the stimulation site to the recording site. Complete lesions increased the TED by factors of 2.6-3.1 (p < 0.05), whereas incomplete lesions did not significantly increase the TED. Larger minimum path lengths were found for cases that had an increased TED. The TED was quantitatively predictable based on a conduction velocity of 0.38-0.49 m s(-1), which is typical of rabbit hearts. The TED significantly increases when a linear lesion is complete, suggesting that an intraoperative measurement of the TED may help to improve ablation lesions and outcomes. Predictability of the TED based on the viable tissue path suggests that quantitative TEDs for clinical lesions may be anticipated provided that the conduction velocity is considered.

Temporal Pattern of Conduction Recurrence During Radiofrequency Ablation for Typical Atrial Flutter

INTRODUCTION

Conduction recurrence during radiofrequency (RF) ablation of cavotricuspid isthmus for typical atrial flutter is common. Understanding the temporal pattern of recurrences could help to predict a durable bidirectional block (BDB) and optimize the procedure.

METHODS AND RESULTS

We analyzed atrial flutter ablations in 108 consecutive patients (85 males, age 63 +/- 11 years). RF energy was delivered through 8-mm tip or 4-mm cooled-tip catheter. On average, 18 +/- 11 pulses were necessary to achieve BDB. The time to recurrence of conduction after RF cessation was recorded. Early and late conduction recurrences were defined as < or =10 minutes and >10 minutes, respectively. Patients were observed for > or =30 minutes after bidirectional cavotricuspid isthmus (CTI) block was achieved. Conduction did not recur in 46 patients. In 8 cases, no block was achieved. A total of 167 conduction recurrences were recorded in the remaining 54 cases (1-10 per case). Of these, in 53 patients, recurrences were classified as early (98%) and 14 patients had late recurrences (8%). Thirteen patients had both early and late recurrences (24%). All but one late recurrence were preceded by at least one early recurrence. Absence of early recurrence had negative predictive value of 98%, while any early recurrence had positive predictive value of 26% for subsequent late conduction recovery.

CONCLUSION

Incidence of isthmus conduction recurrence rapidly decayed during the waiting period. Absence of conduction recurrence within 10 minutes after first successful RF delivery was highly predictive of persistent BDB.

A New and Simple Method for Distinguishing Complete from Incomplete Block Through the Cavotricuspid Isthmus

BACKGROUND

A complete line of block (CLOB) in the cavotricuspid isthmus (CTI) is the endpoint of typical atrial flutter ablation. Before CTI block is obtained, a progressive CTI conduction delay due to an incomplete line of block (InLOB) can be difficult to distinguish from CLOB. The purpose of this study was to assess a new simple approach based on the changes in atrio-ventricular (AV) conduction delays during septal and lateral right atrial pacing, to distinguish a CLOB from an InLOB during typical atrial flutter (AFL) ablation.

METHODS AND RESULTS

Forty patients who presented an InLOB before a CLOB, and a stable (AV) conduction delay at 600 ms cycle length pacing (when in sinus rhythm), during AFL ablation were included in this study. A 24-pole mapping catheter was positioned so that 2 adjacent dipoles bracketed the targeted CTI line of block (LOB), with proximal dipoles lateral to the LOB and distal dipoles in the coronary sinus. Two pacing sites were lateral (position L1 and L2) and one was septal (position S) to the LOB, with locations L1 and S closest to the LOB. During L1, L2 and S site pacing, the delay between the pacing artefact and the peak of the R wave in a surface ECG (lead II) was measured. We measured the following conduction delays (mean +/- SD in ms), during InLOB versus CLOB: (L1 to R) 320.5 +/- 68.0 versus 367.0 +/- 62.0, p = 0.001; (L2 to R) 333.0 +/- 59.0 versus 338.0 +/- 62.0, p = 0.663, (S to R) 259.4 +/- 51.5 versus 247.1 +/- 55.5, p = 0.987. We calculated the following data during an InLOB versus a CLOB: (L1R-L2R) -12.3 +/- 7 versus 20.2 +/- 12.7, p = 0.001; (L1R-SR) 51.1 +/- 21.5 versus 120.1 +/- 16.6, p < 0.05. The sensitivity, specificity, positive and negative predictive values for CLOB with (L1R-SR > 94 ms) and with (L1R-L2R > 0 ms) were respectively; 100%, 98%, 98% and 100%.

CONCLUSIONS

This study establishes that lateral versus septal right atrial pacing sites combined with the measure of AV conduction delay on a surface ECG can be useful to distinguish a CLOB from an InLOB during AFL ablation.

Differential Pacing for Distinguishing Slow Conduction from Complete Conduction Block of the Tricuspid-Inferior Vena Cava Isthmus after Radiofrequency Ablation for Atrial Flutter—Role of Transverse Conduction through the Crista Terminalis

BACKGROUND

Partial conduction block has been suggested a predictor of recurrence of atrial flutter (AFL).

AIM

The aim of this study was to assess transverse conduction by the crista terminalis (CT) as a problem in evaluating isthmus block and the usefulness of differential pacing for distinguishing slow conduction (SC) and complete conduction block (CB) across the ablation line.

METHODS

We assessed 14 patients who underwent radiofrequency catheter ablation of the eustachian valve/ridge-tricuspid valve isthmus for typical AFL. Activation patterns along the tricuspid annulus (TA) suggested incomplete CB across the isthmus. In these patients, atrial pacing was performed from the low posteroseptal (PS) and anteroseptal (AS) right atrium (RA) while the ablation catheter was placed at the ablation line where double potentials (DPs) could be recorded. The pattern of activation of the RA free wall was assessed by a 20-pole catheter positioned along the CT during pacing from the coronary sinus (CS) ostium (CSos) and low lateral RA (LLRA).

RESULTS

Faster transverse conduction across the CT resulted in simultaneous or earlier activation of the distal halo electrodes than of the more proximal electrodes, suggesting incomplete conduction block across the isthmus. CB (13) and SC (1) were detected as changes in the activation times of the first and second components of DPs (DP1, DP2) during PS RA pacing and AS RA. Similar changes in the activation times DP1 and DP2 during AS RA pacing as compared to PS RA reflected SC through the isthmus, whereas increased DP1 activation time and decreased of DP2 activation time reflected complete conduction block across the isthmus.

CONCLUSIONS

Transverse conduction across the CT influences the sequence of activation along the TA after isthmus ablation. Differential pacing can distinguish SC from complete conduction block across the ablation line in the isthmus.

Histopathologic Background for Resistance to Conventional Catheter Ablation of Common Atrial Flutter

Histopathologic examination of the cavotricuspid isthmus in which a large-tip catheter was necessary to achieve conduction block is presented. No thickened myocardium or prominent trabeculation was observed on the ablation line. A small cardiac vein extending through the isthmus across the ablation scar was detected. The remaining myocardial cells were distributed along the small cardiac vein. It is possible that the luminal blood flow of the small cardiac vein protects the surrounding atrial muscle from effective delivery of radiofrequency energy.

The usefulness of surface 12-lead electrocardiogram to predict intra-atrial conduction block after successful atrial flutter ablation

Intraatrial conduction block at the inferior vena cava-tricuspid annulus isthmus was shown to predict successful atrial flutter ablation. However, its demonstration requires the use of several electrode catheters. Thus, a simple approach using surface 12-lead ECG to prove the conduction block would be valuable. Twenty-two patients were prospectively studied during low septal and low lateral atrial pacing before and after successful atrial flutter ablation. Creation of the conduction block was confirmed by comparing the sequence of atrial activation using 3 multipolar catheters during atrial pacing before and after ablation. During low septal pacing, there was no significant difference before and after ablation in P-wave width, axis, or morphology. During low lateral atrial pacing, there was a significant P-wave axis rotation towards the right (from -67 +/- 27 degrees to +13 +/- 35 degrees, P <.001), and P-wave polarity in limb lead II changed from predominantly negative to predominantly positive in 21 of 22 patients. There was also an increase in P-wave width (from 136 +/- 32 to 169 +/- 36 ms, P <.001) and stimulus-to-QRS interval (from 268 +/- 61 ms to 343 +/- 95 ms, P <.001) during low lateral pacing that was not observed during low septal pacing. We conclude that creation of a conduction block in the inferior vena cava-tricuspid annulus isthmus modifies surface 12-lead ECG during low lateral atrial pacing only. We also suggest that P-wave polarity in limb lead II during low lateral pacing could be used as a noninvasive marker of unidirectional counter-clockwise conduction block during atrial flutter ablation.

Large tip electrodes for successful elimination of atrial flutter resistant to conventional catheter ablation

The most widely accepted criterion for successful radiofrequency catheter (RFC) ablation of typical atrial flutter is the development of bi-directional isthmus block. In a subset of patients, conventional RFC ablation fails to achieve this endpoint because deeper and wider lesions are required. We investigated the efficacy of a long 8-mm tip catheter in these cases. One hundred and seventy-four consecutive patients (137 male; 61 +/- 9 years) with recurrent typical atrial flutter underwent conventional RFC ablation first with a standard 4 mm tip catheter. In resistant cases (n = 52), ablation was continued using a large tip 8-mm catheter when the 4-mm tip catheter failed. Resistant atrial flutter was identified when 21 RFC pulses failed to reach the selected endpoint of bi-directional isthmus block or in cases of transient bi- directional block (at least 3 episodes). In 122 of the 174 patients (70%) conventional atrial flutter ablation was successfully performed with 13 +/- 5 RFC applications. In the remaining 52 subjects (30%), the ablation procedure was completed using the large tip electrode catheter. In 30 of these 52 patients (58%), the catheter was changed because of persistent intra-atrial conduction after 21 RFC pulses and in 22 (42%) because of intermittent conduction block after 11 +/- 5 applications. Using the large tip electrode catheter, the selected endpoint was achieved in all patients of both groups with 3 +/- 2 RFC pulses (power output of 50-60 W, pulse duration of 60 sec). No post-procedure complications were observed. After 15 +/- 5 months of follow-up, 16 patients (9%) had recurrence of atrial flutter. Five of the patients had been in the resistant group. In patients with atrial flutter resistant to conventional ablation therapy, the long tip (8-mm) catheter appears to be a safe and effective alternative to use of the conventional 4-mm tip catheter.

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.

Differential pacing for distinguishing block from persistent conduction through an ablation line

BACKGROUND

Because complete linear conduction block is necessary to minimize the recurrence of reentrant tachycardias such as typical atrial flutter, we investigated a simple technique to recognize a persistent gap or complete linear block.

METHODS AND RESULTS

We prospectively evaluated cavotricuspid isthmus conduction in 50 patients (age 63+/-8 years, 43 men) after radiofrequency ablation. The distal and proximal bipoles of a quadripolar catheter placed close to the ablation line were successively stimulated during recording from the ablation line. We hypothesized that because the initial and terminal components of local potentials reflected activation at the ipsilateral and contralateral borders of the ablation lesion, a change to a more proximal pacing site without moving the catheter would prolong the stimulus to the initial component timing, whereas the response of the terminal component would depend on the presence of block or persistent conduction. A shortening or no change in timing of the terminal component would indicate block, whereas lengthening would indicate persistent gap conduction. The results were compared with previously described criteria for isthmus block. Ninety-two sites were assessed: 17 before and 75 after the achievement of complete isthmus block. The timing of the initial component was delayed by 19+/-9 ms, and the terminal component was advanced by 13+/-8 ms after block and delayed by 12+/-9 ms in case of persisting conduction. The sensitivity, specificity, and positive and negative predictive values for linear block were 100%, 75%, 94%, and 100%, respectively.

CONCLUSIONS

An accurate assessment of isthmus block or persistent isthmus conduction is possible with this technique of differential pacing.