Complete Line Of Block Research Articles

Confirmation of the achievement of linear lesions using "activation vectors" based on omnipolar technology.

Although differential pacing conventionally has been used to confirm the achievement of block across linear lesion sets, high-resolution mapping demonstrates that pseudo-block is observed in 20%-30% of cases. The purpose of this study was to examine the reliability and versatility of a method using "activation vectors" based on omnipolar technology to confirm the block line. Linear ablation was performed during pacing, with the HD Grid catheter (Abbott) placed beside the linear lesion opposite the pacing site. The endpoint of complete linear lesion was complete inversion of the activation vectors to the opposite direction. When inversion of the activation vectors was not observed after 10 minutes of radiofrequency (RF) application, high-resolution mapping was performed to assess whether complete block was achieved. In 33 patients, 24 cavotricuspid isthmus lines, 11 mitral isthmus (MI) lines, 16 posterior lines, and 2 intercaval lines were performed using this method. Of the total of 53 lines, 10 (18.9%) required intermediate evaluation of the block line with high-resolution mapping because of the absence of inversion of activation vectors despite 10 minutes of RF application, resulting in incomplete block with endocardial gaps or epicardial conductions. Additional RF applications finally achieved inversion in direction of activation vectors in the 10 lines. In total, the present method can diagnose achievement of complete block line with 100% accuracy, whereas conventional differential pacing misdiagnosed incomplete block with epicardial conduction in posterior lines in 3 cases and in MI lines in 2 cases. Confirmation of complete linear lesions using "activation vectors" based on omnipolar technology is a reliable and versatile method.

Characterizing Recurrence Following Hybrid Ablation in Patients With Persistent Atrial Fibrillation.

It is widely accepted that atrial fibrillation (AF) accounts for half of arrhythmia recurrences following endocardial catheter ablation of AF. An epicardial-endocardial approach (hybrid) has emerged as an alternative to endocardial ablation alone for the treatment of AF, yet recurrence after a hybrid procedure has not been well characterized. This retrospective study is aimed at characterizing recurrence following hybrid ablation for patients with persistent AF. Patients with persistent AF (N=108) received both endocardial and epicardial ablation of the posterior left atrial wall using catheter ablation and a small midline surgical approach (hybrid). Presence of atrial flutter or AF was determined with ambulatory monitoring (n=22) or electrocardiogram analysis (n=86) at each follow-up visit. Recurrence mode was confirmed by electrophysiology study for those patients undergoing subsequent catheter ablation after hybrid ablation. Patients were followed for a mean ± standard deviation of 25 ± 14 months. Of patients who had a recurrence, 53% (n=33) were in atrial flutter and 47% (n=29) were in AF. Of those who had a recurrence with atrial flutter, 14 received repeat ablation for either left (n=11) or left/right (n=3) atrial flutter and 3 received AF ablation. Half of ablations for atrial flutter recurrence following the hybrid procedure involved the mitral isthmus. Atrial flutter accounts for about half of arrhythmia recurrences post-hybrid ablation. If catheter ablation of the mitral isthmus is considered during the hybrid procedure to prevent subsequent occurrence of perimitral flutter, bidirectional block must be performed to ensure a complete line of block.

Linear ablation for atrial fibrillation guided by acoustic imaging: “How does it sound?”

Despite advances in techniques on catheter ablation of atrial fibrillation (AF), a substantial proportion of patients after ablation had recurrences of AF, and even after multiple repeated procedures. Pulmonary vein isolation remains the cornerstone of most AF ablation procedures, and additional ablation strategies such as creation of lines of conduction block in the left atrium (LA) and right atrium (RA) and ablation targeting onpulmonary vein triggers, the autonomic ganglia, or complex fractionated electrograms have been employed in either the initial or the repeat procedure with variable success. Catheter-based linear atrial ablation attempts to replicate the surgical Maze procedure, in which up to a 90% long-term success rate of maintaining sinus rhythm has been reported. The comparatively lower success rate of catheter vs surgically delivered linear ablation could be explained by multiple factors such as inadequate line continuity and transmurality, difference in line design, and additional effect of surgical procedures on autonomic ganglia. Among these factors, uncertainty in creating a complete line of block is thought to be the main Achilles tendon of catheter-based approach, not only because it is unable to eliminate AF but also because it is potentially proarrhythmogenic. In this issue of HeartRhythm, Eyerly et al report their experience of using intracardiac acoustic radiation force impulse imaging (ARFI) in animals to guide the creation of a complete line of block. This technology is based on the principle that focused and short duration intracardiac ultrasound will create an acoustic force on myocardial tissue. These pulses induce local tissue displacements that are influenced by tissue characteristics. Thus, protein denaturation following catheter blation will result in a “stiffer” myocardium compared with he surrounding untreated myocardium and thus provide an ndicator of the adequacy of catheter ablation, almost like an ndirect “palpation” of the tissue characteristics. The authors have demonstrated previously in an in vitro porcine myocardium model that this technology is capable of “visualizing” radiofrequency ablation (RFA)-induced lesions of dimension within 1 mm (axial) to 2 mm (lateral).

Local Coronary Flow Is Associated With an Unsuccessful Complete Block Line at the Mitral Isthmus in Patients With Atrial Fibrillation

The addition of a mitral isthmus (MI) block line after pulmonary vein isolation could lead to a favorable outcome of catheter ablation in patients with atrial fibrillation (AF). However, it is sometimes tough to create a complete MI block line, and the cooling effect because of the local coronary flow may prevent the creation of a successful MI block line. This study enrolled 81 AF patients in whom the creation of an MI block line was attempted in those with persistent or pacing-inducible AF after pulmonary vein isolation. A local coronary artery (LCA) across the MI block line was observed in 43 (53%) of 81 patients, and a bidirectional MI block was successfully accomplished in 53 (65%) of 81 patients, at the estimated MI line. The ratio of a successful MI block line was significantly lower in the patients with an LCA than in those without an LCA (42% versus 92%; P<0.001). The mean diameter of the coronary sinus (0.59 ± 0.18 versus 0.82 ± 0.22 cm; P<0.001) and length of the estimated MI line (33.4 ± 9.9 versus 29.4 ± 7.1 mm; P=0.032) were significantly shorter in the patients with a successful MI block line than in those without a successful MI block line. In the multivariable analysis, an LCA at the MI and a larger coronary sinus diameter were independent risk factors for an unsuccessful MI block line. Local coronary flow at the MI is associated with an increased incidence of an unsuccessful MI block line.

Utility of virtual unipolar electrogram morphologies to detect transverse conduction block and turnaround points of typical atrial flutter

BackgroundNoncontact mapping is useful for the diagnosis of various arrhythmias. Virtual unipolar electrogram morphologies (VUEM) of the conduction block and the turnaround points, however, are not well defined. We compared the VUEM characteristics of a transverse conduction block in the posterior right atrium (RA) with those of contact bipolar electrograms obtained during typical atrial flutter (AFL).MethodsContact bipolar electrograms were used to map the posterior RA during typical AFL in 16 patients. Twenty points of the VUEM recorded along the block line were analyzed and compared with contact bipolar electrograms.ResultsSeventeen AFLs were analyzed. Fifteen AFLs showed an incomplete transverse conduction block in the posterior RA by contact bipolar mapping. A double potential on the block line corresponded to the two components of the VUEM, in which the second component showed an Rs, RS, or rS pattern. At the turnaround point, a fused double potential of the contact bipolar electrograms corresponded to a change of the second component of the VUEM from an rS to a QS morphology. Two AFLs showed a complete block line in the posterior RA. The contact bipolar electrogram showed double potentials from the inferior vena cava to the superior vena cava, whereas the second component of the VUEM remained in an unchanged Rs, RS, or rS pattern.ConclusionVUEM analysis was a reliable method for identifying the posterior block line during AFL. This method may also be applicable for detecting block lines and turnaround points of circuits in other unmappable arrhythmias.

Sequence of Double Potentials Recorded by the Decapolar Electrode Placed along the Block Line Can Identify Persistent Gap Conduction

Background: In patients with atrial flutter (AF), a complete block line of cavotricuspid isthmus (CTI) is identified by a continuous corridor of double potentials (DP) separated by an isoelectric interval. Methods: Twenty-nine patients with typical AF underwent radio-frequency (RF) catheter ablation during coronary sinus pacing. Initially, we anatomically delivered sequential point-by-point RF application in the CTI. If complete block line was not created, then we tried to assess the sequence of DP recorded by the decapolar electrode placed along the initial ablation line. Since the terminal component (DPt) reflects the persistent conduction through the initial ablation line, we hypothesized that earliest DPt with reversal of initial polarity in adjacent DPt would indicate the point of gap conduction. Results: CTI conduction was successfully interrupted by initial linear ablation in six patients (one-line group). Among other 23 patients, DPt-guided gap conductions were identified in nine patients (another one-point group). In eight of these patients, a single application of RF energy successfully interrupted CTI conduction. One-line and another one-point groups had significantly shorter application time and fluoroscopic duration compared with those of remaining 14 patients. Conclusions: Decapolar electrode placed along the block line crossing the CTI is useful to detect gap conduction which can avoid repeat scanning and lead to target ablation.

Significance of Local Coronary Artery Flow as a Complete Block Line at the Mitral Isthmus in Patients with Atrial Fibrillation

Significance of Local Coronary Artery Flow as a Complete Block Line at the Mitral Isthmus in Patients with Atrial Fibrillation

Detour Conduction Can Mimic Complete Conduction Block at the Cavo‐Tricuspid Isthmus

A 54-year-old man with typical atrial flutter underwent linear ablation at the cavo-tricuspid isthmus. Though standard tricuspid annulus (TA) mapping and differential pacing suggested complete isthmus conduction block, electroanatomic mapping revealed that detoured conduction through a residual conduction gap around the inferior vena cava far from the TA mimicked complete conduction block. Though the double potential interval along the block line was not long enough to guarantee a complete line of block after eliminating the conduction gap, electroanatomic remapping accurately confirmed a complete block line, suggesting electroanatomic mapping may be the most reliable method to confirm complete isthmus conduction block.

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

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. 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%. 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.

Importance of atrial flutter isthmus in postoperative intra-atrial reentrant tachycardia.

In survivors of congenital heart surgery, intra-atrial reentrant tachycardia (IART) often develops. Previous reports have emphasized the atriotomy scar as the central barrier around which a reentrant circuit may rotate but have not systematically evaluated the atrial flutter isthmus in such patients. We sought to determine the role of the atrial flutter isthmus in supporting IART in a group of postoperative patients with congenital heart disease. Nineteen postoperative patients with IART underwent electrophysiological studies with entrainment mapping of the atrial flutter isthmus for determining postpacing intervals. Radiofrequency ablation was performed at the identified isthmus in an effort to create a complete line of block. Twenty-one IARTs were identified in 19 patients, with a mean tachycardia cycle length of 293+/-73 ms. The atrial flutter isthmus was part of the circuit in 15 of 21 (71. 4%). In the remaining 6 of 21, the ablation target zone was at sites near atrial incisions or suture lines. Ablation was successful in 19 of 21 (90.4%) IARTs and in 14 of 15 (93.3%) cases at the atrial flutter isthmus. In most of our postoperative patients, the atrial flutter isthmus was part of the reentrant circuit. The fact that the atrial flutter isthmus is vulnerable to ablation suggests that whenever IART occurs late after repair of a congenital heart defect, the atrial flutter isthmus should be evaluated. These data support the theory that some form of conduction block between the vena cava is essential for the establishment of a stable substrate for the atrial flutter reentrant circuit.

Role of the tricuspid annulus and the eustachian valve/ridge on atrial flutter. Relevance to catheter ablation of the septal isthmus and a new technique for rapid identification of ablation success.

Typical atrial flutter (AFL) results from right atrial reentry by propagation through an isthmus between the inferior vena cava (IVC) and tricuspid annulus (TA). We postulated that the eustachian valve and ridge (EVR) forms a line of conduction block between the IVC and coronary sinus (CS) ostium and forms a second isthmus (septal isthmus) between the TA and CS ostium. Endocardial mapping in 30 patients with AFL demonstrated atrial activation around the TA in the counter-clockwise direction (left anterior oblique projection). Double atrial potentials were recorded along the EVR in all patients during AFL. Pacing either side of the EVR during sinus rhythm also produced double potentials, which indicated fixed anatomic block across EVR. Entrainment pacing at the septal isthmus and multiple sites around the TA produced a delta return interval < or = 8 ms in 14 of 15 patients tested. Catheter ablation eliminated AFL in all patients by ablation of the septal isthmus in 26 patients and the posterior isthmus in 4. AFL recurred in 2 of 12 patients (mean follow-up, 33.9 +/- 16.3 months) in whom ablation success was defined by the inability to reinduce AFL, compared with none of 18 patients (mean follow-up, 10.3 +/- 8.3 months) in whom success required formation of a complete line of conduction block between the TA and the EVR, identified by CS pacing that produced atrial activation around the TA only in the counterclockwise direction and by pacing the posterior TA with only clockwise atrial activation. (1) The EVR forms a line of fixed conduction block between the IVC and the CS; (2) the EVR and the TA provide boundaries for the AFL reentrant circuit; and (3) verification of a complete line of block between the TA and the EVR is a more reliable criterion for long-term ablation success.