Conduction properties of the crista terminalis in patients with typical atrial flutter: basis for a line of block in the reentrant circuit

Interpretation of Typical and Atypical Atrial Flutters by Precision Electrocardiology Based on Intracardiac Recording

Atrial flutter is a term encompassing multiple clinical entities. Clinical manifestations of these arrhythmias range from typical isthmus-dependent flutter to post-ablation microreentries. Twelve-lead electrocardiogram (ECG) is a diagnostic tool in typical flutter, but it is often unable to clearly localize atrial flutters maintained by more complex reentrant circuits. Electrophysiology study and mapping are able to characterize in fine details all the components of the circuit and determine their electrophysiological properties. Combining these 2 techniques can greatly help in understanding the vectors determining the ECG morphology of the flutter waveforms, increasing the diagnostic usefulness of this tool.

Typical Atrial Flutter Mapping and Ablation

Isthmus-dependent flutter represents a defeated arrhythmia. Possibly one of the most outstanding successes in terms of understanding the mechanism behind it has led to an effective, relatively simple, and safe targeted therapy. Technology, fulfilling a number of the clinical electrophysiologist's dreams, has linked diagnosis and therapy in computerized systems showing real-time imagines of the right atrium, the arrhythmia circuit, and the ablation target. The entire history of clinical electrophysiology is contained in its path and atrial flutter needs to be regarded with immense respect for a large amount of knowledge that its study always engenders."

Pathophysiology of Typical Atrial Flutter

Nowadays, the pathophysiology mechanism of initiation and maintenance of reentrant arrhythmias, including atrial flutter, is well characterized. However, the anatomic and functional elements of the macro reentrant arrhythmias are not always well defined. In this article, we illustrate the anatomic structures that delineate the typical atrial flutter circuit, both clockwise and counterclockwise, paying attention to the inferior vena cava-tricuspid isthmus (CTI) and crista terminalis crucial role. Finally, we describe the left atrial role during typical atrial flutter, electrophysiologically a by-stander but essential in the phenotypic electrocardiogram (ECG).

Ultra-high resolution mapping of reverse typical atrial flutter: electrophysiological properties of a right atrial posterior wall and interatrial septum activation pattern

PURPOSE

We aimed to elucidate the right atrial posterior wall (RAPW) and interatrial septum (IAS) conduction pattern during reverse typical atrial flutter (clockwise AFL: CW-AFL).

METHODS

This study included 30 patients who underwent catheter ablation of CW-AFL (n = 11) and counter-clockwise AFL (CCW-AFL; n = 19) using an ultra-high resolution mapping system. RAPW transverse conduction block was evaluated by the conduction pattern on propagation maps and double potentials separated by an isoelectric line. The degree of blockade was evaluated by the %blockade, which was calculated by the length of the blocked area divided by the RAPW length. IAS activation patterns were also investigated dependent on the propagation map.

RESULTS

The average %blockade of the RAPW was significantly smaller in patients with CW-AFL than those with CCW-AFL (25 [3-74]% vs. 67 [57-75]%, p < 0.05). CW-AFL patients exhibited 3 different RAPW conduction patterns: (1) a complete blockade pattern (3 patients), (2) moderate (> 25% blockade) blockade pattern (2 patients), and (3) little (< 25% blockade) blockade pattern (6 patients). In contrast, the little blockade pattern was not observed in CCW-AFL patients. Of 11 CW-AFL patients, 4, including all patients with an RAPW complete blockade pattern, had an IAS activation from the wavefront from the anterior tricuspid annulus (TA), and 6 had an IAS activation from the wavefronts from both the anterior TA and RAPW. One patient had IAS activation dominantly from the wavefront from the RAPW.

CONCLUSIONS

RAPW transverse conduction blockade during CW-AFL was less frequent than during CCW-AFL, which possibly caused various IAS activation patterns.

Ultrahigh resolution electroanatomical mapping of the transverse conduction of the right atrial posterior wall in cases with and without typical atrial flutter

INTRODUCTION

The right atrial posterior wall (RAPW) is known to form a conduction barrier during typical atrial flutter (AFL). We evaluated the transverse conduction properties of RAPW in patients with and without typical AFL using an ultrahigh resolution electroanatomical mapping system.

METHODS AND RESULTS

This study included 41 patients who underwent catheter ablation of AF, typical or atypical AFL, in whom we performed RAPW mapping with an ultrahigh resolution mapping system during typical AFL and coronary sinus ostial pacing with three different pacing cycle lengths (PCLs) (1) PCL1: PCL within 40 ms of the AFL cycle length in patients with typical AFL or 250-300 ms for those without, (2) PCL2: 400 ms, (3) PCL3: PCL just faster than the sinus rate. Local RAPW conduction block was evaluated by propagation mapping and local double potentials separated by an isoelectric line. The functional block was defined as areas blocked during shorter PCLs but conductive during longer PCLs. The degree of blockade was calculated by dividing the blocked length by RAPW length (%blockade). Only two patients demonstrated a fixed complete RAPW block (100%, %blockade). Thirty-one patients demonstrated a partial block of RAPW, and the %blockade during PCL1-3 was 49.4 ± 19.8%, 39.5 ± 19.2%, and 35.0 ± 22.9% in this group, respectively. Functional block areas were frequently observed above the fixed block area adjacent to the RA-inferior vena cava junction. Transverse conduction block was more frequently observed in patients with typical AFL at any longitudinal level of RAPW.

CONCLUSION

RAPW transverse conduction block is lower-side dominant and greater in patients with typical AFL than those without.

Management of atrial fibrillation-flutter: uptodate guideline paper on the current evidence

The term 'flutter' and 'fibrillation' were first coined to differentiate the differences between fast, regular contractions in Atrial Flutter (AFLUT) with irregular, vermiform contractions of Atrial Fibrillation (AFIB). Management of these two diseases has been a challenge for physicians. Rate control (along with rhythm control) is the first line of management for symptomatic AFIB/AFLUT with Rapid Ventricular Rate (RVR). In some situations, atrial rhythms may not be well controlled by these anti-arrhythmic drugs, making cardioversion to sinus rhythm necessary. Anti-coagulation therapy in both the disease population is essential. Catheter ablation is an effective treatment option in certain patients that have AFIB/AFLUT refractory to medical management. Newer techniques like left atrial appendage (LAA) has been developed and is a highly attractive concept for the future in the management of AFIB/AFLUT. Newer novel drugs targeting specific ion channels are approaching the stages of clinical investigation. However, while advances in technologies have helped elucidate many aspects of these diseases, many mysteries still remain. This literature review serves as one of the guideline papers for current up-to-date management on both AFIB and AFLUT.

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.

Structural and functional inverse cardiac remodeling after cavotricuspid isthmus ablation in patients with typical atrial flutter

INTRODUCTION AND OBJECTIVES

The purpose of the present study is to determine the structural and functional cardiac changes that occur in patients at 1-year follow-up after ablation of typical atrial flutter.

METHODS

We enrolled 95 consecutive patients referred for cavotricuspid isthmus ablation. Echocardiography was performed at ≤6h post-procedure and 1-year follow-up.

RESULTS

Of 95 patients initially included, 89 completed 1-year follow-up. Hypertensive cardiopathy was the most frequently associated condition (39%); 24% of patients presented low baseline left ventricular systolic dysfunction. We observed a significant reduction in right and left atrial areas, end-diastolic and end-systolic left ventricular diameters, and interventricular septum. We observed substantial improvement in right atrium contraction fraction and left ventricular ejection fraction, and a reduction in pulmonary hypertension. Changes in diastolic dysfunction pattern were observed: 60% of patients progressed from baseline grade III to grade I; at 1-year follow-up, this improvement was found in 81%. We found no structural differences between paroxysmal and persistent atrial flutter at baseline and 1-year follow-up, exception for basal diastolic function.

CONCLUSIONS

In patients with typical atrial flutter undergoing cavotricuspid isthmus catheter ablation, we found inverse structural and functional cardiac remodeling at 1-year follow-up with much improved left ventricular ejection fraction, right atrium contraction fraction, and diastolic dysfunction pattern. Full English text available from:www.revespcardiol.org.

The undetermined geometrical factors contributing to the transverse conduction block of the crista terminalis

BACKGROUND

The crista terminalis (CT) is known to be a functional barrier during typical atrial flutter (AFL). The relationship between the CT structural characteristics and its transverse conduction block, however, has not been understood well.

METHODS

This study consisted of AFL (group 1, N = 15) and non-AFL patients (group 2, N = 13). The CT structural characteristics were determined with intracardiac echocardiography. A 20-pole electrode catheter was located along the CT and pacing at progressively faster rates from either low anterolateral right atrium (LRA) or coronary sinus (CS) was applied.

RESULTS

The CT height, width, and area were significantly greater in group 1 than in group 2 (P < 0.001). In both groups, at the longest pacing cycle length during CS pacing resulting in CT transverse conduction block at some levels, the width and area were significantly greater at the levels with block than at those without block. During LRA pacing, the area was also significantly larger at the levels with block than at those without in group 1, but not in group 2. The slope angle of CT ridge was significantly steeper at the levels with block than at those without in both groups (P < 0.01), but that was not the case with CS pacing. CT arborization in its inferior portion was more frequently documented in group 1 than group 2 (P < 0.05).

CONCLUSIONS

The CT structural characteristics that may influence its transverse conduction differ between LRA and CS pacing. Steep slope and arborization of the CT are implicated as a geometric factor in its transverse conduction block.

Electrophysiological mechanisms of atrial flutter

Atrial flutter (AFL) is a common arrhythmia in clinical practice. Several experimental models, such as tricuspid regurgitation model, tricuspid ring model, sterile pericarditis model and atrial crush injury model, have provided important information about reentrant circuit and can test the effects of antiarrhythmic drugs. Human AFL has typical and atypical forms. Typical AFL rotates around the tricuspid annulus and uses the crista terminalis and sometimes sinus venosa as the boundary. The tricuspid isthmus is a slow conduction zone and the target of radiofrequency ablation. Atypical AFL may arise from the right or left atrium. Right AFL includes upper loop reentry, free wall reentry and figure-of-8 reentry. Left AFL includes mitral annular AFL, pulmonary vein-related AFL and left septal AFL. Radiofrequency ablation of the isthmus between the boundaries can eliminate these arrhythmias.

The Role of Left Atrial Muscular Bundles in Catheter Ablation of Atrial Fibrillation

OBJECTIVES

We sought to investigate the imaging of the left atrial (LA) muscular bundle and the relationship between the bundle and inducibility of tachyarrhythmia after pulmonary vein isolation (PVI).

BACKGROUND

Noninducibility is used as a clinical end point of atrial substrate ablation after PVI. However, little is known about the role of the LA muscular bundles in tachyarrhythmia after PVI.

METHODS

Forty-three consecutive patients with paroxysmal atrial fibrillation who underwent catheter ablation were included. Bi-atrial isochronal mapping was performed with the NavX system (St. Jude Medical Inc., St. Paul, Minnesota) during sinus rhythm. After 4 PVI, inducible organized LA flutter with or without transforming to atrial fibrillation (AF) (LA flutter/AF) was ablated with additional lines at the roof and/or mitral isthmus.

RESULTS

The existence of bilateral muscular bundles was an independent predictor of LA flutter/AF after PVI (p = 0.02). Patients with LA flutter/AF after PVI had a greater index of the double potentials (5.4 +/- 3.4% vs. 2.8 +/- 1.8%, p = 0.006) and interpotential interval (33 +/- 5 ms vs. 29 +/- 4 ms, p = 0.02) than without LA flutter/AF. The muscular bundles were identified in 28% patients using 16-slice multidetector computed tomography, which were identical to the isochrone map. Patients with noninducible LA flutter/AF after PVI plus the additional linear ablation had a lower recurrence rate as compared with the patients without it (19% vs. 75%, p = 0.02).

CONCLUSIONS

Left atrial muscular bundles may provide a conduction block line and barrier, which is important for the formation of LA flutter/AF after PVI. The noninducibility of LA flutter/AF achieved after additional linear ablation may contribute to a better outcome in RF ablation of paroxysmal atrial fibrillation.

Electrophysiologic and Anatomical Characteristics of the Right Atrial Posterior Wall in Patients With and Without Atrial Flutter Analysis by Intracardiac Echocardiography

BACKGROUND

The posterior right atrial transverse conduction capability during typical atrial flutter (AFL) is well known, but its relationship to the anatomical characteristics remains controversial.

METHODS AND RESULTS

Thirty-four AFL and 16 controls underwent intracardiac echocardiography after placement of a 20-polar catheter at the posterior block site during AFL or pacing. In 31 patients, the effective refractory period (ERP) at the block site was determined as the longest coupling interval that resulted in double potentials during extrastimuli from the mid-septal (SW) and free (FW) walls. The block site was located 3.0-29.0 mm posterior to the crista terminalis (CT) in each AFL and control patient. The CT area indexed to the body surface area was larger in AFL patients than in control patients (16.4+/-6.5 mm(2)/m(2) vs 11.3+/-6.4 mm(2)/m(2), p=0.01), and was positively correlated to age (r=0.34, p=0.02). The ERP was longer in the AFL patients than in controls (SW: median value 600 [270-725] ms vs 220 [200-253] ms; FW: 280 [230-675] ms vs 215 [188-260] ms, p<0.05 for each).

CONCLUSIONS

A functional block line was located on the septal side of the CT in all patients. A limited conduction capability and age-related CT enlargement might have important implications for the pathogenesis in AFL.

Action potential morphology heterogeneity in the atrium and its effect on atrial reentry: a two-dimensional and quasi-three-dimensional study

Atrial fibrillation (AF) is believed to be perpetuated by recirculating spiral waves. Atrial structures are often characterized with action potentials of varying morphologies; however, the role of the structure-dependent atrial electrophysiological heterogeneity in spiral wave behaviour is not well understood. The purpose of this study is to determine the effect of action potential morphology heterogeneity associated with the major atrial structures in spiral wave maintenance. The present study also focuses on how this effect is further modulated by the presence of the inherent periodicity in atrial structure. The goals of the study are achieved through the simulation of electrical behaviour in a two-dimensional atrial tissue model that incorporates the representation of action potentials in various structurally distinct regions in the right atrium. Periodic boundary conditions are then imposed to form a cylinder (quasi three-dimensional), thus allowing exploration of the additional effect of structure periodicity on spiral wave behaviour. Transmembrane potential maps and phase singularity traces are analysed to determine effects on spiral wave behaviour. Results demonstrate that the prolonged refractoriness of the crista terminalis (CT) affects the pattern of spiral wave reentry, while the variation in action potential morphology of the other structures does not. The CT anchors the spiral waves, preventing them from drifting away. Spiral wave dynamics is altered when the ends of the sheet are spliced together to form a cylinder. The main effect of the continuous surface is the generation of secondary spiral waves which influences the primary rotors. The interaction of the primary and secondary spiral waves decreased as cylinder diameter increased.

Rate-Dependent Block in the Sinus Venosa of the Swine Heart during Transverse Right Atrial Activation: Correlation Between Electrophysiologic and Anatomic Findings

Rate-dependent block in the sinus venosa.

INTRODUCTION

Whether the crista terminalis or the sinus venosa result in rate-dependent block during transverse activation of the right atrial activation remains unknown. In the present study, right atrial activation at different cycle lengths was studied in the swine heart using high-resolution noncontact mapping (Endocardial Solutions). The location of the block was tagged and correlated with postmortem anatomical findings.

METHODS AND RESULTS

Eight pigs were studied using noncontact mapping to obtain right atrial geometry and detailed sequence of activation using noncontact endocardial mapping. During sinus rhythm, activation proceeded uninterrupted craniocaudally along the sinus venosa and crista terminalis with similar conduction velocities (1.08+/-0.17 and 1.17+/-0.14 m/sec, respectively). Proximal coronary sinus stimulation was used to create transverse activation of the posterior right atrial wall. A rate-dependent decrease in conduction velocity occurred in the sinus venosa region (0.93+/-0.21, 0.82+/-0.14, and 0.52+/-0.09 m/sec at 500, 400, and 300 ms, respectively; P<0.05). The line of block verified by isopotential mapping and double potentials was obtained at cycle lengths of 240+/-30 ms. This line of the block was tagged with radiofrequency current lesions. Postmortem, all lesions were located in the sinus venosa region, 9.8+/-4.1 mm from the posteromedial edge of the crista terminalis. This region showed abrupt changes in muscle fiber thickness and orientation as well as in collagen content.

CONCLUSIONS

The sinus venosa and not the crista terminalis results in a rate-dependent line of block during transverse right atrial activation. The morphologic characteristics of the sinus venosa appear to facilitate block in this region.

Site Specificity of Transverse Crista Terminalis Conduction in Patients with Atrial Flutter

INTRODUCTION

The causes of transcristal conduction (TC) in patients with atrial flutter (AFL) are unknown.

METHODS AND RESULTS

In two groups of patients referred for AFL ablation, 36 had cavotricuspid isthmus (CTI) dependent flutter (Group I) and 24 had lower (n = 21) or upper loop reentry (n = 5) (Group II). After ablation, isthmus block was evaluated by pacing from the coronary sinus (CS) and low lateral right atrium and by alternative techniques, including mapping with electrodes spanning the CTI or electroanatomic mapping. After bidirectional CTI block was verified, 21/36 (58%) in Group I showed TC with CS pacing, including low TC in 16 (including 11 showing "pseudo" CTI conduction), higher TC in 6 and multiple breaks in 3. However, 8 with low TC during CS pacing showed unidirectional block by pacing outside of the CS os. Twelve (50%) in Group II had TC during CS pacing after bidirectional CTI block, with low TC in 5 (2 mimicking residual CTI conduction) and higher breaks in 9. There was no significant difference in the incidence of TC during CS pacing after CTI block between groups. In seven autopsied hearts, the muscle orientation between the proximal CS musculature and Eustachian ridge were examined. Muscular connections between the CS and Eustachian ridge coursing toward the orifice of inferior vena cava were found in one of the hearts.

CONCLUSIONS

It is concluded that in patients with bidirectional CTI block, pacing from the CS may be associated with TC mimicking a conduction leak through the isthmus. Pacing just outside the CS os helps distinguish pseudo from true isthmus block.

Conduction Characteristics at the Crista Terminalis During Onset of Pulmonary Vein Atrial Fibrillation

INTRODUCTION

Focal atrial fibrillation (AF) may initiate with an irregular rapid burst of atrial ectopic (AE) activity from a pulmonary vein (PV) focus, but how AF is maintained it is not known. The crista terminalis (CT) is an important line of block in atrial flutter (AFL), but its role in AF has not been determined. The aim of this study was to examine the conduction properties of the CT during onset of AF.

METHODS AND RESULTS

In 10 patients (mean age 38 +/- 8 years), we analyzed conduction across the CT during onset of focal AF from an arrhythmogenic PV and during pacing from the same PV at cycle lengths of 700 and 300 ms. A 20-pole catheter was positioned on the CT using intracardiac echocardiography. In 10 control patients with no history of AF, we analyzed conduction across the CT during pacing from the distal coronary sinus at 700 and 300 ms. In all 10 AF patients, AF was initiated with 1 to 9 AE beats (median 5) from a PV. During sinus rhythm, there were no split components (SC) recorded on the CT. During PV AE activity, discrete SC were recorded on the CT in all patients over 6.3 +/- 0.9 bipoles (3.7 +/- 0.3 cm). Maximal splitting of SC was 66 +/- 31 ms (37-139). There was an inverse relationship between AE coupling intervals and the degree of splitting between SC in all patients. Degeneration to AF was preceded by progressive decrement across the CT. SC were recorded during PV pacing at 700 and 300 ms (maximal distance between SC of 24 +/- 3 ms and 43 +/- 5 ms, respectively, P < 0.001). Maximum SC at CT in controls was 13 +/- 8 ms at 700 ms (P = 0.06 vs AF patients) and 16 +/- 9 ms at 300 ms (P < 0.01 vs AF patients).

CONCLUSION

(1) These observations provide evidence of anisotropic, decremental conduction across the CT during onset of focal AF and during pacing from the same PV. A line of functional conduction block develops along this anatomic structure (CT). Whether this line of block acts as an initiator of AF or simply contributes passively to nonuniform fibrillatory conduction is unknown. (2) In some patients with focal AF, development of conduction block along the CT may provide a substrate for typical AFL.

Functional characterization of the crista terminalis in patients with atrial flutter: implications for radiofrequency ablation

OBJECTIVES

The aim of the study was to investigate the conduction properties and anisotropy of the crista terminalis (CT) in patients with atrial flutter (AFL) using non-contact mapping.

BACKGROUND

The CT is a posterior barrier during typical AFL. However, the CT has transverse conduction capabilities in patients with upper loop re-entry (ULR).

METHODS

Twenty-two patients (16 males, 63 +/- 15 years) with typical AFL and ULR were included. Non-contact mapping of the right atrium during AFL and pacing from coronary sinus (CS) and low anterolateral right atrium (LARA) was performed to evaluate transverse conduction across the CT. During ULR, the longitudinal (CV(L)) and transverse (CV(T)) conduction velocity along and across the CT were measured. The width of the CT conduction gap was evaluated to guide radiofrequency ablation (RFA).

RESULTS

No transverse CT gap conduction was found during typical AFL. Transverse CT gap conduction was found in three patients during CS pacing and in three patients during LARA pacing. During ULR, CV(L) was greater than CV(T) (1.28 +/- 0.43 vs. 0.73 +/- 0.30 m/s, p < 0.001). The CV(L)/CV(T) ratio was 1.95 +/- 0.77, which was inversely related to the CT gap width (15.7 +/- 6.8 mm) (p < 0.001). The RFA of the CT gap was successful in 18 patients. Four patients had recurrence of arrhythmias during the follow-up of 11 +/- 3 months.

CONCLUSIONS

Most of the CT conduction gaps were functional and only appeared during ULR. The width of the CT gap was inversely related to the anisotropic ratio of the CT. The RFA of the CT gap was effective in eliminating ULR.

High-Resolution Mapping Around the Crista Terminalis During Typical Atrial Flutter:. New Insights into Mechanisms

INTRODUCTION

The aim of this study was to delineate activation patterns around the crista terminalis (CT) using high-resolution noncontact mapping.

METHODS AND RESULTS

Twenty-six patients with typical atrial flutter (20 counterclockwise and 6 clockwise) were enrolled in the study. A noncontact mapping system was used to map atrial flutter. There were three activation patterns around the line(s) of block. Type I (n = 6) showed activation around a single complete line of block located in the CT. Type II (n = 17) showed activation around a single incomplete line of block with a conduction gap in the CT. Type III (n = 3) showed activation around double lines of block, one located in the CT and the other located in the sinus venosa region. Simultaneous activation around the tricuspid annulus and through the CT gap could result in double loop reentry (n = 12). After successful ablation of the cavotricuspid isthmus (CTI) in 24 patients, upper loop reentry was still induced in 12 patients with double loop reentry. Subsequent ablation of the CT gap was performed successfully in these 12 patients, and no arrhythmia was inducible thereafter. During the follow-up period of 8.4 +/- 4.1 months, there was no recurrence of atrial flutter in any patient.

CONCLUSION

During typical atrial flutter, the CT might be an incomplete barrier. Simultaneous conduction through the CTI and CT gap could result in double loop reentry. Radiofrequency ablation of the CTI and CT gap was effective in eliminating this arrhythmia.

Conduction Properties of the Crista Terminalis in Patients with Atrial Flutter Due to Amiodarone Therapy for Atrial Fibrillation

Some patients with atrial fibrillation (AF) treated by antiarrhythmic drugs (AAD) can develop typical atrial flutter, but the mechanism is not clear. This study included 21 patients with AF. Group I (n = 7) had typical atrial flutter due to amiodarone therapy. Group II (n = 7) did not develop atrial flutter after amiodarone treatment. Group III (n = 7) did not receive AAD treatment. A 7 Fr, 20-pole electrode catheter was placed along the CT identified by fluoroscopy and intracardiac echocardiography. After restoration of the sinus rhythm, decremental pacing near the CT was performed until 2 to 1 atrial capture. Complete transverse conduction block was defined as the appearance of double potentials with opposite activation sequence along the CT. Focal transverse conduction delay was defined as the appearance of double potentials at > or = 2 recording sites. Focal transverse conduction delay was observed during pacing at the cycle length of 693 +/- 110 ms in group I, 360 +/- 97 ms in group II and 343 +/- 109 ms in group III (P = 0.001). Complete transverse conduction block was observed during pacing at the cycle length of 391 +/- 118 ms in group I and 231 +/- 23 ms in group II (P = 0.001), but not in group III. In conclusion, focal transverse conduction delay in the CT was common in patients with AF. A predisposition to the line of the conduction block in the CT might contribute to the conversion of AF to typical atrial flutter due to amiodarone therapy.

Global Right Atrial Mapping Delineates Double Posterior Lines of Block in Patients with Typical Atrial Flutter:

Double Posterior Lines of Block in Typical Atrial Flutter.

INTRODUCTION

The crista terminalis (CT) has been shown to be a barrier to transverse conduction during typical atrial flutter (AFL). However, some studies have demonstrated the presence of functional block in the sinus venosa region but not at the CT. The aim of this study was to define these regions of block in the right atrium using a three-dimensional noncontact mapping system.

METHODS AND RESULTS

In 39 AFL patients (33 men and six women, mean age 56 +/- 13 years), a noncontact multielectrode array was used to reconstruct electrograms in the right atrium. Isochronal and isopotential propagation mapping was performed during AFL and during pacing from the coronary sinus ostium and the low lateral wall (cycle length from 600 to 240 msec) in sinus rhythm after creation of isthmus block. A single line of block along the CT area was found in 18 patients (46%). Two lines of block were found in 21 patients (54%), with the first line located along the CT area. The second was located in the sinus venosa region in 20 patients (51%) and in the lateral wall in 1 patient (3%). In all patients, the block in the lower part of the CT was observed during AFL (60%) and during pacing at all cycle lengths (48%-62%). The length and proportion of block were inversely proportional to pacing cycle length.

CONCLUSION

Double lines of block were frequently observed in patients with AFL, and both lines may form the posterior boundaries of the AFL circuit. Block was fixed in the lower part of the CT and was functional in the upper part of the CT.

Noncontact mapping of ectopic atrial tachycardias: different characteristics of isopotential maps and unipolar electrogram

The success rate for catheter ablation of ectopic atrial tachycardia (AT) has been limited by the inherent difficulty in localizing the site of origin within the complex three-dimensional structures of the atria. The objective of the study was to determine the usefulness of a noncontact mapping system for catheter ablation of AT. Radiofrequency ablation of 25 ATs was performed using a noncontact mapping system. Three different characteristics of isopotential maps and unipolar electrogram morphologies were observed: Group 1: Isopotential maps displayed a narrow, sharp ring of colors around a white, center spot. Unipolar electrograms revealed a Q-S morphology with a rapid dV/dt. Group 2: Isopotential maps displayed a broad ring of colors with little or no white spot in the center. Unipolar electrograms revealed a low amplitude, broad and smooth Q-S morphology in front of a second component with a rapid dV/dt. Group 3: Isopotential maps displayed a broad ring of colors. Unipolar electrogams revealed a low amplitude and fractionated waveform followed by endocardial breakthrough with a gradual dV/dt. Radiofrequency catheter ablation was successful in all ATs of groups 1 and 2, and failed in two of three ATs in group 3. The overall success rate was 92%. No severe complications were observed. Noncontact isopotential mapping is helpful to identify and characterize the origin of ectopic AT. Ablation success is associated with the characteristics of isopotential maps and unipolar electrogram morphologies. The overall success rate was 92%.

Noncontact three-dimensional mapping and ablation of upper loop re-entry originating in the right atrium

OBJECTIVES

This study was aimed at delineating the reentrant circuit of right atrial (RA) upper loop re-entry using noncontact three-dimensional mapping.

BACKGROUND

Various forms of atypical atrial flutter including lower loop re-entry and left atrial flutter have been demonstrated. However, little is known about upper loop re-entry in the RA.

METHODS

The study population consisted of eight patients (65 +/- 12 years, seven men) with atypical atrial flutter. Right atrial activation during atrial flutter was visualized using a noncontact mapping system (EnSite-3000 with Clarity Software, St. Paul, Minnesota) for a three-dimensional reconstruction of the endocardial depolarization. The narrowest part of the re-entrant circuit was targeted using radiofrequency catheter ablation.

RESULTS

Noncontact mapping showed macro-re-entry confined to the RA free wall with RA activation time accounting for 100% of the cycle length (214 +/- 21 ms) in all eight patients. Two patients had counterclockwise activation, and six patients had clockwise activation around the central obstacle, which was composed of the crista terminalis, the area of functional block, and superior vena cava. The lower turn-around points were located at the conduction gap in the crista terminalis. Radiofrequency linear ablation of the conduction gap in the crista terminalis was performed and eliminated atrial flutter in six patients without recurrence during a follow-up of 3.2 +/- 1.1 months.

CONCLUSIONS

Atypical atrial flutter could arise from upper loop re-entry in the RA with conduction through the gap in the crista terminalis. Radiofrequency linear ablation of the conduction gap was effective in eliminating this atrial arrhythmia.

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.

Intercaval block in normal canine hearts : role of the terminal crest

BACKGROUND

The intriguing monotony in the occurrence of intercaval conduction block during typical atrial flutter suggests an anatomic or electrophysiological predisposition for conduction abnormalities.

METHODS AND RESULTS

To determine the location of and potential electrophysiological basis for conduction block in the terminal crest region, a high-density patch electrode (10x10 bipoles) was placed on the terminal crest and on the adjacent pectinate muscle region in 10 healthy foxhounds. With a multiplexer mapping system, local activation patterns were reconstructed during constant pacing (S(1)S(1)=200 ms) and introduction of up to 2 extrastimuli (S(2), S(3)). Furthermore, effective refractory periods were determined across the patch. If evident through online analysis, the epicardial location of conduction block was marked for postmortem verification of its endocardial projection. Marked directional differences in activation were found in the terminal crest region, with fast conduction parallel to and slow conduction perpendicular to the intercaval axis (1.1+/-0.4 versus 0.5+/-0.2 m/s, P<0.01). In the pectinate muscle region, however, conduction velocities were similar in both directions (0.5+/-0.3 versus 0.6+/-0.2 m/s, P=NS). Refractory patterns were relatively homogeneous in both regions, with local refractory gradients not >30 ms. During S(3) stimulation, conduction block parallel to the terminal crest was inducible in 40% of the dogs compared with 0% in the pectinate muscle region.

CONCLUSIONS

Even in normal hearts, inducible intercaval block is a relatively common finding. Anisotropic conduction properties would not explain conduction block parallel to the intercaval axis in the terminal crest region, and obviously, refractory gradients do not seem to play a role either. Thus, the change in fiber direction associated with the terminal crest/pectinate muscle junction might form the anatomic/electrophysiological basis for intercaval conduction block.

Atypical right atrial flutter patterns

BACKGROUND

The purpose of our study was to define the incidence and mechanisms of atypical right atrial flutter.

METHODS AND RESULTS

A total of 28 (8%) of 372 consecutive patients with atrial flutter (AFL) had 36 episodes of sustained atypical right AFL. Among 24 (67%) of 36 episodes of lower loop reentry (LLR), 13 (54%) of 24 episodes had early breakthrough at the lower lateral tricuspid annulus, whereas 11 (46%) of 24 episodes had early breakthrough at the high lateral tricuspid annulus, and 9 (38%) of 24 episodes showed multiple annular breaks. Bidirectional isthmus block resulted in elimination of LLR. A pattern of posterior breakthrough from the eustachian ridge to the septum was observed in 4 (14%) of 28 patients. Upper loop reentry was observed in 8 (22%) of 36 episodes and was defined as showing a clockwise orientation with early annular break and wave-front collision over the isthmus. Two patients had atypical right AFL around low voltage areas ("scars") in the posterolateral right atrium.

CONCLUSIONS

Atypical right AFL is most commonly associated with an isthmus-dependent mechanism (ie, LLR or subeustachian isthmus breaks). Non-isthmus-dependent circuits include upper loop reentry or scar-related circuits.

Differences in organization between acute and chronic atrial fibrillation in dogs

OBJECTIVES

The purpose of this study was to determine differences in acute and chronic atrial fibrillation (AF) "organization" in canine models.

BACKGROUND

Electrophysiologic changes occur during atrial remodeling, but little is known about how remodeling affects AF organization. We hypothesized that atrial remodeling induced by long-term rapid atrial rates heterogeneously decreases AF organization.

METHODS

In seven dogs, acute AF was induced by atrial burst pacing, and in eight dogs chronic AF was created by six weeks of continuous rapid atrial pacing. Atrial fibrillation was epicardially mapped from the right atria (RA) and left atria (LA). Atrial cycle length (CL), spatial organization and activation maps were compared. Spatial organization was quantified by an objective signal processing measure between multiple electrograms. RESULTS In acute AF, mean CL was slightly shorter in the LA (124 +/- 16 ms) than it was in the RA (131 +/- 14 ms) (p < 0.0001). In chronic AF, LA CL (96 +/- 14 ms) averaged 24 ms shorter than RA CL (121 +/- 18 ms) (p < 0.0001). Right atria and LA in acute AF had similar levels of organization. In chronic AF, the LA became approximately 25% more disorganized (p < 0.0001) while the RA did not change. In acute AF, a single broad wave front originating from the posterior and medial atrium dominated LA activation. In chronic AF, LA activation was more complex, sustaining multiple reentrant wavelets in the free wall and lateral appendage.

CONCLUSIONS

Acute and chronic AF exhibit heterogeneous differences in CL, organization and activation patterns. The LA in chronic AF is faster and more disorganized than it is in acute AF. Differences in the models may be due to heterogeneous electrophysiologic remodeling and anatomic constraints. The design of future AF therapies may benefit by addressing the patient specific degree of atrial remodeling.

Typical atrial flutter ablation: conduction across the posterior region of the inferior vena cava orifice may mimic unidirectional isthmus block

INTRODUCTION

The aim of this study was to map the low right atrium before and after radiofrequency ablation of the inferior vena cava-tricuspid annulus (IVC-TA) isthmus in patients with typical atrial flutter (AFI) to better understand the electrophysiologic meaning of incomplete or unidirectional block following the ablation procedure and its relationship with AFI recurrence.

METHODS AND RESULTS

We performed atrial mapping in 12 patients using a "basket" catheter in the IVC orifice, Halo catheter in the right atrium, and multipolar catheters in the coronary sinus (CS) and His region. In patients in sinus rhythm, atrial activation was analyzed during pacing from the CS and low lateral right atrium (LLRA) before and after ablation. Atrial activation propagated across the isthmus and posterior region of the IVC orifice simultaneously before ablation. Mapping during AF1 in four patients showed that the crista terminalis was a site of functional block. After ablation, evaluation of Halo catheter recordings in three patients showed apparent unidirectional counterclockwise block, whereas analysis of basket catheter recordings demonstrated complete bidirectional block. The apparent conduction over the isthmus during pacing from proximal CS was due to conduction along the posterior part of the IVC orifice, which activated the LLRA despite complete isthmus block.

CONCLUSION

Our results demonstrate that limited endocardial mapping may yield a pattern compatible with unidirectional block in the IVC-TA isthmus, although bidirectional block is present at this anatomic level.

Right atrial focal atrial fibrillation: electrophysiologic characteristics and radiofrequency catheter ablation

INTRODUCTION

Information about focal atrial fibrillation (AF) originating from the right atrium has not been well described. The purposes of this study were to demonstrate the electrophysiologic characteristics and radiofrequency catheter ablation in patients who had right atrial focal AF.

METHODS AND RESULTS

From January 1996 to September 1998, 172 patients with clinically documented attacks of paroxysmal AF were referred to this institution for electrophysiologic study and/or radiofrequency catheter ablation. Anterior free wall, crista terminalis, and right and left superior pulmonary veins were mapped simultaneously. Eight patients (4.7%) had right atrial focal AF, consistent activation sequence, irregular fibrillation interval (mean fibrillation interval: 164 +/- 11 msec), and episodes of exit block from the initiating foci observed. The presumed ablation site was chosen on the basis of the earliest bipolar activity relative to an atrial electrogram reference during the initiation of AF. After application of 2 +/- 1 radiofrequency pulses, AF was eliminated without recurrence during the follow-up period (mean: 14 +/- 8 months; range: 3 to 25). Twenty-four-hour Holter monitoring showed that the number of atrial premature beats decreased significantly at the 3-month follow-up (4,216 +/- 411 vs 135 +/- 14 beats/day).

CONCLUSION

Right atrial focal AF is one subgroup of focal AF, and it can be cured by radiofrequency catheter ablation.