CLINICAL RESEARCH: ELECTROPHYSIOLOGY
Functional characterization of the crista terminalis in patients with atrial flutter: implications for radiofrequency ablation
Tu-Ying Liu, MD*
,
Ching-Tai Tai, MD*
,*,
Bien-Hsien Huang, MD,
Satoshi Higa, MD,
Yenn-Jiang Lin, MD*,
Jin-Long Huang, MD*,
Yoga Yuniadi, MD,
Pi-Chang Lee, MD*,
Yu-An Ding, MD* and
Shih-Ann Chen, MD*
* National Yang-Ming University School of Medicine, Taipei, Taiwan
Division of Cardiology, Department of Medicine, Chutung Veterans Hospital, Chutung, Taiwan
Taipei Veterans General Hospital, Taipei, Taiwan
Manuscript received August 3, 2003;
revised manuscript received October 30, 2003,
accepted November 25, 2003.
* Reprint requests and correspondence: Dr. Ching-Tai Tai, Division of Cardiology, Taipei Veterans General Hospital, 201 Sec. 2, Shih-Pai Road, Taipei, Taiwan.
ct.tai{at}msa.hinet.net
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Abstract
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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 (CVL) and transverse (CVT) 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, CVL was greater than CVT (1.28 ± 0.43 vs. 0.73 ± 0.30 m/s, p < 0.001). The CVL/CVT 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.
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Abbreviations and Acronyms
| | AFL | = atrial flutter | | CS | = coronary sinus | | CT | = crista terminalis | | CTI | = cavotricuspid isthmus | | CV | = conduction velocity | | LARA | = low anterolateral right atrium | | MEA | = multielectrode array | | RA | = right atrium | | RFA | = radiofrequency ablation | | ULR | = upper loop re-entry |
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The crista terminalis (CT) is an elongated muscular prominence between the superior vena cava and inferior vena cava in the posterolateral wall of the right atrium (RA). It had been demonstrated as a line of conduction block during typical atrial flutter (AFL) (1–5). However, there was evidence to suggest the presence of transverse conduction across the CT during atrial pacing (6,7). Furthermore, during atypical AFL of lower and upper loop re-entry (ULR), transverse propagation of the activation wavefront across the CT had been shown to be a critical part of reentrant circuits (8,9). Therefore, we hypothesized that the CT had functional transverse conduction properties depending on the direction of the activation wavefront. Because conventional mapping techniques could not directly investigate CT transverse conduction, the aim of this study was to use high-resolution non-contact mapping for characterization of CT conduction in patients with AFL.
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Methods
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Patient characteristics.
Twenty-two patients (16 men and 6 women, 63 ± 15 years old) with spontaneous typical AFL and atypical AFL constituted the study population. The atypical AFL was demonstrated to be ULR in each patient. Eight patients had cardiovascular diseases, including five with hypertension, three with hypertrophic cardiomyopathy, and three with coronary artery disease (Table 1).
Electrophysiologic study.
Informed written consent was obtained from all patients. All antiarrhythmic drugs except amiodarone were discontinued for at least five half-lives before the study. As described previously (9), a 7-F, 20-pole, deflectable Halo catheter with 10-mm paired spacing (Cordis-Webster Inc., Baldwin Park, California) was positioned around the tricuspid annulus to simultaneously record the RA activation in the lateral wall and the cavotricuspid isthmus (CTI). A 7-F, deflectable, decapolar catheter with 2-5-2 mm interelectrode spacing (Daig Corp., Minnetonka, Minnesota) was inserted into the coronary sinus (CS) via the right internal jugular vein. The position of the proximal electrode pair at the ostium of the CS was confirmed with contrast injection. A 9-F sheath was placed in the left femoral vein to introduce a non-contact mapping catheter.
Before study, all patients were in sinus rhythm. Pacing from proximal CS and low anterolateral right atrium (LARA) was performed at two different cycle lengths of 500 and 300 ms. After baseline study, burst and decremental LARA or CS pacing was performed to induce AFL. The RA activation sequences were recorded during sinus rhythm, atrial pacing before and after CTI ablation, and AFL to see if there was transverse conduction in the CT.
Non-contact mapping system.
The non-contact mapping system (EnSite 3000, Endocardial Solutions Inc., St. Paul, Minnesota) has been described in detail elsewhere (10). Briefly, the system consisted of an inflatable multielectrode array (MEA) catheter, a reference patch electrode, amplifiers, and a Silicon Graphics workstation. Raw data detected by the MEA was fed to the Silicon Graphics workstation via an amplifier. Before deployment of the MEA, heparinization was performed to maintain the activated clotting time between 250 and 300 s throughout the study. The MEA catheter was deployed over a 0.035-inch J-tipped guide wire, which headed into the superior vena cava. The MEA was advanced to the mid-chamber of the RA (mean RA diameter was 41 ± 7.4 mm), parallel to the CT (mean distance from the CT to the MEA center was 13 ± 1.6 mm) and inflated for mapping. The system located any catheter in relation to the MEA using a "locator" signal, which was used to construct a three-dimensional computer model of the virtual endocardium, providing a geometry matrix for the inverse solution, and to display and track the position of the catheter on the virtual endocardium. Using mathematical techniques to process the potentials detected by MEA, the system was able to reconstruct more than 3,000 unipolar electrograms simultaneously and superimpose them onto the virtual endocardium, producing isopotential maps with a color range representing voltage amplitude. On the isopotential maps, a wavefront was defined as a discrete front of endocardial depolarization presenting as a region of negative polarity. During review of the recorded data, we always started high-pass filter setting at 2 Hz to preserve the slow conduction on the isopotential map.
Study protocol.
Localization of CT
During typical AFL, a line of conduction block was noted in the posterolateral RA (Fig. 1A). Both the contact and non-contact electrograms on the line of block showed double potentials. Using intracardiac echocardiography, the line of block was demonstrated to be located in the CT. During ULR, the activation wavefront propagated around the superior vena cava and upper CT and crossed the CT conduction gap (Fig. 1B). The conduction velocities of the wavefront propagation along (longitudinal) and across (transverse) the CT during ULR were measured accordingly.
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Figure 1 Propagation maps during typical atrial flutter (AFL) and upper loop re-entry (ULR). The non-contact mapping in Case 6 is displayed. (A) The propagation map of typical AFL in the right posterolateral view is shown on the left. The unipolar virtual electrograms are shown on the right. During clockwise typical AFL, the activation wavefront descends in the right atrium (RA) posterior wall and septum (a to c), travels through the cavotricuspid isthmus (not shown), and ascends in the RA anterior and lateral walls (d to f). Virtual electrograms along the crista terminalis (CT) show double potentials resulting from different wavefront propagation direction on each side of the CT. (B) The propagation map of ULR in the same patient is shown. The activation wavefront propagates down in the posterior RA (a to b), crosses a conduction gap in the CT (b to c), proceeds upward in the anterolateral RA, and turns around the superior vena cava (c to d) to complete the re-entrant circuit (d to a). Virtual electrograms (Virtual 9) on the CT show low amplitude potential between the first and second deflection, suggesting the presence of a conduction gap. IVC = inferior vena cava; SVC = superior vena cava.
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Measurement of conduction velocity (CV)
The non-contact mapping system displays the Cartesian coordinates relative to the MEA center of points on the virtual endocardium. It is therefore possible to calculate the distance between two points using the mathematical formula (11):
where d = distance, x1, y1, and z1 = the Cartesian coordinates at three-dimensional surface point 1, and x2, y2, and z2 = the Cartesian coordinates at three-dimensional surface point 2.
The time taken for the wavefront to pass across a distance was determined by observing propagation of the peak negative point of the wavefront on the isopotential map and confirmed by the time interval between the peak negative amplitude of electrograms at the beginning and end of the distance measured (Fig. 2). The CV was calculated as distance/time. It was measured down the propagation route along the CT as the longitudinal CV, and down the propagation route across the CT as the transverse CV. The anisotropic ratio was defined as longitudinal CV/transverse CV.
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Figure 2 Measurement of conduction velocity. The propagation map and the virtual electrograms demonstrate the measurement of longitudinal conduction velocity in Case 6. Propagation of the activation wavefront is shown on the left. The surface distance (D) is measured between the first and the last virtual locations. On the right, the virtual unipolar electrograms are displayed. Time interval (T) between the first and the last peak negative deflections in the virtual unipolar electrograms is measured. The conduction velocity is calculated using the surface distance divided by time interval (D/T).
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Measurement of the width of CT gap
When the tachycardia wavefront propagated through the CT gap, the shape of the wavefront initially converged toward the gap, remained constricted for a short distance when going through the CT, and finally diverged as the wavefront spread out and conducted away. During animation of the isopotential map, using the filter setting of 2 Hz, the contour lines of voltage converged and turned as they passed the edge of the CT gap. To be clinically conservative, we defined the edge of the gap at the location adjacent to the convergence of the isopotential contour lines. We hypothesized that this location corresponded to the end of the blocking part of the CT (Fig. 3). Therefore, the width of the CT gap was measured as the surface distance between the edges of the gap.
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Figure 3 (A) The measurement of the width of the crista terminalis (CT) gap. During animation of the isopotential map while the activation wavefront propagates through the gap, the contour lines of voltage converge and turn as they pass the edge of the CT gap. The location adjacent to the convergence of the isopotential contour lines is defined as the edge of the gap. Therefore, the width of the CT gap is measured as the surface distance between the edges of the gap. (B) The propagation of activation wavefront across the CT conduction gap in Case 6. The marked blue line represents the measurement of the width of the CT gap.
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Radiofrequency ablation (RFA) and follow-up
For typical AFL, the CTI was ablated using an 8-mm tipped ablation catheter with a continuously linear approach (Daig Corp., Minnetonka, Minnesota). The energy setting was 70 W, 60°C, 120 s. The end point was bidirectional CTI conduction block confirmed by contact and non-contact mapping (12). For ULR, the conduction gap in the CT was targeted using a 4-mm tipped ablation catheter (Daig Corp., Minnetonka, Minnesota) with a sequential point-by-point approach. The energy setting for each pulse was 50 W, 60°C, 40 s. The end points were bidirectional CTI and CT gap conduction block and inability to re-induce AFL.
After hospital discharge, all patients were monitored closely in the outpatient clinic. Long-term efficacy was assessed clinically on the basis of the clinical symptoms, the resting surface 12-lead electrocardiogram, and 24-h Holter monitoring.
Statistical analysis.
Continuous data were expressed as mean ± SD. The Wilcoxon signed ranked test was used to compare the longitudinal and transverse CV. In regression analysis offered by the computerized SPSS program (SPSS 11.0 for Windows, SPSS Inc., Chicago, Illinois), the inverse model (Y = b0 + b1/X) was used to investigate the relationship between the anisotropic ratio (Y) and the CT gap width (X). In this situation, r2 was calculated to represent the variability in Y that may be accounted for by knowing the value of X. A value of p < 0.05 was considered statistically significant.
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Results
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Transverse conduction in the CT during atrial pacing and AFL.
As shown in Table 1, during typical AFL, there was no conduction gap in the CT in all patients. During pacing from proximal CS at 500 and 300 ms, 3 of 22 patients had a transverse conduction gap in the CT. During pacing from LARA at 500 and 300 ms, 3 of 22 had a transverse conduction gap in the CT.
Conduction properties of the CT during ULR.
All patients had pacing-induced ULR. During ULR, the longitudinal CV (1.28 ± 0.43 m/s) was significantly greater than the transverse CV (0.73 ± 0.30 m/s) (p < 0.001). The anisotropic ratio of the CT was 1.95 ± 0.77 (range, 1.03 to 3.79). The width of the CT conduction gap was 15.7 ± 6.8 mm (range, 5 to 34 mm) (Table 1). In regression analysis, using the inverse model of the SPSS program, the anisotropic ratio was inversely correlated with the width of the CT conduction gap (r2 = 0.483, p < 0.001) (Fig. 4).
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Figure 4 The relationship between the anisotropic ratio (CVL/CVT) and the width of the crista terminalis (CT) gap. The distribution of the anisotropic ratio of longitudinal/transverse conduction velocities (Y-axis) and the width of crista gap (X-axis) are plotted, showing the inverse relationship between anisotropic ratio and the width of the CT gap. CVL = longitudinal conduction velocity; CVT = transverse conduction velocity.
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RFA and follow-up.
The RFA of the CTI was successfully performed in 21 patients and failed to attain CTI conduction block in 1 patient. Subsequent RFA of the CT gap was successfully performed in 18 patients. Two patients could not tolerate the ablation procedure because of chest pain, and one could not achieve complete bidirectional CT gap block. There were no complications during the ablation procedure. During the follow-up of 11 ± 3 months, 18 of 22 patients (82%) had no recurrences of typical AFL and ULR. One patient without achievement of CTI conduction block had recurrence of typical AFL, and three patients without achievement of complete CT gap block had recurrence of ULR.
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Discussion
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Major findings.
This study demonstrated that the CT was a line of block during atrial pacing and typical AFL, but it had a conduction gap during ULR, suggesting the transverse conduction properties of the CT are functional. The anisotropic ratio of the CT during ULR was inversely correlated with the width of the conduction gap. The RFA of the CT conduction gap could eliminate ULR.
Transverse conduction properties of the CT.
During typical AFL, the CT has been demonstrated as a posterior barrier and a line of conduction block (1–3). Whether there is transcristal conduction during slow pacing in sinus rhythm is still controversial (4–7). Whereas Tai et al. (4) and Chen et al. (5) showed fixed block in the CT, Arenal et al. (6) and Schumacher et al. (7) demonstrated transcristal conduction during slow pacing. In some patients, complete transverse block of the CT was not achieved, even during pacing until 2-to-1 atrial capture or extrastimulation with a short coupling interval (7). Furthermore, the transcristal conduction is variable during different rhythms. In this study, no patients during typical AFL and only 6 of 22 patients during atrial pacing had transcristal conduction, but all patients had transverse conduction through a CT gap during ULR. We believe that the success or failure of transcristal conduction is determined by the underlying source-sink relationship, which reflects a complex interaction of several factors such as fiber orientation, gap junction distribution, and wavefront curvature.
Anisotropy of the CT.
Spach et al. (13) first demonstrated that in canine CT, conduction was faster in direction parallel to the intercaval axis than in direction perpendicular to the axis. They attributed such anisotropic properties to the variations in the geometric arrangement of the gap junctions in the direction of propagation, especially in tissues with scarce side-to-side electric coupling between cells resulting from microfibrosis (14). Becker et al. (15) used high-resolution mapping in animal study and confirmed the anisotropic conduction properties of the CT. Furthermore, they mentioned that the refractory properties also contributed to the conduction block, which happened in the longitudinal direction. Therefore, it seemed that the conduction in CT depended on both the regional differences of the active membrane ionic properties and the anisotropic passive electrical properties. Cabo et al. (16) studied propagation in two-dimensional sheep cardiac tissue and proposed that conduction through an anatomic isthmus increased the curvature of the wavefront and decreased the CV. In the present study, using non-contact mapping during ULR, the activation wavefront propagation along and across the CT could be evaluated. During ULR, the transverse CV was significantly less than the longitudinal conduction velocities. Furthermore, the anisotropic ratio was inversely related to the width of the conduction gap. Therefore, as the CT conduction gap narrowed, the transverse conduction slowed down, and the anisotropy of the CT increased.
Clinical implications.
First, because the transverse conduction capacities of the CT were functional and occurred in low prevalence during atrial pacing, this finding provided the rationale for conventional evaluation of CTI conduction block after ablation by atrial pacing. Second, in patients with RA typical AFL and ULR, three-dimensional non-contact mapping was not only a useful tool to determine the reentrant circuits but also a practical guide to navigate the RFA targets. Finally, the method used to define the width of the CT gap under non-contact mapping was useful in delineating the target for RFA, and RFA of the CT gap was effective in eliminating ULR.
Conclusions.
In patients with AFL, most of the CT conduction gaps were functional and only appeared during ULR. The anisotropic ratio of CT was inversely correlated to the width of the CT conduction gap. The RFA of the CT gap was effective in eliminating ULR.
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Footnotes
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Supported in part by grants from the Taipei Veterans General Hospital (VGH 92-37), Taiwan, Republic of China.
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