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Usefulness of Pre-Procedure Cavotricuspid Isthmus Imaging by Modified Transthoracic Echocardiography for Predicting Outcome of Isthmus-Dependent Atrial Flutter Ablation
Usefulness of Pre-Procedure Cavotricuspid Isthmus Imaging by Modified Transthoracic Echocardiography for Predicting Outcome of Isthmus-Dependent Atrial Flutter Ablation Jan-Yow Chen, MD, Kuo-Hung Lin, MD, Ying-Ming Liou, PhD, Kuan-Cheng Chang, MD, and Shoei K. Stephen Huang, MD, Taichung, Taiwan; Temple, Texas
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 6 1,548.3 vs 413.8 6 195.5 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. (J Am Soc Echocardiogr 2011;24:1148-55.) Keywords: Atrial flutter, Catheter ablation, Cavotricuspid isthmus, Eustachian ridge, Transthoracic echocardiography
Radiofrequency (RF) catheter ablation has become the first-line therapy for cavotricuspid isthmus (CTI)–dependent atrial flutter.1-4 Achievement of bidirectional conduction block across the CTI and the resulting noninducibility of tachycardia after ablation are the goals of this procedure.1,2,5-8 Although the total success rate of atrial flutter ablation is high, the probability of failed bidirectional block with a conventional catheter is still significant, and the use of a second ablation catheter with a different tip is often needed for successful ablation.9-13 In addition, a significant incidence of difficult From the Division of Cardiology, Department of Medicine, China Medical University Hospital, Taichung, Taiwan (J.-Y.C., K.-H.L., K.-C.C.); the Department of Life Science, National Chung-Hsing University, Taichung, Taiwan (J.-Y.C., Y.-M.L.); and the Section of Cardiac Electrophysiology and Pacing, Scott & White Healthcare, Texas A&M University Health Science Center, Temple, Texas (S.K.S.H.). Reprint requests: Shoei K. Stephen Huang, MD, Scott & White Healthcare, Section of Cardiac Electrophysiology and Pacing, 2401 South 31st Street, Temple, TX 76508 (E-mail: [email protected]). 0894-7317/$36.00 Copyright 2011 by the American Society of Echocardiography. doi:10.1016/j.echo.2011.06.007
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ablation with a requirement for extended procedural time with atrial flutter has been reported.9,10,14-17 Difficult or prolonged procedures may be associated with increased risk for procedurerelated complications. This is particularly true for patients with underlying heart failure, ischemic heart disease, or poor clinical condition. Therefore, the identification of patients at risk for having difficult and prolonged procedures before ablation is important. The CTI is a region of atrial tissue in the inferior portion of the right atrium that is bounded posterolaterally by the inferior vena cava (IVC) and anteromedially by the annulus of the tricuspid valve. The CTI plays a critical role in the reentrant circuit of CTI-dependent atrial flutter. The Eustachian ridge (ER) is an elevated linear ridge on the CTI that divides the isthmus into the anterior sub-Eustachian portion and the down-slope of the ER leading to the IVC.18 Imaging studies including angiography, intracardiac echocardiography (ICE), and multiple-detector computed tomography have been used to evaluate the isthmus.14,17,19-25 Anatomic variability of CTI and ER, demonstrated by right atrial angiography, has been shown to be strongly related to a difficult and prolonged ablation procedure.17,23,25 In particular, the presence of a long CTI with a pouch confirmed by right atrial angiography and ICE is correlated with the requirement for long duration of RF applications.14,21,26 In
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addition, a prominent ER, demonstrated using ICE, has CTI = Cavotricuspid isthmus also been reported to be an anatomic barrier to CTIICE = Intracardiac dependent atrial flutter echocardiography ablation.21 However, invasive IVC = Inferior vena cava imaging tools such as ICE and angiography may not be suitable ER = Eustachian ridge for preprocedural evaluation. RF = Radiofrequency Transthoracic echocardiography is a conventional method for TR = Tricuspid regurgitation the evaluation of the right atrium27-29 and can be performed noninvasively before RF ablation to anticipate procedural difficulty and to plan appropriately. We have previously reported preliminary data supporting the successful use of transthoracic echocardiography to visualize a long CTI recess in a flutter case before ablation.30 However, the usefulness of preprocedural transthoracic echocardiography for CTI and ER imaging to predict outcome of CTI-dependent atrial flutter ablation and to identify the patients at risk for prolonged and difficult procedures has not been well described. In this study, we evaluated the feasibility of preprocedural transthoracic echocardiography using a modified apical long-axis view to characterize the morphology of CTI and ER and to correlate morphology with the outcomes of RF catheter ablation for CTI-dependent atrial flutter. We also discuss the role of preprocedural transthoracic echocardiography for identifying patients at risk for prolonged and difficult ablation procedures and to assist in procedure planning. Abbreviations
METHODS Study Population This prospective study included 42 consecutive patients (30 men, 12 women; mean age, 62 614 years) who underwent electrophysiologic evaluation and RF catheter ablation for recurrent or refractory symptomatic CTI-dependent atrial flutter. Nineteen patients (45%) had structural heart disease, including coronary artery disease (n = 11), hypertensive cardiovascular disease (n = 3), valvular heart disease (n = 1), dilated nonischemic cardiomyopathy (n = 3), and congenital heart disease (n = 1). One patient had failed a previous RF ablation procedure for atrial flutter. Three patients had undergone prior cardiac surgery. Informed consent was obtained from each patient. The study protocol was approved by the institutional review board. Two-Dimensional Transthoracic Echocardiography Transthoracic echocardiography was prospectively performed 1 day before RF catheter ablation, with images obtained using a 1.6-MHz to 3.2-MHz S3 probe (Sonos 4500; Philips Medical Systems, Bothell, WA). The same experienced sonographer obtained all images from each patient during quiet respiration. The physicians who performed the atrial flutter ablation procedures were blinded to the echocardiographic results. For image acquisition, the probe was placed initially in the fifth intercostal space at the left midclavicular line. We designed a modified apical long-axis view with a slightly more right-sided adjustment in the orientation of the transducer to visualize the CTI and ER. After a standard apical long-axis view is obtained, the head of the echocardiographic probe is adjusted slightly toward the patient’s right side (Figure 1), so that the right atrium, right ventricle, tricuspid valve,
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and IVC will appear. The IVC is an important anatomic clue. By adjusting transducer orientation from this landmark, the CTI, which extends from the tricuspid valve to the IVC, can be evaluated in more detail. The echocardiographic imaging parameters, including CTI length, the presence or absence of a pouch or recess, the type of ER morphology, and the presence or absence of significant tricuspid regurgitation (TR) ($3+), were selected for comparison between patients with normal ablation times and those with prolonged ablation times. The boundaries of the CTI adjacent to the septal leaflet of the tricuspid valve and the IVC are defined as the septal CTI and inferior CTI, respectively. The ER was evaluated in detail from the septal CTI to the inferior CTI region. The heights of the ER at either the septal CTI or the inferior CTI were measured using the electronic calipers incorporated in the ultrasonography software. The length of the CTI was measured at end-systole. CTI length was defined as the distance between the IVC and the tricuspid annulus. The presence or absence of a pouch or recess was carefully evaluated throughout the CTI (Figure 2). A pouch is defined as a broad depression or concavity within the CTI, and a recess is defined as a focal or localized depression within the CTI.18,25,26 A prominent ER was noted when the amplitude of ER was greater than the average value of all enrolled patients (>9 mm), with the appearance of an elevated membrane outlining the anterior part of IVC orifice. In addition, a CTI with a prominent ER may show a ‘‘peak and valley’’ appearance.21 On the basis of the ultrasonographic morphology, we defined an extensive ER as a prominent ER extending from the septal CTI to the inferior CTI (Figure 3). Patients were considered to have nonextensive ERs if the echocardiographic morphology demonstrated either a diffusely low amplitude ER or an ER that was only focally prominent (Figure 4). A focally prominent ER was defined if only a focal but not continuously prominent ER could be found. RF Catheter Ablation The ablation procedure was performed by more than one attending electrophysiologist, and each performer was blinded to the preablation echocardiographic findings. A 6-Fr decapolar electrode catheter (Daig Corporation, Minnetonka, MN) was placed in the coronary sinus via the right internal jugular vein. A duodecapolar catheter (Halo; Biosense Webster, Del Mar, CA) was placed along the tricuspid annulus to record electrograms of the right atrial septum and free wall, and a 8-mm-tip ablation catheter (Boston Scientific Corporation, Natick, MA) was used for linear ablation of the isthmus in all patients. Twelve-lead surface electrocardiograms and intracardiac electrographic signals were simultaneously recorded and digitally stored. A continuous and unmodulated RF current was delivered by a generator (EPT-1000 XP; EP Technology, Boston Scientific Corporation). RF ablation was performed with a linear drag lesion from the tricuspid annulus to the IVC with a preset temperature of 60 C, maximum power of 100 W, and 60-sec preselected pulse duration. The end points of ablation success were defined as complete bidirectional isthmus conduction block and noninducibility of CTI-dependent atrial flutter after ablation.2,9 The ablation time required to achieve complete isthmus conduction block was recorded in each patient. If complete conduction block could be achieved in 10 min of RF applications, the atrial flutter ablation was considered a straightforward procedure. Procedures requiring >10 min were considered difficult according to the criteria in the previous report.9,10
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Figure 1 Echocardiographic images of the ER and CTI. (A) A modified apical long-axis view reveals the tricuspid valve (TV), IVC, and right ventricle (RV). The arrow indicates the CTI without a pouch or recess. The amplitude of the ER was measured using the electronic calipers incorporated in the ultrasonography software (between the crosses). (B) The method to obtain the modified apical view is demonstrated. After a standard apical long-axis view (probe A plane) is obtained, the placement of the probe is adjusted slightly toward the right side (probe B plane). Thereafter, the right atrium (RA), RV, TV, and IVC will appear.
Figure 2 Echocardiographic images of a pouch on the CTI. (A) The CTI margins on the echocardiographic image are indicated by asterisks. A deep pouch (yellow arrow) was identified in the isthmus by transthoracic echocardiography. (B) Illustration of the anatomy of the CTI including a pouch is shown. The margins of the CTI are outlined by yellow dots. The yellow arrow indicates the pouch. Statistical Analysis Continuous data were compared using Student’s t tests and are expressed as mean 6 SD. Categorical data were compared using c2 tests or Fisher’s exact tests as appropriate. Four ultrasonographic parameters, including CTI length, the presence or absence of a pouch
or recess, significant TR ($3+), and ER morphology, were selected for comparison between patients in the straightforward group and the difficult group. The relative influence of these four variables on the outcome of ablation therapy was tested by multivariate logistic regression analysis. Interobserver and intraobserver agreement was
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Figure 3 Echocardiography of an extensive ER. The ER was continually prominent from the septal (A) to the inferior (B) CTI. The red arrow indicates the CTI without pouch or recess, the yellow arrow indicates the ER on the septal CTI, and the white arrow indicates the ER on the inferior CTI. (C) The corresponding anatomy of the extensive ER is illustrated. assessed using data from all study patients. Intraobserver and interobserver agreement in measuring CTI length was analyzed using Spearman’s correlation coefficient; k statistical analysis was used to determine the degree of intraobserver and interobserver agreement in the determination of the presence of a pouch or recess, significant TR, and an extensively prominent ER. Observer agreement was categorized as poor, fair, moderate, good, or excellent according to k values of <0.20, 0.20 to 0.39, 0.40 to 0.59, 0.60 to 0.79, and >0.80, respectively. P values < 0.05 were considered statistically significant for all analyses.
RESULTS Ablation Time and Ablation Outcomes Complete bidirectional isthmus block was achieved within 10 min of RF application in 28 patients (straightforward group) but could not be achieved with 10 min of ablation in 14 patients (difficult group). The ablation time in the difficult group was significantly longer than that in the straightforward group (1,638.6 6 1,461.3 vs 369.9 6 138.5 sec,
P = .006). Baseline characteristics were similar between the two groups (Table 1).
ER Morphology and Ablation Outcomes The echocardiography images of the 42 patients were of sufficient quality to allow evaluation. Preprocedural transthoracic echocardiography showed extensive ERs in 13 patients. The remaining 29 patients had either diffusely low amplitude (n = 17) or focally prominent (n = 12) ERs (nonextensive ERs). The ablation time in patients with extensive ERs was significantly longer than in patients with nonextensive ERs (1,638.4 6 1,548.3 vs 413.8 6 195.5 sec, P = .015; Figure 5). CTI block was not achieved in two patients with extensive ERs. CTI block after ablation was achieved successfully in all patients with nonextensive ERs. Difficult procedures were also noted in more patients with extensive ERs than in those with nonextensive ERs (10 of 13 vs four of 29, P < .001). However, difficulty in achieving isthmus block was equally uncommon in patients with diffusely low amplitude ER and those with focally prominent ERs (two of 17 vs two of 12, P = 1.0).
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Figure 4 (A,B) Echocardiography of a diffusely low amplitude ER. The ER was diffusely low in amplitude from the septal (A) to the inferior (B) CTI. (C,D) A patient with a focally prominent ER. The ER showed a low-amplitude ER in the septal CTI (C) but with a focally prominent ER near the inferior CTI (D). The yellow arrow indicates the ER on the septal CTI, and the white arrow indicates the ER on the inferior CTI.
Predictors of Ablation Outcome by Echocardiographic Imaging of the CTI Univariate analysis showed a significantly higher incidence of extensive ER in the patients with difficult procedure (straightforward group vs difficult group, three of 28 vs 10 of 14; P < .001). The difficult group also showed longer CTIs (straightforward group vs difficult group, 31.5 6 4.1 vs 35.5 6 3.3 mm; P = .003) and a higher incidence of the presence of a pouch or recess (2 of 28 with one pouch and one recess vs seven of 14 with three pouches and four recesses, P = .003) by univariate analysis. In addition, a trend toward a higher incidence of significant TR ($3+) in the difficult group (straightforward group vs difficult group, two of 28 vs three of 14; P = .313) was found on uni-
variate analysis. Multivariate analysis including variables of CTI length, the presence of a pouch or recess, ER morphology, and the presence of significant TR revealed that the presence of extensive ER was the only significant independent predictor of difficulty in achieving complete isthmus block (Table 2). Intraobserver and interobserver agreement in measuring CTI length (as indicated by Spearman’s rank correlation coefficient) was 0.933 (P < .01) and 0.899 (P < .01), respectively. Analysis of k statistics indicated excellent results for differentiating the presence or absence of a pouch or recess (k = 0.926, P < .01, and k = 0.932, P < .01, respectively), determining the presence or absence of significant TR (k = 0.896, P < 0.01, and k = 0.896, P < .01, respectively),
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Table 1 Clinical characteristics of study patients in the straightforward and difficult groups Variable
Straightforward group (n = 28)
Age (y) Men/women SHD Clinical AFL (CCW/CW) AFL CL (msec) LA diameter (mm)
61.2 6 15.1 19/9 12 25/3 228.6 6 32.5 40.1 6 8.4
Difficult group (n = 14)
P
63.9 6 11.7 .57 11/3 .72 7 .66 12/2 1.00 236.1 6 25.4 .45 43.9 6 5.4 .13
AFL, Atrial flutter; CCW, counterclockwise; CL, cycle length; CW, clockwise; LA, left atrium; SHD, structural heart disease. Data are expressed as mean 6 SD or as numbers.
and determining the presence or absence of an extensive ER (k = 0.943, P < .01, and k = 0.893, P < .01, respectively). DISCUSSION The CTI plays a critical role in the reentrant circuit of CTI-dependent atrial flutter and is the target for catheter ablation. Linear RF catheter ablation across the CTI can achieve bidirectional conduction block across the CTI and abolish the reentrant circuit and thereafter eliminate the isthmus-dependent atrial flutter.1,2,5-8 However, complete bidirectional isthmus conduction block may be difficult to achieve after a prolonged ablation procedure in some patients with CTIdependent atrial flutter.9,18,25 Variations in muscle fiber orientation and myocardial thickness in this region have been reported to explain the difficulty in achieving bidirectional isthmus block in these patients.9,15,16,31 Imaging studies have shown that the morphology of the isthmus and ER frequently present as anatomic variants.21 CTI morphology also has been demonstrated to be related to difficulty in RF ablation of atrial flutter.14,21 In previous studies, the detailed morphology of the ER and the CTI was evaluated using right atrial angiography or two-dimensional or three-dimensional ICE.17,20,21,24,26 However, angiography and ICE are invasive procedures and may not be suitable for preprocedural evaluation. Additionally, the quantitative measurement of CTI and ER is difficult because the plane visualized by ICE is often an oblique line, and consequently the measurements do not correspond with perpendicular cross-sectional anatomy.21 Transthoracic echocardiography is a well-established and convenient noninvasive method to evaluate the right atrium. The present study confirmed that preprocedural transthoracic echocardiography, using a modified apical long-axis view, is useful to characterize the morphology of the CTI and ER. Additionally, we found that an extensive ER identified on transthoracic echocardiography is a strong predictor for difficult ablation in CTI-dependent atrial flutter. When such an extensive ER is found before ablation, a more aggressive ablation strategy should be considered. A significant incidence of difficult and prolonged procedures for ablation therapy of atrial flutter has been reported.17 In our study, a prolonged procedure was strongly associated with the anatomic characteristics of CTI and ER, and a prolonged ablation procedure may increase the possibility of procedure-related complications and risks. Preprocedural transthoracic echocardiography provides a feasible method to evaluate the CTI and ER before the ablation procedure and identify patients at risk for difficult procedures and complications.
Figure 5 Time to achieve complete isthmus block in patients with different types of ER. The ablation time in patients with extensive ERs was significantly longer than in patients with nonextensive ERs (1,638.4 6 1,548.3 vs 413.8 6 195.5 sec, P = .015).
In addition, different types of ablation catheters have been shown to be more effective in specific patterns of CTI.17 The different efficacy of an 8-mm-tip ablation catheter and an irrigated-tip catheter has been reported in patients with straight versus concave CTIs.17 Therefore, the results of preprocedural transthoracic echocardiography used to identify the anatomic characteristics of the CTI and ER may guide the operator to make specific adjustments in procedure planning, such as preparation of the ablation facilities, selection of an effective ablation catheter, and selection of the mapping methods and imaging tools used. The goals of these adjustments are to increase ablation efficacy, reduce procedure time, and reduce the risk for procedure-related complications in patients with serious medical comorbidities or with histories of previously failed procedures. In the present study, we used transthoracic echocardiography to evaluate the architecture of the CTI and ER. The percentage of difficulty in achieving bidirectional isthmus block was significantly higher in patients with extensive ER who had prolonged ablation times. However, there was no significant difference in the incidence of difficulty in isthmus block between patients with generally low and focally prominent ERs. A prominent ER has been previously reported to be a predictor of difficulty in achieving isthmus block.21 However, ER morphologies can be divided into extensive versus focally prominent ERs on the basis of transthoracic echocardiography. In the present study, we found that only an extensive ER, not a focally prominent ER, was strongly associated with a difficult procedure for atrial flutter ablation. A prominent ER may cause difficulty in catheter manipulation and endocardial contact on the portion between the ER crest and the tricuspid annulus.18,25 An extensive ER is considered to result in more difficulty in catheter manipulation and endocardial contact than a focally prominent ER because of its anatomic characteristics; therefore, achieving bidirectional block of CTI is more difficult. Long CTIs, pouched isthmuses, and significant TR ($3+) have been demonstrated in patients with atrial flutter and were found to
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Table 2 Predictors of atrial flutter ablation with difficulty in achieving complete isthmus conduction block by transthoracic echocardiography Variable
Straightforward group (n = 28)
Difficult group (n = 14)
Univariate P value
Multivariate P value
Odds ratio
95% confidence interval
Extensive ER Pouch or recess CTI (mm) TR ($3+)
3 2 31.6 6 4.1 2
10 7 35.0 6 3.8 3
<.001 .003 .003 .313
.024 .125 .549 .237
10.217 5.917 1.088 4.752
1.362–76.622 0.610–57.383 0.826–1.434 0.358–63.053
be associated with difficulty in achieving isthmus block.17,18,21,25,26 In the present study, we showed that a long CTI and a pouched isthmus were associated with difficult atrial flutter ablation, on the basis of univariate analysis. There was also a trend toward a higher incidence of significant TR ($3+) in patients with difficult procedures on univariate analysis. However, using multivariate analysis, we found that an extensive ER was the only independent predictor of difficulty in achieving bidirectional isthmus block.
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Limitations It is possible that the factors influencing the ablation success for atrial flutter include not only ER and CTI morphologies but also the underlying disease substrate, atrial myocardial characteristics, atrial flutter conduction pattern in the CTI, the ablation catheter used, and the ablation technique. It is difficult to control all of these variables, but we consistently used an 8-mm-tip ablation catheter in every patient in our study, to minimize technique-related confounding factors. The ablation procedure was performed by more than one attending electrophysiologist, and each performer was blinded to the pretreatment echocardiographic findings. However, the results of the ablation therapy may have been related to the specific operator rather than to anatomic factors. Another limitation was the relatively small population in the study, and the results may need to be confirmed in a larger scale study.
CONCLUSIONS Transthoracic echocardiography using a modified apical long-axis view is useful to evaluate the anatomy of the CTI before ablation procedures for CTI-dependent atrial flutter. The presence of an extensive ER on echocardiography is a strong predictor for a difficult ablation procedure. Early decision and the selection of a more aggressive ablation strategy are suggested for these patients before the procedure, particularly in patients who are at high risk for developing procedurerelated complications and those with histories of failed ablations.
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ACKNOWLEDGMENTS We thank Hsiu-Chen Lu for her help in figure creation. We are also grateful to Pei-Chi Hung and the staffs of our echocardiography and electrophysiology laboratories for their kind support of this study.
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in patients with and without history of common atrial flutter. Circulation 1999;99:3017-23. Gami AS, Edwards WD, Lachman N, Friedman PA, Talreja D, Munger TM, et al. Electrophysiological anatomy of typical atrial flutter: the posterior boundary and causes for difficulty with ablation. J Cardiovasc Electrophysiol 2010;21:144-9. Morton JB, Sanders P, Davidson NC, Sparks PB, Vohra JK, Kalman JM. Phased-array intracardiac echocardiography for defining cavotricuspid isthmus anatomy during radiofrequency ablation of typical atrial flutter. J Cardiovasc Electrophysiol 2003;14:591-7. Sinha A, Nanda NC, Misra V, Khanna D, Dod HS, Vengala S, et al. Live three-dimensional transthoracic echocardiographic assessment of transcatheter closure of atrial septal defect and patent foramen ovale. Echocardiography 2004;21:749-53. Fukumoto A, Yaku H, Doi K, Ito H, Numata S, Hayashida K, et al. Continuous thrombus in the right and left atria penetrating the patent foramen ovalis. Circulation 2005;112:e143-4. Pharr JR, West MB, Kusumoto FM, Figueredo VM. Prominent crista terminalis appearing as a right atrial mass on transthoracic echocardiogram. J Am Soc Echocardiogr 2002;15:753-5. Chen JY, Hsu HB, Chang KC, Huang SKS. An extensive recess in the cavotricuspid isthmus identified by transthoracic three-dimensional echocardiography in atrial flutter ablation. J Cardiovasc Electrophysiol 2009;20:1291. Cabrera JA, Sanchez-Quintana D, Ho Sy, Medina A, Anderson RH. The architecture of the atrial musculature between the orifice of the inferior caval vein and the tricuspid valve: The anatomy of the isthmus. J Cardiovasc Electrophysiol 1998;9:1186-95.
ERRATUM In the article entitled "Improved Semiautomated Quantification of Left Ventricular Volumes and Ejection Fraction Using 3-Dimensional Echocardiography with a Full Matrix-array Transducer: Comparison with Magnetic Resonance Imaging," (J Am Soc Echocardiogr 2005;18:779-788) the name of one of the authors was listed incorrectly. The correct listing is Juan Luis GutierrezChico, MD.
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 6 1,548.3 vs 413.8 6 195.5 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. (J Am Soc Echocardiogr 2011;24:1148-55.) Keywords: Atrial flutter, Catheter ablation, Cavotricuspid isthmus, Eustachian ridge, Transthoracic echocardiography
Radiofrequency (RF) catheter ablation has become the first-line therapy for cavotricuspid isthmus (CTI)–dependent atrial flutter.1-4 Achievement of bidirectional conduction block across the CTI and the resulting noninducibility of tachycardia after ablation are the goals of this procedure.1,2,5-8 Although the total success rate of atrial flutter ablation is high, the probability of failed bidirectional block with a conventional catheter is still significant, and the use of a second ablation catheter with a different tip is often needed for successful ablation.9-13 In addition, a significant incidence of difficult From the Division of Cardiology, Department of Medicine, China Medical University Hospital, Taichung, Taiwan (J.-Y.C., K.-H.L., K.-C.C.); the Department of Life Science, National Chung-Hsing University, Taichung, Taiwan (J.-Y.C., Y.-M.L.); and the Section of Cardiac Electrophysiology and Pacing, Scott & White Healthcare, Texas A&M University Health Science Center, Temple, Texas (S.K.S.H.). Reprint requests: Shoei K. Stephen Huang, MD, Scott & White Healthcare, Section of Cardiac Electrophysiology and Pacing, 2401 South 31st Street, Temple, TX 76508 (E-mail: [email protected]). 0894-7317/$36.00 Copyright 2011 by the American Society of Echocardiography. doi:10.1016/j.echo.2011.06.007
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ablation with a requirement for extended procedural time with atrial flutter has been reported.9,10,14-17 Difficult or prolonged procedures may be associated with increased risk for procedurerelated complications. This is particularly true for patients with underlying heart failure, ischemic heart disease, or poor clinical condition. Therefore, the identification of patients at risk for having difficult and prolonged procedures before ablation is important. The CTI is a region of atrial tissue in the inferior portion of the right atrium that is bounded posterolaterally by the inferior vena cava (IVC) and anteromedially by the annulus of the tricuspid valve. The CTI plays a critical role in the reentrant circuit of CTI-dependent atrial flutter. The Eustachian ridge (ER) is an elevated linear ridge on the CTI that divides the isthmus into the anterior sub-Eustachian portion and the down-slope of the ER leading to the IVC.18 Imaging studies including angiography, intracardiac echocardiography (ICE), and multiple-detector computed tomography have been used to evaluate the isthmus.14,17,19-25 Anatomic variability of CTI and ER, demonstrated by right atrial angiography, has been shown to be strongly related to a difficult and prolonged ablation procedure.17,23,25 In particular, the presence of a long CTI with a pouch confirmed by right atrial angiography and ICE is correlated with the requirement for long duration of RF applications.14,21,26 In
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addition, a prominent ER, demonstrated using ICE, has CTI = Cavotricuspid isthmus also been reported to be an anatomic barrier to CTIICE = Intracardiac dependent atrial flutter echocardiography ablation.21 However, invasive IVC = Inferior vena cava imaging tools such as ICE and angiography may not be suitable ER = Eustachian ridge for preprocedural evaluation. RF = Radiofrequency Transthoracic echocardiography is a conventional method for TR = Tricuspid regurgitation the evaluation of the right atrium27-29 and can be performed noninvasively before RF ablation to anticipate procedural difficulty and to plan appropriately. We have previously reported preliminary data supporting the successful use of transthoracic echocardiography to visualize a long CTI recess in a flutter case before ablation.30 However, the usefulness of preprocedural transthoracic echocardiography for CTI and ER imaging to predict outcome of CTI-dependent atrial flutter ablation and to identify the patients at risk for prolonged and difficult procedures has not been well described. In this study, we evaluated the feasibility of preprocedural transthoracic echocardiography using a modified apical long-axis view to characterize the morphology of CTI and ER and to correlate morphology with the outcomes of RF catheter ablation for CTI-dependent atrial flutter. We also discuss the role of preprocedural transthoracic echocardiography for identifying patients at risk for prolonged and difficult ablation procedures and to assist in procedure planning. Abbreviations
METHODS Study Population This prospective study included 42 consecutive patients (30 men, 12 women; mean age, 62 614 years) who underwent electrophysiologic evaluation and RF catheter ablation for recurrent or refractory symptomatic CTI-dependent atrial flutter. Nineteen patients (45%) had structural heart disease, including coronary artery disease (n = 11), hypertensive cardiovascular disease (n = 3), valvular heart disease (n = 1), dilated nonischemic cardiomyopathy (n = 3), and congenital heart disease (n = 1). One patient had failed a previous RF ablation procedure for atrial flutter. Three patients had undergone prior cardiac surgery. Informed consent was obtained from each patient. The study protocol was approved by the institutional review board. Two-Dimensional Transthoracic Echocardiography Transthoracic echocardiography was prospectively performed 1 day before RF catheter ablation, with images obtained using a 1.6-MHz to 3.2-MHz S3 probe (Sonos 4500; Philips Medical Systems, Bothell, WA). The same experienced sonographer obtained all images from each patient during quiet respiration. The physicians who performed the atrial flutter ablation procedures were blinded to the echocardiographic results. For image acquisition, the probe was placed initially in the fifth intercostal space at the left midclavicular line. We designed a modified apical long-axis view with a slightly more right-sided adjustment in the orientation of the transducer to visualize the CTI and ER. After a standard apical long-axis view is obtained, the head of the echocardiographic probe is adjusted slightly toward the patient’s right side (Figure 1), so that the right atrium, right ventricle, tricuspid valve,
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and IVC will appear. The IVC is an important anatomic clue. By adjusting transducer orientation from this landmark, the CTI, which extends from the tricuspid valve to the IVC, can be evaluated in more detail. The echocardiographic imaging parameters, including CTI length, the presence or absence of a pouch or recess, the type of ER morphology, and the presence or absence of significant tricuspid regurgitation (TR) ($3+), were selected for comparison between patients with normal ablation times and those with prolonged ablation times. The boundaries of the CTI adjacent to the septal leaflet of the tricuspid valve and the IVC are defined as the septal CTI and inferior CTI, respectively. The ER was evaluated in detail from the septal CTI to the inferior CTI region. The heights of the ER at either the septal CTI or the inferior CTI were measured using the electronic calipers incorporated in the ultrasonography software. The length of the CTI was measured at end-systole. CTI length was defined as the distance between the IVC and the tricuspid annulus. The presence or absence of a pouch or recess was carefully evaluated throughout the CTI (Figure 2). A pouch is defined as a broad depression or concavity within the CTI, and a recess is defined as a focal or localized depression within the CTI.18,25,26 A prominent ER was noted when the amplitude of ER was greater than the average value of all enrolled patients (>9 mm), with the appearance of an elevated membrane outlining the anterior part of IVC orifice. In addition, a CTI with a prominent ER may show a ‘‘peak and valley’’ appearance.21 On the basis of the ultrasonographic morphology, we defined an extensive ER as a prominent ER extending from the septal CTI to the inferior CTI (Figure 3). Patients were considered to have nonextensive ERs if the echocardiographic morphology demonstrated either a diffusely low amplitude ER or an ER that was only focally prominent (Figure 4). A focally prominent ER was defined if only a focal but not continuously prominent ER could be found. RF Catheter Ablation The ablation procedure was performed by more than one attending electrophysiologist, and each performer was blinded to the preablation echocardiographic findings. A 6-Fr decapolar electrode catheter (Daig Corporation, Minnetonka, MN) was placed in the coronary sinus via the right internal jugular vein. A duodecapolar catheter (Halo; Biosense Webster, Del Mar, CA) was placed along the tricuspid annulus to record electrograms of the right atrial septum and free wall, and a 8-mm-tip ablation catheter (Boston Scientific Corporation, Natick, MA) was used for linear ablation of the isthmus in all patients. Twelve-lead surface electrocardiograms and intracardiac electrographic signals were simultaneously recorded and digitally stored. A continuous and unmodulated RF current was delivered by a generator (EPT-1000 XP; EP Technology, Boston Scientific Corporation). RF ablation was performed with a linear drag lesion from the tricuspid annulus to the IVC with a preset temperature of 60 C, maximum power of 100 W, and 60-sec preselected pulse duration. The end points of ablation success were defined as complete bidirectional isthmus conduction block and noninducibility of CTI-dependent atrial flutter after ablation.2,9 The ablation time required to achieve complete isthmus conduction block was recorded in each patient. If complete conduction block could be achieved in 10 min of RF applications, the atrial flutter ablation was considered a straightforward procedure. Procedures requiring >10 min were considered difficult according to the criteria in the previous report.9,10
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Figure 1 Echocardiographic images of the ER and CTI. (A) A modified apical long-axis view reveals the tricuspid valve (TV), IVC, and right ventricle (RV). The arrow indicates the CTI without a pouch or recess. The amplitude of the ER was measured using the electronic calipers incorporated in the ultrasonography software (between the crosses). (B) The method to obtain the modified apical view is demonstrated. After a standard apical long-axis view (probe A plane) is obtained, the placement of the probe is adjusted slightly toward the right side (probe B plane). Thereafter, the right atrium (RA), RV, TV, and IVC will appear.
Figure 2 Echocardiographic images of a pouch on the CTI. (A) The CTI margins on the echocardiographic image are indicated by asterisks. A deep pouch (yellow arrow) was identified in the isthmus by transthoracic echocardiography. (B) Illustration of the anatomy of the CTI including a pouch is shown. The margins of the CTI are outlined by yellow dots. The yellow arrow indicates the pouch. Statistical Analysis Continuous data were compared using Student’s t tests and are expressed as mean 6 SD. Categorical data were compared using c2 tests or Fisher’s exact tests as appropriate. Four ultrasonographic parameters, including CTI length, the presence or absence of a pouch
or recess, significant TR ($3+), and ER morphology, were selected for comparison between patients in the straightforward group and the difficult group. The relative influence of these four variables on the outcome of ablation therapy was tested by multivariate logistic regression analysis. Interobserver and intraobserver agreement was
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Figure 3 Echocardiography of an extensive ER. The ER was continually prominent from the septal (A) to the inferior (B) CTI. The red arrow indicates the CTI without pouch or recess, the yellow arrow indicates the ER on the septal CTI, and the white arrow indicates the ER on the inferior CTI. (C) The corresponding anatomy of the extensive ER is illustrated. assessed using data from all study patients. Intraobserver and interobserver agreement in measuring CTI length was analyzed using Spearman’s correlation coefficient; k statistical analysis was used to determine the degree of intraobserver and interobserver agreement in the determination of the presence of a pouch or recess, significant TR, and an extensively prominent ER. Observer agreement was categorized as poor, fair, moderate, good, or excellent according to k values of <0.20, 0.20 to 0.39, 0.40 to 0.59, 0.60 to 0.79, and >0.80, respectively. P values < 0.05 were considered statistically significant for all analyses.
RESULTS Ablation Time and Ablation Outcomes Complete bidirectional isthmus block was achieved within 10 min of RF application in 28 patients (straightforward group) but could not be achieved with 10 min of ablation in 14 patients (difficult group). The ablation time in the difficult group was significantly longer than that in the straightforward group (1,638.6 6 1,461.3 vs 369.9 6 138.5 sec,
P = .006). Baseline characteristics were similar between the two groups (Table 1).
ER Morphology and Ablation Outcomes The echocardiography images of the 42 patients were of sufficient quality to allow evaluation. Preprocedural transthoracic echocardiography showed extensive ERs in 13 patients. The remaining 29 patients had either diffusely low amplitude (n = 17) or focally prominent (n = 12) ERs (nonextensive ERs). The ablation time in patients with extensive ERs was significantly longer than in patients with nonextensive ERs (1,638.4 6 1,548.3 vs 413.8 6 195.5 sec, P = .015; Figure 5). CTI block was not achieved in two patients with extensive ERs. CTI block after ablation was achieved successfully in all patients with nonextensive ERs. Difficult procedures were also noted in more patients with extensive ERs than in those with nonextensive ERs (10 of 13 vs four of 29, P < .001). However, difficulty in achieving isthmus block was equally uncommon in patients with diffusely low amplitude ER and those with focally prominent ERs (two of 17 vs two of 12, P = 1.0).
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Figure 4 (A,B) Echocardiography of a diffusely low amplitude ER. The ER was diffusely low in amplitude from the septal (A) to the inferior (B) CTI. (C,D) A patient with a focally prominent ER. The ER showed a low-amplitude ER in the septal CTI (C) but with a focally prominent ER near the inferior CTI (D). The yellow arrow indicates the ER on the septal CTI, and the white arrow indicates the ER on the inferior CTI.
Predictors of Ablation Outcome by Echocardiographic Imaging of the CTI Univariate analysis showed a significantly higher incidence of extensive ER in the patients with difficult procedure (straightforward group vs difficult group, three of 28 vs 10 of 14; P < .001). The difficult group also showed longer CTIs (straightforward group vs difficult group, 31.5 6 4.1 vs 35.5 6 3.3 mm; P = .003) and a higher incidence of the presence of a pouch or recess (2 of 28 with one pouch and one recess vs seven of 14 with three pouches and four recesses, P = .003) by univariate analysis. In addition, a trend toward a higher incidence of significant TR ($3+) in the difficult group (straightforward group vs difficult group, two of 28 vs three of 14; P = .313) was found on uni-
variate analysis. Multivariate analysis including variables of CTI length, the presence of a pouch or recess, ER morphology, and the presence of significant TR revealed that the presence of extensive ER was the only significant independent predictor of difficulty in achieving complete isthmus block (Table 2). Intraobserver and interobserver agreement in measuring CTI length (as indicated by Spearman’s rank correlation coefficient) was 0.933 (P < .01) and 0.899 (P < .01), respectively. Analysis of k statistics indicated excellent results for differentiating the presence or absence of a pouch or recess (k = 0.926, P < .01, and k = 0.932, P < .01, respectively), determining the presence or absence of significant TR (k = 0.896, P < 0.01, and k = 0.896, P < .01, respectively),
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Table 1 Clinical characteristics of study patients in the straightforward and difficult groups Variable
Straightforward group (n = 28)
Age (y) Men/women SHD Clinical AFL (CCW/CW) AFL CL (msec) LA diameter (mm)
61.2 6 15.1 19/9 12 25/3 228.6 6 32.5 40.1 6 8.4
Difficult group (n = 14)
P
63.9 6 11.7 .57 11/3 .72 7 .66 12/2 1.00 236.1 6 25.4 .45 43.9 6 5.4 .13
AFL, Atrial flutter; CCW, counterclockwise; CL, cycle length; CW, clockwise; LA, left atrium; SHD, structural heart disease. Data are expressed as mean 6 SD or as numbers.
and determining the presence or absence of an extensive ER (k = 0.943, P < .01, and k = 0.893, P < .01, respectively). DISCUSSION The CTI plays a critical role in the reentrant circuit of CTI-dependent atrial flutter and is the target for catheter ablation. Linear RF catheter ablation across the CTI can achieve bidirectional conduction block across the CTI and abolish the reentrant circuit and thereafter eliminate the isthmus-dependent atrial flutter.1,2,5-8 However, complete bidirectional isthmus conduction block may be difficult to achieve after a prolonged ablation procedure in some patients with CTIdependent atrial flutter.9,18,25 Variations in muscle fiber orientation and myocardial thickness in this region have been reported to explain the difficulty in achieving bidirectional isthmus block in these patients.9,15,16,31 Imaging studies have shown that the morphology of the isthmus and ER frequently present as anatomic variants.21 CTI morphology also has been demonstrated to be related to difficulty in RF ablation of atrial flutter.14,21 In previous studies, the detailed morphology of the ER and the CTI was evaluated using right atrial angiography or two-dimensional or three-dimensional ICE.17,20,21,24,26 However, angiography and ICE are invasive procedures and may not be suitable for preprocedural evaluation. Additionally, the quantitative measurement of CTI and ER is difficult because the plane visualized by ICE is often an oblique line, and consequently the measurements do not correspond with perpendicular cross-sectional anatomy.21 Transthoracic echocardiography is a well-established and convenient noninvasive method to evaluate the right atrium. The present study confirmed that preprocedural transthoracic echocardiography, using a modified apical long-axis view, is useful to characterize the morphology of the CTI and ER. Additionally, we found that an extensive ER identified on transthoracic echocardiography is a strong predictor for difficult ablation in CTI-dependent atrial flutter. When such an extensive ER is found before ablation, a more aggressive ablation strategy should be considered. A significant incidence of difficult and prolonged procedures for ablation therapy of atrial flutter has been reported.17 In our study, a prolonged procedure was strongly associated with the anatomic characteristics of CTI and ER, and a prolonged ablation procedure may increase the possibility of procedure-related complications and risks. Preprocedural transthoracic echocardiography provides a feasible method to evaluate the CTI and ER before the ablation procedure and identify patients at risk for difficult procedures and complications.
Figure 5 Time to achieve complete isthmus block in patients with different types of ER. The ablation time in patients with extensive ERs was significantly longer than in patients with nonextensive ERs (1,638.4 6 1,548.3 vs 413.8 6 195.5 sec, P = .015).
In addition, different types of ablation catheters have been shown to be more effective in specific patterns of CTI.17 The different efficacy of an 8-mm-tip ablation catheter and an irrigated-tip catheter has been reported in patients with straight versus concave CTIs.17 Therefore, the results of preprocedural transthoracic echocardiography used to identify the anatomic characteristics of the CTI and ER may guide the operator to make specific adjustments in procedure planning, such as preparation of the ablation facilities, selection of an effective ablation catheter, and selection of the mapping methods and imaging tools used. The goals of these adjustments are to increase ablation efficacy, reduce procedure time, and reduce the risk for procedure-related complications in patients with serious medical comorbidities or with histories of previously failed procedures. In the present study, we used transthoracic echocardiography to evaluate the architecture of the CTI and ER. The percentage of difficulty in achieving bidirectional isthmus block was significantly higher in patients with extensive ER who had prolonged ablation times. However, there was no significant difference in the incidence of difficulty in isthmus block between patients with generally low and focally prominent ERs. A prominent ER has been previously reported to be a predictor of difficulty in achieving isthmus block.21 However, ER morphologies can be divided into extensive versus focally prominent ERs on the basis of transthoracic echocardiography. In the present study, we found that only an extensive ER, not a focally prominent ER, was strongly associated with a difficult procedure for atrial flutter ablation. A prominent ER may cause difficulty in catheter manipulation and endocardial contact on the portion between the ER crest and the tricuspid annulus.18,25 An extensive ER is considered to result in more difficulty in catheter manipulation and endocardial contact than a focally prominent ER because of its anatomic characteristics; therefore, achieving bidirectional block of CTI is more difficult. Long CTIs, pouched isthmuses, and significant TR ($3+) have been demonstrated in patients with atrial flutter and were found to
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Table 2 Predictors of atrial flutter ablation with difficulty in achieving complete isthmus conduction block by transthoracic echocardiography Variable
Straightforward group (n = 28)
Difficult group (n = 14)
Univariate P value
Multivariate P value
Odds ratio
95% confidence interval
Extensive ER Pouch or recess CTI (mm) TR ($3+)
3 2 31.6 6 4.1 2
10 7 35.0 6 3.8 3
<.001 .003 .003 .313
.024 .125 .549 .237
10.217 5.917 1.088 4.752
1.362–76.622 0.610–57.383 0.826–1.434 0.358–63.053
be associated with difficulty in achieving isthmus block.17,18,21,25,26 In the present study, we showed that a long CTI and a pouched isthmus were associated with difficult atrial flutter ablation, on the basis of univariate analysis. There was also a trend toward a higher incidence of significant TR ($3+) in patients with difficult procedures on univariate analysis. However, using multivariate analysis, we found that an extensive ER was the only independent predictor of difficulty in achieving bidirectional isthmus block.
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Limitations It is possible that the factors influencing the ablation success for atrial flutter include not only ER and CTI morphologies but also the underlying disease substrate, atrial myocardial characteristics, atrial flutter conduction pattern in the CTI, the ablation catheter used, and the ablation technique. It is difficult to control all of these variables, but we consistently used an 8-mm-tip ablation catheter in every patient in our study, to minimize technique-related confounding factors. The ablation procedure was performed by more than one attending electrophysiologist, and each performer was blinded to the pretreatment echocardiographic findings. However, the results of the ablation therapy may have been related to the specific operator rather than to anatomic factors. Another limitation was the relatively small population in the study, and the results may need to be confirmed in a larger scale study.
CONCLUSIONS Transthoracic echocardiography using a modified apical long-axis view is useful to evaluate the anatomy of the CTI before ablation procedures for CTI-dependent atrial flutter. The presence of an extensive ER on echocardiography is a strong predictor for a difficult ablation procedure. Early decision and the selection of a more aggressive ablation strategy are suggested for these patients before the procedure, particularly in patients who are at high risk for developing procedurerelated complications and those with histories of failed ablations.
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ACKNOWLEDGMENTS We thank Hsiu-Chen Lu for her help in figure creation. We are also grateful to Pei-Chi Hung and the staffs of our echocardiography and electrophysiology laboratories for their kind support of this study.
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17. Da Costa A, Romeyer-Bouchard C, Dauphinot V, Lipp D, Abdellaoui L, Messier M, Thevenin J, et al. Cavotricuspid isthmus angiography predicts atrial flutter ablation efficacy in 281 patients randomized between 8mmand exertinally irrigated-tip catheter-tip catheter. Eur Heart J 2006;15: 1833-40. 18. Asirvatham SJ. Correlative anatomy and electrophysiology for the interventional electrophysiologist: right atrial flutter. J Cardiovasc Electrophysiol 2009;20:113-22. 19. Da Costa A, Mourot S, Romeyer-Bouchard C, Thevenin J, Samuel B, Kihel A. Anatomic and electrophysiological difference between chronic and paroxysmal forms of common atrial flutter and comparison with controls: an observational study. Pacing Clin Electrophysiol 2004;27: 1202-11. 20. Simon RD, Rinaldi CA, Baszko A, Gill JS. Electroanatomic mapping of the right atrium with a right atrial basket catheter and three-dimensional intracardiac echocardiography. Pacing Clin Electrophysiol 2004;27:318-26. 21. Scaglione M, Caponi D, Donna PD, Riccardi R, Bocchiardo M, Azzaro G, et al. Typical atrial flutter ablation outcome: correlation with isthmus anatomy using intracardiac echo 3D reconstruction. Europace 2004;6:407-17. 22. Komatsu S, Okuyama Y, Omori T, Oka T, Mizuno H, Honda T, et al. Evaluation of the cavotricuspid isthmus and right atrium by multidetector-row computed tomography in patients with common atrial flutter. Heart Vessels 2005;20:264-70. 23. Heidb€ uchel H, Willems R, van Rensburg H, Adams J, Ector H, Van de Werf F. Right atrial angiographic evaluation of the posterior isthmus. Relevance for ablation of typical atrial flutter. Circulation 2000;101:2178-84. 24. Cabrera JA, Sanchez-Qintana D, Ho SY, Medina A, Wanguemert F, Gross E, et al. Angiographic anatomy of the inferior right atrial isthmus
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ERRATUM In the article entitled "Improved Semiautomated Quantification of Left Ventricular Volumes and Ejection Fraction Using 3-Dimensional Echocardiography with a Full Matrix-array Transducer: Comparison with Magnetic Resonance Imaging," (J Am Soc Echocardiogr 2005;18:779-788) the name of one of the authors was listed incorrectly. The correct listing is Juan Luis GutierrezChico, MD.