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Right Atrial Cavotricuspid Isthmus: Anatomic Characterization with Multi–Detector Row CT¹

¹ From the Departments of Radiological Sciences (F.S., L.P., O.A., K.K., A.R.) and Cardiology (S.K., S.V.G., J.N.), University of California, Irvine, University of California Medical Center, 101 The City Drive, Route 140, Orange, CA 92868-3298. Received May 10, 2007; revision requested July 11; revision received August 16; accepted September 12; final version accepted November 1. Address correspondence to F.S. (e-mail: fsaremi{at}uci.edu).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 
Purpose: To retrospectively evaluate the anatomic characteristics of the right atrial cavotricuspid isthmus (CTI) by using 64-section multi–detector row computed tomography (CT).

Materials and Methods: Institutional review board approval and waiver of informed consent were obtained for this HIPAA-compliant study. The anatomic region of the CTI was evaluated in 201 patients (116 men and 85 women; mean age, 58 years ± 11 [standard deviation]) who underwent coronary multi–detector row CT. CTI length was assessed along three parallel isthmic levels (paraseptal, central, and inferolateral). Central isthmus depth was classified as straight (3 mm), concave (>3 to 5 mm), or pouchlike (>5 mm). Measurements were obtained during three cardiac phases: midsystole, middiastole, and atrial contraction. Subthebesian recess dimensions and eustachian ridge width were measured. Distances from the atrioventricular node artery to the coronary sinus, from the right coronary artery (RCA) to the inferior vena cava, and from the RCA to the tricuspid valve annulus were measured. Software was used for statistical analysis.

Results: At middiastole, the paraseptal isthmus (mean length, 20 mm ± 3.5; range, 11–34 mm) was significantly shorter than the central isthmus (24 mm ± 4.3; range, 12–43 mm) and the central isthmus was shorter than the inferolateral isthmus (27 mm ± 4.8; range, 13–45 mm) (P < .001). The longest CTI measurements were obtained during midsystole, and the shortest were obtained during atrial contraction (40% variation per cardiac cycle). Isthmus contraction occurred primarily in the posterior segment of the central isthmus (RCA to inferior vena cava distance). At middiastole, the central isthmus was straight in 8% of patients, concave in 47% of patients, and pouchlike (>5 mm) in 45% of patients. The mean depth was greater during atrial contraction (6.3 mm ± 2.1) than in midsystole (4.3 mm ± 1.5) and middiastole (5.1 mm ± 1.8) (32% variation during cardiac cycle). A subthebesian recess greater than 5 mm deep was identified in 45% of patients. In 24% of patients, a thick eustachian ridge greater than 4 mm was seen. The atrioventricular node artery passed close to the coronary sinus wall (mean distance, 2.1 mm ± 0.7; range, 1–6 mm).

Conclusion: Cardiac multi–detector row CT provides extensive information regarding the size and morphology of the CTI and its related structures.

Supplemental material: http://radiology.rsnajnls.org/cgi/content/full/247/3/658/DC1

© RSNA, 2008

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 
The area between the inferior vena cava (IVC) and the tricuspid valve (TV) is termed the cavotricuspid isthmus (CTI). This area is the target of catheter-directed ablation procedures, which constitute the treatment of choice for atrial flutter (1–4). Results of autopsies and angiographic and echocardiographic studies have shown that the anatomy of this structure is highly variable (5–12): Patients with a short and straight CTI require fewer radiofrequency ablation applications and shorter x-ray exposure (8). Obstacles such as a large eustachian ridge and/or valve, a deep subthebesian recess, and other pouchlike recesses may also lead to longer and more difficult ablation sessions (5,7,13,14). Preprocedural knowledge about the anatomic details of this region can thus save time and improve the success rate and safety of the procedure by helping the electrophysiologist choose the appropriate region in which to perform the ablation.

Three-dimensional (3D) imaging information can be used for integration with electroanatomic mapping data for real-time guided ablations. Results of right atrial (RA) angiography may provide a general guide to CTI anatomy, but this technique does not provide detailed anatomic definition. Intracardiac echocardiography can help better define the CTI anatomy but is not widely available (10,11). Multi–detector row computed tomography (CT), and especially 64-channel CT scanners, are becoming increasingly more available for cardiac angiography studies (15,16). This technology has been well validated as a useful tool for assessment of pulmonary venous and left atrial anatomy prior to atrial fibrillation ablation procedures (17).

To our knowledge, however, no systematic evaluation of the anatomy of the CTI with multi–detector row CT has been performed. We hypothesized that cardiac multi–detector row CT can provide detailed information about the CTI and can enable evaluation of the variability of CTI anatomy in different cardiac phases. Thus, the purpose of our study was to retrospectively evaluate the anatomic characteristics of the RA CTI by using 64-section multi–detector row CT.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 
Patients
Of 217 consecutive patients who underwent coronary CT angiography from February 2006 to June 2006, 183 were self referred, while the others were referred by a physician because of suspicion of coronary artery disease. Sixteen patients were excluded because of substantial artifacts created by surgical clips (n = 7), prosthetic heart valves (n = 1), pacemaker leads (n = 2), or motion (n = 3) or technical (n = 3) problems. The remaining 201 examinations were included in this study. There were 116 men and 85 women (mean age, 58 years ± 11 [standard deviation]; range, 31–86 years). The study, which was approved by our institutional review board with a waiver of informed consent, was compliant with the Health Insurance Portability and Accountability Act.

Patient Preparation
Oral and intravenous metoprolol were used as needed to achieve a target heart rate of less than 65 beats per minute. A sublingual nitroglycerin tablet (0.4–0.8 mg) was given 1 minute before image acquisition, unless contraindicated. The mean heart rate immediately before data acquisition was 61 beats per minute ± 5 (standard deviation) (range, 43–73 beats per minute).

Scanning Protocol and Image Reconstruction
A 64-section multi–detector row CT scanner (Aquilion; Toshiba, Tustin, Calif) was used. Contrast enhancement was achieved with 75 mL ± 1.4 iohexol (Omnipaque [350 mg iodine per milliliter]; Amersham Health, Cork, Ireland) injected at 4–5 mL/sec through an 18-gauge catheter into an antecubital vein. It was followed by injection of 50 mL of 15%–20% solution of contrast material diluted with saline at a rate of 5 mL/sec to allow washout of highly concentrated contrast material from the right heart. In our experience, a diluted contrast material–saline chase in a concentration of 15%–20% provides enough contrast for the evaluation of right heart anatomy without causing substantial artifacts. Scanning parameters were as follows: number of detector rows, 64; section thickness, 0.5 mm; table feed per rotation, 7.2 mm; gantry rotation time, 400 msec; tube voltage, 120 kVp; and tube current, 400 mA. Start delay was defined by bolus tracking in the descending aorta at the tracheal bifurcation, and scanning was automatically initiated 4 seconds after a threshold of 180 HU was reached. A retrospective electrocardiographically gated volumetric data set was acquired during a single breath hold. The mean scanning time was 9.1 seconds ± 1.4 (range, 8–14 seconds). Depending on the heart rate throughout the examination, axial sections were reconstructed and synchronized to the electrocardiographic data by using a nonsegmented (65 beats per minute) or segmented (>65 beats per minute) image reconstruction algorithm. When necessary, R-wave indicators were manually repositioned to improve the quality of synchronization. Axial sections were obtained with a thickness of 0.5 mm (increment, 0.3 mm) and a cardiac CT angiography algorithm. Diastolic axial images were reconstructed on the basis of a relative delay strategy at 70%, 75%, and 80% of the R-R interval. A second reconstruction approach was performed, and additional data sets were reconstructed at atrial contraction and mid–ventricular systole phases corresponding to 0% and 30% intervals, respectively. The reconstructed data sets were transferred to an off-line 3D workstation (Vital Images, Minnetonka, Minn) for further analysis.

CT Data Analysis and Measurements
Multiplanar reformations of the axial images (short axis, two chamber, and four chamber) were rendered and evaluated in consensus by two authors (F.S. and S.V.G., with 15 and 2 years of experience in CT data interpretation, respectively). Depending on the individual anatomy of interest, different visualization techniques, such as multiplanar reformation, maximum intensity projection, virtual endoscopy, and 3D reconstruction with tissue sculpturing were used. Overall image quality was subjectively evaluated and was classified as excellent, good, or poor primarily on the basis of common image-degrading artifacts related to motion, background noise, metal, and large calcifications.

Previously described nomenclature (5,18–21) was used for the CTI (Table E1, http://radiology.rsnajnls.org/cgi/content/full/247/3/658/DC1). A general evaluation of the CTI on 3D images was performed for shape, contour, and the presence of pouches or recesses. All measurements were performed and recorded on each image by a research student (L.P., with 1 year of experience in cardiac imaging) and were confirmed by another author (F.S.). Each distance was measured twice, and the values were averaged. The length of the CTI was measured along the three parallel levels described by Cabrera et al (5) as the paraseptal (medial) isthmus, the central (inferior) isthmus, and the inferolateral (lateral) isthmus (Fig 1). For consistency, measurements of the isthmus length were made at mid–ventricular systole (30% of the R-R interval), mid–ventricular diastole (70%), and atrial contraction (0%).

View larger version (88K): [in this window] [in a new window] [Download PPT slide]   Figure 1a: (a) Right anterior oblique view of internal structures of RA and (b) right anterior oblique endocardial views (right image is magnified to show detail) of right atrioventricular junction show boundaries of Koch triangle () and RA CTI. The CTI lies between the orifice of the IVC and the attachment of the septal TV (STV, yellow arrows). Three levels (green arrows) of the CTI are shown: the inferolateral isthmus (ILI), the central isthmus (CI), and the paraseptal isthmus (PSI). The central and paraseptal isthmi are common targets for ablation of atrial flutter. The anterior part of the paraseptal isthmus between the coronary sinus (CS) ostium margin and the attachment of the septal TV is called the septal isthmus (SI). In other words, the septal isthmus is part of the RA vestibule (white double-headed arrow) at the level of the paraseptal isthmus. The septal isthmus is often the target for ablation of the slow pathway in atrioventricular node (AVN) reentrant tachycardia. The Koch triangle is bordered posteriorly by a fibrous extension from the eustachian valve and/or ridge (ER) called the tendon of Todaro (TT, white dotted line in b) and anteriorly by the attachment of the septal TV. The paraseptal isthmus forms the base of the Koch triangle, consisting of the ostium of the coronary sinus and the septal isthmus. The apex of the triangle is the anatomic location of the central fibrous body. The AVN resides in the Koch triangle near the apex and continues distally with the penetrating bundle of His. The bundle of His starts being surrounded by the connective tissue of the central fibrous body immediately subjacent to the membranous septum (M). In the magnified view of the CTI (right image in b), the projected anatomic course of the AVN artery (AVNa) in relation to the septal isthmus is shown. The AVN artery arises from the penetrating U-turn of the right coronary artery (RCA) near the start of the posterior descending artery (PDA). AAo = ascending aorta, CT = crista terminalis, EV = eustachian valve, OF = oval fossa, RAA = RA appendage, RV = right ventricle, SVC = superior vena cava, ThV = thebesian valve, TR = tricuspid valve level (bordered by yellow and white arrows in b).

View larger version (119K): [in this window] [in a new window] [Download PPT slide]   Figure 1b: (a) Right anterior oblique view of internal structures of RA and (b) right anterior oblique endocardial views (right image is magnified to show detail) of right atrioventricular junction show boundaries of Koch triangle () and RA CTI. The CTI lies between the orifice of the IVC and the attachment of the septal TV (STV, yellow arrows). Three levels (green arrows) of the CTI are shown: the inferolateral isthmus (ILI), the central isthmus (CI), and the paraseptal isthmus (PSI). The central and paraseptal isthmi are common targets for ablation of atrial flutter. The anterior part of the paraseptal isthmus between the coronary sinus (CS) ostium margin and the attachment of the septal TV is called the septal isthmus (SI). In other words, the septal isthmus is part of the RA vestibule (white double-headed arrow) at the level of the paraseptal isthmus. The septal isthmus is often the target for ablation of the slow pathway in atrioventricular node (AVN) reentrant tachycardia. The Koch triangle is bordered posteriorly by a fibrous extension from the eustachian valve and/or ridge (ER) called the tendon of Todaro (TT, white dotted line in b) and anteriorly by the attachment of the septal TV. The paraseptal isthmus forms the base of the Koch triangle, consisting of the ostium of the coronary sinus and the septal isthmus. The apex of the triangle is the anatomic location of the central fibrous body. The AVN resides in the Koch triangle near the apex and continues distally with the penetrating bundle of His. The bundle of His starts being surrounded by the connective tissue of the central fibrous body immediately subjacent to the membranous septum (M). In the magnified view of the CTI (right image in b), the projected anatomic course of the AVN artery (AVNa) in relation to the septal isthmus is shown. The AVN artery arises from the penetrating U-turn of the right coronary artery (RCA) near the start of the posterior descending artery (PDA). AAo = ascending aorta, CT = crista terminalis, EV = eustachian valve, OF = oval fossa, RAA = RA appendage, RV = right ventricle, SVC = superior vena cava, ThV = thebesian valve, TR = tricuspid valve level (bordered by yellow and white arrows in b).

View larger version (62K): [in this window] [in a new window] [Download PPT slide]   Figure 2: Anatomic evaluation of paraseptal isthmus (PSI) and septal isthmus at multi–detector row CT. By using a short-axis (SAX) view at the level of the AVN artery, a four-chamber (4ch) view is obtained through the center of the coronary sinus ostium at the base of the Koch triangle. Paraseptal isthmus length (green arrow) and septal isthmus length (white arrow) can be measured with this projection. Magnified view of paraseptal isthmus (right) demonstrates anatomic landmarks of this region. Note the enlarged eustachian ridge. Also note the close proximity of the AVN artery to the wall of the coronary sinus as it travels in the inferior pyramidal space. Yellow arrows = septal TV, IVS = interventricular septum, LA = left atrium, LV = left ventricle, MV = mitral valve.

View larger version (111K): [in this window] [in a new window] [Download PPT slide]   Figure 3: A–D, Multi–detector row CT projections for measuring length and depth of the CTI. By using, C, a four-chamber view at the base of the Koch triangle, RV two-chamber views are reformatted parallel to the septum at the level of, A, the inferolateral and, B, the central isthmus. A 3D view of the CTI, D, can be used for better localization. The central isthmus length (green arrows) is the closest distance between the anterior margin of the IVC and the TV annulus (red line in C). Inferolateral isthmus length (blue arrows) is the distance between the lateral margin of the IVC to the TV annulus. The depth of the central isthmus (red arrow in B) can be measured on the RV two-chamber view from the deepest point of the isthmus to the perpendicular line connecting the anterior margin of the IVC and the TV annulus. In this patient, the central isthmus is 16 mm long and 8 mm deep, and inferolateral isthmus length is 27 mm. AA = ascending aorta, LV = left ventricle, RVOT = RV outflow tract, STV = septal TV, SVC = superior vena cava.

Statistical Analysis
Statistical analysis was performed by using software (SAS, version 9.1.3; SAS Institute, Cary, NC). Statistics for all continuous data were reported as means ± standard errors. Comparisons were performed by using Student paired t tests. Observed means of difference scores for the comparison of paraseptal, central, and inferolateral isthmus lengths, as well as the comparison of RCA-to-IVC and RCA-to-TV intervals and central isthmus depth at each of the three cardiac phases (0%, 30%, and 70%), were calculated. We report 95% confidence interval estimates of the difference score means for each of these comparisons. We also report results of the statistical test for each by using P < .05 to indicate statistical significance.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 
General Observations
Overall image quality was classified as excellent in 60%, good in 31%, and poor in 9% of the studies. Anatomic boundaries of the CTI were best visualized on posterior views of 3D images of the heart, where the CTI appeared as a concave quadrilateral structure bordered anteriorly by the tricuspid ring, posteriorly by the IVC, and medially by the coronary sinus ostium. Internal structures such as the eustachian ridge, the septal attachment of the TV, and the coronary sinus ostium were best seen on 3D endoscopic views of the isthmus and were easily verified in four-chamber and short-axis planes. The optimal view for measuring the length of the paraseptal isthmus was the four-chamber plane, but the profile of the isthmus was better viewed on the RV two-chamber plane (Fig 2). The best views for measuring the length of the central and inferolateral isthmi were the RV two-chamber and four-chamber planes (Fig 3). The RV two-chamber plane was the best view for measuring the depth of the CTI and the dimensions of the subthebesian recess. The four-chamber view was excellent for measurement of the eustachian ridge thickness, visualization of the eustachian valve, and assessment of the spatial relation of the AVN artery to the septal wall of the coronary sinus (Fig 2).

Measurements
CTI lengths.—Middiastole images showed a wide variation in the length of the paraseptal isthmus (mean length, 20 mm ± 3.5; range, 11–34 mm), the central isthmus (24 mm ± 4.3; range, 12–43 mm), and the inferolateral isthmus (27 mm ± 4.8; range, 13–45 mm) (Tables 1, 2). The central isthmus length was greater than 30 mm in 16 patients (8%). The mean length of the septal isthmus was 12.5 mm ± 2.5. The paraseptal isthmus was significantly shorter than the central isthmus and the central isthmus was significantly shorter than the inferolateral isthmus at all three cardiac phases (P < .001) (Fig 4).

View larger version (27K): [in this window] [in a new window] [Download PPT slide]   Figure 4: Graph of results of comparison of length of three levels of the CTI at three cardiac phases (atrial contraction [0%], mid–ventricular systole [30%], and middiastole [70%]). The paraseptal isthmus (PSI) was significantly shorter than the central isthmus (CI) and the central isthmus was significantly shorter than the inferolateral isthmus (ILI) (P < .001) at all three cardiac phases.

Depth and morphology of CTI.—At middiastole, the morphology of the central isthmus was straight in 8%, concave in 47%, and deep (pouchlike) in 45% of patients (Fig 6a) (Tables 3, 4). At atrial contraction, the isthmus morphology was straight in 2%, concave in 29%, and deep in 69% of patients. The mean depth was significantly greater at atrial contraction (6.3 mm ± 2.1) than at mid–ventricular systole (4.3 mm ± 1.5) and middiastole (5.1 mm ± 1.8) (P < .001). There was an average variation in depth of 32% during the cardiac cycle (Fig 7). The depth of the central isthmus decreased 19% when moving from atrial systole toward mid–ventricular diastole. The depth was also 19% shallower in mid–ventricular systole than in middiastole (Fig 5). In reviewing the CTI morphology on RV two-chamber views (middiastole), we found a subgroup (28%) with a distinct hook-shaped margin in profile (Fig 6a). In this subgroup, there were essentially two segments: a concave or pouchlike posterior segment near the IVC and an anterior segment that was straight and corresponded to the RA vestibule. The RCA was located near the junction of the two segments. In the majority of patients, we noticed that during atrial contraction, the shortening of the CTI was primarily due to posterior segment contraction (smaller and deeper than in other cardiac phases) while the straight segment remained relatively unchanged (Fig 6a).

View larger version (74K): [in this window] [in a new window] [Download PPT slide]   Figure 6a: (a) Long-axis two-chamber right anterior oblique views of right heart through central isthmus of CTI demonstrate three distinct morphologies: straight, concave or pouchlike, and hook shaped. The profile appearance of the CTI changes in different phases of the cardiac cycle, particularly with atrial contraction, when it gets deeper and shorter. As shown in the hook-shaped variant, the posterior part of the CTI, which is closer to the IVC, has nearly disappeared with atrial contraction. (b) Three-dimensional posterior views of heart. CTI length varies in different individuals (top row) and different cardiac phases (bottom row). Knowledge of these anatomic variants before catheter ablation will save time and increase the success rate. Green arrows = length of central isthmus.

View larger version (111K): [in this window] [in a new window] [Download PPT slide]   Figure 6b: (a) Long-axis two-chamber right anterior oblique views of right heart through central isthmus of CTI demonstrate three distinct morphologies: straight, concave or pouchlike, and hook shaped. The profile appearance of the CTI changes in different phases of the cardiac cycle, particularly with atrial contraction, when it gets deeper and shorter. As shown in the hook-shaped variant, the posterior part of the CTI, which is closer to the IVC, has nearly disappeared with atrial contraction. (b) Three-dimensional posterior views of heart. CTI length varies in different individuals (top row) and different cardiac phases (bottom row). Knowledge of these anatomic variants before catheter ablation will save time and increase the success rate. Green arrows = length of central isthmus.

View larger version (92K): [in this window] [in a new window] [Download PPT slide]   Figure 7: Anatomic variability of central isthmus of the CTI (red arrows) and the subthebesian recess (yellow circles) at different phases of the cardiac cycle. Upper row: Posterior 3D views of CTI. Middle and lower rows: Right anterior oblique (two-chamber) views of right heart at central and paraseptal levels of the CTI, respectively. The shortest length is seen during atrial contraction, and the longest length is seen at midsystole. The subthebesian recess also shows temporal variation in size during the cardiac cycle.

View larger version (23K): [in this window] [in a new window] [Download PPT slide]   Figure 5: Graph of results of comparison of six mean measurements (paraseptal isthmus [PSI] length, central isthmus [CI] length, inferolateral isthmus [ILI] length, the distance from the RCA to the IVC, the distance from the RCA to the TV annulus [TV], and central isthmus depth) at three cardiac phases (atrial contraction [0%], mid–ventricular systole [30%], and middiastole [70%]). There is wide variation in measurements during one cardiac cycle. The shortest lengths and the deepest value for the CTI are evident at atrial contraction. The length of the posterior segment (RCA to IVC) is much greater and shows more variation during the cardiac cycle than is seen in the anterior segment (RCA to TV annulus).

View larger version (78K): [in this window] [in a new window] [Download PPT slide]   Figure 8a: The subthebesian recess is a diverticular extension of the CTI under the coronary sinus (CS). (a) Posterior 3D view (left) and short-axis (SAX) (right) images at level of coronary sinus demonstrate relatively large subthebesian recess inferior to the thebesian valve (white arrow). AA = ascending aorta, LA = left atrium. (b) Endoscopic right anterior oblique view of RA displays internal aspects of the isthmic region and demonstrates the spatial relation of the subthebesian recess (STR) with the coronary sinus (CS) and IVC. Presence of a large subthebesian recess may act as an anatomic barrier to accessing the coronary sinus or may impair local radiofrequency delivery during ablation of isthmus-dependent flutter. ER and green arrows = eustachian ridge, EV and red arrows = eustachian valve, NCS = noncoronary sinus, OF = oval fossa, RAA = RA appendage, STV and white arrows = attachment of septal TV, SVC = superior vena cava, ThV and blue arrow = thebesian valve.

View larger version (150K): [in this window] [in a new window] [Download PPT slide]   Figure 8b: The subthebesian recess is a diverticular extension of the CTI under the coronary sinus (CS). (a) Posterior 3D view (left) and short-axis (SAX) (right) images at level of coronary sinus demonstrate relatively large subthebesian recess inferior to the thebesian valve (white arrow). AA = ascending aorta, LA = left atrium. (b) Endoscopic right anterior oblique view of RA displays internal aspects of the isthmic region and demonstrates the spatial relation of the subthebesian recess (STR) with the coronary sinus (CS) and IVC. Presence of a large subthebesian recess may act as an anatomic barrier to accessing the coronary sinus or may impair local radiofrequency delivery during ablation of isthmus-dependent flutter. ER and green arrows = eustachian ridge, EV and red arrows = eustachian valve, NCS = noncoronary sinus, OF = oval fossa, RAA = RA appendage, STV and white arrows = attachment of septal TV, SVC = superior vena cava, ThV and blue arrow = thebesian valve.

View larger version (76K): [in this window] [in a new window] [Download PPT slide]   Figure 9: Four-chamber images of the heart are the best views for characterizing the eustachian valve and/or ridge (arrows), which varies in size and thickness in different individuals. In 24% of our patients, a thick eustachian ridge (>4 mm) was seen. A distinct eustachian valve arising from the eustachian ridge (a thick eustachian ridge with a valve) was also seen in 18% of patients. Each of these images was obtained in a different patient.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 
Preprocedural knowledge of CTI morphology may help predict selection of the effective radiofrequency ablation catheter and may prevent the need for an expensive crossover to a second ablation catheter. Recently, image integration systems for catheter ablation procedures have been introduced (22–24). Three-dimensional multi–detector row CT data can be used for future integration with fluoroscopic and angiographic images or electroanatomic data.

Previous reports of investigations in human hearts (5–12) have pointed to the anatomic variability of the CTI length (Table E2, http://radiology.rsnajnls.org/cgi/content/full/247/3/658/DC1). It has also been shown that most diameters are larger in patients with chronic atrial flutter (and a larger RA) than in patients with paroxysmal atrial flutter or control groups (6,25). In our study, middiastolic values revealed a wide variation in the length of the isthmus; these findings were close to reported cadaveric measurements of normal isthmi (5,6). In our measurements, the paraseptal isthmus was significantly shorter than the central isthmus and the central isthmus was significantly shorter than the inferolateral isthmus at all three cardiac phases. A linear relationship between isthmus length and number of radiofrequency applications has been reported (7,8). It has also been demonstrated that patients with a short (35 mm) and straight (<2 mm deep) CTI require three times fewer radiofrequency ablation applications and shorter duration of x-ray exposure than patients with other CTI morphologies (including deep, pouchlike recesses) (8). Whereas in most of the reported studies, in vivo measurements of the CTI were performed in a single cardiac phase, we extended our measurements to other phases of the cardiac cycle to evaluate the anatomic variability of this important structure with every heartbeat. The CTI was found to be longest at all three parallel levels during mid–ventricular systole. At this phase, the central isthmus length was greater than 30 mm in 32% of patients. Our measurements showed a total variation in length of 40% during one cardiac cycle.

The presence of a large subthebesian recess or deep pouches is associated with significantly more radiofrequency applications than is the presence of a straight isthmus (11,12). The subthebesian recess is an extension of a pouchlike isthmus under the orifice of the coronary sinus. Local radiofrequency delivery may be impaired by this structure as an area of limited blood flow results in delayed catheter tip cooling. In one angiographic study of the CTI, this pouch was observed in 47% of patients and had a mean depth of 4.3 mm ± 2.1 (range, 1.5–9.4 mm) (7). In our series, a deep subthebesian recess combined with a pouchlike (>5 mm) central isthmus was seen in 45% of middiastolic phase images. This finding would be useful in preprocedural planning, where the presence of a large pouch would dictate a central approach to the ablation. In around 28% of patients, we found a hook-shaped morphology, with a concave or pouchlike segment posteriorly (at the IVC side) and a flat vestibular part anteriorly. This morphology has been previously described (6,7,12). The pouches vary in size during the cardiac cycle, becoming deeper with atrial contraction. Variation of length and depth during the cardiac cycle is marked and may be a contributory factor in difficult ablation procedures.

Information related to the size of the eustachian ridge and the presence of an enlarged eustachian valve is important and can be demonstrated with multi–detector row CT. A large eustachian ridge is an anatomic barrier and forms a line of fixed conduction block during typical atrial flutter (13,14,26). It has been demonstrated that in patients with large eustachian ridges, paraseptal isthmus block can be achieved only after complete ablation of the enlarged eustachian ridge (11). Cabrera et al (5) demonstrated that 26% of their heart specimens had a thickened eustachian ridge; the mean thickness was 3.2 mm ± 0.8. Results of an angiographic study by Heidbuchel et al (7) showed an enlarged eustachian valve in 24% of patients, with a consequent increase in the number of ablation pulse applications necessary for achievement of successful block. In our study, a thick eustachian ridge greater than 4 mm was seen in 24% of patients. A distinct eustachian valve arising from the eustachian ridge was seen in 18% of our patients. This result correlates well with the angiographic data reported by Heidbuchel et al.

Although uncommon, injury to coronary arteries has been described as a complication of ablation of the CTI (27–30). Multi–detector row CT clearly shows the relationship of the RCA or AVN artery to the RA wall in most good-quality studies. Endocardial proximity of the AVN artery to the RA wall at the septal isthmus can potentially predispose this vessel to injury. Given the shared anatomy of the septal isthmus, for ablation of the slow pathway in AVN reentrant tachycardia and treatment of atrial flutter, anatomic knowledge regarding the course of the AVN artery may be helpful in avoiding vascular injury during these procedures. Anatomic study of human hearts has revealed that the RCA is located less than 4 mm from the endocardial surface of the CTI in 47% of hearts and that the AVN artery passes close to the septal isthmus wall at a mean depth of 3.5 mm ± 1.5 (5,29). The results of our study showed mean distances to the RA wall of 3.2 mm ± 1.6 for the RCA and 2.1 mm ± 0.7 for the AVN artery.

Our study had limitations. Cardiac CT is currently not used to evaluate patients prior to catheter ablation of atrial flutter. In the absence of data, it is difficult to justify offering this imaging test to patients with atrial flutter before an ablation procedure. However, on the basis of the quality of the images provided by this technique, the extent of endocardial and 3D information obtained, and the capacity of multi–detector row CT to obtain these data in a matter of few seconds, CT angiography can be considered for selected patients in whom bidirectional isthmus block cannot be easily achieved. Our study was performed among a group of patients with no structural heart disease and no history of cardiac arrhythmia. Special considerations are involved in obtaining high-quality images in patients with tachycardia and irregular rhythm. Increased temporal resolution with 256-section or dual-source scanners can overcome this problem. We found good correlation between our middiastolic length measurements and reported data in cadaveric human hearts. Obviously, our length measurements will be different from those reported in patients with chronic atrial flutter.

In conclusion, cardiac multi–detector row CT provides information in different phases of the cardiac cycle regarding the size, depth, and anatomic variants of the CTI. Our study demonstrates that cardiac multi–detector row CT provides extensive anatomic information about regions of the heart that are the targets of ablation procedures for atrial flutter.

	ADVANCES IN KNOWLEDGE

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 

• Cardiac multi–detector row CT provides information in different phases of the cardiac cycle regarding the size, depth, and anatomic variants of the cavotricuspid isthmus (CTI).
  
• Our results indicate that the length and depth of the isthmus vary significantly (P < .001) during the cardiac cycle.
  

	IMPLICATION FOR PATIENT CARE

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 

• Detailed anatomic information about the CTI may have potential for use in ablation of atrial flutter.
  

	FOOTNOTES

 

Abbreviations: AVN = atrioventricular node • CTI = cavotricuspid isthmus • IVC = inferior vena cava • RA = right atrium • RCA = right coronary artery • RV = right ventricle • 3D = three-dimensional • TV = tricuspid valve

Author contributions:

Guarantor of integrity of entire study, F.S.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, F.S., L.P., A.R.; clinical studies, F.S., S.V.G.; statistical analysis, F.S., L.P., O.A., K.K., A.R.; and manuscript editing, F.S., S.K., O.A., J.N.

Authors stated no financial relationship to disclose.

	References

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION ADVANCES IN KNOWLEDGE IMPLICATION FOR PATIENT CARE References

 

1. Poty H, Saoudi N, Nair M, Anselme F, Letac B. Radiofrequency catheter ablation of atrial flutter: further insights into the various types of isthmus block—application to ablation during sinus rhythm. Circulation 1996;94(12):3204–3213.[Abstract/Free Full Text]
2. Cauchemez B, Haïssaguerre M, Fischer B, Thomas O, Clementy J, Coumel P. Electrophysiological effects of catheter ablation of inferior vena cava-tricuspid annulus isthmus in common atrial flutter. Circulation 1996;93(2):284–294.[Abstract/Free Full Text]
3. Morady F. Radio-frequency ablation as treatment for cardiac arrhythmias. N Engl J Med 1999;340(7):534–544.[Free Full Text]
4. Wellens HJ. Catheter ablation for cardiac arrhythmias. N Engl J Med 2004;351(12):1172–1174.[Free Full Text]
5. Cabrera JA, Sanchez-Quintana D, Ho SY, et al. Angiographic anatomy of the inferior right atrial isthmus in patients with and without history of common atrial flutter. Circulation 1999;99(23):3017–3023.[Abstract/Free Full Text]
6. Cabrera JA, Sanchez-Quintana D, Farre J, Rubio JM, Ho SY. The inferior right atrial isthmus: further architectural insights for current and coming ablation technologies. J Cardiovasc Electrophysiol 2005;16(4):402–408.[Medline]
7. Heidbuchel 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(18):2178–2184.[Abstract/Free Full Text]
8. Da Costa A, Faure E, Thevenin J, et al. Effect of isthmus anatomy and ablation catheter on radiofrequency catheter ablation of the cavotricuspid isthmus. Circulation 2004;110(9):1030–1035.[Abstract/Free Full Text]
9. Chang SL, Tai CT, Lin YJ, et al. The electroanatomic characteristics of the cavotricuspid isthmus: implications for the catheter ablation of atrial flutter. J Cardiovasc Electrophysiol 2007;18(1):18–22.[CrossRef][Medline]
10. 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(6):591–597.[CrossRef][Medline]
11. Scaglione M, Caponi D, Di Donna P, et al. Typical atrial flutter ablation outcome: correlation with isthmus anatomy using intracardiac echo 3D reconstruction. Europace 2004;6(5):407–417.[Abstract/Free Full Text]
12. Da Costa A, Romeyer-Bouchard C, Dauphinot V, et al. Cavotricuspid isthmus angiography predicts atrial flutter ablation efficacy in 281 patients randomized between 8 mm- and externally irrigated-tip catheter. Eur Heart J 2006;27(15):1833–1840.[Abstract/Free Full Text]
13. Nakagawa H, Lazzara R, Khastgir T, et al. Role of the tricuspid annulus and the eustachian valve/ridge on atrial flutter: relevance to catheter ablation of the septal isthmus and a new technique for rapid identification of ablation success. Circulation 1996;94(3):407–424.[Abstract/Free Full Text]
14. Huang JL, Tai CT, Liu TY, et al. High-resolution mapping around the eustachian ridge during typical atrial flutter. J Cardiovasc Electrophysiol 2006;17(11):1187–1192.[CrossRef][Medline]
15. Mollet NR, Cademartiri F, van Mieghem CA, et al. High-resolution spiral computed tomography coronary angiography in patients referred for diagnostic conventional coronary angiography. Circulation 2005;112(15):2318–2323.[Abstract/Free Full Text]
16. Raff GL, Gallagher MJ, O'Neill WW, Goldstein JA. Diagnostic accuracy of noninvasive coronary angiography using 64-slice spiral computed tomography. J Am Coll Cardiol 2005;46(3):552–557.[Abstract/Free Full Text]
17. Jongbloed MR, Dirksen MS, Bax JJ, et al. Atrial fibrillation: multi-detector row CT of pulmonary vein anatomy prior to radiofrequency catheter ablation—initial experience. Radiology 2005;234(3):702–709.[Abstract/Free Full Text]
18. Ho SY, Anderson RH, Sanchez-Quintana D. Atrial structure and fibres: morphologic bases of atrial conduction. Cardiovasc Res 2002;54(2):325–336.[Abstract/Free Full Text]
19. Anderson RH, Brown NA. The anatomy of the heart revisited. Anat Rec 1996;246(1):1–7.[CrossRef][Medline]
20. Ho SY, Anderson RH. How constant anatomically is the tendon of Todaro as a marker for the triangle of Koch? J Cardiovasc Electrophysiol 2000;11(1):83–89.[CrossRef][Medline]
21. Anderson RH, Ho SY, Becker AE. Anatomy of the human atrioventricular junctions revisited. Anat Rec 2000;260(1):81–91.[CrossRef][Medline]
22. Tops LF, Bax JJ, Zeppenfeld K, et al. Fusion of multislice computed tomography imaging with three-dimensional electroanatomic mapping to guide radiofrequency catheter ablation procedures. Heart Rhythm 2005;2(10):1076–1081.[CrossRef][Medline]
23. Dong J, Calkins H, Solomon SB, et al. Integrated electroanatomic mapping with three-dimensional computed tomographic images for real-time guided ablations. Circulation 2006;113(2):186–194.[Abstract/Free Full Text]
24. Ector J, De Buck S, Adams J, et al. Cardiac three-dimensional magnetic resonance imaging and fluoroscopy merging: a new approach for electroanatomic mapping to assist catheter ablation. Circulation 2005;112(24):3769–3776.[Abstract/Free Full Text]
25. Da Costa A, Mourot S, Romeyer-Bouchard C, et al. Anatomic and electrophysiological differences between chronic and paroxysmal forms of common atrial flutter and comparison with controls. Pacing Clin Electrophysiol 2004;27(9):1202–1211.[CrossRef][Medline]
26. Olgin JE, Kalman JM, Fitzpatrick AP, Lesh MD. Role of right atrial endocardial structures as barriers to conduction during human type I atrial flutter: activation and entrainment mapping guided by intracardiac echocardiography. Circulation 1995;92(7):1839–1848.[Abstract/Free Full Text]
27. Ouali S, Anselme F, Savoure A, Cribier A. Acute coronary occlusion during radiofrequency catheter ablation of typical atrial flutter. J Cardiovasc Electrophysiol 2002;13(10):1047–1049.[CrossRef][Medline]
28. Raio N, Cohen TJ, Daggubati R, Marzo K. Acute right coronary artery occlusion following radiofrequency catheter ablation of atrial flutter. J Invasive Cardiol 2005;17(2):92–93.[Medline]
29. Sanchez-Quintana D, Ho SY, Cabrera JA, Farre J, Anderson RH. Topographic anatomy of the inferior pyramidal space: relevance to radiofrequency catheter ablation. J Cardiovasc Electrophysiol 2001;12(2):210–217.[CrossRef][Medline]
30. Lin JL, Huang SK, Lai LP, et al. Distal end of the atrioventricular nodal artery predicts the risk of atrioventricular block during slow pathway catheter ablation of atrioventricular nodal re-entrant tachycardia. Heart 2000;83(5):543–550.[Abstract/Free Full Text]

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