The authors have declared that no competing interests exist.
The aim of this study was to provide useful information about the cavotricuspid isthmus (CTI) and surrounding areas morphology, which may help to plan CTI radio-frequency ablation. We examined 140 autopsied human hearts from Caucasian individuals of both sexes (29.3% females) with a mean age of 49.1±17.2 years. We macroscopically investigated the lower part of the right atrium, the CTI, the inferior vena cava ostium and the terminal crest. The paraseptal isthmus (18.5±4.0 mm) was significantly shorter than the central isthmus (p<0.0001), and the central isthmus (24.0±4.2 mm) was significantly shorter than the inferolateral isthmus (29.3±4.9 mm) (p<0.0001). Heart weight was positively correlated with all isthmus diameters. Three different sectors of CTI were distinguished: anterior, middle and posterior. The middle sector of the CTI presented a different morphology: trabeculae (N = 87; 62.1%), intertrabecular recesses (N = 35; 25.0%) and trabecular bridges (N = 18; 12.9%). A single sub-Eustachian recess was present in 48.6% of hearts (N = 68), and a double recess was present in 2.9% of hearts (N = 4) with mean depth = 5.6±1.8mm and diameter = 7.1±3.4mm. The morphology of the distal terminal crest was varied; 10 patterns of the distal terminal crest ramifications were noted. There were no statistically significant differences in any of the investigated CTI parameters between groups with different types of terminal crest ramifications. The presence of intertrabecular recesses (25.0%), trabecular bridges (12.9%) and sub-Eustachian recesses (48.6%) within the CTI can make ablation more difficult. We have presented the macroscopic patterns of final ramifications of the terminal crest within the quadrilateral CTI area.
The cavotricuspid isthmus (CTI) is a part of the right atrium located between the inferior vena cava (IVC) ostium and the tricuspid valve. The CTI is a relatively new concept that was first introduced by Cosio et al. (1993); this region of the heart plays an essential role in the atrial flutter circuit [
Knowledge of the detailed anatomy of this region can significantly improve the safety and success rate of ablation procedures. The morphology and muscular architecture of the CTI in the human heart, regardless of its relevance to clinical practice, is not yet fully understood. There have been only a few anatomical studies on this topic, and only three of them comprehensively investigated the majority of CTI dimensions [
This study was conducted in the Department of Anatomy, Jagiellonian University Medical College (Cracow, Poland) and was approved by the Bioethical Committee of Jagiellonian University Medical College (KBET/51/B/2013). In our study we personally collected hearts only from deceased person who did not express objection, when alive, and if family did not express objection. In accordance with Polish Law our Bioethical Committee waived the need for written or verbal informed consent. These samples were not procured from a tissue bank or donation center.
We studied 140 autopsied human hearts from Caucasian individuals of both sexes (29.3% females) with a mean age of 49.1±17.2 years and an average body mass index (BMI) of 27.7±6.1 kg/m2 and a mean body surface area of 1.9±0.2 m². We collected the hearts during routine forensic medical autopsies performed in the Department of Forensic Medicine, Jagiellonian University Medical College from July 2013 until November 2015. The primary causes of death were: suicide, murders, traffic accidents and home accidents. The exclusion criteria included severe anatomical defects, heart surgeries or heart grafts, evident severe macroscopic pathologies of the heart or vascular system found during autopsy (aneurysms, storage diseases), heart trauma and macroscopic signs of cadaver decomposition. None of the 140 individuals had a history of any type of arrhythmia.
The hearts were dissected together with the proximal portions of the great vessels: the ascending aorta, pulmonary trunk, superior vena cava, IVC, and all of the pulmonary veins. We weighed the hearts before fixation using an electronic laboratory scale with a precision of 0.5 g (BSA-L Laboratory). After dissection, all of the hearts were fixed by immersion in 10% paraformaldehyde solution for a maximum of two months until the time of measurement [
The right atrium was opened in a routine way using an intercaval incision extending from the orifice of the superior vena cava to the orifice of the IVC without sectioning the orifices. If necessary, additional cuts were made to present the investigated area in a better way. We obtained linear measurements using YATO electronic calipers (YT–7201) precise to 0.03 mm. All of the measurements were made by two independent researchers in order to reduce bias. If the measurement differences between the researchers exceeded 10%, both measurements were repeated. The mean of the two measurements was calculated and approximated to a tenth of a decimal place.
The lower part of the right atrium, CTI, IVC ostium and terminal crest (TC) were investigated. The CTI is the quadrilateral-shaped area bounded medially by the paraseptal isthmus, laterally by the inferolateral isthmus, anteriorly by the septal tricuspid leaflet attachment and posteriorly by the Eustachian valve and ridge. The following measurements were made (
paraseptal isthmus (or septal isthmus/Koch’s triangle base)–width of the closed-line segment tangential to the left contour of the coronary sinus bounded by the point where it touches the tricuspid annulus anteriorly and by the left end of the Eustachian ridge posteriorly;
central isthmus (or inferior isthmus)–width of the closed-line segment bounded by the point where it touches the septal leaflet anteriorly and by the midpoint of the Eustachian ridge posteriorly, parallel to the paraseptal isthmus;
inferolateral isthmus–width of the closed line segment bounded by the right end of the septal leaflet anteriorly and by the right end of the Eustachian ridge posteriorly, parallel to the paraseptal and central isthmus;
the diameter of the IVC ostium;
the height of the Eustachian valve, measured as the length between the free edge of the valve and its attachment site to the right atrium;
the length of the Eustachian ridge between the paraseptal and inferolateral isthmus;
the total length of the septal tricuspid leaflet attachment;
the shortest length between the paraseptal and inferolateral isthmus (CTI length);
the thickness of the Eustachian ridge;
the depth and diameters of the sub-Eustachian recesses;
the diameter of the coronary sinus ostium;
the diameter of the right atrioventricular ring.
AV–atrioventricular; CS–coronary sinus ostium; FO–fossa ovalis; IVC–inferior vena cava.
We distinguished three morphological sectors within the CTI (between the central and inferolateral isthmus): anterior, middle and posterior. The antero-posterior dimensions of the parts noted above at the level of the central isthmus were measured, and their morphology were evaluated. We also calculated the CTI area. The presence of the sub-Eustachian recess (also known as the sub-Thebesian recess or the sinus of Keith) was assessed.
We used transillumination to macroscopically evaluate patterns of the final ramifications of the distal TC muscle fibers into the lower part of the right atrium.
The data are presented as mean values with the corresponding standard deviations or percentages. We performed statistical analyses with STATISTICA v12 (StatSoft Inc., Tulsa, OK, USA). A p value of less than 0.05 was considered to be statistically significant. The Shapiro-Wilk test was used to determine if the quantitative data were normally distributed. To verify homogeneity of variance, we performed Levene’s test. We also used the Student’s
The mean heart weight was 441.0 ± 119.1 g.
Scatter plots of age and (A) paraseptal isthmus; (B) central isthmus; (C) inferolateral isthmus; (D) cavotricuspid isthmus (CTI) length; (E) Eustachian ridge/valve length; (F) CTI area.
Scatter plots of body mass index (BMI) and (A) paraseptal isthmus; (B) central isthmus; (C) inferolateral isthmus; (D) cavotricuspid isthmus (CTI) length; (E) Eustachian ridge/valve length; (F) CTI area.
Scatter plots of heart weight and (A) paraseptal isthmus; (B) central isthmus; (C) inferolateral isthmus; (D) cavotricuspid isthmus (CTI) length; (E) Eustachian ridge/valve length; (F) CTI area.
N | Mean | SD | Min | Max | Median | Q1 | Q3 | |
---|---|---|---|---|---|---|---|---|
140 | 49.1 | 17.2 | 17.0 | 94.0 | 50.0 | 37.0 | 60.0 | |
140 | 27.7 | 6.1 | 17.7 | 50.6 | 26.2 | 23.7 | 29.9 | |
140 | 441.0 | 119.1 | 150.0 | 750.0 | 440.0 | 372.3 | 524.8 | |
140 | 18.5 | 4.0 | 9.8 | 29.4 | 18.0 | 15.9 | 21.0 | |
140 | 24.0 | 4.2 | 14.4 | 35.1 | 23.8 | 21.3 | 26.5 | |
140 | 29.3 | 4.9 | 18.0 | 51.8 | 29.3 | 26.2 | 31.4 | |
140 | 21.5 | 4.9 | 10.9 | 39.0 | 21.5 | 18.7 | 23.7 | |
140 | 25.0 | 5.6 | 9.1 | 40.1 | 24.7 | 21.4 | 28.8 | |
99 | 5.0 | 2.3 | 1.0 | 11.4 | 4.9 | 3.1 | 6.6 | |
140 | 25.5 | 4.1 | 15.7 | 37.3 | 25.1 | 22.7 | 27.5 | |
67 | 3.6 | 1.9 | 1.2 | 8.5 | 2.9 | 2.1 | 4.5 | |
140 | 39.2 | 7.2 | 24.8 | 61.2 | 34.9 | 39.1 | 42.3 | |
72 | 7.1 | 3.4 | 3.1 | 17.9 | 8.1 | 5.9 | 10.6 | |
72 | 5.6 | 1.8 | 2.1 | 10.8 | 5.5 | 4.6 | 6.9 | |
140 | 28.9 | 4.7 | 17.1 | 42.7 | 28.5 | 25.8 | 31.6 | |
140 | 9.4 | 2.7 | 4.0 | 18.3 | 9.0 | 7.5 | 11.0 | |
140 | 10.1 | 2.7 | 3.3 | 21.5 | 10.1 | 8.6 | 11.6 | |
140 | 9.2 | 3.0 | 3.3 | 19.1 | 8.9 | 7.2 | 11.3 | |
140 | 8.8 | 3.5 | 1.9 | 17.3 | 8.2 | 6.2 | 10.4 | |
140 | 517.3 | 181.5 | 187.6 | 1295.2 | 504.3 | 398.8 | 594.8 |
BMI–body mass index, CTI–cavotricuspid isthmus, N–number of samples, SD–standard deviation, Q1 and Q3—lower and upper quartiles
Total | Males | Females | p | |||||
---|---|---|---|---|---|---|---|---|
N | N | Mean | SD | N | Mean | SD | ||
140 | 99 | 48.2 | 15.7 | 41 | 51.6 | 20.9 | 0.347 | |
140 | 99 | 27.1 | 4.1 | 41 | 28.2 | 7.4 | 0.891 |
|
140 | 99 | 475.9 | 99.3 | 41 | 397.6 | 108.3 | 0.000 |
|
140 | 99 | 18.6 | 4.1 | 41 | 18.3 | 3.7 | 0.695 | |
140 | 99 | 24.1 | 4.3 | 41 | 23.0 | 3.5 | 0.179 | |
140 | 99 | 29.3 | 4.9 | 41 | 28.7 | 4.6 | 0.760 |
|
140 | 99 | 21.3 | 4.2 | 41 | 21.6 | 6.5 | 0.702 |
|
140 | 99 | 25.1 | 5.7 | 41 | 24.4 | 5.6 | 0.730 | |
99 | 69 | 5.2 | 2.3 | 30 | 5.0 | 2.4 | 0.650 | |
140 | 99 | 25.5 | 4.3 | 41 | 25.8 | 3.8 | 0.346 |
|
67 | 42 | 3.7 | 2.1 | 23 | 3.4 | 1.4 | 0.934 |
|
140 | 99 | 39.4 | 6.8 | 41 | 38.2 | 6.2 | 0.685 | |
72 | 51 | 8.9 | 3.7 | 21 | 7.9 | 2.4 | 0.334 | |
72 | 51 | 5.7 | 1.9 | 21 | 5.3 | 1.6 | 0.496 | |
140 | 99 | 28.7 | 4.7 | 41 | 29.5 | 4.5 | 0.458 | |
140 | 99 | 9.5 | 2.8 | 41 | 9.0 | 2.5 | 0.414 | |
140 | 99 | 10.2 | 2.7 | 41 | 9.8 | 2.6 | 0.591 |
|
140 | 99 | 9.2 | 3.2 | 41 | 9.5 | 4.9 | 0.453 |
|
140 | 99 | 9.1 | 4.2 | 41 | 9.3 | 3.4 | 0.604 |
|
140 | 99 | 515.3 | 165.9 | 41 | 522.4 | 220.5 | 0.910 |
*—non-parametric
BMI–body mass index, CTI–cavotricuspid isthmus, N–number of samples, SD–standard deviation, Q1 and Q3—lower and upper quartiles
We distinguished three different sectors of CTI between the central and inferolateral isthmus: anterior (smooth), middle (trabeculated) and posterior (membranous) (
The anatomical position of samples has not been maintained during the taking photos to get a better picture of cavotricuspid isthmus sectors. (A) trabeculae (N = 87; 62.1%); (B) intertrabecular recesses (N = 35; 25.0%); (C) trabecular bridges (N = 18; 12.9%); *–electrocardiological catheter.
The Eustachian valve was present in 70.7% of hearts (N = 99). Its height was positively correlated with the width of the inferolateral isthmus (r = 0.21; p = 0.05). When the Eustachian valve was present, the central and inferolateral isthmus were significantly longer compared with specimens without the valve (p = 0.0.3 and p = 0.006, respectively). Moreover, the inferolateral and paraseptal isthmus width were positively correlated with the valve’s height (r = 0.27; p = 0.02 and r = 0.4; p = 0.001, respectively).
The single sub-Eustachian recess was present in 48.6% of hearts (N = 68), and the double recess was present in 2.9% of hearts (N = 4) (
CS–coronary sinus ostium; ER–Eustachian ridge.
We found that the morphology of the distal TC presented considerable variability. Based on transillumination of the lower-right atrium walls, we were able to macroscopically classify the distal TC ramifications into the lower part of the right atrium. The division was made on the basis of the main muscle band course (
Smaller bands branching from the major crest were not presented with the exception of types B and C in which the main muscle band is absent. CSO–coronary sinus ostium; CTI–cavotricuspid isthmus; EuchV–Eustachian valve; FO–fossa ovalis; IVC–inferior vena cava; SL–septal leaflet; SVC–superior vena cava.
Type | N | % | Description |
---|---|---|---|
36 | 25.7% | Thick muscular bundle from the distal crest to the vestibule of the tricuspid valve | |
22 | 15.7% | Many thinner bundles radiated from the distal crest beyond the CTI (to the right) | |
20 | 14.3% | Bundles of the distal crest radiated in fan-like fashion, obliquely in the CTI area | |
10 | 7.1% | Two thick muscular bundles from distal crest to the vestibule of the tricuspid valve and to the Eustachian ridge | |
9 | 6.4% | Thick bundle extended obliquely through CTI to the coronary sinus ostium, below the Eustachian ridge/valve | |
8 | 5.7% | Two thick muscular bundles from distal crest to the vestibule of the tricuspid valve going through and beyond the CTI | |
7 | 5.0% | Two thick muscular bundles from distal crest to the vestibule of the tricuspid valve and to the coronary sinus ostium | |
5 | 3.6% | Thick muscular bundle extending to the tricuspid valve beyond the CTI | |
3 | 2.1% | Thick muscular bundle from the distal crest to the Eustachian ridge | |
20 | 14.3% | The combination of the above mentioned patterns |
CTI–cavotricuspid isthmus, N- number of samples
There have only been three anatomical studies that have comprehensively investigated the majority of CTI dimensions [
Present study | Cabrera et al. (1998) [ |
Cabrera et al. (2005) [ |
Saremi et al. (2008) [ |
|
---|---|---|---|---|
140 | 28 | 30 | 201 | |
cadavers | cadavers | cadavers | MDR-CT |
|
18.5±4.0 | 26.4±4.0 | 24.0±4.0 | 20.0±3.5 | |
24.0±4.2 | - | 19.0±4.0 | 24.0±4.3 | |
29.3±4.9 | 31.0±4.0 | 30.0±3.0 | 27.0±4.8 | |
25.5±4.1 | 31.0±5.0 | - | - | |
N = 67 (47.9%) | N = 7 (25%) | N = 8 (26.7%) | N = 49 (24%) | |
3.6±1.9 | - | 3.2±0.8 | 2.8±1.8 | |
single—N = 68 (48.6%); double—N = 4 (2.9%) | - | N = 25 (80%) | N = 114 (56.7%) | |
7.1±3.4 | - | 14.0±3.0 | 7.3 ±2.3 | |
5.6±1.8 | - | 2.9±1.2 | 7.7±2.6 | |
9.4±2.7 | 9.5±2.0 | - | 9.1±2.0 | |
10.1±2.7 | 12.0±2.0 | - | - | |
9.2±3.0 | 8.0±4.0 | - | - | |
8.8±3.5 | 10.0±4.0 | - | - |
*middiastole (70% of Cardiac Cycle)
CTI–cavotricuspid isthmus; MDR-CT–multi-detector row computed tomography, N–number of samples
Although not the shortest, the inferolateral and central isthmuses are considered to be better places for ablation [
The TC plays an important role in typical atrial flutter. It provides a barrier to conduction transversely across it. The transverse conduction block of the TC occurs more likely in thick bundles. On the other hand, fast conduction velocities can be observed in the longitudinal direction of the TC (anisotropy) [
The size of the Eustachian valve and ridge may also affect negatively CTI ablation [
Sub-Eustachian recesses are common findings with a prevalence reaching 80% [
The majority of anatomical obstacles are unfortunately detected only at the time of CTI ablation, which significantly prolongs the procedure time and reduces the success rate. Meanwhile, even a vague assessment of CTI area contributes significant safety and benefits to pre-procedural ablation by identifying unfavorable anatomy. The CTI can be imaging using computed tomography, magnetic resonance imaging, right atrium angiography, and transesophageal, transthoracic or intracardiac echocardiography [
The primary limitation of our study is that all of the measurements were made on autopsied, structurally normal heart specimens that had been fixed in formaldehyde. This fixing might have resulted in some slight changes in the size and shape of the hearts. However, the use of 10% paraformaldehyde did not cause significant changes in the dimensions of the atrial tissue; the dimensions of fixed hearts are similar to those that are unfixed [
The publication of this manuscript was supported by the Faculty of Medicine, Jagiellonian University Medical College KNOW (Leading National Research Centre 2012–2017) funds. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.