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

The Effects of Valvular Heart Disease on Atrial Conduction During Sinus Rhythm

Different arrhythmogenic substrates for atrial fibrillation (AF) may underlie aortic valve (AV) and mitral valve (MV) disease. We located conduction disorders during sinus rhythm by high-resolution epicardial mapping in patients undergoing AV (n = 85) or MV (n = 54) surgery. Extent and distribution of conduction delay (CD) and block (CD) across the entire right and left atrial surface was determined from circa 1880 unipolar electrogram recordings per patient. CD and CB were most pronounced at the superior intercaval area (2.5% of surface, maximal degree 6.6%/cm²). MV patients had a higher maximal degree of CD at the lateral left atrium than AV patients (4.2 vs 2.3%/cm², p = 0.001). A history of AF was most strongly correlated to CD/CB at Bachmann’s bundle and age. Although MV patients have more conduction disorders at the lateral left atrium, disturbed conduction at Bachmann’s bundle during sinus rhythm indicates the presence of atrial remodeling which is related to AF episodes.

Crista Terminalis as the Anterior Pathway of Typical Atrial Flutter: Insights from Entrainment Map with 3D Intracardiac Ultrasound

BACKGROUND

The precise location of truly active reentry circuits of typical atrial flutter (AFL) has not been well identified. The purpose of this study was to verify our hypothesis that the posterior block line is located along the posteromedial right atrium (PMRA) and the crista terminalis (CT) is the anterior pathway of AFL, with real-time intracardiac echo (ICE).

METHODS

The entire right atrium (RA) three-dimensional activation and entrainment mapping were evaluated during AFL in 18 patients using CARTO sound.

RESULTS

The CT was clearly visualized by ICE and the local electrograms along the CT were single potentials in all the patients. The CT was recognized as the truly active anterior pathway based on entrainment mapping in all patients. Double potentials were recorded along the PMRA. Entire RA entrainment mapping could be performed in 16 patients. The reentry circuits were separated into three passages. The first was around the tricuspid annulus (TA), the second the anterior superior vena cava (SVC; AFL waves passed between the anterior SVC and RA appendage), and the last the posterior SVC (between the posterior SVC and upper limit of the PMRA). All three of these passages were active in four, around the TA and anterior SVC in eight, around the TA and posterior SVC in three, and around only the anterior SVC in one patient.

CONCLUSIONS

The CT functions as the anterior pathway of typical AFL, and the posterior block line was located along the PMRA. Dual or triple circuits were recognized in the majority of AFL patients.

A three-dimensional human atrial model with fiber orientation. Electrograms and arrhythmic activation patterns relationship

The most common sustained cardiac arrhythmias in humans are atrial tachyarrhythmias, mainly atrial fibrillation. Areas of complex fractionated atrial electrograms and high dominant frequency have been proposed as critical regions for maintaining atrial fibrillation; however, there is a paucity of data on the relationship between the characteristics of electrograms and the propagation pattern underlying them. In this study, a realistic 3D computer model of the human atria has been developed to investigate this relationship. The model includes a realistic geometry with fiber orientation, anisotropic conductivity and electrophysiological heterogeneity. We simulated different tachyarrhythmic episodes applying both transient and continuous ectopic activity. Electrograms and their dominant frequency and organization index values were calculated over the entire atrial surface. Our simulations show electrograms with simple potentials, with little or no cycle length variations, narrow frequency peaks and high organization index values during stable and regular activity as the observed in atrial flutter, atrial tachycardia (except in areas of conduction block) and in areas closer to ectopic activity during focal atrial fibrillation. By contrast, cycle length variations and polymorphic electrograms with single, double and fragmented potentials were observed in areas of irregular and unstable activity during atrial fibrillation episodes. Our results also show: (1) electrograms with potentials without negative deflection related to spiral or curved wavefronts that pass over the recording point and move away, (2) potentials with a much greater proportion of positive deflection than negative in areas of wave collisions, (3) double potentials related with wave fragmentations or blocking lines and (4) fragmented electrograms associated with pivot points. Our model is the first human atrial model with realistic fiber orientation used to investigate the relationship between different atrial arrhythmic propagation patterns and the electrograms observed at more than 43000 points on the atrial surface.

Crista terminalis, musculi pectinati, and taenia sagittalis: anatomical observations and applied significance

Background. The complex architecture of the right atrium, crista terminalis (CT), and the musculi pectinati (MP) poses enormous challenges in electrophysiology and cardiac conduction. Few studies have been undertaken to substantiate the gross features of MP, in relation to the CT, but there is still scarcity of data regarding this. We tried to reinvestigate the gross arrangement of muscle bundles in the right atrium. Methods. Utilizing 151 human hearts and orientation of MP and its variations and relationship to the CT were investigated along with taenia sagittalis (TS). Patterns of MP were grouped in 6 categories and TS under three groups. Result. A plethora of variations were observed. Analysis of all the specimen revealed that 68 samples (45%) were of type 1 category and 27 (18%) fell into type 2 category. Prominent muscular columns were reported in 12 samples (8%). 83 samples (55%) presented with a single trunk of TS. Multiple trunks of TS were reported in 38 samples (25%). Conclusion. Samples with type 6 MP and type B/type C TS, which have a more complex arrangement of fibers, have a tendency to be damaged during cardiac catheterization. Nonetheless, the area as a whole is extremely significant considering the pragmatic application during various cardiac interventions.

Electrophysiologic characteristics of the Crista terminalis and implications on atrial tachycardia in rabbits

The objective of this study was to evaluate the electrophysiologic characteristics of Crista terminalis (CT) and their implication in the pathogenesis of atrial tachycardia in rabbits. For this purpose, 27 New Zealand rabbits were used. Using standard glass microelectrode technique, cellular action potentials (APs) of CT and pectinate muscle (PM) were recorded in normal Tyrode's perfusion and Tyrode's perfusion with 4 μM isoproterenol. Longitudinal conduction velocity (V(L)) and transverse conduction velocity (V(T)) of CT were measured. As our data show, CT tissue had a trend of spontaneous phase IV depolarization. Conduction anisotropy (V(L)/V(T)) of CT was 4.53 ± 0.91. The duration of the AP of CT was longer than that of PM cells. APD(20) and APD(90) for CT were 28.1 ± 3.5 and 145.3 ± 7.1 ms; and for PM cells were 21.8 ± 4.1 and 125.3 ± 6.3 ms, respectively (all P values < 0.01). The early and delayed action depolarizations were recorded after isoproterenol perfusion. A fast paroxysmal irregular rhythm was recorded which could be arrested by 0.1 mmol/l Isoptin. It was, therefore, concluded that the latent autorhythmicity, trigger activity, and conduction properties of CT might provide the electrophysiologic basis for the occurrence and sustenance of atrial arrhythmia.

A computer study of the effects of branching dimension on safety factor distribution and propagation in a cardiac conduction network

Branching conduction networks are responsible for coordinated distribution of activation throughout the heart, but the effects of branching geometry on the efficiency of distribution and the safety of propagation remain unclear. We have developed a simplified computer model to investigate this issue in a systemic fashion. A simplified 2D model that reproduces key features of the right atrial pectinate muscle network has been developed. This consists of a large main strand that gives rise to regularly spaced perpendicular branches. Safety factor (SF) and activation time (AT) within the network are estimated for a range of different branch dimensions. The SF is reduced as branch dimension is increased due to the larger current load and is least at the proximal edge of the junction between the main strand and branches. On the other hand, activation efficiency depends on appropriate balance between the load imposed by branching and source which they subsequently provide. With repeated stimulation at progressively decreasing coupling intervals, the SF and conduction fall within the network, but the locations of block varied with branching dimension, again reflecting spatial variation in the balance between current source and current load. We hypothesize that the observed geometry of the branching network optimizes distribution efficiency and propagation safety.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

A tissue-specific model of reentry in the right atrial appendage

INTRODUCTION

Atrial fibrillation is prevalent in the elderly and contributes to mortality in congestive heart failure. Development of computer models of atrial electrical activation that incorporate realistic structures provides a means of investigating the mechanisms that initiate and maintain reentrant atrial arrhythmia. As a step toward this, we have developed a model of the right atrial appendage (RAA) including detailed geometry of the pectinate muscles (PM) and crista terminalis (CT) with high spatial resolution, as well as complete fiber architecture.

METHODS AND RESULTS

Detailed structural images of a pig RAA were acquired using a semiautomated extended-volume imaging system. The generally accepted anisotropic ratio of 10:1 was adopted in the computer model. To deal with the regional action potential duration heterogeneity in the RAA, a Courtemanche cell model and a Luo-Rudy cell model were used for the CT and PM, respectively. Activation through the CT and PM network was adequately reproduced with acceptable accuracy using reduced-order computer models. Using a train of reducing cycle length stimuli applied to a CT/PM junction, we observed functional block both parallel with and perpendicular to the axis of the CT.

CONCLUSION

With stimulation from the CT at the junction of a PM, we conclude: (a) that conduction block within the CT is due to a reduced safety factor; and (b) that unidirectional block and reentry within the CT is due to its high anisotropy. Regional differences in effective refractive period do not explain the observed conduction block.

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

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Comparative effects of single- and linear triple-site rapid bipolar pacing on atrial activation in canine models

Nonuniform conduction may cause block and/or delay, thereby providing a substrate for the onset and maintenance of reentrant atrial arrhythmias. We tested the hypothesis that linear triple-site, bipolar, rapid pacing (LTSBRP) of the right atrium generates more uniform wave-front propagation compared with single-site, bipolar, rapid pacing (SSBRP), thereby reducing and/or eliminating conduction block and delay that is otherwise present. Five dogs with pericarditis and three normal dogs were studied. Three plunge-wire electrode pairs were placed 5–7 mm apart in both perpendicular and parallel configurations at the superior aspect of the crista terminalis and were used to pace at 200- and 300-ms cycle lengths for ≤6 s. During pacing, 380 electrograms were recorded simultaneously from electrode arrays placed epicardially on the atria, which produced activation sequence maps for each pacing episode. Local conduction-velocity vectors were computed for each site during each episode. Histograms of absolute velocity vector angles from the x-axis (of the crista terminalis) were plotted to assess uniformity of wave-front propagation, and the magnitude of each vector was computed to assess the local speed. LTSBRP showed 1) more uniform linear activation wave fronts compared with SSBRP, 2) velocity vectors with a more uniform magnitude and direction compared with SSBRP, 3) a predominant absolute velocity vector angle vs. a scattered angle distribution with SSBRP, and 4) shorter right atrial activation time and faster mean epicardial speed than SSBRP for each pacing cycle length. LTSBRP created a more uniform wave-front propagation with less or no conduction block and/or delay compared with SSBRP.

Vector Mapping in Localizing the Transverse Conduction Site of the Crista Terminalis in Patients with Typical Atrial Flutter

BACKGROUND

The difference in the conduction properties of the crista terminalis (CT) along its course, has not been fully clarified. Using the vector mapping method, we localized the transverse conduction (TC) site of the CT and elucidated its conduction capabilities in patients with typical atrial flutter (AF).

METHODS

The TC site of the CT was localized by the analysis of the polarity reversal of the double potentials recorded at 10 sites along the CT using a 20-pole deflectable catheter in 17 patients. The conduction capabilities of the TC site were analyzed during incremental pacing delivered from 100 beats/min to 2-to-1 local capture at the low anterior (LARA) and posterior (LPRA) right atrium.

RESULTS

At a pacing rate of 100 beats/min, TC at a single site was observed in 15 patients during LARA pacing and 7 patients during LPRA pacing, respectively. TC sites were distributed from superior to middle third of the CT in all patients. TC was bidirectional in 4 sites, but was unidirectional in the remaining 14 sites. Following an increase in the pacing rate, TC was blocked in all 7 sites during LPRA pacing and 11 of 15 sites during LARA pacing. Shift in the location of the TC site was not observed in any of the patients before TC block. The conduction block rate during pacing from LARA was significantly higher than that from LPRA (211 +/- 59 beats/min vs 145 +/- 66 beats/min, P < 0.01).

CONCLUSIONS

The superior to middle third of the CT provides TC capabilities. The TC across the CT was caused by a preferential conduction site and most of these TC were unidirectional, and stable in location irrespective of the change in the conduction rate.

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

Rate-dependent block in the sinus venosa.

INTRODUCTION

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Relationship Between Anatomic Location of the Crista Terminalis and Double Potentials Recorded During Atrial Flutter:

INTRODUCTION

The activation sequence in typical atrial flutter (AFL) around the tricuspid annulus is well described. However, activation of the remainder of the right atrium (RA) is not well defined. Previous studies have shown a linear block at the crista terminalis (CT) during AFL. The aim of this study was to evaluate the relationship between the location of the CT and the line of block by intracardiac echocardiography (ICE).

METHODS AND RESULTS

Twenty-one patients with typical AFL were included in the study. The ICE imaging catheter (9-French with 9-MHz ultrasound transducer) was advanced to the RA. Under ICE guidance, a 20-pole roving catheter was used to map double potentials (DPs) during AFL, and three-dimensional images of the RA were reconstructed. During counterclockwise (CCW), clockwise (CW) AFL, or both, a line of conduction block manifested by DPs was identified at a septal site adjacent to the CT in 12 patients and in the posteroseptal RA in 9 patients.

CONCLUSION

The functional line of block in CCW and CW AFL is localized not at the CT but at the septal edge of the CT or in the posteroseptal RA.

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

OBJECTIVES

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Impaired Longitudinal Conduction in Crista Terminalis is Necessary for Sustenance of Experimental Atrial Flutter

Sustained atrial flutter (AFL) can be induced by creating a lesion between the vena cava in dogs. In previous studies on this model, the crista terminalis (CT) was often injured, and thus, role of CT in sustained reentry was not well understood. We hypothesized that impaired longitudinal conduction in CT is necessary for sustained AFL. In 16 anesthetized, open-chest dogs, linear radiofrequency ablation of the intercaval region was performed without interrupting CT. Intra-atrial conduction times (IAT) along CT were measured using a plaque electrode (25x35 mm) containing 30 bipolar electrodes before and after additional ablation of CT (group A, n=10) or the pectinate muscle (PM) region (group B, n=6). In group A, IAT along CT was 27 +/- 5 ms at baseline and was increased to 43 +/- 3 ms after ablation of CT (P<0.001). In group B, IAT along CT was 28 +/- 4 ms at baseline and 27 +/- 3 ms after ablation of PM (P=NS). Sustained AFL lasting >20 minutes was induced in 10/10 dogs in group A only after additional ablation of CT, and in 0/6 dogs in group B (P<0.001). The cycle lengths of AFL after ablation of the intercaval region and additional ablation of CT were 119 +/- 14 and 140 +/- 14 ms, respectively (P<0.01). There was a significant positive correlation between the cycle length of AFL and IAT along CT (r2=0.63, P<0.001). These results indicate that longitudinal conduction property in CT and not in PM strongly affects sustenance of AFL in this model.

Effects of acute atrial dilation on heterogeneity in conduction in the isolated rabbit heart

INTRODUCTION

Atrial dilation plays an important role in the development and persistence of atrial fibrillation (AF). The mechanisms by which atrial dilation increases the vulnerability to AF are not fully understood.

METHODS AND RESULTS

In 11 isolated rabbit hearts, the right atrium was acutely dilated by increasing the intra-atrial pressure from 2 to 9 and 14 cm H2O. A rectangular mapping array of 240 electrodes (spatial resolution 0.5 mm) was positioned on the free wall of the right atrium. The atrium was paced from four different sites at intervals of 240 and 125 msec. At normal atrial pressure (2 cm H2O), conduction was uniform in all directions with an anisotropy ratio between 1.5 and 1.7. Increasing the pressure to 9 cm H2O decreased the normalized conduction velocity during rapid pacing by 18%. The incidence of areas of slow conduction and conduction block increased from 6.6% and 1.6% to 10.2% and 3.3%. At 14 cm H2O, conduction velocity decreased by 31% and the percentage of slow conduction and block further increased to 11.5% and 6.6% (P < 0.001). The appearance of lines of intra-atrial block was largely dependent on the pacing site. Whereas during pacing at the cranial part of the crista terminalis no increase in conduction delays occurred, pacing from the low right atrium unmasked several lines of block oriented parallel to the major trabeculae and the crista terminalis. In an additional series of six hearts the left atrium also was mapped. The effect of dilation of the left atrium was comparable to that of the right atrium. Increasing the atrial pressure to 14 cm H2O increased the amount of intra-atrial conduction block threefold to fourfold.

CONCLUSION

Acute atrial dilation results in slowing of conduction and an increase of the amount of intra-atrial conduction block. The increase in spatial heterogeneity in conduction was related to the anisotropic properties of the atrial wall.

Relation between transverse conduction capability and the anatomy of the crista terminalis in patients with atrial flutter and atrial fibrillation: analysis by intracardiac echocardiography

Although crista terminalis (CT) has been identified as the barrier to transverse conduction during typical atrial flutter (AFL), the relation between transverse conduction capabilities and anatomy of the CT remains unclear. The aim of the study was to evaluate that relation using intracardiac echocardiography (ICE). Ten patients with typical AFL (group AFL), 7 patients with paroxysmal atrial fibrillation (PAF) (group AF) and 8 patients without PAF or AFL (group N) underwent electrophysiologic testing. Using ICE images, the maximum diameter of the short axis of the CT (dCT) was measured and mapping and pacing catheters were positioned precisely. From extrastimulation delivered 1-2 cm anteriorly (free wall) or posteriorly (posterior wall) to the CT, the effective refractory period (CT-ERP) was determined as the longest coupling interval that resulted in split potentials at the mapping catheter positioned along the CT, a finding consistent with a transverse conduction block at the CT. The dCT was greater in group AFL than in groups AF and N (5.0+/-0.8 vs 4.3 +/-0.7, p<0.05 and 4.2+/-0.4 mm, p<0.01, respectively). The CT-ERP was longer during pacing from the posterior wall than from the free wall (307+/-68 vs 266+/-29 ms, p<0.05) as a whole group. The CT-ERP for the posterior wall pacing was longer in group AFL than in group N (339+/-80 vs 255+/-13, p<0.05). CT-ERP did not correlate with dCT; however, dCT was greater in patients with split potentials at the CT than in patients without them (4.9 +/-0.8 vs 4.1+/-0.5 mm, p<0.05). Therefore, the transverse conduction block of CT was more likely to occur in a thick CT. A limited transverse conduction capability of the CT is related to its thickness and might contribute to the development of typical AFL.

The terminal crest: morphological features relevant to electrophysiology

OBJECTIVE

To investigate the detailed anatomy of the terminal crest (crista terminalis) and its junctional regions with the pectinate muscles and intercaval area to provide the yardstick for structural normality.

DESIGN

97 human necropsy hearts were studied from patients who were not known to have medical histories of atrial arrhythmias. The dimensions of the terminal crest were measured in width and thickness from epicardium to endocardium, at the four points known to be chosen as sites of ablation.

RESULTS

The pectinate muscles originating from the crest and extending along the wall of the appendage towards the vestibule of the tricuspid valve had a non-uniform trabecular pattern in 80% of hearts. Fine structure of the terminal crest studied using light and scanning electron microscopy consisted of much thicker and more numerous fibrous sheaths of endomysium with increasing age of the patient. 36 specimens of 45 (80%) specimens studied by electron microscopy had a predominantly uniform longitudinal arrangement of myocardial fibres within the terminal crest. In contrast, in all specimens, the junctional areas of the terminal crest with the pectinate muscles and with the intercaval area had crossing and non-uniform architecture of myofibres.

CONCLUSIONS

The normal anatomy of the muscle fibres and connective tissue in the junctional area of the terminal crest/pectinate muscles and terminal crest/intercaval bundle favours non-uniform anisotropic properties.