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

Speckle Tracking Echocardiography of the Right Atrium: The Neglected Chamber

The right atrium (RA) plays a pivotal role in electromechanical and endocrine regulation of the heart. Its peculiar anatomical features and phasic mechanical function make it distinct from ventricles. Various invasive and noninvasive techniques have been used to elucidate RA structure and function. Of these modalities, echocardiography has distinct advantages over others. Several conventional measures of RA function through echocardiography have been described in the literature, but they are load dependent. A relatively new technique is speckle tracking-derived strain, which is relatively less dependent on loading conditions. Speckle tracking echocardiography tracks acoustic scatters (speckles) of myocardium frame-by-frame to calculate strain or deformation of the myocardium. Speckle tracking echocardiography has been used extensively for strain assessment of the right and left ventricle to detect subtle disease pathology, to gain mechanistic insight, as a marker of ischemic metabolic memory, as an endpoint in clinical trials, and as a functional assessment tool. The RA is a relatively neglected chamber, as it is mostly studied for assessment of atrial mass lesions, for electrophysiological studies, and in animal models for physiological assessment. However, its role in the systolic and diastolic function of the right heart, pulmonary vascular pathology, congenital heart diseases, and combined electromechanical activation phenomena has been less explored or unexplored. Speckle tracking echocardiography is an ideal tool for the assessment of the RA because of its regional and global functional characterization, angle independence, and high temporal resolution.

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.

Anatomic and electrophysiologic differences between chronic and paroxysmal atrial flutter: intracardiac echocardiographic analysis

BACKGROUND

It remains unknown why atrial flutter (AFL) occurs as either a chronic or paroxysmal arrhythmia.

PURPOSE

The aim of the study was to compare intracardiac echocardiographic (ICE) images of the crista terminalis (CT) and transverse conduction properties of the CT between chronic and paroxysmal forms of common AFL.

METHODS

Chronic AFL (n = 7) was defined as non-self-terminating AFL lasting >1 month, and paroxysmal AFL (n = 8) was defined as an intermittent arrhythmia with symptomatic episodes of 24 hours maximum duration. ICE images of the right atrium were recorded with a 9 F 9-MHz intracardiac ultrasound catheter during pullback at 0.5-mm intervals from the superior vena cava to the inferior vena cava triggered by electrocardiogram and respiration. The two-dimensional image of the right atrium was reconstructed into a three-dimensional (3-D) image.

RESULTS

Three-dimensional images from patients with chronic AFL showed the CT to be thick and continuous, and conduction across the CT was blocked at a pacing rate just above sinus rhythm in all seven patients. In contrast, 3D images from paroxysmal AFL showed the CT to be thin and discontinuous, and conduction across the CT during midseptal pacing was observed in five of the eight patients.

CONCLUSION

The nature of AFL is determined, at least in part, by anatomic and electrophysiologic characteristics of the CT.

Tachycardia circuit in typical atrial flutter: the role of a posterolateral line of block in the perpetuation of the tachycardia

BACKGROUND

The essential boundaries in typical atrial flutter (AF) are unknown.

METHODS

To examine the role of the tricuspid annulus (TA) and posterolateral line of block (LB) in maintaining AF, single extrastimuli were delivered during AF both around the LB and the TA in 29 patients. Single extrastimuli were delivered from the superior, middle, and inferior third of the anterior LB, superior, middle, and inferior third of the posterior LB, and the superior, lateral, inferior, and septal portions of the TA. The longest coupling interval (LCI) of single extrastimuli that reset AF and subsequent return cycle (RC) were analyzed.

RESULTS

The resetting response showed two patterns (groups 1 and 2). The differences between the AF cycle length (AFCL) and the LCI (AFCL-LCI) at the superior, lateral, inferior, and septal portions of the TA were the shortest, and were significantly shorter than those at the other sites (P < 0.0001) in group 1. However, the AFCL-LCI at the superior, middle, and inferior third of the anterior LB, and the superior, lateral, inferior, and septal portions of the TA were the shortest, and were significantly shorter than those at the other sites (P < 0.0001) in group 2. The difference between the RC and the AFCL exhibited the same two patterns, similar to the AFCL-LCI. In group 1, a single extrastimulus produced an artificial conduction across the LB, but AF was not reset.

CONCLUSIONS

Two types of reentry circuits exist in AF; one has its essential reentry circuit confined to the TA and thus the LB acts as a bystander, while the LB and the TA are essential boundaries in the other one.

Anatomical characteristics of the cavotricuspid isthmus in patients with and without typical atrial flutter: Analysis with two- and three-dimensional intracardiac echocardiography

INTRODUCTION

The cavotricuspid isthmus (CTI) is crucial in the ablation of typical atrial flutter (AFL), and consequently the CTI anatomy and/or its relation to resistant ablation cases have been widely described in human angiographic studies. Intracardiac echocardiography (ICE) has been shown to be a useful tool for determining detailed anatomical information. Thus, this technology may also allow the visualization of the anatomical characteristics of the CTI, providing an opportunity to further understand the anatomy.

AIM

We conducted a study to compare the anatomy of the CTI between the patients with and without AFL and to characterize the anatomy of the CTI in the patients with AFL resistant to ablation.

MATERIALS AND METHODS

Twelve patients with typical AFL and 20 without AFL were enrolled in the study. Two-dimensional (2D) intracardiac echocardiography (ICE) was performed. The recordings were obtained with a 9F, 9-MHz ICE catheter from the right ventricular outflow tract to the inferior vena cava by pulling the catheter back 0.3 mm at a time under guidance with echocardiographic imaging in a respiration-gated manner. Three-dimensional (3D) reconstruction of the images of the CTI were made with a 3D reconstruction system. After the acquisition of the ICE, the CTI ablation was performed in the patients with AFL.

RESULTS

The 2D and 3D images provided clear visualization of the tricuspid valve, coronary sinus ostium, fossa ovalis and Eustachian valve/ridge (EVR). The CTI was significantly longer in the patients with AFL than in those without AFL (median length 24.6 mm (range 17.0-39.1 mm) versus median length 20.6 mm (range 12.5-28.0 mm), respectively, P < 0.05). However, a deep recess due to a prominent EVR was observed in 9 of 12 (75%) patients with AFL and in 12 of 20 (60%) patients without AFL (N.S.). A deep recess and the relatively long CTI were related to aging in all the study patients, and that relationship was similar in a limited number of patients without AFL. In five patients with AFL resistant to ablation, a deep recess and prominent EVR were observed.

CONCLUSIONS

The 2D and 3D ICE were useful for visualizing the complex anatomy of the CTI and identifying the anatomical characteristics of the CTIs refractory to ablation therapy. The anatomical changes observed in the CTI region may simply be the result of aging and may partially be involved in the development of AFL.

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.

Coronary sinus morphology in different types of supraventricular tachycardias

BACKGROUND

Atrioventricular nodal reentry tachycardia (AVNRT) is based on the concept of dual AV node pathways that are functionally and anatomically distinct. The bigger coronary sinus ostium (CSO) in patients with AVNRT compared to other supraventricular tachycardias (SVTs) may produce separation of atrial inputs into the AV node or create anisotropic conduction, thus giving rise to a different AV nodal physiology. Previous studies measuring the size of the CSO using CS angiography between patients with AVNRT and other SVTs showed conflicting results. Besides, no previous studies have compared the CS morphology of the different forms of AVNRT.

OBJECTIVES

This study compares the size and morphology of the CS among patients with typical AVNRT, atypical AVNRT and accessory pathways mediated reentrant tachycardia (AVRT).

METHODS

Ninety-six patients with clinically documented SVTs were divided into three groups. The diameter of the CS was measured in LAO projection during end ventricular systole (by choosing the last ventricular inward motion). The CSO as well as 5, 10 and 15 mm inside the CS were measured. CS morphology is defined as either wind-sock shape or tubular shape.

RESULTS

The size of the CS ostium was 13.58 +/- 3.98, 15.93 +/- 4.86 and 12.50 +/- 2.83 mm for the atypical AVNRT, typical AVNRT and AVRT, respectively (p = 0.03). There was significant difference in the size of the CS from the ostium until 15 mm into the CS between 1) typical AVNRT and AVRT, 2) typical AVNRT and atypical AVNRT. Typical and atypical AVNRT patients had more windsock morphology CS (13/32, 40.6% and 10/32, 31.2%) compared to AVRT which had only one (1/32, 3.1%) windsock morphology (p = 0.002).

CONCLUSION

The easier CS cannulation in patients with typical AVNRT could be due to a bigger CS size and to a more windsock morphology. The CS size and morphology may be a very important substrate of tachycardia in patients with AVNRT.