Left Atrial Anomalous Muscular Band

Case Report, Literature Review, and Role of Three-Dimensional Echocardiography

Abstract

Anomalous fibromuscular bands in the left atrium were already described in the 19^th century. Recently, the greater attention to the anatomy of the left atrium and the technological improvement have made their finding more frequent. Here, we present six cases, out of approximately 30,000 unselected echocardiograms, in which the use of the three-dimensional echo allowed a better definition of their anatomy, course, and motility.

INTRODUCTION

Anomalous muscular bands in the left atrium were already described at the end of the 19^th century.[¹] They are composed of fibrous and muscular tissues[²] and were historically an incidental finding during surgical procedure.[³] Recently, the greater attention to the anatomy of the left atrium required by modern procedures and the technological improvement of echo – machines have made their finding more frequent.[^4,5] Nonetheless, they are quite rare, 22 cases among 1100 autopsies performed by Yamashita et al.[⁶] Here, we present six cases of patients with incidental finding of abnormal atrial band, in which the use of the three-dimensional (3D) echo has allowed a better definition of their anatomy, course, and motility.

CASES REPORTS

Case #1

A 71-year-old man was referred for a transthoracic echocardiography (TTE) after coronary artery bypass grafting. The examination revealed a mobile and filiform mass in the left atrium, in the absence of sign/symptoms suspected for endocarditis. The transesophageal study transesophageal echocardiogram (TEE) confirmed the presence of the mass originating from the atrial edge of the right superior pulmonary vein and projecting its free edge in the left atrium. The length was about 2 cm, and thickness was 3 mm [Figure 1 and Video 1].

Figure 1: Transesophageal multiplane 3D-reconstruction. 3D = Three dimensional

Case #2

A 84-year-old man with an aortic bioprosthesis recently implanted was addressed for suspected prosthetic malfunction. TEE revealed an anomalous thin and mobile band attached to the atrial wall close to the lateral commissure and crossing the mitral valve during the diastole [Figure 2 and Video 2].

Figure 2: Transesopgaheal four chamber view of mitral valve

Case #3

An asymptomatic 18-year-old boy was referred for a better evaluation of a mass of uncertain origin found in the left atrium at a first-line examination performed due to a grade 1 apical systolic heart murmur. In parasternal long-axis view, a thin and bright tendon was seen connecting the anterior superior wall of the left atrium to the free edge of the anterior mitral valve leaflet, near A2 scallop. Moreover, we found an anomalous tendon chord between the mitral valve and the left ventricular basal-inferior wall, in apparent continuity with the atrial tendon. However, the 3D-reconstruction showed that there was no continuity between the two structures, the ventricular one was inserted on the posterior mitral leaflet [Figure 3 and Video 3]. Valve opening was not reduced but mild insufficiency was evident.

Figure 3: Transtoracic 3D-reconstruction of the mitral valve seen “en face” from the left atrium (upper left) and multiplanar reconstruction. The tendon is attached to the thickened edge of the anterior leaflet (arrows). 3D = Three dimensional

Case #4

A young male (36 years), without known heart disease, was admitted to our emergency department for palpitations. A supraventricular tachycardia was diagnosed and an electrophysiological study (EPS) was performed. At preprocedural TEE, we found a filamentous band between the fossa ovalis and the ligament of Marshall, without any hemodynamic consequence. At the EPS, a focal atrial tachycardia and a typical atrial flutter were induced and successfully ablated. At a 9-month follow-up, there was no relapses of tachycardia [Figure 4 and Video 4].

Figure 4: Transthoracic two chamber apical view (left) and transesophageal multiplane 3D-reconstruction (right)

Case #5

A 77-year-old man with bladder cancer was admitted for fever and urinary tract infection. He had a mechanical aortic valve implanted more than 10 year before for severe aortic stenosis. At TTE, the prosthesis showed normal function and no vegetations, but two filamentous masses were present in the left atrium. The TEE allowed to better characterize the anatomy of the two masses: the first, thin and very mobile, originated at the outlet of the left atrial appendage projecting its free edge into the left atrial cavity and the second, thin, was fixed, like a bridge, between the mitroaortic membrane and the mitral annulus [Figure 5 and Video 5].

Figure 5: Transesophageal surgical view of left atrial appendage outlet (left) and mitral valve (right)

Case #6

A 79-year-old woman was referred to our hospital because of dyspnea and urinary tract infection with negative blood culture. TTE showed a suspicious image attached to mitral valve and crossing the valve during the diastole. TEE was performed to exclude endocarditis. 3D TEE revealed an anomalous muscular band attached to the atrial wall close to the lateral commissure [Figure 6 and Video 6].

Figure 6: Transesopgaheal four chamber view (left) and 3D-surgical view (right). 3D = Three dimensional

DISCUSSION

The prevalence of atrial bands is very low. We found our first case in 2012; since then, as our awareness has improved, we have found only five more cases out of approximately 30,000 unselected echocardiograms performed (0.02%). This figure is, however, about 100 times lower than the 2% prevalence in Yamashita’s study;[⁶] it is likely that many cases were not detected by TTE due to small band size, poor operator attention, and poor image quality. The left atrium can be explored well with the transesophageal approach but the number of TEE in our laboratory is much lower than the transthoracic ones (about 12% of all examinations). The percentage found by Yamashita, on the other hand, could suffer from a selection bias.

The significance of these bands is uncertain. Their embryologic origin is not well understood. In our patient #1, the band was clearly attached to the interatrial septum. In our patient #4, the course between the fossa ovalis and the so-called “Coumadin ridge” resembles that of the membrane of the cor triatriatum. In the case of Arya et al.[⁷] the chord insertion near the left lower pulmonary vein is similar to that of a supravalvular mitral ring. In 19 out of 22 cases in the Yamashita series and in the case of Saito et al.,[⁸] the bands originated in the left atrial side of fossa ovalis. These cases suggest the possibility that bands are a remnant of the tissue of the right horn of the venous sinus from which the septum primum develops. In other cases of our series (#2, #3, #5, and #6), there is no clear relationship with the septum but rather with the anteriorsuperior wall of the left atrium.

The association between atrial fibrillation and atrial bands is not clearly identified.[⁹] EPS so far have not shown arrhythmogenic activity of the atrial bands.[¹⁰] Moreover, anomalous atrial band may interfere with the manipulation of the catheter during ablation procedures.[¹¹]

Although most atrial bands are incidental findings in asymptomatic patients, there are reports of patients with cryptogenic stroke,[¹²] moderate-to-severe mitral regurgitation[^5,13,14] and even endocarditis.[¹⁵] In just one case of our series, the band was inserted on the mitral valve, without interfering with the valve opening; however, there was more than trivial insufficiency. The young age of the patient recommends a careful and prolonged follow-up

CONCLUSIONS

The prevalence of anomalous atrial bands is very low; in the vast majority of cases, they have no clinical significance, but it is important to be aware of their existence, as an incorrect interpretation of the images could lead to inappropriate medical or surgical treatment; their presence could interfere with intracavitary procedures. The use of the 3D-echo helps to anatomically localize the insertion and the course of the bands, and above all, to evaluate the interference with the functioning of the mitral valve.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.