Asian Cardiovasc Thorac Ann 2001;9:225
© 2001 Asia Publishing EXchange Pte Ltd
Invited Commentary
Paolo Angelini, MD
|
Department of Cardiology Texas Heart Institute 6624 Fannin, Suite 2780 Houston, Texas, USA
|
|
|
 |
Invited Commentary
|
|---|
Cases such as that described above by Dhaliwal and colleagues, of an unusual malformation featuring primary dilatation of the left atrium or some of its segments, appear periodically in the medical literature. At this time, it may be useful to try to organize our knowledge of the subject matter, while recognizing that it is still fairly incomplete and the issue is not yet covered in any cardiology textbook.
Especially when referring to congenital heart defects, it is important to mention the basics of the related normal embryologic development.1 The postnatal left atrium must be understood as the combination of three embryonic components: the left atrial body, as strictly defined; the atrial septum, the product of partial fusion of the septum primum and the septum secundum; and the sinus of the pulmonary veins that are partially reabsorbed into the posterior wall of the body of the left atrium. The embryologic left atrium does not require the presence of an atrial septum or normal drainage of the pulmonary veins; it is formed by atrial myocardium that features musculi pectinati only at the level of the characteristic finger-like appendage, whereas the rest has a smooth inner surface.
Two main types of left atriomegaly can be distinguished. Diffuse dilatation of the left atrium may be either primary (unaccompanied by causative hemodynamic lesions in the presence of myocardial wall degenerative changes) or secondary (as a consequence of any cardiac condition that elevates left atrial pressure). In all such cases, the whole of the left atrium shows diffuse enlargement, with variable degrees of myocardial degeneration and/or hypertrophy. Segmental left atrial dilatation is a specific entity characterized by discrete dilatation of a localized segment. This is more consistent with the definition of an aneurysm (as a sac formed by the localized dilatation of the wall of an artery, a vein, or the heart). Such conditions are generally (probably always) congenital in origin. At least three distinct locations of segmental left atrial dilatation have been reported: the left atrial appendage (with a normal-sized body of the left atrium), which may or may not be accompanied by a defect of the left-sided pericardium; the posteroinferior wall, featuring a large communication with the body of the left atrium and located caudally to the pulmonary veins behind the left ventricle; and the atrial septum, located at the level of the fossa ovalis and formed by the redundant septum primum.
The case reported here by Dhaliwal and colleagues was of selective congenital left atrial appendage aneurysm (LAAA). This condition has been described with a consistent clinical presentation, although it is likely that many asymptomatic patients may go undiagnosed throughout a normal life. LAAA is quite rare and most reported cases have occurred in the absence of an associated cardiac defect, but a substantial proportion have a defect of the adjacent pericardium. In a 1996 review of 48 patients, typical symptoms were arrhythmias at a young age (with atrial fibrillation in the older age group) and episodes of systemic embolism.2 Some patients reported chest pain and/or shortness of breath in adulthood. The radiologic sign of LAAA is a fairly typical enlarge-ment of the cardiac silhouette at the left mid-border, in the absence of signs of enlargement of the body of the left atrium. Findings on transthoracic (or better, trans-esophageal) echocardiography, computed tomography, and magnetic resonance imaging, and observations at surgery or autopsy are limited to a selective but frequently quite large (14 to 18 cm) left atrial appendage dilatation. The relatively small communication with the body of the left atrium is surrounded by a muscular ridge.3 Most consistently, the aneurysm is superimposed on the antero-lateral wall of the left ventricle, over which it leaves a sizable depression, with apparent secondary deformity of the left ventricular cavity and the mitral valve. The most interesting and unsolved puzzles related to LAAA concern its nature and the pathophysiological reasons why a low pressure (or so presumed) left atrial appendage can gradually grow within the pericardial cavity juxtaposed to the high pressure and dense mass of the left ventricle. Unfortunately, no report is yet available of LAAA cavity phasic pressures. It is quite likely that the mechanism of preservation and progression of LAAA relates to a valve-like behavior of its neck. We can hypothesize that if systolic obliteration of the LAAA neck is caused by contraction of the muscular ridge or by bending during ventricular contraction, the left ventricle may transmit its pressure to the LAAA vesicle that is constrained by the pericardial space.3 The presence of LAAA in the scenario of a pericardial defect may suggest an enactment of the mechanism of strangulated hernia, but this condition has also not yet been studied hemodynamically.
The surgical indication is obvious in most cases in which atrial fibrillation, LAAA clot, or systemic embolism have occurred, but not in their absence. A left thora-cotomy approach and off-pump removal of the LAAA is usually the preferred surgical technique, and should be accompanied by a quick and uncomplicated recovery.
|
References
|
|---|
-
Angelini P. Embryology and congenital heart disease. Tex Heart Inst J 1995;22:1–12.[Medline]
-
Gold JP, Afifi HY, Ko W, Horner N, Hahn R. Congenital giant aneurysms of the left atrial appendage: diagnosis and management. J Card Surg 1996;11:147–50.[Medline]
-
Victor S, Nayak VM. Aneurysm of the left atrial appendage. Tex Heart Inst J 2001;28:111–8.[Medline]
TOP
Invited Commentary
References
