Multislice cardiac computed tomography in the evaluation of adults with atrial septal defects
JAVIER COURTIS, MANUEL VACA
Instituto Oulton, Córdoba, Argentina.
(5000) Córdoba, Argentina E-mail
Recibido 29-ENE-18 – ACEPTADO despues de revisión el 01-MARZO-2018.
There are no conflicts of interest to disclose.
The complex anatomy of the heart may make differentiation of type, size, and extent of an atrial septal defect (ASD) difficult. Modern techniques of multislice cardiac computed tomography triggered by ECG are ideal for the detailed analysis of the interatrial septum and its associated pathologies. This review of clinical cases offers a detailed description, from the visual point of view, of the different types of ASD.
Atrial septal defects (ASD) constitute 5% to 10% of all congenital heart diseases, and up to 30% of cases that appear in the adult age, with ostium secundum (OS) being the most common type (70% to 80%) of ASD in adults. Other less frequent forms of ASD include: ostium primum (OP) (15%); sinus venosus (SVASD) (10%) and coronary sinus ASD (CS) (<1%) .
Although echocardiography constitutes an imaging modality of first choice in the diagnostic evaluation of these patients, often complex anatomy may make a proper diagnosis and an accurate assessment of ASD difficult. For this reason, cardiac multislice computed tomography (MSCT) has turned into an excellent option in cases where ultrasound cannot yield the diagnosis in detail and help in therapeutic planning for the different types of ASD.
The goal of this presentation is providing a practical resource, based on MSCT imaging, to evaluate adult patients with ASD, including the rarer variants.
CLINICAL CASES Patient # 1. 44-year-old woman with hypothyroidism, who consulted due to palpitations and atypical precordial pain. In the clinical examination, systolic murmur was detected in a pulmonary focus, and inferior ischemia was detected by myocardial SPECT; but because of the low probability of severe obstructive CAD, and as in echocardiogram it was not possible to obtain appropriate images due to poor acoustic window, MSCT was conducted (Toshiba AquilionTM64). osASD was visualized, as well as dilatation of both right chambers and the pulmonary artery (Figure 1). The patient was surgically intervened, closing the septal defect with autologous pericardial patch, showing optimal evolution and complete reversion of symptoms.
Figure 1. Ostium secundum ASD. (A) Aortic transvalular axial cut. (B) Four chambers.
(C) Biatrial short axis. (D) Right ventricular (RV) dilatation.
Patient #2. 45-year-old woman, consulting because of FC II stress dyspnea. Echocardiogram was conducted, showing pulmonary hypertension with right chamber dilatation and cardiac magnetic resonance with increased Qp/Qs and possible interatrial septal defect of the superior venous type. For all these reasons, MSCT was conducted, which showed ASD of the type superior sinus venosus and right superior pulmonary vein draining into the superior vena cava (Figure 2). The patient refused the surgical treatment to the date of this publication, adding episodes of palpitations and progression of dyspnea.
Figure 2. Superior sinus venosus ASD and partial anomalous venous drainage.
(A) Four chambers. (B and C) Sagittal cut. (D) RV dilatation.
Patient # 3. 59-year-old, hypertensive and dyslipidemic man, who consulted due to dyspnea and chest angina of recent onset. Graded ergometer test was clinically negative and electrocardiographically uncertain, and due to persistence of symptoms and the ambiguous functional test, MSCT was made. The images showed obstructive and severe atheromatous lesions in the proximal thirds of the Anterior Descending and Right Coronary arteries. Also, a persistent left superior vena cava and a small ASD of the coronary sinus type were observed, besides fistulous tracts communicating the left atrium to the coronary sinus (Figure 3). Subsequently, combined cardiac catheterization was made, where the coronary lesions found in MSCT, saccular aneurysmal dilatation of the coronary sinus, mild pulmonary hypertension, and slightly elevated Qp/Qs were corroborated. The patient was treated surgically (complete myocardial revascularization surgery and ASD clipping), presenting a favorable immediate post-surgical period, and excellent evolution in the long term, with full resolution of symptoms.
Figure 3. Coronary sinus ASD and left atrial – coronary sinus fistula.
(A) Four chambers.
(B) Basal short axis. (C) Five chambers. (D) Axial cut. (E and F) 3D.
(G and H) Coronary arteries MIP reconstruction.
Atrial septal defect (ASD) is the term applied to the patent communication between both atria . Congenital heart disease (CHD) is almost a third of the main congenital anomalies in the world, and it is estimated that the prevalence in adult patients with CHD is 3000 per million inhabitants (3/1000) [3-5].
During fetal development, the interatrial septum (IAS) originates as a consequence of the growth of the two septa that appear sequentially, which normally end up fusing to shape a single septum. In the fetus, the OS is located in the center of the septum, thus allowing the oxygenated blood from the placenta to be drained directly from the right atrium into the systemic circuit with the aim of avoiding the lungs. In the normal embryological development, the second septum, the septum secundum (SS) covers the ostium secundum of the septum primum (SP) and ends up fusing with the latter after birth. osASD occurs when the SS fails to cover the OS. In turn, in the OPASD, the SP does not reach its destiny generating a persistent communication between the atria, with a variable amount of septum intact and attached to the basal wall. This anomaly is commonly associated to a proximal anomaly of the ventricular septum; a combination known as “atrioventricular canal defect”. On the other hand, ASD of the SV type is eccentric in the IAS, whether in its superior or inferior regions, and at the level of the entry sites of the superior or inferior venae cavae (superior sinus venosus [SSV] or inferior sinus venosus [ISV]). SSV ASD is much more common than ISV, and the eccentric superior position of the defect allows a communication between the left atrium (LA) and the superior vena cava; besides the partial anomalous pulmonary venous return is usually associated to this type of ASD. Finally, in CS ASD, also known as “roofless”, there is partial or complete absence of the superior wall that separates the coronary sinus (CS) of the left atrial floor, which leads to blood flow derivation through the defect. A frequently associated anomaly in these cases is persistent left superior vena cava, which drains and therefore dilates the CS [5-6].
All these defects in the interatrial septum produce the pathophysiological result of volume overload, which leads to a dilatation of all the right circuit structures (atrium, ventricle, pulmonary artery); and if the defect becomes chronic, myocardial fibrosis with subsequent ventricular dysfunction. Although most patients with ASD present a left-to-right short-circuit, the reverse derivation may also occur. In fact, the direction and strength of the blood flow through the septal defect are determined by the size of the defect and the atrial pressures; the latter in turn depend on ventricular compliance; if this decreases in the RV (by sustained and very high pulmonary hypertension), there will be a reduction of the derivation from left to right, until the development of an inverted short-circuit. The pulmonary vascular bed is also remodeled because of the proliferation of myointimal cells and an increase in collagen; both effects leading to arteriolar narrowing and pulmonary hypertension .
In the last decade, MSCT has been widely accepted in noninvasive evaluation of significant CAD in a selected patient. But this is not the only contribution by MSCT; also, structural heart disease is being evaluated by it, given the great virtues of the method for a detailed description of cardiac anatomy. Although echocardiography is still the gold standard of diagnostic methodologies, MSCT provides an accurate morphology of ASD, besides supplementing the information to detect other associated cardiac or extracardiac anomalies and therapeutic planning. MSCT is particularly useful in SVASD and CS ASD, given the difficulty for echocardiography to obtain an optimal evaluation of these cardiac regions. Finally, an MSCT report should include the following elements: total length of the interatrial septum, maximum diameter of ASD and the shortest length of the edges of the defect.
The knowledge on normal anatomy, its variants and ASD constitute a true challenge for cardiologists because of their clinical, interventionist and surgical implications in these cases. MSCT, by providing a thorough analysis of ASD, will probably play an increasingly significant role in the evaluation of these patients.
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