Atrial septal defect overview


 * Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S. [mailto:psingh@perfuse.org]; Assistant Editor(s)-In-Chief: Kristin Feeney, B.S. [mailto:kfeeney@perfuse.org]

Overview
Atrial septal defects (ASD) refer to a group of congenital heart diseases that involve the inter-atrial septum. The inter-atrial septum is the tissue that separates the right and left atria from each other. This tissue prevents arterial and venous blood from mixing with each other. If there is a defect in this septum, a direct communication between the atria can occur, which allows shunting, resulting in mixing of arterial and venous blood. It is possible for blood to travel from the left side of the heart to the right side of the heart, or vice versa. Shunting can result in cyanosis. 

Epidemiology and demographics
Atrial septal defect are common heart defects and comprises approximately 7% of all the congenital heart disorders. . ASD is associated with a slight female preponderance of 2:1.

Natural History, Complications and Prognosis
The natural history of atrial septal defect depends on the location, the size of the defect, the amount of shunting of blood and the presence of associated congenital anomalies. A small atrial septal defect may remain asymptomatic throughout the life and/or may close spontaneously in infants. Patients with isolated atrial septal defects generally survive to adulthood. It can also present in adulthood with the insidious development of symptoms. Complications like pulmonary hypertension, atrial fibrillation, right heart failure and stroke can occur if large sized defects are left uncorrected. The mortality rate for surgical intervention repair is less than 1% for atrial septal defect patients under the age of 45, with no history of heart failure or pulmonary artery hypertension.

Causes
Like other congenital heart defects, the cause of an ASD is not known. Ostium secundum is the commonest type of atrial septal defect. Often the defect occurs sporadically. However, ASD has been found to occur with increased incidence in some genetic disorders such as the Holt-Oram syndrome (heart-hand syndrome), Down syndrome, Noonan syndrome,Treacher Collins syndrome, and the thrombocytopenia-absent radii (TAR) syndrome.

History and Symptoms
Atrial septal defect patients may present with symptoms that are due to left-to-right shunting of blood. Symptoms such as difficulty breathing, exercise intolerance, and fatigue may be seen.

Physical Examination
Volume overload of the right side of heart can lead to right heart failure that may present with symptoms of swelling of the extremities, difficulty breathing and signs such as hepatomegaly and an elevated jugular venous pulse. On cardiovascular examinations there is a fixed splitting of second heart sound. Also, a systolic ejection murmur that is attributed to the increased flow of blood through the pulmonic valve can be heard.

Electrocardiogram
The ECG findings may show a prolonged PR interval (first degree heart block). The prolongation of the PR interval is probably due to the enlargement of the atria that is common in ASD. Other findings include right bundle branch block (RBBB), right axis deviation, right ventricular hypertrophy (RVH), atrial fibrillation and atrial flutter.

Echocardiography
Echocardiography along with doppler ultrasound are the preferred imaging modalities to diagnose atrial septal defect. On transthoracic echocardiography, an atrial septal defect may be seen on color flow imaging as a jet of blood from the left atrium to the right atrium. Usually transesophageal echocardiography is a better tool for diagnosing atrial septal defects than transthoracic echo. Trials have demonstrated that transesophageal echocardiography is superior to transthoracic echocardiography in diagnosing sinus venosus ASD.

Treatment
Atrial septal defects can remain asymptomatic until the fourth decade of life. The treatment can involve either a medical or surgical approach. Surgical closure further could be divided into percutaneous repair or open heart surgery involving either suture or patch closure.

Medical Therapy
Medical therapy has a limited role in the definitive treatment of ASD. Medical therapy is often used to manage arrhythmias and some of the comorbidities associated with atrial septal defect such as stroke and migraine.

Percutaneous Closure
Percutaneous closure is commonly performed for ostium secundum ASDs. This procedure is still not FDA approved for the treatment of other types of atrial septal defects like sinus venosus ASD, coronary sinus ASD, or primum ASD. With appropriate patient selection, percutaneous closure has been demonstrated to be as successful, safe and effective as surgical closure. Additionally, percutaneous closure has been associated with fewer complications and a reduced average length of hospital stay compared to surgical care.

Surgical Closure
Surgical closure is the most common treatment method for atrial septal defect patients and has been the gold standard for many years. It is still the most popular method for repair of defects like sinus venosus ASD, coronary sinus ASD, or primum ASD. However, surgery is contraindicated in patients with severe irreversible pulmonary artery hypertension, Eisenmenger's syndrome and no evidence of a left-to-right shunt.