Grown-up Congenital Heart Disease (GUCH)

Septal defects

Atrial septal defect

Introduction

Atrial septal defect (ASD) is common, accounting for approximately 7 percent of congenital heart disease. The ASD’s can occur in several different anatomic portions of the atrial septum, and the location of the defect generally reflects the abnormality of embryogenesis that led to the anomaly. The functional consequences of an ASD are determined by its diameter, the anatomic location and the presence or absence of other cardiac anomalies.

Classification

The various forms of ASD’s are differentiated from each other by the structures of the heart involved and the formation during embryological development.

The ostium secundum defect is the most frequent form of ASD (70%), localized at the fossa ovalis with a diameter of about 1 – 2 cm. It commonly arises from an enlarged foramen ovale, inadequate growth of the septum secundum or excessive absorption of the septum primum.

The sinus venosus defect (15% of all ASD’s) is localized high in the atrial septum, at the inflow of the superior caval vein. Note that in 80-90% of patients this defect is accompanied by an anomalous pulmonary venous drainage of the right pulmonary vein into the right atrium. Inferior sinus venosus defects do exist, but are very exceptional.

The ostium primum defect is localized low in the atrial septum at the atrioventricular junction. It forms the atrial component of the category of congenital heart disease referred to as atrioventricular defects, with a common atrioventricular junction and an abnormal atrioventricular valve.

The coronary sinus defect, localized at the atrial ostium of the coronary sinus, is rare and usually accompanied by other cardial defects like anomalous drainage of the superior vena cava.

Pathophysiology

The presence of an ASD will in all cases gradually lead to a left to right shunt across the defect. At birth the volume of blood shunting from systemic to pulmonary circulation is small, because the right ventricle is still relatively thick-walled and noncompliant. In response to a decrease in pulmonary vascular resistance after birth, the right ventricle remodels and its compliance increases. This leads to a decrease in right atrial pressure and an increase in shunt volume across the defect during the first years of life.

The blood shunts during the late systole and early diastole, leading to a diastolic volume overload of the right atrium and right ventricle, but also the pulmonary veins and arteries. This volume overload of the pulmonary circulation will consequently lead to right-sided dilatation. The end diastolic increase in pressure of pulmonary circulation can result in systemic venous stuwing. This stuwing is augmented by another mechanism caused by the right ventricular volume overload; deviation of the ventricular septum to the left and the decrease in left ventricle preload because of the left to right shunt, lead to a decrease in stroke volume of the left ventricle. The renine-angiotensin system is activated, leading to an increase in intravascular volume and signs of venous stuwing. The right-sided volume overload is usually well tolerated for years, but in adulthood hemodynamic factors can influence the shunt size in both directions. If the right ventricle will start failing due to chronic volume overlad, the left to right shunt can decrease. If the left ventricle function will decline due to hypertension or coronary artery disease, the lef to right shunt can increase. In 10-20% of adult patients with an isolated ASD pulmonary hypertension will develop, leading to a decrease in left to right shunt and eventually right to left shunt with cyanosis (Eisenmenger syndrome).

Evaluation and therapy

Most ASDs less than 8mm in diameter close spontaneously in infants, however above the age of 4 years spontaneous closure is unusual. During childhood and early adulthood most patients with moderate to large uncorrected ASDs are asymptomatic. Most of them will become symptomatic during adulthood (usually from the age of 40) and require closure of the defect. Indications for closure of an ASD in adulthood are development of symptoms and a high rate of shunt flow. Decreased exercise tolerance, fatigue, dyspnoe, syncope and paradoxal embolization are manifestions of such symptomatic ASDs that warrant closure of the defect. Atrial arrhythmias are usually one of the first presenting symptoms, however these symptoms alone are not an indication for closure, since the incidence after the procedure is not likely to be reduced.

When closure of the ASD is indicated, this can be performed with surgery or percutaneous intervention. Surgical closure is usually performed using a patch of pericardium or Dacron. Prior to surgery, a comprehensive noninvasive evaluation is essential to exclude pulmonary hypertension and associated anatomic defects such as anomalous pulmonary and systemic venous connections. In nearly all cases, echocardiography can resolve these questions, obviating the need for cardiac catheterization.Transcatheter closure avoids cardiopulmonary bypass, thoracotomy, and atriotomy, and is associated with excellent outcomes. As a result, this approach has largely replaced surgery in many centers for patients with a defect that is less than 20 mm in diameter.

Outcome

The short- and long-term outcomes are generally excellent after either surgical or transcatheter closure of an isolated ASD in children. Several investigations showed that there is almost no increase in long-term mortality or serious morbidity compared to controls, following surgical repair of an ASD under 25 years of age. The perioperative mortality is low (< 1%) and there are few perioperative complications (about 10%). However late in adulthood about 50% of all patients develop sinusknoopdysfunctie and symptomatic supraventricular tachyarrhythmias.

When the ASD is closed percutaneously the short-term outcomes (less than one year) are excellent, with reported procedure success rates of 88 to 98%.