ORGANUM
ASD (ostium secundum defect) occurs as an isolated anomaly in 5% to 10% of all congenital heart defects. It is more common in females than in males (male/female ratio of 1:1). About 30% to 50% of congietal heart defects have an ASD as part of the cardiac defect.
Three types of ASD exist - secundum defect, primum defect and sinus venosus defect. Another rare form of defect is coronary sinus ASD. Patent formane ovale (PFO) does not normally produce a left to right intracardiac shunt.
Ostium secondum defect is the most common type of ASD, accounting for 50% to 70% of all ASDs. This defect is present at the site of fossa ovalis, allowing left-to-right shunting of blood from the left atrium to the right atrium. Anomalous pulmonary venous return is present in about 10% of cases.
Ostium primum defects occur in about 30% of all ASDs, if those that occur as part of a complete endocardial cushion defect (ECD) are included. Isolated ostium primum ASD occurs in about 15% of all ASDs.
Sinus venosus defect occurs in about 10% of all ASDs. The defect is most commonly located at the entry of the superior vena cava (SVC) into the RA (superior vena caval type) and rarely at the entry of the inferior vena cava. The former is very commonly associated with anomalous drainage of the right upper pulmonary vein (into the RA), and the latter is often associated with anomalous drainage of the right lung into the IVC ('scimitar syndrome').
In coronary sinus ASD, there is a defect in the roof of the coronary sinus and the LA blood shunts, through the defect and the coronary sinus ostium into the RA, which produces clinical pictures similar to those in other types of ASD.
Mitral valve prolapse (MVP) occurs in 20% of patients with either ostium secundum or sinus venous defects.
Infants and children with ASDs are usually asymptomatic
A relatively slender body build is typical (the body weight of many is less than 10th percentile)
A widely split and fixed S2 and a grade 2 to 3/6 systolic ejection murmur are characteristic findings of ASD in older infants and children. With a large left-to-right shunt, a mid-diastolic rumble resulting from relative tricuspid stenosis may be audible at the lower left sternal border.
Classic auscultatory findings (and ECG and CXR findings) of ASD are not present unless the shunt is reasonably large - at least Qp/Qs of 1.5 or greater). The typically auscultatory findings may be absent in infants and toddlers, even i those with a large defect, if the RV is poorly compliant.
Right axis deviation of +90 to +160 degrees and mild right ventricular hypertrophy (RVH) or right bundle branch block (RBBB) with an rsR' pattern in V1 are typical findings. In about 50% of patients with sinus venousus ASD, the P axis is < 30 degrees.
Cardiomegaly with enlargement of the RA and RV may be present
A prominent PA segment and increased pulmonary vascular markings are seen when the shunt is significant.
A two-dimensional echo is diagnostic. The study shows the position as well as the size of the defect, which can best be seen in the subcostal four chamber view. In secundum ASD, a dropout can be seen in the midatrial septum. The primum type shows a defect in the lower atrial septum; the SVC type of sinus venouses defect shows a defect in the posterosuperior atrial septum
Indirect signs of a significant left-to-right shunt include RV enlargement and RA enlargement, as well as dilated PA, which often accompanies an increase in the flow velocity across the pulmonary valve.
Pusled doppler reveals characteristic flow pattern with maximum left-to-right shunt occuring in diastole. Color flow mapping ehances the hemodynamic status of the ASD.