Congenital Heart Disease part 1

ATRIAL SEPTAL DEFECT:

Atrial septal defect may not uncommonly remain undiagnosed until adulthood.
Atrial septal defect types include:

• Secundum atrial septal defect (located in the region of the fossa ovalis and its surrounding)
• Primum atrial septal defect (partial atriaventricular septal defect, partial atrioventricular canal, located near the crux, atrioventricular valves are typically malformed resulting in various degrees of regurgitation
• Superior sinus venosus (located near the superior vena cava entry, associated with partial or  complete connection of right pulmonary veins to superior vena cava, right atrium)
• Inferior sinus venosus defect (located near the inferior vena cava entry)
• Unroofed coronary sinus (separation from the left atrium can be partially or completely missing)

Associated lesions include anomalous pulmonary venous connection, persistent left superior vena cava,  pulmonary valve stenosis  and mitral valve prolapse.
The shunt volume depends on right ventricle/left ventricle compliance, defect size, and left atrial/right atrial pressure. A simple atrial septal defect results in left to right shunt because of the higher compliance of the right ventricle compared with the left ventricle (relevant shunt in general with defect size > 10mm), and causes right ventricle volume overload  and pulmonary overcirculation. Reduction in left ventricle compliance or any condition with elevation of left atrial pressure (hypertention, ischaemic heart disease, cardiomyopathy, aortic and mitral valve disease) increase left to right shunt. Reduced right ventricle compliance (pulmonic stenosis, pulmonary arterial hypertention, other right ventricle disease) or tricuspid valve disease may decrease left to right shunt or eventually cause shunt reversal resulting in cyanosis.
Patients frequently remain asymptomatic until adulthood. However, the majority develop symptoms beyond the fourth decade including reduced functional capacity, exertional shortness of breath and palpitations (supraventricular tachyarrhythmias) and less frequently pulmonary infections and right heart failure.

VENTRICULAR SEPTAL DEFECT

As an isolated finding,  ventricular septal defect is the most common congenital heart malformation at birth, if bicuspid aortic valve is not counted. It is mostly diagnosed and -when indicated- treated before adulthood. Spontaneous closure is frequent. Several locations of the defect within the interventricular septum are possible and can be divided into four group :

• Perimembranous/paramembtranous/conoventricular (located in themembranous septum with possible extension into inlet, trabecular or outlet septum; adjacent to tricuspid and aortic valve. aneurysms of the membranous septum are frequent and may result in partial or or complete closure)
• Muscular/trabecular (completely surrounded by muscle, various locations, frequently multiple, spontaneous closure particularly frequent)
• Outlet supracristal/subarterial/subpulmonary (located beneath the semilunar valves in the conal or outlet septum; often associated with progressive aortic regurgitation due to prolapse of the aortic cusp)
• Inlet/Atrioventricular canal (inlet of the ventricular septum immediately inferior to the atrioventricular valve apparatus, typically occuring in Down Syndrome)

Often there ios single defect, but multiple defects do occur. Ventricle septal defect is also a comnmon component of complex anomalies such as tetralogy of fallot, transposition of the great arteries etc.  Spontaneous closure of a ventricle septal defect can occur.

The direction and magnitude of the shunt are determined by pulmonary vascular resistance, the size of the defect, lef ventricle/ right ventricle systolic and diastolic function, and the presence of right ventricular outflow tract obstruction.