TOC | Cardiology ATRIAL SEPTAL DEFECT
The magnitude of the left-to right shunt through an ASD depends on the defect size, the diastolic properties of both bentricles, & the relative impedance in the pulm & systemic circulations. The left-to right shunt causes diastolic overloading of the right ventricle & increased pul blood flow.
The pts are usually asymptomatic, but may develop atrial arrhythmias, pulm arterial hypertension, directional & then right -to-left shunting of blood, and cardiac failure.
S1 is normal or split, S2 is widely split & fixed, midsystolic pulm. ejection murmur, middiastolic rumbling murmur, loudest at the 4th intercostal space along LSB due to increased flow across the tricuspid valve.
In pts with ostium primum defects, an apical thrill & holosystolic murmur indicate assoc. mitral or tricuspid incompetence or a ventricular septal defect.
With increase in the pulm vascular resistance, there is diminution of the left-to-right shunt. Both the pulm & tricuspid murmurs decrease in intensity, the pulm component of S2 & a systolic ejection sound are accentuated, the 2 components of S2 may fuse, & a diastolic murmur of pulm. incompetence appears. Cyanosis & clubbing accompany the development of a right-to-left shunt.
In adult with atrial fibrillation & ASD, the physical findings may be confused with the findings of mitral stenosis with pulm hypertension because the tricuspid flow murmur & widely split S2 may be mistakenly to represent mitral stenosis diastolic murmur & mitral "opening snap".
in ostium secundum defect: right axis deviation & an rSr' pattern.
in ostium primum: left axis deviation & superior orientation & counterclockwise rotation of the QRS loop in the frontal plane. Varying degree of RVH & RAE may occur with each defect.
Echocardiogram with color Doppler flow
pulm. arterial & right ventricular dilatation, anterior systolic (paradoxical) or flat interventricular septal motion if significant right ventricular volume overload is present. The defect may be visualized directly from different angles.
Surgical repair in those with significant left-to-right shunt, i.e. pulm.-to-systemic flow ration > 2:1.
Medical Rx for any arising complications as atrial arrhythmia, PSVT, resp. tract infection, etc.
Exam: In most adults with this anomaly, pulm. pressures are normal & a gradient and shunt from aorta to pulm artery persist throughout the cardiac cycle, resulting in a characteristic thrill and a continuous "machinery" murmur at left sternal border with a late systolic accentuation at the upper left sternal edge.
SX: In adults who were born with a large left-to-right shunt through the ductus arteriosus, pulm vasc. obstruction with pulm hypertension, right-to-left shunting, and cyanosis have usually developed. The leading causes of death in adults are congestive heart failure & infective endocarditis.
DX: Echocardiogram quantifies L. ventricular & atrial size. The magnitude of the shunt can also be determined by radionuclide flow studies. Cardiac cath. establishes the presence & severity of a lef-to-right shunt & whether pulmonary hyperension is present. Angiography can define its anatomy.
RX: surgical repair is recommended for pts with symptoms or large shunts.