Primum Atrial Septal Defect

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Primum Atrial Septal Defect illustration

The endocardial cushions separate the atrioventricular valves and form the lower portion of the atrial septum and the upper portion of the interventricular septum. Primum atrial septal defect is a form of endocardial cushion defect involving the lowest part of the atrial septum, between the atrioventricular valves. Primum atrial septal defect is nearly always associated with abnormal development of the atrioventricular valves, most commonly a cleft mitral valve. Atrial septal defects result in left-to-right shunting of blood at the atrial level, which causes right ventricular and right atrial dilatation. With prolonged dilatation, right ventricular dysfunction and atrial arrhythmias can occur. In addition, long standing pulmonary overcirculation can lead to pulmonary vascular obstructive disease. Cleft mitral valve can result in mitral insufficiency and left atrial dilatation.

Surgical technique

Repair of primum atrial septal defect requires the use of cardiopulmonary bypass and aortic cross- clamping. The right atrium is opened, and the cleft mitral valve leaflet is repaired with interrupted sutures. ASD closure starts with sutures placed along the tricuspid valve annulus at the crest of the ventricular septum. Next, sutures are placed along the rim of the defect adjacent to the coronary sinus. Care is taken to place these sutures superficially to avoid injury to the atrioventricular conduction pathway. The remainder of the defect is closed with running suture. A synthetic patch or autologous pericardium is commonly used for repair of primum atrial septal defect. Cardiopulmonary bypass time and aortic cross-clamp time required to complete repair are short to moderate.


Postoperative considerations

The postoperative course following repair of primum ASD is usually uncomplicated. Invasive monitors used include arterial and central venous catheters. An LA line is used when needed for hemodynamic management. LA pressure acts as a surrogate for left ventricular end diastolic pressure, an excellent indicator of left ventricular performance. Non-invasive monitors include NIRS (near-infrared spectroscopy) probes to assess adequacy of regional and global perfusion and traditional pulse oximetry. Vasoactive agents might include epinephrine and/or milrinone. Numerous other agents are available and are tailored to the specific needs of the patient, targeting adequate oxygen delivery to the tissues of the body and optimization of cardiac output. In contrast to the repair technique used for the repair of secundum ASD, the repair of this defect requires sutures to be placed very near atrioventricular conduction tissue. Arrhythmia following repair of primum atrial septal defect is a potential complication. Atrioventricular pacing equipment should be readily available. In addition, mitral stenosis or insufficiency is a potential postoperative complication. Care is taken during the repair of the mitral valve cleft to avoid mitral stenosis or insufficiency. Length of hospital stay required following repair of primum atrial septal defect averages 4 to 7 days.