Atrial Septal Defect
An Atrial Septal Defect (ASD) refers to a defect in the interatrial septum which allows the shunting of blood between the two atria (Smith & McKay, 2003). The incidence of this defect is 5-10% amongst children with congenital heart disease and is found more commonly in females as compared to males (Wiell Cornell Cardiothoracic Surgery, 2003). There are three main kinds of ASDs found most commonly, viz. secundum ASD (most common), primum ASD and sinus venosus ASD (NMT Medical, 2009).
The treatment options for an ASD vary according to the size of the defect and its location (NMT Medical, 2009). Moreover, factors such as the age of the patient and concomitant risk factors also need to be considered before choosing any particular kind of treatment (Wiell Cornell Cardiothoracic Surgery, 2003). The medical management of an ASD consists of the use of ionotropic drugs such as digoxin and diuretics to maintain an adequate fluid balance. Moreover, patients may require prophylaxis for bacterial endocarditis during any dental and surgical procedures (Wiell Cornell Cardiothoracic Surgery, 2003). Repair of an ASD can be carried out either endoscopically or via an open surgical repair procedure.
Open Surgical Repair Procedure
The underlying principle of the open surgical repair procedure of an ASD is to close the existing defect in the atrial septum by either approximating the edges of the defect or closing it with stitches or by closing the defect with a patch of synthetic material (NMT Medical, 2009). The repair of an ASD is a clean procedure. Prior to the surgery, any anticoagulants that the patient was previously taking are discontinued and the patient is kept NPO (nothing per oral) for a minimum period of 12 hours (Baylor College of Medicine, 2004).
The initial step in the surgery is the provision of general anesthesia to the patient. The preparatory steps for the surgery once the patient is under anesthesia include, intubating the patient using an endotracheal tube and putting the patient on a mechanical ventilator, insertion of IV lines and Foley’s catheter and a nasogastric (NG) tube (Baylor College of Medicine, 2004). Once these measures have been taken, a transesophageal echocardiogram (TEE) is performed in order to give the surgeon a clear idea of the size, location and extent of the ASD (Baylor College of Medicine, 2004).
The procedure begins by performing a median sternotomy (Mavroudis & Backer, 2003). The incision is kept as short as possible for aesthetic reasons. An alternative approach is to perform a right thoracotomy but this technique is not commonly used as it carries with it the inherent risk of injury to the right phrenic nerve and air embolism (Mavroudis & Backer, 2003). Moreover, using a median sternotomy also allows for better visualization of the thoracic cavity and detecting the presence of any other associated cardiac defects and repairing them at the same time (Mavroudis & Backer, 2003).
The patient is then put on a cardiopulmonary bypass machine. To achieve this, one aortic cannula and two venous cannulas are used (Mavroudis & Backer, 2003). After cannulation of the right atrium and the superior and inferior vena cava, cold blood cardioplegia is performed via infusing blood through the ascending aorta (Mavroudis & Backer, 2003).
An incision is then made in the right atrium. The choice of the incision type depends on the type of the defect. For a secundum ASD, the incision extends from the right atrial appendage obliquely towards the inferior vena cave, while avoiding the crista terminalis (Mavroudis & Backer, 2003). On the other hand, while repairing a sinus venosus ASD, the incision extends from the right atrial appendage towards the junction of the superior vena cava with the right atrium (Mavroudis & Backer, 2003).
The choice of whether to use a patch to close the defect or to perform closure via suturing depends on the size of the defect, its position and also on the presence or absence of an adequately large ventricle which would serve to accommodate the volume of blood which was previously being shunted (Smith & McKay, 2003).
Direct closure of the defect via suturing is carried out only if the defect is small and the deficiency in the septum is limited to the interatrial septum and does not extend to any venous orifices (Smith & McKay, 2003). When venous orifices are involved, direct suturing would cause the narrowing of the venous passage and would impair blood flow. Moreover, blood flow through a narrowed channel would cause pressure and tension on the surrounding anatomical structures as well (Smith & McKay, 2003). Therefore, in such a case, the use of a patch to close the defect is preferred. The use of a patch of autogenous pericardium is usually preferred (Smith & McKay, 2003). When the choice to use an autologous patch has been made either preoperatively or per operatively, the patch is harvested at the beginning of the surgery. Moreover, stay sutures are placed at the edges to retract them and this graft is place in saline solution while the right atrium is being opened up (Mavroudis & Backer, 2003). Patches of synthetic material such as Goretex can also be used (Baylor College of Medicine, 2004).
Once the defect is visualized, the autologous patch is sutured on to the defect using 5-0 polypropylene sutures (Mavroudis & Backer, 2003). The suturing is started at the inferior end of the defect in the vicinity of the inferior vena cava, taking care to avoid the Eustachian valve. The suturing continues upwards initially adjacent to the crista terminalis and subsequently next to the coronary sinus and then completed (Mavroudis & Backer, 2003). It is important to ensure that the smooth side of the graft is facing towards the left atrium (Smith & McKay, 2003). Moreover, towards the end of the procedure, Valsalva maneuver is performed by the anesthesiologist to ensure the removal of blood and air from the left side of the heart (Mavroudis & Backer, 2003). This maneuver is then repeated once to check for any leaks in the suturing. The incision in the right atrium is then closed and the patient is then weaned off the cardiopulmonary bypass (Mavroudis & Backer, 2003). Chest tubes for drainage and temporary pacing wires are then sutured in place (Baylor College of Medicine, 2004). The sternotomy is then closed using wire sutures and skin sutures are then applied (NMT Medical, 2009).
Post surgically the patient is extubated and transferred to the Cardiovascular Intensive Care Unit (CVICU). Patients need to be monitored for complications such as postoperative bleeding, potential airway problems, wound infection, arrhythmias, endocarditis, myocarditis and reactions to transfused products or anesthesia (NMT Medical, 2009; Mavroudis & Backer, 2003).
Baylor College of Medicine. (2004). Atrial Septal Defect Closure. Retrieved August 3, 2009, from Baylor College of Medicine Department of Surgery: http://www.debakeydepartmentofsurgery.org/home/content.cfm?proc_name=Atrial+Septal+Defect+Closure&content_id=272
Mavroudis, C., & Backer, C. L. (2003). Pediatric cardiac surgery. Mosby.
NMT Medical. (2009). Atrial Septal Defect (ASD). Retrieved August 3, 2009, from NMT Medical, Inc.: http://www.nmtmedical.com/heartrepair.aspx?id=72#4
Smith, A., & McKay, R. (2003). A practical atlas of congenital heart disease . London: Springer.
Wiell Cornell Cardiothoracic Surgery. (2003, December 2). Atrial Septal Defect (ASD). Retrieved August 3, 2009, from Wiell Cornell Cardiothoracic Surgery: http://wo-pub2.med.cornell.edu/cgi-bin/WebObjects/PublicA.woa/3/wa/viewHContent?website=wmc+ct&contentID=1766&wosid=kgUeohr1kWxeQbleTf5Sx0