TSRA Content:
Authors: Syed Faaz Ashraf, MD, and Mario Castro-Medina, MD
This is a revision and update from the previous edition of the TSRA Primer in Cardiothoracic Surgery written by Susheel Kumar, MD.
Atrial Septal Defect (ASD)
A secundum atrial septal defect, the most common type of ASD (80% of ASDs), is a defect in the interatrial septum (embryonic septum primum). A primum ASD (10%), results due to the persistence of the ostium primum and can be associated with atrioventricular canal defects or a cleft in the anterior mitral valve leaflet. The sinus venosus ASD (4-11%) is usually found in the posterior atrium and is often associated with anomalous pulmonary venous drainage.
Indications for Intervention:
Presence of a hemodynamically significant shunt with associated right heart enlargement with or without symptoms. Presence of anomalous pulmonary venous return or a mitral valve cleft with insufficiency. Left to right shunt with a Qp:Qs ratio of >1.5:1. Today the majority of secundum ASDs are closed by transcatheter devices including the Helix and Amplatzer. For ASDs with insufficient rims (<5mm circumferentially) for the device to form an adequate seal, surgery is required. Surgical closure is frequently done between 3 to 5 years of age.
Surgical Technique for Closure of a Typical Secundum ASD:
The patient is placed in a supine position and the chest is prepped and draped. The operation begins with a limited standard median incision followed by a midline sternotomy. The thymus is either split or resected. The pericardium is opened by an inverted T incision and pericardial stay sutures are placed. A piece of the pericardium can be harvested for patch closure, if so chosen. Preliminary dissection of the aorta, superior vena cava (SVC), and inferior vena cava (IVC) is carried out. Heparin is administered and purse strings are placed over the ascending aorta, SVC, and IVC. Aortic cannulation is followed by direct cannulation of the IVC and SVC, and cardiopulmonary bypass (CPB) is initiated. Alternatively, bicaval cannulation can be achieved by placing both cannulas into the SVC and IVC via the right atrial appendage. Any coexisting ductus is dissected and ligated at this stage. Systemic cooling to 32-34 degrees C is initiated, if required. A left sided vent is unnecessary. The SVC and IVC are snared. A cardioplegia purse string is placed over the ascending aorta and a cardioplegia cannula is placed. The ascending aorta is now cross clamped, and the heart is arrested using cold cardioplegia. The right atrium (RA) is opened by an incision parallel to the atrioventricular (AV) groove. The edges of the RA are retracted by appropriately placed silk stay sutures. The interatrial septum is now examined in detail.
The size and location of the ASD is noted. Particular attention should be paid to the margins of the ASD. It is a good idea to inspect the mitral and tricuspid valves, including the pulmonary veins' openings. Small oval secundum defects can be closed primarily. Larger defects require patch closure. An appropriate patch of either autologous pericardium or Gore-Tex is cut out and used to close the ASD with running Prolene suture. Rewarming is initiated as the patch closure is completed. The left side is de-aired through the aortic root vent and the patch suture line before the suture is tied down. The aortic cross clamp is removed while compressing the right coronary artery origin with continuous suction over the root vent. The RA is closed using a double layer of running Prolene and the vena cava are now de-snared. Atrial and ventricular pacing wires are placed. A RA line may be placed if additional venous access is required. Ventilation is resumed. Once the patient is adequately rewarmed, the patient is gradually weaned off CPB. It is common practice to use transesophageal echocardiogram (TEE) to confirm adequate de-airing of the left side before removing the aortic root vent. The SVC is then decannulated. The patient is completely weaned off CPB and the IVC is decannulated. Protamine is administered and the aortic cannula is taken out. Hemostasis is confirmed. Chest tubes are placed. The sternum is closed using steel wires, and the sternal wound is closed in layers.
Variations in Technique:
Sinus venosus ASDs are located close to the junction of SVC or IVC and are almost always associated with anomalies of pulmonary venous drainage. During baffle repair of these lesions on CPB, the patch is designed to route the pulmonary venous blood into the LA while taking care to prevent obstruction of the SVC or IVC opening. The ASD may need enlarging to accommodate the size of baffle needed for adequate flow. Sometimes, a more extensive procedure requiring rerouting of the pulmonary venous blood from the SVC into the LA and reimplanting the proximal SVC into the right atrial appendage (Warden operation) may be necessary.
Primum ASDs require careful attention to the left atrioventricular (AV) valve as the most frequent need for reoperation in these patients is related to left AV valve regurgitation. A cleft in the anterior left AV valve leaflet is closed first, using fine interrupted sutures. The septal defect is closed with a pericardial patch. A mattress suture is placed at the midpoint of the base of the reconstructed leaflet. This is attached to the patch which becomes the raphe between the tricuspid and mitral valves (left and right AV valves). Near the inferior border, the AV node can be damaged; therefore, careful bites near the tricuspid annulus are required. Alternatively, the patch can be routed around the coronary sinus to avoid sutures near the Triangle of Koch. This leaves the coronary sinus blood draining into the left atrium. More medially, deep sutures can injure the aortic valve.
Ventricular Septal Defect (VSD)
VSDs can be divided into 4 categories by anatomical location. Outlet (8% of VSDs) are located beneath the pulmonary valve annulus. Perimembranous (80%) are located by the commissure of the anterior and septal leaflets of the tricuspid valve (TV). Inlet (6%) are more variable with the most common being below the tricuspid valve’s septal leaflet. Muscular (10%) are found along the muscular interventricular septum.
Indications for Intervention:
Some indications for closure of a VSD include: Symptomatic VSD despite medical therapy, Asymptomatic VSD with Qp:Qs >2:1. Moderate to large VSD with pulmonary arterial hypertension, VSD with aortic valve prolapse or insufficiency, and all inlet and outlet VSDs. Spontaneous closure of a large VSD is unlikely after 6 months of age.
Surgical Technique for Closure of a Typical Perimembranous VSD:
Patient positioning, sternotomy, pericardial dissection, cannulation, and initiation of CPB proceed as discussed above for ASD closure. Systemic cooling to 30-32 degrees C is initiated. The SVC and IVC are snared. A cardioplegia purse string is placed over the ascending aorta and a cardioplegia cannula is placed. The ascending aorta is now cross clamped, and the heart is arrested using cold cardioplegia. A left atrial (LA) or left ventricular (LV) vent is placed through a purse string over the right superior pulmonary vein (RSPV). Myocardial protection is maintained by intermittent doses of cardioplegia every 20-30 minutes. The right atrium is opened by an incision parallel to the AV groove. The edges of the RA are retracted by appropriately placed silk sutures. A preliminary inspection is done to detect any associated ASD and the location of the VSD. The anterior and septal leaflets of the tricuspid valve are then retracted using 6-0 Prolene stay sutures or vessel loops around the chords to optimize exposure of the VSD. The anatomy of the VSD is now examined in detail paying particular attention to its proximity to the aortic valve annulus, tricuspid valve, and chords. An appropriately sized Gore-Tex, Dacron, or glutaraldehyde-treated autologous pericardial patch is now tailored. Interrupted or continuous suturing technique using non-absorbable suture is used to close the VSD with the patch. Whatever the technique used, it is important to avoid injury to the conduction system which runs close to the posteroinferior edge of the VSD by taking partial thickness bites over the RV aspect of the septum. The muscle of Lancisi is generally used as a landmark to demarcate the safe and unsafe margins. Anterosuperiorly, one should take care to avoid injury to the aortic valve.
The suturing is then transitioned to the tricuspid annulus. One should avoid injury to the AV node in the Triangle of Koch. The stay sutures are removed from the tricuspid valve and the valve is tested for competency using saline irrigation. A commissuroplasty suture between the anterior and septal leaflets of the TV may sometimes be necessary to reduce tricuspid regurgitation. Rewarming is initiated. Any atrial septal defect is now closed, and the left heart is de-aired through the aortic root vent. The aortic cross clamp is removed with continuous suction over the root vent. The RA is closed using running Prolene and the vena cavae are now desnared. Atrial and ventricular pacing wires are placed and used to pace the heart in case of conduction blocks. An RA line may be placed if central venous access is required. The airway is suctioned, and the lungs are allowed to re-expand. The LA vent is removed when the contractility of the heart has recovered. Flows are reduced and the heart is allowed to eject. The SVC cannula may be taken out at this point. Following TEE confirmation of the absence of air on the left side of the heart, the aortic root vent is removed. The patient is gradually weaned off cardiopulmonary bypass while closely watching the hemodynamics. Modified ultrafiltration may be done at this stage. The IVC is then decannulated and protamine is administered. This is followed by the removal of the aortic cannula. Hemostasis is ensured and the chest is closed over drains.
Most VSDs can be approached through the RA except subpulmonic VSDs and muscular VSDs in the outlet position which are better approached through the pulmonary valve. A right ventriculotomy may be necessary to facilitate exposure of an anterior muscular VSD. An apical LV incision may be necessary to close apical muscular defects.
Patent Ductus Arteriosus (PDA)
A patent ductus arteriosus is an abnormal persistence of the fetal ductus arteriosus in the postnatal period.
The ductus arteriosus directly connects the main pulmonary artery and the distal aortic arch. It exists in utero to channel oxygenated blood derived from the mother through the umbilical veins straight to the systemic circulation, thereby bypassing the pulmonary circulation. The ductus closes in most term infants within hours of their first breath of air and is permanently closed between 2-8 weeks. The most significant risk factor for lack of closure is prematurity. The complications of persistent ductal circulation include congestive pulmonary failure, volume overload to the left heart, and pressure overload to the right ventricle. A large PDA can lead to pulmonary hypertension with Eisenmenger’s physiology (high pulmonary resistance reversing the flow across a VSD such that it becomes a right-left shunt).
Medical closure with NSAIDs (indomethacin or ibuprofen) is the first line in neonates, but ineffective in term infants or older. Percutaneous closure of the PDA via catheter-delivered coils or occlusion devices can be performed, traditionally for patients >5kg in size. However, recently, depending on the morphology of the PDA and expertise of operators, patients <5kg can now be treated percutaneously. Surgical intervention is sought when the duct is refractory to medical therapy or unable to be closed in the catheterization lab.
Indications for Intervention:
Moderate to large PDA with symptoms of left to right shunt, volume overload or reversible pulmonary hypertension. Prior episode of infective endocarditis. Any audible PDA even in the absence of a significant left to right shunt. Closure is contraindicated in patients with fixed (irreversible to nitric oxide) severe pulmonary hypertension.
Surgical Technique for PDA Closure:
Isolated PDAs in infants and children are approached through lateral thoracotomy. The side of the chest to enter is decided by the side of the aortic arch. The patient is placed in a right lateral decubitus position (for left sided aortic arch) with appropriate padding including an axillary roll. The left arm is placed in an abducted position. A pulse oximeter is placed on the lower limbs. The left chest is prepped and draped. The operation begins with the creation of a limited skin incision over the posterolateral aspect of the left chest just below and parallel to the inferior border of the scapula. The latissimus dorsi muscle is cut along the incision, trying to preserve the serratus anterior muscle. The ribs are counted accurately to enter the third or fourth intercostal space. The intercostal muscle is detached along the superior border of the fourth or fifth rib. Care is taken to avoid injury to the lung while entering the space. A rib spreader is used to open up the space. The left lung is retracted anteriorly to expose the descending aorta. The mediastinal pleura over the descending aorta is opened. The superior intercostal vein is either ligated or cauterized. The medial edge of the pleura is dissected anteriorly to expose the ductus. The vagus nerve and the recurrent laryngeal nerve can be seen coursing over the ductus. Care should be taken to avoid injury to the nerve or the ductus itself. The anatomy of the aortic arch, the left subclavian artery, and the ductus should be well demonstrated. Meticulous dissection is done along the superior and inferior borders of the ductus to create space for ligation. The ductus may be test clamped using a vascular forcep. A rise in systolic and diastolic blood pressures, the disappearance of the murmur (which can be auscultated via the endotracheal tube), and persistence of lower limb pulse are confirmatory of ductal occlusion. Following this, an appropriate-sized titanium clip is placed over the aortic end of the ductus taking care to occlude the entire width of the ductus. In larger infants, the PDA can be double, or triple ligated with a 3-0 non-absorbable suture. Hemostasis is ensured and the lung is allowed to re-expand. The chest tube is placed. The chest is closed using pericostal absorbable sutures. The muscles are approximated in layers using running absorbable sutures, and the skin is closed.
Variations in Technique:
Beyond the neonatal period, the ductus is a firmer structure and can be divided between ligatures. In older children, the ductus can be divided between clamps and the ends closed using running Prolene. In adults, the ductus may be extremely calcified and may need a period of circulatory arrest to be closed.
Coarctation of the Aorta
Coarctation of the aorta is a congenital narrowing of the proximal portion of the descending thoracic aorta just distal to the left subclavian artery (isthmic portion of the aorta). It is often associated with hypoplasia of the distal aortic arch and bicuspid aortic valve. The spectrum of presentation varies depending upon the severity of stenosis and ranges from cardiovascular collapse in the neonate to claudication pain in the adult.
Indications for Intervention:
Symptomatic neonates, infants, or older children/adults who are not candidates for catheter intervention. For asymptomatic patients, surgery should be offered if the upper extremity blood pressure is 2 standard deviations above normal or the diameter of the coarctation is <50% of the diameter of the remaining aorta.
Surgical Technique ('Resection and End-to-End Anastomosis'):
The patient is placed in a right lateral decubitus position and the left chest is prepped and draped. The left arm is placed in an abducted position and a roll is placed beneath the right axilla. The temperature of the patient may be allowed to drift down to 35 degrees C as systemic hypothermia has a protective effect against spinal cord ischemia.
A posterolateral skin incision is made and the latissimus dorsi muscle is cut in the line of the incision. It may be necessary to cut some of the posterior fibers of the serratus anterior. The left chest is entered either through the third or fourth intercostal space. Care is taken to avoid any injury to the left lung during chest entry. Upon entry, the left lung is gently retracted anteriorly and inferiorly. The mediastinal pleura over the descending aorta is opened to expose the descending and isthmus portion of the aorta. It is important to identify the phrenic, vagus, and recurrent laryngeal nerves to avoid injury. The aortic arch, the left subclavian artery and left carotid artery branches, the descending aorta, and the ductus are all dissected and mobilized well. The medial flap of the mediastinal pleura is suspended using stay sutures. Heparin is not necessary although some surgeons favor using 50-100 units/kg of heparin. The anesthesiologist is informed, and clamps are placed over the distal aortic arch and descending thoracic aorta. It is useful to maintain a good blood pressure proximal to the clamp to promote blood flow into the lower body through collaterals (although there are fewer collaterals in the neonate compared to an older patient). The ductus is first divided between ligatures and the narrowed portion of the aorta is resected. Care is taken to excise all the ductal tissue. If the distal aortic arch is small, the incision is extended on the undersurface of the arch ('Extended Resection and End-to-End Anastomosis'). In such cases, the proximal clamp is placed higher (but never beyond the origin of the innominate artery to ensure cerebral blood flow).
The proximal and distal aorta are now anastomosed using running Prolene suture (7-0 in neonates, 4-0 in young adults) while the assistant holds the clamps close. At the end of the anastomosis, the distal clamp is removed first followed by the removal of the proximal clamp. The area may be lightly packed to stop suture line bleeding. If the repair has been adequate, any gradient noticed immediately following removal of clamps usually decreases. Some surgeons prefer to re-approximate the mediastinal pleura. A single chest tube is placed, the ribs are approximated using pericostal sutures, and the chest wall muscles are closed in layers.
Variations in Technique:
Several other techniques have been described, including: the subclavian flap technique to augment either the proximal or distal portions of the aorta, prosthetic patch aortoplasty, and prosthetic interposition graft. When the aortic arch is very hypoplastic or the coarctation affects the proximal segment, the repair is better achieved through a midline approach on cardiopulmonary bypass and circulatory arrest or antegrade cerebral perfusion. Challenges faced in coarctation repair in the adult are extensive collaterals, lesser mobility of the aorta, and a higher incidence of spinal cord ischemia.