Abstract
This chapter summarizes the anatomy, biology, pathophysiology, surgical treatment, and outcomes in patients with interrupted aortic arch and ventricular septal defect. Emphasis is placed on diagnostic assessment and surgical decision making in the presence of varying degrees of left ventricular outflow tract obstruction. The hybrid technique for high-risk patients with interrupted aortic arch with ventricular septal defect is also summarized. Finally, early and late postoperative complications and outcomes are included.
Key Words
Interrupted Aortic Arch, Ventricular Septal Defect
Interrupted Aortic Arch
Classification and Anatomy
Interrupted aortic arch (IAA) is a rare but highly lethal form of congenital heart disease, carrying a mortality rate higher than 90% in the neonatal period if not treated. The incidence of IAA is 1% of all congenital heart defects. Celoria and Patton described the currently used anatomic definitions, in which type A is interrupted distal to the left subclavian artery (LSCA); type B is interrupted between the left subclavian and left carotid arteries; in type B1 the origin of the right subclavian artery (RSCA) is on the descending thoracic aorta; and type C is interrupted proximal to the left carotid artery. Type B IAA is the most common (78%), followed by type A (20%) and type C (2%) ( Fig. 46.1 ). All patients have a patent ductus arteriosus, and most have a ventricular septal defect (VSD). Also seen are aortic valve anomalies, truncus arteriosus, and double-outlet right ventricle (RV). The VSD is typically conoventricular in origin and is associated with posterior malalignment of the conal septum and varying degrees of left ventricular outflow tract obstruction (LVOTO) at the subvalvar and/or valvar level. In rare cases, when IAA is not associated with VSD, aortopulmonary window should be suspected. In nearly all patients the aortic arch sidedness is left, but rarely the IAA can be right sided with the descending aorta in the right hemithorax. This has been observed in patients with single-ventricle anatomy.
Many patients with IAA have extracardiac anomalies. Unlike those with coarctation, the predominant extracardiac abnormality in these patients is DiGeorge syndrome. The association of DiGeorge syndrome with type B IAA suggests that both are part of a causally heterogeneous developmental field defect. Using fluorescence in situ hybridization (FISH) analysis, Lewin and colleagues demonstrated that 50% to 80% of patients with IAA type B have 22q11.2 chromosomal deletions. IAA is usually a rare anomaly, but in DiGeorge syndrome it is a common defect.
Conley and associates reported that 36% of their patients with DiGeorge syndrome had type A IAA, and all of their autopsied patients had congenital heart disease. Reports of IAA type A with DiGeorge syndrome are rare. The presence of IAA type B with or without DiGeorge phenotype is an indication for genetic screening for the 22q11 deletion in the patient.
The aortic valve is usually bicuspid (80% to 90%) with varying degrees of commissural fusion and annular hypoplasia. In addition to posterior malalignment of the conal septum relative to the ventricular septum, Jonas has pointed out a prominent muscle bundle on the left ventricular (LV) free wall that can project into the left ventricular outflow tract (LVOT) (muscle of Moulaert), significantly contributing to outflow obstruction ( Fig. 46.2 ).
Embryology
The normal embryology of the aortic arch is a complex interaction of tissues arising from the primitive aortic arches, truncus arteriosus, and left dorsal aorta. Schematic drawing of the postnatal aortic arch illustrates the origins of the various portions of the arch complex ( Fig. 46.3 ). The fourth aortic arch is of particular interest in the pathogenesis of IAA type B. As shown in Fig. 46.3 , aortic arch tissue between the left carotid and left subclavian arteries is derived from the fourth primitive aortic arch. The RSCA, also derived in part from the fourth arch, is often malposed in patients with IAA. This anomaly is especially prevalent in patients with IAA type B, but it can also be associated with coarctation or can be an independent anomaly. When anomalous, the origin of the RSCA is distal to the LSCA, and the artery courses posteriorly to the esophagus, potentially causing esophageal or tracheal compression. When an aberrant RSCA arises distal to the interruption or coarctation, the patient may have decreased blood pressure in the right arm or right vertebral-subclavian steal. It is also noteworthy that an aberrant RSCA is associated with greater degrees of LVOTO because in utero more blood must pass through the ductus and less through the ascending aorta. The LSCA is usually not malposed and takes origin from the descending thoracic aorta, but on rare occasions either SCA can take origin from the ipsilateral pulmonary artery (PA) and require ligation and reimplantation at the time of surgical repair.
Decreased aortic flow potentially leads to atresia or interruption. However, not all children with obstructive arch lesions have intracardiac lesions that decrease aortic flow. Freedom and associates studied this issue in patients with IAA and VSD and found no definitive mechanism for decreased aortic flow, although 50% had LV outflow tract narrowing that was characterized as conoventricular malalignment.
Left-sided outflow tract and arch anomalies may be due to neural crest migratory problems. Cranial neural crest gives rise to ectomesenchyme, which populates pharyngeal arches III, IV, and VI. These primitive vessels contribute to the formation of the carotid arteries, a portion of the aortic arch, the RSCA, and the ductus arteriosus. The tunica media of the aortic arch consists entirely of cranial neural crest cell derivatives. Thus abnormal migration of neural crest cells may have structural consequences and change blood flow patterns. Chromosomal abnormalities may induce abnormalities of the neural crest cells. There is also experimental evidence that fibronectin plays a role in neural crest cell migration and that fibronectin deficiency might result in obliteration of the fourth arch artery in the chick embryo.
Associated Anomalies
Associated cardiovascular anomalies are always present with IAA. The most common is VSD (70% to 80%) and atrial septal defect (ASD) or stretched patent foramen ovale (PFO), which can be quite large and hemodynamically important. Other commonly associated lesions include truncus arteriosus, transposition of the great arteries (TGA) with VSD, aortopulmonary window, and various forms of single ventricle. The frequency of these associated anomalies is shown in Table 46.1 .
| Associated Cardiac Anomalies | n | TYPE OF INTERRUPTED AORTIC ARCH n (%) | ||
|---|---|---|---|---|
| Type A | Type B | Type C | ||
| VSD (isolated) | 44 | 7 (35) | 35 (71) | 2 (100) |
| “Single ventricle” | 8 | 5 (25) | 3 (6) | NA |
| Truncus arteriosus | 7 | 2 (10) | 5 (10) | NA |
| DORV | 5 | 2 (10) | 3 (6) | NA |
| TGA + VSD | 2 | 2 (10) | NA | NA |
| Complete AV canal | 2 | 1 (5) | 1 (2) | NA |
| DOLV | 1 | NA | 1 (2) | NA |
| Isolated v. inversion + VSD | 1 | 1 (5) | NA | NA |
| None (PDA present) | 1 | NA | 1 (2) | NA |
| Total | 71 | 20 (100) | 49 (100) | 2 (100) |
Pathophysiology
The pathophysiology of IAA is similar to neonatal coarctation of the aorta (CoA) with VSD. Systemic blood flow is dependent on ductus patency. As the ductus closes, the infant develops shock, acidosis, and renal failure. The increasing systemic resistance redirects blood flow to the pulmonary circulation, which ultimately results in volume and pressure overload of the heart with resulting pulmonary edema and biventricular failure.
Diagnostic Assessment
IAA presents in a fashion similar to critical coarctation in the newborn. In cases in which prenatal diagnosis was not established, the infant develops tachypnea and poor peripheral perfusion as the ductus closes, generally within the first 7 to 10 days of life. Physical examination reveals tachypnea, tachycardia, a single second heart sound, and hepatomegaly and decreased femoral pulses. There may not be a significant murmur due to the large VSD, though with increasing pulmonary blood flow, a systolic murmur may be noted. Differential cyanosis between the upper and lower body is usually difficult to appreciate because of left-to-right shunting at the VSD level leaving some oxygenated blood traveling to the descending aorta via the ductus arteriosus. However, pulse oximetry may show higher oxygen saturation levels in the preductal arm (usually the right arm) compared with the lower body if the great vessels are normally related. If the great vessels are transposed, the oxygen saturation may be higher in the lower body (reversed differential cyanosis).
Given the common association between IAA type B and DiGeorge syndrome, every infant with suspected IAA should be examined for the DiGeorge stigmata. These include a broad nasal bridge, malar hypoplasia, narrow palpebral fissures, hypertelorism, low-set posteriorly rotated ears, retrognathia, small mouth, and submucosal cleft palate. Given that the stigmata may be difficult to appreciate in the newborn, FISH testing, which probes for submicroscopic deletions in chromosome 22q11.2, should be used. Because patients with DiGeorge syndrome have thymic and parathyroid deficiency of variable degree, the physician must anticipate the possibility of T-cell deficiency and hypocalcemia. The major risk of T-cell deficiency in this patient population is developing graft-versus-host disease after transfusion with nonirradiated blood.
The electrocardiogram (ECG) and chest x-ray findings do not establish a specific diagnosis, but the ECG shows RV hypertrophy, and the chest x-ray demonstrates cardiomegaly with increased pulmonary circulation, suggesting congenital heart disease.
Echocardiography establishes the specific diagnosis. The suprasternal aortic arch view shows the absence of continuity between the ascending aorta and descending aorta, and the ductus is seen connecting to the descending aorta. The LSCA may often be seen arising from the descending aorta. The presence of coexisting defects should be carefully explored. Imaging with computerized tomographic angiography and subsequent three-dimensional model building is extremely useful, especially in cases of suspected abnormal arch anatomy. Cardiac catheterization is rarely helpful unless further ambiguity exists.
Of particular importance is the diagnosis of LVOTO, which may be underrecognized preoperatively. Several echocardiographic indices may identify LVOTO, including the indexed cross-sectional area of the LV outflow tract, the subaortic diameter index, and the aortic valve diameter z score. Salem and associates showed that patients with aortic valve diameter less than 4.5 mm ( z score < −5) subsequently developed LVOTO, whereas those with aortic valve diameter greater than 4.5 mm ( z score > −5) did not. Failure to diagnose and correct significant LVOTO surgically is likely to result in persistent heart failure in the postoperative period.
Preoperative Critical Care Management of Interrupted Aortic Arch
The preoperative critical care management of IAA is similar to that of neonatal CoA. The primary objective is to maintain ductal patency with PGE 1 . Shock and congestive heart failure usually improve after PGE 1 administration, but some infants will require inotropic support and mechanical ventilation. Hyperoxia and hypocarbia should be avoided to lessen the chances of pulmonary overcirculation. It is extremely important that any end organ injury to the brain, kidney, lungs, and heart in the early neonatal period be given adequate time to fully recover with medical treatment before surgery is undertaken. Before operation, all patients should have normal blood gas levels and end-organ indices.
Hypocalcemia is a common finding in patients with IAA, even those who do not have DiGeorge syndrome. These infants require calcium replacement because they are at increased risk for symptomatic hypocalcemia during hyperventilation and transfusion of citrated blood products. Irradiated blood products should be used to prevent graft-versus-host disease in all infant IAA repairs unless DiGeorge syndrome has been specifically excluded. Currently at most institutions all pediatric blood products are irradiated as an extra safety precaution.
Indications and Timing of Surgery
The presence of IAA is an indication for operation in most patients once end-organ evaluation is complete and is typically performed in the first 5 to 10 days of life. In the term infant (above 35 weeks) with a birth weight above 1.5 kg and in the absence of significant irreversible end-organ injury or coexisting noncardiac abnormalities, we prefer primary single-stage repair. This includes amalgamation of the ascending and descending aorta with patch augmentation and closure of atrial and ventricular septal defects.
The preterm infant (less than 35 weeks; less than 1.5 kg) or term newborn with severe coexisting noncardiac abnormalities such as diaphragmatic hernia, genetic syndromes, necrotizing enterocolitis requiring operation, severe but reversible neurologic injury, or end-organ damage requiring months to recover may instead be a candidate for hybrid strategy. In rare case, we have successfully used bilateral PA banding with or without ductal stenting to achieve a stable balanced circulation during the extended recovery period.
Another alternative palliative strategy in these circumstances is IAA reconstruction employing the left common carotid artery with PA banding.
Primary Repair of Interrupted Aortic Arch With Ventricular Septal Defect
Following placement of a nasopharyngeal temperature probe and a Foley urinary catheter, arterial monitoring is achieved with right radial and femoral lines. Venous access is via umbilical or femoral vein, but access in the neck is avoided if the patient is less than 5 kg because of potential superior vena cava thrombosis. A blood pressure cuff is placed appropriately, and cerebral and lower extremity near-infrared spectroscopy monitoring is employed.
Following midline sternotomy and thymus removal (if present) the innominate vein and artery and left common carotid artery (LCCA) are circumferentially and extensively dissected cephalad. The pericardium is opened, and a segment is harvested and treated in glutaraldehyde for VSD closure (alternatively 0.4-mm Gore-Tex is used). The ductus is encircled, and the right PA can be temporarily occluded for hemodynamic stability. We prefer bicaval cannulation, LV venting through the right superior pulmonary vein, and regional cerebral perfusion (30 to 50 mL/kg/min). Heparin is administered, and the innominate artery is cannulated directly or a 3.5-mm Gore-Tex tube is sewn to the innominate artery (right common carotid artery if aberrant RSCA is present) and an 8-mm arterial cannula inserted. A Y adapter is placed on the arterial line, and the ductus is cannulated with an 8-French cannula and snared following bicaval cannulation and vent insertion. Alternatively (not our usual preference), the second cannula can be placed in the descending thoracic aorta at the diaphragm level for retrograde perfusion.
Cardiopulmonary bypass is initiated, ice is placed around the head, and cooling to l8°C is accomplished with systemic vasodilation employing milrinone to achieve homogeneous body temperature. Importantly, a minimum cooling duration of 20 to 30 minutes is used regardless of when the desired temperature is reached.
During this period the arch vessels and descending thoracic aorta are extensively mobilized. The aberrant RSCA is ligated and divided, and intercostal arteries are ligated with clips and divided to allow for a tension-free anastomosis. Care is taken to complete the dissection on the aorta without cautery to avoid left recurrent nerve injury. Head vessel snares are placed appropriately.
With cooling complete the ductal cannula is removed, the purse-string tied, and the ductus ligated. With brain and heart fully perfused, the descending thoracic aorta is clamped first, the ductus divided, and a second suture ligature of 6-0 polypropylene placed beyond the ductal tie. The ascending aorta is now cross-clamped very proximally, cardioplegia infused in the proximal ascending aorta (del Nido, 20 mL/kg), and regional cerebral perfusion commenced. Alternatively, cardioplegia can be delivered through a side port on the aortic cannula during a short period of circulatory arrest.
All residual ductal tissue is completely excised from the descending aorta, mindful that the origin of the LSCA is usually at the level of normal aortic tissue. An incision is made leftward in the ascending aorta and extended onto the LCCA and proximally onto the ascending aorta. A counterincision is made for 5 to 8 mm in the LSCA. The posterior aortic anastomosis is completed starting superiorly at the apex of the LSCA and the LCCA incisions and both corners turned with continuous 6-0 polypropylene ( Fig. 46.4 ). A cutback incision of 5 to 8 mm is now made anteriorly in the descending thoracic aorta. The corners are trimmed and the anastomoses augmented with a hemicone-shaped patch of pulmonary homograft or autologous treated pericardium ( Fig. 46.5 ). Upon completion of the arch anastomosis the descending clamp is removed first, followed by the LSCA, and lastly the LCCA for arch air evacuation. Cold reperfusion of the brain and body is now maintained for 3 to 5 minutes, and then full rewarming is begun.
