PRINCIPLES OF MANAGEMENT OF THE NEONATE WITH CONGENITAL HEART DISEASE

P. SYAMASUNDAR RAO, MD

Introduction

In Chapter 10, an approach to the diagnosis of cyanotic neonate was presented. After the diagnosis of cardiac disease is suspected, a thorough echo-Doppler study should be carried out and the diagnosis is established, as detailed in Chapter 11. In rare instances when a given abnormality cannot be completely defined by echo-Doppler studies, computed tomography (CT) or magnetic resonance imaging (MRI) may become useful in resolving such issues and these techniques were discussed in Chapter 12. Cardiac catheterization and selective cineangiography are seldom necessary for making a diagnosis in the neonate and, therefore, will not be examined in this book. In this chapter, principles of management of congenital heart disease (CHD) in the newborn infants will be reviewed.

General Treatment Measures

Throughout the course of recognition, transfer to a tertiary care facility and investigational studies, avoidance of hypothermia, preservation of neutral thermal environment, scrutinizing for and timely treatment of hypoglycemia and hypocalcemia, watching for acid–base status, treatment of metabolic acidosis with sodium bicarbonate (NaHCO₃), and addressing respiratory acidosis with suction, intubation and assisted ventilation as judged essential are imperative and should be carried out. In babies with cyanotic CHD, 30% to 40% O₂ is adequate, and 100% O₂ is not essential. In the neonates with hypoplastic left heart syndrome (HLHS) no more than 21% O₂ (room air) should be administered. If ductal-dependent CHD is suspected, administration of intravenous prostaglandin E₁ (PGE₁) should be initiated while waiting for confirmation of the diagnosis.

Treatment of Cyanosis

As mentioned above no more than 30% to 40% humidified O₂ is needed because the hypoxemia is due to fixed intracardiac right-to-left shunting in cyanotic CHD. Metabolic acidosis (pH < 7.25), if present, should be taken care of. If there is striking hypercarbia (PaCO₂ > 60 torr) or respiratory depression, intubation and mechanical ventilation are necessary.

In neonates with severe right ventricular outflow tract (RVOT) obstruction, the pulmonary blood flow (PBF) is likely to be dependent upon the ductus arteriosus (DA). The ductus may be kept patent by intravenous PGE₁ infusion. Different cardiac lesions which are ductal flow dependent are shown in Table 13.1. The present recommendations for administration of PGE₁ are 0.05 to 0.1 mcg/kg/min intravenously. If PGE₁ is administered early in the neonatal period, it is effective; the earlier in life it is begun the better is ductal dilatation. A small ductus may be made to open up with PGE₁, but an already closed ductus may not be easy to reopen. Adverse effects include apnea, hyperthermia, flushing and muscular twitching. The side effects have not created significant problems, but development of apnea is of concern and should be watched for. We usually begin PGE₁ at the suggested dose of 0.05 to 0.1 mcg/kg/min, but will quickly decrease the dosage to 0.02 to 0.03 mcg/kg/min once the oxygen saturations improve. This may avoid the need for endotracheal ventilation because of apnea.

Table 13.1. Ductal-dependent cardiac defects

If the cause of cyanosis is persistent fetal circulation, it should be managed accordingly (see Chapter 16). Further management of cyanosis is based on specific cause of hypoxemia and will be reviewed hereunder.

Treatment of Congestive Heart Failure (CHF)

The management of CHF, including inotropic agents, diuretics and afterload reducing agents is similar to that of older children¹ and will not be detailed here except to state that the neonatal myocardial development is incomplete^2,3 and that the myocardial response to inotropic agents and preload and afterload therapy is less than optimal.

Administration of PGE₁ to the newborn with heart failure in the setting of ductal-dependent perfusion to lower part of the body (Table 13.1B) is of particular importance. The prescribed amount of PGE₁ infusion is similar that described in the preceding section.

Specific Measures

The treatment instituted is largely dependent upon the precise physiologic and/or anatomic abnormality that the baby is known to have. These are classified into physiologic and anatomic disturbances, although there is substantial overlap.

Physiologic

The type of treatment is dependent on the hemodynamic abnormality produced by the CHD itself along with the associated cardiac anomalies, and may be discussed under the following categories: decreased pulmonary flow, increased pulmonary flow, poor mixing and intracardiac obstruction.

Decreased PBF     If the PBF is diminished secondary to RVOT obstruction (Table 13.1A), the blood flow may be increased at first with administration of intravenous PGE₁, as described in the prior section. But, the effectiveness of maintaining the ductus patent with PGE₁ is short-lived (days to weeks). The sensitivity of ductal musculature to PGE₁ declines as the baby ages. Consequently, a more permanent method of augmenting pulmonary flow, mostly by surgery, should be pursued. PBF may be augmented by construction of aortopulmonary shunts by surgery. Blalock and Taussig⁴ initially described anastomosis of subclavian artery to ipsilateral pulmonary artery (PA) in 1945. A number of other procedures were subsequently devised to improve PBF and these are descending aorta-to-left PA anastomosis (Potts shunt), ascending aorta-to-right PA anastomosis (Waterston–Cooley shunt), central aortopulmonary Gore-Tex shunt, Gore-Tex interposition graft between the subclavian artery and the PA on the same side (modified Blalock–Taussig [BT] shunt), superior vena cava-to-right PA anastomosis, end-to-end (Glenn shunt), formalin infiltration of the wall of DA and placement of stent into the DA.

Modified BT shunt described by de Leval et al⁵ with an interposition Gore-Tex tube graft between the subclavian artery and the ipsilateral PA is preferred by most surgeons, although some surgeons use central aortopulmonary Gore-Tex graft shunts.

In some babies, though rare, the predominant obstruction is severe pulmonary valve (PV) stenosis. In such infants balloon pulmonary valvuloplasty⁶ may be useful in increasing the PBF. In neonates with atresia of the PV, perforation of the valve^7–10 followed by balloon valvuloplasty may be performed. Stent may be implanted within the ductus arteriosus^10,11 and some groups of workers¹² have successfully used this technique to augment PBF. While this is an attractive nonsurgical alternative, because of limited experience and highly intensive nature of the procedure, most teams caring for the neonate with CHD do not currently choose stenting as a first-line therapeutic choice.

In summary, there are many palliative procedures available to increase PBF in the newborn; however, modified BT shunt appears to be the procedure of choice in the majority of babies with complex CHD associated with severe RVOT obstruction causing decreased PBF.

Increased PBF     Increased PBF and CHF can occur in babies with large interventricular communications; however, because of high pulmonary vascular resistance (PVR) of the neonate, it may take days to weeks before large shunts develop. While CHF can happen with simple ventricular septal defects (VSDs), it is more common with complex CHDs (Table 13.2). At first, optimal anticongestive treatment should be initiated. If the systemic circulation is ductal dependent (see Table 13.1B), infusion of PGE₁ should be set up as discussed in the prior sections.

Table 13.2. Complex neonatal heart defects* requiring pulmonary artery banding

Simple VSDs are repaired under cardiopulmonary bypass and/or deep hypothermia. However, complex CHDs, such as Swiss-cheese type of VSDs, double-inlet left ventricle (DILV) (single ventricle), double-outlet right ventricle (DORV), tricuspid atresia with a large VSD and other complicated CHDs, all without pulmonary stenosis, are not amenable to total surgical correction in the neonatal period. In such situations, banding of the PA¹³ by surgical constriction is used; banding not only helps recovery from CHF but also facilitates attaining normal PA pressure. In the subgroup of patients amenable for total surgical correction, surgery can be performed later. In the subgroup of patients who have single-ventricle physiology, bidirectional Glenn and Fontan procedures can be performed later. If there is associated coarctation of the aorta (CoA), the aortic obstruction must also be addressed at the time of banding of the PA.

Poor mixing     In babies with transposed great vessels, poor mixing between systemic and pulmonary circuits can occur; management will be discussed in section dealing with transposition of the great arteries (TGA).

Intracardiac obstruction     Such obstructions may occur at the level of patent foramen ovale (PFO) and VSD.

Interatrial obstruction     Entire systemic or pulmonary venous return must pass through the PFO in babies with atresia of the atrioventricular and/or semilunar valves and total anomalous pulmonary venous connection (TAPVC). These defects are listed in Table 13.3. There is a tendency for the PFO to remain open because of persistence of fetal flow patterns; however, sometimes the PFO becomes obstructive. Evidence for obstructed PFO may be present in the form of systemic or pulmonary venous congestion, as the case may be, and is confirmed by small-sized PFO by 2-dimensional (2D) echo and high-velocity flow across it by Doppler. The PFO may be enlarged by balloon atrial septostomy.¹⁴ Such a procedure is usually successful, especially in the early neonatal period, because the lower margin of the PFO (septum primum) is thin and frail and can be torn by balloon septostomy. When PFO obstruction develops during the later part of neonatal period or in older infants, balloon atrial septostomy is unlikely to be successful, and in such situations alternative methods such as blade atrial septostomy,¹⁵ static balloon dilatation^16,17 or stent placement^18,19 may have to be used to accomplish relief of interatrial obstruction. If transcatheter methods are not feasible or not successful, surgical atrial septectomy is necessary. If there is no PFO and the atrial septum is intact, the atrial septum may be perforated either by Brockenbrough technique²⁰ or radiofrequency ablation²¹; this should be followed by static dilatation^16,17 or stent placement across the atrial septum.^18,19 For detailed discussion of these transcatheter techniques, the reader is referred to chapters on the role of interventional cardiology in the neonate (Chapter 19).

Table 13.3. Interatrial obstruction

Interventricular obstruction     In some complex cardiac defects such as tricuspid atresia, DILV, and double-outlet right (or left) ventricle, the VSD or bulboventricular foramen, as the case may be, is very small and obstructive at presentation in the neonatal period or spontaneously closes with time.22–25 Such closures cause subpulmonary obstruction, producing reduced PBF, or subaortic narrowing resulting in obstruction to systemic blood flow (SBF) (Table 13.4). If such closure produces diminished PBF, the management is same as that described in the Decreased PBF section (PGE₁ and modified BT shunt). If the VSD/bulboventricular foramen closure results in obstruction to systemic flow, the narrowing should be relieved by directly enlarging the VSD, or the obstruction may be bypassed by Damus–Kaye–Stansel procedure (anastomosis of the proximal stump of the divided PA to the ascending aorta directly or via a prosthetic conduct).^23,26 However, it should be noted that development of significant interventricular obstruction that requires intervention in the neonate is infrequent.

Table 13.4. Interventricular obstruction

Treatment of different cardiac defects is principally related to the anatomic anomaly. Some of the CHDs are only amenable to palliation, and such palliative management was discussed in the above section. Other defects can be repaired and should receive corrective treatment either with surgical or transcatheter methodology, as deemed suitable. These will be briefly reviewed herein. First, the 5Ts—the most common cyanotic CHDs—will be discussed, followed by others; the order of presentation is random and is not based on importance or frequency. For detailed discussion of each individual defect, the reader is referred to Chapters 28 to 41.

TGA     In TGA, the right ventricle (RV) gives rise to the aorta and the LV gives origin to the PA.²⁷ As a result, these babies have parallel circulations instead of a normal in-series circulation. At birth, some intercirculatory mixing across the fetal circulatory pathways, namely, PFO and patent ductus arteriosus (PDA) may provide adequate oxygenation, but the PFO and PDA tend to close spontaneously, with resultant cyanosis and hypoxemia. At first, PGE₁ should be administered (as per the doses given in the preceding sections) to open the PDA and to encourage intercirculatory mixing. If this does not provide adequate oxygen saturation, Rashkind balloon atrial septostomy^14,28 should be performed to improve oxygen saturation while waiting for corrective surgery. In the past, venous switch procedures such as Senning or Mustard between 3 and 6 months of age were used to treat TGA. At present, however, the recommended procedure is arterial switch (Jatene) operation.²⁹ This procedure is performed around one week of age. In this surgery, the aorta and PA are switched and the coronary arteries are moved to the neoaorta, all under cardiopulmonary bypass.

Tetralogy of Fallot (TOF)     TOF consists of 4 abnormalities³⁰: (1) pulmonary stenosis (PS); (2) VSD; (3) right ventricular hypertrophy and (4) dextroposition of the aorta. If TOF babies are acyanotic or have oxygen saturations in the low 80s, they do not require intervention in the neonatal period. Elective surgery between the ages of 6 and 12 months should suffice. If there is significant cyanosis and hypoxemia, surgical correction with closure of VSD and relief of PS may be performed. In the presence of pulmonary atresia, hypoplasia of the PV annulus or arteries, smallish left ventricle (LV), or anomalous course of the coronary artery, total surgical correction may not be feasible in the neonatal period. In these babies, palliation with a modified BT shunt⁵ may be performed. Some babies may be severely hypoxemic and may be dependent on ductal flow; in such babies, PGE₁ should be administered promptly. In rare instances, the predominant obstruction is at the PV level; in these babies, balloon pulmonary valvuloplasty^6,31,32 may be used as an alternative to BT shunt.

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