Surgical Approaches for Common Congenital Heart Diseases



Surgical Approaches for Common Congenital Heart Diseases


Timothy J. Pirolli

Ryan R. Davies

Camille L. Hancock Friesen

Robert D. B. Jaquiss



INTRODUCTION AND BACKGROUND

Congenital malformations of the cardiovascular system occur in approximately 1% of live births and are the most common type of birth defect.1 With advances in fetal imaging, an increasing fraction of congenital heart disease (CHD) cases are diagnosed in utero, and this is especially true for approximately 20% of CHD cases, which may require intervention in the first few months of life.2 For patients not diagnosed prenatally, the institution of mandatory screening of neonates by pulse oximetry has significantly increased the detection of cyanotic CHD cases in a timely fashion.3 The remainder of CHD cases are identified during the evaluation of a cardiac murmur, as part of the investigation of unexplained hypertension, during the screening of asymptomatic populations, or occasionally incidentally.

In the majority of cases, the etiology of CHD remains obscure, and only 20% to 30% of cases have an identifiable genetic cause.4 Copy number variants, single nucleotide variants, and aneuploidy have all been identified in patients with CHD. There are a few well-known examples of aneuploidy strongly associated with CHD, including Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), and Turner syndrome (45, X karyotype). As genetic analyses become more ubiquitous and sophisticated, it seems certain that many more genetic causes for CHD will be discovered.

Given the protean forms which CHD may take, the modes of presentation are not surprisingly widely varied. Perhaps, the most dramatic form of presentation is the neonate with systemic blood flow dependent on patency of the ductus arteriosus. If such patients are undiagnosed, normal ductal closure is associated with the rapid development of shock due to inadequate systemic blood flow. An example of such an anomaly is hypoplastic left heart syndrome (HLHS). In analogous fashion, patients with “ductal-dependent” pulmonary blood flow present with profound cyanosis as the ductus closes, as might be seen in a patient with tetralogy of Fallot (TOF) with severe pulmonary valve hypoplasia or atresia. Less urgent and dramatic manifestations of CHD are seen in children with large left-to-right shunts, such as a ventricular septal defect (VSD), who present with more subtle findings such as tachypnea and diaphoresis with feeding, and associated poor weight gain. Other patients have no signs or symptoms and may be detected when a chest radiograph or other diagnostic test is performed, and the cardiovascular anomaly is incidentally identified.

Regardless of the anomaly, the most common initial diagnostic modality is transthoracic echocardiography, which is quite frequently definitive in diagnosis and in guiding treatment. However, in a number of cases, anatomic and physiologic information derived from the echocardiogram may be augmented by cardiac catheterization, which permits accurate calculation of pulmonary and systemic resistances as well as the magnitude of any left-to-right or right-to-left shunt. In addition, direct measurement of intravascular or intracavitary pressures and gradients can be achieved at catheterization. Advanced three-dimensional imaging with cardiac computed tomography (CT) or cardiac magnetic resonance imaging (MRI) is increasingly undertaken and may facilitate “virtual reality” or three-dimensional printing to permit planning of patient-specific interventions.

The first definitive treatments for CHD were surgical and were accomplished without the use of cardiopulmonary bypass, which had not yet been invented. Beginning in the middle of the last century, surgeons developed techniques to effectively treat simple anomalies such as patent ductus arteriosus (PDA) and coarctation of the aorta.5,6 The next step was the provision of palliative operations to provide additional pulmonary blood flow to children with cyanotic heart disease.7 With Gibbons’ proof-of-concept with a practical cardiopulmonary bypass machine, the era of open-heart surgery began.8 In the ensuing decades, advances in care, equipment, and knowledge permitted surgical solutions for virtually any congenital cardiac malformation.9 More recently, sophisticated and less-invasive catheter-based solutions have been introduced and become standard of care, particularly for the “simpler” congenital malformations.

Because the spectrum of congenital heart disease is so broad and varied, well beyond the scope of this chapter, in the following sections, we will describe considerations relevant for three important forms of CHD. Each will exemplify an important physiologic abnormality: left-to-right shunting illustrated by VSD, cyanotic CHD as seen in TOF, and univentricular circulation as seen in HLHS. These discussions are of necessity somewhat condensed and simplified, and the interested reader is referred to any of a number of excellent textbooks in congenital cardiology and cardiac surgery.



VENTRICULAR SEPTAL DEFECTS


INTRODUCTION

Ventricular septal defects are the most common congenital cardiac defect, with the possible exception of bicuspid aortic valve, and manifest in a variety of sizes and locations in the ventricular septum. Isolated VSDs account for approximately 20% to 30% of all congenital cardiac defects and occur in approximately 1 to 2 per 1000 live births. VSDs are classified by their anatomic location and various classification schemes exist to describe the same anatomic defect. A recent international effort to create a unified classification scheme for VSD nomenclature has resulted in four major categories (perimembranous, inlet VSD, trabecular muscular, and outlet VSD) and various subcategories based on specific location and malalignment of adjacent structures (Table 93.1).10 However, this classification scheme has not been universally adopted, and thus it is critical to have a knowledge of the various synonyms to allow for familiarity. The relative location of each type of VSD is depicted in Figure 93.1.


Pathogenesis

The pathophysiology of a VSD is dependent upon the size of the defect and the relative ratio of the systemic vascular resistance (SVR) to the pulmonary vascular resistance (PVR). The left-to-right shunting of blood is the result of the higher-pressured left ventricle forcing blood through the VSD to the low-pressured right ventricle due to the increased SVR after birth. As the PVR continues to drop in the days and weeks after birth, there will be increased left-to-right shunting across the VSD. Conversely, the shunting may decrease as the size of the VSD becomes smaller with time.

There is no universally accepted classification scheme for VSD size. Clinically, VSDs are often labeled as “small,” “medium,” and “large.” These definitions are variable depending on the size of the patient, but typically in infants small VSDs are considered less than 4 mm in diameter, medium are 4 to 6 mm in diameter and large are greater than 6 mm in diameter.













The degree of shunting may be calculated by cardiac catheterization or MRI as pulmonic to systemic blood flow ratio (Qp:Qs). VSDs with a small shunt (Qp:Qs < 1.5:1) are considered the most common (>50% of VSDs). VSDs with a moderate shunt (Qp:Qs of 1.5-2.3:1) typically result in mild-moderately increased right ventricular and pulmonary arterial pressures, as well as signs and symptoms of congestive heart failure. Large defects (Qp:Qs > 2.3:1) have unrestrictive shunts with minimal pressure gradient between the two ventricles. This equalization (or near-equalization) of ventricular pressures can lead to left ventricular dilation and increased end-diastolic pressures, resulting in increased left atrial pressures, pulmonary venous pressures, and progressive symptoms of heart failure. Echocardiography can estimate the degree of shunting by measuring the pressure gradient across the VSD, but it does not give a precise Qp:Qs.


Clinical Features: Ventricular Septal Defect

The clinical presentation of a VSD is dependent upon the degree of shunting, the age of the patient, and associated congenital heart defects. The increased left-to-right shunting can result in pulmonary congestion from excessive circulation, leading to tachypnea. The increased demands on the left ventricle to maintain systemic cardiac output as blood is shunting across the VSD can lead to high-output failure and subsequent failure to thrive. Any increased demands for cardiac output (such as systemic illness, feeding, anemia, or other stressors on the body) can exacerbate this pathophysiology and associated symptoms.

Infants with moderate or larger VSDs may present with symptoms such as poor feeding, increased respiratory effort, poor weight gain, and tachycardia in the first month or two of life after PVR has declined. Smaller VSDs may be clinically silent until they are discovered later in life, even in adulthood. The discovery of an incidental murmur or symptoms from
increased aortic regurgitation, development of right ventricular outflow obstruction from hypertrophy of infundibular muscles or, rarely, endocarditis may be the inciting event for discovery of a VSD later in life.


Diagnosis: Ventricular Septal Defect

Cardiac auscultation will uncover a systolic murmur, which varies in intensity and location due to the size and anatomy of the VSD. Larger VSDs may also exhibit a diastolic rumble (due to increased flow across the mitral valve) or palpable thrill over the precordium. The initial workup for a VSD often includes the following studies:


Electrocardiogram

Findings on electrocardiogram (EKG) are variable and nonspecific for VSDs. Evidence of left ventricular hypertrophy (increased voltage in leads II, III, aVF, V5, and V6) may be manifested in larger defects due to increased left ventricular workload over time. Evidence of right ventricular hypertrophy (right axis deviation, dominant R wave in V1, dominant S wave in V5 or V6, and QRS duration <120 ms) may be evident in patients with increased PVR. Patients with small VSDs often have normal EKGs.


Chest X-Ray

Patients with small VSDs often have normal-appearing chest x-rays. Larger VSDs with increased left-to-right shunting may have increased vascular markings and cardiomegaly.


Echocardiography

Two-dimensional transthoracic echocardiography is the gold standard for diagnosis. A thorough echocardiogram is critical for identifying the location, size, and number of VSDs; assessing ventricular function; and diagnosing associated congenital heart lesions. Three-dimensional and transesophageal echocardiography may more clearly delineate the VSD anatomy, if warranted.


Other Studies

For well defined, isolated VSDs, further workup is typically not warranted. If there are specific anatomic concerns beyond the VSDs or if there is a need for more hemodynamic data, cardiac catheterization or cardiac MRI may be considered.


MANAGEMENT OF VSD


Medical Management

The goals of medical management of young patients diagnosed with VSDs are directed toward standard therapies for congestive heart failure and to minimize the risk of failure to thrive. Stressors for patients with significant shunts, such as viral infection, may result in acute worsening of symptoms. Frequent monitoring by the cardiologist is necessary to adjust medical regimens and to decide upon timing of surgery.


Timing of Surgery

There is no simple algorithm for timing of surgery for infants with VSDs. Patients with symptoms despite maximal medical therapy, such as frequent hospitalizations or failure to thrive, warrant referral to surgery. Patients with estimated pulmonary artery pressures greater than half-systemic or continued enlargement of left-sided cardiac structures likely warrant surgical closure of their VSD. Patients with smaller VSDs who are asymptomatic may be monitored for spontaneous closure. The presence of associated congenital defects, development of a double-chambered right ventricle, or worsening aortic insufficiency may also be indications for surgery. In patients with suprasystemic pulmonary hypertension, VSD closure is contraindicated.

In patients with unrepaired VSDs who survive until adulthood, pulmonary vascular disease may develop leading to right-to-left shunting (Eisenmenger syndrome) and cyanosis due to chronic elevations of pressure and flow across the VSD.11 These patients are typically inoperable. The American Heart Association (AHA)/American College of Cardiology (ACC) released an evidence based, expert consensus guideline algorithm for surgical closure of VSDs in adults (Algorithm 93.1).


Surgical Approach

Regardless of the location of the VSD, the standard approach for repair is via median sternotomy, although some surgeons may opt for a lower partial sternotomy or right thoracotomy. Patients are placed on cardiopulmonary bypass via bicaval cannulation, often with venting of the left heart via the right superior pulmonary vein. Mild to moderate systemic hypothermia is utilized. In rare circumstances, such as in very small infants, deep hypothermic circulatory arrest may be employed. Myocardial preservation is performed with a cardioplegic diastolic arrest of the heart with aortic cross-clamping. Caval snares are placed and secured to create as bloodless of a surgical field as possible. The options for visualization and approach to repair each type of VSD are dependent upon location and size of the defect(s).


Surgical Approach to Perimembranous VSD or Inlet VSD

With the proximity of the perimembranous or inlet (and many muscular) VSD to the tricuspid valve, the best approach is transatrial with visualization through the tricuspid valve. After the arrest of the heart, the right atrium is opened parallel to the atrioventricular groove. Knowledge of the anatomy within the right atrium is crucial to avoid injuring the conduction system during the repair (Figure 93.2).

With reflection of the anterior and septal leaflets of the tricuspid valve, the margins of the VSD are noted. Primary suture closure of VSDs is not recommended due to the risk of dehiscence, thus a patch of material of the surgeon’s choice (such as autologous pericardium, treated bovine pericardium, Dacron, Gore-Tex) must be cut to size. Occasionally, the septal tricuspid valve leaflet may need to be divided or detached from the annulus to visualize the edges of the defect. The patch is then secured to the rims of the VSD with a continuous or interrupted technique utilizing a polypropylene or small braided pledgeted suture, taking care to avoid injuring the aortic valve, tricuspid valve, and conduction system (Figure 93.3). Care
should be taken to weave around chordal tissue appropriately to avoid ensnaring the chords and creating tricuspid regurgitation. Often, sutures are passed through the tricuspid annulus and buttressed with pledgets or a strip of patch material. The superior aspect of the defect near the aortic valve is most vulnerable to leaving a residual defect. The conduction system follows a course along the inferior margin of a perimembranous or inlet VSD; thus, superficial bites (or bites 3-5 mm away from the margin of the defect) are critical to prevent heart block (Figure 93.3).12






After repair of the VSD, the tricuspid valve should be tested for insufficiency with insufflation of saline into the right ventricular cavity. Commissuroplasty sutures between the anterior and septal or septal and posterior leaflets may need to be placed to decrease tricuspid regurgitation. In rare cases, a right ventriculotomy may be required to visualize the entirety of the defect for closure.


Surgical Approach to Supracristal Ventricular Septal Defect

Due to the position of the supracristal VSD inferior to the pulmonary valve, the ideal approach is transpulmonary. Once the heart is arrested, a transverse (or longitudinal) incision is created in the main pulmonary artery, taking care not to injure the pulmonary valve leaflets. Retraction of the leaflets laterally exposes the edges of the defect. The aortic valve may be visible through the VSD (and may prolapse through the defect) and care must be taken to avoid injuring the aortic valve with the suture needle during closure. As mentioned, patch material includes fresh (or glutaraldehyde treated) autologous pericardium, a modified
bovine pericardium, or a synthetic patch material such as Dacron. However, a Dacron patch should be avoided in this scenario as the Dacron may heal to the ventricular aspect of the pulmonary valve leaflets, resulting in pulmonary insufficiency. The patch is secured to the inferior margin of the defect with a continuous or interrupted technique until the pulmonary valve leaflets are encountered. Then, sutures must be passed through the base of the leaflets, taking care not to injure the pulmonary valve or the adjacent aortic valve. Sutures are passed through the patch and secured (Figure 93.4).13












Surgical Approach to Muscular Ventricular Septal Defects (Including Interventional)

Many muscular VSDs may be repaired via the transatrial approach as described earlier. In select cases of large apical muscular defects, a right ventriculotomy may be necessary to close the defect. Select muscular VSDs may also be closed in the catheterization laboratory or in the operating room via a hybrid technique with a transcatheter technique.

Transcatheter closure of VSDs was first reported in 1988 and advancement in the technology has allowed for expanded
use since that time. Although this topic is beyond the scope of this section, it should be noted that transcatheter closure of congenital perimembranous and muscular VSDs has been reported with improving outcomes. Risks of this procedure include conduction abnormalities, residual shunt, aortic valve distortion, hemolysis, device embolization, and endocarditis.14






For young patients with multiple, typically muscular, VSDs (known as a “swiss-cheese” ventricular septum), repair may be unfeasible. Placement of a pulmonary artery band to limit left-to-right shunting and minimize congestive heart failure may be the first-line treatment to allow for growth and future decision-making.


SURGICAL RESULTS

Surgical closure of isolated VSDs carries a less than 1% mortality risk according to the Society of Thoracic Surgeons (STS) Congenital Heart Surgery Database.15 Complete heart block occurs in 1% to 3% of patients but is increasingly rare for repair of isolated VSDs. Due to the common use of intraoperative transesophageal echocardiogram, significant residual VSDs (>3 mm) that require re-operation are rare. Small residual VSDs are well-tolerated and often close on their own with time.16 There is a small risk of development of a double-chambered right ventricle in patients with a small residual VSD postoperatively, although the frequency of this is unknown.


FOLLOW-UP PATIENT CARE

For patients with repaired VSDs, the need for any additional or ongoing medical or surgical intervention is extraordinarily unlikely. Early routine postoperative follow-up is necessary, but once through the acute convalescence, a patient with repaired VSD should not require an additional intervention. Antibiotic prophylaxis for infective endocarditis is recommended for patients with residual shunts after VSD repair.


FUTURE DIRECTIONS

Surgical closure of VSDs is the gold standard for therapy. Some surgeons advocate for the utilization of smaller incisions (ie, ministernotomy, right thoracotomy, video-assisted thoracoscopic surgery) for surgical repair with comparable results. The expanded role of transcatheter (or hybrid) closure of VSDs continues to be explored, despite higher rates of heart block.


TETRALOGY OF FALLOT


INTRODUCTION

Cyanotic heart lesions have been classically taught in medical school as the four “T’s”; transposition of the great arteries, truncus arteriosus, total anomalous pulmonary venous return, and TOF. Of these, TOF is by far the most common. TOF spans a wide range of physiology, clinical presentation, and management. One thing, all TOF patients share is the ongoing hazard for morbidity and mortality, making it one of the complex congenital cardiac pathologies that mandate life-long surveillance.17 Management and timing of intervention in TOF depends on which end of the pathophysiologic spectrum the patient lies and the philosophical approach to neonatal management chosen by the heart program, which is caring for the child. The mild end of the spectrum, which is sometimes referred to as a “pink TOF,” is one in which the VSD is the dominant feature, and there is minimal right ventricular outflow obstruction. The other end of the spectrum, or “blue TOF,” is composed of infants with right ventricular outflow tract obstruction as the dominant manifestation. At the “blue” end of the spectrum, patients may have such compromised antegrade pulmonary blood flow that the infant presents with symptomatic hypoxic crisis in the neonatal period as the PDA constricts and antegrade pulmonary blood flow proves insufficient. Cyanosis may also evolve over time from very mild to more severe as right ventricular outflow tract obstruction progresses. This progressive cyanosis occurs when there is sufficient obstruction to beget a vicious cycle of progressive right ventricular hypertrophy followed by increased outflow tract obstruction and reduced pulmonary blood flow.

Only gold members can continue reading. Log In or Register to continue

May 8, 2022 | Posted by in CARDIOLOGY | Comments Off on Surgical Approaches for Common Congenital Heart Diseases
Premium Wordpress Themes by UFO Themes