Cardiovascular Dysfunction

Chapter 42


Cardiovascular Dysfunction


Marilyn J. Hockenberry




Cardiovascular Dysfunction


Cardiovascular disorders in children are divided into two major groups—congenital heart disease and acquired heart disorders. Congenital heart disease (CHD) includes primarily anatomic abnormalities present at birth that result in abnormal cardiac function. The clinical consequences of congenital heart defects fall into two broad categories—heart failure (HF) and hypoxemia. Acquired cardiac disorders are disease processes or abnormalities that occur after birth and can be seen in the normal heart or in the presence of congenital heart defects. They result from various factors, including infection, autoimmune responses, environmental factors, and familial tendencies. The pathophysiology review found in Fig. 42-1 describes the flow of blood through the heart.




History and Physical Examination


Taking an accurate health history is an important first step in assessing an infant or child for possible heart disease. Parents may have specific concerns, such as an infant with poor feeding or fast breathing or a 7-year-old who can no longer keep up with friends on the soccer field. Others may not realize that their child has a medical problem because their baby has always been pale and fussy.


Asking details about the mother’s health history, pregnancy, and birth history is important in assessing infants. Mothers with chronic health conditions, such as diabetes or lupus, are more likely to have infants with heart disease. Some medications, such as phenytoin (Dilantin), are teratogenic to fetuses. Maternal alcohol use or illicit drug use increases the risk for congenital heart defects. Exposures to infections, such as rubella, early in pregnancy may result in congenital anomalies. Infants with low birth weight resulting from intrauterine growth restriction are more likely to have congenital anomalies. High-birth-weight infants have an increased incidence of heart disease.


A detailed family history is also important. There is an increased incidence of congenital cardiac defects if either parent or a sibling has a heart defect. Some diseases, such as Marfan syndrome, and some cardiomyopathies are hereditary. A family history of frequent fetal loss, sudden infant death, and sudden death in adults may indicate heart disease. Congenital heart defects are seen in many syndromes such as Down and Turner syndromes.


The physical assessment of suspected cardiac disease begins with observation of general appearance and then proceeds with more specific observations. The following are supplementary to the general assessment techniques described for physical examination of the chest and heart in Chapter 29:






Diagnostic Evaluation


A variety of invasive and noninvasive tests may be used in the diagnosis of heart disease. Some of the more common diagnostic tools that require nursing assessment and intervention are described here.



Electrocardiogram


Bedside cardiac monitoring with the electrocardiogram (ECG) is commonly used in pediatrics, especially in the care of children with heart disease. The bedside monitor provides valuable information about heart rate and rhythm through a graphic display of the ECG tracing and a digital display. An alarm can be set with parameters for individual patient requirements and will sound if the heart rate is above or below the set parameters. Gelfoam electrodes are commonly placed on the right side of the chest (above the level of the heart) and on the left side of the chest, and a ground electrode is placed on the abdomen. Electrodes should be changed every 1 or 2 days because they irritate the skin. Bedside monitors are an adjunct to patient care and should never be substituted for direct assessment and auscultation of heart sounds. The nurse should assess the patient, not the monitor.




Echocardiography


Echocardiography is one of the most frequently used tests for detecting cardiac dysfunction in children. Recent improvements in echocardiographic techniques have made it increasingly possible to confirm the diagnosis without resorting to cardiac catheterization. In more and more cases, a prenatal diagnosis of CHD can be made by fetal echocardiography.


Echocardiography involves the use of ultra-high-frequency sound waves to produce an image of the heart’s structure. A transducer placed directly on the chest wall delivers repetitive pulses of ultrasound and processes the returned signals (echoes).


Although the test is noninvasive, painless, and associated with no known side effects, it can be stressful for children. The child must lie quietly in the standard echocardiographic positions; crying, nursing, or sitting up often leads to diagnostic errors or omissions. Therefore infants and young children may need a mild sedative; older children benefit from psychologic preparation for the test. The distraction of a video or movie is often helpful.



Cardiac Catheterization


Cardiac catheterization is an invasive diagnostic procedure in which a radiopaque catheter is inserted through a peripheral blood vessel into the heart. The catheter is usually introduced through percutaneous technique, in which the catheter is threaded through a large-bore needle that is inserted into the vein. The catheter is guided through the heart with the aid of fluoroscopy. After the tip of the catheter is within a heart chamber, contrast material is injected and films are taken of the dilution and circulation of the material (angiography). Types of cardiac catheterizations include:



Diagnostic catheterizations—These studies are used to diagnose congenital cardiac defects, particularly in symptomatic infants and before surgical repair. They are divided into (1) right-sided catheterizations, in which the catheter is introduced through a vein (usually the femoral vein) and threaded to the right atrium (most common); and (2) left-sided catheterizations, in which the catheter is threaded through an artery into the aorta and into the heart.


Interventional catheterizations (therapeutic catheterizations)—A balloon catheter or other device is used to alter the cardiac anatomy. Examples include dilating stenotic valves or vessels or closing abnormal connections.


Electrophysiology studies—Catheters with tiny electrodes that record the impulses of the heart directly from the conduction system are used to evaluate dysrhythmias and sometimes destroy accessory pathways that cause some tachydysrhythmias.



Care Management


Cardiac catheterization has become a routine diagnostic procedure and may be done on an outpatient basis. However, it is not without risks, especially in neonates and seriously ill infants and children. Possible complications include acute hemorrhage from the entry site (more likely with interventional procedures because larger catheters are used), low-grade fever, nausea, vomiting, loss of pulse in the catheterized extremity (usually transient, resulting from a clot, hematoma, or intimal tear), and transient dysrhythmias (generally catheter induced) (Uzark, 2001). Rare risks include stroke, seizures, tamponade, and death.




Preprocedural Care


A complete nursing assessment is necessary to ensure a safe procedure with minimum complications. This assessment should include accurate height (essential for correct catheter selection) and weight. Obtaining a history of allergic reactions is important because some of the contrast agents are iodine based. Specific attention to signs and symptoms of infection is crucial. Severe diaper rash may be a reason to cancel the procedure if femoral access is required. Because assessment of pedal pulses is important after catheterization, the nurse should assess and mark the pulses (dorsalis pedis, posterior tibial) before the child goes to the catheterization room. The presence and quality of pulses in both feet are clearly documented. Baseline oxygen saturation using pulse oximetry in children with cyanosis is also recorded.


Preparing the child and family for the procedure is the joint responsibility of the patient care team. School-age children and adolescents benefit from a description of the catheterization laboratory and a chronologic explanation of the procedure, emphasizing what they will see, feel, and hear. Older children and adolescents may bring earphones and favorite music so they can listen during the catheterization procedure. Preparation materials such as picture books, videotapes, or tours of the catheterization laboratory may be helpful. Preparation should be geared to the child’s developmental level. The child’s caregivers often benefit from the same explanations. Additional information, such as the expected length of the catheterization, description of the child’s appearance after catheterization, and usual postprocedure care, should be outlined. (See also Prepare the Child and Family for Invasive Procedures, p. 1341.)


Methods of sedation vary among institutions and may include oral or intravenous (IV) medications. The child’s age, heart defect, clinical status, and type of catheterization procedure planned are considered when sedation is determined. General anesthesia may be needed for some interventional procedures. Children are allowed nothing by mouth (NPO) for 4 to 6 hours or more before the procedure according to institutional guidelines. Infants and patients with polycythemia may need IV fluids to prevent dehydration and hypoglycemia.



Postprocedural Care


Patients may recover from the procedure in a recovery unit, their hospital room, or, occasionally, an intensive care unit (ICU). Patients are placed on a cardiac monitor and a pulse oximeter for the first few hours of recovery. The most important nursing responsibility is observation of the following for signs of complications:



• Pulses, especially below the catheterization site, for equality and symmetry (Pulse distal to the site may be weaker for the first few hours after catheterization but should gradually increase in strength.)


• Temperature and color of the affected extremity, because coolness or blanching may indicate arterial obstruction


• Vital signs, which are taken as frequently as every 15 minutes, with special emphasis on heart rate, which is counted for 1 full minute for evidence of dysrhythmias or bradycardia


• Blood pressure (BP), especially for hypotension, which may indicate hemorrhage from cardiac perforation or bleeding at the site of initial catheterization


• Dressing, for evidence of bleeding or hematoma formation in the femoral or antecubital area


• Fluid intake, both IV and oral, to ensure adequate hydration (Blood loss in the catheterization laboratory, the child’s NPO status, and diuretic actions of dyes used during the procedure put children at risk for hypovolemia and dehydration.)


• Blood glucose levels, for hypoglycemia, especially in infants, who should receive dextrose-containing IV fluids



Depending on hospital policy, the child may be kept in bed with the affected extremity maintained straight for 4 to 6 hours after venous catheterization and 6 to 8 hours after arterial catheterization to facilitate healing of the cannulated vessel. If younger children have difficulty complying, they can be held in the parent’s lap with the leg maintained in the correct position. The child’s usual diet can be resumed as soon as tolerated, beginning with sips of clear liquids and advancing as the condition allows. The child is encouraged to void to clear the contrast material from the blood. Generally, there is only slight discomfort at the percutaneous site. To prevent infection, the catheterization area is protected from possible contamination. If the child wears diapers, the dressing can be kept dry by covering it with a piece of plastic film and sealing the edges of the film to the skin with tape. However, the nurse must be careful to continue observing the site for any evidence of bleeding (see Family-Centered Care box and Critical Thinking Case Study).





Congenital Heart Disease


The incidence of CHD in children is approximately 5 to 8 per 1000 live births (Park, 2008). About 2 or 3 in 1000 infants will be symptomatic during the first year of life with significant heart disease that requires treatment (Hoffman and Kaplan, 2002). CHD is the major cause of death (other than prematurity) in the first year of life. Although there are more than 35 well-recognized cardiac defects, the most common heart anomaly is ventricular septal defect (VSD).


The exact cause of most congenital cardiac defects is unknown. Most are thought to be a result of multiple factors, including a complex interaction of genetic and environmental influences. Some risk factors are known to be associated with increased incidence of congenital heart defects. Maternal risk factors include chronic illnesses such as diabetes or poorly controlled phenylketonuria, alcohol consumption, and exposure to environmental toxins and infections. Family history of a cardiac defect in a parent or sibling increases the likelihood of a cardiac anomaly. The risk for CHD increases if a first-degree relative (parent or sibling) is affected. The familial risk is higher with left-sided obstructive lesions.


Congenital heart anomalies are often associated with chromosomal abnormalities, specific syndromes, or congenital defects in other body systems. Down syndrome (trisomy 21) and trisomies 13 and 18 are highly correlated with congenital heart defects. Syndromes associated with heart defects include DiGeorge syndrome, a syndrome characterized by deletion of part of chromosome 22q11 (interrupted aortic arch, truncus arteriosus, tetralogy of Fallot, and posterior malaligned VSDs), Noonan syndrome (pulmonic valve anomalies and cardiomyopathy), Williams syndrome (aortic and pulmonic stenosis), and Holt-Oram syndrome (upper limb anomalies and atrial septal defect [ASD]). Extracardiac defects such as tracheoesophageal fistula, renal abnormalities, and diaphragmatic hernia are seen in association with heart anomalies.



Altered Hemodynamics


To appreciate the physiology of heart defects, it is necessary to understand the role of pressure gradients, flow, and resistance within the circulation. As blood is pumped through the heart, it (1) flows from an area of high pressure to one of low pressure and (2) takes the path of least resistance. In general, the higher the pressure gradient, the faster the rate of flow; the higher the resistance, the slower the rate of flow.


Normally, the pressure on the right side of the heart is lower than that on the left side and the resistance in the pulmonary circulation is less than that in the systemic circulation. Vessels entering or exiting these chambers have corresponding pressures. Therefore, if an abnormal connection exists between the heart chambers (e.g., a septal defect), blood will necessarily flow from an area of higher pressure (left side) to one of lower pressure (right side). Such a flow of blood is termed a left-to-right shunt. Anomalies resulting in cyanosis may result from a change in pressure so that the blood is shunted from the right to the left side of the heart (right-to-left shunt) because of either increased pulmonary vascular resistance or obstruction to blood flow through the pulmonic valve and artery. Cyanosis may also result from a defect that allows mixing of oxygenated and deoxygenated blood within the heart chambers or great arteries, such as occurs in truncus arteriosus.



Classification of Defects


There are typically two classification systems used to categorize congenital heart defects. Traditionally, cyanosis, a physical characteristic, has been used as the distinguishing feature, dividing anomalies into acyanotic defects and cyanotic defects (Fig. 42-2). In clinical practice, this system is problematic because children with acyanotic defects may develop cyanosis. Also, more often, those with cyanotic defects may appear pink and have more clinical signs of HF.



A more useful classification system is based on hemodynamic characteristics (blood flow patterns within the heart). These blood flow patterns are (1) increased pulmonary blood flow; (2) decreased pulmonary blood flow; (3) obstruction to blood flow out of the heart; and (4) mixed blood flow, in which saturated and desaturated blood mix within the heart or great arteries. As a comparison, Fig. 42-3 outlines both classification systems. With the hemodynamic classification system, the clinical manifestations of each group are more uniform and predictable. Defects that allow blood flow from the higher-pressure left side of the heart to the lower-pressure right side (left-to-right shunt) result in increased pulmonary blood flow and cause heart failure (HF). Obstructive defects impede blood flow out of the ventricles; whereas obstruction on the left side of the heart results in HF, severe obstruction on the right side causes cyanosis. Defects that cause decreased pulmonary blood flow result in cyanosis. Mixed lesions present a variable clinical picture based on the degree of mixing and amount of pulmonary blood flow; hypoxemia (with or without cyanosis) and HF usually occur together. Using this classification system, the clinical presentation and management of the most common defects are outlined in the following sections and Box 42-1.



Box 42-1   Defects with Increased Pulmonary Blood Flow



Atrial Septal Defect


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Description—Abnormal opening between the atria, allowing blood from the higher-pressure left atrium to flow into the lower-pressure right atrium. There are three types of ASD:



Pathophysiology—Because left atrial pressure slightly exceeds right atrial pressure, blood flows from the left to the right atrium, causing an increased flow of oxygenated blood into the right side of the heart. Despite the low pressure difference, a high rate of flow can still occur because of low pulmonary vascular resistance and the greater distensibility of the right atrium, which further reduces flow resistance. This volume is well tolerated by the right ventricle because it is delivered under much lower pressure than with a VSD. Although there is right atrial and ventricular enlargement, cardiac failure is unusual in an uncomplicated ASD. Pulmonary vascular changes usually occur only after several decades if the defect is left unrepaired.


Clinical manifestations—Patients may be asymptomatic. They may develop HF. There is a characteristic systolic murmur with a fixed split second heart sound. There may also be a diastolic murmur. Patients are at risk for atrial dysrhythmias (probably caused by atrial enlargement and stretching of conduction fibers) and pulmonary vascular obstructive disease and emboli formation later in life from chronically increased pulmonary blood flow.


Surgical treatment—Surgical patch closure (pericardial patch or Dacron patch) is done for moderate to large defects. Open repair with cardiopulmonary bypass is usually performed before school age. In addition, the sinus venosus defect requires patch placement, so the anomalous right pulmonary venous return is directed to the left atrium with a baffle. ASD 1 type may require mitral valve repair or, rarely, replacement of the mitral valve.


Nonsurgical treatment—ASD 2 closure with a device during cardiac catheterization is becoming commonplace and can be done as an outpatient procedure. The Amplatzer Septal Occluder is most commonly used. Smaller defects that have a rim around them for attachment of the device can be closed with a device; large, irregular defects without a rim require surgical closure. Successful closure in appropriately selected patients yields results similar to those from surgery but involves shorter hospital stays and fewer complications. Patients receive low-dose aspirin for 6 months (Rome and Kreutzer, 2004).


Prognosis—Operative mortality is very low (<1%).



Ventricular Septal Defect


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Description—Abnormal opening between the right and left ventricles. May be classified according to location: membranous (accounting for 80%); or muscular. May vary in size from a small pinhole to absence of the septum, which results in a common ventricle. VSDs are frequently associated with other defects, such as pulmonary stenosis, transposition of the great vessels, PDA, atrial defects, and COA. Many VSDs (20%-60%) close spontaneously. Spontaneous closure is most likely to occur during the first year of life in children having small or moderate defects. A left-to-right shunt is caused by the flow of blood from the higher-pressure left ventricle to the lower-pressure right ventricle.


Pathophysiology—Because of the higher pressure within the left ventricle and because the systemic arterial circulation offers more resistance than the pulmonary circulation, blood flows through the defect into the pulmonary artery. The increased blood volume is pumped into the lungs, which may eventually result in increased pulmonary vascular resistance. Increased pressure in the right ventricle as a result of left-to-right shunting and pulmonary resistance causes the muscle to hypertrophy. If the right ventricle is unable to accommodate the increased workload, the right atrium may also enlarge as it attempts to overcome the resistance offered by incomplete right ventricular emptying.


Clinical manifestations—HF is common. There is a characteristic loud holosystolic murmur heard best at the left sternal border. Patients are at risk for BE and pulmonary vascular obstructive disease.


Surgical Treatment



Nonsurgical treatment—Device closure during cardiac catheterization is being performed in some centers under investigational protocols. One device has been approved for closure of muscular defects, and another is in clinical trials. Early results are encouraging, with successful defect closure and few complications (Rome and Kreutzer, 2004).


Prognosis—Risks depend on the location of the defect, the number of defects, and the presence of other associated cardiac defects. Single-membranous defects are associated with low mortality (<2%); multiple muscular defects can carry a higher risk (Jacobs, Mavroudis, Jacobs, et al., 2004).



Atrioventricular Canal Defect


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Description—Incomplete fusion of the endocardial cushions. Consists of a low ASD that is continuous with a high VSD and clefts of the mitral and tricuspid valves, which create a large central AV valve that allows blood to flow between all four chambers of the heart. The directions and pathways of flow are determined by pulmonary and systemic resistance, left and right ventricular pressures, and the compliance of each chamber, although flow is generally from left to right. It is the most common cardiac defect in children with Down syndrome.


Pathophysiology—The alterations in hemodynamics depend on the severity of the defect and the child’s pulmonary vascular resistance. Immediately after birth, while the newborn’s pulmonary vascular resistance is high, there is minimum shunting of blood through the defect. When this resistance falls, left-to-right shunting occurs and pulmonary blood flow increases. The resultant pulmonary vascular engorgement predisposes the child to development of HF.


Clinical manifestations—Patients usually have moderate to severe HF. There is a loud systolic murmur. There may be mild cyanosis that increases with crying. Patients are at high risk for developing pulmonary vascular obstructive disease.


Surgical Treatment



Prognosis—Operative mortality is less than 5% (Jacobs, Mavroudis, Jacobs, et al., 2004). A potential later problem is mitral regurgitation, which may require valve replacement.



Patent Ductus Arteriosus


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Description—Failure of the fetal ductus arteriosus (artery connecting the aorta and pulmonary artery) to close within the first weeks of life. The continued patency of this vessel allows blood to flow from the higher-pressure aorta to the lower-pressure pulmonary artery, which causes a left-to-right shunt.


Pathophysiology—The hemodynamic consequences of PDA depend on the size of the ductus and the pulmonary vascular resistance. At birth, the resistance in the pulmonary and systemic circulations is almost identical, so that the resistance in the aorta and pulmonary artery is equalized. As the systemic pressure comes to exceed the pulmonary pressure, blood begins to shunt from the aorta across the duct to the pulmonary artery (left-to-right shunt). The additional blood is recirculated through the lungs and returned to the left atrium and left ventricle. The effects of this altered circulation are increased workload on the left side of the heart, increased pulmonary vascular congestion and possibly resistance, and potentially increased right ventricular pressure and hypertrophy.


Clinical manifestations—Patients may be asymptomatic or show signs of HF. There is a characteristic machinery-like murmur. A widened pulse pressure and bounding pulses result from runoff of blood from the aorta to the pulmonary artery. Patients are at risk for BE and pulmonary vascular obstructive disease in later life from chronic excessive pulmonary blood flow.


Medical management—Administration of indomethacin (a prostaglandin inhibitor) has proved successful in closing a PDA in preterm infants and some newborns.


Surgical treatment—Surgical division or ligation of the patent vessel is performed via a left thoracotomy. In a newer technique, video-assisted thoracoscopic surgery, a thoracoscope and instruments are inserted through three small incisions on the left side of the chest to place a clip on the ductus. The technique is used in some centers and eliminates the need for a thoracotomy, thereby speeding postoperative recovery.


Nonsurgical treatment—Coils to occlude the PDA are placed in the catheterization laboratory in many centers. Preterm or small infants (with small-diameter femoral arteries) and patients with large or unusual PDAs may require surgery.


Prognosis—Both surgical and nonsurgical procedures can be done at low risk with less than 1% mortality. PDA closure in very preterm infants has a higher mortality rate because of the additional significant medical problems.


ASD, Atrial septal defect; AV, atrioventricular; BE, bacterial endocarditis; COA, coarctation of the aorta; CPB, cardiopulmonary bypass; HF, heart failure; PDA, patent ductus arteriosus; VSD, ventricular septal defect.



The outcomes of surgical treatment for patients with moderate to severe disease are variable. Patient risk factors for increased morbidity and mortality include prematurity or low birth weight, a genetic syndrome, multiple cardiac defects, a noncardiac congenital anomaly, and age at time of surgery (neonates are a higher risk group). For example, aortic stenosis or coarctation manifesting in the first week of life is more severe and carries a higher mortality than if it becomes apparent at 1 year of age. Outcomes for surgical repair of similar congenital heart defects also vary among treatment centers. In general, the outcomes of surgical procedures have steadily improved in the past decade, with mortality rates for many severe defects below 10% and a decrease in the incidence of complications and length of hospital stay.




Obstructive Defects


Obstructive defects are those in which blood exiting the heart meets an area of anatomic narrowing (stenosis), causing obstruction to blood flow. The pressure in the ventricle and in the great artery before the obstruction is increased, and the pressure in the area beyond the obstruction is decreased. The location of the narrowing is usually near the valve (Fig. 42-4), as follows:




Coarctation of the aorta (narrowing of the aortic arch), aortic stenosis, and pulmonic stenosis are typical defects in this group (Box 42-2). Hemodynamically, there is a pressure load on the ventricle and decreased cardiac output. Clinically, infants and children exhibit signs of HF. Children with mild obstruction may be asymptomatic. Rarely, as in severe pulmonic stenosis, hypoxemia may be seen.



Box 42-2   Obstructive Defects



Coarctation of the Aorta


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Description—Localized narrowing near the insertion of the ductus arteriosus, which results in increased pressure proximal to the defect (head and upper extremities) and decreased pressure distal to the obstruction (body and lower extremities).


Pathophysiology—The effect of a narrowing within the aorta is increased pressure proximal to the defect (upper extremities) and decreased pressure distal to it (lower extremities).


Clinical manifestations—The patient may have high blood pressure and bounding pulses in the arms, weak or absent femoral pulses, and cool lower extremities with lower blood pressure. There are signs of HF in infants. In infants with critical coarctation, the hemodynamic condition may deteriorate rapidly with severe acidosis and hypotension. Mechanical ventilation and inotropic support are often necessary before surgery. Older children may experience dizziness, headaches, fainting, and epistaxis resulting from hypertension. Patients are at risk for hypertension, ruptured aorta, aortic aneurysm, and stroke.


Surgical treatment—Surgical repair is the treatment of choice for infants younger than 6 months and for patients with long-segment stenosis or complex anatomy; it may be performed for all patients with coarctation. Repair is by resection of the coarctated portion with an end-to-end anastomosis of the aorta or enlargement of the constricted section using a graft of prosthetic material or a portion of the left subclavian artery. Because this defect is outside the heart and pericardium, cardiopulmonary bypass is not required and a thoracotomy incision is used. Postoperative hypertension is treated with intravenous sodium nitroprusside, esmolol, or milrinone followed by oral medications, such as ACE inhibitors or beta blockers. Residual permanent hypertension after repair of COA seems to be related to age and time of repair. To prevent both hypertension at rest and exercise-provoked systemic hypertension after repair, elective surgery for COA is advised within the first 2 years of life. There is a 15% to 30% risk for recurrence in patients who underwent surgical repair as infants (Beekman, 2001). Percutaneous balloon angioplasty techniques have proved to be effective in relieving residual postoperative coarctation gradients.


Nonsurgical treatment—Balloon angioplasty is being performed as a primary intervention for COA in older infants and children. In adolescents, stents may be placed in the aorta to maintain patency. Recent studies have demonstrated that balloon angioplasty is effective in children and that aneurysm formation is rare. The high restenosis rate in young infants limits its application in this group (Rome and Kreutzer, 2004).


Prognosis—Mortality is less than 5% in patients with isolated coarctation; the risk is increased in infants with other complex cardiac defects (Jacobs, Mavroudis, Jacobs, et al., 2004).



Aortic Stenosis


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Description—Narrowing or stricture of the aortic valve, causing resistance to blood flow in the left ventricle, decreased cardiac output, left ventricular hypertrophy, and pulmonary vascular congestion. The prominent anatomic consequence of AS is the hypertrophy of the left ventricular wall, which eventually leads to increased end-diastolic pressure, resulting in pulmonary venous and pulmonary arterial hypertension. Left ventricular hypertrophy also interferes with coronary artery perfusion and may result in myocardial infarction or scarring of the papillary muscles of the left ventricle, which causes mitral insufficiency. Valvular stenosis, the most common type, is usually caused by malformed cusps that result in a bicuspid rather than tricuspid valve or fusion of the cusps. Subvalvular stenosis is a stricture caused by a fibrous ring below a normal valve; supravalvular stenosis occurs infrequently. Valvular AS is a serious defect for the following reasons: (1) the obstruction tends to be progressive; (2) sudden episodes of myocardial ischemia, or low cardiac output, can result in sudden death; and (3) surgical repair rarely results in a normal valve. This is one of the rare instances in which strenuous physical activity may be curtailed because of the cardiac condition.


Pathophysiology—A stricture in the aortic outflow tract causes resistance to ejection of blood from the left ventricle. The extra workload on the left ventricle causes hypertrophy. If left ventricular failure develops, left atrial pressure will increase; this causes increased pressure in the pulmonary veins, which results in pulmonary vascular congestion (pulmonary edema).


Clinical manifestations—Newborns with critical AS demonstrate signs of decreased cardiac output with faint pulses, hypotension, tachycardia, and poor feeding. Children show signs of exercise intolerance, chest pain, and dizziness when standing for a long period. A systolic ejection murmur may or may not be present. Patients are at risk for BE, coronary insufficiency, and ventricular dysfunction.



Valvular Aortic Stenosis




Surgical treatment—Aortic valvotomy is performed under inflow occlusion. Used rarely because balloon dilation in the catheterization laboratory is the first-line procedure. Newborns with critical AS and small left-sided structures may undergo a stage 1 Norwood procedure (see Hypoplastic Left Heart Syndrome, Box 42-4).


Prognosis—Aortic valve replacement offers a good treatment option and may lead to normalization of left ventricular size and function (Arnold, Ley-Zaporozhan, Ley, et al., 2008). Results of aortic valvotomy in older children are very good, with mortality and morbidity close to 0% (Shanmugam, MacArthur, and Pollock, 2005). However, aortic valvotomy remains a palliative procedure and approximately 25% of patients require additional surgery within 10 years for recurrent stenosis. A valve replacement may be required at the second procedure. An aortic homograft with a valve may also be used (extended aortic root replacement), or the pulmonary valve may be moved to the aortic position and replaced with a homograft valve (Ross procedure).


Nonsurgical treatment—The narrowed valve is dilated using balloon angioplasty in the catheterization laboratory. This procedure is usually the first intervention.


Prognosis—Complications include aortic insufficiency or valvular regurgitation, tearing of the valve leaflets, and loss of pulse in the catheterized limb.




Pulmonic Stenosis


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Description—Narrowing at the entrance to the pulmonary artery. Resistance to blood flow causes right ventricular hypertrophy and decreased pulmonary blood flow. Pulmonary atresia is the extreme form of PS in that there is total fusion of the commissures and no blood flows to the lungs. The right ventricle may be hypoplastic.


Pathophysiology—When PS is present, resistance to blood flow causes right ventricular hypertrophy. If right ventricular failure develops, right atrial pressure will increase and this may result in reopening of the foramen ovale, shunting of unoxygenated blood into the left atrium, and systemic cyanosis. If PS is severe, HF occurs and systemic venous engorgement will be noted. An associated defect such as a PDA partially compensates for the obstruction by shunting blood from the aorta to the pulmonary artery and into the lungs.


Clinical manifestations—Patients may be asymptomatic; some have mild cyanosis or HF. Progressive narrowing causes increased symptoms. Newborns with severe narrowing are cyanotic. A loud systolic ejection murmur at the upper left sternal border may be present. However, in severely ill patients, the murmur may be much softer because of decreased cardiac output and shunting of blood. Cardiomegaly is evident on chest radiography. Patients are at risk for BE.


Surgical treatment—In infants, transventricular (closed) valvotomy (Brock procedure). In children, pulmonary valvotomy with CPB. Need for surgical treatment is rare with widespread use of balloon angioplasty techniques.


Nonsurgical treatment—Balloon angioplasty in the cardiac catheterization laboratory to dilate the valve. A catheter is inserted across the stenotic pulmonic valve into the pulmonary artery, and a balloon at the end of the catheter is inflated and rapidly passed through the narrowed opening (see figure at right). The procedure is associated with few complications and has proved to be highly effective. It is the treatment of choice for discrete PS in most centers and can be done safely in neonates.


Prognosis—The risk is low for both surgical and nonsurgical procedures; mortality is lower than 1% and slightly higher in neonates (Latson, 2001). Both balloon dilation and surgical valvotomy leave the pulmonic valve incompetent because they involve opening the fused valve leaflets; however, these patients are clinically asymptomatic. Long-term problems with restenosis or valve incompetence may occur.


ACE, Angiotensin-converting enzyme; AS, aortic stenosis; BE, bacterial endocarditis; COA, coarctation of the aorta; CPB, cardiopulmonary bypass; HF, heart failure; PDA, patent ductus arteriosus; PS, pulmonic stenosis.



Defects with Decreased Pulmonary Blood Flow


In this group of defects, there is obstruction of pulmonary blood flow and an anatomic defect (ASD or VSD) between the right and left sides of the heart (Fig. 42-5). Because blood has difficulty exiting the right side of the heart via the pulmonary artery, pressure on the right side increases, exceeding left-sided pressure. This allows desaturated blood to shunt right to left, causing desaturation in the left side of the heart and in the systemic circulation. Clinically, these patients have hypoxemia and usually appear cyanotic. Tetralogy of Fallot and tricuspid atresia are the most common defects in this group (Box 42-3).



Box 42-3   Defects with Decreased Pulmonary Blood Flow



Tetralogy of Fallot


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Description—The classic form includes four defects: (1) VSD, (2) PS, (3) overriding aorta, and (4) right ventricular hypertrophy.


Pathophysiology—The alteration in hemodynamics varies widely, depending primarily on the degree of PS but also on the size of the VSD and the pulmonary and systemic resistance to flow. Because the VSD is usually large, pressures may be equal in the right and left ventricles. Therefore the shunt direction depends on the difference between pulmonary and systemic vascular resistance. If pulmonary vascular resistance is higher than systemic resistance, the shunt is from right to left. If systemic resistance is higher than pulmonary resistance, the shunt is from left to right. PS decreases blood flow to the lungs and consequently the amount of oxygenated blood that returns to the left side of the heart. Depending on the position of the aorta, blood from both ventricles may be distributed systemically.


Clinical manifestations—Some infants may be acutely cyanotic at birth; others have mild cyanosis that progresses over the first year of life as the PS worsens. There is a characteristic systolic murmur that is often moderate in intensity. There may be acute episodes of cyanosis and hypoxia, called blue spells or tet spells (see p. 1337). Anoxic spells occur when the infant’s oxygen requirements exceed the blood supply, usually during crying or after feeding. Patients are at risk for emboli, seizures, and loss of consciousness or sudden death after an anoxic spell.


Surgical Treatment



• Palliative shunt—In infants who cannot undergo primary repair, a palliative procedure to increase pulmonary blood flow and increase oxygen saturation may be performed. The preferred procedure is a modified Blalock-Taussig shunt operation, which provides blood flow to the pulmonary arteries from the left or right subclavian artery via a tube graft (see Table 42-2). In general, however, shunts are avoided because they may result in pulmonary artery distortion.


• Complete repair—Elective repair is usually performed in the first year of life. Indications for repair include increasing cyanosis and the development of hypercyanotic spells. Complete repair involves closure of the VSD and resection of the infundibular stenosis, with placement of a pericardial patch to enlarge the RVOT. In some repairs, the patch may extend across the pulmonary valve annulus (transannular patch), making the pulmonary valve incompetent. The procedure requires a median sternotomy and the use of cardiopulmonary bypass.


Prognosis—The operative mortality for total correction of tetralogy of Fallot is less than 3% (Jacobs, Mavroudis, Jacobs, et al., 2004). With improved surgical techniques, there is a lower incidence of dysrhythmias and sudden death; surgical heart block is rare. Heart failure may occur postoperatively.



Tricuspid Atresia


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Description—The tricuspid valve fails to develop; consequently there is no communication from the right atrium to the right ventricle. Blood flows through an ASD or a patent foramen ovale to the left side of the heart and through a VSD to the right ventricle and out to the lungs. The condition is often associated with PS and TGA. There is complete mixing of unoxygenated and oxygenated blood in the left side of the heart, which results in systemic desaturation, and varying amounts of pulmonary obstruction, which causes decreased pulmonary blood flow.


Pathophysiology—At birth, the presence of a patent foramen ovale (or other atrial septal opening) is required to permit blood flow across the septum into the left atrium; the PDA allows blood flow to the pulmonary artery into the lungs for oxygenation. A VSD allows a modest amount of blood to enter the right ventricle and pulmonary artery for oxygenation. Pulmonary blood flow usually is diminished.


Clinical manifestations—Cyanosis is usually seen in the newborn period. There may be tachycardia and dyspnea. Older children have signs of chronic hypoxemia with clubbing.


Therapeutic management—For neonates whose pulmonary blood flow depends on the patency of the ductus arteriosus, a continuous infusion of prostaglandin E1 is started at 0.1 mcg/kg/min until surgical intervention can be arranged.


Surgical treatment—Palliative treatment is the placement of a shunt (pulmonary-to-systemic artery anastomosis) to increase blood flow to the lungs. If the ASD is small, an atrial septostomy is performed during cardiac catheterization. Some children have increased pulmonary blood flow and require pulmonary artery banding to lessen the volume of blood to the lungs. A bidirectional Glenn shunt (cavopulmonary anastomosis) may be performed at 4 to 9 months as a second stage.


Sep 16, 2016 | Posted by in NURSING | Comments Off on Cardiovascular Dysfunction
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