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نویسنده: اسماعیل نیک راه - سه‌شنبه ۱٠ دی ،۱۳٩٢

Congenital Heart Disease

Congenital anomalies of the heart and cardiovascular system occur in seven to l0 per 1000 live births (0.7%-I.0o/o).

Congenital heart diseases the most common form of congenital

Disease and accounts for approximately3 0o/o of the total

Incidence of all congenital diseases .With the decline in rheumatic heart disease, congenital heart disease has become the principal cause of heart disease with 10% to l5o/o of afflicted children having associated congenital anomalies of the skeletal, genitourinary, or gastrointestinal system. Nine congenital heart lesions comprise more than 80% of congenital heart disease, with a wide range of more unusual and complex lesions comprising the remainder .The population of adults with congenital heart diseases, surgically corrected or uncorrected, is estimated to exceed I million persons in the United

States As a result, it is not uncommon for adult patients with congenital heart disease to present for non cardiac surgery.

Trans thoracic and trancesophageal echocardiography has Facilitated early, accurate diagnosis of congenital heart disease.

Fetal cardiac ultrasonography has permitted prenatal diagnosis of congenital heart defects, allowing subsequent perinatal management. Imaging modalities, such as cardiac magnetic resonance imaging and three-dimensional echocardiography, have increased the understanding of complex cardiac malformations and allow visualization of blood flow and vascular structures. Cardiac catheterization and selective angiocardiography

are the most definitive diagnostic procedures available for use in patients with congenital heart disease. As the success rate of cardiac surgery increases ,more patients with complex

cardiac defects will survive into adulthood and present for

noncardiac surgery.

Advances in molecular biology have provided new understandings of the genetic basis of congenital heart disease.

Chromosomal abnormalities are associated with an estimated

10% of congenital cardiovascular  lesions. Two thirds of these

Lesions occur in patients with trisomy21; the other one third is found in patients with karyotypic abnormalities, such as trisomy l3 and trisomy18, and in patients with Turner's syndrome.

The remaining 90o/o of congenital cardiovascular lesions are postulated to be multi factorial in origin and occur as a result of interactions of several genes with or without external factors

(Rubella, ethanol abuse, Lithium, maternal diabetes mellitus).

A widely used acronym, (cardiac defects, abnormal faces, physic hyperplasia, cleft palate, hypocalcaemia) depicts

a congenital heart disease syndrome attributed to defects in

chromosome22. An increased incidence of congenital heart disease in the offspring of affected adult patients suggests a role for single-gene defects in isolated congenital heart disease.

Signs and symptoms of congenital heart disease in infants and children often include dyspnea, slow physical development, and the presence of a cardiac murmur. The diagnosis of congenital heart disease sap parent during the first week of life in approximately5 0o/o of afflicted neonates and before5 years of age in virtually all remaining patients. Echocardiography is the initial diagnostic step if congenital heart disease is suspected. Certain complications are likely to accompany the presence of congenital heart disease. For example, infective endocarditis is a risk associated with most congenital cardiac anomalies. Cardiac dysrhythmias are not usually a prominent feature of congenital heart disease.

ACYANOTICC ONGENITALH EART

DISEASE

A cyanotic congenital heart disease is characterized by a left-to right Intra cardiac shunt. The ultimate result of this intra cardiac shunt, regardless of its location, is increased pulmonary blood flow with pulmonary hypertension,

ACYANOTICC ONGENITAL HEARTDISEASE

A cyanotic congenital heart disease is characterized by a left-to right intracardiac shunt. The ultimate result of this intra cardiac shunt, regardless of its location, is increased pulmonary blood flow with pulmonary hypertension. right ventricular hypertrophy, and eventually congestive heart failure. The younger the patient is at the time of correction, the greater is the likelihood that pulmonary vascular resistance will normalize. In older patients, if pulmonary vascular resistance is one third or less of the systemic vascular resistance, corrective surgery is likely to prevent or, in some cases ,even causes light regression of pulmonary vascular disease .The onset and severity of clinical symptoms vary with the site and magnitude of the vascular shunt.

Atrial Septal Defect

Atrial septal defect (ASD) accounts for about one third of the

Congenital heart disease detected in adults, with the frequency

 females of two to three times that observed in males.

Anatomically, an ASD may take the form of ostium secundum in the region of the fossa ovalis (often located near the center of the interatrial septum and varying from a single opening to a fenestrated septum), ostium primum (endocardial cushion defect characterized by a large opening in the intertribal septum), or sinus venous located in the upper atrial septum. Secundum ASDs account for 75% of all ASDs. Additional cardiac abnormalities may occur with each type of defect and include mitral valve prolapsed

(ostium secundum) and mitral regurgitation due to a cleft

in the anterior mitral valve leaflet (ostium primum). Most

ASDs occur as a result of spontaneous genetic mutations.

The physiologic cones quinces’ of ASDs are the same regardless of the anatomic location and reflect the shunting of blood from one atrium to the other; the direction and magrritude of the shunt are determined by the size of the defect and the relative compliance of the ventricles .Asma1dl effect( < 0.5c m in diameter)is associated with a small shunt and no hemodynamic squeal .When the diameter of the ASD approache to scar, it is likely that left atrial blood is being shunted to the right atrial (the right ventricle is more compliant than the left ventricle), resulting in increased pulmonary blood flow. A systolic ejection murmur audible in the second left intercostal sauce

Figure may be mistaken for an innocent flow murmur. The electrocardiogram(ECG) may reflect right axis deviation and incomplete right bundle branch block .  Atrial fibrillation and supraventricular tachycardia may accompany an ASD that

rernains uncorrected into adulthood. The chest radiograph is likely to reveal prominent pulmonary arteries .Tran esophageal echocardiography and Doppler color flow echocardiography are both useful for detecting and determining the location of ASDs.

Signs and Symptoms

Because they initially produce no symptoms or striking findings on physical examination, ASDs may remain undetected for years. A small defect with minimal right-to-left shunting (ratio of pulmonary flow to systemic low is < 1.5) usually causes no symptoms and therefore does not require closure. When pulmonary blood flow is 1.5 times the systemic blood flow, the ASD should be surgically closed either in the catch lab or surgically to prevent right ventricular dysfunction and irreversible pulmonary hypertension. Symptoms due to large ASDs include dyspnea on exertion, supraventricular dysrhythmias, right heart failure, paradoxical embolism, and recurrent pulmonary infections. Prophylaxis against infective endocarditis is not recommended for patients with an ASD unless a concomitant valvular abnormality (mitral valve prolapsed or mitral valve cleft) is present.

Management of Anesthesia

An ASD associated with a left-to-right intracardiac shunt

has only .minor implications for the management of anesthesia.

For example, as long as the systemic blood flow remains nornral, the pharmacokinetics of inhaled drugs are not significantly altered despite the increased pulmonary blood flow.

Conversely, increased pulmonary blood flow could dilute drugs injected intravenously. It is unlikely, however, that this potential dilution will alter the clinical response to these drugs because the pulmonary circulation time is brief.

Any change in systemic or pulmonary vascular resistance during the perioperative period will have important implications for the patient with an ASD. For example, drugs or

Events that produce prolonged increases in systemic vascular

resistance should be avoided because this change favors

an increase in the magnitude of the left-to-right shunt at the

atrial level. This is particularly true with a premium ASD defect Associated with mitral regurgitation. Use of high Fro2 will decrease

Pulmonary vascular resistance and increase pulmonary

blood flow and left-to-right shunt. Conversely, decreases

in systemic vascular resistance, as produced by volatile anesthetics or increases in pulmonary vascular resistance due to positive-pressure ventilation of the lungs, tend to decrease the magnitude of the left-to-right shunt.

Another consideration in the management of anesthesia in the presence of ASDs is the need to provide prophylactic antibiotics to protect against infective endocarditis when a cardiac valvular abnormality is present. In addition, meticulously avoiding the entrance of air into the circulation, as can occur through tubing used to deliver intravenous solutions, is imperative. Transients’ urea ventricular dysrhythmias and atrioventricular conduction defects are common during the early postoperative period after surgical repair of an ASD.

Ventricular Septal Defect

Ventricular septal defect (VSD) is the most common congenital cardiac abnormality in infants and children. A large number of VSDs close spontaneously by the time a child\ reaches 2 years of age. Anaton-rically  ,a pproximately7 0o/o of these defects are located in the mernbranous portion of the

intraventricular septum, 20o/o in the muscular portion of the septum, 5olo just below the aortic valve causing aortic regurgitation, and 5o/o near the junction of the mitral and tricuspid valve (atrioventricular canal defect).

Echocardiography with Doppler flow ultrasonography confirms the presence and location of the VSD and color-flow mapping provides information about the magnitude and direction Of the intracardiac shunt. Cardiac catheterization and angiography confirm the presence and location of the VSD and determine the magnitude of the intracardiac shunting and the pulmonary vascular resistance.

Signs and Symptoms

The physiologic significance of a VSD depends on the size of the defect and the relative resistance in the systemic and pulmonary circulations. If the defect is small, there is minimal functional disturbance as pulmonary blood flow is only modestly increased. If the defect is large, the ventricular systolic pressure sequalize and the magnitude of systemic and pulmonary blood flow is determined by the relative vascular resistances of these two circulations. Initially, systemic vascular resistance exceeds pulmonary vascular resistance, and left-to-right intracardiac shunting predominates. Over time, the pulmonary vascular resistance in dcreasesan, the magnitude of the left-to right intracardiac shunting decreases'; ventually, the shunt may be come right to left with the development of arterial hypoxemia (cyanosis) The murmur of a moderate to large VSD is hypo systolic and is loudest at the lower left sternal border. The ECG and chest radiograph remain normal in the presence of a small VSD.

When the VSD is large, there is evidence of left atrial and ventricular enlargement on the ECG. If pulmonary hypertensions

Develops, the QRS axis shifts to the right, and right atrial and ventricular enlargement are noted on the ECG.

The natural history of a VSD depends on the size of the defect and the pulmonary vascular resistance. Adults with small defects and normal pulmonary arterial pressures are generally asymptomatic, and pulmonary hypertension is unlikely to develop. These patients are at risk of developing infective endocarditis even though they may not meet the criteria for surgical correction of the VSD. In the absence of surgical correction, a large VSD eventually leads to left ventricular failure or pulmonary hypertension with associated right ventricular failure. Surgical closure of the defect is recommended in these patients if the magnitude of the pulmonary hypertension s not prohibitive. Once the pulmonary/systemic vascular resistance ratio exceeds 0.7, the risk of surgical closure becomes prohibitive Management of Anesthesia Antibiotic prophylaxis to protect against infective endocarditis is indicated when noncardiac surgery is planned in patients with VSDs. The pharmacokinetics of inhaled and injected drugs is not significantly altered by a VSD. As with an ASD, acute and persistent increases in systemic vascular

Resistance or decrease is pulmonary vascular resistance are undesirable because the such anges can accent rate the magnitude of the left-to-right intracardiac shunt at the ventricular Level. In this regard, volatile anesthetics (which decrease systemic vascular resistance)and positive-pressure ventilation (which increases pulmonary vascular resistance)are well tolerated.

However, there may be increased delivery of depressant Drugs to the heart if coronary blood flow is increased to supply the hypertrophied ventricles. Conceivably, the technique of increasing the inspired concentrations of volatile anesthetics to achieve rapid induction of anesthesia, as is often done in normal children, could result in excessive depression of the heart before central nervous system depression is achieved in children with VSD.

Right ventricular in mandibular hypertrophy may be present in patients with VSDs. Normally, this is a beneficial change

Because it increases the resistance to right ventricular ejection, leading to a decrease in the magnitude of the left-to-right intracardiac shunt. Nevertheless, preoperative events that

Exaggerateth is obstruction to right ventricular outflow, such

As increased myocardial contractility or hypovolemia, must be minimized. Therefore, these patients are often anesthetized with volatile anesthetics. In addition, intravascular fluid volume should be maintained by prompt replacement by crystalloid or colloid (depending on the clinical scenario).

Anesthesia for placement of a pulmonary artery band is often achieved with drugs that provide minimal cardiac depression. If bradycardia or systemic hypotension develops during surgery, it may be necessary to remove the pulmonary artery band promptly. Continuous monitoring of the systemic blood pressure with an intra-arterial catheter is helpful. Administration of positive end-expiratory pressure may be useful in the presence of congestive heart failure but should be discontinued when the pulmonary artery band is in place. The high mortality rate associated with pulmonary artery banding has led to attempted complete surgical correction at an early age. Third-degree atrioventricular heart block may follow surgical closure if the cardiac conduction system is near the VSD.

Premature ventricular beats may reflect the electrical in stability of the ventricle due to surgical ventriculotomy. The risk of

Ventricular tachycardia, however, is low if postoperative ventricular

filling pressures are nonnal.

Patent Ductus Arteriosus

A patent ductus arteriosus (PDA) is present when the ductus arteriosus (which arises just distal to the left subclavian artery and connects the descending aorta to the left pulmonary artery) fails to close spontaneously shortly after birth.

 In the fetus, the ductus arteriosus permits pulmonary arterial blood to bypass the deflated lungs and enter the Descending aorta for orygenation in the placenta. In full-term newborns, the ductus arteriosus causes within 24 to 48 hours after delivery, but in preterm newborns, the ductus arteriosus frequently fails to close. When the ductus arteriosus fails to close spontaneously after birth, the result is continuous flow of blood from the aorta to the pulmonary artery. 1'he pulmonary/systemic blood flow ratio depends on the pressure gradient from the aorta to the pulmonary artery, the pulmon,

Arylsystemic vascular resistance ratio, and the diameter and length of the ductus arteriosus. The PDA can usually be visualized on echocardiography ,with Doppler studies confirming the continuous flow into the pulmonary circulation. Cardiac catheterization and angiography make it possible to quantify the magnitude of the shunting and the pulmonary vascular Resistance and to visualize the PDA.

Signs and Symptoms

Most patients with a PDA are asymptomatic and have only modest left-to-right shunts. This cardiac defect is often detected during a routine physical examination, at which time a characteristic continuous systolic and diastolic murmur is heard. If the left-to-right shunt is large, there may be evidence of left ventricular hypertrophy on the ECG and chest radiograph. If pulmonary hypertension develops, right ventricular hypertrophy is apparent. The presence of

. Patent ductus arteriosus connect ing the arch of the aorta (Ao) with the pulmonary artery (PA) Blood flow is from the high pressure Ao into the PA. The resulting aorta- to-pulmonary artery shunt (left - to- right shunt) leads to increased pulmonary blood f low. A decrease in systemic vascular resistance or an increase in pulmonary vascular resistance decreases the magnitude of the shunt through the ductus arteriosus lVC, inferior vena cava; LA, left atrium; LV, left ventricle, RV, right ventricle; SVC , superior vena cava a PDA increases the risk of infective endocarditis. Surgical ligation of a PDA is associated with low mortality and is unlikely to require cardiopulmonary bypass. Without surgical closure, most patient srema in a symptomatic until adolescence, when pulmonary hypertension and congestive heart failure may occur. Once severe pulmonary hypertension develops,

Surgical or percutaneous closure is contraindicated.

Treatment

It is estimated that 70o/o of preterm infants delivered before 28 weeks of gestation require medical or surgical closure of a PDA. Surgical ligation of a PDA can be performed in neonatal intensive care units with low morbidity and mortality rates. Nevertheless, the risks of surgical closure are significant and include intracranial hemorrhage, infections, and recurrent laryngeal nerve paralysis, especially in infants born at less than 28 weeks of gestation. Inhibition of prostaglandin synthesis with nonselective cyclooxy genasien hibitors(COX- 1, COX-2) appears to be an effective medical aiternative to surgery for closure of a PDA in neonates. Indomethac in, a nonselective cyclooxy geneses inhibitor used for this purpose, has reduced the need for surgery by 600/o and is the first-line of therapy for PDA. Adverse side effects of indomethac in include decreased mesenteric, renal, and cerebral blood flow.

Ibuprofen is a nonselective cyclooxy genasien hibitor that can be used effectively to treat PDA and has less effect on organ blood flow than indornethacin.

Management of Anesthesia

Antibiotic prophylaxis for protection against infective endocarditis is recommended for patients with PDAs who are scheduled for noncardiac surgery. When surgical closure of the PDA is planned through a left thoracotomy, appropriate preparations must be taken in anticipation of the possibility of large blood loss should control of the PDA be lost during attempted ligation. The decrease in systemic vascular resistance produced by volatile anesthetics may improve systemic blood flow by decreasing the magnitude of the left-to-right shunt. Likewise, positive-pressure ventilation of the patient's lungs is well tolerated, as pulmonary vascular resistance, thereby decreasing the pressure gradient across the PDA.

Conversely, increases systemic vascular resistance or

Decreases in pulmonary vascular assistance should be avoided

Because these changes will increase the magnitude of the left-to-right shunt.

Ligation of the PDA is often associated with significant systemic hypertension during the postoperative period. This hypertension can be managed with continuous infusion of vasodilator drugs such as nitroprusside. Long-acting antihypertensive drugs can be gradually substituted for nitroprusside if systemic hypertension persists.

Aorti co pulmonary Fenestration

Aorti co pulmonary fenestration is characterized by a communication between he left side of the ascending aorta and the right wall of the main pulmonary artery, just anterior to the origin of the right pulmonary artery. This communication is due to failure of the aorticopulmonary septum to fuse and completely separate the aorta from the pulmonary artery. Clinical and hemodynamic manifestations of an aorticopulmonary communication are similar to those associated with a large PDA. The diagnosis is facilitated by echocardiography and angiocardiography. Treatment is surgical and requires the use of cardiopulmonary bypass. Management of anesthesia entails the same principles as described for patients with PDAs.

Aortic Stenosis

Bicuspid aortic valves occur in 2o/o to 3o/o of the U.S. population, and an estimated 20% of these patients have other cardiovascular abnormalities, such as PDA or coarctation of the aorta .The deformed bicuspid aortic valve is not stenotic at birth, but with time, thickening and calcification of the leaflets (usually not apparent before 15 years of age) occur with resulting immobility. Tran thoracic echocardiography with Doppler flow studies permits accurate assessment of the severity o f the aortic stenosis and of Left ventricular function. Cardiac catheterization is performed to determine the presence of concomitant coronary artery disease.

Aortic stenosis is associated with a systolic munnur that is audible over the aortic area (second right intercostals pace)and often radiates into the neck. Most patients with congenital aortic stenosis are asymptomatic until adulthood. Infants with severe aortic stenosis, however, may present with congestive Heart failure. Findings in patients with supravalvular aortic stenosis may include characteristic appearance is which the facial bones are prominent, the forehead is rounded, and the upper lip is pursed. Strabismus, inguinal hernia, dental abnormalities, and moderate mental retardation are commonly present.

The ECG in the presence of congenital aortic stenosis typically reveals left ventricular hypertrophy. Depression of the ST segment in the ECG Is likely during exercise, particularly if the pressure gradient across the aortic valve is more than 50mm Hg. Chest radiographs show left ventricular hypertrophy with or without post stenotic dilation of the aorta. Angina pectoris in the absence of coronary artery disease reflects the inability of coronary blood flow to meet increased myocardial oxygen requirements of the hypertrophied left ventricle. Syncope can occur when the pressure gradient across the aortic valve exceeds 50 mm Hg. In the presence of aortic stenosis, the myocardium must generate an intraventricular pressure that is two to three times normal, whereas pressure in the aorta remains within a physiologic range. The resulting concentric myocardial hypertrophy leads to increased myocardial oxygen requirements.

Furthermore, the high velocity of blood flow through the stenotic area predispose so the development of infective endocarditis and is associated with poststenotic dilation of the aorta. In adults with symptomatic aortic stenosis (syncope,angina pectoris,

Congestive heart failure), the indicated treatment is surgical valve replacement.

 Pulmonic Stenosis

Pulmonic stenosis producing obstruction to right ventricular Out flow is valvular in 90o/o of patients; in the remainder' it is supravalvular or subvalvular. Supravalvular pulmonic stenosis often co-exists with other congenital cardiac abnormalities

(ASD, VSD, PDA, tetralogy of Fallot). It is a common

Feature of Williams’s syndrome, which is characterized by infantile hypocalcaemia and mental retardation. Subvalvular pulmonic stenosis usually occurs in association with a VSD.

Valvular pulmonic stenosis is typically an isolated abnormality, but it may occur in association with a VSD. Severe pulmonic stenosis is characterized by transvalvular pressure gradients of more than 80 mm Hg or right ventricular systolic pressures of more than 100 mm Hg. Echocardiography and Doppler flow sturdiest can determine the site of the obstruction and the severity of the stenosis. Treatment of pulmonic stenosis is with percutaueous balloon valvuloplast.

Signs and Symptoms

In asymptomatic patients, the presence of pulmonic stenosis is identified by the presence of a loud systolic ejection murmur, best heard at the second left intercostal space. The intensity and duration of the cardiac murmur parallel the severity of the pulmonic stenosis .Dyspnea may occur on exertion, and eventually right ventricular failure with peripheral edema and ascites develops. If the foramen ovale is patent, right-to-left intracardiac shunting of blood may occur, causing cyanosis and clubbing.

Management of Anesthesia

Management of anesthesia is designed to avoid increases

in right ventricular oxygen requirements. There fore,excessive increases in heart rate and myocardial contractility are undesirable.

The impact of changes in pulmonary vascular resistance is minimized by the presence of fixed obstruction of the pulmonic valve. As a result, increases in pulmonary vascular resistance due to positive-pressure ventilation of the lungs are unlikely to produce significant increases in right ventricular after load and oxygen requirements.

These patients are extremely difficult to resuscitate if cardiac arrest occurs because external cardiac compression is not highly effective in forcing blood across a stenotic pulmonic valve. Therefore, decreases in systemic blood pressure should be promptly treated with sympathomimetic drugs. Liker vise, cardiac dysrhythmias or increases in heart rate that become hemodynamically significant should be rapidly corrected.

Coarctation of the Aorta

Coarctation of the aortal) icily consists of a discrete, diaphragm-like ridge extending into the aortic lumen just distal to the left subclavian a fiery at the site of the aortic duct al attachment (ligamentum arteriosum). This anatomic manifestation is known as postductal coarctation of the aorta and is most likely to manifest in young adults. Less commonly, the coarctation is immediately proximal to the left subclavian artery (preductal); this situation is most likely to present in infants. Coarctation of the aorta is more

Common in males and may occur in conjunction with a bicuspid aortic valve, PDA, mitral stenosis or regurgitation, aneur-1.smso f the circle of Willis, and gonadal dysgenesis (Turner's syndrome).

Signs and Symptoms

Most adults with coarctation of the aorta are asymptomatic, and the problem is diagnosed during a routine physical examination when systemic hypertension is detected in the arms in association the diminished or absent femoral arterial pulses. Characteristically, systolic blood pressure is higher in the arms than in the legs, but the diastolic pressure is similar, resulting in widened pulse pressure in the arms. The femoral arterial pulses are weak and delayed. Systemic hypertension presumably reflects ejection of the left ventricular stroke volume into the fixed resistance created by the narrowed aorta. A harsh systolic ejection murmur is present along the left sternal border and in the back, particularly over the area of the coarctation. In the presence of preductal Coarctation of the aorta, there is no difference in the systemic blood pressures in the arms and legs. Extensive collateral arterial circulation to the distal body through the internal thoracic, intercostal, scapular, and subclavian arteries is likely in the presence of coarctation of the aorta. In this regard, a systolic murmur may be heard in the back, reflecting this collateral blood flow. The ECG shows signs of left ventricular hypertrophy. On the chest radiograph, increased collateral flow through the intercostal arteries causes symmetrical notching of the posterior third of the third through eighth ribs. Notching is not seen in the anterior ribs because the anterior intercostal arteries are not located in costal grooves. The coarctation may be visible as an indentation of the aorta with prestenotic or post stenotic dilation of the aorta, producing the "reversed

E," or "3," signs. The coarctation may be visualized with Echocardiography, and Doppler examination makes it possible to estimate the transcoarctation pressure gradient. Computed tomography, magnetic resonance imaging, and contrast aortography provide precise anatomic information regarding the location and length of the coarctation and the degree of collateral circulation.

When clinical syrnptoms of a previously unrecognized coarctation of the aorta manifest, they are usually characterized as headache, dizziness, epistaxis, and palpitations.

Occasionally, diminished blood flow to the legs causes claudication.

Women with coarctation of the aorta are at increased risk of aortic dissection during pregnancy. Complications of coarctation of the aorta include systemic hypertension, left ventricular failure, aortic dissection, premature ischemic heart disease presumably related to chronic hypertension, infective endocarditis, and cerebral vascular accidents due to rupture of intracerebral aneurysms. Patients with known coarctation of the aorta should be given prophylactic antibiotics prior to dental or surgical procedures.

Treatment

Surgical resection of the coarctation of the aorta should be considered for patients with a transcoarctation pressure gradient of more than 30 mm Hg. Although balloon dilation is a therapeutic alternative, the procedure is associated with a higher incidence of subsequent aortic aneurysm and recurrent coarctation than surgical resection.

Management of Anesthesia

Management of anesthesia for surgical resection of coarctation of the aorta must consider (l) the adequacy of perfusion to the lower portion of the body during cross-clamping of the aorta, (2) the propensity for systemic hypertension during cross-clamping of the aorta, and (3) the risk of neurologic squeal due to ischemia of the spinal cord. Blood flow to the anterior spinal artery is augmented by reticular branches of the intercostal arteries and may be compromised during cross-clamping of the aorta for surgical resection of coarctation of the aorta. Paraplegia after surgical resection of coarctation of the aorta is a rare complication. Continuous monitoring of systemic blood pressure above and below thecoarctation is achieved by placing a catheter in the right radial artery and a femoral artery. By monitoring these pressures simultaneously, it is possible to evaluate the adequacy of the collateral circulation during periods of aortic cross-clamping.

Mean arterial pressures in the lower extremities should be at least 40 mm Hg to ensure adequate blood flow to the kidneys and spinal cord. If the systemic blood pressure cannot be maintained above this level, it may be necessary to use partial circulatory blpass. Som at sensory evoked potentials are useful for monitoring spinal cord function and the adequacy of its blood flow during cross-clamping of the aorta.

Never the less, case reports of paraplegia despite normal sonatas sensory Voked potentials suggest that monitoring posterior (sensory) cord function does not ensure adequate blood flow to the anterior (motor) portion of the spinal cord. Excessive increases in systolic blood pressured uring cross-clamping of the aorta may adversely increase the work of the heart and make surgical repair more difficult .In this situation, the use of volatile anesthetics helpful for maintaining normal Systemic blood pressures. If systemic hypertension pcr.5l515,

Continuous intravenous fusions of nitroprusside should be reconsidered. The disadvantages of levering the systemic blood

Pressure to normal levels is excessively decreased perversion

Pressure in the lower part of the body and inadequate blood flow to the kidneys and spinal cord.

Postoperative Management

Immediate postoperative complications in clued paradoxical

Hypertension, possible squeals of a bicuspid aortic valve

(Infective endocarditis and aortic regurgitation) and paraplegia.

Baroreceptorre flexes activation of the rennin angiotensinaldosterone system, and excessive release o f catecholamine

Have been implicated as possible causes of immediate postoperative, systemic hypertension. Regardless of the etiology,

Intravenous administration of nitroprusside with or without

Esmolol effectively controls' the systemic blood pressure during the early postoperative period. Longer acting antihypertensive

Drugs may be needed if hypertension persists. Paraplegia manifesting during the immediate postoperative period is assumed to reflect ischemic damage to the spinal cord during the aortic cross-clamping required for surgically resection of the coarctation. Abdominal pain may occur during the postoperative period and is presumably due to sudden increases in blood flow to the gastro intestinatlract, Leading to increased vasoactivity.

The incidence of persistent or recurrent systemic hypertension and the survival rate are influenced by the patient's age at the time of surgery. Most of the patients who undergo surgery during childhood are normotensive 5 years later, whereas those who undergo surgery after 40 years of age often manifest persistently stomach per tension.

CYANOTICO NGENITAL

HEART DISEASE

Cyanotic congenital heart diseases characterized by a right to-left intracardiac shunt with as sociatedde creases in pulmonary blood flow and the development of arterial hypoxemia. The magnitude of shunting determines the severity of arterial hypoxemia. Er1'throcl'tosi secondary to chronic arterial hypoxemia results in a risk of thromboembolism, especially when the hematocrit exceeds 70%. Patients with secondary erlthrocytosis may exhibit coagulation defects most likely owing to deficiencies of vitamin K-dependent clotting factors in the liver and defective platelet aggregation. Development of a brain abscess is a major risk in patients with cyanotic congenital heart disease. The onset of a brain

Abscess often mimics a stroke. Survival in the presence of a right-to-left. Tracardiac shunt requires a communication between the hysteric and pulmonary circulations. Tetralogy of Fallot is the prototype of. Most children with, vanotic corrgenital heart disease do these defects not survive to adulthood

without surgical intervention. Principles for the management of a anesthesia are the same for all the cyanotic congenital cardiac defects.

Tetralogy of Fallot

Tetralogy of Fallot, the most common cyanotic congenital heart defect, is characterized, by a large ingle VSD, an aort at hat over rides the right and left ventricles, obstruction to right ventricular out flow (subvalvular, valvular, supravalvular, pulmonary arterial branches), and right ventricular hypertrophy

Several abnormalities may occur in association with tetra logy of

Fallot, including right aortic arch, ASD ("pent logy of Fallot"), and coronary arterial anomalies. Right ventricular hypertrophy

Occurs because the VSD permits continuous exposure of the right ventricle to the high pressure present in the left ventricle.

Right-to-left in tracardiac shunting occurs because of increase

Resistance of flow in the right ventricular out flow, tract, the severity Of which determines the magnitude of the shunt. Because the

resistance of flow across the right ventricular cult flow tract is relatively fixed, changes in system. Rivcascular resistance (drug induced) may affect the magnitude of the shunt.

 I) decreasing systemic vascular resistance in creaser right-to-left intracardiac shunting and accentuate arterial hypoxemia, where as in creases in hysteric vascular resistance(squatting)decrease left-to-right intracardiac shunting with resultant increases in pulrnouary blood flow. Diagnosis Echocardiography's used to establish the diagnosis and

Assess the presence of associate and abnormalities, the level and

Severity of the obstruction to right ventricular out flow, the size of the main pulmonary artery and its branches, and the number and location of the VSDs. Right-to-left shunting through the VSD is visualized by color Doppler imaging, and the severity of the right ventricular outflow tract obstruction can be determined by spectral Doppler measurement.

Cardiac catheterization further confirms the diagnosis and permits confirmation of anatomic and hemodynamic data, including the location and magnitude of the right-to-left shunt, the level and severity of the right ventricular outflow obstruction, the anatomic features of the right ventricular outflow obstruction, the anatomic features of the right ventricular outflow tract and the main pulmonary artery and its branches, and the origin and course of the coronary arteries. Magnetic resonance aging can also provide ruche of this information.

Signs and Symptoms

Most patients with tetra logy of Fallot have cyanosis from birth or beginning during the first year of life. The most common auscultatory finding is an ejection murmur heard along the left sternal border resulting from blood flow across the stenotic pulmonic valve. Congestive heart failure rarely

Develops because the large VSD permits equilibration of intraventricular pressures and cardiac workload. Chest radiographs show evidence of decreasing vascularity, and the heart. is "boot shaped" with an upturned right ventricular apex

and a concave main pulmonary arterial segment. The ECG

is characterized by changes of right axis deviation and right ventricular hypertrophy. Arterial oxygen desideration is present even when breathing l00o/o oxygen (Pao2 usually

< 50 mm Hg). Compensatory eqhropoiesis proportional to the magnitude of the arterial hypoxemia. The Parn2 and arterial pH are usually normal. Squatting is a common feature of children with tetralogy of Fallot .It is speculated that squatting increases the systemic vascular resistance by kinking the large arteries in the inguinal area. The resulting increase in systemic vascular resistanceted to decrease the magnitude of the right-to-left intracardiac shunt, which leads to increased pulmonary blood flow and subsequent improve reprint arterial oxygenate ion.

Hyper cyanotic Attacks Hyper cyanotic attacks are characterized by sudden spells of arterial hypoxemia associated with loosening cyanosis, tachypnea, and, in some instances, loss of consciousnesses, seizures, cerebrovascular accidents, and even death. These attacks can occur without obvious provocation but are often associated with crying or exercise. Their mechanism is not known, but the most likely explanation is

a sudden decrease in pulmonary blood flow due to spasm

of the infundibular cardiac muscle or decreased systemic vascular resistance.

Treatment of hyper cyanotic attacks is influenced by the cause of the pulmonary outflow obstruction. When symptoms reflect a dynamic infundibular obstruction (spasm), appropriate treatment is administration of B-adrenergic antagonists such as esmolol or propranolol. Indeed, chronic oral propranolol therapy is indicated in patients who have recurrent hyper cyanotic attacks caused by spasm of the outflow tract muscle. I f the cause is decreased systemic vascular resistance; treatment is intravenous administration of fluids and/or phenylephrine. Sympathomimetic drugs that display –agonist properties are not selected because they may accentuate the spasm of the infundibular cardiac muscle. Recurrent hyper cyanotic attacks indicate the need for surgical correction of the

Abnormalities associated with tetralogy of Fallot.

These attacks do not occur in adolescents adults. Adults with tetralogy of Fallot manifest dyspnea and limited exercise tolerance. They may also have complications of chronic cyanosis including eqthrocytosis, hyper viscosity, abnormalities of homeostasis, cerebral abscess or stroke, and infective errdocarditis. Cerehrovascular Accident Cerebrovascular accidents are common in children with severe tetralogy of Fallot. Cerebrovascular thrombosis or severe arterial hypoxemia may be the explanation for these adverse responses. Dehydration and polyqthemia may contribute to thrombosis. Hemoglobin concentrations exceeding 20 gl/dL are common in these patents.

Cerebral Abscess A cerebral abscess is suggested by the abrupt onset of headache, fever, and lethargy followed by persistentmes is and the appearance of seizure activity. The most likely cause is arterial seeding into areas of previous cerebral infarction.

Infective Endocarditis Infective endocarditis is a constant danger in patients with tetralogy of Fallot and is associated with a high mortality rate. Antibiotics should be administered to protect against this serious possibility whenever dental or

surgical procedures are planned in these patients.

Treatment

Treatment of tetralogy of Fallot is complete surgical correction

(closure of the VSD with a Dacron patch and relief of right ventricular outflow obstruction by placing a synthetic graft) when patients are extremely young. Infants with pulmonary Artesia undergo Rosella procedures. Without surgery,

mortality exceeds5 0% by 3 years of age .Pulmonic regurgitation due to an incompetent pulmonic valve usually results from surgical correction of the cardiac defects characteristic of tetraiogy of Faliot but poses no major hazard unless the distal pulmonary arteries are hypo plastic, in which case volume overload of the right ventricle secondary to regurgitates blood flow may result. Platelet dysfunction and hypofibrinogenemia are common in these patients and may

Contribute to postoperative bleeding problems. Right-to-left intracardiac shunting often develops through the foramen oval during the postoperative period. Shunting

through the foramen oval acts as a safety valve if the right ventricle is unable to function at the same efficiency as the left ventricle.

In the past, infants underwent one of three palliative procedures to increase pulmonary blood flow. All three palliative procedures in evolved anastomosis of a systemic artery to a pulmonary artery in an oxygenation. These palliative procedures are the Waterston procedure (side-to-side anastomosis of the ascending aorta and the right pulmonary artery), the

Potts operation (side-to-side anastomosis of the descending aorta to the Left pulmonary artery), and the Blalock-Tausig operation (end-to-side anastomosis of the subclavian artery to the pulmonary artery). Often, however, these procedures are associated with long-term complications such as pulmonary hypertension, 1eft ventricular volume overload, and distortion of the pulmonary arterial branches.

منبع : میلر              تاریخ نوشتار : زمستان 92

نویسنده :  زینب السادات شفیع پور     ترم چهارم     ورودی 90       

 دانشکده زینب (ع) لنگرود                 دانشگاه علوم پزشکی گیلان

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