tetralogy of fallot

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tetralogy of fallot

  1. 1. Tetralogy of fallotIntroduction: Tetralogy of Fallot (TOF) is one of the most common congenital heartdisorders (CHDs). This condition is classified as a cyanotic heart disorder,because tetralogy of Fallot results in an inadequate flow of blood to the lungsfor oxygenation (right-to-left shunt) (see the following image). Patients withtetralogy of Fallot initially present with cyanosis shortly after birth, therebyattracting early medical attention. Normal heart Tetralogy of Fallot Louis Arthur Fallot, after whom the name tetralogy of Fallot is derived,was not the first person to recognize the condition. Stensen first described it in1672; however, it was Fallot who first accurately described the clinical andcomplete pathologic features of the defects.Definitions:Tetralogy of Fallot (TOF) is a congenital heart defect which is classicallyunderstood to involve four anatomical abnormalities (although only three of 23
  2. 2. them are always present). It is the most common cyanotic heart defect, and themost common cause of blue baby syndromeEtiology and Pathophysiology: The cause(s) of most congenital heart diseases (CHDs) are unknown, although genetic studies suggest a multifactorial etiology. A study from Portugal reported that methylene tetrahydrofolatereductase (MTHFR) gene polymorphism can be considered a susceptibility gene for tetralogy of Fallot. Prenatal factors associated with a higher incidence of tetralogy of Fallot (TOF) include maternal rubella (or other viral illnesses) during pregnancy, poor prenatal nutrition, maternal alcohol use, maternal age older than 40 years, maternal phenylketonuria (PKU) birth defects, and diabetes. Children with Down syndrome also have a higher incidence of tetralogy of Fallot, as do infants with fetal hydantoin syndrome or fetal carbamazepine syndrome. As one of the conotruncal malformations, tetralogy of Fallot can be associated with a spectrum of lesions known as CATCH 22 (cardiac defects, abnormal facies, thymic hypoplasia, cleft palate, hypocalcemia). Cytogenetic analysis may demonstrate deletions of a segment of chromosome band 22q11 (DiGeorge critical region). Ablation of cells of the neural crest has been shown to reproduce conotruncal malformations. These abnormalities are associated with the DiGeorge syndrome and branchial arch abnormalities. The hemodynamics of tetralogy of Fallotdepend on the degree of right ventricular (RV) outflow tract obstruction (RVOTO). The ventricular septal defect (VSD) is usually nonrestrictive, and the RV and left ventricular (LV) pressures are equalized. If the obstruction is severe, the 24
  3. 3. intracardiac shunt is from right to left, and pulmonary blood flow may be markedly diminished. In this instance, blood flow may depend on the patent ductusarteriosus (PDA) or bronchial collaterals.Epidemiology  Tetralogy of Fallot (TOF) represents approximately 10% of cases of congenital heart disease (CHD), occurs in 3-6 infants for every 10,000 births, and is the most common cause of cyanotic CHD. This disorder accounts for one third of all CHD in patients younger than 15 years.  In most cases, tetralogy of Fallot is sporadic and nonfamilial. The incidence in siblings of affected parents is 1-5%, and it occurs more commonly in males than in females. The disorder is associated with extracardiac anomalies such as cleft lip and palate, hypospadias, and skeletal and craniofacial abnormalities. Genetic studies indicate that in some patients with tetralogy of Fallot, there may be 22q11.2 deletion and other submicroscopic copy number alterations.[4]  Tetralogy of Fallot is also observed in other mammals, including horses and rats.Diagnosis of Tetralogy of Fallot:History: The clinical features of tetralogy of Fallot (TOF) are directly related tothe severity of the anatomic defects. Most infants with tetralogy of Fallot havedifficulty with feeding, and failure to thrive (FTT) is commonly observed.Infants with pulmonary atresia may become profoundly cyanotic as theductusarteriosus closes unless bronchopulmonary collaterals are present.Occasionally, some children have just enough pulmonary blood flow and do not 25
  4. 4. appear cyanotic; these individuals remain asymptomatic, until they outgrowtheir pulmonary blood supply. At birth, some infants with tetralogy of Fallot do not show signs ofcyanosis, but they may later develop episodes of bluish pale skin during cryingor feeding (ie, "Tet" spells). Hypoxic tet spells are potentially lethal,unpredictable episodes that occur even in noncyanotic patients with tetralogy ofFallot. The mechanism is thought to include spasm of the infundibular septum,which acutely worsens the right ventricular (RV) outflow tract obstruction(RVOTO). These spells can be aborted with relatively simple procedures. A characteristic fashion in which older children with tetralogy of Fallotincrease pulmonary blood flow is to squat. Squatting is a compensatorymechanism, of diagnostic significance, and highly typical of infants withtetralogy of Fallot. Squatting increases peripheral vascular resistance (PVR) andthus decreases the magnitude of the right-to-left shunt across the ventricularseptal defect (VSD). Exertional dyspnea usually worsens with age.Occasionally, hemoptysis due to rupture of the bronchial collaterals may resultin the older child.The rare patient may remain marginally and imperceptibly cyanotic, oracyanotic and asymptomatic, into adult life.Cyanosis generally progresses with age and outgrowth of pulmonaryvasculature and demands surgical repair. The following factors can worsencyanosis in infants with tetralogy of Fallot: Acidosis Stress Infection Posture Exercise 26
  5. 5. Beta-adrenergic agonists Dehydration Closure of the ductusarteriosusThe predominant shunt is from right to left with flow across the VSD into theleft ventricle (LV), which produces cyanosis and an elevated hematocrit value.When the pulmonary stenosis is mild, bidirectional shunting may occur. Insome patients, the infundibular stenosis is minimal, and the predominant shuntis from left to right, producing what is called a pink tetralogy. Although suchpatients may not appear cyanotic, they often have oxygen desaturation in thesystemic circulation.Symptoms generally progress secondary to hypertrophy of the infundibularseptum. Worsening of the RVOTO leads to RV hypertrophy, increased right-to-left shunting, and systemic hypoxemia.Physical ExaminationMost infants with tetralogy of Fallot (TOF) are smaller than expected for age.Cyanosis of the lips and nail bed is usually pronounced at birth; after age 3-6months, the fingers and toes show clubbing.A systolic thrill is usually present anteriorly along the left sternal border. Aharsh systolic ejection murmur (SEM) is heard over the pulmonic area and leftsternal border. When the right ventricular (RV) outflow tract obstruction(RVOTO) (eg, from pulmonary atresia) is moderate, the murmur may beinaudible (more cyanotic patients have greater obstruction and a softermurmur). The S2 is usually single (the pulmonic valve closure is not heard).During cyanotic episodes, murmurs may disappear, which is suggestive oflessened RV outflow to the pulmonary arteries. In individuals withaortopulmonary collaterals, continuous murmurs may be auscultated. Thus, an 27
  6. 6. acyanotic patient with tetralogy of Fallot (pink tet) has a long, loud, systolicmurmur with a thrill along the RVOTThe following may also be noted: RV predominance on palpation May have a bulging left hemithorax Aortic ejection click Squatting position (compensatory mechanism) Scoliosis (common) Retinal engorgement HemoptysisHematologic StudiesHemoglobin and hematocrit values are usually elevated in proportion to thedegree of cyanosis. Prolonged cyanosis causes reactive polycythemia thatincreases the oxygen-carrying capacity. The oxygen saturation in systemicarterial blood typically varies from 65-70%. All patients with tetralogy of Fallotwho experience significant cyanosis have a tendency to bleed because ofdecreased clotting factors and low platelet count. Hyperviscosity andcoagulopathy often ensue and are particularly deleterious in patients with aright-to-left intracardiac shunt. The usual findings are diminished coagulationfactors, and diminished total fibrinogen, which are associated with prolongedprothrombin and coagulation times.ABG and OximetryArterial blood gas (ABG) results show varying oxygen saturation, but pH andpartial pressure of carbon dioxide (pCO2) are normal, unless the patient is inextremis, such as during a tet spell. 28
  7. 7. Oximetry is particularly useful in a dark-skinned patient or an anemic patientwhose level of cyanosis is not apparent. Generally, cyanosis is not evident until3-5 g/dL of reduced hemoglobin is present.A decrease in systemic vascular resistance (SVR) during exercise, bathing, orfever potentiates a right-to-left shunt and precipitates hypoxemia.Radiologic StudiesImaging studies used in the evaluation of tetralogy of Fallot (TOF) includeechocardiography, chest radiographs, and magnetic resonance imaging (MRI).EchocardiographyDuctusarteriosus, muscular ventricular septal defect (VSD), or atrial septaldefect (ASD) is accurately diagnosed with color-flow Dopplerechocardiography. The coronary anatomy can be revealed with some degree ofaccuracy, and valvar alterations can be detected with ease. In many institutions,echocardiography is the only diagnostic study used before surgery.Echocardiograms will usually reveal a large VSD with an overriding aorta andvariable degrees of right ventricular (RV) outflow tract obstruction (RVOTO).RadiographyInitially, chest radiographs may not reveal any abnormality; however,diminished vascularity in the lungs and diminished prominence of thepulmonary arteries gradually become apparent.The hallmark of tetralogy of Fallot is the classic boot-shaped heart (coeur ensabot) (see the following image). 29
  8. 8. Uplifted apex and absence of pulmonary artery segment typifies the "coeur ensabot" (ie, boot-shaped heart) of tetralogy of Fallot.Magnetic resonance imagingMRI provides good delineation of the aorta, RVOT, VSDs, RV hypertrophy,and the pulmonary artery and its branches.[9] MRI can also be used to measureintracardiac pressures, gradients, and blood flows.Drawbacks to MRI include the need for prolonged imaging times and therequirement for sedation in small children to prevent motion artifacts.Additionally, sick infants cannot be observed when enclosed in an MRI tunnel.ElectrocardiographyThe use of electrocardiography (ECG) may be limited if multiple ventricularseptal defects (VSDs) or coronary artery anomalies are present or if the distalpulmonary artery cannot be visualized adequately.Right axis deviation (+120° to +150°) with right ventricular (RV) enlargementmay be seen.[10] Combined ventricular hypertrophy and right atrial hypertrophymay be present.If RV hypertrophy is absent on ECG, the diagnosis of tetralogy of Fallot shouldbe in doubt. 30
  9. 9. A typical preoperative ECG is shown below. Typical preoperative electrocardiogram (ECG) for tetralogy of Fallot.Partial or complete right bundle branch block may be present; this is especiallytrue of patients after surgical repair (see the following image).Typical findings on postoperative electrocardiogram (ECG) for tetralogy ofFallot.Cardiac Catheterization and AngiographyCardiac catheterization provides angiographic visualization of ventricular andpulmonary artery size. Catheterization also helps obtain pressure and oxygensaturation measurements in different chambers and identifies any possibleshunts. In the presence of preexisting shunts, angiograms should be obtainedbefore complete surgical repair.Cardiac catheterization findings include the following: Assessment of the pulmonary annulus size and pulmonary arteries 31
  10. 10. Assessment of the severity of right ventricular (RV) outflow tract obstruction (RVOTO) Location of the position and size of the ventricular septal defect (VSD) Eliminating/ruling out possible coronary artery anomaliesAutomatic internal cardiac defibrillator (AICD) placement is recommended inpatients with sustained ventricular tachycardia and those resuscitated after asudden death event.[11, 12]Angiograms help identify coronary artery anomalies (see the image below);however, catheterization is not mandatory in all patients. Cardiac catheterizationis extremely useful if the anatomy cannot be completely defined byechocardiography, if disease in the pulmonary arteries is a concern, or ifpulmonary vascular hypertension is possible.This angiogram shows a catheter in the right ventricle—severe infundibularstenosis.Diagnostic ConsiderationsWide variation in the basic anatomic morphology, pathophysiology, clinicalsigns and symptoms, and surgical methods of therapy is noted for tetralogy ofFallot (TOF). Pathophysiology primarily depends on the severity of the right 32
  11. 11. ventricular (RV) outflow tract (RVOT) obstruction. RVOT obstructiondetermines the severity of right-to-left shunting, which is typical.Other conditions to consider when evaluating a patient with suspected Tetralogyof Fallot with pulmonary stenosis include acute anemia, asthma and reactiveairway disease, bacteremia and sepsis, cardiogenic shock, Ebstein malformationof the tricuspid valve, pseudotruncusarteriosus, pulmonary atresia, septic shock,and ventricular septal defect (VSD).Differential Diagnoses Aortic Stenosis Pediatric Acute Respiratory Distress Syndrome Pediatric Apnea Pediatric Bronchiolitis Pediatric Foreign Body Ingestion Pediatric Patent DuctusArteriosus Surgery Pediatric Pneumonia Pneumothorax Pulmonic Valvular Stenosis Sickle Cell AnemiaPrehospital ManagementInfants with cyanosis and/or respiratory distress, including those with tetralogyof Fallot (TOF), require oxygen. Blow-by O2 (BBO2) is the least objectionable.Use the open-end of a cannula or tube.Permit the baby to remain with the mother or father. Do not provoke the infantby attempting to start an intravenous (IV) line, especially if one is not skilled inpediatric IV placement. However, an intraosseous (IO) insertion could be animmediate life-saving tool in emergent situations 33
  12. 12. Emergency Department ManagementThe emergency physician should be able to recognize and treat a hypercyanoticepisode (tet spell) as one of the very few pediatric cardiology emergencies thatmay present to the emergency department (ED).Hypercyanotic episodes are characterized by paroxysms of hyperpnea,prolonged crying, intense cyanosis, and decreased intensity of the murmur ofpulmonic stenosis. The mechanism is secondary to infundibular spasm and/ordecreased systemic vascular resistance (SVR) with increased right-to-leftshunting at the ventricular septal defect (VSD), resulting in diminishedpulmonary blood flow. If left untreated, it may result in syncope, seizure,stroke, or death.Treatment for the acute setting of hypercyanosisPlace the baby on the mothers shoulder with the infants knees tucked upunderneath. This provides a calming effect, reduces systemic venous return, andincreases SVR.Oxygen is of limited value, as the primary abnormality is reduced pulmonaryblood flow.Morphine sulfate, 0.1-0.2 mg/kg intramuscularly (IM) or subcutaneously (SC),may reduce the ventilatory drive and decrease systemic venous return.Phenylephrine, 0.02 mg/kg IV, is used to increase SVR.Case reports in the literature describe using a dexmedetomidine infusion toameliorate symptoms in hypercyanotic neonates.[13] Caution is warranted andthe drug must be carefully titrated by initiating at a very low dose of 0.1-0.125mcg/kg/hour (without a bolus).[14] A case report of a 3-year old child withhistory of tetralogy of Fallot repair at age 9 months describes atrial standstillfollowing mitral valve replacement.[15] 34
  13. 13. Treating acidosis with sodium bicarbonate may reduce the respiratory centerstimulating effect of acidosis.As a last resort, use general anesthesia.Medical TreatmentAsymptomatic infants need no special medical treatment.Surgery is the definitive treatment for the cyanotic patient with tetralogy ofFallot (TOF).The primary role of medical therapy is in preparation for surgery. Most infantshave adequate saturations and usually undergo elective repair. In infants withacute cyanotic episodes, placing them in a knee-chest position may provehelpful in addition to administering oxygen and intravenous (IV) morphine.In severe episodes, IV propranolol (Inderal) may be administered, which relaxesthe infundibular muscle spasm causing right ventricular (RV) outflow tractobstruction (RVOTO). Progressive hypoxemia and the occurrence of cyanoticspells are indications for early surgery.Consult a pediatric cardiologist and pediatric surgeon.Surgical ConsiderationsBecause tetralogy of Fallot (TOF) is a progressive disorder, most infants requiresome type of surgical procedure. The timing of complete surgical repair isdependent on numerous variables, including symptoms and any associatedlesions (eg, multiple ventricular septal defect [VSD], pulmonary atresia).Currently, the trend is to perform a complete surgical procedure (oftenelectively) before the age of 1 year and preferably by the age of 2 years. Studieshave shown, however, that surgery is preferably done at or about 12 months of 35
  14. 14. age. The majority of patients born with tetralogy of Fallot now thrive well intotheir adult years.Most surgeons today recommend the primary corrective procedure, and currentresults are excellent. Infants with cyanosis are stabilized by administeringprostaglandins (to maintain the ductus in an open state). The use ofprostaglandins has significantly decreased the need to perform urgent surgery.Instead of performing systemic-to-pulmonary artery shunts on critically illcyanotic-hypoxic infants, surgeons now have the luxury of having extra time toassess the patients anatomy and to perform the primary procedure on anelective basis.Primary repair avoids prolonged right ventricular (RV) outflow obstruction andthe subsequent right ventricular hypertrophy (RVH), prolonged cyanosis, andpostnatal angiogenesis.Factors that increase risk for early repair of tetralogy of Fallot (TOF) includethe following: Low birth weight Pulmonary artery atresia Major associated anomalies Multiple previous surgeries Absent pulmonary valve syndrome Young or old age Severe annular hypoplasia Small pulmonary arteries High peak RV–to–left ventricular pressure ratio Multiple VSDs Coexisting cardiac anomalies 36
  15. 15. ContraindicationsContraindications to primary repair in tetralogy of Fallot include the following: The presence of an anomalous coronary artery Very low birth weight Small pulmonary arteries Multiple VSDs Multiple coexisting intracardiac malformationsPalliative ProceduresThe goals of palliation for tetralogy of Fallot (TOF) are to increase pulmonaryblood flow independent of ductal patency and to allow pulmonary artery growthand even total correction. Occasionally, an infant with pulmonary atresia or ananomalous left anterior descending (LAD) coronary artery that crosses the rightventricular (RV) outflow tract (RVOT) may not be a surgical candidate forestablishing transannular RV–to–pulmonary artery continuity and may requireplacement of a conduit.Although artificial conduits can be used, infants with extremely smallpulmonary arteries may not tolerate total correction in infancy. These infantsmay require palliation instead of corrective surgery. Various types of palliativeprocedures have been developed, but the current procedure of choice is theBlalock-Taussig shunt.The Potts shunt has been abandoned because of a tendency toward increasedpulmonary blood flow and increasing difficulty with takedown at the time ofcorrective surgery. The Waterston shunt is sometimes used, but it also increasespulmonary artery blood flow. This shunt is more related to pulmonary arterystenosis, which generally requires reconstruction. The Glenn shunt is no longerused because of difficulty in performing a subsequent definitive repair. 37
  16. 16. Blalock-Taussig shuntGiven the problems associated with the aforementioned shunts, placement ofthe modified Blalock-Taussig shunt (using a Gore-Tex graft between thesubclavian artery and pulmonary artery) is the procedure of choice (see thefollowing images). Advantages of the modified Blalock-Taussig shunt include:(1) preservation of the subclavian artery, (2) suitability for use on either side,(3) good relief of cyanosis, (4) easier control and closure at time of primaryrepair, (5) excellent patency rate, and (6) decreased incidence of iatrogenicpulmonary/systemic artery trauma. This image shows completed blocking with a Taussig shuntThis image shows a closed ventricular septal defect and closure of rightventriculotomy with Gore-Tex. 38
  17. 17. The mortality rate is reportedly less than 1% when placing this shunt. However,the Blalock-Taussig shunt elicits a few complications, including hypoplasia ofthe arm, digital gangrene, phrenic nerve injury, and pulmonary artery stenosis.The longevity of palliation after shunt placement varies according to thepatients age at the time of surgery and the type of shunt.Other palliation proceduresOther forms of palliation that are rarely used today include patching of theRVTO without cardiopulmonary bypass (CPB). This procedure can causedestruction of the pulmonary valve and significant intrapericardial adhesions,and the increased pulmonary artery blood flow can result in congestive heartfailure (CHF); therefore, its role is limited to treatment of infants with tetralogyof Fallot complicated by pulmonary atresia and/or hypoplasia of the pulmonaryartery.In very ill neonates with multiple medical problems, balloon pulmonaryvalvulotomy has been shown to increase oxygen saturation, thus obviating theneed for emergency palliative surgery. However, perforation of the pulmonaryartery is a risk with this procedure in neonates. A study by Park et al indicatedthat shunting or primary repair of neonates with symptomatic tetralogy of Fallotproduced similar mortality and results.A study by Robinson et al found that intraoperative balloon valvuloplasty isassociated with significant longitudinal annular growth, with normalization ofannular size over time. This technique may be most useful in patients withmoderate pulmonary stenosis and moderate pulmonary valve dysplasia.Corrective SurgeryPrimary correction is the ideal operation for treatment of tetralogy of Fallot(TOF) and is usually performed under cardiopulmonary bypass (CPB). The 39
  18. 18. aims of the surgery are to close the ventricular septal defect (VSD), resect thearea of infundibular stenosis, and relieve the right ventricular (RV) outflow tractobstruction (RVOTO).Before cardiopulmonary bypass is initiated, previously placed systemic-to-pulmonary artery shunts are isolated and taken down. Patients then undergocardiopulmonary bypass. Associated anomalies, such as atrial septal defect(ASD) or patent foramen ovale, are closed.Postoperative Monitoring and ResultsAll infants undergoing open-heart procedures are sent to the pediatric intensivecare unit (PICU). Hemodynamic parameters must be followed postoperatively.One study of children who underwent complex open heart surgery proceduresfound short-term outcome may be predicted by the amount of inotropic andpressor support received in the ICU. The greater the support, the worse theoutcome.All infants initially remain intubated on a ventilator until cardiac andrespiratory statuses stabilize. To maintain systemic peripheral perfusion,adequate cardiac output and atrial pacing may be required. Patients should beweighed daily to follow volume status. Patients with heart block should havetemporary atrioventricular (AV) pacing. If intrinsic conduction has not returnedin 5-6 days, the patient probably needs a permanent pacemaker.ResultsThe outcome of surgical repair is excellent with minimal morbidity andmortality. To date, no difference in operative mortality rates has been notedbetween transventricular and transatrial approaches.[21]The occasional patient may have an elevated right ventricle (RV)–to–leftventricle (LV) pressure ratio. This may be due to a number of causes includinga residual ventricular septal defect (VSD), pulmonary artery stenosis, and 40
  19. 19. pulmonary artery and valve atresia. These patients tend to do poorly, andechocardiography is warranted to find the cause. Surgical revision may berequired to correct the etiology of the high RV pressures. As in previous studies,it is now apparent that preservation of pulmonary annulus can decrease the rateof reoperation.With improved techniques, excellent results with early 1-stage repair in infantshave been reported. Overall, the mortality rate in most series is 1-5% when therepair is performed primarily or after a systemic-to-pulmonary artery shunt.Similarly, the mortality rate of infants undergoing palliative shunt placement islow (0.5-3%). The survival rate at 20 years is approximately 90-95%.Improved techniques of myocardial protection with hypothermia, cardioplegia,and even total circulatory arrest are providing excellent results by enablingmore precise anatomic repairs in younger infants. Nevertheless, infantsreceiving complete correction before age 1 year have an increased riskcompared with patients older than 1 year.Revision/reoperationThe literature suggests that approximately 5% of individuals will need arevision/reoperation at some point. Indications for early reoperation include aresidual VSD or a residual RV outflow tract obstruction (RVOTO). ResidualVSDs are poorly tolerated in patients with tetralogy of Fallot (TOF), becausethese individuals cannot tolerate an acutely imposed volume overload. Small,residual VSDs are common after surgical repair and are usually clinicallyinsignificant.A residual VSD with a 2:1 shunt or an RVOTO of greater than 60 mm Hg is anurgent indication for reoperation. Surgery can be performed with low risk andcan result in dramatic improvements. Occasionally, pulmonary valveinsufficiency may increase and may be associated with RV failure. 41
  20. 20. Once tetralogy of Fallot has been repaired in infancy or childhood, about 5% ofindividuals require repair or replacement of the pulmonary valve. Because ofbetter results from surgery in the present era, long-term survivors areincreasingly reported. In most of these individuals, pulmonary regurgitation isthe clinical presentation and can be treated with a prosthetic tissue valve.Thisproblem is generally treated with a pulmonary valve replacement. Porcinevalves are preferred over mechanical valves, because they have lesser tendencyto thrombose.Surgical ComplicationsEarly postoperative complications following repair of tetralogy of Fallot (TOF)include the creation of heart block and residual ventricular septal defects(VSDs). Ventricular arrhythmias are more common and are reportedly the mostfrequent cause of late postoperative death. Sudden death from ventriculararrhythmias has been reported in 0.5% of individuals within 10 years of repair.The arrhythmias are thought to occur in fewer than 1% of patients having anearly operation. As with most heart surgery, the risk of endocarditis is lifelong,but the risk is much less than in a patient with an uncorrected tetralogy of Fallot.Medication:The goals of tetralogy of Fallot (TOF) therapy are to reduce the ventilatorydrive, increasing systemic venous return, and to increase peripheral vascularresistance.AnalgesicsAnalgesic agents reduce ventilatory drive. In addition, pain control ensurespatient comfort and promotes pulmonary toilet. Most analgesic agents have 42
  21. 21. sedating properties, which are beneficial for patients who are havinghypercyanotic episodes.Morphine sulfate (Duramorph, Astramorph, MS Contin)Morphine is the drug of choice (DOC) for narcotic analgesia because of itsreliable and predictable effects, safety profile, and ease of reversibility withnaloxone.This agent is administered intravenously (IV), may be dosed innumber of ways, and is commonly titrated until the desired effect is obtained.Alpha-adrenergic AgonistsAlpha-adrenergic agents improve hemodynamic status by improvingmyocardial contractility and increasing heart rate, resulting in increased cardiacoutput. Peripheral resistance is increased by vasoconstriction, increased cardiacoutput, and elevated blood pressure.PhenylephrinePhenylephrine is a strong postsynaptic alpha-receptor stimulant with little beta-adrenergic activity. This drug produces vasoconstriction of arterioles, therebyincreasing peripheral venous return.PrognosisEarly surgery is not indicated for all infants with tetralogy of Fallot (TOF),although, without surgery, the natural progression of the disorder indicates apoor prognosis. The progression of the disorder depends on the severity of rightventricular (RV) outflow tract obstruction (RVOTO). In the present era ofcardiac surgery, children with simple forms of tetralogy of Fallot enjoy goodlong-term survival with an excellent quality of life. Late outcome data suggestthat most survivors are in New York Heart Association (NYHA) classification I,although maximal exercise capability is reduced in some. 43
  22. 22. Sudden death from ventricular arrhythmias has been reported in 1-5% ofpatients at a later stage in life, and the cause remains unknown. One study foundleft ventricular longitudinal dysfunction to be associated with a greater risk ofdeveloping life-threatening arrhythmias.Continued cardiac monitoring into adultlife is necessary. For some time, it has been suspected that certain children mayhave inherited a predispostion to developing long QT syndrome. A 2012 studyby Chiu confirmed this suspicion.If left untreated, patients with tetralogy of Fallot face additional risks thatinclude paradoxical emboli leading to stroke, pulmonary embolus, and subacutebacterial endocarditis. In most of these children the causes of stroke have beenrelated to thromboemboli, prolonged hypotension/anoxix and polycythemia.What is often forgotten is that residual shunts or a patent foramen ovale are alsoknown causes of strokes. The investigation of strokes in these children usuallybegins with a CT scan of the brain followed by an ECHO.Without surgery, mortality rates gradually increase, ranging from 30% at age 2years to 50% by age 6 years. The mortality rate is highest in the first year andthen remains constant until the second decade. No more than 20% of patientscan be expected to reach the age of 10 years, and fewer than 5-10% of patientsare alive by the end of their second decade.Most individuals who survive to age 30 years develop congestive heart failure(CHF), although individuals whose shunts produce minimal hemodynamiccompromise have been noted, albeit rarely, and these individuals achieve anormal life span. However, cases of survival of patients into their 80s have beenreported. Due to advanced surgical techniques, a 40% reduction in deathsassociated with tetralogy of Fallot was noted from 1979 to 2005.As might beexpected, individuals with tetralogy of Fallot and pulmonary atresia have theworst prognoses, and only 50% survive to age 1 year and 8% to age 10 years. 44

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