Andersons pediatric cardiology 929

and are not cyanosed With increasing right ventricular hypertrophy, the subpulmonary obstruction becomes more marked and, as the shunt is reversed, the patients exhibit signs and progression as described for the group with moderate obstruction Presentation With “Absent Pulmonary Valve.” When tetralogy is complicated by so-called absence of the leaflets of the pulmonary valve, which are usually present in rudimentary form, the presentation is characteristic yet different from the previously described groups The majority with this complication present in infancy with respiratory symptoms of inspiratory and expiratory stridor, dyspnea caused by lobar collapse, or sometimes lobar emphysema These features reflect compression of the bronchial tree by the grossly dilated proximal pulmonary arteries Although bronchial obstruction may lead to lobar collapse and subsequent infection, partial obstruction may produce a ball-valve effect, resulting in emphysema Because there is stenosis at the site of the rudimentary leaflets of the pulmonary valve, symptoms directly related to abnormal hemodynamics are unusual Squatting Squatting, along with other postures, may alleviate the degree of cyanosis, dyspnea, or feeling of faintness induced by exercise The means by which squatting alleviates the symptoms of cyanosis and dyspnea have caused considerable debate Irrespective of the precise mechanisms, there is little doubt that squatting causes an abrupt increase in systemic venous return and a rise in systemic vascular resistance Right-to-left shunting is decreased by an increase in systemic vascular resistance This results in immediate improvement of effective pulmonary blood flow and an increase of arterial oxygenation Hypercyanotic Attacks An important and sometimes dramatic feature of patients with tetralogy is the occurrence of unprovoked severe cyanosis, which may lead to reduced cardiac output and be accompanied by transient loss of consciousness.14 These episodes, which are most common between 6 months and 2 years of age,15 are potentially dangerous, as they may lead to cerebral damage or even death.14 The majority last between 15 and 60 minutes, but an individual spell may be of shorter duration or can last for several hours Initial presentation of infants or children may be with a history of episodic loss of consciousness or convulsions, episodes of going floppy or pale, transient vacant episodes, or episodes of becoming deeply cyanosed followed by loss of consciousness or sleep Another striking feature of these spells may be episodes of very rapid deep respiration or hyperpnea or a high-pitched abnormal cry The episodes are usually sufficiently dramatic or unusual for parents to volunteer information, but specific questioning concerning their presence should be part of every outpatient assessment In 1958, Wood postulated that the spells resulted from infundibular spasm or shutdown.14 Many now believe that the concept of infundibular “spasm,” considered as a primary phenomenon, is unsupported by the anatomy or physiology of the subpulmonary infundibulum They suggest that the “shutdown” is secondary to other primary physiologic influences, such as dehydration, or tachycardia-induced reduction in right ventricular preload, systemic vasodilation in response to fever, or other sympathetic activity Irrespective of their etiology, the occurrence of such episodes should lead to prompt treatment with continuous beta blockade and referral for surgery or interventional catheterization as dictated by the institutional protocols Physical Examination The essential abnormal cardiac findings in the neonate with severe TOF are cyanosis and, on auscultation, a systolic ejection murmur with a single second heart sound Overt clubbing of the fingers and toes is typically not detected until 2 or 3 years of age; therefore it is unusual today in the West The baby may grow normally, although a higher proportion weigh less than would be expected Some degree of facial dysmorphism is quite common, and typical features of associated syndromes may be obvious, such as DiGeorge, Goldenhar, or Down syndromes All patients should undergo chromosomal analysis on presentation with specific fluorescent in situ hybridization for the 22q11 deletion Pulses are almost always normal in all limbs, aortic coarctation being exceedingly rare in symptomatic neonates with TOF The cardiac impulse may be normal, or the parasternal right ventricular impulse may be increased The first heart sound is normal, but the second is characteristically single In contrast to patients having pulmonary stenosis with an intact ventricular septum, pulmonary ejection sounds in the second or third intercostal space or third and fourth heart sounds are virtually never found in children with tetralogy An aortic ejection click may sometimes be heard at the lower left sternal edge or the apex The duration of the systolic ejection murmur will vary depending on the degree of infundibular stenosis The shorter the murmur, the tighter the stenosis and, in turn, the greater the cyanosis Coexisting “absent pulmonary valve syndrome” is characterized by an additional long, loud, early diastolic decrescendo murmur from pulmonary regurgitation, which should be easily distinguishable from a continuous murmur When a loud continuous murmur is heard in the neonatal period, and clinical features are otherwise compatible with the diagnosis of tetralogy, it is more likely to originate from flow through major aortopulmonary collateral arteries than the arterial duct The patient is likely to have coexisting pulmonary atresia In these patients, cyanosis may not be so marked since pulmonary blood flow is more adequately maintained through the collateral arteries Children with tetralogy in whom subpulmonary obstruction is minimal or absent at birth exhibit tachypnea, dyspnea, and intercostal or subcostal recession This group has a large left-to-right shunt, with an increased flow of blood to the lungs A prominent parasternal impulse and hepatomegaly may be present On auscultation, the second sound is split, possibly with an accentuated pulmonary component Investigations Although the diagnosis of TOF is usually made from clinical assessment, confirmation is now provided largely by cross-sectional echocardiography Before describing the typical echocardiographic features, however, the plain chest radiograph and electrocardiogram are discussed, as these are usually carried out as part of the general cardiac assessment of a child Chest Radiograph In the acyanotic patient with tetralogy, the plain chest radiograph may be normal Most patients have the usual arrangement of thoracic and abdominal organs together with a left-sided heart, but tetralogy may occur with a mirror-imaged arrangement, when the heart is usually right-sided With the usual atrial arrangement, up to one-third of patients with tetralogy have a right aortic arch Of all subjects with a right aortic arch, three-quarters have TOF with or without pulmonary atresia The diagnosis is even more likely if there are reduced pulmonary vascular markings The latter is usually reduced in cyanotic patients, the lung fields being strikingly oligemic in neonates when subpulmonary obstruction is severe In contrast, vascular markings will be normal when infundibular stenosis is moderate When subpulmonary obstruction is minimal,