PAUL L. ARONSON

DEFINITION OF THE COMPLAINT

Vomiting is defined as the forceful contraction of abdominal muscles and the diaphragm in a coordinated fashion expelling the gastric contents through an open gastric cardia into the esophagus and out through the mouth. The medullary vomiting center coordinates this process of vomiting via efferent pathways of the vagus and phrenic nerves. Stimulation of the medullary vomiting center occurs either directly or through the chemoreceptor trigger zone. Direct stimulation may occur through afferent vagal signals from the gastrointestinal tract or other sites including but not limited to the vestibular system, the cerebral cortex, or the hypothalamus. The chemoreceptor trigger zone in the area postrema of the fourth ventricle can be activated by noxious sights and smells or by chemical stimuli in the blood secondary to medications, metabolic abnormalities, and certain toxins.

Gastroesophageal reflux is not vomiting but rather regurgitation, and despite being projectile at times, is an effortless return of gastric contents into the mouth without nausea or coordinated muscular contractions.

COMPLAINTS BY CAUSE AND FREQUENCY

It is important to remember that vomiting is not a diagnosis but rather a symptom of an underlying pathologic process that requires a thorough evaluation. The causes of vomiting can be grouped based on age of presentation (Table 3-1) or etiology (Table 3-2).

QUESTIONS TO ASK AND WHY

Thorough history taking is imperative for formulating an accurate differential diagnosis and eventually discovering the correct etiology of vomiting. Consideration of the vomiting duration and pattern, the content of the emesis and associated symptoms provides a framework for creating a differential diagnosis. The following questions may help provide clues to the correct diagnosis:

• What is the duration of vomiting?

—Acute episodes of vomiting carry a much different differential diagnosis than either chronic or cyclic vomiting. Acute vomiting is mostly due to infectious or metabolic conditions though it may also be caused by toxic ingestions or surgical emergencies, such as appendicitis and ovarian torsion. Chronic vomiting tends to have a gastrointestinal etiology and may be due to a partial mechanical obstruction as seen in hiatal hernia, or chronic gastrointestinal diseases, such as inflammatory bowel disease or celiac disease. Other conditions causing prolonged vomiting include peptic ulcers, dysmotility syndromes, increased intracranial pressure, psychogenic disturbance, pregnancy, and lead poisoning. Cyclic vomiting tends to be extraintestinal and is usually due to migraine or migraine equivalents, cardiac arrhythmias, or ureteral pelvic junction (UPJ) obstruction. Inborn errors of metabolism, while rare, are another cause of cyclic vomiting especially if associated with episodic neurologic symptoms.

• Is there any timing pattern to the vomiting?

—Episodes of vomiting that occur with a regular diurnal pattern are also helpful clues. Early morning vomiting can be very ominous due to increased intracranial pressure but could also occur secondary to morning sickness from pregnancy. Vomiting after eating specific foods may be due to a food allergy. Vomiting patterns may also become apparent if secondary gain is achieved, such as absence from school or tests, or it may be associated with school phobia. Vomiting that occurs shortly after eating is consistent with esophageal or gastric outlet obstructions or peptic ulcer disease, though may also be due to psychogenic vomiting.

• Is the vomiting effortless?

—Gastroesophageal reflux occurs in almost all newborns, but by 6 months of age, less than 5% of children are symptomatic. It tends to be effortless, not associated with pain or morbidity. Rarely will reflux be severe enough to cause discomfort and arching, Sandifer syndrome (in which the reflux mimics seizure activity), or poor weight gain at which point medical therapy may be necessary. True vomiting tends to be a more noxious event often causing pain and retching.

• Is there bilious emesis?

—The presence of bilious emesis suggests an obstruction distal to the ampulla of Vater but may also be present in nonobstructed patients after prolonged episodes of vomiting due to a relaxed pylorus. Bilious vomiting in a neonate should be treated as a surgical emergency until proven otherwise. Neonates with bilious emesis may have intestinal obstruction associated with malrotation and midgut volvulus or less commonly, intestinal atresias. The absence of bilious emesis is also important, especially in neonates, because obstruction proximal to the ampulla ofVater (e.g., pyloric stenosis) may cause frequent nonbilious emesis.

• Is there any blood in the vomitus?

—Either a Gastroccult or Hematest must first confirm the presence of blood in emesis. If blood is present then hematemesis must be distinguished from hemoptysis. The blood in hematemesis ranges from bright red to coffee-ground depending on its length of time in contact with gastric contents, but tends to be darker red in color, acidic and associated with retching or gastrointestinal complaints. The blood in hemoptysis is bright red, frothy, alkaline, and associated with respiratory symptoms. Hematemesis may be due to peptic ulcers, Mallory-Weiss tears, esophagitis, esophageal varices, acute iron ingestion, gastritis, vascular malformations, or bleeding diatheses.

• Is undigested food present in the vomitus?

—The presence of undigested food material is very common in children with gastroesophageal reflux who present with episodes of effortless postprandial regurgitation. Other conditions that predispose to undigested food in emesis include esophageal atresia or strictures, esophageal or pharyngeal (Zenker’s) diverticulum, or achalasia. Old food present in the emesis may signify a gastric outlet obstruction or a gastric motility disorder.

• Is fecal material present in the emesis?

—The presence of fecal material in the emesis is uncommon but when present suggests a distal intestinal obstruction such as Hirshsprung disease, peritonitis, gastrocolic fistula, or bacterial overgrowth in the stomach or small intestine.

• Is diarrhea occurring with the vomiting?

—The presence of diarrhea and vomiting suggests a gastrointestinal disorder of which an infectious gastroenteritis is the most common, though if chronic in nature can be due to inflammatory bowel disease or celiac disease. Isolated vomiting tends to have a far greater differential involving many other organ systems. Isolated vomiting may occur in serious conditions, such as increased intracranial pressure, lower lobe pneumonia, intentional or unintentional medication or toxin ingestions, and diabetic ketoacidosis.

•Is there any abdominal pain?

—When vomiting is accompanied by abdominal pain, the location of the abdominal pain, as well as the descriptive nature of the pain, can be clues as to the etiology. Pain in the right lower quadrant may be due to an acute appendicitis, whereas right upper quadrant pain is more likely to be gall bladder or hepatic in origin. Lower quadrant pain may also occur with ovarian torsion or pelvic inflammatory disease. The most common cause of diffuse abdominal pain with vomiting is gastroenteritis. Colicky pain tends to occur with an obstructed hollow viscous or urinary calculi, whereas well-localized sharp pain tends to occur when parietal peritoneum is inflamed. Flank or lateral pain signifies a renal etiology. Pain from peptic ulcer disease is often alleviated with vomiting, whereas pain secondary to pancreatitis or biliary tract disease is not improved with vomiting.

• Is fever present?

—The presence of fever in a patient with vomiting is common. It may signify an infectious gastrointestinal process, such as acute viral gastroenteritis, bacterial enteritis, appendicitis, hepatitis, pancreatitis, peritonitis, or an acute extraintestinal infection, such as sepsis, meningitis, acute otitis media, pharyngitis, or urinary tract infections. Other causes of fever include inflammatory conditions, such as inflammatory bowel disease.

• Are there any other associated symptoms present?

—Other information that may help in narrowing the differential includes the presence of weight loss, headache, lethargy, and poor school performance, as well as environmental and infectious exposures.

The following cases present less common causes of vomiting in children.

CASE 3-1

Seven-Week-Old Boy

TODD A. FLORIN

HISTORY OF PRESENT ILLNESS

The patient is a 7-week-old African-American boy who presents with a 2-day history of frequent vomiting. The vomiting is nonprojectile, nonbilious, and on one occasion, streaked with blood. Oral intake was poor. He had urinated once over an 18-hour period. On the day of admission he had profuse, watery diarrhea. No one in the family has had vomiting or diarrhea.

MEDICAL HISTORY

The patient was born at term weighing 3300 g. He was delivered via cesarean section due to arrested descent. Because of feeding difficulties in the nursery he was discharged home on a lactosefree formula. Since then his oral intake has been appropriate. He has not required previous hospitalization. He has received his first hepatitis B immunization.

PHYSICAL EXAMINATION

T 38.1°C; RR 50/min; HR 170 bpm; BP 86/38 mmHg; SpO₂ 88% in room air

Weight 10th percentile (4.0 kg); Length 25th percentile; Head circumference 10th percentile

Examination revealed an infant who was crying but consolable (Figure 3-1). The anterior fontanelle was open and slightly sunken. The mucous membranes were moist and the sclerae were nonicteric. The lungs were clear to auscultation and the cardiac examination was normal without any murmurs. The abdomen was soft and mildly distended without hepatomegaly or splenomegaly. The extremities were cool. He had no rashes, good tone, and a symmetric neurologic examination.

DIAGNOSTIC STUDIES

Laboratory evaluation revealed 24 500 white blood cells/mm³ with 9% band forms, 24% segmented neutrophils, 40% lymphocytes, 20% monocytes, and 5% atypical lymphocytes. The hemoglobin was 15.2 g/dL and the platelet count was 577 000 cells/mm³. Red blood cell morphology noted mild anisocytosis, poikilocytosis, and burr cells. Serum chemistries were significant for a CO₂ of 10 mmol/L and cerebrospinal fluid cell counts, glucose and protein were normal; no bacteria were identified on Gram stain. His urine was dark yellow and turbid with a specific gravity of 1.038, a pH of 5.5, 3+ protein, and 5-10 granular casts without bacteria, nitrites, or white blood cells. On chest radiograph, the cardiac silhouette and lung fields were normal.

COURSE OF ILLNESS

The patient’s oxygen saturation on pulse oximeter increased to 93% when oxygen was administered by nasal cannula. Four extremity blood pressures were obtained as follows: right arm, 90/32 mmHg; left arm, 88/42 mmHg; right leg, 80/40 mmHg; left leg, 76/35 mmHg. On arterial blood gas (ABG), the pH was 7.01; PaCO₂ 18 mmHg; PaO₂ 232 mmHg; bicarbonate level, 4.7 mEq/L; and base deficit, 24.7. The patient received multiple normal saline boluses and bicarbonate in an attempt to correct his metabolic acidosis. The appearance of the patient (Figure 3-1) in conjunction with the ABG suggested a diagnosis.

DISCUSSION CASE 3-1

DIFFERENTIAL DIAGNOSIS

Vomiting in early infancy can be a very worrisome symptom. The most common cause of emesis in this age group is gastroesophageal reflux, which can be physiologic or due to overfeeding. Anatomic obstruction should always be considered. Obstructive lesions include malrotation with a volvulus, esophageal or intestinal atresia, pyloric stenosis, meconium ileus, congenital adhesions or bands, incarcerated hernia, intussusception, and Hirschsprung disease. The level of the obstruction will determine whether the vomitus is bilious or the abdomen is distended. Infectious causes include gastroenteritis, sepsis, urinary tract infection, meningitis, pneumonia, and pericarditis. Neurologic causes, such as subdural hematoma, hydrocephalus, and mass lesions, should also be considered. Bloody streaks in the emesis could be due to a milk protein allergy, gastroenteritis, necrotizing enterocolitis, or achalasia.

Metabolic and endocrine disorders must be considered in this child who presents with vomiting and a significant metabolic acidosis. These disorders include congenital adrenal hyperplasia (CAH), adrenal hypoplasia, inborn errors of metabolism, including both amino acid and organic acid disorders, and galactosemia.

DIAGNOSIS

The patient was cyanotic, a feature best visualized with the contrast of his lips to the white portion of the blanket (Figure 3-1). An arterial blood gas (ABG) with co-oximetry measurements revealed acidosis with a pH of 7.01; PaCO₂, 18 mmHg; and PaO₂, 232 mmHg. Co-oximetry readings revealed an oxyhemoglobin was 78.2%, methemoglobin 21.8%, and lactate level of 2.7 mmol/L confirming the diagnosis of methemoglobinemia.

INCIDENCE AND EPIDEMIOLOGY OF METHEMOGLOBINEMIA

Although methemoglobinemia is a relatively uncommon condition in pediatrics, it may cause significant cyanosis and even death. Methemoglobin is a derivative of normal hemoglobin in which the iron component has been oxidized from the ferrous (Fe²⁺) to the ferric (Fe³⁺) state. The oxidized iron (Fe³⁺) is unable to reversibly bind oxygen. Therefore, the oxidation of hemoglobin to methemoglobin produces a functional anemia by impairing the ability of the blood to transport oxygen. Methemoglobin occurs regularly in the body but rarely exceeds levels of 2% of the total hemoglobin because of antioxidant reactions in the body that reduce methemoglobin back to hemoglobin. The most important of these antioxidant reactions utilize either NADH-cytochrome b5 reductase or NADPH-methemoglobin reductase, although the latter system is largely inactive unless stimulated by the presence of methylene blue as a cofactor. NAPDH-methemoglobin reductase reduces methylene blue, an action that has important therapeutic implications as described in the treatment section below.

Methemoglobin levels increase when there is a disturbance in the balance between the oxidation and reduction of heme iron. Infants are at an increased risk of methemoglobinemia for two main reasons: (1) an immature NADH-dependent enzyme system (cytochrome b5 and cytochrome b5 reductase) resulting in lower levels of these enzymes and (2) fetal hemoglobin is more easily oxidized than adult hemoglobin. Both of these concerns are heightened in a state of metabolic acidosis. Methemoglobinemia can be caused by exposure to oxidant drugs and chemicals, development of enteritis and/or acidosis, or inherited conditions (Table 3-3). The most common oxidizing agents in acquired methemoglobinemia include sulfonamides, aniline dyes, chlorates, quinones, benzocaine, lidocaine, metoclopramide, dapsone, and phenytoin. In young babies, topical anesthetics, such as topical benzocaine and lidocaine, are common causes of methemoglobinemia as a result of their use as remedies for circumcision and tooth eruption pain. Ingestion of well water nitrates can also cause methemoglobinemia. Gastroenteritis results in an oxidant stress as nitric oxide is released in the enteric endothelium, and can cause methemoglobinemia in infants. Less common causes include inherited deficiencies of erythrocyte methemoglobin reductase or the presence of M hemoglobin (congenital methemoglobinemia).

CLINICAL PRESENTATION

The clinical presentation of patients with methemoglobinemia depends on the concentrations of both hemoglobin and methemoglobin (Table 3-4). Increasing methemoglobin levels are associated with progressively more severe symptoms. Patients with lower hemoglobin percent concentrations are affected at lower percentage levels of methemoglobin. Patients with methemoglobin concentrations less than 10% rarely have symptoms unless they are already anemic. Most patients with concentrations between 10% and 25% will have cyanosis but few other symptoms. Levels from 30% to 50% are associated with confusion, dizziness, fatigue, headache, tachypnea, and tachycardia. Levels greater than 50% are associated with severe acidosis, arrhythmias, seizures, lethargy, and coma. Lethal levels occur at around 70%.

DIAGNOSTIC APPROACH

Diagnosing a rare pediatric condition, such as methemoglobinemia, depends on having a high index of suspicion. Methemoglobinemia should be considered in cyanotic children without evidence of cardiac or pulmonary disease.

Bedside examination of blood. In a cyanotic patient, differentiating methemoglobin from deoxyhemoglobin is important. On white filter paper, blood containing a high level of methemoglobin turns chocolate brown, whereas blood containing deoxygenated hemoglobin appears dark red or purple initially but turns bright red on exposure to atmospheric oxygen.

Pulse oximetry. Oxygen saturation measured by pulse oximetry will be falsely elevated in the presence of high levels of methemoglobin. Most pulse oximeters use two wavelengths of light to determine “functional oxygen saturation,” which is the ratio of oxyhemoglobin to all hemoglobin capable of carrying oxygen. Normally, all hemoglobin present can potentially carry oxygen so that functional and true oxygen saturation are equal. Because methemoglobin does not carry oxygen, it does not register as functional hemoglobin on the typical pulse oximeter. At normal methemoglobin levels (<2%), this exclusion is not important; however, at high methemoglobin levels (>10%) the functional and true oxygen saturations differ substantially resulting in unreliable pulse oximetry readings. Due to light absorption characteristics of methemoglobin, the pulse oximetry readings will not drop below 82% unless accompanied by an increased level of deoxyhemoglobin. Newer generation pulse oximeters are available that use eight wavelengths of light and are able to accurately measure methemoglobin and carboxyhemoglobin continuously.

Arterial blood gas. Methemoglobinemia should be strongly suspected when there is a “saturation gap” in a cyanotic patient: a normal or elevated arterial partial pressure of oxygen (PaO₂) from an ABG with a low oxygen saturation on pulse oximetry.

Co-oximetry. Co-oximeters are spectrophotometers that measure light absorbance at different wavelengths, including the wavelengths for methemoglobin, oxyhemoglobin, deoxyhemoglobin, and carboxyhemoglobin. Co-oximeters accurately distinguish methemoglobin from oxyhemoglobin and provide a definitive diagnosis. Sulfhemoglobin and methylene blue (the treatment for methemoglobinemia) both produce erroneously elevated methemoglobin levels on routine co-oximetry. Therefore, co-oximetry generally should not be used to monitor response to methylene blue treatment. Newer generation co-oximeters are able to distinguish sulfhemoglobin and methemoglobin.

Potassium cyanide test. Elevated sulfhemoglobin levels can also cause a cyanotic appearance with a normal PaO₂, and can be mistaken for methemoglobin on some co-oximeters. If a newer generation co-oximeter that accurately detects sulfhemoglobin and methemoglobin is not available, the potassium cyanide test can be used to distinguish between these two hemoglobins. Methemoglobin reacts with cyanide to form cyanomethemoglobin. The formation of cyanomethemoglobin turns the blood from chocolate brown to bright red. Sulfhemoglobin appears dark brown initially and does not change color after the addition of potassium cyanide.

Additional studies. Although methemoglobinemia does not directly cause hemolysis, many of the agents that provoke methemoglobinemia can trigger hemolysis. Tests that evaluate for hemolysis (e.g., complete blood count, reticulocyte count, haptoglobin, and lactate dehydrogenase) and end-organ damage (e.g., electrolytes, liver function, creatinine, glucose) should be considered.

TREATMENT

Treatment depends on the methemoglobin level and the patient’s symptoms. In all cases, the causative agent or process should be identified and eliminated or treated, if possible. Generally, consider administering specific therapy in symptomatic patients with methemoglobin levels greater than 20% or asymptomatic patients with methemoglobin levels greater than 30%. Consider treating patients with concurrent problems that impair oxygen delivery, such as anemia, cardiac disease, or pulmonary disease even if their methemoglobin levels are low. Symptomatic patients should receive proper airway management and supplemental oxygen as necessary. Intravenous methylene blue, after reduction to leukomethylene blue by NADPH-methemoglobin reductase, aids in the reduction of methemoglobin back to hemoglobin. It is the treatment of choice and should reduce methemoglobin levels significantly within 1 hour of administration. Exchange transfusions or hyperbaric oxygen may be necessary for those patients with extremely high levels that do not respond to methylene blue therapy or those patients with severe disease in whom methylene blue therapy is contraindicated (e.g., severe G6PD deficiency).

G6PD is the first enzyme in the hexose mono-phosphate shunt, which is the sole source of NADPH in the red blood cell. Patients with G6PD may not produce sufficient NADPH to reduce methylene blue to leukomethylene blue. As a result, methylene blue therapy may not be effective and may induce hemolysis in patients with G6PD deficiency, and is thus generally contraindicated in these patients.

SUGGESTED READINGS

1. Annabi EH, Barker SJ. Severe methemoglobinemia detected by pulse oximetry. Anesth Analg. 2009;108:898.

2. Barker SJ, Curry J, Redford D, Morgan S. Measurement of carboxyhemoglobin and methemoglobin by pulse oximetry: a human volunteer study. Anesthesiology. 2006;105:892.

3. Blanc PD. Methemoglobinemia. In: Olson KR, ed. Poisoning and Drug Overdose. New York: McGraw Hill; 2007: 262-264.

4. Osterhoudt KC. Methemoglobinemia. In: Erickson TB, Ahrens WR, Aks SE, et al., eds. Pediatric Toxicology. New York: McGraw Hill; 2010:492-500.

5. Pollack ES, Pollack CV. Incidence of subclinical methemoglobinemia in infants with diarrhea. Ann Emerg Med. 1994;24:652-656.

6. Umbreit J. Methemoglobin – it’s not just blue: a concise review. Am J Hematol. 2007;82:134-144.

7. Wright RO, Lewander WJ, Woolf AD. Methemoglobinemia: etiology, pharmacology, and clinical management. Ann Emerg Med. 1999;34:646-656.

CASE 3-2

Nine-Month-Old Girl

PAUL L. ARONSON

HISTORY OF PRESENT ILLNESS

The patient is a 9-month-old girl who presents with a 12-day history of poor feeding, decreased activity, irritability, and frequent nonbloody, nonbilious emesis with feeds. Ten days ago she was diagnosed with viral gastroenteritis and 6 days prior to admission was treated with amoxicillin for an acute otitis media. Today she presents with continued emesis and decreased urine output having only two wet diapers in the previous 18 hours. The patient has a history of poor feeding and frequent episodic bouts of emesis lasting 2-3 days at a time. The parents deny any fever, diarrhea, cough, gagging with feeds, rash, bloody stools, ill contacts, recent travel, or animal exposure. Her diet consists of Nutramigen formula and various infant foods.

MEDICAL HISTORY

The patient is the full-term product of an uncomplicated pregnancy, labor, and delivery and was well until 3 months of age when she developed episodic vomiting. The emesis was nonbloody and nonbilious lasting 1-3 days and associated with decreased activity. It began while transitioning from breast milk to cow’s milk-based formula at the age of 3 months and was therefore attributed to a “feeding intolerance.” At 4 months she was changed to a soy-protein-based formula and then, finally, at 6 months Nutramigen was started without any relief in her symptoms. She was treated with ranitidine starting at 7 months for suspected gastroesophageal reflux. A sweat test performed at 8 months of age was normal.

PHYSICAL EXAMINATION

T 37.3°C; RR 50/min; BP 85/53 mmHg; HR tachycardic

Weight 6.5 kg (<5th percentile; 50th percentile for 5 month old); Length 66.5 cm (<5th percentile) and Head circumference 43.5 cm (25th percentile)

The patient was fussy but nontoxic appearing with scant nasal discharge and dry oral mucosa. She was tachypneic with clear lungs bilaterally. She had a soft systolic murmur at the lower left sternal border with a prominent S3 gallop. The liver edge was palpated 2 cm below the right costal margin and her spleen tip was also palpable. The extremities were warm and well perfused. There were no rashes and her neurologic examination was normal for age.

DIAGNOSTIC STUDIES

Laboratory analysis revealed 10 200 white blood cells/mm³ with 41% segmented neutrophils, 53% lymphocytes, and 6% monocytes. The hemoglobin was 11 g/dL and the platelet count was 232 000 cells/mm³. Serum electrolytes sodium 128 mmol/L, potassium 4.5 mmol/L, chloride 100 mmol/L, bicarbonate 20 mEq/L, blood urea nitrogen 19 mg/dL, creatinine 0.3 mg/dL, glucose 84 mg/dL, calcium 9.2 mg/dl. Her arterial blood gas showed a pH 7.43, PaCO₂ 31 mmHg, and PaO₂ 270 mmHg.

COURSE OF ILLNESS

A chest radiograph revealed mild cardiomegaly and a small right pleural effusion. An electrocardiogram (ECG) (Figure 3-2) was diagnostic.

DISCUSSION CASE 3-2

DIFFERENTIAL DIAGNOSIS

This patient presented with recurrent episodes of emesis with intermittent asymptomatic periods consistent with cyclic vomiting. Quantitative criteria for the diagnosis of cyclic vomiting include at least four episodes of vomiting per hour during the peak intensity and a frequency of no more than nine episodes per month. This is in contrast to chronic vomiting in which the patient has less frequent episodes of vomiting and less symptom-free days.

Cyclic vomiting frequently has a nongastrointestinal etiology. Causes include migraine headaches, abdominal migraines, and metabolic disorders including adrenal insufficiency, amino acidurias, and organic acidurias. Urea cycle defects may be present as episodic vomiting and neurologic symptoms due to hyperammonemia. Renal disorders such as ureteropelvic junction obstruction and renal calculi, as well as intermittent cardiac arrhythmias may also cause cyclic vomiting. Familial dysautonomia (Riley-Day syndrome) and Munchausen syndrome by proxy must also be considered. Gastrointestinal etiologies include pancreatitis, malrotation with intermittent volvulus, and intestinal duplications.

In patients with significant tachycardia and cyclic vomiting, an intermittent cardiac tachyarrhythmia must be strongly considered. The source of tachyarrhythmias include sinus, supraventricular, and ventricular. Differentiation of supraventricular tachycardia from sinus tachycardia may be difficult at times. Sinus tachycardia rarely exceeds 220 bpm in infants and 180 bpm in children and adolescents, has a normal P wave morphology and P wave axis, and varying heart rates due to changes in vagal and sympathetic tone.

Antidromic supraventricular tachycardia (SVT) due to an accessory pathway such as in Wolff-Parkinson-White (WPW) syndrome or SVT with a preceding bundle branch block (see later) may result in a widened QRS complex that resembles ventricular tachycardia. The absence of P waves and the presence of a wide QRS complex that is dissimilar to the QRS complex during sinus rhythm are more diagnostic of ventricular tachycardia (Figure 3-3).

DIAGNOSTIC TESTS

Diagnostic testing in the patient with cyclic vomiting is usually determined by the history and physical examination. The diagnosis of SVT was suspected in this patient by auscultation of a rapid heart rate or palpation of a pulse rate that was too rapid to count. Confirmation of a diagnosis of SVT is made by an ECG demonstrating a narrow complex tachycardia with a heart rate above 220 bpm in infants or 180 bpm in children and adolescents, often without discernable P waves and a fixed rate (Figure 3-4). As discussed earlier, if an accessory pathway or bundle branch block is present, a wide complex supraventricular tachycardia may be present, although this is less common. Diagnosis may also be made after resolution of the tachycardia with vagal maneuvers or adenosine which do not resolve ventricular tachycardias (discussed further under Treatment).

DIAGNOSIS

The ECG in this patient revealed a narrow complex tachycardia of 270 bpm consistent with SVT (Figure 3-2). After applying ice to her face without success, she was cardioverted to a normal sinus rhythm with intravenous adenosine. An echocardiogram revealed mild left ventricular dilation, mild mitral valve regurgitation, and a small pericardial effusion but good cardiac function without any structural defects. She was initially treated with digoxin and during the following 2 days and had normalization of her cardiac examination with resolution of her hepatomegaly. A repeat ECG prior to discharge showed mild right atrial enlargement and normal sinus rhythm without signs of preexcitation (i.e., no shortened PR interval or delta wave) (Figure 3-5). At discharge, she was transitioned to propranolol and after 2 months on therapy her weight had increased to the 25th percentile. In retrospect, her history of episodic feeding intolerance was likely due to episodes of supraventricular tachycardia.

INCIDENCE AND ETIOLOGY OF SUPRAVENTRICULAR TACHYCARDIA

SVT is a generic term encompassing a group of cardiac arrhythmias originating above the atrioventricular (AV) node. It is the most common sustained accelerated nonsinus tachyarrhythmia with an incidence of 1 per 250 to 1 per 1000 children. Two mechanisms account for virtually all cases of SVT: (1) an abnormal or enhanced normal automatic rhythm and (2) a reentrant rhythm. Approximately 75% of patients with a reentrant rhythm will exhibit findings of preexcitation with a shortened PR interval and initial slurred upstroke of the QRS (delta wave) (Figure 3-6). Children less than 12 years are more likely to have an accessory atrioventricular connection while in adolescence, nodal reentry tachycardia increases in frequency.

Reentrant rhythms account for more than 90% of all cases of SVT. Two separate conducting pathways must be present which lead to a cyclic pattern of excitation resulting in SVT. These pathways may be either within the atrium or atrioventricular. Atrial reentry rhythms may lead to either atrial fibrillation or atrial flutter.

Atrioventricular reentrant rhythms may be either through the AV node (nodal), or associated with an accessory atrioventricular pathway termed the bundle of Kent. Tachycardia may result from transmission of the impulse antegrade through the AV node and His-Purkinje system or through the accessory pathway with retrograde conduction through myocardium. The accessory pathway or AV node, respectively, then completes the circuit. This orthodromic reciprocating tachycardia (ORT) is the most common pattern seen in WPW syndrome and results in the typical narrow complex QRS tachycardia. Rarely the ante-grade impulse travels via the accessory pathway and retrograde through the AV node and His-Purkinje system resulting in antidromic reciprocating tachycardia (ART).

Preexcitation occurs in 75% of those with accessory pathways. This implies that the accessory pathway can conduct the impulse in antegrade fashion from the atria to the ventricle. Bypassing the intrinsic delay of the AV node results in a shortened PR interval and a slurred upstroke of the QRS, the so-called delta wave (Figure 3-6). Twenty-five percent of accessory pathways will only transmit impulses in retrograde fashion from the ventricle to the atrium resulting in a normal (no evidence of preexcitation) resting ECG.

SVT secondary to increased automaticity or atrial and junctional ectopic tachycardias occurs more commonly in children with postoperative congenital heart disease or cardiomyopathies.

TYPICAL PRESENTATION

Approximately 50% of children present with their episode of SVT in the first year of life. Signs and symptoms of SVT depend on the age at presentation and the duration of the tachycardia. Episodes of SVT may last only a few seconds or may persist for hours. Many children tolerate these episodes extremely well, and it is unlikely that short paroxysms are dangerous. Infants with SVT exhibit nonspecific symptoms such as poor feeding and irritability, and will therefore often present with congestive heart failure because the tachycardia often goes unrecognized for a prolonged period. Episodes lasting more than 6-24 hours may result in an acutely ill child with evidence of cardiopulmonary distress resulting in tachypnea, vomiting, lethargy, and ashen color. Physical findings in such cases include pallor, tachypnea, diaphoresis, hepatomegaly, and poor peripheral perfusion.

Older children may complain of lightheadedness, chest tightness, palpitations, and fatigue. Chest pain or discomfort is less common. The patient may become faint, dizzy, or even syncopal. If the rate is exceptionally rapid or if the attack is prolonged, heart failure may ensue.

DIAGNOSTIC RATIONALE

ECG. An ECG should be performed on any patient with tachycardia that is not felt to be due to normal sinus tachycardia. Patients with SVT have a very rapid and regular ventricular rate usually exceeding 220 bpm. The P waves are usually absent but when present have an abnormal axis and may precede or follow the QRS. Pending the results of the ECG, a chest radiograph or even echocardiogram may need to be performed.

TREATMENT

Treatment of SVT depends on the etiology and the duration of symptoms. Automatic rhythms are difficult to treat medically but respond well to ablation surgery.

Acute treatment of reentrant tachycardias depends on the age and stability of the patient. In hemodynamically stable children, vagotonic maneuvers should be attempted while obtaining intravenous access. Vagal maneuvers in the infant consist of placing ice over the mouth to stimulate the diving reflex or placing the infant’s knees to the chest, while in older children should be asked to strain or breath hold. In patients who do not respond to simple vagal maneuvers, medical cardioversion should be attempted. Adenosine, a nucleoside derivative that blocks the orthodromic conduction at the AV node, is the medication of choice. Intravenous verapamil and propranolol can break SVT but are contraindicated in the acute setting for infants and children because of the risk of bradycardia, hypotension, and cardiac arrest. If these modalities fail or if the patient is hemodynamically unstable, synchronized electrical cardioversion should be performed immediately.

Once a patient has been successfully converted to a normal sinus rhythm, first line maintenance therapy is the β-blocker propranolol for most infants and older children, although digoxin is also used. Infants should be monitored for hypoglycemia after initiating propanolol, and are often able to be weaned off therapy as the SVT is usually self-limited. In children with evidence of preexcitation syndrome (e.g., Wolff-Parkinson-White), digoxin and calcium channel blockers are contraindicated and those patients are usually managed with β-blockers.

Radiofrequency ablation of the accessory pathway is one choice for definitive treatment. Success rates range from approximately 80% to 95%, depending on the location of the bypass tract or tracts. Surgical ablation of bypass tracts can also be successful in selected patients.

SUGGESTED READINGS

1. Rowe PC, Newman SL, Brusilow SW. Natural history of symptomatic partial ornithine transcarbamylase deficiency. N Engl J Med. 1986;314:541-547.

2. Losek JD, Endom E, Dietrich A, Stewart G, Zempsky W, Smith K. Adenosine and pediatric supraventricular tachycardia in the emergency department: multicenter study and review. Ann Emerg Med. 1999;33(2):185-191.

3. Salerno JC, Seslar SP. Supraventricular tachycardia. Arch Pediatr Adolesc Med. 2009;163(3):268-274.

4. Kleinman ME, de Caen AR, Chameides L, et al. Part 10: Pediatric Basic and Advanced Life Support: 2010 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations. Circulation. 2010; 122:S466-S515.

CASE 3-3

Three-Year-Old Girl

AMY FELDMAN

HISTORY OF PRESENT ILLNESS

The patient is a 3-year-old Caucasian female presenting with a 1-year history of intermittent vomiting, increasing in frequency during the past 2 weeks. During the past year the patient has had nonbloody, nonbilious emesis approximately one time per day. The emesis is not associated with eating, nor does it occur at a specific time of the day. Occasionally, she wakes from sleep with emesis. She complains of photophobia and a sensation that there is a foreign body in her eyes. Her mother states that she seems to urinate more than other children. She denies abdominal pain, diarrhea, and rashes. Her mother denies noticing any lethargy, change in appetite, change in behavior, change in balance, or change in vision.

On the day prior to admission, her primary care physician began treatment with cefixime for presumed sinusitis after the patient had 3 days of cold symptoms and fever to 38.8°C.

MEDICAL HISTORY

The patient’s medical history is significant for failure to thrive since birth. She has always been below the 5th percentile for weight and height. Her family history is significant for a mother with Graves disease and two maternal cousins on dialysis for unknown reasons.

PHYSICAL EXAMINATION

T 36.8°C; RR 24/min; HR 118/min; BP 98/55 mmHg

Weight 11.1 kg (<5th percentile); Height 86 cm (<5th percentile)

Physical examination revealed a thin pale female in no acute distress. She had moist mucous membranes and a small amount of clear nasal discharge. Her optic discs were not able to be visualized. Her neck was supple with full range of motion. Cardiovascular and pulmonary examinations were normal. Her abdomen was soft, nontender, and nondistended without any masses, hepatomegaly, or splenomegaly. She had no rashes, petechiae, or purpura. Cranial nerves 2-12 were intact. She had normal speech, gait, and reflexes.

DIAGNOSTIC STUDIES

Laboratory evaluation revealed a normal complete blood count. Serum chemistries were as follows: sodium, 128 mmol/L; potassium, 2.0 mmol/L; chloride, 105 mmol/L; bicarbonate, 21 mEq/L; blood urea nitrogen (BUN), 37 mg/dL; creatinine, 2.2 mg/dL; glucose, 89 mg/dL; calcium, 7.9 mg/dL; phosphorus, 3.1 mg/dL; and magnesium, 2.0 mg/dL. Liver function tests were normal. Urinalysis showed a specific gravity of 1.010, pH of 6.5, trace blood, 3+ protein, 1+ glucose, and hyaline casts. Urine electrolytes were as follows: sodium 38 mmol/L, potassium 22 mmol/L, and chloride 37 mmol/L. A chest radiograph was normal as was an ECG. A renal ultrasound displayed small echo-genic kidneys. A brain MRI was normal.

COURSE OF ILLNESS

The patient received an intravenous bolus of normal saline and was admitted to the hospital with a diagnosis of renal failure of unknown etiology. Her electrolytes slowly normalized throughout hospitalization after IV and oral supplementations. While in the hospital, she underwent an ophthalmologic slit-lamp evaluation which provided a diagnosis (see Figure 3-7).

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