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.
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.
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.
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, PaCO231 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.
FIGURE 3-2. Patient’s initial ECG.
DISCUSSION CASE 3-2
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).
FIGURE 3-3. ECG demonstrates wide complex rhythm of ventricular tachycardia.
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).
FIGURE 3-4. ECG demonstrates supraventricular tachycardia at the rate of 300 beats/min.
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.
FIGURE 3-5. Patient’s subsequent ECG with enlargement of P wave indicating atrial enlargement (circle).
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.
FIGURE 3-6. Shortened PR interval (circle) with delta wave (rectangle) as seen in preexcitation syndromes such as Wolff-Parkinson-White.
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.
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.
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 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.
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