Rosen & Barkin's 5-Minute Emergency Medicine Consult (593 page)

None

Surgical consultation concurrent with correction of electrolytes and fluid deficits

Follow growth pattern after surgery.

Suggestive clinical presentation combined with lab evaluation should lead to imaging and correction of electrolyte abnormalities.

• Heller RM, Hernanz-Schulman M. Application of new imaging modalities to the evaluation of common pediatric conditions.
  J Pediatr
  . 1999;135:632–639.
  
• Krogh C, Fischer TK, Skotte L, et al: Familial aggregation and heritability of pyloric stenosis
  JAMA.
  2010;303:2393–2399.
  
• Mahon BE, Rosenman MG, Kleiman MB. Maternal and infant use of erythromycin and other macrolide antibiotics as risk factors for infantile hypertrophic pyloric stenosis.
  J Pediatr
  . 2001;13:380–384.
  
• Najmaldin A, Tan HL. Early experience with laparoscopic pyloromyotomy for infantile hypertrophic pyloric stenosis.
  J Pediatr
  . 1995;30–37.
  
• Safford SD, Pietroban R, Safford KM, et al: A study of 11003 patients with hypertrophic pyloric stenosis and the association between surgeon and hospital volume and outcome.
  J Pediatr Surg
  . 2005;40:967–973.
  
• Siddiqui S, Heidel RE, Angel CA, et al: Pyloromyotomy: randomized control trial of laparoscopic vs. open technique.
  J Pediatr Surg.
  2012;47:93–98.
  

CODES

537.0 Acquired hypertrophic pyloric stenosis

BASICS

A disorder of myocardial repolarization characterized by a prolonged QT interval on the electrocardiogram

• The pathophysiology is complex and incompletely understood:
  
  • Alteration in cardiac sodium, potassium, or calcium ion flow
    
  • Imbalance in the sympathetic innervation of the heart
    
• Prolonged ventricular repolarization results in lengthening of QT interval on surface ECG:
  
  • “Pause-dependent” lengthening due to short–long–short sequence in which a sinus beat is followed by an extrasystole (short), then a postextrasystolic pause (long), concluding with a ventricular extrasystole (short)
    
  • “Adrenergic-dependent” pauses found in congenital cases
    
• Symptoms often preceded by vigorous exercise, emotional stress, or loud noise.
  
• Nocturnal bradycardia can lengthen QT interval, causing sleep-related symptoms.
  
• Re-entrant rhythm can lead to torsades de pointes, ventricular tachycardia, and ventricular fibrillation.
  
• Hemodynamic compromise following dysrhythmia leads to syncope or death.
  
• Independent risk factor for sudden cardiac death.
  

• 10 genes linked to long QT syndrome:
  
  • Autosomal recessive form associated with deafness (Jervell and Lange–Nielsen syndromes)
    
  • Autosomal dominant form not associated with deafness (Romano–Ward syndrome)
    
  • Adrenergic stimulation (fright, exertion, delirium tremens, and loud auditory stimulus) becomes prodysrhythmic in certain genotypes, while sleep-related symptoms are found in others.
    
• 10–15% of carriers have baseline normal QTc.
  
• Death occurs in 1–2% of untreated patients per year.
  
  • Drug-induced QT prolongation may also have a genetic background.
    
  • Congenital form occurs in 1 in 3,000–5,000, with mortality of 6% by age 40 yr.
    

• Diagnosis suspected in the young with syncope, cardiac arrest, or sudden death
  
• Syncope following emotional stress or exercise suggestive
  
• Death occurs without preceding symptoms in 10% of pediatric patients.
  

• Drugs:
  
  • Complete list at
    www.QTDrugs.org
    
  • Class Ia antidysrhythmics—quinidine, procainamide, disopyramide
    
  • Class III antidysrhythmics—sotalol, ibutilide, amiodarone
    
  • Antibiotics—erythromycin, pentamidine, chloroquine, trimethoprim–sulfamethoxazole
    
  • Antifungal agents—ketoconazole, itraconazole
    
  • Psychotropic drugs—phenothiazines, haloperidol, risperidone, STCAs
    
  • Cisapride
    
  • Antihistamines
    
  • Organophosphates
    
  • Narcotics—methadone
    
• Electrolyte abnormalities
  
  • Hypokalemia
    
  • Hypomagnesemia
    
  • Hypocalcemia
    
• Cardiac
  
  • Bradyarrhythmias
    
  • Arteriovenous block
    
  • Mitral valve prolapse
    
  • Myocarditis
    
  • Myocardial ischemia
    
• CNS
  
  • Subarachnoid hemorrhage
    
  • Stroke
    
• Congenital (idiopathic)
  
• Other
  
  • Protein-sparing fasting
    
  • Anorexia nervosa
    
  • Hypothyroidism
    
  • Hypothermia
    

DIAGNOSIS

• Palpitations
  
• Light-headedness
  
• Dizziness
  

• Syncope
  
• Near syncope
  
• Seizure
  
• Family history of syncope or sudden death
  
• Congenital deafness
  
• Medication use
  

Cardiac monitor:

• ECG
  
• QTc (QT corrected for heart rate) >0.44 sec in men and >0.46 sec in women
  
• QT measured from beginning of quasi-random signal to end of T wave:
  
  • Measured best in the limb leads and should be averaged over 3–5 beats
    
  • There is no expert consensus on best heart rate correction (QTc) formula.
    
  • Bazett formula (QT divided by square root of RR interval) is most commonly used
    
  • Increase in QT variability
    
• T-wave abnormalities (T-wave alternans, biphasic)
  
• Appearance of U waves
  
• Ventricular tachycardia
  
• Ventricular fibrillation
  
• Torsades de pointes
  

• Full electrolytes including calcium and magnesium
  
• Toxicology screen
  

Echocardiography to exclude other cardiac causes

• ECG stress testing to induce a prolonged QT interval in suspected cases
  
• Holter monitoring of QTc
  
• Genetic counseling/testing in suspected congenital forms
  
• Familial ECG testing
  

• Myocardial infarction
  
• Hypertrophic cardiomyopathy
  
• Valvular defect
  

TREATMENT

• Supplemental oxygen
  
• IV access
  
• Monitor
  

• IV access
  
• Monitor
  
• Determine hemodynamic stability
  
• Unstable patients require immediate cardioversion
  

• IV magnesium sulfate for torsades de pointes
  
• IV potassium to serum levels of 4.5–5 mEq/L
  
• Temporary transvenous cardiac pacing (rates from 100–120 beats/min) for recurrences of torsades de pointes refractory to magnesium sulfate therapy (shortens QTc)
  
• IV isoproterenol for refractory cases or hemodynamically unstable patients with acquired long QT (ineffective in congenital cases) who do not respond to transvenous pacing
  
• Remove any offending medications and correct metabolic derangements.
  
• Consult with cardiology in those with symptomatic long QT regarding use of β-blockers at maximum doses.
  
• No ED treatment needed (in consultation with cardiology) for those with suspected idiopathic long QT and no history of syncope, family history of sudden cardiac death, or ventricular arrhythmias.
  
• Pacemaker or defibrillator placement with or without cervicothoracic stellectomy (to reduce adrenergic stimulation) may be required in high-risk patients.
  
• β-Blockers prevent 70% of cardiac events in congenital cases.
  

• Magnesium sulfate: 2 g (peds: 25–50 mg/kg) IV bolus over 2–3 min followed by IV infusion at 2–4 mg/min
  
• Isoproterenol: 1 μg/min (peds: 0.05–0.1 μg/kg/min) IV continuous infusion, titrate for effect, up to 10 μg/min
  

Propranolol: 2–3 mg/kg/d (peds: 2–3 mg/kg/d) PO (in consultation with cardiology)

FOLLOW-UP