TABLE 77.3 LIFE-THREATENING CAUSES OF TACHYCARDIA Sinus tachycardia Anaphylaxis Hypoxia Hypoglycemia Sepsis Shock Pheochromocytoma Poisoning (see Table 63.4 ) Myocarditis Pericardial effusion with tamponade Cardiac Supraventricular tachycardia Ventricular tachyarrhythmias Atrial flutter EVALUATION AND DECISION The child with tachycardia requires rapid assessment for the presence of hypoxia, hypoglycemia, an existing life-threatening arrhythmia, or shock ( Fig 77.1 ) Respiratory distress with cyanosis or low pulse oximetry (less than 90%) demands immediate provision of supplemental oxygen and further management of airway and breathing (see Chapters Airway and 99 Pulmonary Emergencies ) Hypoglycemia typically presents with tremor, anxiety/irritability, diaphoresis, and/or altered mental status and can be confirmed by measuring rapid blood glucose level If an arrhythmia is suggested by an extremely rapid heart rate or a concerning tracing on the bedside cardiac monitor, a 12-lead electrocardiogram (EKG) and rhythm strip are necessary to confirm this impression and to guide further treatment (see Chapter 86 Cardiac Emergencies ) Children with congenital heart disease or a family history of sudden death are at increased risk for a life-threatening tachyarrhythmia Consultation with a pediatric cardiologist and/or emergent echocardiography is warranted In patients with shock, additional history and physical findings may help guide the clinician Although the etiology may not be initially apparent, rapid treatment is imperative (see Chapter 10 Shock )