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An infant has an abnormal tracing on the heart rate monitor.
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II. IMMEDIATE QUESTIONS
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What is the heart rate? The heart rate in newborns varies from 70–190 beats/min. It is normally 120–140 beats/min but may decrease to 70–90 beats/min during sleep and increase to 170–190 beats/min with increased activity such as crying. See Table 48–1 for normal heart rate values.
Is the abnormality continuous or transient? Transient episodes of sinus bradycardia, tachycardia, or arrhythmias (usually lasting <15 seconds) are benign and do not require further workup. Episodes lasting >15 seconds usually require full electrocardiogram (ECG) assessment.
Is the infant symptomatic? A symptomatic infant may need immediate treatment. Signs and symptoms of some pathologic arrhythmias include tachypnea, poor skin perfusion, lethargy, hepatomegaly, and rales on pulmonary examination. All of these signs and symptoms may signify congestive heart failure (CHF), which may accompany arrhythmias. CHF resulting from rapid cardiac rhythms is unusual with heart rates <240 beats/min.
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III. DIFFERENTIAL DIAGNOSIS
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Heart rate abnormalities. Heart rates in the normal newborn vary dramatically. Some evidence, using computer programs to assess heart rate variability in the neonatal period, suggests that the lower heart rates early on are due to the inability of the infant's sympathetic system to inhibit the parasympathetic (or vagal) response.
Tachycardia. Heart rate >2 standard deviations (SD) above the mean for age (see Table 48–1).
Benign causes. Postdelivery, heat or cold stress, painful stimuli, medications (eg, atropine, caffeine, epinephrine, intravenous glucagon, pancuronium bromide, tolazoline, and isoproterenol).
Pathologic causes
Common. Fever, shock, hypoxia, anemia, sepsis, patent ductus arteriosus, and CHF.
Uncommon. Hyperthyroidism, metabolic disorders, cardiac arrhythmias, and hyperammonemia.
Bradycardia. Bradycardia is a heart rate >2 SD below the mean for age (see Table 48–1). Transient bradycardia is fairly common in newborns; rates range from 60–70 ...