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  1. Problem. An infant has an abnormal tracing on the heart rate monitor.

  2. Immediate questions

      1. 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 42–1 for normal heart rate values.

      1. Is the abnormality continuous or transient? Transient episodes of sinus bradycardia, tachycardia, or arrhythmias (usually lasting <15 s) are benign and do not require further workup. Episodes lasting >15 s usually require full electrocardiogram (ECG) assessment.

      1. 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.

  3. Differential diagnosis

      1. Heart rate abnormalities

          1. Tachycardia is a heart rate >2 standard deviations (SD) above the mean for age (see Table 42–1).

              1. Benign causes

                  1. Postdelivery.

                  1. Heat or cold stress.

                  1. Painful stimuli.

                  1. Medications (eg, atropine, theophylline [aminophylline], epinephrine, intravenous glucagon, pancuronium bromide, tolazoline, and isoproterenol) can cause tachycardia.

              1. Pathologic causes

                  1. More common. Fever, shock, hypoxia, anemia, sepsis, patent ductus arteriosus, and CHF.

                  1. Less common. Hyperthyroidism, metabolic disorders, cardiac arrhythmias, and hyperammonemia.

          1. Bradycardia. Bradycardia is a heart rate >2 SD below the mean for age (see Table 42–1). Transient bradycardia is fairly common in newborns; rates range from 60–70 beats/min.

              1. Benign causes

                  1. Defecation.

                  1. Vomiting.

                  1. Micturition.

                  1. Gavage feedings.

                  1. Suctioning.

                  1. Medications (eg, propranolol, digitalis, atropine, and infusion of calcium, long-acting β-blockers to treat hypertension given within 24 h of delivery).

              1. Pathologic causes

                  1. More common. Hypoxia, apnea, convulsions, airway obstruction, air leak (eg, pneumothorax), CHF, intracranial bleeding, severe acidosis, and severe hypothermia.

                  1. Less common. Hyperkalemia, cardiac arrhythmias, pulmonary hemorrhage, diaphragmatic hernia, hypothyroidism, and hydrocephalus.

      1. Arrhythmias

          1. Benign arrhythmias include any transient episode (<15 s) of sinus bradycardia and tachycardia and any of the benign causes of sinus tachycardia and bradycardia noted in Section III, A, 1 and 2. Sinus arrhythmia, a phasic variation in the heart rate often associated with respiration, is also benign.

              1. Premature atrial beats can occur in the newborn and are usually benign. The QRS is narrow, and the T waves are often discordant. (See the example in Figure 42–1C.) They tend to decrease in number or go away entirely in the first few months of life. A workup is usually not indicated unless the infant has the premature atrial beats in association with structural cardiac disease.

              1. Unifocal premature ventricular beats are fairly frequent in the newborn. The QRS is wide, and the T wave is discordant with the sinus T wave. (See Figure 42–1D.) If seen in a newborn, obtain a 12-lead ECG. Do not treat unless the infant is symptomatic. Sometimes premature ventricular contractions (PVCs) become less frequent when the sinus rate increases. PVCs tend to decrease in number or go away entirely in the first few months of life.

              1. Benign bradycardia is unusual but not rare.

          1. Pathologic arrhythmias

              1. Supraventricular tachycardia (SVT) is the most common type of cardiac ...

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