A 6-year-old girl is referred to the emergency department by her pediatrician with a 3-month history of intermittent palpitations. The episodes occur several times per week but are not associated with any particular activity or time of day. They sometimes occur with exercise but may occur at rest. There is a gradual onset of the rapid heart rate, and the episodes resolve spontaneously with rest. The first episode occurred after the patient was given an over-the-counter cold remedy. They are less frequent since being advised to avoid stimulants. The longest episode lasted 20 minutes. There is no associated chest pain, shortness of breath, or dizziness. There is no history of syncope. The patient takes no medications and has no known allergies. The family history is noncontributory with respect to congenital heart disease or arrhythmia. The patient attends first grade. Her energy level is commensurate with that of her peers.
In the emergency department, the girl is acyanotic and in no distress. She is comfortable, alert, and interactive. The heart rate is 144 beats per minute, and the respiratory rate is 24 breaths per minute. The blood pressure is 86/52 mm Hg in the right arm. Pulse oximetry on room air is 98%. The head and neck examination is unremarkable. The chest is clear to auscultation. The cardiac examination has a fast and regular rhythm. There is a normal first heart sound and soft physiologically split second heart sound. There is no click. There is an S3 gallop. There is a 2/6 systolic regurgitant murmur heard beast at the apex. The pulses are full and equal. The abdomen is soft without hepatomegaly. The extremities are warm and well perfused.
An electrocardiogram was performed in the emergency department (Fig. 1).