Consultation with the Specialist: Cardiac Dysrhythmias

Case Study

An anxious mother has rushed her 2-month-old boy to your office because of irritability, diminished appetite, decreased physical activity, and pallor that have become more prominent over the past 2 to 3 hours. On arrival, your nurse evaluates him immediately and calls you because of her concerns.

The infant is lethargic and pale. His pulse rate is 240 beats/min and respiratory rate is 60 breaths/min. His weight is 4.5 kg. Capillary refill is 4 to 5 seconds, rectal temperature is 36.6°C (98°F), and lungs are clear. His abdomen is soft, and his liver edge is palpable 3 cm below the right costal margin. The anterior fontanelle is flat and soft. His eyes, ears, and throat appear normal.

This is the first episode of this type that this infant has experienced. He is on a 20 kcal/oz proprietary formula and is not receiving any medications. His mother cares for him, and she knows of no exposure to infectious diseases. He has no siblings. He weighed 3.45 kg at birth.

While obtaining an electrocardiogram, which demonstrates a ventricular rate of 240 beats/min with narrow QRS complexes, findings consistent with paroxysmal supra ventricular tachycardia, you apply an ice bag to the infant’s face. There is no change in the cardiac rate, even though you repeat the maneuver twice. You consider direct current cardioversion, but no such apparatus is available in your office. You are able to get an intravenous drip started and administer adenosine 0.1 mg/kg by rapid push. The tachycardia persists; 2 minutes later you repeat the adenosine at a dose of 0.15 mg/kg. This proves effective, with the heart rate slowing suddenly to 160 beats/min. The electrocardiogram now demonstrates a short PR interval and wide QRS complex with pre-excitation (delta wave), characteristic features of the Wolff-Parkinson-White (WPW) syndrome.

The patient remains …