Clinical Practice Case 9

You should be very worried about this infant's appearance. She has respiratory distress with grunting respirations and mottled colour with irritability. This clinical picture suggests lung tissue disease, which is often complicated by hypoxemia.

The child is in severe respiratory distress. Your first actions are to call for additional help so that you can quickly place the infant on high-flow oxygen, a cardiac monitor and pulse oximeter, and establish vascular access. The infant has good respiratory effort, so there is no obvious need to provide ventilatory support at this time.

This infant has a tachycardia (>200/min) with poor perfusion.

Since the heart rate is well in excess of 200/min and the history does not suggest a cause for shock producing tachycardia (ie, a sinus tachycardia), this is most likely a supraventricular tachycardia (SVT). Once you see a fast rhythm on the monitor, your next decision is to determine if the rhythm is narrow or wide.

A narrow rhythm (≤.08 sec) is supraventricular, whereas a wide rhythm (>0.08 sec) may be either a supraventricular rhythm with aberrant conduction or ventricular tachycardia (VT). Since this discrimination is often difficult, you should treat wide-complex tachycardia as VT unless the child is known to have aberrant conduction. When the patient is poorly perfused with a wide-complex tachycardia, early synchronized cardioversion is indicated. If the child has narrow-complex tachycardia, you may attempt pharmacologic conversion if IV or I0 access is readily available.

In this case, recommendations for management are based on the Algorithm for Pediatric Tachycardia With Pulses and Poor Perfusion.

With poor perfusion, the infant will likely require synchronized cardioversion. But if you have vascular access established (or it can be readily established), you may first attempt to convert the rhythm with a dose of adenosine, using 0.1 mg/kg (maximum first dose 6 mg) by rapid IV infusion. You may also attempt to convert the rhythm with a vagal maneuver by placing iced water in a bag or glove on the infant's face (without obstructing the infant's nose), provided the vagal maneuvers do not delay pharmacologic or electrical cardioversion. 

This infant is irritable and fairly vigorous despite the poor perfusion. In this setting, the experienced provider may consider the use of sedation prior to cardioversion. Provide sedation agents cautiously using a small dose of a benzodiazepine (midazolam, 0.05 mg/kg is a reasonable choice) to provide sedation for the shock 

The presence of good pulses indicates that this infant has adequate perfusion and does not need immediate cardioversion. Instead, you may attempt vagal maneuvers and adenosine after IV/IO access is established. In addition, you should seek consultation with a pediatric cardiologist or other knowledgeable providers to help with management.

Since the infant has vascular access available, giving a dose of adenosine (0.1 mg/kg) is reasonable. Remember that this drug requires a 2-syringe method of rapid administration. A 3-way stopcock is often used so that the drug can be given quickly and followed immediately by a flush of isotonic saline to help deliver the drug to the central circulation. If the initial dose is not effective, you can double the dose and give that dose once.

The infant has improved perfusion following successful cardioversion to a sinus rhythm. The infant still has evidence of lung tissue disease, which is likely secondary to pulmonary edema from congestive heart failure induced by the tachycardia.

At this time the best approach is often careful observation rather than administration of a vasoactive drug. Recall that SVT may be induced by catecholamines, so giving a catecholamine may re­initiate the SVT. You should obtain an ECG to analyze the rhythm. The experienced provider may look for the presence of delta waves or other abnormalities. In addition, if not already obtained, consultation with a pediatric cardiologist is indicated.

The initial decision making (differential diagnosis) of the causes of a narrow-complex tachycardia is between SVT versus sinus tachycardia.

The child with sinus tachycardia typically has a history compatible with a cause of the tachycardia, such as shock, sepsis, a high fever, or vomiting and diarrhea leading to serious dehydration.

SVT is typically associated with an extra conduction pathway for impulse conduction in the heart. Other cardiac causes of narrow-complex tachycardia include atrial flutter and atrial fibrillation, but these are uncommon rhythms in infants unless they have underlying congenital heart disease.

As previously noted, wide-complex tachycardia may result from aberrant conduction of an SVT, but you should treat a wide-complex tachycardia as VT unless the child is known to have aberrant conduction.

Wide-complex tachycardia is a relatively uncommon rhythm in children, but it can be seen in children with cardiomyopathy, myocarditis, congenital heart disease, drug ingestions (particularly tricyclic antidepressants), and electrolyte disturbance, particularly hyperkalemia.

In children with abnormal heart function or anatomy from any of the reasons noted above, hypomagnesemia or hypocalcemia may predispose to the development of VT.