Case
I’m calling from the newborn nursery and I’m the charge nurse on for today. I have a 1-day old newborn infant that on auscultation has a slow heart rate. I counted an average pulse rate of 90 beats per minute. The baby looks well and seems to be feeding OK. I’ve called the pediatrician and she’s coming to see the baby this afternoon after clinic, but she asked me to call you. Anything I should be worried about?
What am I thinking?
As with any arrhythmia, the first thing I think about is the clinical status of the patient. In this situation, is the bradycardia impacting the ability of this newborn to live—namely maintaining homeostatic metabolism, eating, and gaining weight? A patient who is not acidotic, able to feed, and is gaining an appropriate amount of weight is less of a concern for immediate intervention. Once I have established that the patient is clinically OK, I need to understand the rhythm and I will be looking for some form of tracing, best performed with a 15-lead ECG. The most common reason an electrophysiologist gets involved for bradycardia in a newborn is sinus bradycardia, which often is a sign of other issues rather than the diagnosis. As long as the patient is clinically stable, I have time to perform a work-up.
| Differential diagnosis |
|---|
| Likely |
Sinus bradycardia
|
| Possible |
| Blocked premature atrial contractions Sinus bradycardia secondary to induced hypothermia |
| Rare |
| Congenital hypothyroidism (sinus bradycardia) Congenital heart block Long QT syndrome (sinus bradycardia, 2:1 atrioventricular block) Sick sinus syndrome or heterotaxy syndrome (left atrial isomerism) secondary to congenital heart disease |
History and physical
History is paramount in the work-up of a newborn infant with bradycardia. While this may seem counterintuitive given the short history outside of the womb, the history should involve what occurred antenatally and in the immediate postnatal period. Foremost, what is the clinical status of the patient? This should always be the first concern in any arrhythmia case and should drive decision-making and actions. Any suggestion of instability due to bradycardia may require immediate action with the consultation of a pediatric cardiologist and preferably, a pediatric electrophysiologist. With a clinically stable patient, history questions may help with diagnostic considerations. Most cases of neonatal bradycardia are due to sinus bradycardia (see Fig. 1.1 ). Causes of sinus bradycardia can include respiratory-related issues such as apnea of prematurity and/or respiratory pauses. Sinus bradycardia could also be the result of medication given during or after delivery. Bradycardia during fetal life may suggest blood flow insufficiency from the placenta or underlying genetic predisposition such as congenital heart disease or Long QT syndrome. It may also suggest an underlying arrhythmia such as blocked atrial premature beats (see Figs. 1.2 and 1.3 ). The most common ectopic arrhythmia noted in the normal newborn is that of atrial premature beats. In the neonate with congenital heart block, there is a higher incidence of maternal lupus and this history should be elicited.
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