During a recent sleep study, my 10 year old daughter was found to have 15 episodes for third degree heart block. We went back to the pediatric cardiologist who placed her on a 24 hour holter monitor. The report said "several episodes of sinus pause less than 2.5 seconds in duration ... no heart block and very rare episodes of supraventricular ectopy." The it said the study was felt to be "within normal limits."
What is supraventricular ectopy. Why is it "normal"? And why would heart block be present during a sleep study, but not during the holter monitoring?
Dear tbarn: During sleep, it is normal for our heart rate to slow down a bit, compared to when we are awake. In fact, the vagal nerve, which slows down the heart rate, is active during sleep. Low grades of heart block [prolonged conduction between the upper (atria) and lower (ventricles) cardiac chambers] can be noted during sleep in childhood and is usually benign. The mildest form is called first degree block, and sometimes we see second degree block (also called Type I Wenckebach) where a beat will be dropped. The most severe form of heart block, called third degree or complete atrio-ventricular block, is not normal and must be evaluated further. There is a complete lack of electrical communication between the upper and lower chambers with third degree heart block. This usually indicates abnormal function of the atrioventricular node that conducts the electricity in the heart.
As you might imagine, each day, out heart rate ranges will be different according to our level of activity, and the same occurs during sleep. So a holter monitor or a sleep study on any given day, may not show the same findings. Benign heart block can occur sporadically. If your daughter was having a sleep study, there must have been concern about the possibility of sleep apnea or obstructed breathing during sleep. If those are present, the heart rate will usually slow down. The electrocardiogram (ECG) tracings performed during the sleep study to track heart rate are reasonably good, but may not be as accurate as a true ECG. Therefore, it may are may not be true that third degree AV block was present. Finally, supraventricular beats are extra beats from the upper heart chambers that are almost always benign and cause no hemodynamic compromise.
If you have further questions, you should get clarification from the pediatric cardiologist who arranged for your daughter’s evaluation.
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