Pacemaker for 3 year old

My three-year-old has congenital second degree AV block. We have been told to expect that it will progress to 3rd degree heart block at some point and a pacemaker will be needed. Most recently, we did a holter due to issues during his sleep (restlessness and crying often about his feet feeling "prickly"). The monitor showed that during his sleep, my son's heart rate is dropping to 36 beats per minute. During the day, he has more 2nd degree heart block than in the past, and his average heart rate is down. He gets as low as 40-50 beats per minute during the day, but was still able to reach 152 beats per minute when running. He has not yet shown 3rd degree heart block, and he doesn't seem to have symptoms during the day other than having a hard time waking up, and seeming crankier than usual. Here is my question. If he doesn't have complete heart block yet, how low of a heart rate is too low when sleeping? At what point do we say, "We can't let his heart rate drop any lower at night, so it's time for a pacmaker."? Just so you know, the cardiologists will discuss his numbers and decide whether or not he needs a pacemaker this Friday. I just have been thinking a lot about it and would appreciate a medical opinion. Thanks in advance.
Stacey

[finetilthree]

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