CPVD - Heart Attack Alarm

My great great niece who is a very active four year old has had a preliminary diagnosis of CPVD.
She's had three heart attacks, and no doubt will have more.
I'm asking if anyone can recommend a heart monitor that a four year old child would be comfortable with, which will send out alerts to mobile phones or otherwise sound an alarm.
I have looked at several fitness monitor watches, and they are either not up to the job or unsuitable for a child.
Her parents and gran are taking it in turns to stay awake all night to ensure she is okay.
The consultant was asked for his advice on bed monitors, and he suggested a restless child would have the alarms going off several times a night, and so wouldn't help.
If anyone can give me some advice I would be immensely grateful, as being the tech minded one of the clan, it has fallen on me to investigate what is out there, and frankly I'm flabbergasted to find so little.