I am sorry to hear about your little one. Brain demyelination due to any cause can result in central sleep apnea. A 2mm small ASD should ideally not cause any apnea. If his apnea monitor is going off twice at night, he probably needs adjustment with his CPAP machine if he is on one, or he needs to be put on one if he is not on it. Irregular heart beat could be the result of apnea. However, yes, irregular heart beat in the presence of a ASD should be investigated further. Please call up his cardiologist and sleep specialist and get this investigated. Take care!
ASD is rarely symptomatic in children. I would agree with his cardiologist that since the ASD has almost closed to 2mm, it is likely to close by itself and unlikely to pose any issues. Rapid heart beat and apnoea are unlikely to be related to the ASD. While apnoea could be related to delayed myelination or other causes, the irregularity in heart beat may require further evaluation. I would suggest discussing this with his primary care pediatrician initially and depending on the cause(s) diagnosed/ suspected, it can be managed accordingly or specialist care may be sought.
Hope this is helpful.
Thank you both for your response. It has turned out that he has Secondary Bradyarrhythmia due to his problems with his CNS.