I've never had the VNS done but my Epileptologist and family Dr. have told me that my rapid or irregular heartbeat can increase my seizures. Also if a person has temporal lobe epilepsy that can have a connection with the heart rate and if it's going to fast or to slow. After I found out I had a rapid heartbeat
my seizures increased a lot. You may want to speak with a heart specialist and have your son have an echocardiogram done to be sure he isn't having more seizures do to heart problems. This is what my Dr. ordered for me. I wish you and your family the best of luck and May God Bless All of You!