Chances of arrhythmia with a clear ekg, chest x ray, and blood tests? I know they can go undetected. 18 years old. Feel occasional heart palpitations

Low. The chances of a significant arrhythmia are very low given your negative test results. Teenagers will often have a bit of flipflop feeling in their chest or palpitation. These are usually normal. The use of energy drinks and chocolate can increase these episodes. Your doctor is best suited to determine the need for further testing, such as 24 hr holter monitoring.
Holster monitor or . You can try holster monitor or better yet get tested multifunction cardiogram! http://en.M.Wikipedia.Org/wiki/multifunction_cardiogram.