I've had palpitations for months. ekg showed palpitations also. doc wants a halter monitor. stress, cancer, broken ribs here. can this be the cause?

You probably used the wrong term. EKG does not show palpitation, probably it showed ectopic beats which could be consistent with palpitation. You should have Holter monitoring if palpitation affects your daily activities or well being or you have some other sx along with palpitation such as lightheadedness, shortness of breath or chest pain. Holter is indicated if you have underlying heart problem

Yes, you should have a holter monitor to determine the frequency & context (stress, diet, exercise, etc.) of the rhythm detected on your EKG & whether they coincide with symptoms. Some abnormalities need no treatment. Some need meds. Some require more aggressive intervention, like an implanted defibillator. Of the conditions you mentioned, some anti-cancer drugs can have cardiac side-effects.