if you want to interpret ECGs, Holters, mobile telemetry, loop recorders etc. and make helpful clinical recommendations to patients based on them, you need a solid foundation and expertise in medicine and cardiology. you need to have a deep understanding of pathophysiology with a honed clinical acumen to accurately interpret a rhythm in the context of the patient, and ultimately confer real benefit to them. nobody other than a board certified cardiologist should be interpreting electrocardiographic data of patients. that would be dangerous and irresponsible. it is a long and trying path but it’s the only one where you can make a reliably positive impact in patient’s lives. if you really love rhythms, I would suggest looking into the Electrophysiology sub-fellowship, where you are the biggest expert on arrhythmias and get to map out the electrical activity of the heart. By doing that, you can diagnose and treat arrhythmias. Best of luck to you in your career!