When would A-Fib be considered high risk decision making

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My physician and I are trying to determine if a patient is being treated in the hospital for A-Fib, when would the medical decision making be considered high risk? The patient is in a CVR but is on Sotalol treatment. The doctor feels it should be high since he says the patient can die from an arrythmia but I say moderate since it is RX management and the rate is controlled w/out documentation of associated symptoms (SOB...). The patient has HTN controlled and mild pulmonary HTN as well. I would appreciate any practical examples I can provide to him. Of course this is assuming all other high/comprehensive level criteria has been met. Thanks!