My Pulse Rate Is Usually High Over100 . For Several

My pulse rate is usually high over100 . For several days it is 64 . I take a daily atenolol which usually keeps things steady. Past history one episode of ventricular tachachardia during a surgery. Smart anaethesiologist. I am 90years old and very tired and nauseated . I have severe adrenal insufficiency. I have app appt. later this week. Any suggestions?make that pcp md.