Emergency Medicine NP here - so also not a cardiologist, but I deal with a flutter and fib pretty frequently.
The following for educational purposes, and is not intended as medical advice for your specific condition
As noted the first question is what is the nature/cause of your atrial flutter. For some folks it just happens, for others it can be related to thyroid issues, electrolyte imbalances, or perhaps a stressor on the body such as sepsis.
Also - the HR of 150 is classic for atrial flutter at 2:1 conduction. Most patients cannot live at 150 bpm for any real period of time (hours to days) and need to either have the rate controlled via medication or the atrial flutter resolved. These patients are usually symptomatic with some combination of weakness, fatigue, palpitations, chest pain, shortness of breath, and sometimes other less specific stuff like nausea. In the ER we generally will use meds to slow the rate and use electricity to fix the rhythm only if the meds do not work. Sometimes the meds alone will convert the patient, but this is not common.
If the meds can easily and well control the rate a patient can follow with cardiology outpatient. If we are having difficulty the patient will be admitted to be evaluated by cardiology in the hospital.
The stroke risk for flutter does appear to be less than atrial fibrillation, but still greater than baseline, so there can be an argument depending on age, other comorbidities, gender, and preference about the risks and benefits of anticoagulation.
The mainstay of definitive treatment for atrial flutter (and often fibrillation) is ablation. How quickly this is done can widely vary based on location, urgency, and patient preference.
Next, as DDM questioned, when considering activity it is imporntant to consider how difficult was the flutter to control/convert and what meds/interventions were used? How well controlled is the flutter and which medications are being used? Is there concurrent anti coagulation? How well does the patient tolerate exercise once “controlled”. (Edit - is there any degree of heart failure associated with the flutter? I forgot to include in my initial post an echocardiogram to evaluate for this, as cardiomyopathy/failure can trigger/cause flutter and fib and can limit physical activity. This can also dictate which treatments are used)
For someone newly diagnosed I would most likely ask them to refrain from any potentially stressful or dangerous activity/exercise initially until most of the variables are accounted for and controlled as well as possible. It could possibly be premature to rule out diving forever once this diagnosis is made, but there are a lot of moving targets that need to be considered, and a person who wanted to dive with a flutter may need to acknowledge there may be some additional risk in doing so.
