Brief Answer:
need to find underlying cause, likely thyroid and meds.

Detailed Answer:
Thank you for asking

I read your question and i understand your concern, heart rate of 46 BPM on rest is low and is called sinus bradycardia. With you having history of hypothyroidism some times despite euthyroid status being achieved it takes some time to get the heart rate back to normal as heart has compensated hypertrophied. If you have any of the following symptoms then you need a cardiac assessment for this bradycardia.

Near-fainting or fainting (syncope)
Dizziness
Weakness
Fatigue
Shortness of breath
Chest pains
Confusion or memory problems
Easily tiring during physical activity

Bradycardia has multiple possibilities. They all need to be ruled out one by one. Here are some of the following
Heart tissue damage related to aging
Damage to heart tissues from heart disease or heart attack
High blood pressure (hypertension)
Heart disorder present at birth (congenital heart defect)
Infection of heart tissue (myocarditis)
A complication of heart surgery
Underactive thyroid gland (hypothyroidism)
Imbalance of mineral-related substances necessary for conducting electrical impulses (electrolytes)
Repeated disruption of breathing during sleep (obstructive sleep apnea)
Inflammatory disease, such as rheumatic fever or lupus
The buildup of iron in organs (hemochromatosis)
Medications, including some drugs for other heart rhythm disorders, high blood pressure and psychosis

Your ekg and thyroid levels are normal that is good. Let do some more test. Tilt table test to connect fainting with bradycardia. Exercises tolerance test to see correlation between exercise and increasing heart rate if any.

Apart from it sleep apnea may also cause bradycardia. So obesity gets involved indirectly too. Even Electrolytes imbalance can lead to slow heart rate.

Next step would be management. Treating underlying condition like thyroid or any infection or medication stoppage causing bradycardia should be stopped and if the problem still persists pace makers can be considered for the achievement of sinus rhythm and rate of above 60.

I hope it helps. Take good care of yourself and dont forget to close the discussion please.

Regards
Khan

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