Good evening! please help me with a medical problem. I am 21 years old and at the age of 7 I was diagnosed with hashimoto thyroiditis, tachycardia and mitral valve prolapse with grade 1 mitral regurgitation. At the age of 16 I discovered that I also have a cold lump on my thyroid. At 17, my tachycardia got worse, so I was recommended 25 mg metoprolol when needed. Everything was fine, until 2 years ago when the beatings started to be different, for example, even if I had a small pulse, I still felt very strong. I put on a holter, and the result was sinus tachycardia with periods of bradycardia, grade ii type I atrioventricular block. A doctor recommended corlentor, but I read the leaflet and it didn't seem right. What should I do? And what could be the possible cause of this block, can it advance? Thank you!