Hello and welcome – Hopefully, others here who have been through RAI will chime in here.
I do know that in a small percentage of cases, hyperthyroidism returns after RAI, particularly if the initial dose was not enough to fully destroy all remaining thyroid tissue.
TSH can remain suppressed for quite some time in Graves’ patients, so Free T4 and T3 are better benchmarks for monitoring your treatment. If the T3/T4 show that you are in fact still hyperthyroid, you can select from the original three treatment options: anti-thyroid medications, RAI, and surgery.
I would definitely push your doc about what he/she proposes for next steps, especially with the rapid heart rate. If you decide that a second opinion might be helpful, the “Looking for a Doctor” thread in the announcements section of the forum has several options for finding a doctor near you.
Take care – and keep us posted!