Some time ago we had a discussion (with some hilarious posts) about frequent loo visits to pee during AF and it was a question which I put during a consultation but didn't get an definitive answer.
I had a recent run of SVT episodes and the same trotting to the loo occurred. Apparently it is because of ANP (Atrial Natriuretic Peptide) which controls body water, sodium, potassium and some other chemicals and is released by the stretching of the atria. The atria are stretched by (amongst other things) blood volume during AF and SVT.
So, the next time you need to fill and refill the commode folks, blame ANP!