The “HARO ECG seat” from Hamberger Medical is designed to detect cardiac arrhythmia early on. Sensors for a 6-channel ECG are built into the seat to do this.
For those long sits where your legs might get numb, try supporting your weight from the feet. Like squatting with your ass only touching the toilet seat instead of resting on it.
I have a toilet seat that opens for me when I walk up, lights up the bowl for me, is heated, has an air filter for smells, a bidet and blow dryer, and closes when I leave. Might as well give it a pulse-ox and ECG while I'm at it.
If you just have the seat paired with a normal American toilet, I don't think it does much. But the seat with the Toto toilet, which has FAR less water in the bowl when doing your business, is very effective when things don't go off to the side or not fully underwater. It's always annoyed me how much smellier toilets can be in Europe if you miss the deep but narrow "chute."
I'm being downvoted, but very serious. There's a great product by Kardia that is handheld, and can be used in a lot of different configurations. It would be easy to adopt that to a harness you wear all day to record your EKG and not just while sitting on the shitter.