Palpitations

Like your husband Nana I have had palpitations and normal ECGs taken.

No doctor satisfactorily explained why I had these palpitations, but all of them told me not to worry about them.

I finally worked out by trial and error that most of them are part of an allergic reaction (which the medical profession generally deny can be the case, but the symptoms disappear if I take an antihistamine) but can also be caused by stress.

As a young adult I had palpitations every time I was due to visit my parents. It took me years to admit to myself that my mother's critical attitude to everything I did and said was the trigger.

They're very disconcerting. I had them quite badly when I was supporting my parents with cancer, first one and then the other, while our DC were having various problems and DH wasn't well. When these little problems all resolved themselves so did the palpitations. Mine was caused by stress. It didn't help the situation I was in at the time though!

I hope your DH's test come back ok and all is well.

I have had them all my life. (Hospitalised age 2).
There are so many causes, most of them benign. No point in getting stressed as this will very likely make things worse.
Just wait until he has the results of the 24 hr ECG and he will most likely be prescribed something like a beta blocker. Just one little tablet 2-3 times a day.
Do not worry.