Hi
@rhibeth1 , and welcome. You will find lots of friendly help here and you can also find out lots of useful information from the search feature at the top of the page.
If your dad is in the very early stages of dementia it is a good idea to arrange Power of Attorney for health and finance straight away and register them at the same time. These will save a lot of problems as time goes on and if you leave it until you need them your dad may no longer be capable of giving his consent. you can do it on the government website - all others will charge you a fee for doing it as well as the government fee -
https://www.gov.uk/power-of-attorney
When MIL was diagnosed several years ago she saw the specialist nurse for her initial assessments, then had ecg etc and saw the psychologist for her diagnosis and treatment. Just before the first lockdown mum was both assessed and diagnosed and prescriptions organised by the nurse.
If your dad hasn't had his blood tests and ecg yet they may be organising them first. The ecg isn't part of the screening for dementia - it is because some alzheimers medication cannot be given if the person has any heart problems.