Have a look at EU directive 93/42/EEC:
Article 1
Definitions, scope
1. This Directive shall apply to medical devices and their accessories. For the purposes of this Directive, accessories shall be treated as medical devices in their own right. Both medical devices and accessories shall hereinafter be termed devices.
2. For the purposes of this Directive, the following definitions shall apply:
(a) 'medical device' means any instrument, apparatus, appliance, material or other article, whether used alone or in combination, including the software necessary for its proper application intended by the manufacturer to be used for human beings for the purpose of:
- diagnosis, prevention, monitoring, treatment or alleviation of disease,
- diagnosis, monitoring, treatment, alleviation of or compensation for an injury or handicap,
- investigation, replacement or modification of the anatomy or of a physiological process,
- control of conception,
(Emphasis mine).
You will need to word the intended use of the device carefully without touching this subjects when selling in the EU, then you are okay.
Even if you get around this thing being a medical device but instead a fitness/wellness device (still possible by a little margin), I advise you to have a look at BS EN 60601-2-27 and 60601-1 for reference what are the requirements for a medical grade device. Fells better to make it so, still.
At least I would suggest that you integrate series resistors above 100k into all leads except RLD, reconsider your R7/R8. The "perfect" isolation should withstand 6kV (optocouplers, DC DC converters) under all applicate climate conditions, this frees you from worries that if ever somebody will get defibrillated while wearing your stuff it conducts the shock to some poor bystander even under the worst conditions.(Still a risk but not completely neglectable. Forseeable abuse: A person with a cardiological condition might abuse your widget to monitor himself, gets into ventrilation and a household member might use the already-present AED! Even when you are not guilty, the court might require your presence for a while)
Batteries and a thick fat high-IP plastics housing and creepage distances, and a radio link will fulfill that easily.
Assess and note your risks and make your spec accordingly.
EDIT: And you really want to go for AgCl Ag electrodes. The wet ones. And with conductive polymer body, giving some additional series resistance.