I think the bedside one has 12. I specifically mentioned the 6 lead device because there is also a cheaper single lead device of the same name which, while useful, gives the Doc far less information and data.
I read the device blurb and noted that apparently three contact pads yields six leads, which I do not profess to understand! As for the number of leads I had at the weekend, I don't know but was still peeling contact buttons off my chest when I got home...
Of course it's not an either or situation. They're 2 entirely different appliances for use in entirely different circumstances. Having one of them doesn't affect the need or desirability of having the other.
A defibrillator has only one use, to deal with VF, which is probably going to be untreatable while on passage. Other cardiac problems could crop up where ECG information sent for professional advice could be useful. I don’t think it would be part of most sailors’ kit unless a member of the crew were known to be at risk though.
It would be helpful if you would explain why you say the scan watch is better. As far as I can see the scanwatch is equivalent to a single lead ECG whereas the Kardia gives a 6 lead reading.
VF or ventricular fibrillation is what a defibrillator will correct. As stated before, the chances of someone surviving recovery from this without full support are not good, which makes its use on passage of limited help. There are other forms of dysrhythmia, such as the common AF or atrial fibrillation which do not lead to immediate death but which may disable the sufferer and need treatment. The correction of these, when needed requires specialised treatment, either electrical or with drugs. On passage, AF or one of the tachycardias would not be treatable without the right drugs to hand and all one could do would be to rest the subject. Communicating the ECG could be useful in assessing the risk and expediting treatment or having the sufferer taken off by lifeboat or helicopter.
An Apple watch or a good Android watch will give you a similar ECG single lead reading, as far as I'm aware, and also a blood oxygen reading. Both are also fully waterproof. I'm personally more interested in having a monitor from which I can email results to my doctor to give the fullest possible picture and he tells me that a 6 lead reading is far more useful and informative than a single lead reading. However, I'm saying all this with no direct experience or knowledge of the Withings.
If you follow the logic of your first para there's absolutely no point in having any ECG on a boat offshore. My reason for having it is to be able to email to my doctor and take his advice which could be anything from "don't worry" to Mayday. A 6 lead is superior to a single lead in that regard. Keeping my phone charged is an essential safety requirement on my boat. The Kardia does not need to be charged. Your #10 certainly seemed to me you're advocating strongly for Withings.As I said, yes a medical pro will find a 6-lead thingy much more useful. But, on a boat offshore, you probably don’t need anything fancy ‘cos your cardiologist will be many days away from you. A ‘better’ ECG isn’t going to make a blind bit of difference to the treatment you get for your heart condition while on your boat
The Withings produces a PDF which you can send to a doc - as does the Kardia.
The Apple watch is twice the price and can’t go more than a few hours without a charge. The Withings will do a slow Atlantic crossing on one charge.
I’m not advocating for Withings, I’m simply saying that I find it a useful and better system when I’m on my boat.