@moey2720 You have a lot of complex issues, and so it’s very important that you have a doctor whom you trust who can work with you in navigating these. The thoughts below are more general comments for your consideration.
First, regarding your question about using an Apple Watch or Kardia device with a pacemaker: they are not incompatible, and you can use both. However, a pacemaker has electrodes inside the heart that record the heart’s electrical activity very accurately. Thus, if you have fast heartbeats, they should be well detected by the pacemaker, although there are exceptions and technical situations where it may not be sufficient. In general, however, a pacemaker would provide the most accurate determination as to whether or not you have atrial fibrillation (a fast heart rhythm in the top chambers of the heart) and how much of it you have.
Importantly, while some people with atrial fibrillation feel their heart racing, other people do not. That’s because the top chambers are racing, but your pulse is driven by the bottom chambers—the ventricles. In some people, not all of the signals from the top chambers make it to the bottom chambers, so part of the heart is racing while the main part that controls your pulse may be normal or slow in its rate.
You asked a lot about whether or not a Watchman device or blood thinners are needed. This, again, is something that is very important to discuss with your doctor. In general, when atrial fibrillation is present, the top chambers are not squeezing effectively. All of us are born with a left atrial appendage, a small cul-de-sac or reservoir in the top left chamber of the heart. Ninety percent of the clots that form in the heart in patients with atrial fibrillation come from that area. If a clot forms (because the blood doesn’t circulate effectively in AF, it may clot) and leaves the heart it can plug an artery; if that artery is in the brain, the part of the brain doesn’t get enough blood and oxygen and those cells die: a stroke. If you are at risk for a stroke, the ways to prevent it in AF are either to use a blood thinner so that clots do not form, or to place a plug in the appendage (the pouch where blood is most likely to stagnate and clot), such as a Watchman device or a different device. This, in the long term, may eliminate the need for blood thinners and prevent the risk of stroke, because clots cannot form in the appendage and then leave the heart to plug arteries in other parts of the body.
The risk of stroke is not determined only by whether or not atrial fibrillation is present, but also by other risk factors. There is a scoring system called the CHA₂DS₂-VASc score, with each letter representing a risk factor: congestive heart failure, hypertension, age over 65, prior stroke or TIA, vascular disease, age over 75, and female sex. Thus, determining whether or not you are at risk is important in guiding these decisions, and the score is one tool widely used clinially. Getting back to my previous point, it is really important that you have a doctor you trust who is well-versed in this area and can guide you through it.
Best of luck as you navigate these complex decisions.