Well...at least he's getting medical attention.
In older folks, a common cause of rapid heart rate
is a condition also termed "Rapid Atrial Fibrillation
." However, this does not account for each and every case. You can also have pain old "tachycardia," which is a heart rate above 100 beats per minute, as well as another one called "Supraventricular Tachycardia
," where the top chambers of the heart (Atria) are moving faster than the ones on the bottom of the heart (ventricles).
I would say that your grandfather likely has the first problem (atrial fibrillation - "A-Fib"), and they may choose to modify his medications, or he may undergo a treatment for this called "cardiac ablation." This will help to desensitize the heart somewhat so that it will reduce the speed.
When the heart beats too fast, then it doesn't do such a good job at pumping blood. This can cause problems, yes, but it certainly is not an indicator of anyone nearing death or dying.
Not to worry so much....okay?
Hope this helps you.