Not familiar with the paper this is from, but Atrial Fibrilation isn’t a heart attack (it can cause one, or a stroke). The human heart has 4 chambers, the left and right atria are on top and the left and right ventricles are on the bottom. In super layman’s terms, blood enters the heart from the lungs into the left atria and from the body into the right atria, passes through valves into the ventricles, and then is passed into the body (from the left ventricle) or the lungs (right ventricle). Normally the atria squeeze, there’s a slight pause to allow blood to enter the ventricles, then the ventricles squeeze. In A-fib, the atria just quiver, they don’t squeeze. It can be fairly benign and people can walk around for months without knowing they’re in A-fib because the blood will just drop into the ventricles and the ventricles do the work of pumping blood out into the lungs and the body. But the problem is that in A-fib some blood tends to hang out in the atria and it doesn’t completely empty, so eventually it can clot and now you have a huge clot hanging out inside your heart. If that clot decides to move it can go out into your body and end up in one of the coronary arteries (the arteries on the outside of your heart that supply your heart muscle itself with blood) and cause a heart attack, it can go to your brain and cause a stroke, or it can go into the lungs and cause a pulmonary embolism (PE). So usually people with A-fib are put on blood thinners to keep the clotting from occurring, or if the A-fib is too high of a rate (rapid A-fib) they’re sometimes given medication or cardioverted (shocked) out of it.
Like another commenter stated, in guessing they stimulated the vagus nerve which converted his heart rhythm into sinus rhythm, which is the normal heart rhythm.
Your left it’s your heart, my left if it’s mine.
Stimulating the vagus nerve can drop your heart rate quite a bit, sometimes enough to cause them to pass out. If someone’s heart is weak or diseased and their vagus nerve is stimulated enough that their heart rate drops too low too fast, their heart might not be able to recover and they can just die. It’s why a lot of old people die on the toilet, the act of pooping stimulates the nerve and boom they’re gone (see Elvis).
Sticking a fork in an outlet is a great way to give yourself Ventricular Fibrilation which is just like Atrial Fibrilation except that the Ventricles, not the Atria, are quivering. And when the Ventricles are quivering they aren’t pumping so no blood is moving out into your body and you have no pulse and you are dead.
Fun fact, AEDs and defibrillators don’t shock asystole (flatline). They shock 2 rhythms, in hope of stopping the heart so that it might restart in a better rhythm (have you tried turning it off and back on again?) V-fib is one of the 2 rhythms. Ventricular tachycardia (V-tach) is the other. In V-tach your ventricles are beating very very fast. You can still be alive and still have a pulse in V-tach (or not), which is why they say never to apply an AED to someone who is still alive, because it could recognize the V-tach, shock them and kill them.