Here's the same content in plain, everyday language:

Normally, the heart's upper chambers (atria) send an electrical signal down to the lower chambers (ventricles) to make them beat, in perfect sync. In a "complete block," that signal gets completely cut off between the top and bottom of the heart. The atria and ventricles now beat completely independently of each other, each doing their own thing at their own speed - that's why the text says "no relationship between P wave timing and QRS-T timing" on an ECG. The ventricles have to rely on a backup pacemaker further down (in the AV node/bundle area), which beats slowly on its own, around 15-40 times a minute.

Think of it like this: the atria have been "bossing around" the ventricles for a while, making them beat faster than they naturally would. When the connection suddenly breaks (complete block), the ventricles don't instantly start beating on their own - they need a few seconds to "wake up" and find their own rhythm. This gap lasts about 5 to 30 seconds.

Here's the problem: your brain can only handle being without blood flow for about 4-7 seconds before you pass out. So during that gap where the heart isn't beating properly, the person faints. This is called syncope.

In short: Complete heart block breaks the connection between the heart's top and bottom halves. When it happens suddenly, there's a brief dangerous pause before a backup rhythm kicks in, and that pause can make someone faint (or in worse cases, be fatal) - which is why a pacemaker is used to protect against it.

The summary table at the bottom is just comparing the different degrees of heart block (first-degree just shows a delayed signal with no dropped beats, and presumably second- and third-degree types follow with worse symptoms, though that part of the table is cut off in your photo).