I just watched the episode after Hank gets shot by the cartel guys. (I know, we're way behind.) I had to pause it to say to my husband "Oh my God. For once in the entire history of television, they didn't shock a flatline." They actually had an exchange between medical personnel that went something like "Defib?" "No reason, he's flatlined." OH MY GOD THANK YOU.
Explanation for people who may not know: You know the common scene where someone's heart stops, the monitor flatlines and goes "beeeeeeeeeeee…", the doctors grab the defibrillator, stick the paddles on the patient's chest, yell "CLEAR!" and shock the patient multiple times until their heart starts beating again? In real life, if you've flatlined, the defibrillator won't do any good. It's not a jump-start.
A defibrillator, as the name suggests, helps if your heart is in fibrillation. Normally, the different parts of your heart are electrically activated in a certain order. A small area at the top of your heart starts the electrical activation for each beat, and then the signal moves through your heart in a certain order. This causes the familiar shape of the ECG, like the bottom panel of this image. As each part of your heart is electrically activated, the heart muscle contracts. As long as this happens in the right order, your heart pumps blood like it's supposed to. But during fibrillation, the electrical activation gets all out of order and chaotic, so that your heart is just kind of twitching and not pumping properly. Your heart is trying to start a normal beat, but it's being blocked by the chaotic electrical signals already running around. When this is happening, the monitor won't show a flatline. It'll show an irregular, jagged, scribbly-looking line, like the top panel of the same image. The shock administered by the defibrillator paddles stops the chaos by bringing your whole heart to the same voltage for a moment. This actually makes your heart flatline for a moment, as you can see in this ECG -- the black arrow shows where the defibrillation shock was applied. The idea is that, once the fibrillation is stopped, your heart can re-start beating normally again on its own.
In other words, a defibrillator stops your heart momentarily. If your heart has already stopped, then trying to stop it more isn't going to do any good.
But every single TV hospital scene treats the defibrillator like a jump-start, and it makes me grind my teeth in annoyance. I was shocked (no pun intended) when Breaking Bad actually got it right. I already had a lot of respect for the writers, but I gained even more respect for them with that scene.