Asystole is a state in which the heart is not beating and has no electrical activity. As there is no cardiac output, asystole is incompatible with life. Untreated for more than a couple of minutes, it will result in irreversible brain damage and then death.
We will all end up in asystole.
Myths and misconceptions about asystole abound:
1) Asystole is a completely flat line.
Although the appearance of asystole on an electrocardiogram (ECG) is known colloquially as "flatline", a completely flat line is relatively uncommon as an ECG trace. The most common cause of such a trace is that the leads have fallen off - which should be the second thing to check. The first is the patient. If they are sitting up in bed reading the paper and sipping a cup of tea, you can be quite sure they are not in asystole. Asystole can actually be quite wavy; the important thing is that the patient looks dead and the normal waves of the ECG are absent.
2) Asystole can be rescued by shock
Asystole is not a shockable rhythm. All those films and TV programmes that show an ECG monitor emitting a forlorn, constant tone and displaying a flatline trace - prompting medical personnel to shout "CLEAR!"and leap to the rescue with a defibrillator - are rubbish.
Defibrillators, as the name suggests, stop the heart fibrillating (fluttering in a rapid and ineffective way). They do this essentially by stopping electrical activity in the heart and letting it re-start. The "precordial thump" - slamming the closed fist into a patient's chest - is a poor-man's defibrillator and attempts the same thing. If the heart has stopped, defibrillation will do exactly nothing. The appropriate response is cardiopulmonary resuscitation (CPR).
3) Most patients recover with CPR
Media depictions of CPR often seem to put this idea across. I really, really wish it were true. It is not true. Most patients who go into cardio-respiratory arrest die. There is no set length of time for which resuscitation is carried out; attempts are stopped when the team believes there is no longer a chance of recovery. According to a large Swedish study (Swedish healthcare is excellent) around 2% of patients presenting with asystole will leave hospital alive.
4) Asystole and cardiac arrest are the same thing
Cardiac arrest is the situation in which the heart no longer pumps effectively and there is circulatory failure. This situation can arise with heart rhythms other than asystole. These include Ventricular Fibrillation and pulseless Ventricular Tachycardia. In some cases, the ECG picture can look completely normal but there is no cardiac contraction and no pulse. This is known as pulseless electrical activity or electro-mechanical dissociation.
http://www.emedicine.com/EMERG/topic44.htm
Engdahl J, Bang A, Lindqvist J, Herlitz J: Can we define patients with no and those with some chance of survival when found in asystole out of hospital?. Am J Cardiol 2000 Sep 15; 86(6): 610-4