Cardiac Rhythm Recognition and Electrical Therapy
Shockable versus non-shockable
Only two rhythms are defibrillated: ventricular fibrillation and pulseless ventricular tachycardia. Asystole and pulseless electrical activity (PEA) are non-shockable and are treated with high-quality CPR, epinephrine, and a search for reversible causes (hypovolemia, hypoxia, acidosis, hypo/hyperkalemia, hypothermia, toxins, tamponade, tension pneumothorax, thrombosis). Differentiate fine VF from asystole by checking leads and connections and confirming in more than one lead; true asystole with a flat line across leads should never be shocked. Artifact from CPR or a loose lead can mimic both.
Electrical therapy distinctions
Defibrillation is unsynchronized and is used for VF and pulseless VT. Synchronized cardioversion is used for unstable tachyarrhythmias with a pulse, such as rapid atrial fibrillation, atrial flutter, or supraventricular tachycardia, and for VT with a pulse - the machine must sense the QRS so the shock lands outside the vulnerable period. Transcutaneous pacing is for symptomatic bradycardia that does not respond to atropine, with electrical and mechanical capture verified.
Traps
The most common error is selecting synchronized cardioversion for pulseless VT or VF - the synchronizer may fail to sense and deliver no shock. Others include shocking asystole, mistaking PEA for a shockable rhythm, and forgetting that monomorphic VT with a pulse and instability is cardioverted, not defibrillated.
Rule of thumb
No pulse and organized rhythm equals PEA: do not shock, hunt for the cause. Pulse plus instability plus fast equals synchronized cardioversion. No pulse plus chaotic or wide fast equals defibrillate.