Table 1.

Definitions of the 7 Classes

Class	Definition
Aystole	No heartbeats at all for a period of 4 s or more
EB	Heart rate is lower than 40 beats per minute; fewer than 5 beats occur within a period of 6 s
ET	Heart rate is higher than 140 beats per min; more than 17 beats occur within a period of 6.85 s
VF	A rapid fibrillatory, flutter, or oscillatory waveform for at least 4 s
VT	Five or more consecutive ventricular beats within a period of 2.4 s (a heart rate of 100 beats per min)
SR	Heart rate between 40 and 100 beats per min, for 8 s
AF	Tachyarrhythmia characterized by predominantly uncoordinated atrial activation with consequent deterioration of atrial mechanical function

AF indicates atrial fibrillation; EB, extreme bradycardia; ET, extreme tachycardia; SR, sinus rhythm; VF, ventricular fibrillation; and VT, ventricular tachycardia.