The doctor quickly recognized the patient was in v-fib and started CPR immediately.

v-fib 是 ventricular fibrillation 的缩写形式，ventricular 指"心室的"，fibrillation 指"纤维性颤动"。 v-fib 即"心室颤动"，是一种致命的心律失常，心脏无法有效泵血，需要立即进行心肺复苏和电除颤治疗。