nonrhythmic s deliberately not rhythmic Usage(s) A daylong ECG showed that bouts of angina pectoris led to a bizarre, nonrhythmic twitching of the heart. And this is the sort of speed-up that can lead to fibrillation (a futile, nonrhythmic quivering) of the lower part of the heart, which means death. As soon as he got out his breathing fell off, inevitably, but not all the way to its original and inefficient nonrhythmic pattern.