arrhythmia (n.)

in medicine, "irregularity of pulse" (arrhythmia cordis), 1888, from Greek noun of action from arrhythmos "irregular, unrhythmical," from a- "not" (see a- (3)) + rhythmos "measured flow or movement, rhythm; proportion, symmetry" (see rhythm). Nativized form arrhythmy, in reference to metrics, is attested from 1844.