arrhythmia
Think of a healthy heartbeat as a steady drumbeat — even, on time and never missing a stroke. An arrhythmia is any departure from that rhythm: the beat may run too fast, too slow, or simply lose its even spacing. The word literally means “no rhythm,” though in practice it covers anything irregular, not only the total chaos that name suggests.
Normally each beat starts in the heart's natural pacemaker and spreads along a fixed electrical pathway. An arrhythmia arises when that signal misfires, speeds up, slows down, or finds an abnormal route. Causes range from harmless extra beats and caffeine to scarring after a heart attack, electrolyte imbalance, thyroid disease or inherited channel disorders.
Not all arrhythmias are dangerous. Many people have occasional skipped or extra beats that are entirely benign and need no treatment. Others — particularly fast rhythms from the ventricles — can be life-threatening. The clinical task is to tell apart the trivial from the serious, usually with an electrocardiogram, and to treat only when symptoms or risk justify it.
A patient complaining of an occasional “flip-flop” in the chest wears a portable monitor for two weeks; the recording shows isolated extra beats — an arrhythmia, but a benign one needing only reassurance.
Most palpitations turn out to be benign extra beats rather than a dangerous rhythm.
Arrhythmias are broadly grouped by rate (too fast = tachyarrhythmia, too slow = bradyarrhythmia) and by origin (above the ventricles = supraventricular, within them = ventricular). The diagnosis almost always rests on an ECG capturing the rhythm.