a cardiac arrhythmia whose basis is a disturbance in atrial activity. Atrial fibrillation often occurs with heart defects, cardiosclerosis, rheumatic endocarditis, and thyrotoxicosis, but there is no generally accepted theory to explain how it develops.

A distinction is made between paroxysmal and continuous atrial fibrillation. Continuous fibrillation may be tachyrhythmic (rapid), with a pulse of 90 to 150–180 beats per minute, or bradyrhythmic (slow), in which the pulse is never more than 60–80 beats per minute. The tachyrhythmic form is associated with sensations of palpitations, pounding, general excitement, and weakness. Patients with the bradyrhythmic form usually do not sense the arrhythmia, which is often detected only by electrocardiographic examination.

Although atrial flutter arises from the same conditions as atrial fibrillation, it is distinguished from atrial fibrillation in that the number of atrial impulses reaches 300 and the pulse may be as rapid as 240–300 beats per minute. A distinction is made between regular flutter, in which every second or third impulse travels successfully from the atria to the ventricles, and irregular flutter, in which the alternation of atrial and ventricular contractions is irregular. Atrial flutter is more difficult for patients to tolerate than is fibrillation.

Cardiac arrhythmias are treated with cardiac glycosides, quinidine, Novocainamid, Inderal, Aimalin, potassium salts, cocarboxylase, and electropulse therapy.