bradycardia /-kär″dē·ə/ [Gk, bradys, slow, kardia, heart] , a condition in which the heart rate is less than 60/min. Bradycardia takes the form of sinus bradycardia, sinus arrhythmia, and second- or third-degree atrioventricular block. Sinus bradycardia may be caused by excessive vagal tone, decreased sympathetic tone, or anatomical changes. It is common in athletes and is relatively benign. It may even be beneficial in acute myocardial infarction (especially inferior). Pathological bradycardia may be symptomatic of a brain tumor, digitalis toxicity, heart block, or vagotonus. Cardiac output is decreased, causing faintness, dizziness, chest pain, and eventually syncope and circulatory collapse. Treatment may include administration of atropine, implantation of a pacemaker, or change in medical treatment.
