Bradycardia-tachycardia syndrome is a particular manifestation of the sick sinus syndrome in which the sinus node is faulty either in its impulse formation or the transmittal of the impulse to the atrium. In such cases, it is often associated with episodes of supraventricular tachycardia. Detection of the bradycardia-tachycardia syndrome usually requires ambulatory monitoring. Sinus pauses of 2 seconds are generally considered abnormal, particularly if symptoms accompany the rhythm disturbances. Between one-half and three-quarters of patients with the sick sinus node syndrome have episodes of tachycardia and may develop syncope when there is prolonged asystole following a run of supraventricular tachycardia. Many patients with this syndrome also have additional conduction defects, such as atrioventricular block, intraventricular condition defect, and/or bundle branch block. One confounding feature of the syndrome is its intermittent nature. Repeat episodes of ambulatory monitoring may be required to document the diagnosis.