Mobitz II heart block, second-degree or partial atrioventricular block characterized by the sudden nonconduction of an atrial impulse and a periodic dropped beat without prior or subsequent lengthening of the P-R interval. This kind of block usually results from bilateral impaired conduction in the bundle branches. It may be caused by anterior myocardial infarction, myocarditis, drug toxicity, electrolyte disturbances, rheumatoid nodules, and various degenerative diseases. Syncopal attacks, which occur without warning when the patient is upright or recumbent, are common in Mobitz II heart block, which may be transient or suddenly progress to complete block. Long-term therapy may require implantation of a pacemaker. Also called type II AV block.
