Concealed conduction: an indication for temporary demand pacing.

A lthough cardiac pacemakers have a proved place in the treatment of chronic heart block,1,2 there have been some differences of opinion regarding the efficacy of artificial pacing in heart block complicating acute myocardial infarction. Second degree atrioventricular (A-V) block can be divided into type I (Wenckebach) and type II ( ‘sI bjt ) . The former is the type usually associated with inferior myocardial infarction and has a better prognosis than type II which is most often associated with anterior infarction.’ Since type II A-V block usually results from extensive damage to the bundle branches, complete heart block with a slow, ineffective pacemaker focus may result, and artificial pacing must he immediately available. ’ ’ This is contrast to type I A-V block which is usually due to ischemia of the A-V node and is generally transient.6 Although complete heart block may occur in this situation, the pacemaker focus is usually located high in the junctional tissue and the rhythm is better regarded clinically as a form of atrioventricular dissociation rather than complete heart block. , Since this latter rhythm disturbance is almost always reversible, artificial pacing is not needed as long as the ventricular rate remains above 50 beats per mmute.35 The site of the infarction, the rate of the subsidiarv pacing focus, and the clinical condition of the