Complete heart block in acute myocardial infarction: A clinical evaluation of the intracardiac bipolar catheter pacemaker

Abstract The incidence of complete heart block is probably greater than recognized in earlier studies. It is suggested that modern technics of constant cardiac monitoring would indicate that the discrepancy could have resulted from at least two sources. Complete heart block may be transient in some patients and appear to be of little consequence. However, patients presenting in this manner may be more likely to have periods of asystole later in the hospital course. The ability to immediately re-institute electrical pacing may be lifesaving. The onset of complete heart block may be closely followed by cardiac arrest during the interval preceding establishment of a lower intrinsic pacemaker. Periodic electrocardiograms would be unlikely to document complete heart block in either of these circumstances. Complete heart block occurs most frequently in infarctions resulting from occlusion of the right coronary artery associated with the electrocardiographic picture of inferior infarction. Complete heart block developing in the setting of acute myocardial infarction frequently is accompanied by other complications of infarction, especially congestive heart failure and shock. This combination results in an especially poor prognosis. The absence of congestive heart failure was the best prognostic sign in our series of patients, being associated with no mortality. Patients without shock had a 28 per cent mortality, and patients without cardiac arrest, a mortality of 29 per cent. Cardiac arrest poses a serious threat to survival. The insertion of a pacemaker catheter within 15 minutes after onset of complete heart block will reduce the incidence of this complication. Pacemaker insertion is not a benign procedure in the setting of acute myocardial infarction. The type of catheter currently in use can be difficult to manipulate and may cause significant arrhythmias during insertion. This technic also requires movement of the patient to nonpatient areas for visualization of the catheter during insertion. This is usually at a time in the course of infarction when as little movement as possible is desirable. For these reasons, we currently consider it to be in the best interest of the patient not to insert a pacemaker catheter unless complete heart block intervenes. Second degree heart block was noted to develop in about 8.7 per cent of all of our patients with acute infarction; less than half of these went into complete heart block. On the other hand, 2 patients were documented to develop complete heart block directly from normal sinus rhythm. When intracardiac catheter stimulation is utilized, the patient is not aware of artificial pacing, and the use of the external jugular system allows the patient complete freedom of movement during pacing. The incidence of complete heart block persisting in survivors of our study is greater than previously reported. This probably represents the survival of patients who would otherwise have succumbed from atrioventricular nodal infarction. Modern methods of management preclude the acceptance of “death” as an end-point in acute myocardial infarction. Thirty-seven per cent of patients suffering cardiac arrest after complete heart block developed in myocardial infarction survived their infarction to return to normal life. The role of an intracardiac catheter pacemaker was felt to be essential in a significant number of these patients. The role of the catheter pacemaker as a preventive measure against cardiac arrest would also appear valuable provided its use is limited to certain clinical situations. At present it would appear to be a useful adjunct in patients who experience complete heart block during acute myocardial infarction, provided proper facilities are available for insertion and that the physician is adept in handling problems that may arise during insertion or while the catheter is in place inside the heart.