RIGHT BUNDLE-BRANCH BLOCK OF UNKNOWN AGE IN THE SETTING OF ACUTE ANTERIOR MYOCARDIAL-INFARCTION - AN ATTEMPT TO DEFINE WHO SHOULD BE PACED PROPHYLACTICALLY

It is widely accepted that patients presenting with acute anterior myo cardial infarction and acute onset of right bundle branch block should be prophylactically paced in contrast with those who have a chronic b undle branch block. The admitting physician is faced with the dilemma of how to act if the age of this conduction disturbance is unknown. Th is problem has further intensified in recent years, with the introduct ion of thrombolytic treatment, where insertion of a central vascular l ine is associated with increased morbidity. The objectives of this stu dy were to define clinical or electrocardiographic parameters that may help the admitting physician to decide whether patients presenting wi th an anterior wall myocardial infarction and a right bundle branch bl ock of unknown age should be prophylactically paced. We examined prosp ectively the in-hospital clinical course of 39 consecutive patients pr esenting with an acute myocardial infarction in whom the age of a righ t bundle branch block upon admission was unknown (group C, n = 39) and compared it with two similar groups of patients who presented with an acute right bundle branch block (group A, n = 38) and with a known ch ronic right bundle branch block (group B, n = 22). Thirty-three patien ts (33%) died, with cardiogenic shock being the leading cause of death in the entire population. Prophylactic pacing, which was carried out in 66% and 54% of patients in groups A and C, respectively, did not re duce mortality rates. No clinical or electrocardiographic variables on admission were predictive to support prophylactic pacing in group C. In 10 of 46 (22%) patients who were prophylactically paced with a tran svenous electrode, the following complications attributed to the proce dure were detected: (1) either rapid sustained ventricular tachycardia (during implantation) that was unresponsive to overdrive pacing, or v entricular fibrillation necessitating electrical defibrillation (4 pat ients); (2) recurrent episodes of rapid nonsustained ventricular tachy cardia, which stopped only after the pacemaker was turned off (1 patie nt); (3) complete AV block (1 patient); (4) fever appearing on She thi rd or fourth day after implantation (3 patients); and (4) a large hema toma in the groin in 1 patient who was treated with thrombolysis short ly before pacemaker electrode insertion. Thus, the complications of tr ansvenous temporary pacing in the era of thrombolysis may outweigh any theoretical advantage.