790-6 The Incidence and Clinical Relevance of Bundle Branch Block in Patients with Acute Myocardial Infarction Treated with Thrombolytic Agents

In the pre-thrombolytic era the occurrence of new bundle branch block in the setting of acute myocardial infarction ranged between 6 to 12%. Whether thrombolytic therapy alter the incidence and clinical relevance of bundle branch block during acute myocardial infarction is unclear. In 324 consecutive patients with acute myocardial infarction admitted under the Gusto I protocol the incidence of new onset bundle branch block (BBB) was examined with respect to the infarct related artery (IRA). Each patient underwent continuous 12 lead ECG rnonitoring for a period of 24 – 72 hours using a system which stored any ST change persisting for more than 60 seconds.Of the 324 patients, the overall incidence of BBB was found to be 28% (n=91), transient BBB was seen in 24.3% (n=79) of patients, persistent BBB in 3.7% (n=12) and alternating right and left BBB in 2.2% (n=7). When examined with respect to the infarct related artery, patients with LAD infarcts had a higher incidence of BBB as compared to those with infarcts in the RCA/Circumflex distribution (LAD 39% vs. RCA 26% and Circumflex 15.6%, p<0.05). The occurrence of right or left BBB was not predicted based on the infarct related artery, being equally distributed in patients with LAD/RCA infarcts. Mortality in the overall population was 5% (n=16). Persistent BBB, irrespective of the infarct related artery, was predictive of a higher mortality (33%=4/12) than transient (5%=4/79), or no BBB (3.4%=8/233) (p<0.01).In conclusion1) In this population, the occurrence of persistent BBB is lower than previously reported. Whether this is secondary to the use of thrombolytic agents requires further evaluation. 2) LAD occlusion is associated with a higher incidence of BBB. 3) The occurrence of either right or left 8BB was not predicted by the occluded artery. 4) Persistent BBB predicts a worse prognosis