Lidocaine suppression of junctional escape impulses during AV block in inferior wall myocardial infarction

We present a patient who had a complete heart block with narrow QRS complexes, complicating an inferior wall myocardial infarction. He had a stable junctional escape rhythm during antiarrhythmic therapy in the early phase of heart block. In contrast, when antiarrhythmic therapy was instituted in the late phase, suppression of the junctional escape focus was observed. This observation may suggest a role for late phase ischemic metabolites in potentiating lidocaine's suppressive effect on automaticity, leading to instability and possible suppression of the junctional rhythm that did not occur during the early (autonomic) phase AV block.