Effects of Intravenous Amiodarone on Refractory Periods of the His Purkinje System

Summary

In 4 patients an intrahisian second degree AV block occurred during oral amiodarone (Am) therapy (daily dose of 400 mg) and disappeared 3 months after the end of Am. To assess a relation between Am and intrahisian A V block, 150 mg of Am were injected in 26 patients (pts) with prolonged HV interval and/or infrahisian block induced by programmed atrial (A) extrastimulus technique. His Purkinje anterograde effective refractory period (HP ERP) was the longest HI H2 interval in which conduction to the ventricles failed to occur (H1 = His bundle electrogram of the A paced rhythm, H2: His bundle electrogram after the extrastimulus); HP functional RP (HP FRP) was the shortest propagated V1-V2 interval and HP relative RP (HP RRP) was the longest HI H2 interval with H2-V2 > H1-V1. The HP RP were studied before and after Am at the same A paced rhythm. HP-RP increased (2 to 12%) in 9pts; HP-AV-conduction was abnormal (spontaneous HV interval > 55 ms, HV interval after Ajmaline ≥ 100 ms, intrahisian second degree A V block during A pacing a rate ≤ 150 b/min) in 6 pts. HP-RP could not be calculated in 8 pts: an AV nodal block occurred after inj. of Am. The HP-A V -conduction was normal in these pts. HP RP were identical in 7 pts, shorter in 2 pts. In these pts the HP-A V -conduction was normal.

In conclusion, intravenous Am lengthened HP RP in 9 pts out of 26 (34%). This effect was more frequent in pts with abnormal HP-A V -conduction. Am should be used with carefulness in pts with abnormalities of HP-conduction. The occurrence of a second or third degree A V block with normal QRS during oral Am therapy indicates an electrophysiological study to determine the level of the block which might be within A V node or HP system.