Actions of halothane and isoflurane on Purkinje fibers in the infarcted canine heart: conduction, regional refractoriness, and reentry

The actions of halothane (HAL) and isoflurane (ISO) on conduction and regional refractoriness were studied in infarcted canine hearts to compare their effects on reentry in vitro. In two anesthetic groups of 8 hearts, high and low dose effects were assessed using action potentials recorded from Purkinje fibers located in the nonischemic and ischemic regions. An extrastimulus technique was used to determine the relationship between delay of conduction of premature impulses into the more refractory ischemic region and induction of reentrant responses. At high doses (HAL 0.60 mM and ISO 0.64 mM, approximately 2.3 minimum alveolar anesthetic concentration MAC]) both anesthetics decreased (P < or = 0.05) the effective refractory period for direct intracellular stimulation of nonischemic fibers (local ERP, initial control: 294 +/- 8 ms); the decrease with HAL (-29 +/- 6 ms) was smaller (P < or = 0.05) than with ISO (-50 +/- 7 ms). HAL and ISO also decreased (P < or = 0.05) the coupling interval of the earliest premature impulse which conducted into the infarct (system effective refractory period SERP], control: 301 +/- 7 ms) by -31 +/- 11 and -44 +/- 8 ms, respectively. In contrast, the functional refractory period (FRP) in the ischemic region (control:354 +/- 4 ms) was increased by HAL (26 +/- 8 ms; P < or = 0.05) but decreased by ISO (-14 +/- 4 ms, P < or = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)