Electrophysiological basis for XXXX caused by @entity63 . Role of the subendocardium.

@entity296 @entity1165 @entity63 @entity235 @entity1563 @entity3971 @entity591 @entity10389 @entity2224 @entity741 @entity943
The major electrophysiological changes during the first 10 min of @entity741 caused by complete obstruction of a coronary artery are a reduction in membrane potential, a decrease in action potential amplitude and upstroke velocity, and a prolongation of recovery of excitability following an action potential. Conduction velocity in the direction parallel to the long axis of @entity296 ( @entity10389 ) and in the transverse direction (VT) in normal myocardium are in the order of 40 cm/s and 20 cm/s respectively. During @entity63 , conduction velocity decreases and lowest values for @entity10389 are in the order of 20 cm/s, for VT around 10 cm/s, before the ischemic tissue becomes inexcitable. Calculated dimensions of a possible re-entrant circuit in acutely ischemic myocardium (the product of refractory period and conduction velocity) are in the order of 7 to 8 cm. Re-entrant circuits of such dimensions were indeed demonstrated by simultaneous recording of 125 extracellular potentials from the epicardial surface of the ventricles during spontaneously occurring @entity943 after @entity1563 . Previous studies provided evidence that premature ventricular depolarization which initiate re-entry originated in the subendocardium, and the present experiments confirmed this. Destruction of the subendocardium of isolated, Langendorff perfused @entity235 hearts, including the Purkinje system, by intracavitary application of @entity3971 , did not, however, abolish ectopic activity during either @entity63 or reperfusion, although the nature of the @entity943 during @entity63 was different from those in intact hearts. Coupling intervals of ectopic beats were longer in @entity3971 -treated hearts than in intact hearts, but the site of origin of initial ectopic beats leading to @entity1165 could not be determined. Re-entrant circuits with revolution times in the order of 340 to 400 ms accounted for the @entity591 observed in @entity3971 -treated hearts. In contrast to intact hearts, these @entity591 never degenerated into @entity2224 , indicating that an intact Purkinje system may be a necessary requirement for @entity2224 to occur during acute, regional @entity741 .
