Occurrence and transmission of localized repolarization abnormalities in vitro.

Abnormal delay of repolarization leading to prolonged reduction of membrane potential could lead to arrhythmias. Transmission of this type of abnormality from an "abnormal" to a "normal" segment of Purkinje fiber was studied as follows: In a double compartment bath one segment was superfused with unmodified Tyrode's solution and the other with solutions known to induce abnormal prolongation of action potential duration (manifest by prolonged step-like delays in repolarization, or "secondary plateaus" and "early afterdepolarization," that is, activations arising as a consequence of the prolonged depolarized membrane potential). Transmission of abnormalities varied. Complete transmission of secondary plateaus and early afterdepolarizations led to action potentials configurationally similar throughout the fiber. Selective transmission of early afterdepolarization led to the occurrence of new premature action potentials in the normal segment. Cycle length prolongation favored both the occurrence and the transmission of abnormalities. After addition of lidocaine or high potassium ion solutions to the normal segment, shortening of action potential duration occurred and was transmitted from normal to abnormal segment. In this way, reversal of abnormality throughout the fiber occurred via an intervention applied selectively to the normal segment. Observations in this study may be relevant to arrhythmias and their treatment.