Ability of Activation Recovery Intervals to Assess Action Potential Duration During Acute No‐Flow Ischemia in the In Situ Porcine Heart

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Abstract
The ability to assess transmural changes in action potential duration during acute no-flow ischemia is essential to an understanding of the tachyarrhythmias that occur in this setting. The purpose of this study was to determine if activation recovery intervals determined from unipolar electrograms would provide this information. We recorded simultaneously transmembrane action potentials and unipolar electrograms from sites located as closely together as possible in the center and at the lateral margin of the ischemic zone during acute no-flow ischemia and correlated the changes in activation recovery intervals obtained from the unipolar electrograms to the changes in action potential duration. We found that the activation recovery intervals provided an accurate measure of the changes in action potential duration during acute no-flow ischemia provided the electrograms had a well-defined, single negative component to the QRS complex with a maximum negative dV/dt > 10 V/sec and a single positive component to the T wave having a maximum positive dV/dt > 1.6 V/sec. Electrograms meeting these criteria comprised 90% of the electrograms recorded at the margin of the ischemic zone throughout 60 minutes of no-flow ischemia. In the center of the ischemic zone, 75% of the recorded electrograms met these criteria for the first 20 minutes of no-flow ischemia. Thereafter, the percentage declined and after 40 minutes of no-flow ischemia, none of the electrograms recorded in the center of the ischemic zone met these criteria. Activation recovery intervals obtained from unipolar electrograms provide an accurate assessment of changes in action potential duration throughout the ischemic zone during acute no-flow ischemia, provided the characteristics of the electrograms meet specific predetermined criteria.