[Late potentials and delayed intrinsic deflections in acute regional ischemia of the heart].

Waveforms occurring at the end of the QRS complex or during the ST-segments, T wave, or diastolic intervals are defined as "late potentials". Whether late potentials reflect delayed regional activation is still under discussion. A correlation with electrophysiological parameters directly indicating delayed activation has not yet been made. The present study was performed in isolated porcine hearts (n = 12) perfused according to the Langendorff method. An ischemic zone was produced by occlusion of the anterior descending branch of the left coronary artery. Unipolar epicardial electrograms were recorded by means of nonpolarizable electrodes using DC-amplifiers (0-1250 Hz). We measured the intrinsic deflection of the ischemic zone electrogram and compared it to deflections within the ST-segments of the normal zone. When activation of the ischemic zone was progressively delayed, the intrinsic deflections and the deflections within the ST-segments were also progressively delayed. When 2:1 block at the edge of the ischemic zone occurred, deflections within the ST-segments showed the same sequence. When premature stimuli were applied, both deflections could be delayed until they outlasted the ST-segment duration. If this occurred, ventricular tachycardia developed. Our data demonstrate a definite correlation between late potentials and delayed intrinsic deflections, and suggest that late potentials in acute regional ischemia are due to extracellular current flow which might be sufficient to induce malignant ventricular dysrhythmias.