The evidence of transmural unidirectional block by experimental current induced ventricular tachycardia in the canine heart.
Under normal circumstances, excitation of the heart spreads from the endocardial site to the epicardial site via the Purkinje fiber. The purpose of this study is to observe whether the transmural unidirectional block exists near the current induced local clamp during sustained ventricular tachycardia. Twelve open chested dogs were used and the local transmural electrograms were taken by three plunge electrodes consisting of two pairs of bipolar ones which were located at the epicardial site and the endocardial site respectively. Evidence of the unidirectional block was detected by means of excitation order between the endocardial site, the epicardial site and the conduction direction. We used the concept of intrinsic deflection for documentation of the conduction direction, i.e., an opposite change of the initial deflection of the local electrogram indicates a reversal of direction. Ventricular tachycardia was induced by a current with 3-5 mA to the midwall of the myocardial muscle. Results showed that the change of conduction order and the reverse direction of conduction were seen simultaneously, and ventricular tachycardia was converted to ordinary rhythm by the incision at the epicardial site of myocardium. These results may prove that the unidirectional block is the major qualification for the detection of re-entry.
D000818:Animals; D004285:Dogs; D004558:Electric Stimulation; D006327:Heart Block; D006329:Heart Conduction System; D013610:Tachycardia / Q000209:etiology