Hiromichi Tsuchihashi

Ventricular Fibrillation Studied by the Microelectrode Method

Capillary ultramicroelectrodes were inserted into ventricular muscle fibers of dogs in ventricular fibrillation and action potentials obtained were compared with deflections of unipolar direct lead, adjoining bipolar direct lead or other electrocardiograms taken simultaneously. In most stages of ventricular fibrillation neither synehronism nor any other regular time relationship could he found between them. Microelectrodes inserted at two points variously distant on various regions of the ventricular surface also failed to show any regular time relationship. Total incoordination of ventricular muscle fibers was thus supported.

Function of Potential Bypass Tracts for Atrioventricular Conduction

Function of potential bypass tracts for the atrioventricular conduction was examined in isolated rabbit hearts using microelectrodes, a suction electrode, and bipolar electrocardiographic leads. After the normal A-V conduction was blocked by acetylcholine, conduction to the ventricle occurred with a much shorter A-V conduction time and without significant QRS change, when a point at the root of the inferior vena cava was stimulated. By analyzing the site of delay, this route was presumed to go from the right atrium to the lower portion of the His bundle bypassing the A-V node. When a point inferior to this point was stimulated, marked shortening of conduction time and marked QRS change occurred. This second tract seemed to exist between the right atrium and ventricle bypassing the specialized system. The third tract was found when an anterior point on the right atrium was stimulated. The conduction was markedly prolonged without changing the QRS. This route seemed to enter some point of the A-V node, inducing a detour within the node.

Action of Ryanodine on Mammalian Cardiac Muscle: Histological Determination of the Site of Retrograde Atrioventricular Block

In our previous study, three types of intra-cellular potentials were found in a small area in the region adjacent to the postero-inferior margin of the membranous portion of the interventricular septum of the isolated dog heart. From the electrophysiologieal behavior of these cells, it was presumed that the cells of the third type were the point of block for retrograde conduction in cases of unidirectional A-V conduction, and that those of the first type lay upstream from the point of retrograde conduction block, whereas those of the second type lay- downstream beyond the blocking point. In this study, histological examination was used to find the origins of these three types of potentials. When a potential of one or another type was found the mieroelectrode tip was gently cut off and later localized histologically. It was found that all three types of potential originated from the ventricular portion of the specialized museilar tissue, that the origin of the third type was just above or at the bifurcation of the bundle of His, and that the origin of the first type was distal while that of the second type was proximal to the origin of the third type. Thus, the deduction from the electrophysiological behavior was proved by the histological examination. This gave further evidence for our belief that there is a sensitive point for retrograde conduction block in unidirectional A-V conduction just above the bifurcation of the bundle of His.

U vector loop or arc in normal subjects and in those with left ventricular hypertrophy

Abstract 1. 1. U-loop vectorcardiograms were obtained from 30 normal subjects and from 31 subjects with left ventricular hypertrophy, by the method of differential vectorcardiography. Four of the subjects with left ventricular hypertrophy were excluded from the present study because of the complication of myocardial infarction. 2. 2. The U loop of normal subjects showed a constant configuration. It resembled a small, slightly curved club and was inscribed almost in the direction of continuation of the terminal limb of the T loop, so that a term such as U vector segment or U vector arc might be preferable to the term U vector loop . The T-U junction vector was directed to the left, inferiorly, and mostly anteriorly. This finding of the U loop, together with that of the T loop, which was inscribed clockwise in the frontal plane and counterclockwise in the horizontal and left sagittal planes, with its long axis directed to the left, inferiorly, and slightly posteriorly or anteriorly, constituted characteristic features of the normal T-U loop. 3. 3. The U loop of left ventricular hypertrophy began with a marked bend at the T-U junction and extended in various directions, resembling also a small curved club, but sometimes much larger than normal U loops. Occasionally, the U loop was inscribed as in normal cases, in continuation of the terminal limb of the T loop, but in such cases the T loop itself was abnormal. All cases of left ventricular hypertrophy showed such a feature of the T-U loop in at least one planar projection; there was one exception, however, a case in which normal features were retained in all three planes. 4. 4. There was a tendency toward relatively slight left ventricular hypertrophy in those cases which retained normal features in any one of the planes or those which showed abnormality in the U loop only, whereas there was relatively marked left ventricular hypertrophy in those cases which showed a distinct abnormality also in the T loop. 5. 5. Such U-loop abnormalities were already evident in the early stage of left ventricular hypertrophy when there were no (or minute) evidences of it in ordinary electrocardiograms, including the U-wave changes. Thus, they are useful for diagnostic purposes in detecting slight left ventricular hypertrophy.

Correlation of ECG, VCG, and pathologic findings in subendocardial infarcts and infarct-like lesions experimentally produced by administration of substrances of high molecular weight

Abstract 1. 1. Various substances of high molecular weight, epinephrine, and other drugs were administered to 169 rabbits, with formation of myocardial infarction or infarct-like lesions in 168. Correlative study with electrocardiograms and autopsy findings was made together with the records of 15 other control rabbits. Among these 162 rabbits with subendocardial infarcts or infarct-like lesions were the subjects of this study. 2. 2. In subendocardial infarcts or infarct-like lesions the incidence of depression of the S-T segment or flattening or inversion of the T wave was much less than expected. No S-T-T changes could be noticed in about one third of all of the cases in spite of the presence of the lesions at autopsy. In another third the changes were so slight that they became evident only after comparison with control records. These results suggest that, in clinical practice, slight segmental depression or T-wave changes should not always be regarded as indicating a reversible myocardial injury or ischemia, even if no other clinical signs of infarction exist. 3. 3. As for QRS changes due to subendocardial infarcts or infarct-like lesions, a definitely abnormal Q wave appeared in none of the cases. However, especially in the examination of 20 rabbits which showed infarcts or infarct-like lesions in the subendocardial layer of the anteroseptal region, a marked decrease in the R wave in the right precordial leads was encountered occasionally when the lesions were relatively large. 4. 4. Vectorcardiograms in addition to electrocardiograms were obtained in 25 rabbits. The vectorcardiograms showed diagnostic evidence of infarction in 5 instances in which the electrocardiograms showed no significant abnormality. In most of them the abnormal change was diminution in the initial anterior portion of the QRSsE loop due to subendocardial infarcts or infarct-like lesions in the anteroseptal region.

Properties of the fibers in the pathways along the anterior and posterior portions of the left A-V ring

A comparison was made of the electrophysiological properties of the fibers between the previously reported conduction pathways from the left atrium to the right atrium and to the ventricle (left A-V ring pathways) and the ordinary atrial muscle, using perfused isolated rabbit hearts. Each fiber within these pathways showed action potential with a well-developed plateau phase. The plateau phase of these action potentials was distinctly shortened by an infusion of 1 x 10-6 g/ml of acetylcholine. When the heart was perfused by Tyrode solution with 15 mM KCl, the trans-membrane potential of the ordinary atrial muscle fiber showed a decrease of resting potential and of amplitude of action potential. The fibers within these pathways, however, were more resistant to the high potassium solution than the ordinary atrial fibers. A slow diastolic depolarization was observed in the fibers of the pathway when 1-isoproterenol (1 x 10-5 g/ml) was applied locally. These findings suggest that the fibers within the left A-B ring pathways possess similar electrophysiological properties to the specialized fibers in the atria.