Franklin D. Johnston

The determination and the significance of the areas of the ventricular deflections of the electrocardiogram

Abstract By measuring the areas of the ventricular deflections of the electrocardiogram it is possible to determine the mean electrical axis of QRS, which gives the direction in which the excitatory process spreads over the average element of ventricular muscle, and the mean electrical axis of T, which gives the inverse of the direction in which the recovery process spreads over the average element of ventricular muscle. If all the ventricular muscle passed through the period of excitation in the same time and in the same way, the area of QRS and the area of T would be equal in absolute magnitude, but opposite in sign, and the area of QRST would be zero. The area of QRST is a measure of the electrical effects produced by local variations in the excitatory process. The mean electrical axis of QRST gives the direction of the line along which these local variations are greatest. The local variations in the excitatory process which determine the mean electrical axis of QRST are dependent upon factors that act upon different parts of the ventricular muscle with different intensities. They are not materially influenced by the course of the excitatory process over the ventricular muscle.

Electrocardiograms that represent the potential variations of a single electrode

Abstract In order to simplify the analysis of the curves obtained by leading from the precordium and for certain other purposes, we have devised leads that record the potential variations of a single electrode. Electrodes are placed on the right arm, left arm, and left leg in the usual way and connected through like resistances to a central terminal. The resistances used for this purpose should be large in comparison with the resistance of the body in standard leads. Theoretical considerations and experiments on a model indicate that under these circumstances the potential variations of the central terminal are negligible. The curves obtained by leading from an exploring electrode in contact with any part of the body to the central terminal represent the variations in potential produced by the heartbeat in the region in contact with the former. The potential variations of the right arm, left arm, and left leg are recorded by leading from the electrodes placed on these extremities to the central terminal. They may be compared with the potential variations that occur in various parts of the precordium. To increase the resistance in the input circuit of our recording apparatus we have connected the string galvanometer to the balanced plate circuit of a one-stage vacuum-tube amplifier

Recommendations for Standardization of Leads and of Specifications for Instruments in Electrocardiography and Vectorcardiography

By COMMITTEE MEMBERS: CHARLES E. KOSSMANN, M.D., CHAIRMAN, DANIEL A. BRODY, M.D., GEORGE E. BURCH, M.D., HANs H. HECHT, M.D., FRANKLIN D. JOHNSTON, M.D., CALVIN KAY, M.D., EUGENE LEPESCHKIN, M.D., HUBERT V. PIPBERGER, M.D., AND by MEMBERS OF THE SUBCOMMITTEE ON INSTRUMENTATION: * HUBERT V. PIPBERGER, M.D., CHAIRMAN, GERHARD BAULE, PH.D., ALAN S. BERSON, M.S., STANLEY A. BRILLER, M.D., DAVID B. GESELOWITZ, Ph.D., LEO G. HORAN, M.D., AND OTTO H. SCHMITT, Ph.D.

The interpretation of the galvanometric curves obtained when one electrode is distant from the heart and the other near or in contact with the ventricular surface

Abstract When the exploring electrode is placed in the left ventricular cavity of the dogs heart, the QRS group of the curve obtained is represented by a single deflection. The direction of this deflection is upward, indicating that the potential of this cavity is negative throughout the QRS interval. When this electrode is placed in the right ventricular cavity, the curve obtained is similar but may show a small preliminary dip preceding the main upstroke. When the exploring electrode is placed on the epicardial surface, its potential is conspicuously different from that of the nearest portion of the ventricular cavity only during the period when the excitation wave is spreading outward through the subjacent ventricular wall. Before the endocardial surface becomes active and after the epicardial surface has been fully activated, there is no electromotive force across the ventricular wall, and a lead from the epicardial surface is, in effect, a lead from the ventricular cavity. The occurrence in an epicardial lead of an upward deflection which precedes the main downstroke is therefore attributed to late activation of the endocardial surface. The main downstroke is due to electric forces produced by the progress of the excitatory process outward through that portion of the ventricular wall lying between the exploring electrode and the ventricular cavity. The intrinsic deflection marks the arrival of the excitation wave beneath the exploring electrode, and hence the extinction of the electromotive force across the subjacent ventricular wall. The sudden upstroke which constitutes this deflection occurs as this electrode assumes the potential of the ventricular cavity. The same principles may be applied to the interpretation of the curves obtained by placing the exploring electrode upon a portion of the ventricular surface of the dogs heart that has been injured. Pure monophasic curves may be obtained by means of such leads if the region injured is one where the intrinsic deflection occurs late and does not rise far above the zero level.

The substitution of a tetrahedron for the Einthoven triangle

Abstract In an experiment on a cadaver, a potential difference was rhythmically impressed upon two small electrodes thrust into the heart or its immediate neighborhood. The resulting differences in potential between a central terminal and four electrodes connected to it through equal resistances were recorded with the string galvanometer. The four electrodes were on the two arms, the left leg, and the left interscapular region. By assuming that the electrical field generated in the trunk was equivalent to that of a centric doublet in a homogeneous spherical conductor and that the four electrodes were at the apices of a tetrahedron inscribed in this sphere, the experimental and the theoretical amplitudes of the deflections in the four leads could be compared. In general, it may be said that, with one exception, the deflections in the limb leads had the relative magnitudes expected. The deflections in the lead from the back were much smaller than anticipated. The last result is attributed to circumstances peculiar to the single experiment performed.

The mechanism of auricular paroxysmal tachycardia

A URICULAR paroxysmal tachycardia was long ago described and recognized as a clinical entity, but the fundamental mechanism or mechanisms responsible for this disorder have not yet been finally ascertained.‘, 2 Unlike auricular flutter and auricular fibrillation, it cannot be readily induced in experimental animals, and cannot, therefore, be easily studied by this met,hod. Speculations as to its nature must, therefore, be based on pertinent observations on man. We propose to discuss from this standpoint the following features of this disturbance : (1) the form of the anricular deflect.ions; (2) the effects of exertion, vagal stimulation, digitalis, quinidine, and other drugs upon the auricular rate and the duration of the paroxysms; (3) similarities, differences, and relations between it and auricular flutter and fibrillation; (4) the spontaneous occurrence of auriculoventricular block in a small number of cases and the difficulty or impossibility of producing it in most of the others; and (5) the occurrence of alternation in the auricular cycle length. We wish particularly to examine the su ggestion3 that auricular paroxysmal tachycardia is caused by circus rhythm involving one of the specialized auricular nodes. When Mines4 described circus rhythm he suggested that it might be responsible for some cases of paroxysmal. tachycardia in man. Iliescu and Sebastian? were among the first to su ggest that auricular paroxysmal tachycardia is due to circus contraction. Their reasoning was based chiefly on the a,ction of quinidine in this disorder. Lewis2 pointed out that the tot.al amount of auricular muscle is not sufficiently large to accommodate a circus mechanism at known rates of conduction in aurieular

The occurrence in angina pectoris of electrocardiographic changes similar in magnitude and in kind to those produced by myocardial infarction

Abstract The pronounced electrocardiographic changes which sometimes occur during a paroxysm of angina pectoris indicate that the disturbance of the coronary circulation which occurs in this condition is at times as great as that produced by the sudden occlusion of a large coronary artery. Attacks of anginal pain may occur which are accompanied by pro-found alterations of the electrocardiogram under circumstances which make it necessary to assume that the attendant myocardial ischemia is due to a change in the caliber of the coronary arteries affected, rather than to an increase in the work of the heart alone. Nicotine or some other constituent of cigarette smoke sometimes induces coronary “spasm” in patients who are subject to angina pectoris.

The form of the electrocardiogram in experimental myocardial infarction: III. The later effects produced by ligation of the anterior descending branch of the left coronary artery☆☆☆

Abstract One to four days after ligation of the anterior descending branch of the left coronary artery or one of its subdivisions, the anterior surface of the dogs heart was explored by means of direct and semidirect leads. In taking these leads, the exploring electrode was paired with an indifferent electrode placed on the left hind leg, and the connections were so made that relative negativity of the former electrode produced an upward deflection in the completed record. The curves obtained under these circumstances by leading directly from the epicardial surface of the infarcted region have a characteristic outline. The initial and usually the sole deflection of the QRS group is a tall summit. The downward movement which normally precedes the intrinsic deflection in direct leads from the ventricular surface is absent. The intrinsic deflection is likewise absent, or is greatly reduced in amplitude in which case it is often represented by a deep notch on the descending limb of the initial upward deflection. The RS-T segment and T-wave are usually represented by a U-shaped depression, sometimes followed by a small summit. Curves of similar form are obtained when the exploring electrode is separated from the epicardial surface by a pad of gauze soaked in physiological salt solution or by the precordial tissues of the intact chest wall. The curves in question are very much like those obtained by introducing the exploring electrode into the cavity of the left ventricle. They owe their characteristic form to the absence of the electrical forces normally produced by the portion of the ventricular wall deprived of its blood supply.

The form of the electrocardiogram in experimental myocardial infarction

Abstract Ligation of the septal branch of the left coronary artery in the dog is usually followed by infarction of a large part of the ventricular septum. Immediately after this vessel is obstructed the electrocardiogram shows displacement of the RS-T segment of the ventricular complex. Later, disturbances of intraventricular or atrioventricular conduction develop; right bundle-branch block occurred in all three of our experiments. In one instance the right branch block complexes were not strikingly different from those usually obtained after the right branch of the His bundle has been cut, in spite of the fact that a large part of the septal muscle was dead. In right bundle-branch block the precordial electrocardiograms may be characteristic in every respect when the standard electrocardiograms are not. Under these circumstances precordial leads are of great value in locating the conduction defect. When the potential variations of the precordium are small, the precordial electrodes should not be paired with a single electrode, but with a central terminal connected through like resistances of 5000 ohms or more to all three extremity electrodes. The R deflection of the levocardiogram is not abolished by infarction of the septum but is frequently absent in Lead I after ligation of the anterior descending and in Lead III after the ligation of the circumflex branch of the left coronary. This deflection is not of septal origin. The muscle responsible for the preliminary deflections of the levocardiogram is widely distributed, and it is probable that most of the endocardial surface of the left ventricle is active before the first summit of the levocardiogram is written.

The form of the electrocardiogram in experimental myocardial infarction: IV. Additional observations on the later effects produced by ligation of the anterior descending branch of the left coronary artery

Abstract Direct leads from the surface of infarcts that extend completely through the left ventricular wall yield ventricular complexes practically identical with those obtained by leading from the neighboring parts of the ventricular cavity. When the galvanometer connections are so made that relative negativity of the exploring electrode produces an upward deflection, these curves consist of a tall initial summit followed by a U-shaped final deflection which sometimes ends with a slight elevation above the base line. In direct leads from regions where the inner layers of muscle are dead or have been replaced by scar tissue and where the outer layers are still living and responding to the excitatory process, the QRS group is characterized by the presence of both an abnormally large initial summit and a conspicuous intrinsic upstroke. A pronounced downward movement usually separates these two deflections but may be absent. In the subacute stages of infarction the RS-T segment is often flat or depressed and the T-wave upright and abnormally large in leads from the marginal portions of the infarct. These changes in the final portion of the ventricular complex are usually associated with QRS deflections of the kind observed when only the inner layers of muscle are involved. Unlike these QRS changes, they persist for a very short time. They are due to disturbances affecting the recovery process in muscle that has been damaged, and not to the disappearance of electrical forces normally produced by muscle that has been killed.