Richard Ashman

Partial bundle-branch block: A theoretical consideration of transient normal intraventricular conduction in the presence of apparently complete bundlebranch block

Abstract 1. 1. Eight cases of partial bundle-branch block of varying degrees are presented with abstracts of their clinical histories, complete physical and laboratory data and electrocardiographic studies. 2. 2. Three unusual cases of transient Type II, intraventricular or bundle-branch block are recorded with sudden transition from complete bundle-branch block to normal intraventricular conduction times in response to respiratory maneuvers. The possible mechanical or nervous factors concerned in the production of the changes are considered to be anoxemia as well as fatigue. Vagus effect may be contributory. 3. 3. We have stressed especially the importance of the recognition of this transient type of disturbance because of its better prognostic outlook. When present it must be relieved by therapeutic rest before necessary surgical or intravenous procedures are to be undertaken. 4. 4. The increased risk assumed in submitting patients, in the presence of bundle-branch block, to a procedure that may apparently only slightly effect the blood pressure and the heart is emphasized. 5. 5. The theories of partial heart-block with special reference to and the intraventricular counterparts of the accepted Types I and II of auriculoventricular types are discussed at some length. 6. 6. The theoretical reasons for the danger of precipitating fatal ventricular fibrillation in the presence of bundle-branch block are given.

A supernormal phase in conduction and a recovery curve for the human junctional tissues

Abstract 1. 1. Two cases of A-V heart-block are reported which we believe illustrate the supernormal phase in conduction. 2. 2. Our second case, in which the argument for the supernormal is less strong, is of additional interest because of ( a ) the unprecedented length of the P-R intervals, which reach 1.01 seconds; ( b ) the variation in the duration of the rest intervals and of the P-R intervals, permitting the graphic representation of a recovery curve of conductivity, and ( c ) the spreading of the QRS group and the decrease in the amplitude of the chief ventricular deflection with longer ventricular rest periods.

Normal Duration of the Q-T Interval

The relation between the average heart cycle length and the Q-T interval was studied on 432 men, 425 women and about 200 children. With exceptions to be given in the final report, these subjects were free from heart disease. In addition, the principal finding for the normal subjects has been confirmed from the study, being continued, of 700 adults and about 200 children with heart disease. The subjects were subdivided into groups according to sex and age. The principal groups are the younger adult males, the younger adult females, the older males, the older females, and the children. The adult subjects with heart disease were separated according to sex. In every group, without exception, the averages of the Q-T intervals at each cycle length fall closely along a curve represented by the empirical formula, Q-T = K log [10(C + k)]. C represents the cycle length in seconds, while K and k are constants. For the younger male adults, K was 0.373, and for the females, 0.385. K for all the normal children was 0.376, but became 0.375 when girls, aged 12 to 14 inclusive, were eliminated. For elderly men, K is approximately 0.380, and for women, 0.390. The other constant k, is +0.07 for women, and is very close to, if not precisely at, this value for the other groups. For all groups with heart disease, the value of k remains substantially as given, whereas the value of K rises. The cube root, square root and straight line formulæ proposed by Fridericia, 1 by Bazett 2 and by Adams, 3 respectively, are inexact. Bazetts formula, using constant 0.39 or 0.40, gives values which are appreciably too low at short cycle lengths and too high at the long cycles.

Heart-block with and without convulsive syncope

Abstract 1. 1. Two clinical cases of heart-block are presented which show unusually significant therapeutic responses. The spectacular results of barium chloride therapy as well as the effects of other drugs are discussed in detail. 2. 2. An explanation of the mechanism of heart-block is offered. 3. 3. Analysis of the electrocardiograms brings to light many interesting abnormalities in the cardiac mechanism in the interpretation of which facts of fundamental physiological importance are both applied and illustrated. The effects upon conduction of changes in the auricular rate; the occurrence of P-R intervals of unprecedented length, ranging up to a full second; remarkable shifts in the location of the auricular and also of the ventricular pacemaker, and ventricular combination complexes of various types are illustrated and discussed.

The “latency theory” of heart-block and interpolated ventricular premature beats☆

Abstract Experimental evidence has been presented which shows that the fundamental postulates of the “latency theory” of partial heart-block are not valid for conduction in the turtle heart. From an examination of interpolated ventricular premature beats it is concluded that the observed phenomena do not compel us to accept that theory for the human heart.

A case of dextrocardia with right (functional left) ventricular predominance, ventricular ectopic beats, and retrograde conduction

Abstract This paper presents an electrocardiographic study of a case of dextrocardia which is unusual in two respects. (1) The electrical axis during the time of inscription of the chief ventricular deflections lies at approximately −100° instead of the usual +105°. This indicates pronounced predominance of the functional left (systemic) ventricle. (2) Ventricular ectopic beats appear. Occasional premature ventricular impulses are transmitted in a retrograde direction to the auricles.

Interference Dissociation in Contrast to Reciprocating Rhythm.

There is apparently no certain way of distinguishing between interference dissociation and reciprocating beats in the individual case, barring some accidental irregularity which affords a certain clue. There are, however, 2 criteria which serve to differentiate the conditions, (1) auricular regularity or irregularity and (2) P wave direction. If P waves are clearly upright in leads I and II or I, II, and III, it becomes certain that one is dealing with interference and not with reciprocation. If the auricles are regular, as is true in one of our cases, then the mechanism is in all probability interference. It would be a rare coincidence which would make the progressive prolongation of retrograde conduction time such as to make the auricle regular; reciprocation therefore practically always presents an irregular contra-directional auricular activity. Electrocardiograms are presented to call attention to the electrocardiographic differential diagnosis between “Interferenz Dissoziation” (Mobitz 1 ) or Dissociation with Interference (Wenckebach and Winterberg 2 ) and the entirely different mechanism of reciprocating beats for which it may be mistaken. The tracings show some conduction defect also, but this is not at all related to the unusual mechanism of interference which does not require the presence of defective conduction for its inception. Interference dissociation will necessarily appear when there is free A-V conduction, complete V-A block, and an auricular rhythm which is slower than the ventricular. Under these conditions, those auricular impulses which follow the idioventricular beats by a great enough interval will reach the ventricle, since they encounter no absolutely refractory muscle in the conducting path. The ventricular beats they arouse will be premature. In our cases, as in the great majority of reported examples, the idioventricular pacemaker is supraventricular, i. e., in the His bundle or A-V node.

Electrographic Studies of Conductivity in Cardiac Muscle.

This abstract presents the results of studies with the string galvanometer which confirm and extend previous observations 1 upon the recovery of conductivity, and the effect of the blocked impulse upon subsequent conduction in the quiescent, excised, atropinized turtle heart. The previous work was with the kymograph. The observations were incidental to experiments directed toward other ends. They are based upon studies of approximately 30 turtle hearts, from some 15 of which simultaneous myograms and electrograms were obtained. These demonstrate that although the electrical and mechanical conduction intervals may not appear identical, the curves illustrating the recovery of conductivity are parallel. The electrical are more accurate than the mechanical. The results fall into three divisions. (1) Curves illustrating the recovery of conductivity between auricle and ventricle, with and without compression at the A-V groove. These are similar to those already published, 1 excepting that in some the deviation of the individual points from a smooth curve is less pronounced. They demonstrate that not only are conduction times for all rest intervals increased by compression, but also that the curve returns much less promptly to a resting level. A recovery curve for the human heart was reported by Ashman and Herrmann. 2 (2) Confirmation of the fact that a very premature blocked impulse may have no detectable influence upon the conduction time of a subsequent impulse; that a slightly later blocked impdse has a moderate effect; and that an impulse arriving at the compressed muscle so late as to just fail of transmission to the ventricle, has, on the average, 65 per cent as great an effect as a transmitted impulse. These results are identical with those previously reported. A similar phenomenon has been reported by Lewis and Master3 for the mammalian heart.

Duration of Electrogram and of Mechanical Response of Turtle Ventricle.

The effect of varying rates and volumes upon the duration of the phases of the isometric contractions of the ventricle has frequently been investigated. The influence of these factors upon the duration of the electrogram, and particularly the correlation of mechanical and electrical changes, have not been so fully determined. It is with this correlation, and with certain effects of fatigue, that this abstract deals. The excised turtle ventricle was perfused with slightly alkaline (pH 7.5—7.8), well-oxygenated and strongly buffered Ringers solution. During temporary suspension of perfusion, the isometric responses to single induction shocks at varying rates were recorded. Both mechanical and electrical responses were simultaneously photographed on the electro-cardiographic film. As illustrated in figure 1, the total duration of the electrical response (measured from the apex of the R-wave to the end of the T) and the duration of the phases of rising and falling tension within the ventricle are similarly influenced by changes in cycle length (rate). In contrast are the effects of filling (fiber length) upon the durations of the electrical and mechanical responses. Contrary to previous report (turtle), 1 we find that increased filling, up to the limits of ventricular capacity, prolong the electrical response only very slightly or not at all.∗ The phases of rising and falling tension, on the other hand, increase with augmented filling (figure 2).

Evidence Against the “Latency Theory” of Partial A-V Block.

There are two fundamentally opposing explanations of the characteristic groupings of beats separated by a pause when occasionally the ventricle fails to follow the auricle in low grade heart block (Wenckebachs periods). The “latency theory”, Mobitz, 1 holds that the velocity of conduction through the muscular elements is invariable with constant auricular rate, and that the gradual prolongation of A-V interval following the pause in partial block is due to the arrival of the sinus impulse at the A-V junction at progressively earlier times during the recovery in the excitability on the ventricular side of the junction. Thus the impulse is regarded as arriving at the junction, pausing a moment, and then going forward. The duration of the pause is supposed to depend upon the excitability of the tissue immediately beyond the boundary plane. That such a conception is inadequate is regarded as certain by some, and yet it is difficult to secure direct evidence against it. The first evidence herein outlined is obtained from excised turtle hearts, rendered quiescent by removal of the sinus and driven at varying rates by break induction shocks applied to an auricle. In one experiment, after a 10 second rest, the auricle was twice stimulated, the interval between auricular responses measuring 3.026 seconds. The first A-V conduction time was 0.526 second; the second, 0.538. A 3 second rest was, therefore, almost sufficient for complete recovery of conductivity. In a second test after a 10 second rest the interval between the 2 transmitted auricular impulses was again practically 3 seconds, hut an auricular response which was not transmitted to the ventricle was interpolated between the two, 1.156 second before the following transmitted auricular response. Although the ventricle did not respond to the interpolated impulse, the conduction time for the next impulse increased from the expected 0.540 second to 0.652 second.