Treatment of Disturbances of the Rhythm of Cardiac Activity

In the reanimation department of the Hospital, and in the Mobile Reanimation Centre, which are the clinical base of the Laboratory of the Experimental Physiology of Reani­mation of the Organism of the Academy of Medical Scien­ces, much attention is paid to study of the pathogenesis and spe­cific treatment of disturbances of cardiac rhythm, as well as to the treatment of terminal states due to traumatic shock, loss of blood or respiratory insufficiency of various aetiology. 

As we know various forms of disturbance of the rhythm of car­diac activity, causing disorders of haemodynamics, can lead to the development of a terminal state including cardiac arrest. ‘In fact’, wrote Lang, ‘death as a result of cardiac insufficiency due to a prolonged attack of paroxysmal tachycardia is still not a rare occurrence.’ The most dangerous forms of arrhythmia, of course, are those leading to an immediate fatal outcome, namely ventricular fibrillation and asystolia. In that connection study of their pathogenesis and search for the most effective therapeutic measures permitting normalization of cardiac rhythm are some of the most important problems of reanimatology in recent years.

The most effective therapeutic measure when paroxysmal tachy­cardia of the ventricles develops has proved, as with ventricular fibrillation, to be that of defibrillation of the heart by means of a condenser discharge.

The possibility of treating certain forms of chronic disorders of cardiac rhythm by means of electric impulse therapy was first posed by Zuckerman and Gurvich. A year later Lown eliminated an attack of paroxysmal tachycardia in a patient by means of the electric impulse method. This highly effective method is now being em­ployed more and more widely in medical practice, and is being used not only to treat terminal or preterminal states, but also in the normal conditions of surgical and therapeutic practice.

From the great experience now accumulated of treating ventri­cular paroxysmal tachycardia and fibrillating auricular arrhyth­mia, there is every reason to believe that electric impulse therapy is not only more effective than medication, but also safer. Accord­ing to Lukosewicute’s findings, positive results were ob­tained in 100 per cent of cases of treating various forms of paro­xysmal tachycardia; in cases of fibrillation and palpitation of the auricles, the number varied between 85.7 and 88.2 per cent. Rather different but also very hopeful results have also been reported of the treatment of patients suffering from these disturbances of car­diac rhythm. Normalization has been reported for 89.1 per cent of cases of paroxysmal tachycardia and 94 per cent of those suffering from fibrillation and palpitation of the auricles, Other authors report approximately the same results.

The number of complications developing due to the effect of an electrical impulse on the heart, generated by Gurvich’s defibrillator system, is comparatively low. The most im­portant are the so-called postinversional disturbances (ventricular fibrillation, extrasystolia, ventricular tachysystolia, etc.) and ‘nor­malization’ embolisms. The last occur comparatively rarely (in less than 1.5 per cent of all cases of auricular fibrillation or pal­pitation, in which sinusal rhythm has been restored). The trans­formation of rhythm after electric impulse therapy apparently depends on the gravity of the principal pathological process. An important role in this respect is played by hypoxia of the myocardium, arising as a result of the impairment of co­ronary and peripheral circulation, and also prior administration of cardiac glycosides and of anti-arrhythmic drugs.

Interesting results are obtained if we compare the findings of the clinical observations of the Laboratory’s workers in conditions of emergency reanimation with those obtained by authors employing the given method in the planned treatment of therapeu­tic patients. When the electric impulse method was used to eli­minate fibrillation, arrhythmia or attacks of paroxysmal tachycar­dia, ventricular fibrillation occurred in 6.2 per cent of all the cases so treated. In planned treatment this dangerous complication developed much less often, in approximately 0.5 per cent of cases.

The more frequent development of fibrillation when electric impulse therapy is used in reanimation practice may be due to its being used in emergency conditions to treat patients who had previously been receiving regular treat­ment with cardiac glycosides and anti-arrhythmic drugs. The cli­nical research carried out in our Laboratory indicates that the more serious the patient’s condition the more justified are the in­dications for employing the electric impulse method. From our point of view this approach to the problem is the most rational.

In analysing our own clinical material and comparing it with the literature, we discovered that the effect of anti-arrhythmic drugs or of an electric impulse on the heart in the great majority of cases can be assessed as ‘all or nothing’, as was shown by the fact that there are three variants of the outcome of anti-arrhythmic treatment: (a) restoration of the function of the sinusal node; (b) transformation of one form of pathologic rhythm into another; (c) maintenance of the original form of pathologic rhythm.

It was also established that patients can sometimes develop tachycardia with an extremely high rate of cardiac contraction — 180 to 240 per minute. This was initially classified as ‘paroxysmal’ in accordance with the accepted view and attempts were made, without success, to eliminate it by means of electric impulse therapy. Contrary to our expectations, instead of eliminating the attack, it sometimes even increased the fre­quency of the rhythm slightly. And it was very characteristic that the administration of anti-arrhythmic drugs also had a partial effect, expressed in a slight decrease in the number of cardiac contractions.

Clinical observations thus served as the basis for differentiating several forms of tachycardia that had been grouped together by the formal sign of high frequency of rhythm. The true paroxysm of tachycardia is a kind of reaction of the heart to the action of the threshold electric impulse, following the law of ‘all or nothing’. As to the other type, its most typical feature is a gradual increase and a just as gradual decrease in rhythm, and an absence of therapeutic effect when the electric impulse method or certain pharmaceutical agents are employed, which allows us to suppose that there are different mechanisms governing the deve­lopment of these forms of allorrhythmia.

There is still an opinion, according to the literature, that an attack of paroxysmal tachycardia is linked with activation of one of the heterotopic centres of automaticity. At the same time, a number of findings that contradict this conception have accumulated in recent years. With such an explanation of ‘cardiac racing’, it is difficult, in par­ticular, to explain the possibility of suppressing the tachycardia by the action of a single electric impulse. The experimental find­ings indicate that a defibrillating current has a stimulant effect, incompatible with the idea of depressing a func­tioning heterotopic focus. It is also not clear why the condenser discharge, which has such an active effect on the ectopic centre, has no noticeable influence on the activity of the sinusal node, although the nature of spontaneous depolarization of the various sectors of the conductive system is in principle the same.

The clinical findings obtained served as the basis to explain the pathogenesis of paroxysmal tachycardia in the light of the theory of circular circulation of stimulation. Cessation of an attack of tachycardia corresponds to the idea that it is underlain by para­biotic inhibition developing in various sectors of the cardiac con­ductive system because of too rapid a rhythm of stimulation (exo­genous or generated by the heart itself).

At the moment the blocked sectors are stimulated, all other musculature can leave the re­fractory phase, and then the sectors that were last to be stimu­lated become similar to heterotopic centres of automaticity, i.e. they themselves become centres of new stimulation. The idea that such a mechanism might exist was first advanced by Wenckebach in connection with reverse extrasystoles. The essential diffe­rence between paroxysmal tachycardia and ventricular fibrillation apparently is that the latter involves the presence of many blocked sectors of the conductive system, whereas in the former it must be supposed that only one such sector exists. Its location is what determines the pattern of the ECG and the clinical features of the attack.

A predisposing moment in the development of an attack of tachycardia, as we know, is local ischaemia or some other cause (e.g. infection) that reduces the lability of the tissues of this sector, in other words, its ability to assimilate a sufficiently high rhythm of stimulation. In such conditions a quickening of sinusal automaticity or a casual extrasystole can lead to blocking of the stimulant wave in some link of the conductive system and thus a sector of the myocardium remaining unstimulated. From then on realization of the mechanism of ‘return’ stimulation described de­pends on one condition: the stimulation must overcome the zone of the blockade only when the main mass of the myocardium leaves the refractory state. Then the sector last stimulated be­comes the source of an impulse that spreads rapidly along the main paths of the conductive system.

The stability of the cycle of alternating stimulation of the in­dividual sectors of the myocardium depends on the length of the delay of the stimulant wave in the zone of functional block. A slight shift is apparently sufficient to disturb the strict temporal relations and end the attack of paroxysmal tachycardia, which can be effected by any factor that changes the conditions of conduction in the zone of the block (neuroreflex influences, drugs, etc.).

On the basis of the above, suppression of an attack of tachycardia as the result of a single electric stimulus would be explained as fol­lows: a strong impulse, in all probability, can cause simultaneous stimulation of the whole heart, followed by a general pause. It can be supposed that the disturbed conduction is restored during this pause and the next impulse from the sinusal node leads to restoring normal contractions of the heart. With such a concep­tion of the arrhythmic effect of the impulse, it becomes obvious that it can only develop if there is circular circulation of the sti­mulus. But if the tachycardia is due to the action of a nomotopic or heterotopic focus of automaticity a condenser discharge will have no effect.

Our own clinical observations and the findings of other authors allow us to conclude that contraindications for the application of the electric impulse method have not yet been established in practice. When treating patients in terminal states one cannot consider such things as the relative ease of eli­minating disturbances of cardiac rhythm by medicaments, or the shortness of the attack, etc. This becomes particularly clear when treating myocardial infarction, complicated by cardiogenic shock. Preliminary attempts to administer anti-arrhythmic agents usually only lead to irre­versible waste of time and increase the danger of ventricular fibrillation developing.

The application of electric impulse therapy can sometimes be hampered by the need for intervention on a background of general anaesthesia, especially in cases of severe disorders of haemodynamics and respiration. This has made it urgent to search for a method of anaesthesia optimal in regard to the character and fea­tures of its action on the organism (passage of a strong impulse through the thoracic cage) and to the specific nature of the patho­logical process.

The analysis of clinical observations indicated that the applica­tion of electric anaesthesia in disturbances of cardiac rhythm in patients in terminal states is the method of choice. It enables the time needed to prepare the patient for the session of cardioversion to be reduced. An essential advantage of this form of anaesthesia is (a) its short duration (under five seconds) and (b) that it has no noticeable effect on respiratory and circulatory functions. Pa­tients regain consciousness immediately after its cessation; many notice sensations of one sort or another of an unpainful character that accompany the action of interferential currents. The absence of complications, the simplicity of the method, and the portability of the apparatus allow use of the technique of brief electric anaesthesia to be re­commended for patients of the most serious category, and for emergency services.