CARDIOSTIMULATION (grech, kardia heart + lat. stimulatio motivation; synonym electrostimulation of heart) — a method of treatment of disturbances of a cordial rhythm by impact on a myocardium of ventricles electric impulses of a certain power and frequency.
according to Chardak (W. L. Chardack, 1972), the first attempts to influence electric impulses on cordial activity were made in 18 century. In 1932 Mr. A. S. Hyman created the first device for To. with a hand gear and electrodes — «pacemaker». In 1952 Mr. Zoll (R. M. of Zoll) applied in clinic with the resuscitation purpose K. outside electrodes for increase at a sick rhythm of cordial reductions.
Further development To. received as a method of treatment of a full cross heart block (see. Heart block ). An opportunity by means of electropulse devices to impose an artificial rhythm of reductions to ventricles of heart was estimated at once by clinical physicians and accepted as the only method of treatment of similar patients.
From the beginning of development of surgery on open heart the idea of creation of the implanted artificial pacemaker appeared. By 1959 the first devices — electrocardiostimulators (EX-) for implantation [W. W. Glenn et al., were created 1959; L. D. Abrams et al., 1960]. In the USSR in 1962 the group of engineers and doctors designed intrakorporalny stimulator EKS-2 («Mosquito»).
Impulses from EX-are brought to heart by means of special conductors — electrodes which have a current-carrying metal part and the isolating outside cover. On one end of an electrode there is an electric socket for connection with EX-, on another — a contact head for connection with the fabric which is subject to stimulation.
In addition to EX-with constant power supplies, there were models of devices with other systems of power supply providing rather long period of their functioning. E.g., implantation in a body of the sick radio-receiving device with electrodes was made, and the sending device with the block of batteries was located ekstrakorporalno. Impulses from the sending device were caught by the block implanted to the patient and through electrodes excited heart.
By the principle of inductive communication of two coils, one of which with electrodes was implanted to the patient, and another was imposed over the first on skin, other device was created. At the same time impulses were generated EX-and transferred to the outside coil on inductive communication, directed in the implanted device and transferred to heart. Both methods did not find broad application as did not provide steady
K. V to the USSR implantation of the first artificial pacemaker to the patient with a full cross heart block V. S. Savelyev y made 1962. The significant contribution to development and deployment of this method to a wedge, practice were brought by the Soviet scientists E. B. Babsky, Yu. Yu. B redikis, V. E. Belgov, etc.
In the USSR the whole network kardiol is created. the centers which are actively dealing with problems K.
According to Yu. Yu. Bredikis (1972), growth of implantation EX-reaches in Sweden up to 100 primary implantations a year on 1 million inhabitants, in Germany — 50, in Denmark and Norway — 45, in Finland — 21. On the statistical researches conducted in ChSSR, on 1 million population a year 60 — 80 implantations EX-are required.
Essence of a method K. consists in irritation of a muscle of heart impulses of electric current of the set power and frequency which, depending on a phase of a cardial cycle, it answers with systolic reduction of ventricles.
On to lay down. to influence To. it can be directed both to increase, and to an urezheniye of a rhythm of cordial reductions, and also to potentiation of ineffective reductions of a myocardium at different types of disturbance of cordial activity.
Depending on a way of contact of the tail of an electrode with heart distinguish endocardial and myocardial stimulation.
EX-represents the device having the power supply and the functioning electronic circuit, at the exit a cut electric impulses of constant frequency and the set parameters are generated. Reliability To. depends on amplitude of the stimulating impulse. For steady and effective To. it shall exceed the threshold size of irritation of a muscle of heart by 2 — 3 times, then the muscle will answer each new impulse with reduction. Preston (G. of A. Preston, 1966), Sauton (E. Sowton, 1970) was established that the smaller ratio can lead to disturbance of stimulation. Researches showed that the threshold of stimulation of a myocardium (the smallest size of amplitude of an electric impulse capable to bring a muscle of heart into excitement) is individual for each patient. It depends on degree of a hypoxia of a myocardium, water and electrolytic balance, acid-base equilibrium and other reasons.
A threshold of stimulation of a myocardium depending on a method K. can fluctuate from 1 — 2 mV up to 9 century. In the domestic device EKS-2 the impulse of 6 century is used.
The essential characteristic of an impulse — its duration, edges considerably defines amount of the energy sent to heart. In the majority of types in lots produced the EX-duration of an impulse — 0,5 — 8 ms. As showed Larsson (F. Larsson, 1969) and A.S. Rovnov et al. (1972), the frequency of stimulation is within 60 — 80 impulses in 1 min. at limited physical. loads of the patient provides quite satisfactory blood circulation.
Depending on appointment and design features EX-are subdivided into two main types: 1) extracorporal (outside); 2) intrakorporalny, intended for implantation in a human body.
Extracorporal EX-can be stationary, receiving food from electric network, and the portable (fig. 1) having autonomous system of power supply from various batteries, accumulators. Extracorporal EX-allow to change over a wide range the power and frequency of an impulse and therefore can be used for all types of stimulation, including and through skin.
Intrakorporalny EX-are completely independent devices; they are bottletight in a metal casing or are filled in with epoxy. As system of their power supply usually use the mercury-zinc batteries ensuring continuous functioning within 3 — 3,5 years. In the figure 2 the Soviet implanted pacemaker EKS-2 with two myocardial electrodes (weight of 125 g) is presented. In the USSR pacemaker EKS-4 with the extended endurance — to 5 years is created. In the USA Wilson — Gretbach LTD manufactured the battery for EX-on a lity, during the use a cut a number of firms («Robert and Karyer», Medtronik, Biotronik, Kordis) created 10 years, EX-with a warranty period of work.
A new step in a solution of the problem of power supply EX-was creation of radio isotope batteries. Over 3000 patients in the world use EX-with the radio isotope power supply only of Medtronik.
The All-Russian Research Institute of clinical and experimental surgery of M3 of the USSR together with other research institutes is developed the first domestic implanted pacemaker on isotope ( 238 Pu) the REKS-A1 power supply with the term of functioning not less than 10 years. In March, 1975 B. V. Petrovsky implanted the first domestic pacemaker with the radio isotope power supply.
A wedge, experience of use To. revealed danger of emergence of the competing rhythm — an artificial parasystole (see. Premature ventricular contraction ) at patients with the incomplete alternating form of an atrioventricular block. It caused the necessity of development as EX-from a constant, not changing frequency of an impulsation — asynchronous EX-, and the devices capable to detain the electric impulses following one after another depending on a condition of spontaneous activity of ventricles of heart — synchronous EX-.
Example of a domestic fixed rate pulse generator is EKS-2. Modern electronics allowed to create synchronous EX-, received the name «demand-stimulator» (to demand from the English word demand, the requirement). The principle of the scheme EX-provides introduction in it of the device which is slowing down carrying out an impulse at emergence of the heart following a tooth P reductions of ventricles in connection with recovery of normal conductivity of an impulse on an atrioventricular node of Ashoff — Tavara (fig. 3). At disappearance of own reductions of heart the impulsation of a demand-stimulator again automatically joins.
Also the stimulator giving impulses synchronously with the ECG QRS complex of the appearing spontaneous reductions of ventricles is created. EX-catches the appearing reduction of ventricles (QRS) and gives the stimulating impulse in a phase of the refractory period that does not cause an additional ventricular systole. At disappearance of the QRS complex or urezheniya it below a certain frequency limit the stimulator begins to work in the asynchronous mode with a frequency established in it.
Between a demand-stimulator and a S-synchronous stimulator there is an essential difference in profitability of an expenditure of energy. If in the last useless wasting of energy for the stimulating impulse moving in a refractory phase at spontaneous activity of ventricles is observed, then in a demandstimulyator at the same spontaneous activity of ventricles energy is spent only for work of schemes of strengthening and braking of delivery of an impulse, i.e. its expense is much less.
Achievement of modern electronics was creation R-synchronous EX-which allowed to recover most physiologically and effectively lost function of the carrying-out system of heart. During the use of this EX-the additional electrode for registration of its potential is hemmed to an auricle. The signal from an auricle is given in the amplifier of the device, and then with a delay in 0,10 — 0,16 sec. (fiziol, the period of passing of a signal from a sinus node to ventricles) the stimulating impulse is given for ventricles of heart. Increase of atrial reductions leads to increase in number of the stimulating impulses and according to ventricular systoles. Thus, function of the carrying-out system of heart is completely modelled. At increase of number of atrial reductions more than 150 in 1 min. the stimulator automatically stops increasing the frequency of the stimulating impulses, remaining at this level, and at emergence of blinking or an atrial flutter passes into the mode of demand-stimulation with a frequency of 60 — 80 impulses of 1 min.
The EX-types (demand-stimulator, QRS-and P-synchronous stimulators) described above received the name of the biomanaged pacemakers. Their implantation is possible at all types of cross heart blocks, but special need for them arises at intermittent forms of cross blockade (fig. 4).
Other burning issue of a constant To. need of increase in term of work of electrodes is. Service life of myocardial electrodes makes from 3 to 7 years, then the break of a current-carrying part or disturbance of isolation with the termination of stimulation is observed. It happens because of difficult conditions in which there are implanted electrodes testing one year prior to 30 million oscillating motions. Most often the break of an electrode is observed at the level of a mezhreberye or at the place of its implementation in a myocardium that it is connected with oscillating motions of heart and edges, and disturbance of isolation comes more often in close proximity to a pacemaker that, apparently, is connected with traumatization during operative measures for the purpose of replacement of a stimulator. Everyone 2 — the 3rd operation for replacement EX-is followed by need of correction of an integrity of electrodes. The existing designs EX-share on bielektrodny and monoelectrode. The break of one of them in a zone, unavailable to correction (outside fabrics of a front chest wall) forces to transfer the patient to the mode of monoelectrode stimulation. At availability of the place of break an electrode it is possible to connect and recover the isolating cover. Failure of two conductors dictates at once need of replacement of all stimulating system.
In a little more favorable conditions there is that part of an endocardial electrode, edges is located in a venous bed. However other part it — from the place of an entrance to a vein to the connecting connector with a stimulator — is in the same working conditions, as myocardial electrodes. Therefore these sites of an endocardial electrode for the same reasons as described above can fail.
In this regard the great value gets the choice of materials of which make electrodes. Reliability and duration of a constant To. in huge degree depend on their resistance to long mechanical loadings and electrochemical processes. Search of optimum materials for improvement funkts, characteristics of electrodes is conducted constantly.
Urezhayushchy cardiostimulation. For an urezheniye of a rhythm of cordial reductions at tachyarrhythmias in a wedge, practice influence heart steam rooms and the combined electric impulses. Stimulators for an urezheniye of a rhythm differ from speeding up by the principle of action. All stimulators for urezhayushchy To. are outside. In the USSR it is developed figurative EX-for the speeding-up and pair (urezhayushchy) stimulation, and also in a monitor cardiocomplex — the block for cardiosynchronized urezhayushchy stimulation. Three modes urezhayushchy are provided in the last To. hearts: P, pair, combined with a tooth, and R, pair, combined with a tooth. The mechanism of delay of a cordial rhythm is explained by features of response of a myocardium to the stimulating impulses depending on a phase of a cardial cycle, on to-ruyu these impulses influence. There are periods with the maximum excitability of heart to electric impulses when it answers each of them with systolic reduction, and the periods of his not excitability when the myocardium completely loses ability to answer additional irritation during excitement (systole); this period carries the name of the absolute refractory period. After this excitability of heart begins to be recovered. The period of its recovery is the share of the second knee of a tooth of T and carries the name of a negative refrakternost. The electric impulse lasting 2 — 3 ms operating during this period i.e. right after the period of an absolute refrakternost, causes depolarization of heart without muscular contraction. This results from the fact that the electric potential and excitability of heart after a systole are recovered before readiness of a myocardium for reduction. After depolarization of heart the refractory pause follows, i.e. artificial lengthening of the refractory period turns out.
P, combined with a tooth, on an ECG electric stimulation is that the stimulating impulse moves in a phase of a relative refrakternost after natural reduction of ventricles from an impulse of a sinus node. It causes depolarization of heart with lengthening of the refractory period and therefore the following impulse of a sinus node gets to it and does not cause response of ventricles in the form of systolic reduction. As a result of such influence heart rate decreases twice.
At electric stimulation by pair impulses the first of them causes hemodynamically active reduction, and the second — only depolarization of heart with lengthening of the refractory period. At the same time own rhythm is suppressed and artificial is imposed. Use of pair stimulation allows to urezhat heart rate for 50% as well as during the use of P, combined with a tooth, on an ECG of electric stimulation. On Laytvuda (R. Lightwood, 1966), big degree of an urezheniye can be reached by use of triple electric impulses.
Selection of parameters of impulses is very important for achievement of efficiency of urezhayushchy stimulation: amplitudes, frequencies of following of pair or triple impulses, an optimum interval from a tooth of P (or other signal) to an electric impulse at the combined stimulation or between impulses at pair or triple stimulation.
Stimulation by the pair and combined impulses is carried out more often by an endocardial electrode and the outside special device. EX-for urezhayushchy stimulation considerably differ from the stimulators which are speeding up a cordial rhythm. On the device they are difficult electronic devices which give the chance to give dual impulses lasting 2 — 3 ms with a frequency of repetition of couples up to 150 of 1 min., to change amplitude of impulses ranging from 0 to 10 in and the distance between impulses estimated in ms (to 500).
Urezhayushchy stimulation with good effect is applied at tachycardias after heart operations.
At supraventricular, and sometimes and at ventricular tachycardia, tolerant to action of medicamentous means, with success apply a number of modifications of extracorporal temporary stimulation to stopping of an attack. So-called capture of a rhythm, i.e. imposing to an auricle of an artificial rhythm with a frequency exceeding the frequency of its own geterotopny rhythm concerns to them. In several seconds To. stop, there comes the preautomatic pause, after a cut heart begins to work in a normal rhythm. In other modification the frequency of fascinating stimulation is smoothly reduced, bringing it to size lower, than heart rate at tachycardia, and then stop; at the same time the normal rhythm is usually recovered. At last, the method of the so-called sliding stimulation is developed. Select frequency To., very close to heart rate at tachycardia, but not matching it. As a result the impulse at each reduction of heart as if slides on a cardial cycle, and one of impulses through a nek-swarm time matches passing on a myocardium of an excitation wave and stops its circulation. Applying To. for stopping of ventricular tachycardia, it is necessary to have a defibrillator. Also implanted demand-stimulators based on a method of capture of a rhythm and applied to treatment of patients with a Bouveret's disease are developed. Extracorporal To. superfrequency impulses (400 — 600 in in 1 min.) allows to transfer forms of an atrial flutter, uncontrollable by means of drugs, to a ciliary arrhythmia, drug treatment a cut it is rather well developed.
Carefully it is necessary to apply urezhayushchy stimulation by the patient with the acute myocardial infarction which is followed by tachycardia and a tachyarrhythmia. Stimulation by the pair and combined impulses by the patient with an acute myocardial infarction is still insufficiently studied though this category of patients has a number of cases of its successful use.
Speeding up To. use for treatment sinoaurikulyarny and atrioventricular heart blocks (see), sinus bradycardia (see), disturbances of a rhythm at myocardial infarction (see) and during the intra cardial X-ray contrast researches for management of a cordial rhythm.
Extracorporal To. by means of endocardial electrodes apply in resuscitation practice to potentiation of cordial reductions at different types of disturbance of a rhythm, cordial weakness, at the myocardial infarction proceeding with disturbances of a rhythm and a cross heart block, and also the patient with a cross heart block during preparation for implantation constant EX-.
Extracorporal To. by means of cutaneous electrodes it is shown at resuscitation of the persons which are in unconsciousness.
Asynchronous intrakorporalny To. by means of myocardial or endocardial electrodes apply at total cross block with a syndrome of Morganyi — Adams — Stokes (a stable form); synchronous — at the alternating form of a cross heart block.
Methods of percutaneous and puncture carrying out electrodes for pericardiac and epicardial stimulation of practical application have no since do not provide reliable and long imposing of a rhythm.
Urezhayushchy To. (steam rooms and the combined electric impulses) apply at stable forms Bouveret's disease (see) and takhisistolichesky ciliary arrhythmia (see) with heart rate more than 130 in 1 min., tolerant to action of medicamentous means. At supraventricular Bouveret's diseases (except a ciliary arrhythmia) with success apply frequent short-term electrostimulation of auricles (Yu. Yu. Bredikis, A.S. Dumchyus, 1972, etc.).
Implantation EX-is carried out under inhalation anesthesia (see).
Make left-side for myocardial cardiac activation thoracotomy (see) on the IV—V mezhreberye). Use also extra pleural access to heart through a bed of the resected xiphoidal shoot and transsternal access by a partial lower sternotomy. Apply two electrodes with the tail in the form of a direct string, a needle or a spiral which implement directly in a cardiac muscle by means of a needle conductor to myocardial stimulation and fix P-shaped seams. The free ends of electrodes bring to a front chest wall through a mezhreberye. Under a big pectoral muscle (at women it is possible to use retromammary space) create a bed for the device where place EX-after connection to electrodes. At the same time the artificial rhythm is imposed to ventricles of heart with a frequency, on to-ruyu the implanted device is adjusted. Control of heart rate is made, watching cardiac performance on pulse of the patient, and also by means of a cardioscope.
For endocardial stimulations the electrode of a special design (mono - or bipolar) under control of a X-ray screen televisual apparatus is entered through v. cephalica or one of superficial veins of a neck into a cavity of a right ventricle. The end of an electrode with a contact head is brought to a top in intertrabecular cracks, than fixing it is reached. The electrode can be bipolar when in the tail there are two contact plates connecting to an endocardium, but apply monopolars a ny electrode more often. As the second pole serves the EX-case. Stability of endocardial stimulation in the bipolar and monopolar modes is identical if energy of an impulse exceeds threshold value. However monopolar mode K. demands bigger power consumption in connection with resistance from fabrics along the line of an impulse.
If at use of the mode bipolar To. polarity of stimulation does not matter, in the mode mono polar To. giving of a negative charge on an endocardial electrode is optimum that, according to H. J. Thalen, Yu. Yu. Bredikis (1968, 1970), provides steady To. at lower energy of an impulse.
Endocardial stimulation has a number of essential advantages before myocardial. The most important of them — an opportunity to avoid a thoracotomy, to-ruyu patients of old age hard transfer. In some cases operation with use of endocardial stimulation can be carried out under local anesthesia. Besides, an impression is made that the endocardial electrodes made of the same materials as myocardial, are capable to function more long time that depends on more favorable conditions for their functioning in a human body. And, at last, use of an endocardial electrode made possible carrying out effective and reliable temporary outside To. At the same time the endocardial electrode is entered by a puncture method into a subclavial vein or a vein of an elbow bend and advanced in a cavity of a right ventricle; the distal end of an electrode is connected to EX-. During the use for this purpose of a monopolar electrode the second pole EX-is connected through a simple adapter to a syringe needle, to-ruyu entered subcutaneously on an outer surface of the left shoulder where it is during all cardiostimulation, being the second electrode.
Control of cardiostimulation
is applied To control of work of the implanted pacemaker and forecasting of the period of its functioning a complex of special methods of a research. One of the most available methods — electrocardiographic. On an ECG perpendicular to the isoline impulses are registered, for to-rymi response of ventricles in the form of the electrocardiographic representation of systolic reduction follows. According to teeth of R on an ECG blows of pulse wave on a beam artery are palpated.
Very informative control method of function of a pacemaker is the method of the analysis of its impulses registered from a body surface of the patient. The analysis of impulses and comparison of their parameters with data of the previous inspections allow not only to estimate function of a pacemaker, but also to predict it for some period.
There is also a method of topical diagnosis of an arrangement of poles of a dipole of the implanted pacemaker. By means of graphic registration of potentials of the impulses defined from a body surface of the patient apply the equipotential lines which are located tsirkulyarno around dipoles of a pacemaker on a traffic. It allows to define an arrangement of poles of a dipole in the presence of the functioning system of cardiostimulation. Poles of a dipole are localized in places of contact of electrodes with fabric. During the carrying out bipolar myocardial stimulation both poles of a dipole are at insignificant distance from each other and are projected on a top of heart. At monopolar endocardial stimulation one of poles of a dipole is projected in the field of a right ventricle of heart, another — in the place of implantation of a pacemaker, the case to-rogo is the second pole.
At emergence of defect of the conductor there is a redistribution of electric field caused by short circuit of a point of defect of the conductor on an intercellular lymph, and formation of a new electric chain that leads to emergence in this point of one of poles of a dipole.
The method of topical diagnosis of an arrangement of poles of a dipole of the implanted pacemaker allows to diagnose gaps and insignificant defects of isolation of the conductor which cannot be diagnosed by other methods.
Complications can be connected as with an operative measure, and technical defects in the most EX-and electrodes. At suppuration in a bed implanted EX-it is necessary to remove all stimulating system, to carry out sanitation of a purulent cavity and to repeatedly implant the EX-new system. All the time of treatment of a purulent wound of the patient is on temporary endocardial stimulation outside EX-. At disturbance of an integrity of one sh myocardial electrodes in the place, unavailable to recovery (a chest cavity, a mezhreberye) transfer of the patient in the mono-electrode mode of stimulation is shown. For this purpose the broken electrode is unscrewed from the EX-terminal and screw a metal cap on the released terminal, the Crimea connects current-carrying contact with the EX-case. Thus, the case of a stimulator becomes the second pole of the stimulating system.
Technical failure in the implanted pacemaker or premature exhaustion of power food leads to the termination of stimulation and demands repeated operation with the purpose of replacement it. Operation is not difficult, but demands big skill and care in the address with electrodes at their allocation from cicatricial unions since the isolating cover of electrodes after stay in a human body becomes extremely fragile and is easily damaged. Except danger of damage of an electrode, repeated operations lead to the increased danger of development of suppurative processes.
At introduction of an endocardial electrode to a right ventricle perforation of its wall is possible. In these cases the tip of an electrode which is going beyond a cordial shadow radiological is defined; the artificial rhythm unstable and often is not imposed. The emergency thoracotomy is necessary for sewing up perforative openings before development a wedge, pictures of a cardiac tamponade.
After introduction and fixing of an endocardial electrode to a wall of a right ventricle its dislocation can be observed. At the same time the end of an electrode is thrown out output department of a right ventricle or an auricle, is more rare in the lower vena cava, and stimulation stops. Recovery of adequate stimulation requires a repeated operative measure.
To a wedge, to complications postoperative increase in a threshold of stimulation of a myocardium can be referred, a cut can arise on 2 — 3rd week of stimulation and depends on loss of fibrin and the organization of fibrous fabric on site of contact of an electrode with a muscle of heart. In this case To. it can be broken partially or completely. According to Sauton (1971), this complication causes 7% of failures at use of standard pacemakers. In such cases for recovery adequate To. implantation of the device with the increased parameters of stimulation is required.
At use of fixed rate pulse generators emergence of the competing rhythms with the subsequent threat of development of fibrillation of ventricles in patients with an incomplete form of a cross heart block is possible. It results from imposing at each other of the rhythms caused by a pacemaker and those separate impulses of a sinus node which pass through the blocked site of the carrying-out system. As a result the muscle of heart answers with systolic reductions each of these impulses. At the same time the frequency of reductions increases, the rhythm becomes wrong, initial points of excitement have various localization, systoles follow one by one with the minimum refractory period. As a result the cavity of a ventricle does not manage to be filled with blood, reductions of a muscle become ineffective, cordial emission falls, the hypoxia of a myocardium and the increased his excitability to electric impulses, and then fibrillation of ventricles develops. At emergence of the first signs of a similar complication transfer of the patient into stimulation is shown by the biomanaged pacemakers.
To. it is more and more widely applied not only to treatment of patients with disturbances of a rhythm and conductivity of heart, but also to diagnosis of these disturbances, to establishment topics of anomaly of conduction paths in a myocardium (see. Electrophysiologic research of heart ) and purposeful selection of pharmaceuticals by the patient with various arrhythmias.
Bibliography: Bredikis Yu. Yu. Electric cardiac activation in clinical practice, M., 1967, bibliogr.; it, Electric cardiac activation at tachycardias and tachyarrhythmias, M., 1976; Pipiya V. I. and Tedeev A. A. Some disturbances of a heart rhythm at asynchronous electrocardiostimulation and bioup-ravlyaemy stimulation, Tbilisi, 1977; Savchuk B. D., Kostenko I. G. and Oparin V. S. The complications arising at surgical treatment of a cross heart block, Grudn. hir., No. 5, page 34, 1970, bibliogr.; Gibbon’s surgery of the chest, ed. by D. C. Sabis-ton a. F. C. Spencer, Philadelphia, 1976.
H. H. Malinovsky.