TACHYCARDIA

From Big Medical Encyclopedia

TACHYCARDIA (Greek tachys bystry, fast + kardia heart) — increase in frequency of cordial sokrarashcheniye (for children 7 years and for adults at rest over 90 blows 1 minute are more senior). T. at children is defined with age norm of cordial reductions: at newborns is normal — 120 — 140 in 1 min., by 5 — 6 years decreases to 90 blows in 1 min.

Distinguish T. physiological and pathological. Under physiological T. understand increase in heart rate under the influence of nek-ry influences at absence patol. changes of cardiovascular system. A source of a heart rhythm at physiological T. always the sinus and atrial node is. Physiological T. arises at an exercise stress, emotional pressure (nervousness, anger, fear), under the influence of various environmental factors (high temperature of air, a hypoxia), upon sharp transition to vertical position — orthostatic T. (see. Orthostatic changes of blood circulation), a deep breath — a so-called reflex of Goering — Breyer (see Breath), after reception of excessive amount of food, exciting drinks. The T belongs to physiological. as a result of effect of nek-ry medicines (group of atropine, sympathomimetics, corticosteroids, «arteriolar vazodilatator, etc.).

Reason of pathological T. there can be noncardiac diseases and various defeats of cardiovascular system. T. at noncardiac pathology has nomotopny character more often (sinus T.), and at heart diseases of T. quite often happens ge-terotopny — supraventricular (atrial and atrioventricular) or ventricular (see. Arrhythmias of heart , Bouveret's disease ). So, at fervescence on 1 ° heart rate increases by 6 — 8 blows in 1 min. (Libermeyster's law). Changes of heart rate at flu, a typhoid, tubercular meningitis and a number of nervous and mental diseases (so-called relative bradycardia) do not submit to this law. Pathological T. can be a consequence of reflex influences (at damage of bronchial tubes, skin, peritoneums, mucous membranes), a thyrotoxicosis, acute blood loss, anemia, bad painful attacks (e.g., renal colic), neurosises, organic lesions of subcrustal structures and diencephalic area, irritation of a sympathetic nervous trunk (an infection, a tumor), affective psychoses. Most often pathological T. arises at various defeats of cardiovascular system (rheumatism, myocardites, heart diseases, a myocardial infarction, a cardiosclerosis, a pulmonary heart, a circulatory unefficiency of various etiology). As pathological consider also T. at an exercise stress if heart rate is higher taken for norm at this loading (it is observed, e.g., at latent heart failure).

Both physiological, and pathological T. can be a constant (at chronic anemias, alcoholism, a thyrotoxicosis, a circulatory unefficiency, occasionally at inborn features of a sinus and atrial node) and pristupoobrazny, arising on a miscellaneous, often long, time (at an exercise stress, emotions, hypertensive crises, a pheochromocytoma, etc.). A special form is the Bouveret's disease.

Nomotopny (sinus) T. often meets at various noncardiac pathology: at neurosises as manifestation of frustration of century of N of page, at defeat of subcrustal nodes inf. process, defeat of diencephalic area, increase in level of hormone of a thyroid gland (thyrotoxicosis), hyperthermia, irritation of a sympathetic nervous trunk some patol. process (tumor, lymphoma). Quite often sinus T. it is observed also at cardial pathology. It usually is one of mechanisms of compensation at a circulatory unefficiency of various etiology, but maybe display of intoxication of a myocardium at infections (myocardites, a subacute septic endocarditis, overdose of cardiac glycosides).

Geterotopny T. in most cases — manifestation of organic lesions of a myocardium, but can be caused also by various infections and intoxications, including overdose of cardiac glycosides.

To emergence of T. conducts one of two main electrophysiologic mechanisms — increase in automatism and a repeated entrance of excitement (the re-entry mechanism, cm. Bouveret's disease).

Understand increase in speed of development of slow diastolic depolarization in cells of a sinus node as increase in automatism and more bystry achievement of threshold size by it, necessary for emergence of the extending excitement in heart.

The ectopic center where impulses are generated, is created under the influence of various factors (an inflammation, change of pH of electrolytes, a hypoxia, nervous influences). Frequency of these impulses usually considerably high frequencies of impulses, coming from sinus node. As a result the ectopic center becomes a pacemaker. This mechanism is observed at hetero-topnoy T. — not Bouveret's disease (atrial and nodal), slow ventricular tachycardia (the accelerated idioventricular rhythm).

Heart (see) possesses perfect systems of self-regulation. However any of the parties of its activity is not free from the regulating influence of a nervous system. Humoral influences are closely connected with nervous influences. In a pathogeny of sinus T. neyrogumoral-ny mechanisms have the leading value. Increase in a tone of a sympathetic nervous system causes increase in products of catecholamines and influence of a vagus nerve weakens urezhayushchy a cordial rhythm. It leads to increase in heart rate. Increase of a cordial rhythm reduces duration of a diastole and reduces the volume of the blood which is returned to a left ventricle from an aorta at aortal insufficiency. Narrowing of the left venous opening and a spasm of the smallest branchings of a pulmonary artery limit a stroke output of a left ventricle. For maintenance of the minute volume of blood, necessary for life, the number of cordial reductions increases. Most brightly it comes to light at an exercise stress at patients with a mitral stenosis. To development of T. also build-up of pressure in the right auricle promotes (Bainbridge reflex). T. at patients with a thyrotoxicosis it is considerably connected with the increase in a tone of sympathoadrenal system developing at this disease what favorable action of beta-blockers testifies to. At anemias of various etiology of T., increasing the minute volume of blood, compensates decrease in its oxygen capacity. Decrease in the ABP (orthostatic hypotension, shock) causes T. as a result of irritation of baroreceptors of an aortic arch (a kardiovazalny reflex). The mechanism T is similar. at dehydration and blood loss. Kardiovazalny reflexes are combined with cardio-cardial, making the regulatory mechanism of maintenance of the ABP level, necessary for life, and minute volume of blood. Build-up of pressure in the right auricle (an exercise stress, heart failure) is caused by irritation of the baroreceptors located in the mouth of pulmonary veins (Bainbridge reflex) that leads to emergence of T. At increase in filling of auricles there is fuller and accelerated relaxation of a myocardium of ventricles. Ventricles according to the law of Starlinga (see Starlinga the law) begin to work in other mode, to-ry promotes unloading of auricles.

At physical activity mobilization of cordial activity considerably is the reflex act on impulses from receptors of muscles, irritants are the chemical agents released from muscle fibers at their reduction. However T. comes very quickly, in several seconds after the beginning of work when the level of chemical agents differs from the level of rest few. This increase is explained by the fact that the excitement arising in a motive zone of bark of cerebral hemispheres occupies also the areas adjusting the circulator and respiratory device. Increase of cordial reductions is connected with weakening of the braking influence of a vagus nerve.

At a hyperthermia of various etiology (most often inf. processes) T. it is connected with temperature increase of the blood washing a sinus node.

Shortening of a diastole at T., remaining it is long, reduces blood supply of a myocardium, leads to development of dystrophic changes in a muscle of heart and promotes development of a decompensation.

At sinus T. subjective symptoms often are absent or are expressed slightly (heartbeat, feeling of weight, pain in heart). Beginning and end of T. (at a pristupoobrazny form) gradual, a rhythm correct, with heart rate 100 — 150 in 1 min. At auscultation the I tone is increased and can be split; The II tone can weaken because of decrease in a stroke output and force of a zakhlopyvaniye of semi-lunar valves; the cantering rhythm as a result of merge of atrial tone to the III tone can be listened. The noise existing earlier usually weaken or even disappear, however nek-ry noise (e.g., presystolic noise of a mitral stenosis) amplify. At heart rate apprx. 150 in 1 min. the stroke output goes down for 70 — 80%, and minute — for 30 — 50%. If at the same time adequate blood supply of a brain and other bodies is not provided, there is reflex vasoconstriction of kidneys, abdominal organs, muscles. At long T. this narrowing is not enough for maintenance of datum level of the ABP therefore there can occur his falloff up to development of a collapse (see the Collapse). In the presence of heart disease (see Heart diseases inborn, the Heart diseases acquired) or the expressed atherosclerosis (see) the decompensation of a myocardium can quickly develop. The lowered coronary blood stream at T. at patients with coronary heart disease (see) — the frequent reason subendokardial-ache ischemia and even a necrosis of a myocardium. Decrease in a blood-groove in kidneys can lead to development of an acute renal failure (see), and insufficiency of blood supply of abdominal organs — to cause a meteorism (see), dynamic intestinal impassability (see Impassability of intestines), formation of round ulcers. The reduction of a cerebral blood-groove causes weakness, dizziness and even aphasia, spasms. A wedge, manifestations are very variable and depend on duration of T., numbers of cordial reductions. The most expressed symptomatology is noted at a paroxysmal form with number of reductions more than 180 — 200 in 1 min. At short-term T. and unsharp uchashcheniye of a rhythm (to 150 ud. in 1 min.) complaints and disturbances of a hemodynamics can be absent.

Not paroxysmal nodal T. meets at a serious illness of heart (a fresh myocardial infarction, especially lower localization, a cardiosclerosis, myocardites, the inborn and acquired heart diseases); it is occasionally observed in the absence of organic lesions of heart. Approximately in half of cases it is connected with intoxication cardiac glycosides. On an ECG existence of an independent atrial rhythm (usually ciliary arrhythmia) with atrioventricular dissociation and not Bouveret's nodal Bouveret's disease is characteristic. At simultaneous excitement of auricles and ventricles the tooth P merges with a ventricular complex; if excitement of ventricles precedes excitement of auricles, the tooth P follows the QRS complex. Usually a tooth P negative in assignments of II, III, aVF, V4 — V6, a form of the QRS complex is not changed. Wedge, a picture is defined by symptoms of a basic disease or intoxication cardiac glycosides, and also heart rate. For diagnosis often it is necessary to resort to registration of the esophageal or intracavitary ECG.

From ventricular T. most often the paroxysmal form meets (see. Bouveret's disease). Not paroxysmal ventricular T. (the accelerated idioventricular rhythm, idioventricular T., slow ventricular T., the replacing ventricular T.) arises at depression of function of a sinus node and increase in automatism of ventricles that is characteristic of intoxication drugs of a foxglove, an acute myocardial infarction, a hyperpotassemia. On an ECG rhythmically arising widened deformed ventricular complexes in the form of jogs from 3 to 20 complexes, and sometimes and more, with a frequency of rhythm of 90 — 110 ud are registered. in 1 min., between these jogs the periods of a sinoatrial rate are located.

Mnogoformny ventricular T. (ventricular anarchy or before-fibrillyatornaya ventricular T.) quite often progresses in fibrillation of ventricles. On an ECG ventricular complexes, the coming from several ectopic centers, various in a form and duration, in ventricles, with a frequency usually apprx. 160 ud are registered. in 1 min.

«Bidirectional» T. it is characterized by alternation of ventricular complexes with a deviation of an electrical axis of heart sharply to the left (a corner an alpha 30 — 90 °) and sharply to the right (a corner an alpha more than 90 °). Arises at functional blockade of front or back branches of the left leg of a ventriculonector. Almost always there is a constant blockade of the right leg of a ventriculonector (see the Heart block). Differential diagnosis is difficult and demands the endocardiac electrocardiogram for the proof of blockade of this or that branch and a leg of a ventriculonector.

At duplication (double) T. there are two independent ectopic centers with activity, close on frequency, or a retrograde atrioventricular block of various degree (see Arrhythmias of heart).

Diagnosis of T. it can be put already at a research of pulse. However it is absolutely not enough since therapy is based on a form of tachycardia. Therefore registration of an ECG in 12 standard assignments is obligatory. Frequent and this research does not allow to identify a form of tachycardia since identification of teeth P, their relations to ventricular complexes in some cases is possible only at use esophageal or intracavitary (a thicket intra atrial) an electrocardiography (see Ezofa-gokardiografiya, Elektrokardiografiya). According to the ECG which is written down from a body surface it is usually possible to distinguish supraventricular T. from ventricular that has crucial importance in the choice of methods of treatment. As diagnostic reception it is possible to use various methods of irritation of a vagus nerve (see. Vegetative reflexes): pressure upon a carotid sine (Chermak's reflex — Goering), on eyeballs (an Aschner's reflex — Danyini), Valsalva's test (breath holding on 10 — 15 sec. on an exhalation). These tests, to-rye it is necessary to carry out at registration of an ECG and auscultation of heart, allow to distinguish supraventricular tachycardia from ventricular. Tests can cause undesirable effects (up to an asystolia) even in the absence of cardial pathology.

On an ECG at sinus T. the shortened intervals P — P and R — R, equal each other are registered. After each tooth P the ventricular complex follows. With a big frequency teeth P and T can merge. Conducting vagal tests allows to slow down a rhythm and to divide these teeth. At long and high-frequency T. there comes the depression of a segment of ST and the negative tooth of T appears. Unlike paroxysmal T. beginning and end of sinus T. gradual, heart rate does not exceed 150 in 1 min., and vagal tests slow down a rhythm. Sinus T. differs from ventricular in a usual form of the QRS complexes, from blinking and an atrial flutter — the correct heart rhythm and well-marked teeth of River. If the diagnosis is not clear, apply registration of the esophageal or intracavitary ECG which is accurately revealing atrial teeth, ventricular complexes and communication between them. After the termination of long T. (a thicket paroxysmal) on an ECG the negative tooth of T and a depression of a segment of ST as a result of ischemia of a myocardium — a so-called posttakhikardialny (post-tachycardic) symptom of Kossio can be registered.

Ectopic atrial rhythm (not paroxysmal atrial T.) it is characterized by existence on an ECG, in comparison with sinus, an atrial tooth of P changed forms. Meets at various cardial pathology, but sometimes it is found also in almost healthy faces. The exact diagnosis is possible only on the basis of the analysis of data of the intracavitary ECG.

Treatment is directed first of all to elimination of the basic patol. process (rheumatism, myocarditis, etc.). Also correction of metabolic disturbances — appointment (or cancellation) drugs of potassium (see), anti-anginal (is not less important at coronary heart disease), anti-inflammatory drugs (see. And ntianginaljny means, Anti-inflammatory drugs). At the phenomena of intoxication cardiac glycosides (see) their urgent cancellation since fibrillation of ventricles is possible is necessary. Sinus T., not breaking a hemodynamics and well transferable it is subjective, does not demand medicamentous therapy. It is forbidden to appoint sympathomimetics (see. Adrenomimetichesky means ); exciting drinks (strong tea, coffee, alcohol), spicy food are contraindicated. At neurogenic T. appoint sedatives (Seduxenum, meprobamate, etc.). At a hyperkinetic syndrome beta-blockers give good effect; also Reserpinum, Isoptinum, Amiodaronum are applied. At heart failure cardiac glycosides are shown. In case of not paroxysmal nodal T. cancel cardiac glycosides, appoint drugs of potassium in an optimum dose. However treatment of hl. obr. it has to be directed to the main patol. process. Effect of antiarrhytmic means (Amiodaronum, Rythmodanum, dipheninum) non-constant.

At ventricular T. use drugs of atropine for the purpose of excitement of a sinus node, and also Ajmalinum, novokainamid, lidocaine, Trimecainum, dipheninum, beta-blockers. Cardiac glycosides in case of their use cancel; at bad effect and disturbances of a hemodynamics resort to elektr oimpuljsny therapy (see), edges it is effective only when at the heart of T. the mechanism of a repeated entrance of excitement lies. It is possible to try to apply an artificial pacemaker (see. Cardiostimulation ). The encouraging results are received at operational treatment — excision of the ectopic center or a section of conduction paths at their pathology.



Bibliography: The guide to cardiology, under the editorship of E. I. Chazov, t. 1 — 4, M., 1982; With h about u T. Page of Electrocardiography in clinical practice, N. Y. and. lake, 1979; Hoffman B. F. a. Cranefiel d P.F. Electrophysiology of the heart, N. Y., 1960.


E. Y. Sokolov, S. A. Harkov.

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