Sinoauricular block
Contents:
Description:
Sinoauricular (sinuatrial) block – a kind of a sick sinus syndrome at which carrying out an electric impulse between a sinuatrial node and auricles is blocked. At a sinoauricular block the temporary asystolia of auricles and loss of one or several ventricular complexes takes place. The sinoauricular block in cardiology meets rather seldom. Statistically, this disturbance of conductivity at men develops more often (65%), than at women (35%). The sinoauricular block can come to light at any age.
Sinoauricular block reasons:
The sinoauricular block can develop after heart operation, in the acute period of a myocardial infarction (in 1% of cases), more often at a heart attack of a back wall (I. Markulyak, 1975).
The sinoauricular block can be connected with intoxication cardiac glycosides, quinidine, drugs of potassium, beta адрено - blockers. More often it is registered at damage of a myocardium of auricles, especially near a sinus node, sclerous, inflammatory or dystrophic process. Sometimes it arises after a defibrillation, is very rare — at almost healthy faces at the raised tone of a vagus nerve.
The sinoauricular block is possible at any age. Statistically To. Rasmusen (1971), at men it is observed more often (65%), than at women (35%).
The mechanism of sinoaurnkulyarny blockade is not found out so far. The issue is not resolved in what the blockade reason — in decrease in excitability of auricles "or in suppression of an impulse in the node. According to D. Scherf (1969), the constant form of blockade is connected with organic changes of a sinus node. In recent years the sinoauricular block is considered even more often as a sick sinus syndrome.
Classification:
Distinguish a sinoauricular block of I, II and III degrees.
The sinoauricular block of the I degree on the usual electrocardiogram does not come to light. In this case all impulses generated by a sinus node reach auricles, however they arise less than is normal. The resistant sinus bradycardia indirectly can indicate a sinoauricular block of the I degree.
At a sinoauricular block of the II degree a part of impulses does not reach auricles and ventricles that is followed by emergence on an ECG of the periods of Samoylov-Venkebakh – loss of a tooth of P and the QRST complex associated with it. In case of loss of one cardial cycle, the increased interval of R-R is equal to two main intervals of R-R; at loss of bigger quantity of seryodechny cycles the pause can equal 3 R-R, 4 R-R. Carrying out every second impulse following after one normal reduction is sometimes blocked (a sinoauricular block 2:1) – in this case speak about an allorhythmia.
Unlike an atrioventricular block of the II Art. at which only the QRS complex drops out at a sinoauricular block loss of atrial and ventricular complexes takes place.
At a sinoauricular block of the III degree the total block of momentum transfer from a sinus node is noted that can cause an asystolia and the death of the patient. In certain cases the role of a pacemaker is undertaken by an atrioventricular node, the carrying-out system of auricles or zheluyodochok.
Sinoauricular block symptoms:
Clinical manifestations of a sinoauricular block of the I degree are absent. Auskultativno can define lack of the next reduction of heart through 2-3 normal cycles.
The symptomatology of a sinoauricular block of the II degree depends on the frequency of loss of a sinus impulse. At rare losses of cordial reductions sensations of discomfort behind a breast, dizziness, short wind, the general weakness are noted.
Lack of in a row several cycles of cordial reductions, and also sinoauricular block of the III degree, is followed by feeling of sinking heart, a sonitus, sharp bradycardia. In case of the sinoauricular block caused by organic lesion of a myocardium congestive heart failure develops.
Against the background of asystolia attacks at patients with a sinoauricular block the syndrome of Morganyi-Edemsa-Stoksa which is characterized by sudden dizziness, pallor of skin, flashing of "front sights" before eyes, a ring in ears, a loss of consciousness, spasms develops.
Diagnosis:
The sinoauricular block should be distinguished from a sinus bradycardia, a sinus arrhythmia, the blocked atrial extrasystoles, atrioventricular blockade of the II degree.
The sinoauricular block and sinus bradycardia can be differentiated by means of an atropine test or an exercise stress. At patients with sinoaurnkulyarny blockade at these tests doubles, and then twice the cordial rhythm suddenly decreases (there comes blockade). At a sinus bradycardia the rhythm gradually becomes frequent.
The extended pause at a sinoauricular block is not connected with the act of breath, and at a sinus arrhythmia — is connected.
At the blocked atrial extrasystole on an ECG there is an isolated tooth P while at a sinoauricular block there is no tooth P and the QRST complex associated with it (i.e. completely cardial cycle drops out). Difficulties arise in that case when the tooth P merges with the T tooth preceding the extended pause.
At atrioventricular blockade of the II degree unlike a sinoauricular block the tooth P constantly is registered, the accruing increase in time or the fixed time of an interval P — Q which the blocked wave of River follows is noted.
Sinoauricular block 2 degrees
Treatment of a sinoauricular block:
At a sinoauricular block of the I degree special therapy is not carried out. Sometimes recovery of conductivity is promoted by treatment of a basic disease or cancellation of the drugs promoting disturbance.
At the functional sinoauricular block caused by a vagotonia, good results are yielded by atropine use inside or subcutaneously. Stimulation of automatism of a sinus node is promoted by purpose of sympathomimetics (ephedrine, an alupent, Isadrinum). For improvement of a metaboyolizm of a myocardium cocarboxylase, inosine, ATP are shown.
At a sinoauricular block reception of cardiac glycosides, beta adrenoblockers, antiarrhythmic drugs of a hinidinovy row, salts of potassium, a kordaron, Rauwolfia drugs is contraindicated.
If the sinoauricular block significantly worsens health of the patient or is followed by asystolia attacks, resort to temporary or continuous electric stimulation of auricles (implantation of an electrocardiostimulator).
Forecast:
Succession of events at a sinoauricular block in many respects is defined by a current of a basic disease, extent of disturbance of conductivity, existence of other disturbances of a rhythm. The asymptomatic sinoauricular block does not cause sharp disturbances of a hemodynamics; development of a syndrome of Morganyi-Adams-Stokes is regarded as predictively adverse.
