Sinus bradycardia: causes, symptoms, treatment

While the normal heart rate in most people ranges from 60 to 90 beats per minute, there is often a steady decline, which is defined in cardiology as sinus bradycardia (ICD-10 code is R00.1).

What it is? This is a deviation from the norm, when your heart beats more slowly, that is, less than 60 times per minute. Why sinus? Because the heart rhythm is controlled by the sinus-atrial node, which produces electrical impulses that initiate each heartbeat.

[1], [2], [3], [4]

Epidemiology

Differentiating physiological and symptomatic sinus bradycardia is not easy, therefore statistics regarding their prevalence is unknown.

Although, as practice shows, the treatment requires only a pathological (symptomatic) type of heart rate reduction, especially in the elderly, since the frequency of this symptom increases with age - as the corresponding diseases develop.

[5], [6], [7], [8], [9], [10]

Causes of the sinus bradycardia

The symptom, manifested as a decrease in the rhythm of contractions of the heart, does not necessarily indicate a disease. For example, when a person sleeps, the heart rate is lower than in a waking state. Therefore, sinus bradycardia is distinguished physiological and symptomatic (pathological). And in most cases, doctors can identify its causes.

So, the decrease in heart rate during hypothermia (supercooling of the organism, accompanied by a slowing down of all metabolic processes), as well as the sinus bradycardia that does not show itself in men and women of advanced age is a pathology, is the result of changes in the heart caused by aging.

Sinus bradycardia in athletes - physiological, with a high frequent wandering tone; almost half of them simultaneously have sinus bradycardia and left ventricular hypertrophy, since with increasing volume and internal pressure, due to increased physical exertion, the heart rate decreases. For more details see -  Sports heart

The sinus bradycardia in pregnancy, which occurs in the first half due to the characteristic vomiting of the early toxicosis, also belongs to the physiological one, and at later dates - when the uterus begins to exert mechanical pressure on the lower vena cava. But because of anemia, pregnant women have sinus  tachycardia.

Meanwhile, a persistent slowing of the heart rate may be a symptom of a variety of pathological conditions and diseases: stagnant and hypertrophic cardiomyopathy; infectious myocarditis and endocarditis; postinfarction; hypothyroidism (thyroid hormone deficiency); lack of blood potassium and / or magnesium (leading to an imbalance of electrolytes); arterial hypotension and vegetovascular dystonia; problems with the adrenal gland or pituitary gland; increased intracranial pressure; localized in the brain inflammation (eg, Lyme disease) and neoplasms.

The key causes of sinus bradycardia are disorders in the conduction system of the heart, the main role in which the sinus or sinoatrial node (nodus sinuatrialis) of the right atrium plays the main driver of rhythm. A set of pathological abnormalities in his work, leading to a decrease in heart rate, is a  syndrome of weakness of the sinus node.

However, conduction defects in sinus bradycardia are also associated with violations of the atrioventricular node -  atrioventricular blockade  (AV blockade), the clinical significance of which exceeds the weakness of the sinoatrial node. And problems with conduction of impulses below the AV node are caused by Lenegre syndrome - idiopathic fibrosis and calcification of the conducting system.

[11], [12], [13], [14]

Risk factors

The risk factors for a persistent decline in heart rate include: heart complications infectious and autoimmune diseases; bleeding and hypoxia of any etiology; vegetative hyperreflexia; advanced age; prolonged bed rest; anorexia and "hungry diets"; exposure to toxic substances (poisoning), as well as smoking, alcohol abuse, stress.

Important iatrogenic factor - long-term use of antiarrhythmic drugs that block β-adrenoreceptors or calcium channels (Amiodarone, Verapamil, Propranolol, etc.); cardiac glycosides (digitalis digitalis group); tricyclic antidepressants and neuroleptics of the phenothiazine group, sedatives (including Valocordin and its analogues).

And risk factors for the weakening of the pacemaker and the development of bradycardia: myocardial ischemia, infarction (with scars in the right atrium or interventricular septum), focal and diffuse degenerative changes in the myocardium with damage to the sinus node myocytes (sclerosis, calcification).

[15], [16]

Pathogenesis

As noted by cardiologists, the pathogenesis of sinus bradycardia in parasympathetic hypertension is the overexcitation of the vagus nerve and its branches innervating the zone of the sinoatrial node.

And its dysfunction can be caused by several factors. First, the decrease in heart rate occurs when the full blood flow of the sinus is impaired and the trophism of the cells forming it worsens. Secondly, there is a partial "shutdown" of the automatism of the pacemaker, and it works at a lower speed. As a result, the interval between sinus depolarization of cardiomyocytes (pacemaker neurons) increases, and this can lead to conditions defined as sinus bradycardia with sinus arrhythmia or sinus bradyarrhythmia with supraventricular tachycardia. Similar conditions are called  Frederick's syndrome.

With the weakness of the sinus node, impulses begin to be generated by the bundle of the Hyis, but they appear earlier than the prescribed one and, alternately, contract the muscle fibers of the ventricles of the heart - bypassing its atrium. In such situations, sinus bradycardia and extrasystole can be diagnosed.

The transmission of the impulse itself, which can not freely pass from the sinus cells to the myocardium of the atria, or from the atria to the ventricles - can be violated - because of the AV blockade of the second and third degree.

Also, impulses can be delayed between the atrioventricular node and the atrioventricular bundle (the bundle of His). Then it would be more correct to determine the atrioventricular bradycardia. Read more -  Conductive heart system. Partial impairment of pulse passage with a decrease in heart rate and increased pressure in the right ventricle indicates that this is an incomplete block of the right leg and a sinus bradycardia, which can be with constriction and prolapse of the mitral valve, ischemia and congenital heart defects, acute infarction, and also a side effect of digitalis preparations (cardiac glycosides).

With heart defects associated with interventricular hemodynamics, during the contraction of the ventricles, the pressure that slows the heart rate increases and a sinus bradycardia with systolic overload is established.

Explaining the effect of thyroid hormones on the heart rhythm, experts emphasize that when there is insufficient synthesis of triiodothyronine and thyroxine in patients with thyroid hypothyroidism, not only water-salt metabolism is disturbed, but the excitability of the chromatin interstitial receptors of the sympathoadrenal system decreases. Because of this, the cells capture much less calcium ions, and this leads to a decrease in heart rate, cardiac output and systolic blood pressure.

[17], [18], [19]

Symptoms of the sinus bradycardia

As noted above, sinus bradycardia in ICD-10 is reserved in the 18th grade - among symptoms, signs and abnormalities. And the first signs of sinus bradycardia are a reduction in the heart rate to 58-55 beats per minute, which may not be felt at all, and this is an easy sinus bradycardia.

But as the heart rate decreases, sinus bradycardia can cause certain symptoms associated with cardiac dysfunction and general hemodynamics. Their intensity and range depend on the degree of decrease in the number of cardiac contractions per minute: 55-40 - moderate sinus bradycardia, less than 40 - pronounced sinus bradycardia.

So, among the nonspecific symptoms accompanying the sinus bradycardia of any etiology are allocated: rapid fatigue, a feeling of general weakness, dizziness (down to fainting), a release of cold sweat, mild nausea, heaviness in breathing and a feeling of discomfort in the vaginal space.

A sharp sinus bradycardia - with a decrease in heart rate to 30 beats / min. And below - qualifies as an urgent terminal condition (in particular, with a significant decrease in the volume of circulating blood in trauma and in cases of severe intoxication, cardiogenic shock, hypothyroid coma, etc.). It is manifested by cyanosis and cooling of the extremities, severe dizziness, narrowing of pupils, convulsions, falling of arterial pressure, loss of consciousness and stopping of breathing.

Sinus bradycardia in children and adolescents

In children of younger age group, the heart beats more often than in adults, because the basic physiological processes that ensure the homeostasis of the child's body (body temperature and blood pressure, heart rate, etc.) control the sympathetic department of the autonomic nervous system (VNS).

In newborns, sinus bradycardia is defined as the heart rate less than 100 beats / min. (the norm is about 120-160) and accompanies asphyxia during childbirth. A persistent bradycardia with partial AV-blockade is attributed to signs of congenital systemic lupus erythematosus or a hereditary  syndrome of the extended QT interval.

Also, sinus bradycardia in children may be a consequence of the syndrome of weakness of the sinus node, which develops after cardiac surgery, and with congenital hypertrophy of the right ventricle.

The sinus bradycardia diagnosed by a cardiologist in a teenager can develop due to the same weakness of the sinus node, but in most cases it appears to be a symptom of abnormalities of the VNS, peculiar to the pubertal period (due to hormonal changes).

In some adolescents, this condition is accompanied by manifestations of predominantly sympathicotonia; others have signs of vagotonia, that is, when the parasympathetic department of the VNS "manages" physiology. It is caused genetically and is called parasympathetic hypertonia, which is manifested by increased sweating, arterial hypotension, often there are episodes of sinus bradycardia.

If both departments of the VNS are equally excited, then this is amphotonia, and in different situations bradycardia, sinus bradyarrhythmia and paroxysmal tachycardia (i.e., paroxysmal) can alternate.

Forms

There is no unified systematization of this disturbance of the heart rhythm, and in different sources such kinds of sinus bradycardia are defined as: physiological, symptomatic (pathological or relative), absolute, central, organic (intracardial, i.e., due to primary organic heart disease), extracardiac (not associated with heart disease), degenerative, toxic, idiopathic (unknown etiology).

A vertical sinus bradycardia is distinguished - physiological, associated with a change in the location of the electrical axis of the heart (EOS). In addition, with EKG, a deviation of EOS to the left (characteristic of left ventricular hypertrophy) or its displacement to the right (with possible right ventricular hypertrophy) can be detected. These changes may be asymptomatic, but may manifest as nonspecific symptoms.

Complications and consequences

What is dangerous is a sharp sinus bradycardia, you already know, but a less pronounced symptomatic, toxic or idiopathic reduction in the number of cardiac contractions can also have consequences and complications.

Among them: insufficient supply of blood to certain structures of the heart with the development of pain syndrome (angina); functional cardiac disorders (heart failure); increased thrombus formation; the development of stroke, heart attack, Morgagni-Edams-Stokes syndrome ,   etc.

[20], [21], [22]

Diagnostics of the sinus bradycardia

Diagnostics include pulse measurement, blood pressure, auscultation with a stethoscope, blood tests (biochemical, thyroid hormone and electrolyte levels, rheumacomplex).

Anamnesis should contain information about all the patient's diseases and medications taken.

The most important role is played by instrumental diagnostics using: electrocardiography with 12 leads (and also 24-hour Holter), echocardiography, if necessary, ultrasound or chest MRI.

Sinus bradycardia on the ECG will be visible by decreasing the heart rate (the intervals between the teeth R will be longer), by the presence of a sinus rhythm (the P tooth is always positive and is fixed ahead of each ventricular complex - QRS); by a wider QRS-complex.

Pulses that appear inside or below the bundle of the His on the ECG will create a wide QRS complex with a heart rate of 20 to 40 beats / min.

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Differential diagnosis

Differential diagnosis of cardiac rhythm abnormalities - including  sinus arrhythmia, depolarization disorders, as well as the  syndrome of early ventricular repolarization  - is also performed on the basis of ECG, normal and with physical exertion.

Also, bradycardia or bradyarrhythmia can occur due to problems with the transmission of electrical impulses by the ventricles, and violation of intraventricular conduction is detected in patients with cardiac ischemia and the presence of cardiac valve pathologies caused by atherosclerosis, endocarditis, or rheumatism.

More information in the material -  Violation of the rhythm and conduction of the heart.

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Treatment of the sinus bradycardia

According to the experts of the European Society of Cardiology, for most people the treatment of sinus bradycardia is not required - if the patients do not have symptoms that are clearly associated with delayed heart beat, which adversely affects the general hemodynamics.

Than to treat and how to treat at presence of signs? It depends on the etiology of the lowered heart rate and the accompanying manifestations. If sinus bradycardia causes hypothyroidism, then hormone replacement therapy (levothyroxine) is indicated. Infectious myocarditis requires the use of antibiotics, with a deficiency of potassium and magnesium prescribe K and Mg tablets (Panangan, Kudesan, Kalinor, Potassium orotate, etc.).

Treatment is necessary for dysfunction of the sinus-atrial node with severe clinical symptoms and with severe atrioventricular blockade, and this is exclusively surgical treatment by implantation of a permanent pacemaker.

In other cases - to increase the heart rate - drugs with a positive chronotropic effect, which give drugs blocking M-holinoretseptory, and drugs that stimulate β-adrenoreceptors, can be prescribed. Among them: Atropine, Iazrin (Isoprenaline), Ipratropium bromide (other trade names - Itrop, Atrovent, Vagos, Normosecretol), Orciprenaline (Astomopent, Alupent, Alotec), Ephedrine, Epinephrine (Adrenaline), Noradrenaline.

Tablets (0.01 g) and injection Ipratropium bromide can be prescribed only by a doctor, he also determines the dose (standard - 0.5-1 tablet twice a day). The drug may interfere with urination, sweating, accommodation and bowel movements; dries the mucous in the mouth and reduces appetite. Contraindicated in hypertrophy of the prostate glaucoma, narrowing of the intestine, pregnancy (I trimester).

If there is no atherosclerosis in the medical history, Orciprenaline - 0.05% solution, tablets (20 mg each) can be used. This agent is especially effective in cases of bradyarrhythmia, as well as with a decrease in heart rate after taking cardiac glycosides. The dose and duration of the course of treatment are determined by the attending physician.

A sharp sinus bradycardia, fraught with a stop of breathing, followed by a cardiac arrest, requires  emergency care  - with the introduction of Atropine and cardiac stimulation.

Prevention

There are no specific measures to prevent any form of bradycardia. It is easiest to prevent the effect of the iatrogenic factor, that is, to abandon the drugs that lower the heart rate.

In the rest it remains to adhere to the standard recommendations of doctors: to control the level of cholesterol and blood pressure, to reduce the amount of consumed fats and salt, to have regular physical activity and to quit smoking.

[29], [30], [31], [32]

Forecast

The forecast depends on many factors. In severe forms of sinus bradycardia (less than 40 beats per minute), a "slow" heart does not provide enough blood to meet the needs of the body. This can cause negative consequences and be life-threatening.

A good prognosis in patients with hypothyroidism, because treatment with thyroid hormones can relieve bradycardia and other symptoms.

At one time the prognosis for people with AV blockade of the third degree was poor, with 50% of patients dying within one year after diagnosis. However, the implantation of a permanent pacemaker dramatically improved the situation.

Service in the army and sport

Sinus bradycardia and the army are incompatible if pathology is accompanied by severe heart failure. In asymptomatic mild form or moderate bradycardia, the fate of conscripts is decided by the medical commission, which determines whether or not to be "limitedly fit" to the passage of military service.

And to the question whether it is possible to go in for sports, having a sinus bradycardia, the cardiologist should also respond, after examining the causes of bradycardia. But moderate exercises without serious deterioration of state of health at presence of the given disturbance of a warm rhythm are only welcomed.

[33], [34], [35], [36]