Bradycardia – Variants Of The Norm And Pathology

// Published October 28, 2019 by James Washington

Heart rate indicators reflecting the heart rate allow you to assess the state of the cardiovascular system and draw preliminary conclusions about violations in its activity. The number of heart contractions is a variable value. It depends on such indicators as age, time of day, ambient temperature, fitness of the body, state of health, etc.

In children, heart rate changes every 1-2 years, and, starting from 15 years old and ending with 50 years, the frequency of contractions is about 60-80 beats per minute. Starting from the age of 50, especially in people who lead a low-activity lifestyle, the heart ages and the pulse quickens. Normally, its indicators for people aged 50-60 are 64-84 beats. per minute, and after 60 – 69-89 beats. per minute.

Under the influence of various factors, the pulse can:

  • become more frequent (tachycardia) – more than 80 beats. per minute;
  • slow down (bradycardia) – less than 60 beats. per minute.

Given the dependence of these indicators on many internal and external factors, a person who does not have a medical education cannot independently correctly assess the situation, accompanied by the appearance of a slowing of the pulse, and that is why attempts to independently diagnose or treat bradycardia are not recommended and can be dangerous.

In this article, we will introduce you to the causes, varieties, variants of the norm and pathology, methods for diagnosing and treating this type of deviation of the pulse from normal indicators like bradycardia.

Causes and classification of bradycardia – variants of the norm and pathology

Depending on the localization of the disorders detected in the work of the heart, there are:

  • sinus bradycardia – a slowing of the pulse is caused by violations of automatism in the sinus node;
  • bradycardia with atrioventricular (AB) or sinoatrial (SA) heart block – a slowing of the pulse is caused by a violation of the impulse between the sinus node and the atria and ventricles or atria.

Depending on the causes of development, these types of sinus bradycardia are distinguished:

  • sinus bradycardia of athletes – develops in physically trained people;
  • extracardiac (or neurogenic) – develops in case of neurosis with autonomic dysfunction, neurocirculatory dystonia, peptic ulcer, increased intracranial pressure, hypothyroidism, myxedema, physical effects on the carotid sinus or eyeballs;
  • drug – develops with prolonged or improper use of certain drugs;
  • organic – caused by heart pathologies (myocardial infarction, myocarditis, cardiosclerosis, microcardiodystrophy);
  • toxic – develops with severe intoxications provoked by toxic substances or infections;
  • idiopathic – develops due to unexplained causes.

Bradycardia may be:

  • physiological – the slowdown of the pulse is caused by external factors, this type of bradycardia is a variant of the norm, because the reduction in heart rate occurs due to physiological reasons;
  • pathological – slowing of the pulse can be acute or chronic, caused by the influence of internal or external pathological factors.

Physiological bradycardia

The reasons for the development of physiological bradycardia are such factors:

  1. Age. Bradycardia is caused by age-related changes in the myocardium (cardiosclerosis), which, as a rule, occur after 60-65 years and lead to the fact that cardiac contractility becomes worse and changes occur in the conduction system, leading to a slowing of the pulse at rest.
  2. Good physical fitness. Slow heart rate is the result of frequent physical exertion experienced by many professional athletes. They lead to the fact that the heart muscle is able to contract more strongly than in an ordinary person and maintains normal blood circulation even with a slowed heart rhythm. This is due to the fact that systematic training leads to the appearance of additional muscle fibers in the myocardium. With this reduction in heart rate up to 45-50 beats. per minute, a person continues to feel normal and has no signs of a violation of normal hemodynamics. This kind of bradycardia is usually observed in athletes (for example, football players, runners, swimmers, cyclists, etc.), who during a long period of exercise experience moderate physical exertion.
  3. Moderate hypothermia (hypothermia). Slowing of the pulse is caused by complex cooling of the body, which is accompanied by a decrease in body temperature to 35 ° C or less. In such cases, a slowdown in heart rate is a protective mechanism that occurs in response to an unfavorable factor. That is, the heart switches to the “economy mode” in order not to exhaust the necessary energy resources. After normalizing the temperature, the indicators return to normal.
  4. Stimulation of reflex zones. Slowing of the pulse can occur artificially (i.e., reflexively) when the vagus nerve is stimulated. Such a reflex reaction can be provoked by mild pressure on the eyeballs or massage of the carotid sinus (the branching site of the carotid artery).
  5. Idiopathic bradycardia. This kind of bradycardia can occur both constantly and periodically. It is not possible to establish the cause of such pulse slowdowns even with a comprehensive medical examination. If, in addition to slowing the pulse, a person does not show signs of hemodynamic disturbance, then such a slowing of the pulse is considered physiological and does not require treatment.

Pathological bradycardia

The reasons for the development of pathological bradycardia are such factors:

  1. Pathology of the heart. Heart diseases lead to the appearance of sclerotic areas in the myocardium and / or inflammatory processes that disrupt the functioning of the conductive system and provoke the appearance of bradycardia. Slowing of the pulse can be observed with such pathologies of the heart: focal or diffuse cardiosclerosis, coronary heart disease, myocardial infarction, infectious diseases (myocarditis, endocarditis).
  2. Infections Most infections cause tachycardia, but some infectious pathologies can help slow your heart rate. These include: severe forms of sepsis, some variants of the course of viral hepatitis, typhoid fever.
  3. Hypothyroidism With hypothyroidism, a decrease in the level of thyroid hormones occurs, which affect many physiological processes in the body, including metabolism. One of the signs of their insufficient number is a violation of the functioning of the nervous system and heart, which are manifested by a slowing of the pulse. The following pathologies can lead to the development of hypothyroidism: thyroiditis, congenital hypo- or aplasia of the thyroid gland, poisoning with toxic iodine isotopes, previous injuries or surgical interventions on the thyroid gland, autoimmune thyroiditis, and some infectious diseases.
  4. Increased tone of the parasympathetic nervous system. Parasympathetic innervation of the heart is carried out through the branches of the vagus nerve, and with a pathological increase in its tone, a slowdown in heart contractions will occur. Such a reduction in heart rate can be caused by such diseases and conditions: traumatic brain injury, mediastinal neoplasms, hemorrhagic stroke, neurosis, depression, increased intracranial pressure, peptic ulcer, previous surgery in the mediastinum, head or neck.
  5. Poisoning. Slow heart rate can be a sign of poisoning with such toxic substances: nicotine, lead compounds, some drugs, pesticides and organic phosphorus compounds. Typically, in case of poisoning, the slowing of the pulse develops rapidly, and the severity of bradycardia depends on the number of poisonous compounds that have penetrated the body.
  6. Taking a number of drugs. Bradycardia can be a side effect or a sign of poisoning with certain drugs. As a rule, such a reduction in heart rate is temporary and does not threaten life or health, but with frequent episodes of bradycardia, it is still recommended to consult a doctor to adjust the dosage or replace the drug. In most cases, the cause of the slowing of the pulse is the wrong dosage or violation of the rules of admission. The most pronounced episodes of bradycardia can be caused by the use of such drugs: calcium channel blockers, cardiac glycosides, beta blockers, Morphine, Digitalis, Adenosine, Quinidine, Amisulpride.

Symptoms

Physiological or moderately severe bradycardia in most cases is not accompanied by impaired normal circulation and is asymptomatic. The appearance of signs of a slowdown in heart contractions is usually observed with pathological bradycardia, in which the slowdown of the pulse is less than 40 beats. per minute. In such cases, the patient develops the following symptoms of hemodynamic disturbance:

  • general weakness;
  • darkening in the eyes and flickering of “midges” in front of the eyes;
  • fast fatiguability;
  • cold sweat;
  • dizziness;
  • fainting or fainting conditions.
If such symptoms appear, the patient must consult a cardiologist or arrhythmologist who will conduct a comprehensive examination to identify the cause of bradycardia and prescribe a course of treatment.

Do not postpone the visit to the doctor, because the following dangerous conditions can become the consequences of pathological bradycardia:

  • Morgagni-Adams-Stokes syndrome (periodic episodes of loss of consciousness);
  • unstable blood pressure or arterial hypertension;
  • Ischemic heart disease;
  • angina pectoris;
  • chronic circulatory failure.

Diagnostics

To clarify the diagnosis, a patient with bradycardia can be assigned the following diagnostic examination methods:

  • listening to heart sounds with a stethophonendoscope;
  • ECG analysis at rest and bicycle ergometry;
  • Holter ECG monitoring;
  • Echocardiography;
  • clinical and biochemical tests of urine and blood;
  • transesophageal electrophysiological study of the conduction pathways of the heart (if it is impossible to detect heart block with an ECG);
  • bacteriological analysis of blood or urine (if an infectious disease is suspected);
  • analysis of toxins (with suspected poisoning).

Treatment

The decision on the need for treatment of bradycardia is made individually, taking into account the characteristics of the patient transferring its symptoms and depending on the results of the examination.

Treatment of the physiological form of the disease or bradycardia with a slight slowdown in the rhythm of the heart and the absence of signs of circulatory disorders is not carried out. In such cases, the patient is recommended preventive examinations by a cardiologist, individual selection of physical exertion, walking in the fresh air, rational organization of work and rest, monitoring of blood pressure and heart rate and compliance with the rules of good nutrition (limiting animal fats and salt).

With drug bradycardia, correction of the previously prescribed treatment is performed – a change in dosage or drug withdrawal.

In other cases, the patient is prescribed therapy for the underlying disease, which led to a slowdown in heart rate. Indications for the appointment of medical or surgical treatment of bradycardia are the following conditions and pathologies:

  • dizziness and fainting;
  • frequent episodes of bradycardia causing uncomfortable symptoms or disability;
  • heart rate reduction to less than 40 beats. per minute;
  • chronic pathologies that cause bradycardia;
  • hypotension.

Drug therapy

With the appearance of symptoms of bradycardia such as weakness and dizziness, it is recommended to take medications to stabilize the heart rhythm:

  • preparations based on belladonna, eleutherococcus or ginseng root;
  • Isoprenaline;
  • Isadrin
  • Atropine;
  • Eufillin;
  • Caffeine et al.

The appointment of these drugs can only be performed by a doctor who can choose the right dosage. As a rule, they are taken during an episode of bradycardia, but in some cases, therapy is carried out in courses (weeks or months).

In addition, the patient is prescribed drugs to treat the underlying disease that caused a slowdown in heart rhythm (antibiotics, thyroid hormones, drugs for the treatment of angina pectoris, etc.).

Surgery

In some cases, only surgical treatment can be used to eliminate bradycardia:

  • pacemaker implantation operations;
  • surgery to remove mediastinal tumors.

Indications for pacemaker implantation:

  • acquired AV block of II B-III degree with circulatory failure of III-IV degree or with episodes of attacks of Morgagni-Adams-Stokes;
  • AV blockade II B-III degree, occurring 3-4 weeks after an attack of myocardial infarction and can not be corrected;
  • sick sinus syndrome with episodes of attacks of Morgagni-Adams-Stokes or with circulatory failure of the III-IV degree;
  • atrial fibrillation or atrial flutter with a pulse rate of less than 50 beats. per minute.

Relative indications for pacemaker implantation:

  • congenital form of complete AV blockade in adults with circulatory failure of the III degree;
  • chronic tri- or bifascicular block;
  • QRS complex expansion of more than 0.8 s and an increase in the HV interval of more than 100 ms;
  • congenital form of AV blockade with circulatory failure of the III-IV degree or weak sinus node with episodes of attacks of Morgagni-Adams-Stokes.

The pacemaker model is selected individually depending on the causes of bradycardia and the degree of hemodynamic impairment.

REFERENCES:

  1. https://en.wikipedia.org/wiki/Bradycardia
  2. https://www.heart.org/en/health-topics/arrhythmia/prevention–treatment-of-arrhythmia/living-with-your-pacemaker
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