SINUS BRADYCARDIA: SYMPTOMS, CAUSES, AND TREATMENTS - MEDICINE - 2024

The sinus bradycardia is decreased heart rate below normal values, but always following the patterns of the sinus node. This means that despite the slowing of the heartbeat, normal sinus rhythm is preserved, respecting all the steps of the cardiac cycle.

The term bradycardia is made up of two ancient Greek words: bradys, which means "slow" and kardia, which means "heart." The strictly etymological translation would be "slow heart", which is not incorrect, but from a medical point of view "slow heart rate" is more accepted.

Sinus bradycardia usually has no symptoms; in fact, most of the patients who present it do not manifest discomfort. However, all bradycardic patients should be evaluated, either because a clinical sign associated with it arose or because it was an occasional finding. Treatments will depend on the cause found.

Symptoms

The fundamental characteristic of this condition is the decrease in heart rate. Understanding that in an adult the normal heart rate ranges between 60 and 100 beats per minute, any rate below 60 beats per minute that maintains normal sinus rhythm will be accepted as sinus bradycardia.

Sinus rhythm refers to the normal beat of the heart, following the pattern indicated by the sinus node and which can be clearly reflected on an electrocardiogram.

This means that there are P, Q, R, S and T waves in the respective order and size, with only a certain prolongation in the duration of each one.

Sinus bradycardia is usually asymptomatic; in fact, its diagnosis is often a chance finding during a medical evaluation for another reason.

However, some other clinical signs may accompany bradycardia, which occurs when there is a true underlying condition. Among these associated manifestations are the following:

- Palpitations.

- Fainting.

- chest pain

- dizziness

- Difficulty breathing.

- Fatigue.

Causes

There are normal or physiological causes of bradycardia, as well as abnormal or pathological causes.

Physiological causes

Sinus bradycardia is considered a normal finding in the following circumstances:

Dream

In the Non-REM or Non-REM stage -that is, while there are no rapid eye movements-, a phenomenon known as benign bradycardia occurs, caused by the decrease in neuronal sympathetic activity.

Athletes

People with highly proficient training usually have bradycardia at rest. These individuals have developed a powerful left ventricle capable of generating sufficient cardiac output even at low heart rates.

Syncope

People who have fainted or fainted from non-cardiovascular causes usually have bradycardia without it being considered pathological.

Vagal maneuvers

The stimulation of the carotid sinus or the performance of valsalva maneuvers leads to the appearance of bradycardia. This is normal and expected, in fact it is done many times with that intention.

Youth

Young and healthy people can have a low heart rate without the need for any underlying pathology or for them to exercise regularly.

However, these patients should always be studied, especially if they are going to undergo any surgical procedure.

Pathological causes

There are numerous pathological conditions associated with sinus bradycardia. Among the most important are the following:

Myocardial ischemia

The infarction of the lower wall of the left ventricle is the ischemic event that is most related to the appearance of sinus bradycardia.

This is due to the decrease in the automaticity of the sinoatrial node, losing certain pacemaker conditions and favoring the slowing of the heart rate.

Damage to the cardiac impulse conduction pathways can also occur in myocardial ischemia. In these cases, the atrial node sends the precise information, but it arrives later than usual, causing reflex sinus bradycardia.

Synoatrial node dysfunction

Any sinus node defect that is not caused by ischemia can lead to sinus bradycardia. Failure to generate the electrical impulse is the cause of the drop in heart rate.

Drugs

Many medications, mostly related to the cardiovascular sphere, have among their side effects the appearance of bradycardia.

Beta-blockers, digitalis, verapamil, diltiazem, amiodarone, and clonidine are some of the most frequently used drugs that cause this phenomenon.

Intracranial hypertension

One of the most worrying consequences of intracranial hypertension is bradycardia, which, together with arterial hypertension, represents a warning of encephalic herniation. This scenario forces radical therapeutic measures to be taken in the patient.

Hypothyroidism

The decrease in the functional activity of thyroid hormones results in a decrease in basal metabolism. Among the effects of this condition are fatigue, sensitivity to cold, menstrual disorders and sinus bradycardia.

Hypothermia

Lowering body temperature has an effect similar to hypothyroidism. Bradycardia in these cases also functions as information for health professionals, who must understand that vital functions are compromised and that they must act immediately to raise the patient's temperature.

Water and electrolyte imbalances

Especially hyperkalemia or hyperkalemia has been associated with sinus bradycardia. Potassium plays a fundamental role in cardiac control; therefore, its elevation in plasma causes rhythm disorders, including sinus bradycardia.

Treatment

Regardless of the origin, cases of benign sinus bradycardia do not require specific treatment. In other situations, the first thing to do is try to find the cause of the bradycardia to establish the appropriate therapy: in addition to the electrocardiogram, in the presence of bradycardia, a series of medical and laboratory tests should always be performed.

When sinus bradycardia is symptomatic, certain treatment schemes must be established that will depend on the severity of the condition.

Atropine is the drug of choice and can be used repeatedly until normal heart rate is restored and symptoms decrease.

If atropine does not work, isoproterenol can be tried, which is given in a glucose mixture until bradycardia is controlled.

When drug therapy does not provide symptom relief, an external transcutaneous or transvenous pacemaker may be necessary, which takes over control of the heart rate in place of the sinus node until a permanent pacemaker can be implanted.

References

1. Rawshani, Araz (2017). Sinus Bradycardia: definitions, ECG, causes and management. Clinical ECG interpretation.
2. Mayo Clinic Staff (2017). Bradycardia. Recovered from: mayoclinic.org
3. Liu, EF; Chen, L and Gao, BX (2012). Sinus bradycardia: normal phenomenon or risk factor? Evaluation based on recent evidence. Journal of Insurance Medicine, 43 (2): 102-111.
4. Hafeez, Yamama and Grosmman, Shamai A. (2018). Rhythm, Sinus Bradycardia. StatPearls Publishing.
5. Kirkwood, Graeme (2016). Cardiac Arrhythmias During Sleep. British Heart Rhythm Society.
6. Aliaga, Mireia (2017). Sinus bradycardia: causes, symptoms and treatment. Recovered from: onsalus.com
7. Wikipedia (2018). Sinus Bradycardia. Recovered from: en.wikipedia.org