Heart rate alterations: bradycardia

By Cristiano Antonino On Mar 18, 2023

In the medical field, bradycardia is defined as a heart rate below 60 beats per minute. The heart rhythm is considered regular when it is between 60 and 100 beats per minute

This is why it is conventionally referred to as bradycardia when the heart rate is below 60 beats or beats per minute (bpm)

This type of condition can cause dizziness or subjective feelings of breathlessness (dyspnoea) in the affected person.

In people practising sport and the elderly, bradycardia occurs physiologically and is generally not a cause for concern.

However, when the slowing of the heart rate does not allow the heart to pump enough blood into the body, it is considered a pathological condition.

Find out in this article everything you need to know about bradycardia, what disorders it is most frequently related to, how it is diagnosed and how to treat it.

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What is bradycardia

When the heart rate falls below normal levels, it is called bradycardia.

In an adult person, a heart rate between 60 and 100 beats per minute is considered normal.

A rate below these values is referred to as bradycardia.

This can be classified into:

Mild bradycardia: when the frequency is between 50 and 59 bpm;
Moderate bradycardia: when the heart rate is between 40 and 49 bpm;
Severe bradycardia: when the heart rate falls below 40 beats per minute.

Infants and very young children under one year of age can also suffer from episodes of bradycardia

In these cases, we speak of fetal or neonatal bradycardia and it occurs when the heart rate is below 100 beats per minute, since in infants the heart rate is physiologically higher and is around 110-160 bpm.

As a rule, this type of arrhythmia is not dangerous, and in some individuals such as the elderly and those who practise sports at a competitive level, it can occur physiologically.

In particular, people who engage in intense physical activity develop the so-called ‘athlete’s heart’, a series of structural and functional changes in the cardiovascular system.

These changes include, in addition to the aforementioned bradycardia, systolic murmur and heart tones added on auscultation.

These types of abnormalities, however, are not a cause for concern and do not require any specific treatment.

Bradycardia can become a pathological condition in some individuals

At such low frequencies, in fact, the heart may not be able to pump enough blood, causing a reduction in peripheral oxygenation, resulting in symptoms that can sometimes make even the most mundane daily activities complicated.

Symptoms and Causes

When the heartbeat is too slow and the heart is unable to provide proper oxygenation to the brain and other organs, the subject may present the following symptoms:

Dyspnoea;
Feeling of dizziness;
Profound sense of fatigue;
Confusional states;
Syncope;
Sleep disorders;
Memory disturbances;
Chest pain;
Hypotension.

It is important to remember that various pathologies can cause these symptoms and, for this reason, it is advisable to immediately contact the general practitioner to try to quickly understand what the underlying cause is and to immediately initiate the most suitable treatment for the case.

There are several conditions that can cause pathological bradycardia and, usually, these are pathologies that are capable of altering the normal electrical activity of the cardiac conduction tissue.

These include:

age-related damage to the myocardium (the heart’s muscle tissue);
damage due to myocardial infarction;
arterial hypertension (high blood pressure);
congenital heart disease (cardiac malformations already present at birth);
myocarditis (an infection of the heart tissue);
complications following heart surgery;
hypothyroidism (slow thyroid activity);
electrolyte imbalance, which is necessary for the correct generation and propagation of electrical impulses;
obstructive sleep apnoea (repeated interruption of breathing during sleeping hours);
inflammatory diseases (rheumatic fever, lupus, etc.);
haemochromatosis (excessive iron accumulation in organs);
medication.

Another possible cause, not directly linked to the heart’s electrical activity, may be the abuse of certain drugs.

With regard to neonatal bradycardia, on the other hand, the main cause seems to be related to hypoxia, i.e. a lack of oxygen due to the infant’s respiratory difficulties.

Diagnosis of bradycardia

Only a doctor can determine whether a patient has bradycardia, check the possible causes and understand how serious the problem is.

In order to confirm or exclude the diagnosis of bradycardia, the specialist may prescribe one or more diagnostic tests depending on the case in question.

Here are some tests that may be prescribed for the patient in order to make a correct diagnosis:

Electrocardiogram (ECG): a diagnostic test that uses a specific instrument to record and graphically reproduce the heart’s electrical activity;
Exercise ECG: monitoring of the heart rate during physical activity. The patient is asked to walk on a treadmill or pedal on an exercise bike to assess changes in heart rate during physical activity;
Dynamic ECG according to Holter: a diagnostic methodology in which the electrical activity of the heart is monitored for an interval of time generally between 24 and 72 hours;
Tilt test: a provocative instrumental test that evaluates heart rate and blood pressure behaviour. Under close monitoring, the patient is placed on a couch that is initially placed horizontally and then rotated into a vertical position. This test is the gold standard for investigating the cause of repeated fainting;
Electrophysiological study (SEF): an invasive test that assesses the electrical properties of the heart and its susceptibility to arrhythmias of various kinds;
Sleep monitoring: a test that may be prescribed if the cardiologist considers that bradycardia is linked to episodes of apnoea (cessation of breathing) that occur during sleep.

It may also be necessary to prescribe specific blood tests to assess the presence of any pathologies not directly linked to cardiac activity such as hypothyroidism, the presence of any infections or electrolyte alterations that may be potentially responsible for the onset of bradycardia.

Sometimes, for the recording of sporadic events, the doctor may prescribe the patient the use of special recording devices that can monitor cardiac activity even for months.

The devices usually prescribed for monitoring are the external Loop recorder or the implantable Loop recorder.

When the patient experiences the typical disturbances that are associated with episodes of bradycardia, he or she must press the record button on the device, which will store the electrocardiographic signal in the period before the command and in the period after.

In this way, the doctor can study the heart rhythm during the onset of the disturbances.

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Treatment

Once the diagnosis has been made, the therapy that will be established by the doctor together with his patient will be based on the assessment of the type of problem leading to the alteration in cardiac activity, the severity of the symptoms and the underlying cause.

In cases of functional bradycardia, remember, no intervention is necessary as this type of arrhythmia is generally asymptomatic.

When, however, we are dealing with pathological bradycardia, it becomes necessary to administer the correct therapy.

Let us see what the possible treatments are, depending on the case.

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Treatment of the disease responsible for bradycardia

If the bradycardia is caused by a disease that is not directly linked to cardiac activity, such as hypothyroidism or obstructive sleep apnoea, it is generally sufficient to intervene on the pathology to resolve the bradycardia as well.

Discontinuing or replacing drugs that cause bradycardia

If certain drugs taken by the patient are causing episodes of bradycardia, the cardiologist, after careful analysis, may replace them to improve the patient’s condition.

It is also possible that the specialist may decide to lower the doses of the drugs in question.

In cases where this is not possible, the patient may be advised to have a pacemaker implanted.

Implantation of a permanent pacemaker

Surgery to implant a pacemaker may be necessary if the condition of bradycardia is caused by severe alterations in the transmission of the heart’s electrical impulses.

Once the surgery is performed, it is the pacemaker’s job to generate the electrical impulses needed to regulate the heart rate.

Some of these devices are also capable of recording information on cardiac activity that will be useful to the cardiologist in checking the proper functioning of the device.

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Emergency pharmacological treatment

In cases where the patient presents with severe bradycardia that has suddenly appeared, it will be necessary to carry out pharmacological treatment with catecholamines and sympathomimetic drugs to be administered in an emergency in a hospital or medical clinic.

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