Definition: Bradycardia is strictly defined in adults as a pulse rate less than 60 beats per minute (ppm).
However, few individuals are symptomatic unless the heart rate is less than 50 ppm.
The most resistant athletes can have a resting heart rate in the 30s very low without the need of any intervention with anticholinergics, isoprenaline, adrenaline (epinephrine), chest compressions or the insertion of an emergency pacemaker.
The normal heart rate for adults has been historically considered 60 to 100 beats per minute, sinus bradycardia being defined as a sinus rhythm with a frequency lower than 60 beats per minute.
However, the “normal” heart rate is, in part, the result of the complex interaction between the sympathetic and parasympathetic nervous systems.
It is affected by numerous factors and varies in part with age and physical conditioning.
Physiologically, the heart rate can vary in normal adults from 40 ppm to 180 ppm. However, a relative bradycardia may be greater than 60 ppm if this rate is too slow for the patient’s hemodynamic requirements.
Children tend to have a higher pulse rate at rest than adults and in general, the smaller they are, the faster the heart rate.
Therefore, in a newborn, bradycardia can be defined as a rate below 100 ppm.
Fainting can occur with sinus bradycardia if the heart slows down further. This can occur when the vagus nerve sends a signal to the heart that suddenly lowers the heart rate.
Normal sinus rhythm (RSN) is the characteristic rhythm of the healthy human heart.
It is considered to be present in adults if the heart rate is between 60 and 100 beats per minute, P waves on the electrocardiogram are normal (unless there is concurrent atrial disease) and the rate does not vary significantly.
By conventional definition, bradycardia requires that the heart rate be less than 60 beats per minute with P waves of normal appearance on the surface ECG.
As such, sinus bradycardia is usually considered as sinus rhythm that occurs at a rate of less than 60 beats per minute, although a professional society has advocated a rate of less than 50 beats per minute.
The rate at which a patient is labeled as a bradycardia patient is somewhat dependent on age as the heart rate decreases during early childhood, but tends to increase normally with age.
The heart’s job is to pump blood around the body bringing oxygen and nutrients to organs, muscles and tissues, and transporting wastes such as carbon dioxide to the lungs for expiration.
The cardiovascular system is under the control of the nervous system that increases and decreases the workload of the heart depending on the requirements of the body.
Therefore, if a person is involved in the exercise, their muscles and organs require more blood and oxygen to function, so that the heart and lungs go faster.
If a person is resting or sleeping, then the requirements of the body fall considerably and the heart and lungs slow down.
Anything below 60ppm is known as bradycardia. Bradycardia is not a changed rhythm, it’s just slowed normal sinus rhythm.
The causes of pathological sinus bradycardia include:
- Medications (negative chronotropic).
- Beta blockers.
- Calcium channel blockers.
- Pain (may also cause tachycardia)
- Reflection of Cushing (systemic response to elevated intracranial pressure, which leads to increased pulse pressure, irregular breathing and bradycardia).
- Acute myocardial infarction.
- Sick sinus syndrome.
- Pericardial tamponade.
- Renal insufficiency.
- Severe obstructive jaundice.
- Pleural or peritoneal stimulation.
- Rarely, infection (for example, typhoid fever can cause relative bradycardia).
There are no usual guidelines to avoid bradycardia. When this is the consequence of a side effect of a treatment, it can be prevented by changing the drug or reducing its dose.
In many of the situations, the bradycardia of healthy athletes does not need to be treated. In most cases, it does not require treatment unless you have symptoms as a clear result of a slow heartbeat.
The following are the conditions that produce bradycardia that requires treatment:
Cardiac arrhythmias resulting from sinus node dysfunction. In people with frequent and severe symptomatology of sinus node dysfunction, the main treatment is usually a pacemaker, an apparatus that generates electrical impulses to regulate the heartbeat.
Cardiac arrhythmias resulting from AV node problems. In people with irregularities in the AV node, the passage of heartbeat signals can be blocked in different ways.
Some patients with less severe degrees of AV block do not need treatment.
Others may simply be monitored with frequent EKGs, especially if they do not have any symptoms and have a heart rate that is adequate for their daily activities.
People with the most severe form of AV block (called a third-degree AV block) can be treated with a permanent two-chamber pacemaker, a pacemaker with an electrode in the atrium and one in the ventricle.
In well-trained athletes with bradycardia, the slow heart rate is a sign of overall good health. In other people with bradycardia, the perspective depends on the underlying disorder.
The future of patients with hypothyroidism can be positive, all because the treatment with hormones for the thyroid relieves the bradycardia and other symptoms related to hormone level in the body.
For some older patients, hormone doses may need to be increased slightly after several weeks to prevent heart strain.
At one time, the future for people with third-degree AV block was poor, with half of the patients dying within a year of diagnosis.
Now, however, the installation of permanent pacemakers has increased the chances of a good future for many people with cardiac arrhythmias .