Introduction

Bradycardia is a type of arrhythmia where someone’s heart rate is slower than what is normal. Many factors can potentially cause bradycardia including sleep disorders, particularly sleep-disordered breathing (SDB). 

This article explains bradycardia, its causes, and how it is diagnosed. We will also explore what sleep disorders are and their different types. We will also look at sleep apnoea, an SBD commonly linked to bradycardia. and the possible treatment options for this.

Bradycardia

What is bradycardia?

Most people’s resting heart rate is somewhere between 60 to 100 beats per minute. When someone has bradycardia, their heart rate is lower than 60 beats per minute. 

A slow heart rate means low blood flow and therefore less oxygen supply to the body. This would leave the person feeling weak, dizzy, tired, and faint. Low blood flow to the brain would also result in feeling confused, potentially along with other symptoms.¹ 

Causes and diagnosis

Bradycardia is often symptomatic. It is important to find out what is causing bradycardia. It is done by first looking into the person’s medical history and talking to the patient or caregiver(s) to identify risk factors and potential symptoms.

For example, bradycardia could be a case of a side effect of some medication that someone is taking. Perhaps, they have some other contributing health condition. Accurate identification of the cause of bradycardia can help to inform effective treatment options.

Next, t an electrocardiogram (ECG) t is evaluated for any potential structural issues relating to heart disease.  Additional testing methods may also be used, such as cardiac magnetic resonance imaging (MRI), a cardiac CT scan, transoesophageal echocardiography, and nuclear imaging.¹

These advanced methods are not used regularly in diagnosis; however, the clinician decides based on the individual’s history and presentation whether any of these techniques should be used. 

Lab tests may also be used for differential diagnosis (when tests that identify biomarkers are used to rule out some diagnoses because there are symptoms that show up in multiple conditions). These tests help healthcare professionals to determine which is the most likely cause of the symptoms.¹ 

If someone has nocturnal bradycardia, the clinician will usually assess for sleep apnoea, as this is quite a common cause of bradycardia experienced during the night.¹ 

Sleep disorders

The likelihood of developing a sleep disorder increases as people age. There are many reasons why this may be:

• Poor mental health due to stress relating to finances, work, health, family, and other personal issues 
• Substance misuse
• Other health changes, such as weight changes. (Sleep apnea is more likely to occur in people who are overweight)
• General changes in sleeping patterns.² For example, some people may be working night shifts, which entails disruption and change to their normal sleep routine

Less exercise and having medical illnesses could also contribute to the development of sleeping disorders.² It is important for healthcare providers to be able to accurately identify these factors so that the sleep disorder can be treated most appropriately and effectively.  This is crucial for disorders such as sleep apnoea which, if left untreated, increases the risk of developing other chronic health problems.

Types of sleep disorders

There are many different types of sleep-related disorders. including: 

• Circadian rhythm sleep-wake disorder 
• Sleep-related movement disorder 
• Insomnia
• Sleep-disordered breathing

The last one is often associated with arrhythmias (irregular heartbeat).² In fact, around 50% of people who have sleep-disordered breathing are also found to have some type of arrhythmia.³

Conditions that come under the category of sleep breathing disorders (SBD) include: 

• Hypoxemia disorders
• Nonobstructive hyperventilation
• Sleep apnoea
• Hypopnoea

Apnoea is when breathing completely stops, whilst hypopnea is a condition of reduced airflow by approximately 30%. For someone to be diagnosed with an SBD, the apnea-hypopnea index (AHI) (a measure of how many times apnea or hypopnea occurs in each hour of sleep) has to be greater than 5.²

Usually, an oxygen sleep test that can be done at home is used to measure AHI and make a diagnosis. However, polysomnography may be used if the healthcare team believes the sleep test does not give enough information. This is not a diagnostic tool that is routinely used as it usually requires an inpatient overnight stay.²

Sleep apnoea

Apnoea is defined as when no air is breathed in for at least 10 seconds. Sleep apnoea can be categorised as central sleep apnoea or obstructive sleep apnoea. In central sleep apnea, the breathing rhythm generated by the pontomedullary pacemaker neural networks is temporarily reduced.

In obstructive sleep apnea (OSA), there is a complete occlusion, or blockage, of the upper airway. This means that the airflow is absent and the tongue falls backwards.⁴ However, the body’s survival reflex will kick in and wake the person, so they start breathing again. This is why people with OSA often suddenly wake up gasping, or feeling as though they are choking.

Some factors that may contribute to upper airway obstruction include enlarged tonsils, decreased lung volume, upper airway oedema (swelling), altered craniofacial structures, and obesity. As obesity is a major risk factor for sleep apnea, maintaining a healthy weight (or for those who are overweight, losing weight) would reduce the risk of obstructive sleep apnea and its associated complications.

Around 60-80% of OSA patients are obese. and may have additional factors unrelated to their weight that trigger, or affect, OSA. For example, dysfunction in the upper airway dilator, prematurely waking up from sleep and increased chemosensitivity.⁴ Identifying these factors and ensuring that they receive appropriate treatment would tailor their care more to their individual needs.

Bradycardia and sleep apnoea

Hypoxemia (low concentration of oxygen in the blood) caused by sleep apnoea leads to an increase in bradycardic rhythm disorders, which is the main cause of sleep apnoea fatalities.⁵ For individuals who suffer from bradycardia with sleep apnoea, polysomnography is the best method for monitoring them during sleep and observing patterns that may help determine which treatment is best for them.¹

Pacemakers are usually used to treat bradycardia; however, this is not always the best treatment option. Although they are helpful for some people, pacemakers also come with some disadvantages. Many people also dislike the thought of having an electric device permanently implanted in their bodies.

Therefore, where possible, healthcare providers try to postpone inserting a pacemaker (or where possible, avoid it altogether, and look for alternative treatment options. Treating the cause of bradycardia rather than using a pacemaker to treat bradycardia itself is the preferred and more appropriate option for most people.³

Treating sleep apnoea is most useful for people who only have nocturnal bradycardia (almost 90% improvement seen). Pacemakers are rarely needed for people with nocturnal bradycardia alone.¹

Using treatment methods such as upper airway surgery and continuous positive airway pressure (CPAP) to treat sleep apnoea usually stops bradycardia in these people as well. Losing weight is also shown to be effective, however, this can be difficult for patients to do.⁶ There are many healthcare professionals such as dieticians, clinical psychologists, and other therapists who may be able to support people in doing so.

Some studies have shown that supplementing oxygen is an effective method of treating bradycardia caused by sleep apnoea, although more research is still required for this.⁵

A case study of a patient found that theophylline (a treatment usually used for non-sleep apnoea-related bradycardia) was found to be an effective alternative to current treatments for sleep apnoea patients. More studies are needed to study the risks and benefits of using theophylline in people with sleep apnea as there is currently very little research regarding this.⁶

Summary

To summarise, bradycardia is quite common amongst individuals with sleep apnoea and is what puts those with untreated sleep apnoea at risk of life-threatening complications. While previous, treatment focused on treating bradycardia, research has helped us to understand that treating its cause (which is often sleep apnoea) is a far more effective approach. 

This treatment strategy for bradycardia also avoids unnecessary use of pacemakers, which many people and clinicians prefer to avoid unless there is a clear need for one to be implanted. Leading a healthy lifestyle also plays a key role in the prevention and treatment of sleep apnoea-related bradycardia.