Causes and Risk Factors of Cardiac Arrhythmias

The cardiac electrical system controls the heart rate and makes sure that the various chambers of the heart contract in a completely coordinated way. These tasks are complex and intricate—for instance, when the heart’s electrical signal travels from the atria (upper chambers) to the ventricles (lower chambers), a difference in timing of just a tenth of a second can make a big impact on the efficiency of the heartbeat.

With a system that requires this level of precision and complexity, there are bound to be any number of ways it can be disrupted or disordered. So it should not be a surprise that cardiac arrhythmias, or heart rhythm problems, can result from a host of underlying causes.

This means, among other things, that a critical step in evaluating and treating a person who has a cardiac arrhythmia is to identify, as precisely as possible, the underlying cause.

This article explores the major categories of issues that can cause heart arrhythmias.

Autonomic Imbalance

The autonomic nervous system, in general, controls the bodily functions that we normally don’t consciously think about, like breathing, sweating, and heart rate.

It includes the parasympathetic nervous system, which is associated with rest and digestion, and the sympathetic nervous system, which is associated with the fight-or-flight stress response.

The parasympathetic nervous system involves the vagus nerve, which can slow heart rate. Oppositely, when the sympathetic nervous system is activated, hormones such as adrenaline are released and increase heart rate. Therefore, when there is an imbalance in the autonomic nervous system it can affect the heart.

Vagal overstimulation and bradycardias may result from an episode of vomiting, severe constipation, or urinary obstruction (blockage of flow of urine).

Excess sympathetic response and too much release of adrenaline from acute stress or sudden fright may lead to tachycardias.

These arrhythmias should go away when the autonomic imbalance is resolved. However, treatment options, particularly those related to surgical modification of the autonomic nervous system, are rather limited.

Heart Disease

Any type of heart disease can affect the heart’s electrical system and cause cardiac arrhythmias. The arrhythmias that result from heart disease can span the entire gamut of cardiac arrhythmias—from entirely benign premature atrial complexes, or extra beats in the upper chambers, to extremely dangerous ventricular fibrillation, or disordered electrical activity in the heart's lower chambers.

However, structural heart disease, specifically ischemic heart disease, also called coronary artery disease (CAD), is the most common cause of truly dangerous rhythm disturbances that can cause sudden death. Ischemic heart disease is a narrowing of the arteries that restricts blood flow to the heart.

The risk of sudden death is high in people who have had heart attacks or heart failure, but steps can be taken to substantially reduce that risk. This often includes medications.

Drugs

Especially in people who may have an underlying issue that makes them prone to developing cardiac arrhythmias (for instance, because of underlying heart disease or a genetic condition), various drugs can be the triggering factor that makes an arrhythmia actually occur.

The list of drugs that can trigger arrhythmias is very large, and even includes medications taken to treat arrhythmias. If your healthcare provider recommends that you start an antiarrhythmic medication, some monitoring may be needed, particularly in first few days you are taking it.

Genetic Disorders

Since 2000, researchers have identified several genetic mutations that now explain many previously mysterious cardiac arrhythmias. Here is a list of the most common cardiac arrhythmias now known to be due to genetic conditions:

• Long QT syndrome affects the electrical system of the heart and can cause a fast and chaotic heart rhythm.
• Brugada syndrome is a condition that can cause dangerous ventricular fibrillation during sleep.
• Catecholaminergic polymorphic ventricular tachycardia is a condition in which episodes of ventricular tachycardia are triggered when the heart rate increases with exercise or stress.
• Progressive familial heart block is a slowing or interrupting of electrical signals between the chambers of the heart.
• An inherited bundle branch block affects the bundles of nerves that electrically stimulate the heart.
• Sick sinus syndrome occurs when the sinus node is diseased enough to cause a slow heart rate. When it occurs in young people, the cause may be genetic.
• Familial atrial fibrillation is an inherited irregular heart rhythm in the upper chambers.

While more and more arrhythmias are now known to be due to genes, the genetics of cardiac arrhythmias tend to be quite complex. Genetic testing for cardiac arrhythmias is sometimes recommended depending on the exact nature of the arrhythmia, but it is always an individualized decision about whether or not to be tested.

For close family members of people who have had long QT syndrome, Brugada syndrome, or arrhythmias associated with hypertrophic cardiomyopathy (a thickening of the heart that makes pumping more difficult), genetic testing may be of value in deciding whether treatments should be considered.

Aging

For reasons that are not clear, aging is itself associated with a form of diffuse fibrosis (scarring) within the cardiac muscle that may lead to sick sinus syndrome, heart block, or atrial fibrillation. The cardiac fibrosis of aging is the most common reason for elderly people to require a pacemaker.

In addition, the risk of heart disease increases with age.

Electrolyte or Metabolic Disorders

Various disorders of electrolytes, and of the acidity of the blood, can trigger cardiac arrhythmias. These disorders are most commonly seen in people who have kidney disease or diabetes, are taking certain drugs (especially diuretics), are dehydrated, or are acutely ill.

The electrolyte and metabolic disorders that most prominently cause arrhythmias include:

• Hypokalemia (low potassium levels)
• Hyperkalemia (high potassium levels)
• Hypomagnesemia (low magnesium levels)
• Hypocalcemia (low calcium levels)
• Acidosis (blood too acidic)
• Alkalosis (blood too alkaline)

Anesthesia

Cardiac arrhythmias are quite common in people who are undergoing general anesthesia, or the use of medications to make you unconscious during surgery. While most of these arrhythmias are easily managed, some can become dangerous and difficult to treat.

Anesthesia is associated with cardiac arrhythmias for several reasons, including:

• The anesthetic agents themselves
• Electrolyte and metabolic disorders that may occur during anesthesia
• Fluctuations in blood pressure that may occur during anesthesia
• Autonomic imbalances can occur during anesthesia
• Cardiovascular damage during surgery, especially heart surgery

Cardiac Trauma

Sometimes, arrythmias occur after cardiac or non-cardiac chest surgeries. The exact reason for this is unknown.

Rarely, blunt chest trauma can produce arrhythmias.

Idiopathic

A cardiac arrhythmia is deemed to be idiopathic if, after a thorough investigation, the underlying cause remains unknown.

In recent years, many arrhythmias that used to be classified as idiopathic are now known to be genetic in origin. 

Additional Risk Factors

In addition to all the issues listed above, risk factors for arrhythmias can also include a family history of arrhythmias or cardiac arrest (abrupt loss of heart function and consciousness) or sudden death at a young age. If this is the case, your healthcare provider may recommend heart screening options or genetic testing to help identify any unknown heart conditions.

Additional risk factors include medical emergencies such as:

• Severe respiratory illness or respiratory failure
• Infections
• Acute kidney injury
• Cardiothoracic surgery (surgery on organs within the chest, such as heart or lungs)

One of the best way to minimize your risk of developing cardiac arrhythmias is to do everything you can to reduce your risk of risk for heart disease since ischemia often results from heart disease and can lead to arrhythmia. This includes lifestyle factors such as being active and not smoking or quitting smoking.

Summary

There are many potential causes of cardiac arrhythmias, or heart rhythm problems, but among the most common are nervous system imbalances, heart disease, or genetic conditions.

If you have a family history of arrhythmias, your healthcare provider may suggest heart screenings or genetic tests in some cases.