The main symptom of bradycardia is a heart rate below 60 beats per minute. This abnormally low heart rate can cause the brain and other organs to become oxygen-deprived, which can lead to symptoms such as:
- Shortness of breath
- Chest pain
- Memory difficulties
- Quickly tiring during physical activity
In rare cases when bradycardia goes undiagnosed for an extended period of time, the following complications can occur:
Causes and Risk Factors
Bradycardia is caused by a disruption in the heart's electrical system that controls the heart rate. This disruption can come from four possible causes:
- Sinoatrial node problems - the sinoatrial node, often referred to as the sinus node, is considered to be the natural pacemaker of the heart. This group of cells triggers electrical impulses to the heart, causing it to contract. When this node isn’t working properly it can trigger much slower electrical impulses causing the heart to beat slower.
- Dysfunctional conduction pathways - electrical impulses travel in the heart via conduction pathways. When these pathways do not work properly, the heart rate is affected — a condition often referred to as an atrioventricular block or heart block, of which there are three forms:
- First degree - all of the electrical signals from the atria reach the ventricles, although they are transmitted slower than normal.
- Second degree - only some of the electrical signals from the atria reach the ventricles. When a signal does not reach the ventricles, the heart beat it was meant to trigger does not occur.
- Third degree - none of the electrical impulses make it from the atria to the ventricles. When this happens, a natural pacemaker in the ventricles may step in to take over regulating the heartbeat, although at a rate that is slower than normal.
Other risk factors that may contribute to a disruption of the electrical impulses associated with bradycardia include:
- Congenital heart disease
- Infection of the heart tissue
- Heart surgery
- Hypothyroidism or other metabolic condition
- Damage caused by a heart attack or heart disease
- Electrolyte imbalance in the blood
- Obstructive sleep apnea
- Inflammatory diseases (rheumatic fever or lupus)
- Certain medications
Bradycardia can affect patients of all ages, genders and ethnicities. However, older patients are at an increased risk as well as patients with the following risk factors:
- High blood pressure (hypertension)
- Heavy alcohol use
- Use of recreational drugs
- Psychological stress or anxiety