The heart muscle is responsible for circulating blood throughout the body. When the heart does not operate as it is supposed to and develops an abnormally slow heart rate that is less than 60 beats per minute, the condition is known as bradycardia.
Bradycardia can be life threatening if the heart is unable to maintain a rate that pumps enough oxygen-rich blood throughout the body.
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
Diagnosis of bradycardia will generally begin with the physician taking a medical history and performing a physical exam. During the physical exam, the physician will listen to the patient's heart to detect if there is an abnormal heart rate. Patients are also asked for a detailed description of their symptoms. Symptoms may suggest the presence of bradycardia. If so, or if an abnormal heart rate is observed, the physician may order an electrocardiogram to confirm it. An EKG is a painless procedure that records the electrical activity of the heart.
If the abnormal heart rhythm is intermittent, the patient may need to wear a Holter monitor. This portable device allows the medical team to observe the patient's heart over a longer period of time and helps diagnose the condition if the abnormal rhythm happens while the patient is not at the hospital.
Depending on the patient's symptoms and the results of the other diagnostic tests, an echocardiom may be prescribed. This noninvasive procedure uses a machine called a transducer that bounces sound waves off the heart and back into the transducer. These echoes are then translated into visual images.
Other diagnostics may include the tilt table test and exercise test to look at the relationship between the patient’s heart rate and physical position (sitting or standing), as well as how exercise affects the heart rate. Electrophysiology studies may also be used to look at the heart's electrical system.
Treatment of bradycardia will vary from one patient to another and will depend on the type, severity and cause of their condition. In some cases, when the abnormal heart rhythm is caused by an underlying condition, such as hypothyroidism, treatment may focus on addressing that underlying condition. Treatment options may include adjusting current medication and sometimes surgery.
Because medications that are used to control blood pressure and other conditions — such as beta blockers or calcium channel blockers — may cause bradycardia, a patient's medications may be adjusted.
In some cases, surgery may be needed to implant a pacemaker if other treatment options do not adequately address the condition.
The knowledgeable and highly trained staff at the Cedars-Sinai Heart Institute will work with each patient to determine the best treatment option.