Bradycardia is an arrhythmia characterised by a slow heart rate, usually 60 beats per minute. When the heart rate is too low, the heart may be unable to meet the metabolic needs, such as cardiac output or blood pressure of a person, and cause them to feel faint, dizzy, or collapse. In some people, slow heart rates may be normal during periods of rest, sleep, or if a person is very physically fit, but generally, slow heart rates may limit activity and patients may exhibit symptoms.1
There are many causes for bradycardia. A common cause can be due to abnormalities in the electrical pathway from the sinoatrial (SA) node to the ventricles, impacting the heart’s ability to receive the stimulation from the SA node and adequately “beat.” Under normal circumstances, this impulse starts in the SA node, conducts through the septum via the AV node, and continues to the ventricles. If there is a disruption to the normal electrical conduction, the heart rate may be slowed or in some cases become non-existent.
Additionally, some patients may be diagnosed with a condition called ‘heart block’, whereby the electrical stimulus from the SA node is not conducted to the ventricles or is “blocked” due to conduction issues with the AV node and in turn leading to slow heart rates.
Below is an illustration of normal cardiac electrical conduction.
These classifications are:
Other causes of bradycardia may be: