Bradycardia - Lowered Heart Rate
Bradycardia means a slow heart; less than 60 beats per minute. Normal heart rate is between 60 and 90 beats per minute. A heartbeat is cause by an electrical impulse which forms in the sinoatrial node in the right atrium. From there, the impulse spreads along specialized cells inside the heart muscle. These cells form the so-called cardiac conduction system. The sinoatrial node determines the rate of the heartbeats. From there, the impulse spreads to the muscular walls of the atria, and with the help of the cardiac conduction system, to the ventricles as well. Heart rate is also influenced by the nervous system and hormones; together they react to changes that the body is going through and the heart rate slows accordingly up until bradycardia develops.
Causes of Bradycardia
Bradycardia is a symptom that can be a part of many conditions, but can also be a result of certain chemical substances. Bradycardia can develop from a number of causes.
- One cause of bradycardia is a disorder of the sinus node, causing electrical impulses that are too slow. This is a result of either direct damage to the cardiac cells, or malfunction of the nervous system's regulatory system and hormones that regulate the pumping of the heart according to the body's needs. Bradycardia from these causes leads to a lack of thyroid hormones in the blood. Their role in to increase the oxygen supply to the cells (among other things), and therefore increase heart rate.
- Bradycardia can also be cause by medication. Patients with a heart condition take medication to lower heart rate, thus lowering its effort as well. These include beta-blockers which slow down the heart contractions and therefore conserve the heart muscle. Other medications that can cause bradycardia are antiarrhythmics, medication to treat heart rhythm disorders.
- Causes of bradycardia can also lie in the faulty conduction of the impulse. If the sinus node is working properly but the spreading of the signal to the other cardiac cells is impaired, the signal is blocked. This condition occurs with disordered electrical signals such as an AV block or in relation to serious heart conditions such as myocardial infarction (heart attack) or inflammation of the heart.
- Bradycardia is not only a symptom. In young individuals, especially in athletes, it is a sign of a healthy and strong heart of a trained individual. This is compensation for increased stress on the body, and the heart is strong enough to pump the necessary amount of blood to the body at a lower rate.
- Bradycardia tends to be present in individuals with thyroid conditions, increased intracranial pressure, inflammation and infection.
Manifestations of Bradycardia
Bradycardia is manifested by shortness of breath, increased fatigue, and an intolerance of increased physical stress. This is because with a lowered heart rate, muscles and organs are not receiving enough oxygenated blood. In the event of insufficient blood supply to the brain, dizziness and loss of consciousness can follow. Some patients, however, do not notice any symptoms. Severe bradycardia begins with a heart rate under 40 beats per minute.
It is not difficult to diagnose bradycardia; the simple examination of the peripheral pulse with the finger placed on the wrist can detect a decreased heart rate. During a physical examination with a stethoscope, the slow contractions of the heart can be heard. To confirm a diagnosis of bradycardia, an EKG (electrocardiogram) can be used. This is a painless examination where with the help of electrodes placed on the wrist and chest, the electric activity of the heart is recorded and "written" on paper in the form of curves on a graph.
Bradycardia can be a symptom of a serious illness, but it does not have to be. It may develop independently, or together with other disorders, therefore it is important to identify the cause and treat it accordingly. When taking the medical history it is important to find out what medications the patient is taking. If the patient is on beta-blockers, these should be discontinued and substituted with different medications. In the case that the cause of bradycardia is a thyroid disorder, the disorder should be treated with medication. With a faulty conduction system, the only long-term treatment option is to implant a pacemaker; a device that is implanted under the skin and who's electrodes extend all the way to the heart. A pacemaker is able to transmit electrical impulses in order to stimulate a heartbeat.