A condition when the heart beats become slower than 60 beats per minute, it is medically described as bradycardia or Brady-arrhythmia.
Slower pulse rate is normal for people at the time of sleeping. Athletes undergoing regular training also have lower heart rates between 40 to 60 beats per minute.
Causes of Bradycardia Bradycardia may be present due to certain diseases or people taking medications for slowing down heart rates ( beta-blockers or calcium channel blockers).
Bradycardia is common in elderly people. It may also be seen in infants having congenital heart diseases. The following causes may be responsible for bradycardia:
- Degeneration of heart tissue due to aging
- Damage to heart tissues resulting from heart diseases or heart attacks
- congenital heart defects, defects present at the time of birth
- Mycocarditis or Infection of heart tissue (myocarditis)
- Complications arising after heart surgery
- Hypothyroidism, under-functioning of thyroid gland
- Imbalance of minerals and electrolytes that cause disturbance in conduction of electrical impulses
- Inflammatory disease, such as rheumatic fever or lupus
- Obstructive sleep apnea which is characterized by the repeated disruptions in breathing causing sleep disturbances
- Hemochromatosis, a buildup of iron in different organs
- Medications used for the treatment heart rhythm disorders like high blood pressure
Sinus bradycardia This condition results when the faulty impulse generation in the SA node causes the heart rate to decrease less than 60 beats /minute. Drugs like beta-blockers and calcium-channel blockers are known to be the main causes of sinus bradycardia. Sometimes the impaired impulse conduction to the atrial muscles may be the cause of sinus bradycardia.
Ventricular Bradycardia (VB) due to Hyperkelemia The mineral potassium is very important for regulating the function of the heart muscles, its other cells and nerves. Contractions of the muscles are dependent on the concentration of the potassium in the cells. If the level rises too much the heart beat may become erratic. The change in heart rhythm can sometime become very serious. The hyperkelemia can result in bardycardia. Sometimes it may cause the heart block or ventricular fibrillation.
Heart block (atrioventricular block) Bradycardia may also occur if the electrical signals travelling through the atria are not transmitted to the ventricles. This blockage in the way of electrical signal may occur due to failure of their transmission in the AV node, the bundle of His. It may also result from when the travelling of impulses to the left and right branches of ventricles is affected.
Depending upon the degree to which the signals from the atria reach the ventricles, these are classified in the following categories:
First-degree heart block In this mildest form of heart block, almost all electrical signals from the atria reach the ventricles. However, the rate of signal conduction is slowed down slightly. No treatment is required in such cases if there is no other abnormality in the heart.
Second-degree heart block Not all electric impulses reach the ventricles because some beats getting dropped in the way resulting in a slow and an irregular rhythm.
Third-degree (complete) heart block In this case none of the electrical impulses generated in the atria reache the ventricles. As a consequence of this, the bundle of His or other ventricular tissue starts functioning as an altenate pacemaker for the ventricles. This results in slowing of the heart beats.
Bundle branch block If an electrical signal is interrupted at the end of pathway, i.e. in the right or left bundle branches it is called a bundle branch block. If both the branches are affected, the block can be very serious.
Symptoms of Bradycardia People having bradycardia may show the following symptoms:
- Shortness of breath
- Feeling of dizziness or lightheadedness
- Syncope or fainting
- Confusion and difficulty in concentrating
- Chest pain
- Difficulty in doing exercises
- Difficulty in sleeping
Diagnosis and Treatment of Bradycardia Diagnosis of bradycardia is rather straightforward it can be detected by decrease pulse rate. This can be confirmed by the EKG. No treatment is necessary if the symptoms are not observed. Medications that increase heartbeat can be given. If fainting or serious symptoms persist despite medication, a permanent pacemaker may need to be implanted. A pacemaker is mostly installed in case of complete atrioventricular (A-V) block and brady arrhythmia occurring as a result of sinus node dysfunction.