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You already know about tachycardia or increased heart rate. People can also suffer from decreased heart rate or bradycardia. And the causes of it might range from damage to the heart muscles to problems in the electrical system of the heart. While the normal heart rate is between 60 - 90 beats per minute, people suffering from bradycardia might have a heart rate as low as 35 - 40 beats per minute. In some people, low heart rate is considered as normal. Our expert Dr Santosh Kumar Dora, Consultant cardiology and electrophysiology, Asian Heart Institute, Mumbai, reveals the common causes of bradycardia.
1. Sinus bradycardia: In this condition, the AV node develops a disease, which causes difficulty in the conduction of the electrical impulse for pumping of the blood. This causes the heart rate to fall to 45 beats per minute. In this, the electrical signal passes through the upper chamber but misses the beat at the lower chamber due to the damage of the AV node. This causes alternate beats such that every second impulse that passes through the lower chamber causes a heart beat. Also, if the upper chamber functions properly but the lower chamber fails to get the electrical signal, then the overall heart rate decreases, indicating bradycardia.
2. AV node disease: If the AV node is not conducting at all but the upper chamber shows normal heart rate of 80 beats per minute and the lower heart chamber shows only 40 beats per minute, then the overall heart rate is low. Also, if there is any damage to the AV node, but some parts of the lower chamber muscle have the capability to beat, even then it causes low heart rate.
3. Complete heart block: This condition can result from any damage to the heart muscles or blockage of the arteries due to heart attack or coronary heart disease. In some cases, if the lower chamber of the heart fails to beat properly due to a problem with the AV node, it can lead to complete heart block, which could be life-threatening.
4. Intracranial tumour: Although rare, intracranial tumour might also lead to decreased heart rate. If the pressure inside the brain increases due to the cancerous cells, then it can lower the pressure on the heart rate, leading to bradycardia.
5. Hypothyroidism: Yes, just like high thyroid level can cause tachycardia, low thyroid levels are known to cause bradycardia. It is due to the influence of the thyroid hormones on the sinus node which causes the lower chamber to beat at a lower rate of 40 - 50 beats per minute. And the treatment of bradycardia in such a case, depends on treating hypothyroidism.
6. Medications: In some cases, medications prescribed to treat heart disease or those to lower the blood pressure like beta-blockers and antiarrhythmics can cause a decreased heart rate. Moreover, the risk increases with age as the heart muscles become weak with age.
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