Calcium channel blockers are drugs that are often prescribed to treat certain cardiovascular conditions, such as high blood pressure. High blood pressure can be dangerous because it puts extra strain on the heart and increases a person's risk of developing atherosclerosis. Although these medications are safe for most people, calcium channel blockers can cause some side effects, including a slowed heart rate, or bradycardia.
Calcium Channel Blocker Mechanism
Calcium is needed for muscles to contract. Calcium enters muscle cells via special proteins called calcium channels. Calcium channel blockers keep calcium from entering muscle cells in blood vessels, which makes it harder for these muscle cells to contract, explains MayoClinic.com. This can help dilate blood vessels, which helps lower blood pressure by decreasing the blood vessels' resistance to flowing blood.
Calcium Channel Blockers and Bradycardia
Calcium channel blockers also work on the calcium channels in the heart. Some calcium channel blockers, such as verapamil, actually work better on the heart's calcium channels than on those in vascular tissue. This means they can help decrease the intensity and speed of a patient's heartbeat. On the other hand, by making it harder for calcium to get into heart muscle cells, patients taking calcium channel blockers can develop a slow heart rate, which is also known as bradycardia.
Symptoms
In cases of mild bradycardia, patients may feel no symptoms at all, notes the Merck Manual of Health and Aging. If the heart rate dips below 40 beats per minute, patients may feel tired or fatigued as muscles and other tissues throughout the body may not get enough oxygen. If the heart rate becomes severely depressed, the brain may not get enough oxygen, causing the patient to faint.
Diagnosis
Bradycardia can usually be diagnosed by measuring the patient's pulse. A test known as an electrocardiogram, or ECG, may be used to check the electrical activity of the heart. The bradycardia caused by calcium channel blockers is usually termed sinus bradycardia, where the electrical activity in the heart is normal aside from the slowed heartbeat.
Treatment
If the bradycardia is not causing any serious symptoms, patients taking calcium channel blockers may continue the medication, though they will need to be vigilant for symptoms of a severely slowed heart rate. If calcium channel blockers can no longer be used, other medications for high blood pressure -- such as diuretics, angiotensin converting enzyme inhibitors and beta blockers -- may be used to control blood pressure.
