To understand bradycardia (low heart rate), you first need to know what a normal heart rate is—for an adult at rest, normal heart rate is between 60 and 100 beats per minute.

In the simplest terms, bradycardia is a slower-than-normal heart rate—your heart beats fewer than 60 times a minute. But a slow heart rate is not always worrisome, explains cardiologist Ana C. Iribarren, MD. Examples: While you are sleeping, a heart rate between 40 and 60 beats per minute is common.…and for highly trained athletes, daytime heart rate often is below 60 beats per minute, but that is the heart’s physiological response to their training.

But when should you worry about low heart rate? When your heart can’t pump enough blood to the rest of the body, affecting organs and causing symptoms. This can lead to heart failure, a progressive straining of the heart muscle that can be fatal in later stages. Low heart rate also can sometimes lead to sudden cardiac arrest. Another worrisome manifestation of bradycardia is when you have a normal heart rate at rest, but it doesn’t adapt or rise during physical activity, what it’s called in medical terms: chronotropic incompetence.

Bradycardia Symptoms

While some people with bradycardia have no symptoms, it can cause noticeable effects in others. Even in the absence of symptoms, a resting heart rate below 40 is often considered the threshold for severe bradycardia and can be worrisome. When bradycardia leads to a diminished blood supply to all your organs, most notably the brain, it’s common to feel dizzy, tired and weak. You may have shortness of breath as soon as you start exercising and/or even faint. These symptoms should prompt a doctor visit for an evaluation and possible diagnosis.

Causes of Bradycardia

Bradycardia can be related to the natural aging of the heart, and that’s why regular checkups are so important, especially for older people. Other causes include…

  • Heart attack if the attack affected the heart’s electrical system that control the heart rate.
  • Inflammation of the heart, or myocarditis.
  • Congenital defect, such as an atrioventricular block—a malfunction in the heart’s electrical system.
  • Electrolyte abnormality or imbalance.
  • Hypothyroidism, when thyroid glands are underperforming.
  • Medications, such as blood pressure medications or controlled substances such as opioids. The beta-blockers metoprolol, carvedilol and atenolol can lower the blood pressure, but they can also reduce the heart rate as a side effect. Opioids can slow the heart rate by affecting the sinus node, the heart’s natural pacemaker.
  • Health conditions such as sleep apnea and inflammatory diseases.
  • Conduction abnormalities, or abnormalities in the way electrical impulses move through the heart.
  • Excessive alcohol intake.

Treatment for Bradycardia

If your bradycardia is considered borderline and you don’t have symptoms, you may not need treatment. This is also true if the cause of your bradycardia can be treated and is reversible, such as myocarditis or hypothyroidism, or if it’s a side effect of a medication that can be changed. In other cases, you’re likely to need a pacemaker to regulate your heart rhythm. There are no prescription drugs to treat bradycardia.

Can Bradycardia be Prevented?

A healthy lifestyle can help prevent some causes of bradycardia, such as heart attack. Live a heart-healthy life—get regular exercise, avoid smoking, drink alcohol minimally or not at all, maintain a healthy diet and weight, keep blood pressure and cholesterol under control, and see your doctor regularly so that your heart rate can be monitored along with other health checks.

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