When A Slow Heart Rate Does (And Does Not) Require Attention

If your heart beats too rapidly or has an abnormal or irregular rhythm, it’s cause for concern—but what about a heart that beats too slowly?

“Bradycardia is the term used to describe a heartbeat that is ‘too slow.’ A normal resting heart rate is typically between 60 and 100 beats per minute (bpm); a heart rate that is less than 60 bpm is classified as bradycardia,” explains Joy Gelbman, MD, a cardiologist at Weill Cornell Medicine.

Many athletes and other physically active adults have a resting heart rate that is below 60 bpm, but when they are exercising, their heart rate accelerates; this is healthy and normal. Conversely, physical exertion doesn’t cause a noticeable increase in the heart rates of people who have bradycardia.

How Your Heart Beats

Your heartbeat is controlled by an electrical system within the heart that tells the heart’s chambers when to fill with blood and when to pump it out. The electrical impulses are generated by a cluster of cells in the right atrium that form the sinoatrial node, or SA node. The SA node acts as the heart’s natural “pacemaker,” sending electrical signals that produce a synchronized, steady heart rhythm. However, your heart’s electrical circuitry is vulnerable to various factors that can speed up, slow down, or otherwise interfere with a normal, healthy rhythm.

WHAT YOU SHOULD KNOW

Medications that may slow your heart rate include (but are not limited to):

  • Propranolol (Inderal)
  • Atenolol (Tenormin)
  • Metoprolol (Toprol)
  • Sotalol (Betapace)
  • Amiodarone (Cordarone, Pacerone)
  • Verapamil (Calan, Isoptin, Verelan)
  • Diltiazem (Cardizem)
  • Digoxin (Lanoxin)

Causes of Bradycardia

“Bradycardia can be caused by many things. Sometimes, it can occur in highly trained athletes who have “high vagal tone,” a condition that affects the SA node and slows the heartbeat. Sometimes, bradycardia can be due to a diseased electrical system within the heart, certain infections, and various medications,“ says Dr. Gelbman

Over time, the heart may simply slow down on its own. Bradycardia may also develop after a heart attack or if you have hypothyroidism (an underactive thyroid gland). Or, a problem may develop with the SA node or the electrical pathways in the heart. One common example is an atrioventricular (AV) block, in which the atria and the heart’s bottom chambers (ventricles) don’t communicate well.

Some medications may also cause or worsen bradycardia. These medications include beta blockers used to treat high blood pressure and antiarrhythmic drugs used to treat abnormal heart rhythms. (For more information about medications that may cause bradycardia, see What You Should Know.)

Be Alert for Symptoms

Symptoms that are commonly associated with bradycardia include:

  • Dizziness or lightheadedness
  • Fainting
  • Weakness
  • Fatigue, lack of energy
  • Decreased stamina during physical activity
  • Shortness of breath
  • Chest pains
  • Confusion

If your heart rate drops too low—to about 30 bpm—you run the risk of having inadequate blood flow to your brain and other organs. When your brain doesn’t receive enough blood, oxygen, and nutrients, fainting, confusion, memory problems, and other symptoms may develop.

If you notice any of these symptoms, tell your doctor. If you’ve already been diagnosed with bradycardia but initially had no symptoms, your doctor needs to know if you begin experiencing symptoms, since they could be signs of complications stemming from your slow heart rate. However, these symptoms are common among many different health conditions, and your doctor may need to perform an evaluation and some tests to pinpoint what is causing them.

Diagnosis and Treatment

Your heart rate is routinely checked during doctors’ appointments; don’t be shy about asking what your heart rate is. If your heart rate is below 60 bpm on multiple visits, your doctor may have you wear a 24-hour heart rate monitor to get more information.

If you are diagnosed with bradycardia, your doctor will try to determine if there is an underlying cause. If medication is slowing your heart rate, for example, a change or adjustment in your medication may return your heartbeat to a normal speed.

“In general, if bradycardia is asymptomatic, it does not routinely require treatment. If it is symptomatic, however—for example, if it causes lightheadedness, fainting spells, and/or reduced stamina—it may require treatment with a pacemaker,” says Dr. Gelbman.

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