Slow Heartbeat

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In most healthy people, a normal heart rate is 60 to 100 beats per minute. A resting heart rate below 60 beats per minute is considered bradycardia—a heartbeat that is too slow.

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To help you understand bradycardia, it helps to understand your heart's electrical system. The heart’s pumping action is driven by electrical stimulation within the heart muscle. The heart’s electrical system allows it to beat in an organized pattern. Electrical signals in your heart can become blocked or irregular, causing a disruption in your heart’s normal rhythm. When your heart beats out of rhythm, it may not deliver enough blood to your body.

It is important to realize that for some people with healthy hearts, a rate below 60 beats per minute may be normal. For example, our heart rates may dip below normal range when we sleep, and some athletes experience heart rates below 60 beats per minute when they rest.

If you have a slow heart rate and your heart isn’t pumping enough blood, it could be caused by one of two types of bradycardia that create irregular electrical signals in the heart:

Sick Sinus Syndrome (SSS)

The sinus node is a group of cells located in the right atrium. It is called the heart’s “natural pacemaker” and produces electrical signals that initiate each heartbeat. The electrical impulses travel from the sinus node across the atria to each ventricle, causing them to contract and pump blood out to your lungs and body.

If the sinus node isn’t functioning as it should, you may develop sick sinus syndrome. This means that when starting a heartbeat, the electrical signal either moves too slowly through the sinus node or there are pauses in delivery of the electrical signal. Your heart rhythm may be too slow or it may speed up and slow down intermittently. With SSS, your heart may not pump enough blood to meet your body’s needs.

What Are the Symptoms?

Common symptoms of sick sinus syndrome include:

  • Fatigue, weakness
  • Dizziness or light-headedness
  • Fainting or nearly fainting
  • Shortness of breath
  • Chest pains
  • Trouble sleeping
  • Confusion or difficulty remembering things
  • A sensation of rapid, fluttering irregular heartbeats

What Are the Causes?

Sick sinus syndrome can be caused by an improperly functioning sinus node. This causes your heart to beat too slowly (bradycardia), too fast (tachycardia) or in an irregular fashion.

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Heart Block

Heart block is a type of bradycardia that occurs when the beat that begins in the heart’s upper chambers is unable to pass normally to the lower chambers. (This is sometimes called AV block, because the impulse slows or does not pass through the atrioventricular (AV) node that joins the heart’s upper and lower chambers.) It can result in your heart not pumping enough blood to meet your body’s needs.

There are different kinds of heart block.

  • First-degree heart block – Beats pass from the upper chambers to the lower chambers, but conduction is slower than normal. This is the mildest form of heart block.
  • Second-degree heart block – Not all beats pass from the heart’s upper to lower chambers.
  • Third-degree heart block – Also called complete heart block, this condition occurs when impulses cannot pass from the upper to the lower chambers, so the lower chambers originate their own impulse. The lower chambers beat and pump blood, but at a slower rate and more inefficiently than if they received an impulse from the upper chambers.

What Are the Symptoms?

Mild cases of heart block may cause no symptoms, but more serious forms may cause the following:

  • Fatigue, weakness
  • Dizziness or light-headedness
  • Fainting or nearly fainting
  • Shortness of breath
  • Chest pains
  • Disturbed sleep
  • Confusion or memory impairment
  • Tired during physical activity

What Are the Causes?

Heart block may be caused by:

  • Coronary artery disease
  • Heart attack
  • Diabetes
  • High cholesterol
  • High blood pressure
  • Cigarette smoking
  • Drug or alcohol abuse
  • Excess weight
  • High fat diet
  • Sedentary lifestyle
  • Stress
  • Certain medications (over-the-counter and prescriptions, including decongestants and diet and herbal supplements)
  • Heart surgery
  • Family history of heart disease
  • Congenital heart disorders (heart problems present at birth, usually involving the heart's chambers or valves)
  • Advancing age
  • Gender (males are more susceptible)

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Last Reviewed: March 11, 2010 900245