Pacemaker Dysfunction

The electrical impulses from the heart muscle that cause your heart to contract usually begins in the sinoatrial node, located on the top of the right side of the heart. The sinoatrial node is called the heart's pacemaker.

When something goes wrong with the sinoatrial node, you may develop a consistently slow heartbeat (sinus bradycardia) or the normal pacemaker activity may stop entirely (sinus arrest). If sinus arrest occurs, usually another area of the heart takes over pacemaker activity. This area is called an escape pacemaker. It may be located lower in the upper right chamber of the heart, in the atrioventricular node (also located in the upper right chamber), in the heart's conduction system or even in the lower chamber of the heart, the ventricle.

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Symptoms

Many pacemaker disorders do not cause symptoms. If there are symptoms, they may include:

  • A consistently slow heart rate
  • Fainting, if the heart rate becomes very slow or if the heart is slow in returning to a normal rhythm after a period of rapid beating
  • Periods of slow heartbeats (bradycardia) that alternate with periods of fast (tachycardia), irregular heartbeats (arrhythmia), such as are found sometimes in atrial fibrillation and atrial flutter. (This is a type of sick sinus syndrome sometimes called the bradycardia-tachycardia syndrome.)
  • Weakness and tiredness

Causes and Risk Factors

Older people more commonly have pacemaker problems. In addition to age, pacemaker problems can develop as a result of:

  • An underactive thyroid gland (hypothyroidism)
  • Certain drugs
  • Unknown causes. In this case, the disorder is called sick sinus syndrome
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Diagnosis

The following signs will help your doctor diagnose a pacemaker disorder:

  • A pulse that does not go up during exercise
  • A pulse that varies greatly even if your activity level has not changed
  • A slow pulse, especially if it is an irregular one

Your doctor will usually base his or her diagnosis on your symptoms and on the results of an electrocardiogram. He or she may monitor your heart rhythm using a Holter monitor, which allows your heart rate to be recorded continuously over a 24-hour period.

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Treatments

If you have a pacemaker disorder that is causing symptoms, your doctor may recommend implanting a mechanical pacemaker. This is a device, run by a battery, about the size of a matchbox that helps the heart beat regularly. Pacemakers can be used in cases where the heart rate is slow, where there are alternating periods of fast and slow heart rates or where there is a block in the heart's electrical system.

If you also experience periods of a rapid heart rate, your doctor may also prescribe drugs to slow the heart rate down. These might include a beta-blocker or a calcium channel blocker.

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