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Understanding Rhythms

Understanding Rhythms

Slow Heartbeat (Bradycardia)

Normally, the heart beats about 60 to 100 times per minute. A diagnosis of bradycardia means that your heart rate is slower than 60 beats per minute, either occasionally or all the time. While a slow heart rate might be normal for some people, such as athletes, it can cause uncomfortable or even dangerous symptoms for others.


Causes and Symptoms

Bradycardia can be caused by medicines, including certain drugs used to treat high blood pressure and arrhythmias. More commonly, it is caused by a blockage somewhere along the heart’s electrical pathway. The blockage may be a product of a congenital heart problem, or of the normal aging process.

In either case, the slower your heart beats, the less blood it pumps throughout your body. If your heart beats too slowly, your brain and body might not get enough blood to function well, leading to any or all of the following symptoms:

  • Fatigue, weakness

  • Dizziness

  • Lightheadedness

  • Fainting (syncope) or near fainting

  • Shortness of breath

Types of Arrhythmias

Understanding some common terms in the language of cardiac arrhythmias helps sort through the types of rhythm problems. An arrhythmia is any abnormality in heart rhythm. Arrhythmias are categorized in three main ways:

Rate. If the heart rate is slow, or less than 60 beats a minute, it is considered bradycardia. Alternatively, a fast or rapid heart rate, above 100 beats a minute, is known as a tachycardia.

Location. The location of the problematic electrical circuit helps define the arrhythmia. For instance, a rhythm is called supraventricular if it originates above the ventricles (lower chambers). So, the problem is most likely in the upper chambers (atria). It follows that a ventricular arrhythmia is the result of a problem in the lower chambers (ventricles.)

Irregular. The nature of the heartbeat, whether it is steady or chaotic, is another key to categorizing an arrhythmia. A rapid beat that is irregular and chaotic may be fibrillation, or a quivering beat.

Types of Slow Heartbeat (Bradycardia)

Sick sinus syndrome– The sinus (or sinoatrial) node is the heart’s natural pacemaker, initiating each heartbeat with an electrical signal. Normally, the signal travels from the sinus node to the atria (the heart’s upper chambers) and then on to the ventricles (the lower chambers). When the sinus node is “sick,” or not functioning correctly, it may initiate signals too slowly. Or it may send signals at a normal rate, but a blockage (sinoatrial block) prevents some of the signals from leaving the node to deliver their message to the atria. Some people with sick sinus syndrome experience a fast heart rate (tachycardia), rather than a slow one. Others experience alternating episodes of bradycardia and tachycardia (sometimes called tachy-brady syndrome).

Heart block –Also called “AV block,” this is a blockage in the “AV node,” the electrical pathway between the atria and the ventricles. Heart block may delay electrical signals from reaching the ventricles, or it may block them completely. AV block is diagnosed in three degrees:

First-degree heart block is when signals travel through the AV node more slowly than usual, but they still reach the ventricles.

Second-degree heart block is when some signals are blocked entirely from reaching the ventricles, causing skipped heartbeats.

Third-degree, or complete heart block, can be quite serious. This is when all signals are blocked between the atria and the ventricles, forcing the ventricles to create their own signals, but at a much slower and less-effective rate.


If bradycardia is causing bothersome or dangerous symptoms, a pacemaker may be needed to correct the heart rate. Bradycardia that is caused by medication often can be corrected simply by stopping the medication.

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