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Heart Block Types

Your heartbeat originates from an electrical signal in a cluster of cells called the sinoatrial (SA) node in the upper right chamber, or atrium, of the heart. The electrical signal that causes your heart to beat starts in the SA node, travels via certain electrical conducting tissues of the atrioventricular (AV) node to the lower chambers, or ventricles, of the heart. Heart block, also called AV block, refers to a blockage of electrical conduction from the SA node, the heart's pacemaker.

  1. First-Degree Heart Block

    • First-degree heart block refers to the rate of conduction through the AV node being slower than normal. The American Heart Association states that the length of time for the signal to travel from the atria to the ventricles typically averages a mere 0.2 seconds; however, first-degree heart block occurs if the signal transfer takes more than 0.2 seconds.

      This minor condition usually does not have any outward symptoms; therefore, no treatment is necessary. A slower conduction rate through the AV node merely signifies a slower heartbeat and is not detrimental to a person's health. Athletes and those who take certain heart medications such as digitalis may exhibit first-degree heart block.

    Type I Second-Degree Heart Block

    • Also known as Mobitz Type I second-degree AV block or Wenckebach AV block, this type of heart block may cause dizziness in sufferers. Many of the signals initiated in the SA node do not transmit to the ventricles; therefore, the heart may skip beats. Some people may experience this condition while asleep.

    Type II Second-Degree Heart Block

    • Although occurring less often than the Type I variety, Type II second-degree heart block, or Mobitz Type II second-degree AV block, results in more serious repercussions. The MD Guidelines website asserts that this type of heart block often progresses to third-degree heart block, the most detrimental type of heart block. Causes of Mobitz Type II AV block include previous heart attacks, heart disease, rheumatoid arthritis, infections and the development of scar tissue. To maintain the relationship between heartbeat and the heart's pumping action, doctors will implant a pacemaker, an apparatus that controls heartbeat, in a patient's chest.

    Third-Degree Heart Block

    • Considered the most injurious of all types of heart blocks, third-degree heart block, or complete AV block, takes place when none of the signals from the pacemaker reaches the ventricles at all. Although the ventricles have an alternate system in which certain tissues automatically generate signals to cause the ventricles to contract independently of the pacemaker, this system is faulty since the signal is slow and does not coordinate with the signal derived from the atria. The ventricles, therefore, do not beat in conjunction with the atria, causing the heart to beat irregularly. Sufferers may die if the heart suddenly stops beating altogether, termed cardiac arrest. A permanent implanted pacemaker will regulate and coordinate the beating of the different chambers of the heart to pump blood normally again.

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