Heart Block

Heart Block

What is it?

Your heart’s master pacemaker called the sinoatrial (SA) node. The SA node is a specialized group of cells at the top of your heart's upper-right chamber (the right atrium). Anywhere between 60 and 100 times a minute, the SA node sends an electrical impulse throughout your heart to cause it to beat or contract.

When the SA node sends an electrical impulse, that impulse first travels through the heart's upper chambers (the atria). It then passes through a small group of cells called the atrioventricular (AV) node. The ventricles are the major pumping chambers of the heart. The electrical signal transmitted from the SA and AV nodes trigger the muscle contractions that pump blood out of the heart and into the lungs and body.

Heart Block or an atrioventricular (AV) block is determined when the electrical signals that stimulate heart muscle contractions are partially or totally blocked between the upper chambers (atria) and the lower chambers (ventricles) causing a slower heart beat.

Heart blocks are categorized as follows:

  • First-degree heart block (AV block)
    • The electrical impulses are slowed but the eventually reach the ventricles.
  • Type I second-degree heart block (Mobitz Type I second-degree AV block or Wenckebach AV block)
    • Only some electrical impulses reach the ventricles. The heart may beat slowly, irregularly or both.
  • Type II second-degree heart block (Mobitz Type II second-degree AV block)
    • The electrical impulses are unable to reach the ventricles.
  • Third-degree heart block (complete heart block or complete AV block)
    • No impulses from the atria reach the ventricles, and the ventricular rate and rhythm are controlled by substitute pacemakers which are slower than the heart's normal pacemaker (SA node) and are often irregular and unreliable.
  • Bundle branch block
    • For the left and right ventricles to contract at the same time, an electrical impulse must travel down the right and left bundle branches at the same speed. If there is a block in one of these branches, the electrical impulse must travel to the ventricle by a different route. When this happens, the rate and rhythm of your heartbeat are not affected, but the impulse is slowed. Your ventricle will still contract, but it will take longer because of the slowed impulse. This slowed impulse causes one ventricle to contract a fraction of a second slower than the other.

Causes, Symptoms and Risk Factors

Causes of heart blocks can be:

There may be no symptoms of heart block. If there are, they may include the following:

  • Syncope (fainting)
  • Fatigue
  • Dizziness
  • Lightheadedness
  • Chest pain
  • Shortness of breath

Complete heart block may be a medical emergency with potentially severe symptoms and a serious risk of cardiac arrest (sudden cardiac death). If an artificial pacemaker cannot be implanted immediately, then a temporary pacemaker wire might be used to keep the heart pumping until surgery can be performed.

Our Services (Tests, Procedures and Treatments)

Diagnostic testing and procedures are the first step in establishing a treatment strategy. A doctor may order an electrocardiogram (EKG). The most common procedure which can be useful in correcting a heart block is the insertion of an artificial pacemaker.

First-degree heart block requires no treatment. In other cases, an artificial pacemaker is needed.

St. Luke's Heart & Vascular