Types of Heart Block

First-Degree Heart Block

In first-degree heart block, the electrical signal is slowed as it moves through the heart. When this occurs between the atria and the ventricles, it appears as a slightly longer, flatter line between the P and the R waves on the EKG.

First-degree heart block rarely causes any symptoms. Well-trained athletes and young people are at higher risk for first-degree heart block caused by an overly active vagus nerve. Activity in this nerve slows the heart rate. Some medicines, such as digitalis, also may trigger first-degree heart block.

First-degree heart block usually doesn't require treatment.

Second-Degree Heart Block

In this type of heart block, electrical signals between the atria and ventricles are slowed to a large degree. Some signals can't reach the ventricles. On an EKG, the QRS wave doesn't follow each P wave as it normally would.

If the signal is blocked before it reaches the ventricles, they won't contract and pump blood to the lungs and the rest of the body.

Second-degree heart block is divided into two different types, Mobitz type I and Mobitz type II.

Mobitz Type I

Mobitz Type I is also known as Wenckebach. In Wenckebach the electrical signals are delayed more and more with each heartbeat, until the heart skips a beat. On the EKG, the delay is shown as a line (called the PR interval) between the P and QRS waves. The line gets longer and longer until the QRS wave doesn't follow the next P wave.

Sometimes people with Wenckebach or Mobitz Type I feel dizzy or have other symptoms. Wenckebach is a type of second-degree heart block that is less serious than Mobitz type II.

Mobitz Type II (Second Degree Heart Block)

In this type, some of the electrical signals also don't reach the ventricles. However, the pattern is less regular than it is in Mobitz type I. Some signals move between the atria and ventricles normally, while others are blocked. On an EKG, the QRS wave follows the P wave at a normal speed. Sometimes, though, the QRS wave is missing (when a signal is blocked).

Mobitz type II is less common than type I, but it's usually more severe. Some people with type II need medical devices called pacemakers to maintain their heart rates.

Third-Degree Heart Block

In this type of heart block, none of the electrical signals reach the ventricles. This type also is called complete heart block or complete AV block.

When complete heart block occurs, special areas in the ventricles may create electrical signals to cause the ventricles to contract. This natural backup system is slow and isn't coordinated with the contraction of the atria. On an EKG, the normal pattern is disrupted. The P waves occur at a faster rate than the QRS waves.

Complete heart block can be fatal. It can result in sudden cardiac arrestand death. This type of heart block needs emergency treatment. A temporary pacemaker may be used to keep the heart beating until you get a pacemaker implanted.