Home Cardiovascular Disease Heart Rhythm Problems - Causes & Types

Heart Rhythm Problems - Causes & Types

What happens in the heart during an arrhythmia?

Describing how the heart beats normally helps to explain what happens during an arrhythmia.
The heart is a muscular pump divided into four chambers—two atria located on the top and two ventricles located on the bottom.

Normally each heartbeat starts in the right atrium. Here, a specialized group of cells called the sinus node, or natural pacemaker, sends an electrical signal. The signal spreads throughout the atria to the area between the atria called the atrioventricular (AV) node.

The AV node connects to a group of special pathways that conduct the signal to the ventricles below. As the signal travels through the heart, the heart contracts. First the atria contract, pumping blood into the ventricles, and then a fraction of a second later, the ventricles contract, sending blood throughout the body.

Electric System

Typically the whole heart contracts between 60 and 70 times per minute (more during exercise). Each contraction equals one heartbeat.

An arrhythmia may occur for one of several reasons:

  • Instead of beginning in the sinus node, the heartbeat begins in another part of the heart
  • The sinus node develops an abnormal rate or rhythm
  • A patient has a heart block

What is a heart block?

A heart block is a condition in which the electrical signal cannot travel normally down the special pathways to the ventricles. For example, the signal from the atria to the ventricle may be:

  • delayed, but each one conducted
  • delayed with only some getting through
  • completely interrupted

If there is no conduction, the beat generally originates from the ventricles and is very slow.

What are the different types of arrhythmias?

There are many types of arrhythmias. Arrhythmias are identified by where they occur in the heart, either in the atria or ventricles, and by what happens to the heart's rhythm when they occur.

Arrhythmias arising in the atria are called atrial or supraventricular (above the ventricles) arrhythmias. Ventricular arrhythmias begin in the ventricles. In general, ventricular arrhythmias caused by heart disease are the most serious.

Arrhythmias originating in the atria:

  • Sinus arrhythmia. Cyclic changes in the heart rate during breathing. Common in children and often found in adults.
  • Sinus tachycardia. The sinus node sends out electrical signals faster than usual, speeding up the heart rate.
  • Sick sinus syndrome. The sinus node does not fire its signals properly, so that the heart rate slows down. Sometimes the rate changes back and forth between a slow ( bradycardia) and fast (tachycardia) rate.
  • Premature supraventricular contractions or premature atrial contractions (PAC). A beat occurs early in the atria, causing the heart to beat before the next regular heartbeat.
  • Supraventricular tachycardia (SVT), paroxysmal atrial tachycardia (PAT). A series of early beats in the atria speed up the heart rate (the number of times a heart beats per minute). In paroxysmal tachycardia, repeated periods of very fast heartbeats begin and end suddenly.
  • Atrial flutter. Rapidly fired signals cause the muscles in the atria to contract quickly, leading to a very fast, steady heartbeat.
  • Atrial fibrillation. Electrical signals in the atria are fired in a very fast and uncontrolled manner. Electrical signals arrive in the ventricles in a completely irregular fashion, so the heart beat is completely irregular.
  • Wolff-Parkinson-White syndrome. Abnormal pathways between the atria and ventricles cause the electrical signal to arrive at the ventricles too soon and to be transmitted back into the atria. Very fast heart rates may develop as the electrical signal ricochets between the atria and ventricles.

Arrhythmias originating in the ventricles:

  • Premature ventricular complexes (PVC). An electrical signal from the ventricles causes an early heart beat that generally goes unnoticed. The heart then seems to pause until the next beat of the ventricle occurs in a regular fashion.
  • Ventricular tachycardia. The heart beats fast due to electrical signals arising from the ventricles (rather than from the atria).
  • Ventricular fibrillation. Electrical signals in the ventricles are fired in a very fast and uncontrolled manner, causing the heart to quiver rather than beat and pump blood.

Next: Diagnosis & Treatment


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