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. A fraction of a second later, the ventricles contract, sending blood throughout the body.
Usually the whole heart contracts between 60 and 100 times per minute. 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?
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 (1) delayed, but each one conducted; (2) delayed with only some getting through; or (3) completely interrupted. If there is no conduction, the beat generally originates from the ventricles and is very slow.
There are many types of arrhythmias. Arrhythmias are identified by where they occur in the heart (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.
How does the doctor know that I have arrhythmia?
Sometimes an arrhythmia can be detected by listening to the heart with a stethoscope. However, the electrocardiogram is the most precise method for diagnosing the arrhythmia.
An arrhythmia may not occur at the time of the exam even though symptoms are present at other times. In such cases, tests will be done if necessary to find out whether an arrhythmia is causing the symptoms.
