Heart Block

Arrhythmia is a medical term that refers to a heart rate that is outside the normal range. (Normal is 60 to 100 beats per minute.) An arrhythmia that is too slow is called a bradyarrhythmia or bradycardia.

Heart block is a type of bradycardia (slow heart rate, usually less than 60 beats per minute) that occurs when the beat that originates in the upper chambers of the heart is unable to pass normally to the lower chambers of the heart. (This is sometimes called AV block, because the impulse slows or does not pass through the atrioventricular node that joins the upper and lower chambers of the heart.) There are different kinds of heart block. With first-degree heart block, the beats pass from the upper chambers to the lower chambers, but conduction is slower than normal (more than 0.2 seconds). With second-degree heart block, not all of the beats pass from the heart’s upper to lower chambers, so some are dropped. With third-degree (also called complete) heart block, the impulses cannot pass from the upper to the lower chambers, so the lower chambers originate their own impulse. This means they do beat and pump blood, but at a slower rate and more inefficiently than if by an impulse from the upper chambers.

Normal Rhythm

Every normal heart has a normal rhythm. That rhythm varies from person to person. In most healthy people, the heart at rest beats about 60 to 100 times per minute. A small bunch of heart cells called the sinoatrial node keeps time.