Arrhythmia Overview

An arrhythmia is a disorder of the heart that affects the rate or rhythm at which the heart beats. An arrhythmia occurs when electrical impulses, which direct and regulate heartbeats, don’t function properly. This causes the heart to beat too fast (tachycardia), too slow (bradycardia), prematurely, or with an irregular rhythm.

Heart arrhythmias are very common; nearly everyone will experience an abnormal heart rhythm at least once in their lifetime. In most cases, the arrhythmia will not be serious and will likely go undetected. But some arrhythmias are problematic; at the least, they can be bothersome, and at worst, life-threatening.

How the Heart Works

Your heart is divided into four chambers. Each half of your heart consists of an upper chamber (the atrium) and a lower chamber (the ventricle). The two halves create two pumps on either side of the heart.

In a properly beating heart, electrical charges or impulses follow precise pathways through the heart to each pump. These charges coordinate and direct all of the different functions inside the heart, and any interruption in these pathways or impulses can cause the heart to beat abnormally.

The Heartbeat

Blood enters the heart, arriving first in the atria. After this happens, a single heartbeat involves several steps.

1. The sinus node—a group of cells in the right atrium—sends an electrical impulse to both the right and left atria, telling them to contract.
2. This contraction allows the lower chambers (the ventricles) to relax and fill with blood.
3. While the ventricles fill, the electrical impulse travels to the center of your heart to the atrioventricular node—a group of cells that lie on the pathway between the atria and the ventricles.
4. The impulse exits the node and then travels to your now blood-filled ventricles, telling them to contract.
5. This contraction pushes the blood out of the heart and into your body for circulation.

That is one heartbeat, and the process starts all over again. Under normal conditions, the left and right sides of the heart beat one after the other; this keeps the blood flow moving in one direction, in a continuous pumping fashion.

A normal heart will repeat this process about 100,000 times each day—that is 60 to 100 beats per minute for the average healthy person’s heart while he or she is at rest.

Types of Arrhythmias

Arrhythmias are named and categorized based on three points:

• rate (too slow or too fast)
• origin (whether it is in the ventricles or the atria)
• the beat itself (if it is steady or irregular)

Bradycardia

Bradycardia is a slow heartbeat—when the resting heart rate is less than 60 beats per minute. This weak pace might mean your heart isn’t beating frequently enough to ensure adequate blood flow throughout your body. Types of bradycardia include:

• Sick Sinus: The sinus node is responsible for setting the pace of your heart. If it isn’t sending electrical impulses properly, your heart may be pumping too slowly or irregularly. Scarring near the sinus node, from heart disease or a heart attack, may also slow down or block the electrical impulses as they try to travel through the heart.
• Conduction Block: If your heart’s electrical pathways are blocked, the chambers of the heart may contract slowly or be completely unable to contract. A block can happen anywhere along the heart’s electrical pathways—between the sinus node and atrioventricular (AV) node or between the AV node and the ventricles. These blocks may show no signs other than skipped or slowed heartbeats.

Not all bradycardias are a problem, however. Athletes or people who are physically fit often have bradycardias. Their resting heart rates may be less than 60 per minute because their hearts are more efficient and can pump adequate blood with fewer beats.

Tachycardia

Tachycardia is a fast heartbeat—the resting heart rate is greater than 100 beats per minute. The two most common types of tachycardia are supraventricular tachycardia and ventricular tachycardia.

Supraventricular Tachycardia

Supraventricular tachycardia (SVT) encompasses any arrhythmia that begins above the ventricle. SVTs are usually identified by a burst of rapid heartbeats that begin and end suddenly. These bursts can last a few seconds or several hours and may cause your heart to beat greater than 160 times per minute. The most common SVTs include:

• Atrial Fibrillation: If you have atrial fibrillation, your atrium beats very rapidly; it can be as fast as 240 to 350 beats per minute. The atria are moving so rapidly they aren’t able to contract completely. Instead, they quiver (fibrillate). Some patients can feel this, and it causes discomfort, but not a high pulse. Some of these atrial beats will be transferred to the ventricles and may cause a high pulse rate. A-fib affects mainly older people. Your risk of developing this arrhythmia increases past age 60, mostly due to the wear and aging an older heart experiences. The chances of developing a-fib are also increased if you have or have had high blood pressure or other heart problems. A-fib can be dangerous; if left untreated it can cause more serious conditions, such as stroke.
• Atrial Flutter: The heartbeats in atrial flutter are more rhythmic and constant than the heartbeats in atrial fibrillation. Still, atrial flutter can come and go in sudden bursts, and it can be life threatening. This type of arrhythmia occurs most often in people with heart disease. It also often shows up in the first weeks after heart surgery.

Ventricular Tachycardia

Ventricular tachycardia (VT) is an arrhythmia that begins in the ventricles of the heart. Most VT occurs in people who have had a heart disease or heart-related problems, such as coronary artery disease or heart attack. VT is often caused by an electrical impulse traveling around a scared part of the heart’s muscle. It can cause the ventricles to contract more than 200 times per minute. If left untreated, VT may increase your risk of developing more serious ventricular arrhythmias, including:

• Ventricular fibrillation: Sudden, rapid, irregular, and chaotic heartbeats in the ventricle may be a sign of a dangerous arrhythmia called ventricular fibrillation (v-fib). These erratic electrical impulses, sometimes triggered by a heart attack, cause your heart’s ventricles to quiver (fibrillate). When you have this kind of arrhythmia, your ventricles aren’t able to pump blood into your body, and your heart rate drops quickly. This will make your blood pressure fall, and the blood supply to your body and organs will be diminished. V-fib is the number one cause of sudden cardiac arrest.
• Long QT Syndrome: Long QT syndrome causes potentially fast, chaotic heartbeats that can be so erratic it may cause fainting and even sudden death.

Premature Heartbeats

Premature heartbeats may result in the feeling that your heart has skipped a beat. In reality, your normal heart rhythm has been interrupted by a too-soon beat, and you’re experiencing an extra beat between two normal heartbeats.

Not all tachycardias, bradycardias, or premature heartbeats are unhealthy or a sign of a problem. Again, athletes or people who are physically fit may have bradycardia because their hearts work very efficiently and don’t require as many beats as other less-fit people. Also, it’s normal to have an increased heart speed during exercise; your heart is working hard to provide your tissues with oxygen-rich blood so you don’t fatigue too quickly.