What are heart rhythm problems (arrhythmias)?
An arrhythmia, or heart rhythm disturbance, is a change in the regular beat of the heart. The heart is divided into four chambers: two atria on top and two ventricles on the bottom. Arrhythmias are classified by their location as ventricular or atrial (sometimes called supraventricular meaning above the ventricle) and whether they slow the heart rate: bradycardia (heart rate less then 60 beats per minute); or speed it up: tachycardia (heart rate more than 100 beats per minute).
Are arrhythmias serious?
Heart rhythm disturbances can occur in people without heart disease and in many cases they are harmless. However, some heart rhythm disturbances affect the heart's ability to pump blood around the body. In 2002, arrhythmias caused nearly 38,000 deaths.1 Arrhythmias can lead to sudden cardiac death, or SCD, often brought on by cardiac arrest, when the heart abruptly stops beating. If the heart is not restarted immediately with an electric shock ( defibrillation), death can occur. Most cases of SCD occur in people with heart disease, and SCD accounts for half the deaths from cardiovascular disease.2 Each year, three to four times more men experience SCD than women, but the gender gap closes with older age.1
Who should take medication for heart rhythm problems?
This section will focus on the use of antiarrhythmic medications in people with heart disease (fatty plaque buildup in the arteries of the heart), particularly heart attack patients. Heart rhythm disturbances are common early after heart attack symptoms develop.3 Previously, antiarrhythmic medications were given to heart attack patients to help prevent heart rhythm problems from occurring in the first place. Now it is known that in most cases, these drugs do more harm than good when used preventively (beta blockers are the exception).
Currently, heart rhythm medications are reserved for occasionally treating serious heart rhythm problems when they arise. Implantable cardioverter defibrillators (ICDs) and pacemakers are safer and better than drugs for the long-term treatment of serious heart rhythm problems. Some people with ICDs also take antiarrhythmic medication to reduce the likelihood of shocks.
There are four classes of antiarrhythmic medications categorized according to how they affect heart rhythm disturbances.4 A fifth group exists for drugs that do not fit into the other categories. Some medications have properties from more than one class (e.g., amiodarone). The heartbeat is controlled by an electrical conduction system that sends electrical charges to the heart muscle causing it to expand and contract. Antiarrhythmics work by slowing down the electrical signals in the heart so the heart can resume a regular rhythm.
- Class I antiarrhythmics are sodium channel blockers that block the flow of sodium to the heart. They are further divided into three subclasses (IA, IB, and IC).
- Class II antiarrhythmics are beta blockers that block the stimulating effect of adrenaline on the heart.
- Class III antiarrhythmics block potassium channel blockers that block the flow of potassium to the heart.
- Class IV antiarrhythmics are calcium channel blockers that block the flow of calcium to the heart.
- This “class” is made up of two drugs, digoxin and adenosine. Digoxin and adenosine slow the conduction of electrical impulses through the AV node – a kind of junction box for the electrical signal between the upper and lower chambers of the heart.