How Doctors Diagnose Arrhythmias
If your doctor suspects you have an arrhythmia, he or she may order one or more diagnostic tests to check for an arrhythmia and determine whether it is causing your symptoms.
The electrocardiogram (ECG or EKG) is a simple test that records the electrical activity of your heart. The ECG tracing is a series of waves that represent the electrical events in the heart. By carefully examining the sequence of electrical events on the ECG, doctors are able to diagnose arrhythmias.
Holter monitoring is a continuous recording of the ECG, usually for 24 hours, while the patient goes about his or her usual daily activities. The test is useful for detecting arrhythmias that may not appear during a resting ECG at the doctor's office.
The event recorder is carried over a period of days or weeks, and is used to record abnormal heart rhythms that occur infrequently. When symptoms occur, the patient activates the recorder. The ECG recording can be transmitted over the telephone to the doctor's office or hospital.
When the basic tests do not provide all of the necessary information, an EP study may be done to find out exactly what the problem is and what can be done to control it.
Types of Arrhythmias
There are two general types of arrhythmias: Rapid Heart Rhythms and Slow Heart Rhythms. Here is a brief description of the most common arrhythmias that may require an EP study. (Keep in mind that not every arrhythmia described here will require an EP study.)
- Rapid Heart Rhythms
Rapid heart rhythms (tachycardias) may originate in the atria, AV node, or ventricles. Because the ventricles do most of the pumping, rapid rhythms in the ventricles are generally more serious.
- Supraventricular Tachycardia (SVT)
SVT is a series of very rapid heartbeats that begin in the heart's upper chambers. SVT may occur when an extra pathway exists in the atria, in the AV node, or between the atria and ventricles.
- AV nodal reentrant tachycardia (AVNRT) is the most common form of SVT. In this condition, an extra pathway exists in or next to the AV node. If an electrical impulse enters this pathway, it may start traveling in a circular pattern. This may cause the heart to contract with each cycle, and may result in a very rapid, irregular heartbeat.
Wolff-Parkinson-White (WPW) Syndrome
In WPW, an abnormal "bridge" of tissue connects the atria and ventricles. This extra pathway, called an accessory pathway, makes it possible for electrical impulses to travel from the atria to the ventricles without going through the AV node.
In people with WPW, an arrhythmia can get started when an impulse travels down the AV node to the ventricles, and then up through the accessory pathway to the atria. If the impulse continues to travel in a circular pattern, it may cause the heart to contract with each cycle and may result in a very rapid heartbeat.
Because it is prone to conduct impulses rapidly, an accessory pathway may also allow extremely rapid, and potentially serious, rhythms to occur.
In atrial fibrillation, multiple sites in the atria fire impulses in uncoordinated fashion. As a result, the atria plural beats very quickly and ineffectively.
The AV node, which acts as a "relay station," allows only some of the impulses to travel down the electrical system and stimulate the ventricles. As a result, the heart rhythm is irregular, erratic, and usually (but not always) rapid. Atrial fibrillation may occur once in a while, or it may be long-standing (chronic).