What is an Arrhythmia?
How are Arrhythmias Diagnosed?
The Normal Heart
The Premature Heartbeat
Abnormal Heart Rhythms

The UCSF Electrophysiology Service, Implanted Device Clinic and Catheter Ablation Center are known worldwide. In fact, catheter ablation was developed at UCSF in the 1980's. But just what is an arrhythmia, and how is one diagnosed? What sort of electrical impulses are conducted in a normal heart? What are some of the abnormal heart rhythms that can occur? We have prepared some answers to some of the most frequently asked questions about arrhythmias below.

What is an Arrhythmia?
An abnormal heart rhythm is a change in either the speed or the pattern of the heartbeat -- the heart may beat too slowly, too rapidly or irregularly. A heart which beats too fast or too slow can cause:

· Lightheadedness or dizziness
· Palpitations (skipping, fluttering or pounding in the chest)
· Fatigue
· Chest pressure or pain
· Shortness of breath
· Fainting spells

Sometimes there are no symptoms at all. Left untreated, certain abnormal heart rhythms can cause death. On the other hand, some arrhythmias are common and not associated with any untoward conditions, so called benign arrhythmias. One of the goals of evaluation is to sort out the serious from the benign forms of heart beat disturbances.

How Are Arrhythmias Diagnosed?

If your doctor suspects that you may have an arrhythmia, he or she will order one or more of the following diagnostic tests to determine the source of your symptoms.

Electrocardiogram

The electrocardiogram (ECG) records the heart's electrical activity. Small patches called electrodes are placed on your chest, arms and legs, and are connected by wires to the ECG machine. Your heart's electrical impulses are translated into a wavy line on a strip of moving paper, enabling doctors to determine the pattern of electrical current flow in the heart, diagnose arrhythmias and heart damage.

Holter Monitor
A holter monitor is a small portable machine that you wear for 24 hours, it enables continuous recording of your EKG as you go about your daily activities. You will be asked to keep a diary log of your activities and symptoms. This monitor may detect arrhythmias that might not show up on a resting EKG which only records for a few seconds

Exercise Stress Test
The exercise stress (treadmill) test enables physicians to record your heart's electrical activity which may not occur at rest.

Event Recorder
An event recorder (loop recorder) is a small portable transtelephonic monitor that may be worn for several weeks. This type of recorder is good for patients who do not experience their symptoms very often. The monitor 'loops' a two minute recording into its memory which is continually overwritten, when you experience symptoms you press a 'record' button on the monitor which stores a correlating strip of EKG. The recordings are telephoned through to a 24 hour monitoring station and faxed directly to the requesting physician.

Magnetic Source Imaging
Magnetic source imaging (MSI) is used as an overlay to magnetic resonance imaging (MRI). The device senses weak magnetic fields generated by heart muscle tissue and localizes the arrhythmia non-invasively to save time during the invasive study.

Tilt Table Test
Tilt table testing is used to diagnose vasovagal syncope (fainting or black-out spells) by trying to reproduce the black-out episodes. You will be tilted upright to about 60 degrees on a special table for a period of time with continuous recording of your ECG and blood pressure.

The Electrophysiology Study
The EP study allows doctors to:

1. provoke and examine an arrhythmia under controlled conditions;
2. acquire more accurate, detailed information than with any other diagnostic test;
3. choose the most effective treatment for you;
4. in many cases, provide treatment (i.e. catheter ablation) during the same session.

During the study, doctors insert special electrode catheters -- long, flexible wires -- into veins and guide them into the heart. These catheters sense electrical impulses and may also be used to stimulate different areas of the heart. Doctors can then locate the sites which are causing serious arrhythmias.

The Normal Heart
The heart is muscular and hollow, constantly pumping blood to deliver oxygen and nutrients to the body. It is comprised of four compartments, or chambers- two on the right side and two on the left. The upper chamber on each side, called the atrium (plural: atria ), receives and collects blood. The lower chambers- the ventricles -pump blood. All four chambers work together to move life-sustaining blood through the body.
The heart's rhythmic contractions depend on an electrical system which conducts electrical impulses throughout the heart. The sino-atrial (SA) node (see illustration) is where the electrical impulse normally begins, setting the pace for the heartbeat. The impulse spreads through the atria, causing a contraction and squeezing blood into the ventricles. From the atria, the impulse reaches the atrioventricular (AV) node -a site where each electrical impulse slows down before it passes through to the ventricles. Normally, except at the AV node, the atrium is electrically insulated from the ventricle by fibrous tissue. Through a specialized muscle fiber system, the impulse is distributed throughout both ventricles, causing them to contract and pump blood.

This normal conduction is called normal sinus rhythm - the rhythm is regular and the heart beats 60 to 100 times per minute.

The Premature Heartbeat
A premature heartbeat comes too soon and interrupts the regular rhythm of the heart. Premature beats may originate in the atrium (premature atrial contraction or PAC) or in the ventricles (premature ventricular contraction or PVC), producing a sensation that your heart is "skipping" or "flip-flopping." Although premature beats are more common in people with heart disease, almost everyone has experienced a "skipped" beat once in a while, which may be due to smoking, fatigue, alcohol, caffeine, other stimulants, or may have no apparent cause. Usually single premature beats require no treatment. However, when they are frequent or annoying, your doctor may recommend a test to search for their cause.

Abnormal Heart Rhythms
Click on one of the abnormal rhythms below to learn more:

To learn more about EP Studies at UCSF, please examine our patient guide .

Text by Marilynn Namekawa Wong, R.N., B.S.N., Electrophysiology Arrhythmia Nurse Coordinator