Atrial Fibrillation

Diagnosis

In atrial fibrillation, the electrical signals in the atrial (upper) chambers of the heart are chaotic and the electrical impulses reach the ventricles (lower heart chambers) often at irregular intervals, causing a fast and irregular heartbeat.

A comprehensive diagnosis at Mayo Clinic helps to determine the severity of the atrial fibrillation and its potential to cause more serious conditions, such as stroke.

To diagnose atrial fibrillation, the patient may be asked about or tested for conditions that may trigger the fibrillation, such as heart disease or a thyroid gland problem. The patient may have two heart monitoring tests: active and passive.

Active Tests

These tests involve trying to actively induce an irregular heartbeat while the patient is being closely monitored. They include:

Electrophysiology (EP) testing and mapping
In the EP test, catheters (thin, flexible tubes) with electrodes at the tips, are threaded through the patient's blood vessels to various spots within the heart. Once in place, the electrodes can precisely map the spread of electrical impulses through the heart.

During the test, the electrophysiologist (a cardiologist who specializes in heart rhythms) may use the electrodes to stimulate the heart to beat at rates that may trigger — or halt — an irregular heart beat. This allows the doctor to locate the arrhythmia and the mechanics of the heart that may be causing the irregular heartbeat.

The ability to trigger and then stop an atrial fibrillation may also be used to test various treatment methods for their effectiveness. For example, if catheter radiofrequency ablation (also known as atrial fibrillation ablation) — a catheter-based treatment option for many arrhythmias — is determined by the doctor to be appropriate treatment, the procedure can be performed during EP testing. Read more about atrial fibrillation ablation.

Stress test
Atrial fibrillation may be triggered or worsen when the patient is exercising. During a stress test, the patient may exercise on a treadmill or stationary bicycle, with close monitoring by an ECG of heart activity. The test may involve use of a drug to stimulate the heart, similar to how exercise stimulates it. This may be particularly helpful to patients who have difficulty exercising. The stress test can also be used to detect coronary artery disease.

Passive Tests

These tests involve monitoring the heart during regular activity. They include:

Electrocardiogram (ECG)
In this test, electrodes (sensor patches with wires attached) are placed on the patient's skin to measure the electrical impulses given off by the heart. The ECG measures the timing and duration of each electrical phase in the heartbeat.

Holter monitor
A Holter monitor is a portable ECG device that the patient wears for a day or more to record the heart's electrical activity during the patient's daily routine.

Echocardiogram (Doppler echocardiogram)
This test uses sound waves to produce detailed images of the patient's heart. Through a handheld device (transducer) on the patient's chest, sound waves bounce off the heart and are reflected to produce video images of the heart's size, structure and motion. The echocardiogram can also be used to measure the heart's blood volume and the speed and direction of blood flow through the heart.

Blood tests
These may help rule out thyroid problems or other blood chemistry abnormalities that may lead to atrial fibrillation.