To diagnose a heart arrhythmia, the doctor will usually do a physical exam and ask questions about your medical history and symptoms. Tests may be done to confirm an irregular heartbeat and look for conditions that can cause arrhythmias, such as heart disease or thyroid disease.

Tests to diagnose heart arrhythmias may include:

• Electrocardiogram (ECG or EKG). During an ECG, sensors (electrodes) that can detect the electrical activity of the heart are attached to the chest and sometimes to the arms or legs. An ECG measures the timing and duration of each electrical phase in the heartbeat.
• Holter monitor. This portable ECG device can be worn for a day or more to record your heart’s activity as you go about your routine.
• Event recorder. This wearable ECG device is used to detect sporadic arrhythmias. You press a button when symptoms occur. An event recorder may be worn for a longer period of time (up to 30 days or until you have an arrhythmia or typical symptoms).
• Echocardiogram. In this noninvasive test, a hand-held device (transducer) placed on the chest uses sound waves to produce images of the heart’s size, structure and motion.
• Implantable loop recorder. If symptoms are very infrequent, an event recorder may be implanted under the skin in the chest area to continually record the heart’s electrical activity and detect irregular heart rhythms.

If your doctor doesn’t find an arrhythmia during those tests, he or she may try to trigger the arrhythmia with other tests, which may include:

• Stress test. Some arrhythmias are triggered or worsened by exercise. During a stress test, the heart’s activity is monitored while you ride on a stationary bicycle or walk on a treadmill. If you have difficulty exercising, a drug may be given to stimulate the heart in a way that’s similar to exercise.
• Tilt table test. A doctor may recommend this test if you’ve had fainting spells. Your heart rate and blood pressure are monitored as you lie flat on a table. The table is then tilted as if you were standing up. The doctor observes how your heart and the nervous system that controls it respond to the change in angle.
• Electrophysiological testing and mapping. In this test, also called an EP study, a doctor threads thin, flexible tubes (catheters) tipped with electrodes through the blood vessels to different areas within the heart. Once in place, the electrodes can map the spread of electrical impulses through the heart.Sometimes, a heart doctor (cardiologist) uses the electrodes to stimulate the heart to beat at rates that may trigger — or stop — an arrhythmia. Doing this helps the doctor determine the location of the arrhythmia, its possible causes and the best treatment options. This test may also be done to determine if a person with certain health conditions is at risk of developing heart arrhythmias.