Tests and diagnosis

By Mayo Clinic Staff

Your doctor will likely start with a health history, a physical exam and laboratory tests, including:

  • Blood tests, to check thyroid hormone and potassium levels in your blood, which may lead to some heart rhythm disorders.
  • Chest X-ray, to check if your heart is enlarged.

Next, your doctor will likely recommend heart tests.


An electrocardiogram (ECG) uses small sensors (electrodes) attached to your chest and arms to record electrical signals as they travel through your heart. Your doctor can look for patterns among these signals that indicate the presence of an extra electrical pathway in your heart. This pathway can usually be detected even when you're not currently experiencing an episode of a fast heartbeat.

Your doctor may also ask you to use portable ECG devices at home to provide more information about your heart rate. These devices include:

  • Holter monitor. This portable ECG device is carried in your pocket or worn on a belt or shoulder strap. It records your heart's activity for 24 hours, providing your doctor with a prolonged look at your heart rhythms. Your doctor will likely ask you to keep a diary during the 24 hours, describing any symptoms you experience and recording when they occur.
  • Event recorder. This portable ECG device is used to monitor your heart activity over a period of time ranging from a few weeks to a few months. You activate the recorder only when you experience symptoms of a fast heart rate.

Electrophysiological testing

This test may be used to confirm a diagnosis of Wolff-Parkinson-White syndrome or to pinpoint the location of the extra pathway. Usually, you will be awake but given medication to help you relax. Thin, flexible tubes (catheters) tipped with electrodes are threaded through your blood vessels to various spots in your heart. Once in place, the electrodes can precisely map the spread of electrical impulses during each beat and identify an extra electrical pathway.

March 19, 2014