Brief episodes of atrial fibrillation (AF) are known as paroxysmal atrial fibrillation. These episodes occur for a few minutes to a few hours before the heart returns to a normal rhythm. Paroxysmal AF is harder to diagnose because it is rarely associated with symptoms. Persistent or permanent AF, which can persist for months or years, is easier to diagnose.

There are a variety of ways to diagnose AF. For example, the physician may use a stethoscope to listen for abnormal heart rhythms. Additional tests that may be ordered include:

• EKG (electrocardiogram). An electrocardiogram (EKG) is a recording of the heart’s electrical activity as a graph on a moving strip of paper or video monitor. The pattern that is generated by the electrical impulses reveals whether the heart rhythm is normal or if the heart muscle is damaged.
  
  
  
  
  
• Holter monitor. A continuous EKG is temporarily attached to an ambulatory (freely moving) patient for a 24-hour period (though it can be used for up to five days). This test can detect or diagnose abnormal heartbeats (arrhythmias), as well as cardiac ischemia. It can also help evaluate the effectiveness of any medications, especially antiarrhythmics, the patient may be taking.
  
  
• Blood tests. These tests measure blood oxygen levels, electrolytes and other possible indicators of an underlying cause of AF.
  
  
• Thyroid hormone test. Studies have shown that hyperthyroidism is commonly associated with atrial fibrillation. Patients experiencing their first suspected episode of atrial fibrillation will also likely be asked to undergo a thyroid test.
  
  
• Stress test. An electrocardiogram is performed while the patient exercises in a controlled manner on a treadmill or stationary bicycle at varied speeds and elevations. The reaction of the heart under exertion can be measured and evaluated. It may be ordered to assess the extent of artery damage and/or coronary artery disease.
  
  
• Echocardiogram of the heart and major arteries. This test uses sound waves to track the structure and function of the heart. A moving image of the patient’s beating heart is played on a video screen, where a physician can study the heart’s thickness, size and function. The image also shows the motion pattern and structure of the four heart valves, revealing any potential leakage (regurgitation). During this test, a Doppler ultrasound may be performed to evaluate blood flow in the heart’s chambers, the blood vessels of the arms and legs, and the carotid arteries in the neck. An echocardiogram is useful in detecting structural abnormalities that lead to atrial fibrillation. The evaluation of heart function is also helpful in selecting antiarrhythmic medicines, if needed. 
  
  
  
  
  
• Transesophageal echocardiography (TEE). This test uses a small transducer attached to an endoscope that is inserted through the patient’s mouth and throat, and into the esophagus (the long tube from the throat to the stomach). This will not affect the patient’s ability to breathe freely but might temporarily interfere with swallowing. Once positioned, the transducer can transmit a clear image of the heart’s size and function. It may be used to detect blood clots in the atria. It also allows better assessment of the structure and function of the heart valves.
  
  
  
  
  
• Electrophysiology study (EPS). A test that involves an electrode catheter that is fed through a blood vessel and into the atria and ventricles. Once in place, electrical activity is recorded to assess the presence and source of abnormal heart rhythms, or to see if there has been any progress from medical treatments.