Diagnosis of sick sinus syndrome (SSS) is usually made after a medical history and physical examination by a cardiologist. The syndrome is difficult to diagnose because patients often have few symptoms, and many patients are elderly and have other cardiac conditions. In general, a physician looks for the following combinations of signs, in addition to arrhythmias, to make a diagnosis of SSS.

One or more of the following tests may be used in diagnosing sick sinus syndrome:

• EKG. A recording of the heart’s electrical activity as a graph on a moving strip of paper or video monitor. The highly sensitive electrocardiograph machine helps detect heart irregularities, disease and damage by measuring the heart’s rhythms and electrical impulses.
  
  
  
  
  
• Holter monitor. A continuous EKG that is temporarily attached to an ambulatory (freely moving) patient and run for a 24-hour period (though it can be used for up to five days).
  
  
• Cardiac catheterization. A group of diagnostic tests that are performed with the use of a catheter, or a thin, hollow tube that is inserted into a large blood vessel and fed to a target area (e.g., the heart). Through the catheter, the physician can measure pressure, obtain a tissue sample or perform a coronary angiogram.
  
  
• Tilt table testing. A test in which the patient is strapped to a table that is then tilted. It is used to help determine the cause of unexplained fainting (syncope).
  
  
• Electrophysiology study (EPS). A test that uses an electrode catheter to locate a particular pathway through which electrical impulses travel in the heart and to determine the extent of any abnormal impulses traveling through it.
  
  
• Stress test. An electrocardiogram performed while the patient exercises in a controlled manner on a treadmill or stationary bicycle at varied speeds and elevations.
  
  
• Atropine Test. Atropine sulfate is a medication that, when given intravenously, usually increases the patient’s heart rate to over 100 beats per minute. The bradycardia (slow heart rate) associated with SSS, however, is drug resistant, meaning it does not respond to medications. When atropine sulfate is injected into a patient with SSS, their heart rates rarely rise above 90 beats per minute. Therefore raising the heart rate by atropine sulfate injection is usually attempted before the diagnosis of SSS is confirmed.
  
  
• Adenosine Test. Recently, a different compound called adenosine has also been researched as a test for SSS. Adenosine is a natural metabolic substance that affects heart rate. When given intravenously, adenosine inhibits the sinus node, resulting in a decreased heart rate. Researchers have proposed that patients with SSS may be more sensitive to this reaction than healthy patients. Therefore, patients with SSS will have a marked slowing of the heart rate (a sinus pause) when given adenosine. While it is not a standard test at this time, researchers hope that the accuracy of the adenosine test will eventually eliminate the need for more invasive procedures, such as the electrophysiology study in the diagnosis of SSS.