Diagnosis of a bundle branch block (BBB) begins with a complete medical history and physical examination. A physician will also order a painless test called an electrocardiogram (EKG), which measures the heart’s electrical activity. Once a clear diagnosis of BBB has been made, the physician will try to determine what is causing it.

Tests that may be ordered to determine the cause of bundle branch block include:

• Echocardiogram. This test uses sound waves to visualize the structures and functions 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 muscle’s thickness, size and function. All four of the heart’s chambers can be assessed and measured. The image also shows the motion pattern and structure of the four valves, revealing any potential leakage (regurgitation) or narrowing (stenosis). During this test, a Doppler ultrasound may be done to evaluate cardiac blood flow and to assess the presence and/or severity of any valvular heart disease. This test may also include a stress echocardiogram, which combines a standard echocardiogram with a stress test to evaluate heart function during exercise.
  
  
  
  
  
• Nuclear stress test. A test that includes all the procedures performed during a standard exercise stress test, as well as producing clear pictures of heart muscle on a video monitor. The physician is not only able to compare the heart’s electrical activity at rest and under exertion, but can also determine which parts of the heart are healthy and functioning, and which are not. The test involves the administration of a radionuclide substance called a tracer. Both nuclear and echocardiography stress testing can help in determining whether these abnormalities are related to the presence and severity of coronary artery disease.
  
  
• Electrophysiology study. An invasive test that can be useful in assessing the severity of electrical disturbances that can indicate the presence of a bundle branch block. In some cases preventative implantation of a pacemaker is recommended if the risk of progression to a complete heart block is very high.