Dear Dr Roach: My 35-year-old son recently complained of some chest pain. He went to his doctor, and it was determined that he strained himself exercising. However, the doctor recommended he go for a stress test. By the time he got to a cardiologist, his chest pain was gone, but he underwent a stress test anyhow. His cardiologist wrote: Your stress test looks OK. No major changes in EKG while on the treadmill for 10 minutes. However, the test is not 100% accurate because you have right bundle branch block. Can you explain that to us? Is it serious? What is the treatment and outlook? C.D.S.
Answer: The heart has an electrical conduction system, similar to wires, connecting the pacemaker of the heart (in the top right chamber, the right atrium) to all the other chambers. It does this by way of the atrioventricular node, which continues into the ventricles as the Bundle of His. That structure then breaks into two main bundles of specialized cells that transmit the signal to the ventricles, called the left and right bundle branches.
If the bundle branch is unable to send a signal, it is called a bundle branch block. The electrical impulse will still find its way to the muscle, but it will get there a little slower. This is not enough to cause mechanical problems to the heart, but it can be seen on the electrocardiogram. The presence of a right bundle branch block does make the EKG part of a stress test a little harder to interpret; however, the ability to diagnose heart attack and damage to the heart is largely unimpaired, since the crucial first part of the EKG wave is not affected by a right bundle branch block (unfortunately, a left bundle branch block makes the EKG much less interpretable for diagnosing angina and heart attack).