General responses to selected questions from Joel Braunstein, MD, of Johns Hopkins University and Joseph Toscano, MD.
Question:
I received an electrical shock one year ago in my kitchen. My heart hurts now at times like a knife is going through it and it feels like someone is sitting on my chest. I cannot pass a stress test and have been told I have extra beats, but that everyone has them. A nurse told me they should not hurt. I'm scared there is something wrong. None of my EKGs are normal, either. They said something about sinus rhythm. Could the shock have hurt me? I know you can stop a heart with a shock and you can start it. What happens if you shock a healthy heart?
Answer:
Every normal heart has a natural "pacemaker" called the SA (sinoatrial) node. It is a group of specialized nerve cells in the upper right portion of the heart that send out a small electrical impulse at a regular tempo. When the impulse passes through the heart, it makes the heart muscle squeeze to pump blood. In a normal heart, the SA node sends out an impulse regularly and this results in an even heartbeat. This is called "sinus rhythm" and is the normal rhythm for the heart. In addition to the SA node, any muscle cell in the heart can send out an impulse, causing an "extra" or early heart beat. This serves as a protective mechanism for the heart – in case anything happens to the SA node, some other part of the heart can keep it going. The early beats don’t happen often because the natural rate of the SA node is faster than the natural rate of any of the muscle cells.
Occasionally however, one of these cells will send out an impulse before the SA node. When the muscle cell which sends out the impulse is in one of the top two chambers of the heart (called the atria), the extra or early beat is called a "PAC" (for premature atrial contraction) or "APC" (atrial premature contraction). When the muscle cell which sends out the impulse is in one of the bottom two chambers of the heart (called the ventricles), the extra or early beat is called a "PVC" (for premature ventricular contraction) or "VPC" (ventricular premature contraction). A doctor can tell a PAC from a PVC by its shape on an EKG strip. Isolated PACs or PVCs occur in just about everyone at some time and they do not cause any specific problems. When they occur in large numbers or in combinations or clusters, then there could be more of a problem. For more information about PACs and PVCs, check out the Heartinfo.com link to Arrhythmia: A Patient Guide.
