An Overview of the EKG

The Electrocardiogram (EKG) has been an immensely useful and practical tool in cardiology for over 120 years. Its longevity is amazing if one considers how quickly new technological advances make older tests completely obsolete.

EKG Machines show the heart’s electrical activity, printing the “spikes” on paper for the doctor to read.

EKG provides a snapshot of the heart's electrical activity. Human heart is an amazing high-tech organ that does a lot more than simply pumping blood through our arteries. The heart cells that do this heavy-labor, mechanical work will not function unless there is an electricity current flowing through them. The part of the heart that creates electricity (out of nothing!) is called the sinus node and is located in one of the upper chambers of the heart (the right atrium). It then spreads to the rest of the heart, including the bottom chambers (the ventricles) where the “heavy lifting” and pumping of our heart occurs. In case the sinus node cannot function properly, other heart cells can take over the electrical production, although not quite as efficiently as the sinus node can. If none of the heart cells can create the needed electrical beat then a pacemaker may become necessary.

The EKG reveals the electrical activity in the heart, but why is this so important? What can the heart's electrical activity tell us about our health? It can first tell us whether the heart rhythm is normal or abnormal: is the rhythm too fast? Too slow? Are there any extra or skipped beats or is the rhythm completely erratic, like in atrial fibrillation? Beyond information about the heart’s rhythm, the EKG allows us to diagnose previous heart attacks or, indirectly, severely clogged heart arteries.  If a large part of the heart has been damaged by a previous heart attack that part is electrically silent and shows up on the EKG. The pattern of the heart's electricity also changes in hearts that, because of clogged arteries, receive less oxygen. This is how the stress test (also referred to as a treadmill test) can help diagnose heart disease: by recording the EKG of a patient who walks briskly on a treadmill for a few minutes while attached to an EKG monitor, the EKG pattern reveals any serious oxygen shortage to a large part of the heart. Consider that at a normal, resting heart rate, an 80-90% blockage in the arteries is usually not obvious on the EKG as the demand of the resting heart for oxygen is so low that a 10-20% opening of the artery is plenty to allow things to proceed normally. However, if we stress the heart and ask it to do more, such a blockage prevents the heart from meeting the increased oxygen demand and this problem usually becomes obvious on the stress EKG. 

EKG also gives useful clues when the chambers of the heart (atria or ventricles) become enlarged, thick or weak. And while the EKG may not be a very precise test and can’t give us an answer for everything, it can tell us that something is wrong and point towards the need for more detailed testing. Frequently an abnormal EKG becomes the indication for more specialized heart testing like ultrasound of the heart, nuclear cardiology, CT or MRI of the heart or even invasive direct visualization of the heart and its arteries. As the mechanical behavior of the heart changes when heart disease occurs, so does its electrical behavior. In this way we get early clues from the inexpensive, quick, practical EKG and doctors make a decision whether more expensive, complex and riskier tests are necessary. EKG has stood the test of time: invented in the early 20th century has made it well into the 21st century. It's easy to perform, it requires no needles, no pain, and no radiation -- making it very useful for patients and doctors alike.