EKG Info

Ask the DOC

Last month, the publisher (Kevin Boyle) received an email from a reader asking me to do a column about home electrocardiograph (EKG or ECG) machines. The reader specifically mentioned the KardiMobile EKG device. Before I get into that device, allow me to mention some basics about the science and technology of EKGs.

An EKG machine measures the tiny electrical currents generated in the heart before, during, and after a heartbeat. To begin a heartbeat, an electrical impulse is generated in the sinoatrial node, the heart’s intrinsic pacemaker located in the upper left chamber, known as the atrium. As this impulse travels down the electrical pathway in the heart, it first causes the atrium to depolarize or contract, and then the ventricle. After the heart muscle contracts, it must electrically reset itself to be able to accept the next impulse. This electrical reset is called repolarization. All this electrical activity is tracked by the EKG machine.

The first use of electrocardiography was in the 1870s. By about 1910, EKG units were commercially developed. These units were very large, about the size of a bedroom dresser. Up until the 1980s, EKG units were analog, meaning the electrical impulses from the heart caused a small motor in the EKG machine to move a stylus over a paper graph, creating a recording.

With the advent of the digital age, the motor and stylus were eliminated. The most common EKG units in use today create a 12-lead, or 12-channel, recording using ten electrodes. One electrode for each limb, and six electrodes spaced across the chest. These are called the precordial leads. 12-lead EKGs can be used to diagnose a variety of heart issues, including rhythm disturbances, heart enlargement, heart damage (i.e., from a heart attack), electrical impulse issues, and heart attacks. They are also used to check the performance of implanted devices like pacemakers and defibrillators.

In today’s digital world, EKG devices for home use come in all shapes and sizes, from smart watches to devices like the KardiMobile EKG. But almost all of these devices that are intended for use outside of a medical setting are one lead devices, meaning they only have two electrodes, not ten. Typically, they use the same setup that EMTs use. They will give a one channel recording, not a 12-channel recording. They are most useful at detecting heart rhythm anomalies, for example atrial fibrillation. In most cases, they cannot detect or diagnose abnormalities like a 12-lead recording can, for example a heart attack in progress. On the upside however, they are relatively inexpensive and, when used with a smartphone, they can email the recording directly to the patient’s physician. They are most suited for use by someone who has an ongoing heart rhythm issue like atrial fibrillation or has a pacemaker or defibrillator.

Another useful and inexpensive home health device is a pulse oximeter, which clips onto a fingertip and measures the amount of oxygen in the blood and the heart rate. A normal pulse oximeter, or pulse ox, reading would be between 93 to 98%, however someone with a pulmonary disease like asthma or COPD might have a reading at or below 90%. These units are helpful to have at home for those with these lung diseases, especially during a symptom flare-up. A low pulse ox may be an indication to call the doctor and get to the hospital.

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By Peter Galvin, MD


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