I HOPE YOU DO!
As promised, let's decipher the ECG pattern created electrically when a person's heart is functioning normally and in a healthy way. Please note that I will continue to use the term "suspected healthy" as a best practice, to avoid the impression that we truly check all aspects of health to be able to determine that a person is 100% healthy. In addition, we wish to avoid giving the impression the ECG alone can represent the overall health of the person.
ECG is a medical and professional tool focused on cardiac function (the heart's function) as represented by the neural conductance of the heart. The diagnosis of abnormalities in the heart's function is based upon comparison to the normal ECG pattern created by a normally functioning heart. This is a reminder that we will interpret the electrocardiogram from left to right.
Please note: I will use the term "de-polarization" as bearing the meaning of being neurally excited (activated), and the term "re-polarization" as bearing the meaning of relaxing or recovering at the neural level (de-activated).
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We can clearly distinct three major shapes in the normal ECG pattern above: 1) The P wave; 2) The QRS complex; 3) The T wave. They represent occurrences within the heart in the order that they occur (represented from left to right). The P wave, represents de-polarization of the atria; the QRS complex, represents de-polarization of the ventricles; and the T wave represents the re-polarization of the ventricles.
ECG does not show the re-polarization of the atria, since the re-polarization of the ventricles over-powers the re-polarization of the atria from an electrical standpoint. The de-polarization of the ventricles basically engulfs electrically the re-polarization of the atria. Thus, the ECG shows the contraction of the atria, contraction of the ventricles, and "relaxation" of the ventricles (in this order, from left to right in the ECG pattern).
The Q wave represents initial depolarization of the inter-ventricular septum (IVS); The R wave represents depolarization of the critical mass of the ventricles – resulting in the largest wave form in the ECG pattern created; The S wave represents the final depolarization of the ventricles, at the base of the heart (lowest part of the heart).
Visually, we notice that compared to the baseline (where the pattern begins), the P wave rises above the baseline; the Q wave dips under the baseline; the R wave rises the highest above the baseline; the S wave dips the most underneath the baseline; and finally, the T wave rises above the baseline.
The visual representation of the waves is determined by the relative conductance of the neural impulses compared to the locations of the electrodes. We put electrodes on the body as a mean to record the electrical impulses passing through the heart, and also to give us the option to know the relative location of those neural impulses compared to the electrodes.
Lastly, while extremely rare due to its "weak" electrical amplitude, an ECG might show the U wave. The U wave is hypothesized to be caused by the re-polarization of the inter-ventricular septum (IVS). If shown, the U wave appears shortly after the T wave. It is represented by a very small rise above the ECG baseline.
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In my next post related to ECG, I will explain how to prep a person for ECG, and how the set-up of the ECG leads to the ECG output we get in the form of an electrocardiogram output. Stay tune, more empowering knowledge to come. Knowledge itself is power, you better believe it...doctor's orders...sort of!
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