LEARN TO SPEAK ELECTRICAL!
ECG is a medical tool for healthcare professionals to monitor, assess, and diagnose heart (cardiac) function. Electrocardiography is the process of measuring the heart's electrical activity, which produces an electrocardiogram. The electrocardiogram is a visual printout or digital representation of how electricity changes as it travels through the human heart.
I always claim that ECG is a language based on electricity, with electrical representations of occurrences within the heart as its words. ECG is used as a diagnostic tool, where the key to speaking ECG is to compare everything to the electrical pattern created when neural impulses travel through the heart in a way indicative of healthy heart function.
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Electrical impulses (neural impulses) travel through the heart in a specific and reoccurring order, from one part of the heart to another, time and time again. Thus, each and every beat will create an identical or highly similar pattern registered on the electrocardiogram. Any deviation from the normal pattern representing healthy function, indicates a deviation from healthy function of the heart.
Just as electricity travels through the heart from point A to point B in a one-directional manner, the electrocardiogram will register electrical occurrences representing that same order from left to right. This means that anything that appears on the electrocardiogram to the left represents a cardiac process that occurred before anything that appears to the right of the electrocardiogram. Thus, the ECG language is "spoken" and read from left to right (just like English).
Let's described the heart's structure in a simplified way, so it serves us later on in this mini-series of posts dedicated to ECG. The heart is mainly structured as four chambers, two atria (one atrium, two atria), and two ventricles. The ventricles are bigger than the atria, the left side chambers (left atrium and left ventricle) are about three times bigger compare to their counter-chamber on the right side. Thus, the chambers in order of biggest to smallest are the left ventricle, right ventricle, left atrium, and the smallest is the right atrium.
While in the anatomical position, the atria are located above the ventricles, closer to the head. Separating between the chambers is a wall called the septum. Septum in latin means "a divide", and indeed it divides between the left and right sides of the heart. Furthermore, it is crucial to understand the ultimate function and functional purpose of the heart, before we dive deeper into ECG. The heart can be described as a muscular sack with its opening facing upwards (represented by the aortic valve, leading to the aorta artery).
This anatomical arrangement demand a very specific heart contraction sequence, that end with blood being pumped/ejected very accurately into a relatively narrow opening at the top of the heart. Since heart muscle fibers are stimulated and activated by a neural impulse, the order in which they will be stimulated, will determine the order in which these fibers will contract, and thus determined the direction in which blood will be pushed.
The wrong order of electrical stimulation of heart fibers, can result in cardiac dysfunction, which is always a bad idea. Thus, any change in the order of neural (electrical) activation of cardiac muscle fibers will result in a possible pathology (clinical problem), that will be represented in the electrocardiogram. With that said, due to the nature of an electrocardiogram's tendency to represent the stronger electrical occurrences, some processes might not be shown, as they are over-powered by a stronger electrical phenomenon.
The heart has two leading and natural pacemakers the initiate the electrical excitation of the heart's chambers and muscle fibers. It begins with the sino-atrial node (the SA node or SAN) located in the upper right atrium. The atria are activated first as the electrical current travels to them first, causing them to contract. Afterwards, the electrical impulse travels downwards via electrical conduction pathways, to the second pacemaker known as the atrio-ventricular node (AV node or AVN). At this point the impulses are slowed down while the atria contract.
The impulses must now continue further downwards towards the ventricles through an electrical pathways called the Bundle of His, it carries the neural impulses through the septum dividing the chambers (the Inter-ventricular septum; IVS), until the bundle separates to a right and left bundle branch, then further branch out into the Purkinje Fibers. The Purkinje Fibers contract the entire ventricle and assure contraction of both ventricles together.
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Now we have enough information as a basis for future posts that will deepen our knowledge of the heart operates in suspected healthy people, and sets the basis for learning about abnormal cardiac functions. Last reminder, the electrocardiogram represents the path of neural impulses as they travel through the heart, and the parts of the heart they excite and activate.
In my next post, I will present the ECG pattern that represents normal heart function, and explain it as the basis for future comparisons and ECG interpretation. Maybe if I do a great job, you guys will have an electrifying experience...wink, wink...
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