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Studying for a test? Prepare with these 15 lessons on Circulatory system diseases.
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Ventricular tachycardia, also known as V-tach, is a rapid heart beat that arises from cells in the lower chambers of the heart, also known as the ventricles. And I'm circling them right here. Now the ventricles are the main pumpers that pump blood to the rest of the body. The heart typically beats between 60 and 100 beats per minute, or BPM. So during the time between beats, the ventricular walls relax, and that's when the heart ventricles fill with blood. When the heart beats, these walls contract and they push blood through the great vessels and out to the rest of the body. And this forward movement of blood is actually what makes you feel the pulse. So the pulse you feel on your neck, or on your wrist. So in V-tach, the heart is beating really fast. Sometimes up to 250 beats per minute. Now this is so fast that the heart has a hard time circulating enough blood to the rest of the body. And this might seem a little counterintuitive. Because you'd think if the heart's beating 250 times per minute, it's gonna be circulating a lot of blood. Well let's remember that during the time between beats is when the heart fills. And if the heart's beating 250 times per minute, there's not gonna be a lot of time between beats and there's not gonna be a lot of filling in the ventricles. This decreases the amount of blood circulation to the rest of the body. Sometimes circulation during V-tach is so poor that you don't feel that pulse, because you don't have that forward movement of blood flow since the walls are beating so fast and sometimes even weak. Generally speaking, V-tach can be broken down to two types. So there's focal V-tach, and there is re-entrant V-tach. So just like over here, we're looking at the inside of the heart, except this diagram highlights some of the important structures in the heart's electrical conduction system, and I've taken out the big vessels just to make it more simple. So again, we're still looking at the inside of the heart, just like we were over here. In focal V-tach, there are cells in the ventricles that get irritated. Now these cells might be irritated because of hormones, such as stress hormones, or thyroid hormones. Low levels of oxygen can make ventricular cells irritated. And even stretch in the heart tissue from years of either heart disease or just old age. The stretch can also make ventricular cells irritated. So for whatever reason, the cells are irritated and they're going to over-fire, sending extra stimuli to the ventricular conduction system, which is going to cause the ventricles to beat rapidly, causing a V-tach. In re-entrant V-tach, you have scar formation. Now, a scar is basically a group of dead cells that have been replaced by protein, kind of like a scab. And this group of dead cells disrupts normal electrical conduction. So you end up getting an electrical current that has to go around this patch of dead cells. And it keeps going around and around and around and around. This is a re-entrant circuit. And every time it goes around, it's going to send signal out to all these ventricular conduction cells which is going to spread through the ventricles, and it's going to make the ventricles beat rapidly, hence causing a ventricular tachycardia. So both irritated cells and scar tissue formation are going to make the ventricles fire at a rapid rate. Someone experience V-tach are going to have signs and symptoms similar to those of other diseases with rapid heart rates. Remember, you have the heart beating so fast that it's not able to circulate adequate oxygenated blood to the rest of the body, so someone might complain of shortness of breath because the body's tissues aren't getting enough oxygen, and it's going to make them want to breathe more. A person might also complain of chest pain, and that's basically because the heart itself isn't getting enough oxygenated blood. So they might say they have chest pain. People also complain of the feeling of palpitations. Which is the sensation that the heart is beating out of the chest wall. So people say they can feel the sensation of their heart beating against their chest wall like a drum. Other people feel light-headed or dizzy, and that's because the brain isn't getting enough oxygen. And in extreme cases, oxygen to the brain is so low the person might even faint or pass out. So V-tach is a really serious condition and requires immediate medical attention. Remember we're saying that the heart can't circulate oxygenated blood to the rest of the body. So at some point the person might have inadequate blood pressure. Also, V-tach can turn into the deadly heart arrhythmia called Ventricular Fibrillation. In ventricular fibrillation, the ventricular walls are actually spasming and no blood's circulating. And if this isn't corrected within seconds to minutes, this is going to lead to death. So we diagnose V-tach with an EKG. And you notice that on EKG you have these course wide QRS complexes. And a wide QRS complex means that the QRS complex is greater than three small boxes. And you can appreciate that this QRS complex is bigger than five small boxes, so it's definitely wide. Also by definition, you're going to have a tachycardia, or a heart rate greater than or equal to 100 beats per minute. In this example, the heart rate is somewhere between 300 and 150. So the heart rate's definitely over 100 beats per minute, and this is definitely Ventricular Tachycardia. Now when thinking about risk factors for V-tach, let's think about the two types. So remember in focal you have some sort of irritable cell. What causes general irritability of ventricular cells? Well a classic example is Coronary Artery Disease. In Coronary Artery Disease, blood vessels over time get clogged. And these are the vessels that supply the heart with oxygenated blood. And when the heart doesn't get enough oxygen, those ventricular cells get pretty angry and irritated. Also certain electrolyte abnormalities, like high potassium, low calcium, low magnesium, can make ventricular cells pretty unhappy. Electrolytes play a huge role in electrical conduction and activity within the heart. So you can imagine it having abnormal levels can disrupt normal conduction. We also mentioned that scar tissue formation causes re-entrant tachycardias. And what puts someone at risk for a scar tissue formation? Well the classic example is a heart attack. During a heart attack, part of the heart is deprived of oxygen-rich blood. And that tissue dies, leaving a scar. And this sets the stage for these re-entrant circuits. Because like we said earlier, these scars get in the way of smooth electrical conduction. Other conditions that are associated with scar tissue formation are hypertrophic cardiomyopathy, which is a disease that makes the heart muscles too big, and dilated cardiomyopathy, which is a disease that makes the heart walls blow out like a balloon. So just like with heart attack, these diseases also promote scar tissue formation, which are going to promote those re-entrant circuits.