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Video transcript

ventricular tachycardia also known as v-tach is a rapid heartbeat that arises from cells and 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 policy 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 200 times per minute it's going to be circulating a lot of blood well let's remember that during the time between beats is when the heart fills if the heart's beating 250 times per minute there's not going to be a lot of time between beats and there's not going to 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 reentrant v-tach so just like over here we're looking at the inside of the heart except this diagram highlight 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 selecting 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 hormone 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 metrical is to beat rapidly causing a v-tach and reaction 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 it keeps going around and around and around and around this is a reentrant circuit and every time it goes around is 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 experiencing beat akron has size 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 a sensation of their heart beating against her 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 and ventricular fibrillation the ventricular walls are actually spasming and no blood circulating and this isn't corrected within seconds two minutes this is going to lead to death so we diagnose v-tach with an EKG you notice that on EKG you have these course wide QRS complexes now 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 equal to a hundred beats per minute and in this example the heart rate is somewhere between 300 and 150 so the heart rates 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 uh ventricular cells while 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 particular cells get pretty angry and irritated also certain electrolyte abnormalities like high potassium low calcium low magnesium can make ventricular cells pretty unhappy budget relays play a huge role in electrical conduction and activity within the heart so you can imagine that having abnormal levels could disrupt normal conduction we also mentioned that scar tissue formation causes reentrant tachycardia is 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 the scar and this sets the stage for these reentrant 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 reentrant circuits