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Video transcript

multifocal atrial tachycardia otherwise known as m84 short is a type of super ventricular tachycardia it's classically associated with elderly people with chronic lung disease specifically COPD and in conjunction with old hearts that are predisposed to conduction abnormalities before we talk about what causes MIT let's take a look at the heart so here we're looking at a cross-section of the heart so imagine the heart and we slice it down the middle so we're looking at the inside of the heart over here we have the right atrium and then on this side we have the left atrium because we're looking at the patient's heart the right side is over here and the left side is over here we're looking at the patient the hearts right atrium contains the hearts dominant pacemaker the SA node near the SA node in the atria line multiple automaticity foci which serve as backup Pacers in the event that the dominant SA node fails in a normal heart the heartbeat originates from the SA node the signal travels to the structure here called the AV node and then the signal carries down through the ventricles this signal causes the ventricles to contract and that's when you feel your heartbeat however an m-80 pacemaker activity no longer originates from the SA node but rather from multiple automaticity foci each automaticity focus paces at its own rate so as a result multiple pacing centers or foci fire at the same time but no organized fashion so they're all sending signals to the ventricles to contract since the ventricles are getting signals from multiple pacing centers this is going to cause a tachycardia or heart rate of greater than 100 beats per minute on EKG ma T can be identified and diagnosed based on three main criteria one is that the heart rate is greater than 100 because ma T is a tachycardia you'll also see greater than or equal to three different P wave morphologies which is a fancy word for shapes you and you'll have variation and the PR intervals meaning that they'll be different lengths let's look at an EKG with someone at MIT you'll notice that this person is an attacker cardia we count heart rate by looking at the boxes so we start at an hour interval and we go one box that stands for 300 the next box is 150 beats per minute the next box is a hundred beats per minute so a person would have a heart rate of a hundred if the next hour interval was somewhere over here you'll notice that the RR interval is always less than three boxes so this person is definitely in a tachycardia just like classic MIT there are at least three different shapes of P waves so notice how each P wave looks slightly different and there's variation and the PR interval this PR interval is about four boxes and this one's about five also mit has an e regular rhythm the way I like to look for this is by drawing a dot above the our interval and you can notice after you draw dots above all of these that there isn't even spacing between each dot so this represents an irregular rhythm finally m80 has narrow QRS complexes that means that the QRS complex is less than or equal to 0.12 seconds or three small boxes narrow QRS complexes signify that the abnormality is coming from the atria now why does MIT commonly seen people with heart and lung disease well let's thought that what makes people particularly vulnerable to m80 is atrial distortion where the atria become pathologically enlarged so here I'm drawing enlarged atria and this can be due to years of Co PG coronary artery disease and heart failure especially that this atrial distension is a possible underlying mechanism of MIT however it can't be the only mechanism because we definitely see m-80 in people without pathologically enlarged atria also know that you can see pathological enlargement and the left or the right atria or even both at with mhe and enlarged atrium makes someone more vulnerable to the risk factors of MIT so what are MIT risk factors well anything that increases intracellular calcium and the cardiac myocyte this increase in intracellular calcium leads to spontaneous calcium release during a window time when calcium typically isn't released and this causes untimely depolarization meaning that the myocyte will depolarize during a time when it shouldn't such as a refractory period several things cause increases intracellular calcium such as hypokalemia which is a low level of potassium similarly hypomagnesemia can also cause an increase in intracellular calcium hypomagnesemia can actually promote hypokalemia through potassium wasting in the kidney hypoxia is another common risk factor that we see in m80 and again this is seen in a lot of our patients that have COPD another risk factor is acidemia which is a pathologically low pH again we see this in patients with COPD who have chronic hypoxia as well as people who just suffered a heart attack or myocardial infarction otherwise known as an MI when the heart's compromised it can't circulate blood to the tissue and so people become acidotic finally people with severe infections leading to sepsis can also have acidemia