Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Heart failure wikipedia , lookup
Cardiac contractility modulation wikipedia , lookup
Lutembacher's syndrome wikipedia , lookup
Hypertrophic cardiomyopathy wikipedia , lookup
Cardiac surgery wikipedia , lookup
Myocardial infarction wikipedia , lookup
Jatene procedure wikipedia , lookup
Dextro-Transposition of the great arteries wikipedia , lookup
Atrial fibrillation wikipedia , lookup
Ventricular fibrillation wikipedia , lookup
Heart arrhythmia wikipedia , lookup
Arrhythmogenic right ventricular dysplasia wikipedia , lookup
Lecture 16 Analyzing EKG vectors and MEA Vectors are arrows that point you in a direction, and their size tells you how much current is traveleing through the heart. An EKG is a monitor of electrical events occurring on the surface of the heart. EKG records these events: 5 cardiac vectors 1. Atrial depolarization: Down ant to left 2. Right side of IV septum, up and to the right 3. Big vector for IV septum 4. Left ventricular wall, goes lateral 5. Ventricular Repolarization: IV septum is last to repolarize Electrocardiogram (ECG) • Depolarization wave passes through the heart and the electrical currents pass into surrounding tissues. • Small part of the extracellular current reaches the surface of the body. • The electric potential generated can be recorded from electrodes placed on the skin • An EKG is a comparison of two vectors • It compares the “heart vector” showing current flow on the heart with the reference, “recording lead vector” on the body. Vector diagrams • Vectors are used to describe depolarization and repolarization events • Vectors are arrows which show two things: – Direction or pathway (of charge spread) – Magnitude or size (amt of charge) • Vector analysis explains the waves on an EKG GPS tells you where you are and where you want to go. The EKG shows the same thing. EKG is Extracellular Recording • Only looks at the charge on the outside of fibers! – Resting cell: outside positive – Depolarizing cell: outside negative – Repolarizing cell: outside positive • Depolarization: spread of surface negative charge • Repolarization: spread of surface positive charge Vectors will always be positioned so that head of vector is in area of positive charge; tail is in area of negative charge. Top right atria will repolarize first. Even though electrical current is spreading from top down, the arrow has to point to the positive charge, so it points up and to the right What does that tell you about the recording you obtain from each lead? • Each lead describes the events on the heart from “it’s own point of view” • Reading from several leads gives you different points of view about the same set of repeating events (depol, repol) • What if the recording lead was oriented this way? 12 Lead EKG’s • Read from each lead independently; one at a time over several heartbeats. • See what each lead shows. • 12 leads – 3 bipolar limb leads (I, II, III) – 3 augmented unipolar limb leads • (aVR, aVL, aVF) – 6 precordial leads (chest leads, V1-V6) 6 Leads- bipolar and augmented; all of these are in flat plane Bipolar Leads and Einthoven’s Law • Lead I - The negative terminal of the electrocardiograph is connected to the right arm, and the positive terminal is connected to the left arm. • Lead II - The negative terminal of the electrocardiograph is connected to the right arm, and the positive terminal is connected to the left leg. • Lead III - The negative terminal of the electrocardiograph is connected to the left arm, and the positive terminal is connected to the left leg. • Einthoven’s Law states that the electrical potential of any limb equals the sum of the other two (+ and - signs of leads must be observed). Lead I LA – RA Lead III LL- LA Lead II LL- RA Summary of Events • P wave – atrial depolarization- SA node to the AV node – (mechanical event that will result: atrial systole) • QRS complex- depolarization of ventricles – Q wave- due to left to right depolarization at bundle branch (right has “detour”) – atrial repolarization and diastole (signal obscured) – AV node fires, ventricular depolarization – (mechanical event that will result: ventricular systole) • T wave – ventricular repolarization – (mechanical event that will result: ventricular diastole. ventricles remain somewhat contracted until a few milliseconds after the end of the T repolarization wave.) Intervals & Segments • Segments are flat lines, do not include waves: PR segment, ST segment. • Intervals include at least one wave • P-R interval- from beginning of P to the Q wave. Is time for atrial depolarization plus delay from AV node. Also, time of atrial contraction (more than .2 sec could be 1st degree block) • P-R segment- delay in impulse through AV node. • Phases of EKG • Q-T interval- includes Q and T waves, total time for ventricular depolarization and repolarization; this approximates the time of total ventricular contraction. • T-P segment - end of one cycle to beginning of next • • • • • • • • • • • • • P-P interval - time for one complete cycle (could also use R-R or T-T, etc.) S-T segment: time between ventricular depolarization and repolarization; time of peak ventricular contraction (maximum tension) Cardiac Arrhythmias Tachycardia: abnormally fast heart rate Bradycardia: Abnormally slow heart rate Incomplete Atrioventricular Block: Prolonged P-R interval (1st degree) Complete Atrioventricular Block: P waves and QRS complexes become dissociated (3rd degree) Fibrillation: Complete lack of coordination Electrolyte imbalance Hypernatremia: – Inhibits calcium entry into the cell – Depresses overall heart activity and becomes flaccid; (negative inotropy) Hypercalcemia: – (-, +) – Increased heart irritability – More calcium into cytoplasm – What reflex could augment the decreased chronotropy? Hyperkalemia: – Peaked T waves. Determining the MEA Vector This presentation aims to teach you the trick to visually determine the position of the MEA from the EKG • Know the Orientation of All Leads: it creates a compass (circle) which we can separate into quadrants. This will allow you to estimate the mean conductance. • Use any two leads on an EKG • Given: limb leads I and avF • Goal: to find the MEA vector • Draw 6 circles, with arrows in them showing the vector for each lead. Superimpose lead 1 and lead avF, will get a quadrant. • • • Step 1: Visually, examine the profiles of leads I and aVF Step 2: Superimpose the two diagrams of the heart, and see where the hatched areas overlap. This will be the area which must contain the MEA vector • Step 1: Visually, examine the profiles of leads I and aVF • Step 2: • Superimpose the two diagrams of the heart, and see where the hatched areas overlap. • This will be the area which must contain the MEA vector Mean Axial Shift • Left axis deviations – endomorph- short stature – Pregnancy – Left ventricle hypertrophy – LBBB • Right axis deviations – Ectomorph- tall /thin – Hypertrophy of right ventricle – RBBB