Understanding EKG Waveforms: A Comprehensive Guide, Papers of Physiology

Download Understanding EKG Waveforms: A Comprehensive Guide and more Papers Physiology in PDF only on Docsity! Lab Activity 24 EKG Portland Community College BI 232 Reference: Dubin, Dale. Rapid Interpretation of EKG’s. 6th edition. Tampa: Cover Publishing Company, 2000. 2 Graph Paper 1 second equals 25 little boxes or 5 big boxes 1 second 5 PR Segment • Measured from the end of the P wave to the beginning of the QRS complex • This pause is caused by the slow depolarization within the AV node. 6 PR Interval • PR interval=P wave + PR segment • Indicates AV conduction time (depolarization from the SA node through the AV node) • Duration time is 0.12 to 0.20 seconds 7 QRS Complex • Indicates ventricular depolarization, through the Bundle Branches and Purkinje fibers. (Starts the contraction of the ventricles) • Normally not longer than .10 seconds in duration 10 ST Interval • ST interval=T wave + ST segment • Represents the complete repolarization phase of the ventricle (plateau phase and rapid phase) 11 QT Interval • Represents the duration of ventricular systole (depolarization and repolarization). • General rule: duration is less than half the preceding R-R interval 12 Terminology • Normal Sinus Rhythm (NSR): The SA node is pacing the heart (P wave is present) with a rate of 60-100 beats per minute • Sinus Tachycardia: The SA node is pacing the heart at a rate greater than 100 beats per minute • Sinus Bradycardia: The SA node is pacing the heart at a rate less than 60 beats per minute 15 Rate: 300-150-100-75-60-50 16 Determining Rate • Find an R wave on a thick line, then start counting Start here: It is on a thick line The next R wave is 2.5 large boxes away 2 boxes=150 and 3 boxes = 100 So 2.5 boxes is about 120 beats/minute 17 Axis • Axis refers to the average direction of the movement of depolarization, which spreads throughout the heart to stimulate the myocardium to contract. 20 Influences on Vector Direction • Anything that influences the overall amount of charge flowing through the myocardium will change the average direction the the charge is flowing • Infarction would not have a vector associated with it so the average vector would point somewhat away from that area A v erag e V ecto r 21 Influences on Vector Direction • Hypertrophy would have a larger vector associated with it, so the average would point more toward that area (e.g. left side hypertrophy) Av era ge Vec tor 22 Vectors (Math stuff) • Vectors are described in degrees • Remember a circle is 360°, and a line is 180° • When we calculate the axis, it is expressed as degrees in the frontal plane. • 0° is horizontal to the left • +180° is horizontal to the right • The body is then just divided accordingly (see next slide) • Since a normal vector is down and to the left, it would be between 0° and +90° 25 Limb Leads • If leads I, II, and III are place around the heart, instead of radiating from the heart, you get a triangle. • Lead I = Red • Lead II = Green • Lead III = Blue • Each lead has a positive and negative pole 26 Lead I • Lead I is the leftward axis • If the QRS is pointing up (a positive deflection), the wave of depolarization is going towards the left (toward the positive) - + 27 Axis and Vectors: Lead I • Green lines indicate axes of the heart • The corresponding black lines represent the average vector for that axis in relation to lead I (red line). • Larger vector, larger the deflection on an EKG • Vectors A and B = negative deflections on lead I – This means the vector is moving away from the positive pole • Example EKG: A B C D E A B E D NOTE: Axis D would usually be the closest accurate axis for this picture + A B 30 Lead II • Lead II is a downward axis • If the QRS has a positive deflection, the wave of depolarization is downward towards the left foot (towards the positive) - + 31 Example Vectors: Lead II 32 Lead III • Lead III is a downward axis • If the QRS has a positive deflection, the wave of depolarization is downward towards the right foot (towards the positive) 35 Atrial Fibrillation • This is a result of many sites within the atria firing electrical impulses in an irregular fashion causing irregular heart rhythm. Notice the absence of P waves and the irregular rate. Erratic impulses | | | | | es Sinoatrial oe (SA) node : Left atrium Right em ry atrium Atrioventricular 36 37 Premature Ventricular Complexes (PVC) • The ventricles fire an early impulse which causes the heart to beat earlier causing irregularity in the heart rhythm. 40 Ventricular Fibrillation Notice that the first 2 beats of this EKG are Ventricular tachycardia Ventricular Fibrillation , Abnormal electrical circuits 41 42 ST Elevation ST elevation indicates acute or recent infarction.