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Version: 4/19/1999A Guide to Reading and Understanding the EKGWritten by Henry Feldman, '01Reviewed by Mariano Rey, MD, '76The Online Version is available kghome.htmlThis guide will help you learn to interpret 12-lead EKG patterns. This is not a comprehensive guide toEKG interpretation, and for further reading, the Dubin textbook is the introductory book of choice.This text was developed for use by NYU School of Medicine students, but may be used by any medicalteaching institution, without charge, as long as the document is not modified, distributed in its entiretyand not used for profit, and may not be sold.Errors may be present in this document, and clinical use is at the risk of the user. Users should use their own clinical judgement in treatingpatients. 1999 – Henry Feldman, Mariano Rey

Table of ContentsEKG TRACING .1Figure 1 - EKG Tracing . Error! Bookmark not defined.STEP 1 .1Rate. 1Figure 2 - Determining the Rate . 1Step 2.2Rhythm . 2Figure 3 - Determining the Rhythm Source . 2Step 3.2Axis. 2Figure 4 - The Limb and Augmented Leads in relation to the body. 3Figure 4 - Computing the Axis . 4Figure 5 - All limb and augmented leads . 4STEP 4 .5Precordial Leads. 5Figure 6 - The Precordial Leads . 5STEP 5 .5Hypertrophy . 5Figure 7 - Biphasic P-Waves . 6Figure 8 - RVH . 6Figure 9 - LVH . 7STEP 6 .7Blocks . 7Figure 10 - AV-Block . 7STEP 7 .9Ischemia, Infarct and Injury. 9Transmural Ischemia . 9Sub-Endocardial Ischemia . 10Figure 19 - ST-Segment Depression in subendocardial ischemia. 10Step 8.11Miscellaneous .11Ventricular Fibrillation. 11Tachycardia . 11Sinus Tachycardia . 12Digitalis Toxicity . 13Figure 22 - Digitalis Toxicity . 14Hyperkalemia . 14Figure 23 - Peaked-T Waves consistent with Hyperkalemia. 14CREDITS .15Authors .15Henry Feldman. 15Mariano Rey, MD . 15Other Contributors .15Daniel Fisher, MD. 151

EKG TracingPlease refer to the EKG tracing below if you are not familiar with the labeling of the EKG waveforms.Figure 1- EKG TracingStep 1RateThe first step is to determine the RATE, which can be eyeballed by the following technique. Locatethe QRS (the big spike) complex that is closest to a dark vertical line. Then count either forward orbackwards to the next QRS complex. For each dark vertical line you pass, select the next number offthe mnemonic "300-150-100-75-60-50" to estimate the rate in beats per minute (BPM).In other words if you pass 2 lines before the next QRS, the heart rate (HR) would be less than 150.Remember that this is merely an estimate. You should use real measurements to determine the exactHR (for precise measurement: each large box represents 200msec and small boxes represent 40msec).As an example of using the mnemonic, in the segment of the EKG below, start at the QRS that linesup with the vertical line at "0". Now counting back each vertical line to the previous EKG "300-150100" we notice the HR to be slightly less than 100 (probably around 90-95).Figure 2 - Determining the Rate1

Step 2RhythmNext we need to determine the RHYTHM both its source and its regularity. The prime concern iswhether the source of the rhythm is the SA node (sino-atrial) or an ectopic pacemaker. To determinewhether the source of the rhythm is "sinus" or an ectopic rhythm, you need to look at the relationshipof the P-wave, if present, to the QRS-complex. If there is a P wave before each QRS and the P is inthe same direction as the QRS, the rhythm can be said to be sinus. For instance note in the EKGsegment below that there is a P-wave before each QRS (highlighted in blue) and that it is pointing upas is the QRS segment.Figure 3 - Determining the Rhythm SourceAlso look at the quality and quantity of P-waves before each QRS. There should only be one P-wavebefore each QRS. The P-wave should be in only one direction, and not biphasic (except for leads V1and V2). It should also be closer than 200ms to the QRS. The shape of the P-wave should also begently rounded and not peaked.Step 3AxisNext we need to determine the AXIS of the EKG tracing. To do this we need to understand the basic 6leads and their geometry. The EKG waveform comes from a measurement of surface voltagesbetween 2 leads. A wave that is travelling towards the positive ( ) lead will inscribe an upwardsdeflection of the EKG; conversely a wave traveling away from the positive lead will inscribe adownward deflection. Waves that are traveling at a 90 degree angle to a particular lead will create nodeflection and is called an isoelectric lead.As an example in the pictures below, a wave travelling from the head to the feet would be shown as anupwards deflection in AVF, since it is going towards the AVF lead.The axis is the sum of the vectors, produced by the ekg leads, to produce a single electrical vector.Remember that a positive signal in Lead-I means that the signal is going right to left; this produces avector, which if we take all the leads, we can sum. This summed vector should in general be pointingthe same direction (down-left) for a normal heart; this makes sense if we think of the electricalconduction system of the heart which sends a signal from the SA node (top right) to the purkinjefibers (bottom left). Don't worry if you still don't get it, we'll give you a visual example further downthe page.There are six basic leads discussed below and 6 precordial leads which will be discussed later. Thebasic leads consist of leads I, II and III and the augmented leads AVR, AVL and AVF. These arepresent on the basic 3-lead monitors and also on the 12-lead EKG machines. They consist of leads on2

the left and right shoulders and one on the left side of the abdomen (although conceptually they are onthe wrists and above the ankle; hence their name "limb leads"). A ground lead is placed on the rightankle.Figure 4 - The Limb and Augmented Leads in relation to the bodyYou will notice that leads I, II and III form the sides of an equilateral triangle, while AVR, AVL andAVF bisect the vertices of the triangle. The easiest way to figure out the axis is to draw a normal X-Ygraph and fill in the quadrants that are represented by each lead with a positive deflection.3

There are some tricks to save you time, but first think about a normal EKG plot; in a normal EKGboth leads I and AVF will be positive as the signal tra