For additional ancillary materials related to this chapter. please visit thePoint.
In this chapter you will learn:
1 | a simple method to incorporate everything you have learned into a step-by-step analysis of any EKG
2 | that all good things must come to an end, and we bid you a reluctant and fond farewell!
And that is really all there is to it.
Well, perhaps not quite all. What we need now is a way to organize all of this information, a simple methodical approach that can be applied to each and every EKG. It is important that every EKG be approached in an orderly fashion, particularly while you are still new at this, so that nothing important is missed. As you read more and more cardiograms, what initially may seem forced and mechanical will pay big dividends and will soon seem like second nature.
Two admonitions:
- Know your patient. It is true that EKGs can be read with fair accuracy in a little back room in seclusion, but the power of this amazing tool only really emerges when it is integrated into a total clinical assessment of your patient.
- Read EKGs. Then, read some more. Read them wherever you can find them—in books, in papers, in patients’ charts, on bathroom walls—and read other books; this may be the only EKG book you will ever need, but it should not be the only one you will ever want to read. There are many outstanding textbooks, each with something special to offer.
There are as many approaches to reading EKGs as there are cardiologists. Everyone ultimately arrives at a method that works best for him or her. The following 9-Step Method is probably no better and no worse than most others.
The 9-Step Method for Reading EKGs
Before you start, make sure the standardization mark on the EKG paper is 10 mm high so that 10 mm = 1 mV. Also make sure that the paper speed is correct.
- Heart rate. Determine the heart rate.
- Intervals. Measure the length of the PR and QT intervals and the width of the QRS complexes.
- Axis. Is the axis of the P waves, QRS complexes, and T waves normal, or is there axis deviation?
- Rhythm. Always ask The Four Questions:
- Are there normal P waves present?
- Are the QRS complexes wide or narrow?
- What is the relationship between the P waves and QRS complexes?
- Is the rhythm regular or irregular?
- Are there normal P waves present?
- Conduction blocks.
- Atrioventricular (AV) block. Apply the criteria in Chapter 4.
- Bundle branch block or hemiblock. Apply the criteria in Chapter 4.
- Atrioventricular (AV) block. Apply the criteria in Chapter 4.
- Preexcitation. Apply the criteria in Chapter 5.
- Enlargement and hypertrophy. Apply the criteria for both atrial enlargement and ventricular hypertrophy in Chapter 3.
- Coronary artery disease. Look for Q waves and the ST-segment and T-wave changes described in Chapter 6. Remember that not all such changes reflect coronary artery disease; know your differential diagnoses.
- Other conditions. Is there anything on the EKG that suggests one of the other cardiac or noncardiac conditions discussed in Chapter 7? Are you totally lost? Never hesitate to ask for assistance.
The following pages are memory joggers you can hang onto. In early editions of this book, I suggested you cut these pages out and stick them in that little black book of medical pearls that everyone seemed to tote around. But who carries a little black book anymore? Therefore—if you haven’t thought of this already—take a photo of these pages with your smartphone and file them away for easy access. On the other hand, now that I think about it some more, cut these pages out anyway; the exercise will do you good after sitting and staring bleary-eyed at this book for so long.
The final chapter contains some sample EKGs with which to test yourself. Some are easy; some not so much. And if you are still thinking, “Is this really all there is to it?” The answer—reminding you that information only becomes knowledge with wisdom and experience—is, “Yes!”
Review Charts
- The 12 Leads
- Anterior leads: V2, V3, and V4
- Inferior leads: II, III, and AVF
- Left lateral leads: I, AVL, V5, and V6
- Right leads: aVR and V1
The heart is composed of pacemaker cells, electrical conducting cells, and myocardial cells. Pacemaker cells depolarize spontaneously and initiate each wave of depolarization. The SA node is usually the dominant pacemaker. Electrical conducting cells carry current rapidly and efficiently to distant regions of the heart. Myocardial cells constitute the bulk of the heart. When a wave of depolarization reaches a myocardial cell, calcium is released within the cell (excitation–contraction coupling), causing it to contract.
The P wave represents atrial depolarization. It is small and usually positive in the left lateral and inferior leads. It is often biphasic in leads III and V1. Typically, it is most positive in lead II and most negative in lead aVR.
The QRS complex represents ventricular depolarization. It is usually predominantly positive in most lateral and inferior leads. Across the precordium, the R waves increase in size, progressing from V1 to V5. A small initial Q wave, representing septal depolarization, can often be seen in the left lateral and inferior leads.
The T wave represents ventricular repolarization. It is the most variable waveform, but it is usually positive in leads with tall R waves.
The PR interval represents the time from the start of atrial depolarization to the start of ventricular depolarization.
The PR segment is the time from the end of atrial depolarization to the start of ventricular depolarization.
The QRS interval represents the duration of the QRS complex.
The ST segment represents the time from the end of ventricular depolarization to the start of ventricular repolarization.
The QT interval represents the time from the start of ventricular depolarization to the end of ventricular repolarization.
Calculating the Axis
| Lead I | Lead aVF | |
Normal axis | + | + |
Left axis deviation | + | − |
Right axis deviation | − | + |
Extreme right axis deviation | − | − |
Atrial Enlargement
Look at the P wave in leads II and V1.
Right atrial enlargement is characterized by the following:
- Increased amplitude of the first portion of the P wave
- No change in the duration of the P wave
- Possible right axis deviation of the P wave
Left atrial enlargement is characterized by the following:
- Occasionally, increased amplitude of the terminal component of the P wave
- More consistently, increased P wave duration
- No significant axis deviation
Ventricular Hypertrophy
Look at the QRS complexes in all leads.
Right ventricular hypertrophy is characterized by the following:
- Right axis deviation of greater than 100°
- Ratio of R-wave amplitude to S-wave amplitude greater than 1 in V1 and less than 1 in V6
Left ventricular hypertrophy is characterized by many criteria. The more that are present, the greater the likelihood that left ventricular hypertrophy is present.
Precordial criteria include the following:
- The R-wave amplitude in V5 or V6 plus the S-wave amplitude in V1 or V2 exceeds 35 mm.
- The R-wave amplitude in V5 exceeds 26 mm.
- The R-wave amplitude in V6 exceeds 18 mm.
- The R-wave amplitude in V6 exceeds the R-wave amplitude in V5.
Limb lead criteria include the following:
- The R-wave amplitude in aVL exceeds 11 mm.
- The R-wave amplitude in aVF exceeds 20 mm.
- The R-wave amplitude in I exceeds 13 mm.
- The R-wave amplitude in I plus the S-wave amplitude in III exceeds 25 mm.
The most accurate single criterion: the R-wave amplitude in aVL plus the S-wave amplitude in V3 exceeds 20 for women and 28 for men.
The presence of repolarization abnormalities (asymmetric ST-segment depression and T-wave inversion) indicates clinically significant hypertrophy, is most often seen in those leads with tall R waves, and may herald ventricular dilatation and failure.
The five basic types of arrhythmias are as follows:
- Arrhythmias of sinus origin
- Ectopic rhythms
- Reentrant rhythms
- Conduction blocks
- Preexcitation syndromes
Whenever you are interpreting the heart’s rhythm, ask The Four Questions:
- Are normal P waves present?
- Are the QRS complexes narrow (<0.12 seconds in duration) or wide (>0.12 seconds)?
- What is the relationship between the P waves and the QRS complexes?
- Is the rhythm regular or irregular?
The answers for normal sinus rhythm are the following:
- Yes, P waves are present.
- The QRS complexes are narrow.
- There is one P wave for every QRS complex.
- The rhythm is regular.
Why Arrhythmias Happen
Hypoxia
Ischemia and irritability
Sympathetic stimulation
Drugs
Electrolyte imbalances
Bradycardia
Stretch
Rhythms of Sinus Origin
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
