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Arrhythmia Recognition The Art of Interpretation 2nd Edition Garcia
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This textbook is intended solely as a guide to the appropriate procedures to be employed when rendering emergency care to the sick and injured. It is not intended as a statement of the standards of care required in any particular situation, because circumstances and the patient’s physical condition can vary widely from one emergency to another. Nor is it intended that this textbook shall in any way advise emergency personnel concerning legal authority to perform the activities or procedures discussed. Such local determination should be made only with the aid of legal counsel. 19191-2
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Library of Congress Cataloging-in-Publication Data
Names: Garcia, Tomas B., 1952- author. | Garcia, Daniel J., author
Title: Arrhythmia recognition : the art of interpretation / Tomas B. Garcia, Daniel J. Garcia.
Description: Second edition. | Burlington, Massachusetts : Jones & Bartlett Learning, [2020] | Revision of: Arrhythmia recognition / Tomas B. Garcia, Geoffrey T. Miller. c2004. | Includes bibliographical references and index. Identifiers: LCCN 2019010704 | ISBN 9781449642334 (pbk. : alk. paper)
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Concordance of the QRS Complexes in the Precordial Leads 581
Abnormal Axis Deviation 582
Hemodynamic Status 583
Other Adjuncts to the Diagnosis of WCT 584
Section II: The Algorithms 584
The Brugada Algorithm 584
The Vereckei aVR Algorithm 587
Final Thoughts 590
Chapter Review 592
Chapter 37: Wide-Complex Tachycardia: Putting It All Together 595
Introduction 596
Putting It All Together 596
The Worksheet 596
Case 1 597
Clinical Scenario 597
Final Assessment 604
Case 2 604
Clinical Scenario 604
Final Assessment 609
Case 3 609
Clinical Scenario 609
Final Assessment 613
Case 4 613
Clinical Scenario 613
Final Assessment 617
Case 5 619
Clinical Scenario 619
Final Assessment 627
Chapter 38: Ventricular Fibrillation and Asystole 629
Ventricular Fibrillation 630
Asystole 633
Agonal Rhythm 634
ECG Strips 634
Chapter Review 637
Section 5 Self-Test 638
SECTION 6: Additional Rhythms
Chapter 39: Artificially Paced Rhythms 657
General Overview 658
Pacemaker Code 658
The Pacemaker Spike 660
QRS Morphology in a Paced Rhythm 661
Popular Pacemaker Modes 661
Atrial Demand Pacemaker 661
Ventricular Demand Pacemaker 662
AV Sequential 663
Automatic Pacemaker 663
ECG Strips 665
Chapter Review 670
Chapter 40: Putting It All Together 671
Introduction 672
“Patient’s” 673
The History 674
Physical Examination 675
“Impression” 675
Top 10 “Questions” 676
1. Is the Rhythm Fast or Slow? 676
2. Is the Rhythm Regular or Irregular? 677
3. Do You See Any P Waves? 678
4. Are the P Waves the Same? 678
5. Are the P Waves Upright in Lead II? 678
6. Are the PR Intervals Normal and Consistent? 679
7. What Is the P:QRS Ratio? 680
8. Are the QRS Complexes Narrow or Wide? 681
9. Are the Complexes Grouped or Not Grouped? 681
10. Are There Any Dropped P Waves? 682 Have I Mined for Gold? 682
How Can I Put It All Together? 683
“Points” 684
Let’s Go Through an Example 685
Overall Impression of the Rhythm 685
Question 1: Is the Rhythm Fast or Slow? 685
Question 2: Is the Rhythm Regular or Irregular? 685
Question 3: Do You See Any P Waves? 685
Question 4: Are All of the P Waves the Same? 685
Question 5: Are the P Waves Upright in Lead II? 685
Question 6: Are the PR Intervals Normal and Consistent? 685
Question 7: What Is the P:QRS Ratio? 685
Question 8: Are the QRS Complexes Narrow or Wide? 687
Question 9: Are the Complexes Grouped or Not Grouped? 687
Question 10: Are There Any Dropped Beats? 687
Have I Mined for Gold? 687
Chapter Review 688
7: Final Tests
Resources
Student Resources
Companion Website
ISBN: 9781284184990
Included with the purchase of this text, this companion website contains the following student resources to enhance learning and help arrhythmia recognition skills:
Animations that demonstrate core arrhythmia concepts
High-yield content for learning the critical concept of wide-complex tachycardias
Terminology flashcards
Learning objectives
eBook
Arrhythmia Recognition: The Art of Interpretation, Second Edition
ISBN: 9781449642358
An eBook of this text is available for separate purchase.
Also in the Series…
Once you’ve finished reading Arrhythmia Recognition, you’ll want to read the following texts in the series to familiarize yourself with the subject of 12-lead electrocardiography. These texts present 12-lead ECG interpretation in the same clear, graphics-intensive, ECG-intensive style seen in this text. Choose the 12-lead text that best suits your needs.
12-Lead ECG: The Art of Interpretation, Second Edition
ISBN: 9780763773519
This all-encompassing text is designed to make you a fully advanced interpreter of ECGs.
Introduction to 12-Lead ECG: The Art of Interpretation, Second Edition
ISBN: 9781284040883
This introductory-level text is designed to give beginners a basic knowledge of ECG interpretation.
Instructor Resources
Ordering Information
Instructor’s ToolKit to accompany Arrhythmia
Recognition: The Art of Interpretation, Second Edition
ISBN: 9781284195514
This downloadable resource contains PowerPoint presentations, lecture outlines, and an image bank, including all of the images that appear in this text.
Instructor’s ToolKit to accompany 12-Lead ECG: The Art of Interpretation, Second Edition
ISBN: 9781284046717
This CD contains PowerPoint presentations and lecture outlines to enhance your classroom presentations.
Jones & Bartlett Learning books and products are available through most bookstores and online booksellers. To contact the Jones & Bartlett Learning Public Safety Group directly, call 800-832-0034, fax 978-443-8000, or visit our website, www.psglearning.com.
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To all of the courageous men and women of the armed forces, EMS, fire, and law enforcement departments around our country. You put your lives on the line every day to protect us and our freedom. I thank you. May God bless you and keep you all safe from harm.
Tomas B. Garcia, MD
Dr. Tomas B. Garcia received his undergraduate degree from Florida International University. While applying to medical school, Dr. Garcia was licensed and practiced as an EMT in the state of Florida. Dr. Garcia received his medical degree from the University of Miami. He completed his internship and residency at Jackson Memorial Hospital in Miami, Florida, and subsequently received board certification in both Internal Medicine and Emergency Medicine.
Dr. Garcia taught and practiced in the Emergency Department of the Brigham and Women’s Hospital/ Harvard Medical School in Boston, Massachusetts, and Grady Memorial Hospital/Emory Medical School in Atlanta, Georgia.
His main area of interest is emergency cardiac care, and he lectures nationally on topics related to these issues. In addition to working on the third edition of his book 12-Lead ECG: The Art of Interpretation, published by Jones & Bartlett Learning, Dr. Garcia is spearheading an educational Internet site on electrocardiography and arrhythmia recognition at www.ekgfacts.com.
To my father, Dr. Tomas Garcia, who has always been there for me, helped me, taught me, guided me, and cared about me through the most pleasurable and the most difficult parts of my life. I will never be able to thank you enough for all that you have done for me.
To my mother, Marta Daniel, I cannot thank you enough for all that you have done for me, all of the time you have spent with me, and all of the lessons that you have taught me. Thank you for all of the love you have given me. I have cherished every moment with you.
I love you both very, very much.
—Daniel J. Garcia
Daniel J. Garcia received his bachelor’s degree in the biological sciences from Barry University. He is co-author of the YouTube educational series Arrhythmia Recognition, The Art of Education, which is an educate-the-educator series on the topic of arrhythmia recognition. He currently attends the Tulane University School of Medicine, where he is completing his medical degree. During his time there, he founded the ECG Club of Tulane University and served as its president for 2 years.
Acknowledgments
The decision to write a comprehensive text is easy in most cases. You see a need, you have a concept, and the decision to write the book is made. It is in implementing the idea that the enormity of the decision becomes apparent. Thankfully, many people along the way helped us in achieving our goals.
First and foremost is God. Throughout my life you have opened and closed doors for me in very strange ways. However, the path that you have helped me see has always led me to exactly where I needed to be at that moment. I trust you, and in you, with all my heart and soul.
I would like to give a special hug to my Martica, who took care of me, rubbed my neck, soothed my mind, beat me at Chinese checkers (occasionally. . .), and helped me keep my sanity.
I would like to thank Jones & Bartlett Learning for their support of my projects. I would especially like to
Iwould like to start off by thanking a very special couple, Dr. Robert Conciatori and his lovely wife, Maria. I would like to take this opportunity to let you both know that I consider you to be my second parents. I am eternally grateful for everything you have done for me and for all of the support you have both given me since my birth. You have helped foster my love of history, art, medicine, family, and the need for a good hard hat! Your encouragement and support have helped spur me down my path toward becoming a physician. From the bottom of my heart, I thank and love you both.
To Dr. Pedro Lopez, I will always admire your brilliance and your humility. You truly represent the best of our profession. Thank you for reinforcing my belief that a physician should always strive to be a physician first and a subspecialist second. Both my father and I consider it an honor to have you as a friend.
I would like to also thank Drs. Anthony Conciatori and Christina Vaglica for their patience and for sharing their time and knowledge with me. You both inspire me, and I truly value your support and friendship.
thank Carol Brewer Guerrero, my editor and friend, for her tireless work on all of my projects. You have been supportive and kind to a fault. Jones & Bartlett Learning does not know how lucky they are to have you! I would also like to give special thanks to Lori Mortimer, Kathryn Leeber, Scott Moden, and Troy Liston, whose expertise and hard work in polishing the appearance of this book have transformed it into a beautiful work of art. Finally, I would like to thank all of the copy editors and production team who spent countless hours putting this art piece together.
Finally, I would like to remind my son Daniel that he always has been, and always will be, the most important part of my life. To my mom, my sister, and the rest of the Garcia crew: I love you all deeply. You are the glue that keeps me together in this life.
—Tomas B. Garcia, MD
I would also like to thank Dr. Robert Hendel of Tulane University for coming to my aid without hesitation when I needed it the most. The time I spent shadowing you in clinical practice was truly inspirational and opened my eyes to the beauty and complexity of cardiology.
I would also like to thank Dr. Elma LeDoux who, while functioning as the faculty coordinator for the ECG Club of Tulane University, watched over us and shared with us her expertise and knowledge. In addition, I would like to thank the founding officers of the club and all of the founding members. I would especially like to honor our vice president, Prasad “Prednisone” Akula. You have been not only an excellent leader, but also a great personal friend. Because of each and every one of you, I have learned the true meaning of the phrase “Qui docet discit,” or “He who teaches, learns.”
I would like to give special thanks to Mr. Daniel Ciocca of Christopher Columbus High School. Your class not only taught me the importance of economics, but it also expanded my horizons and made me admire the beauty and philosophy of our shared human nature.
I would also like to thank Drs. Christoph Hengartner, Leticia Vega, and Mr. Michael Bill for their heartfelt support and guidance during my time at Barry University. Last but not least, I would also like to honor and offer my special thanks to Carol Brewer Guerrero, our editor
Jones & Bartlett Learning and the authors would like to thank the following people for reviewing this text.
Renee Andreeff, EdD, PA-C, DFAAPA
D’Youville College Buffalo, New York
Roxie L. Barnes, RN, MSN, CHSE, CCRN Indiana University School of Nursing Bloomington, Indiana
Liz Barrow, RCIS, CEPS Grossmont College El Cajon, California
One of the most important skills for any clinician to master is the ability to recognize and evaluate a rhythm strip. This information is as basic as knowing how to use a stethoscope. However, as our reliance on newer and more advanced technology has increased, our basic clinical and diagnostic skills have begun to deteriorate.
Arrhythmia recognition is, by its very nature, cloaked in objective criteria. We need these criteria to differentiate between the various rhythm abnormalities and to allow us some objectivity when assigning the various treatment strategies. However, if objective criteria were the only variables involved in evaluating a rhythm, computers would have taken over the job of interpreting ECGs and rhythm strips long ago. But, as we all know, computer-assisted interpretation has essentially been unreliable to date. Why? Because arrhythmia recognition is primarily an art. Computers don’t do well with art.
An appreciation of art requires deep, thoughtful study and mastery of a subject and that requires time. However, in our busy, hectic lives, most of us cannot dedicate that much time and effort to just this one aspect of clinical practice. We barely have enough time to keep up with all the new information, let alone revisit the basics In addition, our clinical instructors and educators have to spend more and more time on paperwork and securing reimbursement, and they therefore have less and less time for teaching.
As a result, we rely on specialists to give us a final interpretation of our patients’ strips and ECGs. However, here is an interesting fact: Historically, many cardiologists failed the boards because of an inability to interpret ECGs. Training difficulties apply to them as well. Furthermore, despite the recent resurgence of the acceptance of the generalized terms supraventricular and wide-complex tachycardias by the American Heart Association, the bottom line is that you still are expected to understand the rhythms themselves and their appropriate treatment strategies. This can be a tough assignment, especially when the supraventricular tachycardia presents with wide QRS complexes. In addition,
just as our ability to diagnose complicated arrhythmias has expanded, so too has our ability to provide focused treatment through the use of specialized equipment, more targeted pharmaceutical agents, and more specific treatment protocols. As you can imagine, focused treatments provide better outcomes.
Our old ideas about arrhythmias have also changed with the onset of electrophysiology as a medical subspecialty. Newer techniques bring newer insights and treatments As educators, we need to come face-to-face with this new mindset and come up with new and creative approaches to medical education and training. Hopefully, this book is just one of those small steps.
We can no longer rely on books that present just a few isolated facts and give you a bunch of strips with no guidance as to how to interpret them. We need to understand the whys and hows and be able to distinguish between the various possibilities. We cannot afford to fall back on traditional systems of learning arrhythmia recognition for the patient’s sake and because of our ever-increasing list of problems—a continuously expanding knowledge base, a shrinking time pool to pursue medical education, and medical malpractice.
In order to understand and interpret rhythm strips and ECGs thoroughly, we need to approach the material with three main objectives in mind: (1) We need to understand the objective criteria for each arrhythmia; (2) We need to fully understand the mechanisms involved and the subtleties that can develop within that one rhythm category and in any one patient; (3) We need to be able to put our electrocardiographic findings together with the history, physical exam, and laboratory data to arrive at the correct diagnosis for our patient. ECGs and rhythm strips do not exist in a vacuum. In this book, we will meet these objectives head on.
We will provide you with the objective criteria that are particular to that one rhythm, and then we will discuss the mechanisms and subtleties of each rhythm abnormality. In addition, we will give you various examples of each of the arrhythmias so that you can see these subtleties in action. We will try to provide you with examples that cover the full spectrum of the clinical presentation, including real-life strips that are not “pristine.”
At the end of each chapter, we will provide you with a synopsis of the rhythm, which basically organizes everything in a nutshell for you. This will be helpful when you just want a quick review, or when you just need to look up some quick facts about the rhythm.
Being able to interpret the arrhythmia without knowing the potential clinical causes is not a healthy way to approach arrhythmia recognition. As such, we are providing a differential diagnosis block at the end of each of the chapters to point you in the right clinical direction. Please note that these differential diagnosis boxes are not all-inclusive but contain the major culprits in which the rhythm abnormality is typically found.
The chapters conclude with a review containing fillin-the-blank, multiple-choice, and true or false questions. The purpose of these questions is not to provide you with unanswerable challenges but to re-emphasize the important take-home messages of the chapter.
Each section ends with a review test which provides you with some unknowns. You should spend the time to solve each of the rhythm strips and to understand them. Once you have completed your evaluation, you can turn to the answers for confirmation and further discussion. This is a feature that we feel will strengthen your understanding by providing you with some individualized instruction about each of the strips. In other words, we will work through each strip with you instead of just giving an answer without explanation.
The book ends with two of my favorite features—a chapter on putting it all together and two final tests. I like to think of these two features as working together to put the finishing touches on your studies. The chapter on putting it all together is geared towards strengthening the art of interpretation to the maximum. In this chapter, we try to reinforce the need to evaluate all of the information at your disposal to interpret the rhythm. These sources of information include the history, physical exam, and laboratory data, as well as the ECG and the rhythm strip.
Many of you will be upset that we did not include treatment strategies in this book. We opted not to include it because it typically takes about 2 to 3 years to bring a book from conception to print. Most of the information that you find in medical textbooks, including the references, is obsolete by the time the book hits the shelves. If not, it will be obsolete very shortly afterwards. The only thing more dangerous than a lack of information is wrong information. We encourage you to go on the Internet and review the latest treatment strategies for the various rhythms as you finish each chapter. This way, you will have the most current and up-to-date information available.
A Little More About the Art
When I teach medical students physical diagnosis, they spend the first couple of weeks merely observing patients from afar. They are not to talk to or examine the patient. I demand only that they answer one simple question: Is the patient sick or not sick? They only have only about 10 to 15 seconds to make up their minds, so that they cannot rationalize too much. Their decision has to be made from the gut, based on information that they gain through observation either consciously or unconsciously. It sounds intimidating, yet students amaze me with how quickly they learn this task and how effectively they put these lessons to use. This internal decision maker is an innate part of us all and will never steer you wrong. All you have to do is develop it.
So what does this have to do with rhythm strips? Simple—we are going to use the same approach to learn arrhythmia recognition. The only way to learn arrhythmias is to look at thousands of them and answer the question, “sick or not sick?” Most findings are not as unique from person to person; instead, they vary from person to person and even within the same person at various times (kind of like fingerprints). If you see only one sample strip for each pathology but never see that picture-perfect example again in your life, you will never be able to diagnose it in your patient.
The complex language that is used in electrocardiography can be confusing and overwhelming. Most people buy an advanced textbook on arrhythmias, begin to read it, and then quickly give up. Sound familiar? You have to be very competent at electrocardiography and arrhythmia recognition to be able to understand the written word describing the possible variations. Most of us are visual learners. The simple way to learn about the rhythms—and the one that has been largely underutilized—is to use extensive graphics and to show various examples of each abnormality in order to develop a feel for what you are looking at. After a while, you will begin to feel your gut telling you whether the patient is “sick or not sick.”
The process of learning to interpret rhythm strips is not unlike learning to throw a ball. You can read about the throw, the trajectories, the spin, and the accuracy, but unless you see a few balls thrown and throw hundreds or thousands yourself, you will never really learn to throw a ball. In the same way, you need to see hundreds of strips before you become comfortable. By the time you finish this book, you will be comfortable with the terminology and the concepts.
I have been asked by a few hundred students to teach them what they really need to know. I can sum up the answer in one short, concise statement: you need to
know the changes that your specific patient presented you on their strip! You never know what will be important at any one point in your career; any one factor can cost the patient his or her life and will cost you countless hours of guilt, and possibly millions of dollars! Arrhythmia interpretation is the same whether you are an EMT, paramedic, nurse, resident, attending physician, or a cardiologist. You cannot learn just enough to get by. Does a resident need to know the changes of hyperkalemia that can lead to a lethal arrhythmia? Does a paramedic or nurse need to know that focal atrial tachycardia with block is associated with digoxin toxicity? To whom is it more important to know that a patient with a prolonged QT interval can develop torsade de pointes? It is important to you if you are the only one around at the time.
Learning How to Interpret Arrhythmias
Learning how to make sense of rhythm strips and electrocardiograms is extremely daunting. It requires a lot of time, effort, and an open mind. Since I am my father’s son, I grew up with a pair of unsharpened ECG calipers instead of a baby rattle. And when I started school, I used an ECG ruler to make straight lines. I remember listening to adults discussing ECGs from an early age, and I listened to many a lecture in our house as my father taught medical housestaff and ancillary personnel.
As I matured, I struggled like all beginners, and I have suffered through the various lessons from the school of hard knocks in order to learn what works and what doesn’t. This background has provided me with a strong foundation and given me a distinct point of view because I was recently in your shoes walking the same road that you are now walking. In the Beginner’s Perspective sections, I’ve put together some of the things that helped me along the way and will hopefully provide you with a roadmap to make your journey easier.
Occam’s razor is a scientific principle that states that if you are dealing with competing hypotheses, the simplest
Passing the buck to a higher level doesn’t work with arrhythmias because you may not have enough time to pass it!
In closing, I would like to state that you need to look at everything at your disposal and trust yourself when you are interpreting a rhythm strip. Don’t let anyone talk you out of something that you know is true. Just smile at them and do what is best for the patient. You will not go wrong. Remember that an expert is someone who knows one more fact than you do. However, that one fact may not be relevant to your case, so you may be the true expert!
—Tomas B. Garcia, MD
one (the one with the fewest assumptions) is usually the correct one. In other words, nature is extremely efficient and takes the simplest route to solve a problem. The same is true of the principles of arrhythmia recognition. Despite the fact that every heart gives rise to its own intrinsic and individualized morphologic appearance, the heart is ruled by certain underlying principles. Understand the mechanisms, and you understand the pathology.
We are wholeheartedly committed to making the process of understanding arrhythmia recognition as easy as possible. Rote memorization of the criteria is not as important as understanding why things occur. In order to do this, you should strive to understand the mechanisms involved. Once you figure it out, you will never forget it.
The more I learned, the more I realized the wisdom of those simple concepts, and the more I focused on the lessons I was entrusted to safeguard by some very distinguished educators. Those ECG “secrets,” which are actually fundamental principles of medicine, are what I humbly hope to pass on to you.
—Daniel J. Garcia
CHAPTER
Anatomy and Basic Physiology
Objectives
At the end of this chapter, the student should be able to:
1. Label the structures of the heart visible from an anterior view. (p 6)
2. Identify the structures on the interior of the heart. (pp 6–7)
3. Discuss the flow of blood throughout the two circulatory systems. (p 7)
4. Evaluate how defects/obstructions in the circulatory system will impact the patient by using the simplified pump function of the circulatory system diagram. (pp 7, 8)
5. Indicate how blood flows through the somatic circulatory system by the use of the elastic properties of the muscular layer of the arterial walls. (pp 8–9)
6. Demonstrate proficiency in using the equation for cardiac output in various clinical scenarios. (pp 9–10)
7. Describe the concept of atrial overfilling of the ventricles and explain how it relates to increasing ventricular contractility. (pp 10–11)
8. Analyze the effects of rapid tachycardias on the rapid filling phase of ventricular filling. (p 11)
9. Describe the role of the electrical conduction system in the production of synchronized cardiac contractions. (pp 11–19)
10. Discuss the need for the atrioventricular septum and its role in causing synchronized contractions of the heart. (pp 12, 13)
11. Defend the efficiency of the atrioventricular node and the physiologic block’s role as a cardioprotective mechanism to prevent the transmission of very rapid atrial rates from reaching and depolarizing the ventricles. (pp 12, 13)
12. Draw and label the electrical conduction system of the heart. (p 14)
13. Explain the pacemaker system and the pacemaker hierarchy. (pp 14–15)
14. List the four arrhythmogenic zones. (p 20)
BEGINNER’S PERSPECTIVE
Most authors of textbooks are very proficient in their field, as should be expected. However, this depth of knowledge creates a language and concept barrier between them and beginners who, by definition, do not understand the material fully. This “language difficulty” creates a feeling of helplessness and insecurity that overwhelms many beginners at first. As mentioned in the Foreword , the Beginner’s Perspective boxes have been created as a way for me, recently a beginner myself, to reach out to those just starting and share some of my trials and tribulations. I will focus on key pearls or take-home messages that I found important to develop a deeper understanding of the topic. I hope that by sharing this journey together, we can make the learning process less difficult.
I would sum up this chapter with the expression, “A picture is worth a thousand words.” The strength of this chapter is in its graphics. They help clarify and simplify various difficult concepts. As an example, consider Figure 1-5. I was originally taught the traditional way that focuses on two circulatory systems (pulmonary and somatic) that function in sync with each other to circulate blood. My original impression was of two systems connected at the heart, but the route the blood had to take in this system was difficult to conceptualize. Only after looking at Figure 1-5 and seeing how the blood is actually routed did I realize there is one
true nonstop route with “tubing” crossing over itself at the level of the heart, like a figure eight.
By altering our thinking just a bit, we can see how backups in one section affect the rest of the system. Perhaps unknowingly, we have worked with related concepts all our lives. Take for example a simple hose. We’ve all seen how a kink in the hose causes increased pressure in the section of the hose before the kink and, ultimately, decreased flow out of the hose. We’ve seen how partial obstructions affect the fluid dynamics of the system, how different nozzles affect it, how increases or decreases in water pressure affect it, how the width of the hose affects it, and so forth. Once we understand the system as a continuing circuit, then break it down into the pulmonary and somatic systems, it makes sense.
The same can be said for Figure 1-9 and the concept of afterload, a critical concept discussed in later chapters. It is one thing to talk about how cardiac contraction causes blood to circulate throughout the body; it is another thing to understand how it does so. Figure 1-9 shows us that the left ventricle contracts and the amount of blood held in that chamber is pushed out into the aorta. That volume of blood dilates the aorta by expanding its elastic muscular wall. The pent-up tension in the elastic muscular wall, in turn, increases the internal pressure within the aorta as the walls try to return to a normal relaxed state. Since the valves of
the heart are one-way valves and blood cannot return to the ventricles, the blood has only one way to go: forward. It is that steady pressure on the blood, caused by the release of the elastic muscular tension in the walls of the aorta, that slowly pushes the blood forward throughout the rest of the body and creates circulation. The role of the heart is just to start the process by ejecting that bolus of blood into the aorta; most of the process of circulation takes place after the heart. The passive elastic property built into the arterial walls actually propels the blood to circulate through the brain, the heart itself (through the coronary arteries), and the rest of the body.
Knowing this information is really cool. What else can we derive from it? Well, now we understand where systolic and diastolic pressures come from. Systolic blood pressure is the amount of pressure within the artery immediately after receiving the blood bolus from the heart; it starts the process of moving the blood forward. Diastolic blood pressure is the pressure within the artery when the muscular walls are in a relaxed state—in other words, when there is a marked decrease in the forward flow of the blood.
There are some additional concepts that I used to think were not important for me—that is, until I understood how circulation actually works. Take the advanced concept of afterload, for example. Afterload is defined as the pressure against which the heart must pump to eject blood. If the pressure in the aorta is high, the heart has to work harder to pump the same
amount of blood into it. Now that we understand circulation, we can see how this scenario can be a big problem. Less blood could be ejected from the heart, leading to less blood being circulated; increased tension on the heart could lead to ischemia or dilation of the ventricles, and less blood reaching the organs of the body, such as the brain and the heart itself.
You may be saying, “I’m just a [state your clinical title here]. I don’t need to know about afterload. How does this information affect me?” My question to you is, do you ever give your patient a drug? Drugs alter the tension in the muscular walls. For example, this process is how antihypertensives work, and, to a great extent, how nitroglycerin works. Furthermore, it is a factor in the lack of blood volume in the circulation due to trauma. And those are only a few implications.
The bottom line is, the field of clinical medicine works on mechanics. Arrhythmia recognition is no exception to this rule. Learning should be simple, exciting, and interesting, not to mention fun. Our goal is to provide you with that opportunity; your goal should be to have an open mind.
In closing, when you begin to learn a new subject, you should look for simple descriptions of how things work. There is always time for complexity later. By understanding the simple principles, you are about 95% of the way there. It is the other 5% that require a lifetime to master.
Since you are reading a book on electrocardiography, we assume that you have some basic knowledge of anatomy. However, a review is never a bad thing, so we are going to cover the basic anatomy of the heart and then concentrate on the electrical conduction system.
The heart sits in the middle of the chest at a slight angle pointing downward, to the left, and slightly anterior. Take a look at Figure 1-1
Now, let’s look at the heart itself. First, from an anterior view, and then in cross section.
Anterior View
The right ventricle (RV) dominates the anterior view (Figure 1-2). Most of the anterior surface of the ventricles consists of the RV surface. A key point to remember is that, though the RV dominates this visual view, the left ventricle (LV) dominates the electrical view. We will review this in more detail in Chapter 4, Vectors and the Basic Beat, when we discuss vectors.
The Heart in Cross Section
Figure 1-3 shows a cross-sectional view of the heart. In the following sections, we will cover the function of the heart as a pump and review the electrical conduction system in greater detail.
Aorta
Pulmonary artery
Pulmonary veins
Left atrium
Vein Left
Left anterior descending artery
Left ventricle
Descending aorta
Figure 1-1 Location of the heart in the chest cavity.
The heart consists of four main chambers: the two atria and the two ventricles. The atria empty into their corresponding ventricles. The left ventricle empties into the peripheral circulatory system, and the right ventricle empties into the pulmonary system. Veins bring blood to the heart, while arteries take blood away from the heart. As Figure 1-4 shows, this is a closed system. Blood circulates inside this closed system over and over, taking up oxygen in the lungs and giving it up to the peripheral tissues. This is a simplistic explanation of a very complicated system, but it will suffice for our purposes at this time.
Pump Function Simplified
It is simplest to think of the circulatory system as an engineer would: as a system of interconnected pumps and pipes.
Take a look at Figure 1-5 . We see that there are four pumps in sequence. The two small primer pumps are the atria, whose sole purpose is to push a small amount of blood into the two larger ones, the ventricles. The ventricles differ in size and in the amount of pressure that they can generate. Because of the one-way valves found in the venous system, blood can only flow forward.
Cardiac Output
Blood pressure is critical to life. We need blood pressure to act as the driving force to move blood through the circulatory system in order to deliver oxygen and nutrients to every cell. How does the body maintain blood pressure? It is maintained by both passive and active means. In this section, we will first go over the passive system and then we will discuss the active system.
Suppose you put an extra 70 mL of fluid into a fluid-filled, solid-walled pipe such as a PVC or copper pipe (Figure 1-6). What changes would the extra fluid create in the tube? The pressure in the tube would build up dramatically with every cc of fluid you put into it (Figure 1-7). The pressure would force fluid to run out the open end of the pipe in order to relieve the pressure. That system works well when you have a short amount of pipe and a strong pump. The longer the pipe, the stronger the pump needed.
In one pound of fat tissue in the human body there is one-quarter mile of tubing (Figure 1-8). We can assume that this is true for other types of tissue as well.
How many miles of tubing are in your entire vascular system? A lot! The pump needed to push blood through such a tubing system, if it were rigid, would need to be very strong indeed. What do you suppose such strong forces would do to your red cells, white cells, and platelets? They would destroy them. Therefore, this type of system would not work in our bodies.
Instead of rigid tubing, the human body is composed of elastic tubing. Elastic tubing can bend and allow us to move without any difficulty. It is compressible, allowing external muscle movement to help pump the blood by compressing or milking the tube, causing the fluid to be pushed along. The main advantage to this type
Figure 1-5 Simplified pump function of the circulatory system.
of tubing, however, is its elastic properties. Its elasticity allows the blood vessel to simply distend in order to accommodate for the extra fluid whenever the heart pumps (Figure 1-9).
What would happen to the pressure inside the tube now? It would build up inside the tube, but the distention would distribute the pressure a bit more smoothly. What happens to an elastic band when you stretch it? It wants to go back to its original shape. This built-up energy places constant, smooth pressure on the blood, causing it to flow forward in a smooth fashion, avoiding high shearing pressures and turbulence (Figure 1-9).
The distended arterial walls are, in essence, acting like an additional pump helping to push the blood forward through the circulatory system.
The slow, constant pressure of a distended elastic arterial system wanting to return to normal is the passive way in which the circulatory system functions. Now let’s go over the active system that causes the arterial distention in the first place.
Active Pumping
The blood pressure is maintained actively by the amount of blood that the heart pumps out into the vascular system every minute—in other words, the cardiac output. Cardiac output is, in turn, composed of two variables: the stroke volume and the heart rate. The stroke volume is the amount of blood that the heart ejects during any one contraction. This amount is usually around 70 cc of blood per contraction. Heart rate, as you can
Figure 1-9 Imagine that the bolus of blood that shoots out of the heart is the red area in this figure. Notice how the aorta is distended outward by the additional bolus. As the bolus begins to mix with the rest of the blood, the built-up pressure on the arterial walls is pushing the walls inward. This happens because the elastic walls want to go back to their resting state of relaxation. This pressure causes the blood to move forward smoothly and continuously. The process is repeated over and over with each cardiac contraction.
imagine, refers to the number of times the heart beats in one minute.
Cardiac output is mathematically calculated by taking the amount of blood that the heart can eject in one contraction and then multiplying this by the number of contractions per minute. In other words:
Cardiac Output 5 Stroke Volume 3 Heart Rate
In order to maintain a good hemodynamic balance, the cardiac output has to be within the normal range. Notice however, that you can maintain an adequate cardiac output by altering the two variables. For example, suppose that the stroke volume was 40 cc/min (instead of the normal 70 cc/min). Can you figure out a way that the cardiac output for the heart can be maintained within the normal range? One way would be by increasing the heart rate. That is the reason why, when someone has lost a significant amount of blood (resulting in decreased stroke volume because there is less blood to pump), a tachycardia develops as a compensatory mechanism. The body tries to overcome the deficiency in blood and stroke volume by increasing heart rate.
Now let’s take a closer look at the concept of stroke volume. At the end of systole, the ventricles have just emptied their contents into the arterial system (Figure 1-10). How does the heart fill up the ventricles again? If you remember from basic physiology, the largest amount of ventricular filling occurs during early diastole, when the atrioventricular (AV) valves open
Figure 1-10 This figure shows the heart in late systole. The atria are full but the ventricles are empty.
up and a rush of blood floods the ventricular chamber (Figure 1-11). This is known as the rapid filling phase of diastole.
After the rapid ventricular filling phase of diastole, the ventricles are full with blood. If the ventricles were to contract at this point, the stroke volume of the heart would be at the lower end of normal for most people. Why? Because the ventricles are filled, but not overfilled. It is a well-known fact in muscle physiology that a muscle contracts much more efficiently if it is stretched just a bit (see the Additional Information box). So, how can we overfill the ventricles to allow a bit of muscle stretching? Passive inflow of blood just wouldn’t do it. The answer is made clear when we think about atrial contraction.
If you look at Figure 1-12, you will notice that the atria are completely full of blood during the middle of diastole. They have been filled by the venous blood that is constantly flowing back to the heart. At the end of diastole, when the ventricles are almost full, the atria contract and push the extra blood into the ventricles in order to overfill them (Figure 1-13). The overfilling provided by the atrial contraction stretches the ventricular muscle, allowing for maximal contractility and maximal stroke volume. Better stroke volume means better control over the cardiac output.
You may be asking why we are spending so much time on basic physiology when this is a book on arrhythmias. The reason is that the heart rate is one of the most important variables in the maintenance of
Figure 1-11 In early diastole, the AV valves open, allowing a large amount of blood to rush into the ventricles. This is the rapid filling phase of diastole.
Figure 1-13 The atrial contraction allows an extra amount of blood to enter the ventricles, causing them to stretch and overfill. The slight stretch in the ventricular muscle caused by the atrial kick will maximize stroke volume and cardiac output.
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It was well heated, and there were warm carpets on the floors, but Mr. Bunnikins would not be comforted. He sat in a big arm-chair close to the fire, with his toe-toes drawn up under him, shivering and groaning.
They had a very queer supper of dried potato-pie, dried apple dumpling, and dried lettuce and carrot-cake, for as nothing grows on the cold Island of the Moon, everything to eat has to be brought a long distance in airships, and it all dries up on the way.
The Island of the Moon Chapter III
As Mr Bunnikins-Bunny was very anxious to see the Moon King and his beautiful Palace, they all started out the next morning to visit him. At first they were told that they could not see the King, as he slept all day and was very busy all night, but finally they were invited to come to the Palace that evening, at eight o’clock.
They spent the rest of the day sleighing and seeing the island. The houses were all made of ice, and there were no trees, no flowers,
not even a blade of grass. The people were so huge that they terrified the children, and Rosamund kept tight hold of her father’s paw.
No Bunnies or Squirrels had ever been seen in the Moon before, and the people admired them very much. One little giant girl cried tears as big as dollars, because she could not keep Rosamund for a plaything, and when she picked her up in her big hands to pet her, the poor little bunny was frightened almost to death. As soon as he had eaten his supper, Mr Bunnikins-Bunny hurried off to dress for the Moon King’s Party. He tried one thing and then another, until poor Mrs. Bunnikins was quite tired out trying to help him, and thought he never would be ready in time. At last he decided to wear a beautiful blue velvet suit embroidered in gold, and a very fine green and white hat all trimmed with ostrich feathers. To keep himself warm, he had a velvet cape lined with fur, and, as a finishing
touch, he wore a little gold sword. Mrs. Bunnikins advised him not to, as she was afraid it would be in his way, but Mr. Bunnikins-Bunny insisted that a sword was the proper thing to wear at Court.
Bobtail and Ruddy Squirrel had tied bright red bows on themselves wherever they could find a place, and Rosamund shouted with laughter whenever she looked at them.
The Palace of the Moon King
Chapter IV
The Palace was made entirely of blocks of ice most beautifully carved, the walls being lined with silk, so that nobody could look in. It was brilliantly lighted, and on each of the broad steps stood a giant soldier, in scarlet and gold uniform.
Two big footmen led the Bunnikins-Bunnies and the Gray-Squirrels through one grand room after another, until they came to a great silver door, on which one of the footmen knocked twice with a silver wand. As the door slowly opened, the Bunnikins-Bunnies and the Gray-Squirrels were so dazzled by the flood of light, that for a moment they all covered their faces with their paws. Then they looked up and saw the most wonderful room.
It was made of purest white ice, the floors being covered with great white rugs, and the walls with silvery silk. The furniture was of ivory inlaid with silver, and in every corner stood a tall silver vase full of moon flowers, which perfumed the air.
At one end of the great room was a silver throne, on which was seated a gigantic figure clad in a misty white garment, from which the silvery moonbeams streamed out in every direction, so that the whole room was filled with a shimmering light.
In front of the King was a great round window through which he was intently gazing. His head was quite bald, his cheeks were fat, he had a big mouth, and his eyes were very large and round. As he turned with a pleasant smile to greet the Bunnikins-Bunnies and the Gray-Squirrels, they were very much astonished to recognize the Man in the Moon, whom they had so often seen, sitting high up in the sky.
“Draw the cloud curtain,” he said to one of the footmen, who at once pulled a heavy gray curtain across the great window. Then in a very gentle voice for such a huge being, he added: “Come forward my little people, I am very glad to see you.”
The King of the Moon Chapter V
As they came forward Mr Gray-Squirrel made a polite bow, and Mrs. Bunny and Mrs. Squirrel made nice little courtesies, but poor Mr. Bunnikins-Bunny, in the middle of a most elegant bow, got his legs so twisted up with his sword, that he turned a complete somersault right into the Moon King’s lap!
“Never mind,” said the King, as he kindly helped him to his feet, “accidents will happen. Have a piece of cheese?”
On the broad arm of the King’s throne was a plate full of green cheese, of which he took a large piece himself, after offering it to the Bunnies and the Squirrels.
“Do you make your own cheese?” asked Mrs. Bunnikins-Bunny, as she tasted it.
“It is made for me in the Milky Way,” replied the Moon King. “No cows have been allowed in the Moon, since a very rude one jumped right over my head many years ago.”
Just then there was a loud squeal of terror from the other end of the room. Bobtail had found the queer cheese so horrid, that he simply could not eat it. He had wandered off, hoping to find some dark corner in which to hide it, and had stumbled into a mouse trap, and been caught by the leg.
“Dear! Dear!” said the King, as they all ran to help poor Bobtail. “I am so sorry, but you see mice like cheese almost as much as I do, and so I have to set traps everywhere. Now you shall have a peep from my Look-Out-Window,” he continued, taking Bobtail by the paw.
Far, far below they could see the great round earth looking like a little ball, but it made them all so dizzy, that they did not look very long.
“Do you never get sleepy?” asked Mrs. Gray-Squirrel.
“Not very often,” answered the Moon King. “There are times when I can watch with one eye, and then I have taught the other eye to go to sleep.”
“I thought you had a dog?” said Mr. Bunnikins-Bunny.
“I did have a very fine yellow dog, but alas, I lost him long ago,” and the King, with a sigh, wiped away a tear. “His name was Ebenezer, but we called him Sneezer for short, because he was so fond of mouse patties flavored with pepper, which made him sneeze. He was always chasing cats. One day he heard one miaow, and jumping on the ledge of my Great Window, he slipped and fell out, I don’t know where.
“Since then, however, so many yellow dogs have been seen on the Island of Sirius, that it is now called the Dog Star, and I believe that Sneezer landed there.”
While the King had been talking, the children had crept behind the cloud curtain to try and see the Dog Star Bobtail had leaned out so far that he lost his balance, and would have surely gone to join Sneezer, had not one of the King’s footmen grabbed him by his short tail.
As it was now late, the Bunnikins-Bunnies and the Gray-Squirrels, after thanking the King for his kindness, said good-by, and the cloud curtain being drawn back, the King of the Moon gazed down once more upon the sleeping earth.
The Island of Mars Chapter VI
Early next morning, as soon as the sun had risen and the King of the Moon had gone to bed, the Bunnikins-Bunnies and the GraySquirrels went on board the airship, and sailed off toward the Island of Mars. The children begged Captain Hawk to stop at the Dog Star and see Sneezer, but neither Mr. Bunnikins nor Mr. Gray-Squirrel was willing to, as they were both very much afraid of dogs.
