Understanding Cardiac Electrophysiology: A Conceptually Guided Approach

136 Pages·2016·8.549 MB·English

by  Peter Spector

Understanding Clinical Cardiac Electrophysiology

Understanding
Clinical Cardiac
Electrophysiology
A Conceptually Guided Approach
Peter Spector,
md
Professor of Medicine,
Director, Cardiac Electrophysiology and Cardiac Electrophysiology Laboratory,
University of Vermont Medical Center,
University of Vermont College of Medicine
Burlington, VT, USA
Copyright © 2016 by John Wiley & Sons, Inc. All rights reserved
Published by John Wiley & Sons, Inc., Hoboken, New Jersey
Published simultaneously in Canada
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Library of Congress Cataloging‐in‐Publication Data:
Names: Spector, Peter, author.
Title: Understanding clinical cardiac electrophysiology : a conceptually guided approach / Peter Spector.
Description: Chichester, West Sussex, UK ; Hoboken, NJ : John Wiley & Sons Inc., 2016. |
Includes bibliographical references and index.
Identifiers: LCCN 2015043776 | ISBN 9781118905494 (paperback)
Subjects: | MESH: Electrophysiologic Techniques, Cardiac. | Arrhythmias, Cardiac. |
Atrial Function. | Cardiac Electrophysiology–methods.
Classification: LCC RC683.5.E5 | NLM WG 141.5.F9 | DDC 616.1/207547–dc23
LC record available at http://lccn.loc.gov/2015043776
Set in 10.5/13.5pt Minion by SPi Global, Pondicherry, India
10 9 8 7 6 5 4 3 2 1
1 2016
Contents
Preface, vii
Acknowledgments, ix
About the companion website, xi
Part I: Third‐person omniscient (how we would see EP if we could see EP)
1 Ion channels, 3
2 Action potentials, 9
3 Propagation, 19
4 Arrhythmia mechanisms, 25
5 Anatomy for electrophysiologists, 37
Part II: Doctor’s‐eye view (dealing with incomplete knowledge)
6 Deducing anatomy, 49
7 Electrical activity, electrodes, and electrograms, 59
8 Electrogram analysis: understanding electrogram morphology, 69
9 Differential diagnostic pacing maneuvers, 79
10 Electro‐anatomic mapping, 99
Appendix: What we measure when we record an electrogram, 109
Afterword: Your heart is a computer: from army ants to atrial fibrillation, 115
Suggested reading, 117
Index, 119
v

Preface
Why this book? starting values into future values at arbitrarily distant
times. Often the only way to determine behavior is to
I don’t know about you, but my shelves are brimming iteratively calculate how each new state of the system
with texts on cardiac electrophysiology. EP texts range evolves into the next state. This process of iterative assess-
from colossal reference tomes to “tips and tricks.” ment is tremendously aided by modern computers.
Despite all of the material available to students and Whereas humans may be able to mentally compute a few
practitioners, I was inspired to write this book by the steps, they quickly fatigue and “lose track.” Computers
perception of a void. In the fast‐paced world of clinical never fatigue and are now capable of computing at such
training students are often inundated with the “what” of blinding speeds that they can quickly demonstrate the
electrophysiology without the “why.” Understanding evolution of systems through time.
Clinical Cardiac Electrophysiology is designed to tell the I had been studying cardiac electrophysiology for
story of electrophysiology so that the seemingly dispa- many years but was entirely unaware of the existence of
rate myriad observations of clinical practice come into complex systems or the notion of emergent behavior.
focus as a cohesive and predictable whole. While it can When I was introduced to these ideas by a colleague1 it
be difficult to memorize a thousand words, it is easy to became clear that cardiac electrophysiology is a classic
remember a single story. example of a complex non‐linear dynamic system, and
that the science of such systems can offer many insights
germane to understanding electrophysiology. Over the
Cardiac electrophysiology as a six years leading up to the writing of this book I began
“complex non‐linear system” meeting with some particularly intelligent and curious
colleagues and students to discuss electrophysiology
Science has undergone a revolution of sorts in the past 60 and how it can best be understood. These discussions
years. Despite its incredible accomplishments, science evolved into a weekly meeting of faculty and fellows
had been relatively ill equipped to address the behavior of dubbed “the EP study group.” These meetings had a
systems composed of multiple interdependent parts. An loose and wide‐ranging agenda; the EP study group was
emerging discipline has focused on understanding how more of an ongoing conversation than a lecture. We
such systems change over time. “Systems” as diverse as began with the question: “What are we really measuring
the economy, the brain, and army ants are all “complex when we record electrograms?” This led to a six‐year‐
non‐linear dynamic systems.” The meaning of this unfa- long journey that included a review of vector calculus,
miliar and somewhat daunting phrase is captured by the Maxwell’s equations, discussions of neural networks
expression “the whole is greater than the sum of its parts.” and other forms of artificial intelligence, complexity,
Even with an understanding of how individual elements genetic algorithms, and on and on. This book has in
of such a system “work,” and of the “rules of engagement” part been an attempt to codify the lessons learned and
that govern their i nteractions, it can be difficult or impos- present them to a wider audience. Fear not, this is not a
sible to predict the behavior of complex non‐linear book about the heart as a complex system; but it does
systems more than a short time into the future. There is tell its story informed by this powerful perspective.
often no analytic solution to predict the behavior of
complex systems – i.e., there is no formula that converts 1 Jason H. T. Bates PhD, DSc
vii
viii Preface
“The heart is a computer” left to the biophysicist and biomedical engineer. One of
my goals in the present book is to bridge this culture gap
I have come to appreciate that the heart isn’t “like” a by making the necessary mathematics as accessible as
computer; in a very meaningful way it is a computer. It possible to those who might not normally consider them-
is an enormous parallel processor. Based upon the rules selves that way inclined (I am one such person). Because
that govern the behavior of individual cells, the interac- some respond to mathematics with either panic or coma,
tions between cells, and the structure which connects I have placed the mathematics in an appendix where it
these cells, the heart begins with its current “state” and can safely be ignored by those so inclined.
calculates its next state. From this perspective one can
appropriately say “your heart is a computer; your
What this book isn’t
rhythm is the result of its ongoing calculation.”
Despite the fact that the material and perspective
described above is unfamiliar to most clinical electro- Understanding Clinical Cardiac Electrophysiology is not
physiologists, this book is very much written for a textbook of electrophysiology. It is not a manual of
clinicians. These ideas are harnessed in order to operations for procedures. It does not focus on specific
facilitate a deeper understanding of electrophysiology, diagnostic criteria. It does not address implementation
both to appreciate its infinite aesthetic beauty and in of therapeutic interventions. Numerous other sources
order that such understanding may be used to practice are available for addressing these important aspects of
better electrophysiology. cardiac electrophysiology. If you are going to read only
The proper treatment of cardiac electrophysiology one book about electrophysiology … don’t read this
requires some mathematics, particularly when it comes to one. My objective is to review the principles that under-
the physics of excitable tissue and the development of lie electrophysiology and the analytic tools which, when
computational models. Such mathematics, which is essen- combined with a firm grasp of EP mechanisms, allow
tial for a proper understanding of the subject, is often readers to think through any situation in which they
eschewed by physiologists and medical practitioners and find themselves.