Fogoros' Electrophysiologic Testing

Richard N. Fogoros, John M. Mandrola

• Editore: Wiley-Blackwell
• Anno: 2017
• ISBN:
  9781119235798
• Edizione: 6
• Argomento: Medizin
• Categoria: Physiologie

The classic guide to applying, performing and interpreting EP tests, updated for the latest trends and developments in the field

For more than thirty years, Electrophysiologic Testing has been a trusted introduction to the field of electrophysiology for anyone needing to quickly acquaint themselves with basic concepts and procedures of EP testing, especially medical students, residents, nurses and technicians. At the same time, it also has served as a ready reference for medical practitioners wanting to brush up on aspects of electrophysiology, or to fine-tune their mastery of the field.

Updates and additions featured in the Sixth Edition of this classic guide include extensive new material on the ablation of cardiac arrhythmias, including new chapters on the ablation of atrial fibrillation, typical and atypical atrial flutters and ventricular arrhythmias.

The ultimate guide to applying, performing and interpreting EP tests to optimise the treatment of patients with cardiac arrhythmias, Electrophysiologic Testing, Sixth Edition:

• Clarifies the role of electrophysiology in the evaluation of cardia arrhythmias
• Provides clear summaries of complex topics
• Features a uniquely user-friendly style that makes information easy to digest and recall
• Offers clear, step-by-step guidance on performing EP tests and interpreting their results
• Reviews the latest developments in therapeutic electrophysiology

As with all previous editions, this updated and revised Sixth Editi on was written with the goal of demystifying electrophysiology, and making it readily accessible to virtually anyone with a professional need. To that end, Drs. Fogoros and Mandrola have once again turned in a masterful performance.

Part I
Disorders of the Heart Rhythm: Basic Principles

1
The Cardiac Electrical System

The heart spontaneously generates electrical impulses, and these electrical impulses are vital to all cardiac functions. On a basic level, by controlling the flux of calcium ions across the cardiac cell membrane, these electrical impulses trigger cardiac muscle contraction. On a higher level, the heart’s electrical impulses organize the sequence of muscle contractions during each heartbeat, important for optimizing the cardiac stroke volume. Finally, the pattern and timing of these impulses determine the heart rhythm. Derangements in this rhythm often impair the heart’s ability to pump enough blood to meet the body’s demands.

Thus, the heart’s electrical system is fundamental to cardiac function. The study of the electrical system of the heart is called cardiac electrophysiology, and the main concern of the field of electrophysiology is the mechanisms and therapy of cardiac arrhythmias. The electrophysiology study is the most definitive method of evaluating the cardiac electrical system. It is the subject of this book.

As an introduction to the field of electrophysiology and to the electrophysiology study, this chapter reviews the anatomy of the cardiac electrical system and describes how the vital electrical impulse is normally generated and propagated.

The anatomy of the heart’s electrical system

The heart’s electrical impulse originates in the sinoatrial (SA) node, located high in the right atrium near the superior vena cava. The impulse leaves the SA node and spreads radially across both atria.When the impulse reaches the atrioventricular (AV) groove, it encounters the “skeleton of the heart,” the fibrous structure to which the valve rings are attached, and which separates the atria from the ventricles. This fibrous structure is electrically inert and acts as an insulator—the electrical impulse cannot cross this structure. Thus the electrical impulse would be prevented from crossing over to the ventricular side of the AV groove if not for the specialized AV conducting tissues: the AV node and the bundle of His (Figure 1.1).

Figure 1.1 Anatomy of the electrical system of the heart.

As the electrical impulse enters the AV node, its conduction is slowed because of the electrophysiologic properties of the AV nodal tissue. This slowing is reflected in the PR interval on the surface electrocardiogram (ECG). Leaving the AV node, the electrical impulse enters the His bundle, the most proximal part of the rapidly conducting His–Purkinje system. The His bundle penetrates the fibrous skeleton and delivers the impulse to the ventricular side of the AV groove.

Once on the ventricular side, the electrical impulse follows the His bundle as it branches into the right and left bundle branches. Branching of the Purkinje fibers continues distally to the furthermost reaches of the ventricular myocardium. The electrical impulse is thus rapidly distributed throughout the ventricles.

Hence, the heart’s electrical system is designed to organize the sequence of myocardial contraction with each heartbeat. As the electrical impulse spreads over the atria toward the AV groove, the atria contract. The delay provided by the AV node allows for complete atrial emptying before the electrical impulse reaches the ventricles. Once the impulse leaves the AV node, it is distributed rapidly throughout the ventricular muscle by the Purkinje fibers, providing for brisk and orderly ventricular contraction.

We next consider the character of the electrical impulse, its generation, and its propagation.

The cardiac action potential

The cardiac action potential is one of the most despised and misunderstood topics in cardiology. The fact that electrophysiologists claim to understand it is also a leading cause of the mystique that surrounds them and their favorite test, the electrophysiology study. Because the purpose of this book is to debunk the mystery of electrophysiology studies, we must confront the action potential and gain a basic understanding of it. Fortunately, this is far easier than legend would have it.

Although most of us would like to think of cardiac arrhythmias as an irritation or “itch” of the heart (and of antiarrhythmic drugs as a balm or a salve that soothes the itch), this conceptualization of arrhythmias is wrong and leads to the faulty management of patients with arrhythmias. In fact, the behavior of the heart’s electrical impulse and of the cardiac rhythm is largely determined by the shape of the action potential; the effect of antiarrhythmic drugs is determined by how they change that shape.

The inside of the cardiac cell, like all living cells, has a negative electrical charge compared to the outside of the cell. The resulting voltage difference across the cell membrane is called the transmembrane potential. The resting transmembrane potential (which is –80 to –90 mV in cardiac muscle) is the result of an accumulation of negatively charged molecules (called...