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Electrophysiology of the heart
Book Reviews inductance and capacitive characteristics of the various body tissues. Additional sections carefulIy dehneate the eIectronics of the various instrumentations that have been applied to the study of this problem, with particular emphasis on the high frequency system developed by the author and Mr. Bagno. Experimental evidence, both physical and biologic, of the validity of the electrical method is presented in detail. The monograph is an essential text for any worker who intends to explore this field. In addition, those physicians who keep abreast of the latest advances in cardiovascular physiology will want to own this book. It does, however, contain numerous typographical errors which should be corrected in subsequent editions. SIDNEY ARBEIT, M.D.
Electrophysiology of the Heart, by Brian J. Hoffman and Paul F. Cranefield. Blakeston Division, McGraw-Hill, New York, 1960, pp. 323, $12.50. It should be noted that this book is not being reviewed by an electrophysiologist, but by a cardiologist who has been studying various aspects of electrocardiography for twenty years. This background perhaps explains the great academic and practical value which the reviewer believes exists in this excellent publication. The nine chapters must be read and studied slowiy as the material is abundant and the problems to be resolved are complex. The major substance is the study of the transmembrane action potential of the different tissues such as auricular, ventricular, S-A node, A-V node and Purkinje fibers. The different morphologies of phases 0, 1, 2, 3 and 4 are demonstrated as having major importance and, moreover, must be in agreement for a correct electrocardiographic interpretation. The first chapter is devoted to the methodology involved in registering the special phases by means of microelectrodes. There is a discussion of the action potentials obtained across the cellular membrane in the different cardiac fibers. There is also a section which discusses the unipolar electrocardiogram and once more returns to the observation which the majority of physiologists make, namely, that the remote electrode is influenced by changes in potential which originate in the tissue itself. The viewpoint of the electrocardiographer is different JANUARY
1961
since it is well known that the potential of a given field falls rapidly and in relation to the square of the distance between the electrode and the site from which the potentials originate. Thus, the influence of the cardiac potentials on the distant electrode is always negligible and when the proximal electrode is directly on the heart one may put the distant electrode on any part of any Iimb of the experimental animal and the curve recorded will always be the same. In the same section the authors discuss the relationship between the transmembrane potential and the electrogram and the reason the latter may be considered as a derivative of the monophasic potential. When the derivation is unipolar it is necessary to consider the laws that govern the volume of the conducting media and, therefore, such relationships can only be discussed as analogies. It should be noted that this type of derivation when analyzed by Poisson’s Integral has been shown to have great usefulness in electrocardiographic interpretation. Chapter 2 is devoted to a discussion of excitation and conduction. The electric properties of the excitable cells are studied as well as the core conductor properties; it is emphasized that the transverse resistance of the membrane is higher than the longitudinal resistance on both sides of the membrane. This means that the flow of current will spread along a relatively greater length of fiber (electronic spread). The electric models of the membrane which correspond to a resting and excitable cell are so clear and simple that they could easily be used as teaching material for any level of student. The importance which is given to the ionic gradients and the electromotive force resulting from the gradients of permeability of Na and K is quite correct as an explanation of the principal events. Chapters 3, 4, 5, 6 and 7 study- the action potential of the atrium, ventricle, S-.4 node, A-V node and the Purkinje fibers, respectively. All of these chapters are similarly constructed: after the description of the characteristics of the curve, the authors detail the changes due to frequency, temperature, drugs, ionic ,changes, effects of current flow, acetylcholine, epinephrine, etc. For each of the potentials there is given a great variety of useful data from which I shall choose only a few appropriate and important examples. The authors show that the triangular form
156
Book Reviews
of the atria1 action potential (recovery phases 2 and 3) cannot be identified. This may be related to the lack of the auricular T in the peripheral electrocardiogram. The conduction velocity in the ventricle of the dog is somewhat higher than the classically accepted values and close to 0.9 to 1.0 M./set. The authors insist on the necessity of distinguishing between conduction velocity and measurements of excitation time (sequence of They believe that plunge elecactivation). trodes produce local injury and block. We have used this type of electrode and it does not appear to cause a significant degree of injury since the unipolar derivations obtained from it do not exhibit changes in the RS-T segment. On the other hand, our results arc also in agreement with other workers in that the degree of block is also not very significant. In the sinoatrial node the pacemaker fails to maintain a steady level of resting potential (slow depolarization). It is of great interest to study the cause of the intrinsic rhythmicity. The authors suggest the intriguing possibility that the pacemaker cells contain more sodium and less potassium than the nonpacemaker cells. In such cells the level of E, would be shifted in the direction of depolarization. An increase in permeability to K (PK) associated with repolarization would bring the transmembrane potential close to Ek. The subsequent decrease in PK to the level characteristic of phase 4 would permit the ionic currents carried by Na or other ions to progressively lower the membrane potential and thereby provide depolarization during phase 4. In the chapter on the atrioventricular node the authors study the mechanism of delay. Erlanger pointed out the possibility that the delay occurs as the result of a latency at the transition zone between atria1 fibers and fibers of the atrioventricular node. In the chapter on Purkinje fibers it is interesting to note that the authors believe that the U wave is merely the surface record of repolarizstion of the ventricular Purkinje system, that is, the U wave is the Purkinje fiber T wave. Two arguments favor this: potassium produces marked variations in the U wave and a marked effect on phase 3 or Purkinje potential. In addition, the potential of Purkinje fibers is considerably longer than that of ventricular muscle and the phase of rapid repolarization of Purkinje fibers is coincident in time with the U wave.
In chapter 8, excitability is studied and the authors establish a clear difference between cathodal and anodal stimulation. Four new concepts of the greatest importance are presented : (1) regenerative repolarization, (2) all or none repolarization, (3) propagated repolarization and (4) break reexcitation. It seems likely, as the authors state, that propagation of repolarization exists in the normal heart. Since repolarization propagates very slowly (about 0.2 mm.,/sec.) one would not expect a single pacemaker. Each area which repolarizes before an adjoining area would then contribute to the repolarization of the adjoining area. Therefore, repolarization would be a propagated process with multiple foci of origin. The last chapter is a general revision of the electrophysiology of the heart and is fundamental for every cardiologist and electrocardiologist. As a particular example, one could choose the section on the possible mechanism of repolarization. Anyone who is interested in obtaining a basic understanding of the intrinsic mechanism of electrocardiology and electrophysiology can do so by studying the principles as set forth in this excellent book. DEMETRIOSODI-PALLARES, M.D.
Angiocardiopneumographie klargie: Mithode D’Opacification Vasculaire Gin&ale par Voie Veneuse, by P. Viallet, L. Sendra, L. Chevot, P. Aubry and P. Combe. Masson & Cie, Paris, 1959, pp.110, 4,400 fr. As a rule, opacification of the circulatory system is effected by the venous route. In order to avoid delays in injection, the authors insist on the need for as large a tube as possible from the injection syringe to the venous cannula and on the desirability of a massive flow of physiologic saline solution at the end of the injection to force the contrast medium to the right side of the heart. During the left heart phase, large roentgenograms record opacification of large areas. The method is, therefore, classic. Thanks to the atlas-type format of the book and the use of excellent paper, the authors have been able to include a number of fairly large angiocardiograms of good quality reproduction. The text is extremely concise. R. HEIM DE BALSAC, M.D. THE
AMERICAN
JOURNAL
OF
CARDIOLOGY
Electrophysiology of the Heart, by Brian J. Hoffman and Paul F. Cranefield. Blakeston Division, McGraw-Hill, New York, 1960, pp. 323, $12.50. It should be noted that this book is not being reviewed by an electrophysiologist, but by a cardiologist who has been studying various aspects of electrocardiography for twenty years. This background perhaps explains the great academic and practical value which the reviewer believes exists in this excellent publication. The nine chapters must be read and studied slowiy as the material is abundant and the problems to be resolved are complex. The major substance is the study of the transmembrane action potential of the different tissues such as auricular, ventricular, S-A node, A-V node and Purkinje fibers. The different morphologies of phases 0, 1, 2, 3 and 4 are demonstrated as having major importance and, moreover, must be in agreement for a correct electrocardiographic interpretation. The first chapter is devoted to the methodology involved in registering the special phases by means of microelectrodes. There is a discussion of the action potentials obtained across the cellular membrane in the different cardiac fibers. There is also a section which discusses the unipolar electrocardiogram and once more returns to the observation which the majority of physiologists make, namely, that the remote electrode is influenced by changes in potential which originate in the tissue itself. The viewpoint of the electrocardiographer is different JANUARY
1961
since it is well known that the potential of a given field falls rapidly and in relation to the square of the distance between the electrode and the site from which the potentials originate. Thus, the influence of the cardiac potentials on the distant electrode is always negligible and when the proximal electrode is directly on the heart one may put the distant electrode on any part of any Iimb of the experimental animal and the curve recorded will always be the same. In the same section the authors discuss the relationship between the transmembrane potential and the electrogram and the reason the latter may be considered as a derivative of the monophasic potential. When the derivation is unipolar it is necessary to consider the laws that govern the volume of the conducting media and, therefore, such relationships can only be discussed as analogies. It should be noted that this type of derivation when analyzed by Poisson’s Integral has been shown to have great usefulness in electrocardiographic interpretation. Chapter 2 is devoted to a discussion of excitation and conduction. The electric properties of the excitable cells are studied as well as the core conductor properties; it is emphasized that the transverse resistance of the membrane is higher than the longitudinal resistance on both sides of the membrane. This means that the flow of current will spread along a relatively greater length of fiber (electronic spread). The electric models of the membrane which correspond to a resting and excitable cell are so clear and simple that they could easily be used as teaching material for any level of student. The importance which is given to the ionic gradients and the electromotive force resulting from the gradients of permeability of Na and K is quite correct as an explanation of the principal events. Chapters 3, 4, 5, 6 and 7 study- the action potential of the atrium, ventricle, S-.4 node, A-V node and the Purkinje fibers, respectively. All of these chapters are similarly constructed: after the description of the characteristics of the curve, the authors detail the changes due to frequency, temperature, drugs, ionic ,changes, effects of current flow, acetylcholine, epinephrine, etc. For each of the potentials there is given a great variety of useful data from which I shall choose only a few appropriate and important examples. The authors show that the triangular form
156
Book Reviews
of the atria1 action potential (recovery phases 2 and 3) cannot be identified. This may be related to the lack of the auricular T in the peripheral electrocardiogram. The conduction velocity in the ventricle of the dog is somewhat higher than the classically accepted values and close to 0.9 to 1.0 M./set. The authors insist on the necessity of distinguishing between conduction velocity and measurements of excitation time (sequence of They believe that plunge elecactivation). trodes produce local injury and block. We have used this type of electrode and it does not appear to cause a significant degree of injury since the unipolar derivations obtained from it do not exhibit changes in the RS-T segment. On the other hand, our results arc also in agreement with other workers in that the degree of block is also not very significant. In the sinoatrial node the pacemaker fails to maintain a steady level of resting potential (slow depolarization). It is of great interest to study the cause of the intrinsic rhythmicity. The authors suggest the intriguing possibility that the pacemaker cells contain more sodium and less potassium than the nonpacemaker cells. In such cells the level of E, would be shifted in the direction of depolarization. An increase in permeability to K (PK) associated with repolarization would bring the transmembrane potential close to Ek. The subsequent decrease in PK to the level characteristic of phase 4 would permit the ionic currents carried by Na or other ions to progressively lower the membrane potential and thereby provide depolarization during phase 4. In the chapter on the atrioventricular node the authors study the mechanism of delay. Erlanger pointed out the possibility that the delay occurs as the result of a latency at the transition zone between atria1 fibers and fibers of the atrioventricular node. In the chapter on Purkinje fibers it is interesting to note that the authors believe that the U wave is merely the surface record of repolarizstion of the ventricular Purkinje system, that is, the U wave is the Purkinje fiber T wave. Two arguments favor this: potassium produces marked variations in the U wave and a marked effect on phase 3 or Purkinje potential. In addition, the potential of Purkinje fibers is considerably longer than that of ventricular muscle and the phase of rapid repolarization of Purkinje fibers is coincident in time with the U wave.
In chapter 8, excitability is studied and the authors establish a clear difference between cathodal and anodal stimulation. Four new concepts of the greatest importance are presented : (1) regenerative repolarization, (2) all or none repolarization, (3) propagated repolarization and (4) break reexcitation. It seems likely, as the authors state, that propagation of repolarization exists in the normal heart. Since repolarization propagates very slowly (about 0.2 mm.,/sec.) one would not expect a single pacemaker. Each area which repolarizes before an adjoining area would then contribute to the repolarization of the adjoining area. Therefore, repolarization would be a propagated process with multiple foci of origin. The last chapter is a general revision of the electrophysiology of the heart and is fundamental for every cardiologist and electrocardiologist. As a particular example, one could choose the section on the possible mechanism of repolarization. Anyone who is interested in obtaining a basic understanding of the intrinsic mechanism of electrocardiology and electrophysiology can do so by studying the principles as set forth in this excellent book. DEMETRIOSODI-PALLARES, M.D.
Angiocardiopneumographie klargie: Mithode D’Opacification Vasculaire Gin&ale par Voie Veneuse, by P. Viallet, L. Sendra, L. Chevot, P. Aubry and P. Combe. Masson & Cie, Paris, 1959, pp.110, 4,400 fr. As a rule, opacification of the circulatory system is effected by the venous route. In order to avoid delays in injection, the authors insist on the need for as large a tube as possible from the injection syringe to the venous cannula and on the desirability of a massive flow of physiologic saline solution at the end of the injection to force the contrast medium to the right side of the heart. During the left heart phase, large roentgenograms record opacification of large areas. The method is, therefore, classic. Thanks to the atlas-type format of the book and the use of excellent paper, the authors have been able to include a number of fairly large angiocardiograms of good quality reproduction. The text is extremely concise. R. HEIM DE BALSAC, M.D. THE
AMERICAN
JOURNAL
OF
CARDIOLOGY