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His bundle electrocardiography
American
Heart Journal September, 1973, Volume 86, Number
3
Editorial
His bundle
electrocardiography
Charles F&h, M.D. Douglas P. Zipes, M.D. Indianapolis, Ind.
A
11new techniques introduced into medicine are ultimately judged by their contribution to our understanding of pathophysiology, enhancement of diagnostic ability, insight into the mechanism of therapeutic interventions, and to the over-all management of the ill patient. The technique of His bundle electrocardiography (HBE), although relatively new, has interested many investigators, and has resulted in a number of published studies with considerable unanimity of findings. For this reason, one can attempt to evaluate, even at this early stage of the development, the contribution of HBE to our understanding of the mechanism of arrhythmias and to the management of the patient with heart disease. This editorial was written with a clear understanding that information inherent in HBE is far from complete and that much of it is yet to be realized. The technique of HBE involves passing a catheter across the tricuspid valve, which requires sophisticated and expensive instrumentation and considerable technical skill. However, in experienced hands, the technical aspects of the procedure are
relatively simple and safe. An electrode catheter is introduced percutaneously into the femoral vein with its tip positioned near the septal leaflet of the tricuspid valve. The His potential (H) appears as a welldefined, most often bipolar spike between the low atria1 (A) and ventricular (V) electrograms. The interval between the earliest onset of the surface P wave or a high right atria1 deflection and the low right atria1 deflection (P-A) is a measure of intraatria1 conduction. The interval between A and H (A-H) is a measurement of the conduction across the A-V node and varies in duration from 50 to 120 msec., depending on the cycle length and autonomic influences. The interval from H to V (H-V) is a measure of His-Purkinje conduction time and is determined by the interval between the His deflection and the earliest ventricular activity recorded in any lead. The HV interval is a measure of conduction through the His bundle distal to the recording electrode, the bundle branches, and the I’urkinje system up to the point of ventricular activation. In contrast to a relatively wide range of values for the A-H, the H-V interval is fairly constant measuring 30 to 55
From
the Department of Medicine, Indiana University School of Medicine. the Krannert Institute of Cardiology. and Marion County General Hospital, Indianapolis, Ind. Supported in part by the Herman C. Krannert fund. United States Public Health Service Grants HE-6308. HE-5363 and HE-5749. and the Indiana Heart Association. Received for publication Sept. 11. 1972. Reprint requests to: Charles Fisch. M.D., 1100 West Michigan St., Indianapolis, Ind. 46202.
Vol.
86, No. 3, pp. 289-291
.%#fctrtDcr,
1973
American
Heart Journal
289
290
Fisch and Zipes
msec. with an average value of 45 msec. The ability to separate A-V nodal and His-Purkinje (H-P) conduction has enhanced our understanding of normal and abnormal atrioventricular (A-V) conduction. Abnormal A-V conduction may be due to prolongation of P-A, A-H, H-V, or all three. In patients with a P-R interval in the upper limits of normal, the H-V may be abnormally prolonged and when subjected to atria1 pacing, may reveal latent block of the H-P system and thus aid in the differential diagnosis of syncope. It should be pointed out, however, that the H-V may be normal and the patient may still have periodic complete distal His block. HBE confirmed the fact that when the QRS duration is normal, the A-V block is usually in the A-V node. On the other hand, in the presence of a prolonged QRS, the block may be either in the A-H or in the H-V regions, or in both. Second degree block of the Wenckebach type is most often, but not always, A-V nodal in origin while Type II is nearly always due to a block in the H-V system. Concealed discharge of the bundle of His as a cause of unexpected first or second degree A-V block had been proposed from analysis of the surface ECG and conclusively proved with HBE in the human. Incomplete penetration of the A-V node or bundle of His (concealed conduction) has been repeatedly demonstrated in the human with HBE. HBE clearly confirmed pre-excitation of the ventricles in the Wolff-Parkinson-White (W-P-W) abnormality. In this syndrome, the A-H is normal and the H-V is foreshortened. With atria1 pacing, the A-H lengthens normally, but the A-V conduction by way of the bypass remains unchanged and consequently the H-V shortens, the His deflection eventually becoming lost in or actually following ventricular excitation. The syndrome of short P-R, normal QRS and tachycardia has been shown in some instances to be due to foreshortening of the A-H interval without any change of the H-V period. The exact reason for shortening of the A-H conduction remains obscure. In some of the reported cases, the response of the A-H interval to pacing is qualitatively the same as in the normal but quantitatively much less pronounced. Our understanding of the possible inter-relationship of the electro-
physiologic manifestations of ventricular pre-excitation ’ with anatomic correlates (James, Mahaim, or Kent bypass) must await further studies. The mechanism of antegrade block with preservation of retrograde conduction has been the subject of considerable discussion. HBE clearly demonstrates an H potential between the ventricular and atria1 electrograms, thus strongly supporting unidirectional block with preservation of retrograde V-A conduction. Although the major contribution of the His recording has been to our understanding of A-V conduction and its various aberrations, HBE has provided some help with analysis of ectopic rhythms. For example, HBE demonstrated clearly that many supraventricular tachycardias are due to re-entry within the A-V node and that accelerated idioventricular rhythm, so frequently seen in acute myocardial infarction, is ventricular in origin. The everpresent problem of differential diagnosis of supraventricular aberrancy and ventricular ectopy can be resolved with HBE recording. In the former, H precedes V with a normal H-V time, while in the latter the H deflection is often lost within the ventricular electrogram or, if it precedes the local ventricular electrogram, it follows the earliest moment of ventricular activation recorded in the multiple surface tracings. Rarely, ventricular ectopic impulse will activate the bundle of His before giving rise to a QRS, and in such a situation an H-V shorter than normal will be recorded. There is always the possibility, however remote, that one simply fails to record the H spike during supraventricular rhythm and an erroneous diagnosis of ventricular tachycardia may be entertained. There is little doubt, from the foregoing brief review, that the HBE has and will continue to contribute to our understanding of arrhythmias and that this avenue of investigation should be pursued by those studying mechanisms of arrhythmias and who are thus equipped for routine HBE. On the other hand, the utility of HBE in everyday, routine care of patients with heart disease is much less secure and in fact is yet to be defined. Irrespective of the invasive nature of the procedure, the technical skill and instrumentation required, the ultimate role of
Volume Nwnber
86 3
the HBE in the management of the patient will hinge on two factors, namely: (1) evidence that HBE offers considerable advantage over a carefully analyzed surface ECG correlated with the total clinical picture and, equally important, (2) our ultimate ability to utilize fully the information obtained with the HBE in the actual care of the patient. At present, we are unable to benefit fully from the information inherent in the HBE because complementary, parallel clinical facts are not available. The following two examples will serve to illustrate this point. The recognition from the HBE that a given supraventricular tachycardia is reentrant in origin rather than automatic, will have little effect on the therapy of the arrhythmia until such time that drugs, specific for one or the other of the two mechanisms, becomes available. Similarly, recognition that a prolonged H-V time is the cause of the prolonged P-R interval can be helpful only if the long-term prognosis of the H-V delay is known. Because of the instrumentation and technique involved in recording His bundle activity the surface ECG will remain the method of choice, or perhaps the only method, for diagnosis of cardiac arrhythmias available to the vast majority of physicians. In fact, in emergent situations the lack of HBE should not even raise doubts in the physician’s mind as to whether or not proper treatment will be administered. The availability of cardioversion, a nonspecific therapeutic intervention, makes it possible, after a careful consideration of the total clinical picture, to treat the occasional patient with an undiagnosed life-threatening arrhythmia, without the necessity of having to identify the exact mechanism or site of origin of the arrhythmia. However, such a nonspecific therapeutic approach to arrhythmias may not always be possible nor desirable. For example, patients with arrhythmias suspected to be due to a ventricular aneurysm and considered for aneurysmectomy, must have the arrhythmia properly diagnosed. In such an instance, the HBE may prove to be essential and the patient can be referred to a laboratory designed for such an investigation. In elective situations in which the patients can benefit from HBE, referral for such studies may be desirable.
His bundle electrocardiography
291
Records of the last 40 patients who have undergone HBE in our institution were reviewed for contribution of this technique to the management of these patients. The results from each study were analyzed to determine the potential benefit of HBE to the clinical care of given individuals. In only five instances did the HBE prove to be of significant help by providing information not available after analysis of the surface ECG. In four cases it aided in the differential diagnosis of ventricular and supraventricular arrhythmia with aberrancy, and in one case it identified distal His block in a patient with syncope. HBE has confirmed a number of concepts which evolved from elegant analysis of surface cardiograms. It has generated some new knowledge and will continue to enhance our understanding of arrhythmias. To date, however, its contribution to the management of patients with heart disease has been limited. This is due not only to (1) the fact that much of the clinically needed information can be obtained from the surface ECG, but also in some measure to (2) deficiencies in our knowledge of the basic mechanisms, specific therapy, and prognosis of various arrhythmias. This information, if and when available, will make the data derived from HBE clinically more useful. However, until such parallel information does become available, the HBE will remain of limited value as a clinical tool. REFERENCES 1. Scherlag, B. J., Lau, S. H., Helfant, Ii. H., Stein, E., Berkowitz, \?i. D., and I>amato, A. N.: Catheter technique for recording His bundle activity in man, Circulation 39:13, 1969. 2. Damato, A. N., Gallagher, J. J., and Lau, S. H.: Application of His bundle recordings in diagnosis conduction disorders, Progr. Cardiovasc. Dis. 14:601, 1972. 3. Narula, 0. S., Scherlag, B. J., Samet, P., and Javier, R. P.: Atrioventricular block. Localization and classification by His bundle recordings, Am. J. Med. 50:146, 1971. 4. Rosen, K. M., Rahimtoola, S. H., and Gtunnar, R. M.: Pseudo A-V block secondary to premature nonpropagated His bundle depolarization: Documentation by His bundle electrocardiography,., . _. Circulation 4i:367, 1970. 5. Castellanos. A.. lr.. Castillo. C. A.. Acha. A. S.. and Tessler, M.: His bundle electrograms in patients with short P-R intervals, narrow QRS complexes and paroxysmal tachycardia, Circulation 43:667, 1971. I-.
,(.,
I
Heart Journal September, 1973, Volume 86, Number
3
Editorial
His bundle
electrocardiography
Charles F&h, M.D. Douglas P. Zipes, M.D. Indianapolis, Ind.
A
11new techniques introduced into medicine are ultimately judged by their contribution to our understanding of pathophysiology, enhancement of diagnostic ability, insight into the mechanism of therapeutic interventions, and to the over-all management of the ill patient. The technique of His bundle electrocardiography (HBE), although relatively new, has interested many investigators, and has resulted in a number of published studies with considerable unanimity of findings. For this reason, one can attempt to evaluate, even at this early stage of the development, the contribution of HBE to our understanding of the mechanism of arrhythmias and to the management of the patient with heart disease. This editorial was written with a clear understanding that information inherent in HBE is far from complete and that much of it is yet to be realized. The technique of HBE involves passing a catheter across the tricuspid valve, which requires sophisticated and expensive instrumentation and considerable technical skill. However, in experienced hands, the technical aspects of the procedure are
relatively simple and safe. An electrode catheter is introduced percutaneously into the femoral vein with its tip positioned near the septal leaflet of the tricuspid valve. The His potential (H) appears as a welldefined, most often bipolar spike between the low atria1 (A) and ventricular (V) electrograms. The interval between the earliest onset of the surface P wave or a high right atria1 deflection and the low right atria1 deflection (P-A) is a measure of intraatria1 conduction. The interval between A and H (A-H) is a measurement of the conduction across the A-V node and varies in duration from 50 to 120 msec., depending on the cycle length and autonomic influences. The interval from H to V (H-V) is a measure of His-Purkinje conduction time and is determined by the interval between the His deflection and the earliest ventricular activity recorded in any lead. The HV interval is a measure of conduction through the His bundle distal to the recording electrode, the bundle branches, and the I’urkinje system up to the point of ventricular activation. In contrast to a relatively wide range of values for the A-H, the H-V interval is fairly constant measuring 30 to 55
From
the Department of Medicine, Indiana University School of Medicine. the Krannert Institute of Cardiology. and Marion County General Hospital, Indianapolis, Ind. Supported in part by the Herman C. Krannert fund. United States Public Health Service Grants HE-6308. HE-5363 and HE-5749. and the Indiana Heart Association. Received for publication Sept. 11. 1972. Reprint requests to: Charles Fisch. M.D., 1100 West Michigan St., Indianapolis, Ind. 46202.
Vol.
86, No. 3, pp. 289-291
.%#fctrtDcr,
1973
American
Heart Journal
289
290
Fisch and Zipes
msec. with an average value of 45 msec. The ability to separate A-V nodal and His-Purkinje (H-P) conduction has enhanced our understanding of normal and abnormal atrioventricular (A-V) conduction. Abnormal A-V conduction may be due to prolongation of P-A, A-H, H-V, or all three. In patients with a P-R interval in the upper limits of normal, the H-V may be abnormally prolonged and when subjected to atria1 pacing, may reveal latent block of the H-P system and thus aid in the differential diagnosis of syncope. It should be pointed out, however, that the H-V may be normal and the patient may still have periodic complete distal His block. HBE confirmed the fact that when the QRS duration is normal, the A-V block is usually in the A-V node. On the other hand, in the presence of a prolonged QRS, the block may be either in the A-H or in the H-V regions, or in both. Second degree block of the Wenckebach type is most often, but not always, A-V nodal in origin while Type II is nearly always due to a block in the H-V system. Concealed discharge of the bundle of His as a cause of unexpected first or second degree A-V block had been proposed from analysis of the surface ECG and conclusively proved with HBE in the human. Incomplete penetration of the A-V node or bundle of His (concealed conduction) has been repeatedly demonstrated in the human with HBE. HBE clearly confirmed pre-excitation of the ventricles in the Wolff-Parkinson-White (W-P-W) abnormality. In this syndrome, the A-H is normal and the H-V is foreshortened. With atria1 pacing, the A-H lengthens normally, but the A-V conduction by way of the bypass remains unchanged and consequently the H-V shortens, the His deflection eventually becoming lost in or actually following ventricular excitation. The syndrome of short P-R, normal QRS and tachycardia has been shown in some instances to be due to foreshortening of the A-H interval without any change of the H-V period. The exact reason for shortening of the A-H conduction remains obscure. In some of the reported cases, the response of the A-H interval to pacing is qualitatively the same as in the normal but quantitatively much less pronounced. Our understanding of the possible inter-relationship of the electro-
physiologic manifestations of ventricular pre-excitation ’ with anatomic correlates (James, Mahaim, or Kent bypass) must await further studies. The mechanism of antegrade block with preservation of retrograde conduction has been the subject of considerable discussion. HBE clearly demonstrates an H potential between the ventricular and atria1 electrograms, thus strongly supporting unidirectional block with preservation of retrograde V-A conduction. Although the major contribution of the His recording has been to our understanding of A-V conduction and its various aberrations, HBE has provided some help with analysis of ectopic rhythms. For example, HBE demonstrated clearly that many supraventricular tachycardias are due to re-entry within the A-V node and that accelerated idioventricular rhythm, so frequently seen in acute myocardial infarction, is ventricular in origin. The everpresent problem of differential diagnosis of supraventricular aberrancy and ventricular ectopy can be resolved with HBE recording. In the former, H precedes V with a normal H-V time, while in the latter the H deflection is often lost within the ventricular electrogram or, if it precedes the local ventricular electrogram, it follows the earliest moment of ventricular activation recorded in the multiple surface tracings. Rarely, ventricular ectopic impulse will activate the bundle of His before giving rise to a QRS, and in such a situation an H-V shorter than normal will be recorded. There is always the possibility, however remote, that one simply fails to record the H spike during supraventricular rhythm and an erroneous diagnosis of ventricular tachycardia may be entertained. There is little doubt, from the foregoing brief review, that the HBE has and will continue to contribute to our understanding of arrhythmias and that this avenue of investigation should be pursued by those studying mechanisms of arrhythmias and who are thus equipped for routine HBE. On the other hand, the utility of HBE in everyday, routine care of patients with heart disease is much less secure and in fact is yet to be defined. Irrespective of the invasive nature of the procedure, the technical skill and instrumentation required, the ultimate role of
Volume Nwnber
86 3
the HBE in the management of the patient will hinge on two factors, namely: (1) evidence that HBE offers considerable advantage over a carefully analyzed surface ECG correlated with the total clinical picture and, equally important, (2) our ultimate ability to utilize fully the information obtained with the HBE in the actual care of the patient. At present, we are unable to benefit fully from the information inherent in the HBE because complementary, parallel clinical facts are not available. The following two examples will serve to illustrate this point. The recognition from the HBE that a given supraventricular tachycardia is reentrant in origin rather than automatic, will have little effect on the therapy of the arrhythmia until such time that drugs, specific for one or the other of the two mechanisms, becomes available. Similarly, recognition that a prolonged H-V time is the cause of the prolonged P-R interval can be helpful only if the long-term prognosis of the H-V delay is known. Because of the instrumentation and technique involved in recording His bundle activity the surface ECG will remain the method of choice, or perhaps the only method, for diagnosis of cardiac arrhythmias available to the vast majority of physicians. In fact, in emergent situations the lack of HBE should not even raise doubts in the physician’s mind as to whether or not proper treatment will be administered. The availability of cardioversion, a nonspecific therapeutic intervention, makes it possible, after a careful consideration of the total clinical picture, to treat the occasional patient with an undiagnosed life-threatening arrhythmia, without the necessity of having to identify the exact mechanism or site of origin of the arrhythmia. However, such a nonspecific therapeutic approach to arrhythmias may not always be possible nor desirable. For example, patients with arrhythmias suspected to be due to a ventricular aneurysm and considered for aneurysmectomy, must have the arrhythmia properly diagnosed. In such an instance, the HBE may prove to be essential and the patient can be referred to a laboratory designed for such an investigation. In elective situations in which the patients can benefit from HBE, referral for such studies may be desirable.
His bundle electrocardiography
291
Records of the last 40 patients who have undergone HBE in our institution were reviewed for contribution of this technique to the management of these patients. The results from each study were analyzed to determine the potential benefit of HBE to the clinical care of given individuals. In only five instances did the HBE prove to be of significant help by providing information not available after analysis of the surface ECG. In four cases it aided in the differential diagnosis of ventricular and supraventricular arrhythmia with aberrancy, and in one case it identified distal His block in a patient with syncope. HBE has confirmed a number of concepts which evolved from elegant analysis of surface cardiograms. It has generated some new knowledge and will continue to enhance our understanding of arrhythmias. To date, however, its contribution to the management of patients with heart disease has been limited. This is due not only to (1) the fact that much of the clinically needed information can be obtained from the surface ECG, but also in some measure to (2) deficiencies in our knowledge of the basic mechanisms, specific therapy, and prognosis of various arrhythmias. This information, if and when available, will make the data derived from HBE clinically more useful. However, until such parallel information does become available, the HBE will remain of limited value as a clinical tool. REFERENCES 1. Scherlag, B. J., Lau, S. H., Helfant, Ii. H., Stein, E., Berkowitz, \?i. D., and I>amato, A. N.: Catheter technique for recording His bundle activity in man, Circulation 39:13, 1969. 2. Damato, A. N., Gallagher, J. J., and Lau, S. H.: Application of His bundle recordings in diagnosis conduction disorders, Progr. Cardiovasc. Dis. 14:601, 1972. 3. Narula, 0. S., Scherlag, B. J., Samet, P., and Javier, R. P.: Atrioventricular block. Localization and classification by His bundle recordings, Am. J. Med. 50:146, 1971. 4. Rosen, K. M., Rahimtoola, S. H., and Gtunnar, R. M.: Pseudo A-V block secondary to premature nonpropagated His bundle depolarization: Documentation by His bundle electrocardiography,., . _. Circulation 4i:367, 1970. 5. Castellanos. A.. lr.. Castillo. C. A.. Acha. A. S.. and Tessler, M.: His bundle electrograms in patients with short P-R intervals, narrow QRS complexes and paroxysmal tachycardia, Circulation 43:667, 1971. I-.
,(.,
I