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Intermittent left anterior hemiblock with Wenckebach phenomenon
CASE REPORTS
Intermittent Left Anterior Hemiblock with Wenckebach Phenomenon
STELIO MANGIOLA, Morristown,
MD
New Jersey
A case of intermittent left anterior hemiblock with Wenckebach phenomenon in the anterior division of the left bundle branch is reported. Direct Wenckebach sequences are seen in the conventional electrocardiogram with 3:2 or 4:3 conduction ratios. In the same tracings, groups of beats in which left anterior hemiblock appears suddenly for 1, 2 or more consecutive beats are interpreted as evidence of incompletely concealed Wenckebach phenomenon. An electrocardiogram recorded 10 months later from the same patient showed stable left anterior hemiblock. This is the first reported case, as far as can be determined, of direct Wenckebach sequences in the anterior division of the left bundle branch.
The first 5 cases of intermittent left anterior hemiblock (block in the anterior division of the left bundle branch) were recently reported,l providing evidence for the existence of this “new” intraventricular conduction disturbance. Direct and incompletely concealed Wenckebath sequences in the right and left bundle branches were reported,2 thereby confirming that this type of second degree block may occur in the bundle branches. A case is described here in which progressive or sudden changes in the configuration, duration and mean frontal plane axis of the QRS complex are interpreted as caused by direct or incompletely concealed Wenckebach phenomenon in the anterior division of the left bundle branch. Analysis
From the Cardio-respiratory Section, Department of internal Medicine, Morristown Memorial Hospital and the Department of Internal Medicine, All Souls’ Community Hospital, Morristown, N.J. Manuscript received January 31, 1972; revised manuscript received March 27, 1972, accepted April 21, 1972. Address for reprints: Stelio Mangiola, MD, 26 Madison Ave., Morristown, N.J. 07960.
692
December
1972
of the Electrocardiograms
The electrocardiograms (Fig. 1 to 4) were recorded on November 18 and 20, 1969 from a 60 year old white woman with ischemic heart disease. The strips shown are representative of gradual and sudden changes in the QRS pattern which were repeatedly recorded on both days. Figure 1 shows normal sinus rhythm at a rate of 65 beats/min, intermittent left anterior hemiblock and T wave abnormalities suggestive of anterolateral ischemia. The QRS complex of the second beat has a deeper Q wave in leads I and aVL, a deeper S wave in leads II, III, aVF and Vs, a duration of 9 to 10 msec and a mean axis in the frontal plane of -60”; these changes meet the criteria of Rosenbaum et a1.l for isolated block in the anterior division of the left bundle branch. Figure 2 shows groups of beats that are interpreted as representing direct 3:2 Wenckebach sequences in the anterior division of the left bundle branch. In each lead the first beat is normally conducted, whereas the second and the third show increasing degrees of left anterior hemiblock; the last beat then shows normal intraventricular conduction, thus confirming the presence of the Wenckebach phenomenon. The rate is the same as in Figure 1 and there is slight sinus arrhythmia, but the QRS changes cannot be explained on the basis of rate-dependent aberrant ventricular conduction. The P-R interval remains constant in length. Figure 3 shows 3:2 (lead I) and probably 4:3 (leads II and III) Wenckebath sequences interrupted by ventricular extrasystoles. The postextrasystolic pause is followed by a sinus beat showing normal intraventricular conduction.
The American Journal of CARDIOLOGY
Volume 30
INTERMITTENT
LEFT ANTERIOR
HEMIBLOCK-MANGIOLA
FIGURE 1. In each lead shown, left anterior hemiblock is evident in the second beat. There may be a minor degree of incomplete left anterior hemiblock in the first beat. From the first to the second beat there is lengthening of the QRS interval from 7-8 msec to 9-10 msec, a shift of the mean QRS axis in the frontal plane from -30’ to -60°, deeper Q waves in leads I and aVL and deeper S waves in leads I I, I I I, aVF and Vs.
Figure 4 shows different types of QRS grouping. In lead II (top) the first 2 QRS complexes are normally conducted, but the next 4 beats have the pattern of left anterior hemiblock; the following beat is normal, then left anterior hemiblock is seen for 1 beat, and a normal beat follows again. In lead III 3 beats, and in lead aVF 2 beats with the pattern of left anterior hemiblock are preceded and followed by a normal beat. In leads I and II (bottom) normal QRS complexes alternate with QRS complexes showing the pattern of left anterior hemiblock. The rate is 63 beats/min; there is slight :ainus arrhythmia, and the P-R interval is of constant length. An electrocardiogram recorded 10 months later (not shown) revealed normal sinus rhythm at a rate of 65 beats/min with ocoasional ventricular extrasystoles and a stable pattern of left anterior hemiblock. Normal intraventricular conduction was no longer seen, even after long postextrasystolic pauses.
Discussion Wenckebach phenomenon: This phenomenon may develop in any portion of the conduction system subjected to partial imlpairrnent of conduction. Its
occurrence in the bundle branches was experimentally induced in dogs.3 and documented in man,2.4-14 and Wenckebach sequences in the anterior and posterior division of the left bundle branch were observed in the canine heart15 and indirectly confirmed in man in clinical and experimental cases of trifascicular block. lsls The case reported here is the first direct documentation in conventional electrocardiograms, as far as can be determined, of the Wenckebach phenomenon in the anterior division of the left bundle branch only. This report postulates, in the same tracings, the occurrence of incompletely concealed Wenckebath sequences in the anterior division of the left bundle branch. Two different groups of beats are seen in this case: one characterized by gradual and progressive changes in configuration and duration of the QRS interval, the other characterized by the sudden appearance of left anterior hemiblock for 1, 2, or several consecutive beats. In both, a normal beat occurs
FIGURE 2. Progressive changes in width, axis and configuration of the QRS complexes are seen as a result of direct 3:2 Wenckebath sequences in the anterior division of the left bundle branch.
December
1972
The American Journal of CARDIOLOGY
Volume 30
893
INTERMITTENT
LEFT ANTERIOR
HEMIBLOCK-MANGIOLA
FIGURE 3. Direct Wenckebach sequences, 3:2 (lead I) and probably 4:3 (leads II and Ill), are interrupted by ventricular extrasystales. The postextrasystolic pause is followed by a sinus beat showing normal intraventricular conduction.
after each group, thereby attesting to the improvement in conduction occurring after the block. The conduction disturbance seems to be independent of slight fluctuations in the sinus rate; however, the long pause induced by an extrasystole is followed each time by a beat showing normal intraventricular conduction. Direct sequences: The groups of beats with gradual and progressive changes in configuration and duration of the QRS interval (Fig. 2 and 3) are believed to represent direct Wenckebach sequences in the anterior division of the left bundle branch. A gradual increase in the degree of the hemiblock is clearly seen, and each sequence is followed, with or without a postextrasystolic pause, by a beat showing normal conduction; this pattern is typical of the Wenckebach phenomenon. The direct sequences have conduction ratios of 3: 2 and probably 4:3, which are common in the Wenckebach phenomenon at the atrioventricular junction.
Concealed sequences: The groups of beats in which left anterior hemiblock appears suddenly for 1, 2 or more consecutive beats (Fig. 4) are believed to represent 2:1, 3:2, 4:3 and 5:4 incompletely concealed Wenckebach sequences in the anterior division of the left bundle branch, rather than 2:1, 3: 1, 4:l and 5:l left anterior hemiblock. Two considerations support this interpretation: First, direct Wenckebach sequences are seen in the same tracings. Second, in second degree block at the atrioventricular junction, the occurrence of 3:2, 4:3 and 5:4 Wenckebach block is far more common than the occurrence of 3:1, 4:l and 5:l block; the same is probably true in the bundle branches.2 As in atrioventricular block, a conduction ratio of 2:l may be due to Wenckebach type I rather than to Mobitz type II block. Mechanism of concealment: It has been estimated that an impulse that travels from one division of the left bundle branch to the other division can
FIGURE 4. The transition from normal to abnormal intraventricular conduction is sudden as a result of incompletely concealed Wenckebach phenomenon in the anterior division of the left bundle branch. Sequences of 2:l (leads I and II), 3:2 (lead aVF), 4:3 (lead III) and 54 (lead I I) block are present. (See text.)
894
December
1972
The American Journal of CARDIOLOGY
Volume 30
INTERMIT-TENT
reach the latter in approximately 20 msec (“interpapillary conduction time”) .15 If a sequence of impulses traveling down from the atrioventricular junction propagates in the anterior division, with conduction delays that increase gradually but are all greater than 20 msec, each impulse before completing its journey down the anterior division can arrive from the posterior division and simulate complete left anterior hemiblock when, in reality, a Wenckebach sequence is occurring. The same consideration could apply to a conduction delay in the posterior division. In order for direct Wenckebach sequences in the left anterior division of the left bundle branch to be apparent in the conventional electrocardiogram, the conduction delay in the second beat of a sequence must be less than 20 msec and there must be recovery after a blocked impulse. The Wenckebach phenomenon will be incom:pletely concealed if there are normally conducted beats initiating and terminating groups of beats that are conducted in the anterior division of the left bundle branch with a delay greater than 20 msec. In this event, the impulses can arrive from the posterior division and simulate intermittent complete left a:nterior hemiblock. If the im-
LEFT ANTERIOR
HEMIBLOCK-MANGIOLA
pulse propagation occurs with gradual slowing followed by block and recovery, but all the beats in the tracing are conducted with a delay greater than 20 msec, then Wenckebach phenomenon in the anterior division of the left bundle branch will be completely concealed. The Wenckebach phenomenon in the right or left bundle branches is probably not rare.lO However, it is only seldom evident in the conventional electrocardiogram because, with a conduction delay greater than 40 to 60 msec, retrograde activation of the involved bundle branch from the contralateral ventricle masks the gradual slowing in propagation of the impulse. 2p1g,20 The Wenckebach phenomenon in the anterior or posterior division of the left bundle branch must be even more rarely apparent because a conduction delay greater than only 20 msec is sufficient to cause its concealment. Acknowledgment I am grateful to Drs. Alvin A. Rosenberg and Arthur S. Glushien for their thoughtful review of the manuscript, to Miss Mercedes Blass and Mrs. Catherine Pendola for technical and library assistance, and to Mrs. Renee Gordon for typing the manuscript.
References 1. Rosenbaum MB, Eiirari MV, Levi RJ, et al: Five cases of intermittent left anterior hemiblock. Amer J Cardiol 24:1-7, 1969 2. Rosenbaum MB, Nau GJ, Levi RJ, et al: Wenckebach periods in the bundle branches. Circulation 40:79-86, 1969 3. Scherf D, Shookhoff C: Reizleitungstorungen im Bundel. 2 Mitteiiung. Wien Arch Inn Med 11:425-440, 1925 4. Hoirmann M: Seltene Abarten von unbestandigen Schenkelblock. Cardiologia 7:113-144, 1943 5. Segers M: Les facteurs de controle de la conduction intraventriculaire. Acta Cardiol 2:256-262, 1947 6. Rosenbaum MB, Lepeschkin E: Bilateral bundle branch block. Amer Heart J 50:38-61, 1955 7. Katz LN, Pick A: Clinical1 Electrocardiography. Part 1: The Arrhythmias. Philadelphia, Lea 8 Febiger, 1956, p 624 8. Baiiarino M, Rumoio R: II Fenomeno di Luciani-Wenckebath. Milano, Recordati lndustria Chimica e Farmaceutica. 1967, fig 32 9. Friedberg HD, Schamroth L: The Wenckebach phenomenon in left bundle branc:h block. Amer J Cardiol 24:591593,1969 10. Naruia OS, Samet P: Wenckebach and Mobitz type II A-V block due to block within the His bundle and bundle branches. Circulation 41947-965, 1970 11. Rosen KM, Rahimtooia SH, Chuquimia R, et al: Electrophysiological significance of first degree atrioventricular block with intraventriculalr conduction disturbance. Circula-
December
tion 43:491-502, 1971 12. Steiner C, Lau SH, Stein E, et al: Electrophysiologic documentation of trifascicular block as the common cause of complete heart block. Amer J Cardiol 28:436-441, 1971 13. Vitoio E, Rossi L: Blocco di branca sinistro con allungamento progressivo della conduzione e fenomeno di Wenckebath ventricolare. Minerva Cardioangiol 9:254-260, 1961 14. Puech P, Groileau R, Latour H, et al: L’enregistrement de l’activite electrique du faisceau de His dans les blocs A.-V. spontanes. Arch Mal Coeur 63: 784-809,197O 15. Rosenbaum MB, Eiirari MV, Lazarri JO: The Hemiblocks. Oldsmar, Fla, Tampa Tracings, 1970, p 53, 81 16. Rosenbaum MB: Types of right bundle branch block and J Electrocardiol 1:221-232, their clinical significance. 1968 Types of left bundle branch block and 17. Rosenbaum MB: their clinical significance. J Electrocardiol 2:197-206, 1969 18. Cerqueira-Gomes M, Vasconceios Texeira A: Wenckebach phenomenon in the posterior division of the left bundle branch. Amer Heart J 82:377-381.1971 19. Herrmann GR, Ashman R: Partial bundle branch block: theoretical consideration of transient normal intraventricular conduction in the presence of apparently complete bundle branch block. Amer Heart J 61375-403, 1931 20. Wilson FN, Herrmann GR: Experimental study of incomplete bundle branch block and of the refractory period of the heart of the dog. Heart 8:229-295, 1921
1972
The American Journal of CARDIOLOGY
Volume 30
895
Intermittent Left Anterior Hemiblock with Wenckebach Phenomenon
STELIO MANGIOLA, Morristown,
MD
New Jersey
A case of intermittent left anterior hemiblock with Wenckebach phenomenon in the anterior division of the left bundle branch is reported. Direct Wenckebach sequences are seen in the conventional electrocardiogram with 3:2 or 4:3 conduction ratios. In the same tracings, groups of beats in which left anterior hemiblock appears suddenly for 1, 2 or more consecutive beats are interpreted as evidence of incompletely concealed Wenckebach phenomenon. An electrocardiogram recorded 10 months later from the same patient showed stable left anterior hemiblock. This is the first reported case, as far as can be determined, of direct Wenckebach sequences in the anterior division of the left bundle branch.
The first 5 cases of intermittent left anterior hemiblock (block in the anterior division of the left bundle branch) were recently reported,l providing evidence for the existence of this “new” intraventricular conduction disturbance. Direct and incompletely concealed Wenckebath sequences in the right and left bundle branches were reported,2 thereby confirming that this type of second degree block may occur in the bundle branches. A case is described here in which progressive or sudden changes in the configuration, duration and mean frontal plane axis of the QRS complex are interpreted as caused by direct or incompletely concealed Wenckebach phenomenon in the anterior division of the left bundle branch. Analysis
From the Cardio-respiratory Section, Department of internal Medicine, Morristown Memorial Hospital and the Department of Internal Medicine, All Souls’ Community Hospital, Morristown, N.J. Manuscript received January 31, 1972; revised manuscript received March 27, 1972, accepted April 21, 1972. Address for reprints: Stelio Mangiola, MD, 26 Madison Ave., Morristown, N.J. 07960.
692
December
1972
of the Electrocardiograms
The electrocardiograms (Fig. 1 to 4) were recorded on November 18 and 20, 1969 from a 60 year old white woman with ischemic heart disease. The strips shown are representative of gradual and sudden changes in the QRS pattern which were repeatedly recorded on both days. Figure 1 shows normal sinus rhythm at a rate of 65 beats/min, intermittent left anterior hemiblock and T wave abnormalities suggestive of anterolateral ischemia. The QRS complex of the second beat has a deeper Q wave in leads I and aVL, a deeper S wave in leads II, III, aVF and Vs, a duration of 9 to 10 msec and a mean axis in the frontal plane of -60”; these changes meet the criteria of Rosenbaum et a1.l for isolated block in the anterior division of the left bundle branch. Figure 2 shows groups of beats that are interpreted as representing direct 3:2 Wenckebach sequences in the anterior division of the left bundle branch. In each lead the first beat is normally conducted, whereas the second and the third show increasing degrees of left anterior hemiblock; the last beat then shows normal intraventricular conduction, thus confirming the presence of the Wenckebach phenomenon. The rate is the same as in Figure 1 and there is slight sinus arrhythmia, but the QRS changes cannot be explained on the basis of rate-dependent aberrant ventricular conduction. The P-R interval remains constant in length. Figure 3 shows 3:2 (lead I) and probably 4:3 (leads II and III) Wenckebath sequences interrupted by ventricular extrasystoles. The postextrasystolic pause is followed by a sinus beat showing normal intraventricular conduction.
The American Journal of CARDIOLOGY
Volume 30
INTERMITTENT
LEFT ANTERIOR
HEMIBLOCK-MANGIOLA
FIGURE 1. In each lead shown, left anterior hemiblock is evident in the second beat. There may be a minor degree of incomplete left anterior hemiblock in the first beat. From the first to the second beat there is lengthening of the QRS interval from 7-8 msec to 9-10 msec, a shift of the mean QRS axis in the frontal plane from -30’ to -60°, deeper Q waves in leads I and aVL and deeper S waves in leads I I, I I I, aVF and Vs.
Figure 4 shows different types of QRS grouping. In lead II (top) the first 2 QRS complexes are normally conducted, but the next 4 beats have the pattern of left anterior hemiblock; the following beat is normal, then left anterior hemiblock is seen for 1 beat, and a normal beat follows again. In lead III 3 beats, and in lead aVF 2 beats with the pattern of left anterior hemiblock are preceded and followed by a normal beat. In leads I and II (bottom) normal QRS complexes alternate with QRS complexes showing the pattern of left anterior hemiblock. The rate is 63 beats/min; there is slight :ainus arrhythmia, and the P-R interval is of constant length. An electrocardiogram recorded 10 months later (not shown) revealed normal sinus rhythm at a rate of 65 beats/min with ocoasional ventricular extrasystoles and a stable pattern of left anterior hemiblock. Normal intraventricular conduction was no longer seen, even after long postextrasystolic pauses.
Discussion Wenckebach phenomenon: This phenomenon may develop in any portion of the conduction system subjected to partial imlpairrnent of conduction. Its
occurrence in the bundle branches was experimentally induced in dogs.3 and documented in man,2.4-14 and Wenckebach sequences in the anterior and posterior division of the left bundle branch were observed in the canine heart15 and indirectly confirmed in man in clinical and experimental cases of trifascicular block. lsls The case reported here is the first direct documentation in conventional electrocardiograms, as far as can be determined, of the Wenckebach phenomenon in the anterior division of the left bundle branch only. This report postulates, in the same tracings, the occurrence of incompletely concealed Wenckebath sequences in the anterior division of the left bundle branch. Two different groups of beats are seen in this case: one characterized by gradual and progressive changes in configuration and duration of the QRS interval, the other characterized by the sudden appearance of left anterior hemiblock for 1, 2, or several consecutive beats. In both, a normal beat occurs
FIGURE 2. Progressive changes in width, axis and configuration of the QRS complexes are seen as a result of direct 3:2 Wenckebath sequences in the anterior division of the left bundle branch.
December
1972
The American Journal of CARDIOLOGY
Volume 30
893
INTERMITTENT
LEFT ANTERIOR
HEMIBLOCK-MANGIOLA
FIGURE 3. Direct Wenckebach sequences, 3:2 (lead I) and probably 4:3 (leads II and Ill), are interrupted by ventricular extrasystales. The postextrasystolic pause is followed by a sinus beat showing normal intraventricular conduction.
after each group, thereby attesting to the improvement in conduction occurring after the block. The conduction disturbance seems to be independent of slight fluctuations in the sinus rate; however, the long pause induced by an extrasystole is followed each time by a beat showing normal intraventricular conduction. Direct sequences: The groups of beats with gradual and progressive changes in configuration and duration of the QRS interval (Fig. 2 and 3) are believed to represent direct Wenckebach sequences in the anterior division of the left bundle branch. A gradual increase in the degree of the hemiblock is clearly seen, and each sequence is followed, with or without a postextrasystolic pause, by a beat showing normal conduction; this pattern is typical of the Wenckebach phenomenon. The direct sequences have conduction ratios of 3: 2 and probably 4:3, which are common in the Wenckebach phenomenon at the atrioventricular junction.
Concealed sequences: The groups of beats in which left anterior hemiblock appears suddenly for 1, 2 or more consecutive beats (Fig. 4) are believed to represent 2:1, 3:2, 4:3 and 5:4 incompletely concealed Wenckebach sequences in the anterior division of the left bundle branch, rather than 2:1, 3: 1, 4:l and 5:l left anterior hemiblock. Two considerations support this interpretation: First, direct Wenckebach sequences are seen in the same tracings. Second, in second degree block at the atrioventricular junction, the occurrence of 3:2, 4:3 and 5:4 Wenckebach block is far more common than the occurrence of 3:1, 4:l and 5:l block; the same is probably true in the bundle branches.2 As in atrioventricular block, a conduction ratio of 2:l may be due to Wenckebach type I rather than to Mobitz type II block. Mechanism of concealment: It has been estimated that an impulse that travels from one division of the left bundle branch to the other division can
FIGURE 4. The transition from normal to abnormal intraventricular conduction is sudden as a result of incompletely concealed Wenckebach phenomenon in the anterior division of the left bundle branch. Sequences of 2:l (leads I and II), 3:2 (lead aVF), 4:3 (lead III) and 54 (lead I I) block are present. (See text.)
894
December
1972
The American Journal of CARDIOLOGY
Volume 30
INTERMIT-TENT
reach the latter in approximately 20 msec (“interpapillary conduction time”) .15 If a sequence of impulses traveling down from the atrioventricular junction propagates in the anterior division, with conduction delays that increase gradually but are all greater than 20 msec, each impulse before completing its journey down the anterior division can arrive from the posterior division and simulate complete left anterior hemiblock when, in reality, a Wenckebach sequence is occurring. The same consideration could apply to a conduction delay in the posterior division. In order for direct Wenckebach sequences in the left anterior division of the left bundle branch to be apparent in the conventional electrocardiogram, the conduction delay in the second beat of a sequence must be less than 20 msec and there must be recovery after a blocked impulse. The Wenckebach phenomenon will be incom:pletely concealed if there are normally conducted beats initiating and terminating groups of beats that are conducted in the anterior division of the left bundle branch with a delay greater than 20 msec. In this event, the impulses can arrive from the posterior division and simulate intermittent complete left a:nterior hemiblock. If the im-
LEFT ANTERIOR
HEMIBLOCK-MANGIOLA
pulse propagation occurs with gradual slowing followed by block and recovery, but all the beats in the tracing are conducted with a delay greater than 20 msec, then Wenckebach phenomenon in the anterior division of the left bundle branch will be completely concealed. The Wenckebach phenomenon in the right or left bundle branches is probably not rare.lO However, it is only seldom evident in the conventional electrocardiogram because, with a conduction delay greater than 40 to 60 msec, retrograde activation of the involved bundle branch from the contralateral ventricle masks the gradual slowing in propagation of the impulse. 2p1g,20 The Wenckebach phenomenon in the anterior or posterior division of the left bundle branch must be even more rarely apparent because a conduction delay greater than only 20 msec is sufficient to cause its concealment. Acknowledgment I am grateful to Drs. Alvin A. Rosenberg and Arthur S. Glushien for their thoughtful review of the manuscript, to Miss Mercedes Blass and Mrs. Catherine Pendola for technical and library assistance, and to Mrs. Renee Gordon for typing the manuscript.
References 1. Rosenbaum MB, Eiirari MV, Levi RJ, et al: Five cases of intermittent left anterior hemiblock. Amer J Cardiol 24:1-7, 1969 2. Rosenbaum MB, Nau GJ, Levi RJ, et al: Wenckebach periods in the bundle branches. Circulation 40:79-86, 1969 3. Scherf D, Shookhoff C: Reizleitungstorungen im Bundel. 2 Mitteiiung. Wien Arch Inn Med 11:425-440, 1925 4. Hoirmann M: Seltene Abarten von unbestandigen Schenkelblock. Cardiologia 7:113-144, 1943 5. Segers M: Les facteurs de controle de la conduction intraventriculaire. Acta Cardiol 2:256-262, 1947 6. Rosenbaum MB, Lepeschkin E: Bilateral bundle branch block. Amer Heart J 50:38-61, 1955 7. Katz LN, Pick A: Clinical1 Electrocardiography. Part 1: The Arrhythmias. Philadelphia, Lea 8 Febiger, 1956, p 624 8. Baiiarino M, Rumoio R: II Fenomeno di Luciani-Wenckebath. Milano, Recordati lndustria Chimica e Farmaceutica. 1967, fig 32 9. Friedberg HD, Schamroth L: The Wenckebach phenomenon in left bundle branc:h block. Amer J Cardiol 24:591593,1969 10. Naruia OS, Samet P: Wenckebach and Mobitz type II A-V block due to block within the His bundle and bundle branches. Circulation 41947-965, 1970 11. Rosen KM, Rahimtooia SH, Chuquimia R, et al: Electrophysiological significance of first degree atrioventricular block with intraventriculalr conduction disturbance. Circula-
December
tion 43:491-502, 1971 12. Steiner C, Lau SH, Stein E, et al: Electrophysiologic documentation of trifascicular block as the common cause of complete heart block. Amer J Cardiol 28:436-441, 1971 13. Vitoio E, Rossi L: Blocco di branca sinistro con allungamento progressivo della conduzione e fenomeno di Wenckebath ventricolare. Minerva Cardioangiol 9:254-260, 1961 14. Puech P, Groileau R, Latour H, et al: L’enregistrement de l’activite electrique du faisceau de His dans les blocs A.-V. spontanes. Arch Mal Coeur 63: 784-809,197O 15. Rosenbaum MB, Eiirari MV, Lazarri JO: The Hemiblocks. Oldsmar, Fla, Tampa Tracings, 1970, p 53, 81 16. Rosenbaum MB: Types of right bundle branch block and J Electrocardiol 1:221-232, their clinical significance. 1968 Types of left bundle branch block and 17. Rosenbaum MB: their clinical significance. J Electrocardiol 2:197-206, 1969 18. Cerqueira-Gomes M, Vasconceios Texeira A: Wenckebach phenomenon in the posterior division of the left bundle branch. Amer Heart J 82:377-381.1971 19. Herrmann GR, Ashman R: Partial bundle branch block: theoretical consideration of transient normal intraventricular conduction in the presence of apparently complete bundle branch block. Amer Heart J 61375-403, 1931 20. Wilson FN, Herrmann GR: Experimental study of incomplete bundle branch block and of the refractory period of the heart of the dog. Heart 8:229-295, 1921
1972
The American Journal of CARDIOLOGY
Volume 30
895