Wenckebach periods with repetitive block: Evaluation with His bundle recording

Wenckebach Evaluation

periods with

with

His bundle

repetitive

block:

recording

Ramesh C. Dhingra, M.D. Kenneth M. Rosen, M.D., F. A. C. C. Shahbudin H. Rahimtoola, F.R.C.P. Chicago, Ill.

L

angendorf’ in 1948 introduced the term “concealed conduction” to describe the results of partial penetration of an electrical impulse into the A-V junction. The incompletely penetrating impulse transiently lengthens the A-V refractory period, modifying the conduction of the subsequent impulse. This concept has proved useful in understanding the mechanisms involved in a number of arrhythmias.2-5 Repetitive block of several consecutive atria1 impulses can occur when successive impulses partially penetrate the A-V conducting system without traversing it completely, producing varying periods of ventricular asystole. This phenomenon has been called “repetitive concealed conduction.“2 A-V block Type 1 second-degree (Wenckebach) is characterized by progressive P-R prolongation prior to a single dropped beat. Termination of a Wenckebath cycle with more than one blocked P wave is rare. Langendorf and Pick” reported a patient with Wenckebach periods terminated by several blocked atria1 impulses and suggested that this was a maniFrom

festation of repetitive concealed conduction. In this report we describe two patients with Wenckebach periods and block of two consecutive P waves. In one, the mechanism appeared similar to that previously postulated by Langendorf and Pick. In the second, a new mechanism is described. In this case, long cycle lengths were produced in the His-Purkinje system due to A-V nodal Wenckebach periods. This long cycle prolonged the His-Purkinje refractory period in the subsequent cycle so that the second conducted beat of the Wenckebach period (short cycle) was blocked distal to the His bundle. This occurred during 32 A-V nodal Type I block with resulting 3:l A-V block. Both mechanisms can produce unexpected asystole during Type I seconddegree A-V block. Report

the Department of Adult Cardmlogy. Cook County Hospital, Medicine. The Abraham Lincoln School of Medicine, University Supported in part by NIH contract 71-2478 under the Myocardial Institutes. National Institutes of Health, Department of Health, Received for publication Nov. 16. 1972. Reprint requests to: Kenneth M. Rosen. M.D., Section of Cardiology, Hospital. 840 South Wood St., Chicago. Ill. 60612.

444

American Heart Tournal

of cases

Case 1. A 23-year-old man was admitted to Cook County Hospital for evaluation of Dyncope. Results of a physical examination were essentially negative. Electrocardiograms (ECG) revealed sinus bradycardia at a rate of 53 per minute, a QRS duration of and the Section of Cardiology. of Illinois College of Medicine, Infarction Program, National Education and Welfare. Department

Ortobcr,

of Medicine,

1973

Department of Chicago, III. Heart and I.ung

I-niversity

of Illinois

1’01. 86, No. 4, fifi. 444-448

Volume Number

86 4

Wenckebach periods with repetitive block

44.5

HBE

Fig. 1. Electrophysiological recordings from Case 1. Shown gram (HBE). Pacing impulses are labeled with arrows. rate is 120 per minute, and P-H intervals are listed and waves are blocked proximal to the H potential. Paper speed

are Leads VI, I, II, and III, with His bundle electroHis bundle electrograms are labeled H. The pacing show Wenckebach periodicity. The fifth and sixth P is 100 mm. per second, and time lines are at 1 second.

Fig. 2. Rhythm strip and ladder diagram showing Wenckebach period terminated with two blocked P waves. The upper level of the ladder reflects atrium, the middle two levels A-V node, and the bottom ventricle. The third, fourth, and fifth P waves are conducted with increasing P-R intervals. The sixth and seventh P waves are blocked. A proposed mechanism is presented showing the first P blocked low in the node and the second P blocked at a higher level. (From Langendorf and Pick: Circulation 13:381, 1956, reproduced with permission of the American Heart Association.)

0.10 second, and a P-R interval of 0.14 second. Incomplete right bundle branch block pattern was also noted. Electrophysiological studies. Informed consent was obtained for electrophysiological studies. His bundle electrograms were recorded with the use of previously described techniques.6,’ Atria1 pacing was performed at varied heart rates. The patient was in sinus rhythm at a rate of 60 per minute. P-H interval was 125 msec., P-A 20 msec., A-H 105 msec., and HV 40 msec. Wenckebach periods proximal to the His bundle were noted at a paced rate of 120 per minute. These were generally terminated by one blocked P. Several atypical cycles were recorded, these being terminated by two consecutive P waves blocked proximal to the His bundle (Fig. 1).

Comment. Langendorf and Pick2 postulated that block of two consecutive P waves during a Wenckebach period occurs due to inhomogeneous penetration of the A-V node. They suggested deeper penetration of the first impulse and more superficial penetration of the second impulse (Fig. 2). His bundle electrograms in such cases should record block of both P waves proximal to the His bundle. In the present case, His bundle electro-

grams documented repetitive block proximal to the His bundle. This technique does not allow us to measure the degree of penetration of the A-V node in the two blocked cycles. However, the results are consistent with Langendorf and Pick’s previous hypothesis. Case 2. A 2.5year-old man with corrected tetralogy of Fallot was admitted for cardiac evaluation. ECG’s revealed normal sinus rhythm at a rate of 70 per minute, a P-R interval of 0.16 second, and a QRS duration of 0.16 second with complete right bundle branch block pattern. Electrophysiological studies. The patient was in sinus rhythm at a rate of 65 per minute. The conduction intervals were as follows: P-H 128 msec., P-A 23 msec., A-H 105 msec., and H-V 44 msec. 4:3 and 3:2 Wenckebach periods proximal to H were noted at a paced rate of 150 per minute. The Wenckebach periods were typical during 4:3 conduction (Fig. 3, A). With 3:2 A-V nodal ii:enckebath the following was observed. The first P-H was 140 msec., the second 160 msec., and the third P was blocked proximal to the His bundle. The second P was always blocked distal to H (Fig. 3, B).

Comment. In this case, 3:2 Wenckebach periods proximal to H were associated with 3 :I A-V block. Inhomogeneous conduction

446

Fig. The Note with H-H and

Dhingra,

Rosen, and Rahimfoola

3. \\Tenckebach periods produced with ;Itri:d pacing demonstrating block above und below the His bundle. pacing rate is 150 per minute in both pnnels. (.4) 4:3 \I:enckebach periods proximal to the llis bundle. the long H-H cycle of 730 msec. and the short H-H cycle of 43.5 msec. (H) 3:2 :1-V nodnl LVenckebach 3:l block. The second P wave of each cycle is blocked distal to H and the third proximal to H. The long cycles are 790 msec. and the short 435 mscc. (See text for discussion.) Paper speed is 100 mm. per second the time lines are at I second.

was noted, the first I’ being blocked distal to and the second proximal to the His bundle. The failure of conduction distal to H of the first nonpropagated impulse during 3:l response was easily explainable. It is evident from Fig. 3, R that H potential occurred at alternating long and short intervals. The longer H-H cycles were of 790 msec. duration while the shorter cycles were 435 rnsec. This long-short sequence reflected 3:2 Wenckebach periodicity proximal to H. The refractory period of the ventricular specialized conduction system was presumably prolonged in the cycle following the long H-H, reflecting the relationship of cycle length and refractory period in the His-Purkinje system.* This prolongation of refractoriness was reflected in block distal to H of the second beat of the Wenckebach sequence (short H-H cycle). Since the patient had right bundle

branch block, block distal to H probably occurred in the left bundle branch. The above interpretation was supported by examining conduction during the 4:3 Wenckebach periods. During 4:3 conduction the short H-H cycles were 43.5 msec., identical in length to short cycles during 3:2 conduction. The long H-H cycles were only 730 msec. and shorter than the cycles during 3:l conduction. This slight shortening of long H-II cycles was of critical degree, allowing conduction to occur in the subsequent short cycle. Discussion In 1925, Lewis and Master9 demonstrated that a blocked atria1 impulse could delay the transmission or completely block a subsequent impulse. They also described block of repetitive impulses. Langendorf and Pick2 described block of consecutive impulses during a Wenckel)xch cycle. They

Wenckebach periods with repetitive block

attributed this to repetitive concealed conduction in tlhe A-V junction, suggesting that the first blocked sinus impulse had a deeper penetration of the A-V node augmenting its refractoriness so that the subsequent sinus impulse could not be transmitted. It was postulated that this latter impulse was blocked at a higher level. Such inhomogeneous penetration of the A-V junction coulld be responsible for block of multiple atria1 impulses. Moe and associatesi experimentally demonstrated repetitive concealed conduction with as many as six premature atria1 impulses blocked in succession. Watanabe and Dreifus” demonstrated two levels of A-V nodal block during 3:l response in rabbit hearts and suggested inhomogeneous conduction in the A-V node. Moore,12 employing microelectrode technique in rabbits, defined the s:ites and mechanisms of A-V block of serially concealed premature atria1 impulses and demonstrated decremental conduction w:ithin both the A-V node and His-Purkinje :system. His bundle recording has helped clarify mechanisms (of concealed conduction in man, permitting accurate localization of sites of conduction delay following blocked premature responses.i3J4 This technique was helpful in the present cases. In the first patient repetitive block during Wenckebath beating was localized proximal to the His bundle. This is in keeping with the postulation of inhomogeneous conduction in the A-V node as previously suggested.2 In the second patient, varying depths of penetration were documented with His bundle recording. Block of two successive P waves occurred, one distal and the other proximal to the His bundle. The consecutive blocked P waves did not reflect repetitive concealed conduction. Failure of impulse propagation at the A-V node (during Type I block) produced long cycle lengths in the His-Purkinje system with associated refractory period prolongation. This allowed the second beat of the Wenckebach period (short cycle) to be blocked distal to His bundle. Thus, 3:2 A-V nodal Wenckebath periods were associated with 3:l A-V block. It should be pointed out that the initiation of this 3:l block must have oc-

447

curred with a typical 3:2 Wenckebach period. Clinical implications. Although the abnormalities of conduction demonstrated were induced by atria1 pacing, similar phenomenon could certainly occur during spontaneous beating, explaining unexpected blocked P waves during Type I seconddegree block. In patients with bundle branch block, long R-R cycles could lengthen the refractory period of the functioning bundle branch, causing nontransmission during short subsequent cycles. 3:l A-V block with bundle branch block could thus represent one of the following: (1) 3:l block proximal to H, (2) 3:l block distal to H, or (3) the mechanism described in Case 2. Mechanism No. 2 would appear to be the most serious, suggesting bilateral bundle branch disease.i5 Both types of repetitive block described in this report could produce serious bradyarrhythmias during the course of usually benign Type I second-degree A-V block. Pharmacologic therapy with atropine or isoproterenol, or pacemaker insertion might be necessary. Summary

Two patients are reported in whom repetitive block of two consecutive P waves occurred during Wenckebach beating induced by atria1 pacing. His bundle recordings revealed block proximal to H in the first case, suggesting inhomogeneous conduction in the A-V node. In the second case, long cycle lengths were produced in the HisPurkinje system due to A-V nodal Wenckebath periods. The long cycles prolonged refractory periods in the His Purkinje system so that subsequent beats (short cycles) were blocked distal to H. The repetitive block of consecutive multiple atria1 impulses could result in unexpected degrees of ventricular asvstole durIng usually benign Type I second-degree A-V block. . The authors are grateful to Drs. Richard Langendorf and Alfred Pick for their kind permission to use Fig. 2 from their previous oubhcation. The authors also wish to express their thanks to Mrs. Mary Ellen Rosen for the preparation of the illustrations and to Mrs. Katherine Evans for the preparation of the manuscript.

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REFERENCES 1. Langendorf, R.: Concealed A-V conduction: The effect of blocked impulses on the formation and conduction of subsequent impulses, AM. HEART J. 35~542, 1948. 2. Langendorf, R., and Pick, A.: Concealed conduction. Further evaluation of a fundamental aspect of propagation of the cardiac impulse, Circulation 13:381, 1956. 3. Langendorf, R., Pick, A., Edelist, A., and Katz, L. N. : Experimental demonstration of concealed AV conduction in the human heart, Circulation 32:386, 1965. 4. Scheiner, L. B., and Stock, R. J.: Coupled pacing and coupled pacing with concealed condiction: Report of a case describing a new observation. Circulation 34:759. 1966. 5. Carleton,’ R. A., and Graettinger, J. S.: Evidence of concealed atrioventricular conduction in man, Circulation 34:756, 1966. 6. Scherlag, B. J., Lau, S. H., Helfant, R. H., Berkowitz, W. D., Stein, E., and Damato, A. N.: Catheter techniaue for recording His bundle activitv in man, Circulation 39:13, 1969. 7. Narula, 0. S., Cohen, L. S., Samet, P., Lister, J. W., Scherlag, B., and Hildner, F. J.: Localization of A-V conduction defects in man bv recording of the His bundle electrogram, Am. J. Cardiol. 25:228, 1970.

8.

Moe, G. K., Mendez, C., and Han, J.: Aberrant A-V impulse propagation in the dog heart: A study of functional bundle branch block, Circ. Res. 16:261, 1965. 9. Lewis, T., and Master, A. M.: Observations upon conduction in the mammalian heart: A-V conduction, Heart 12~209, 1925. 10. Moe, G. K., Abildskov, J. A., and Mendez, C.: An experimental study of concealed conduction, AM. HEART J. 67:338, 1964. 11. Watanabe, Y., and Dreifus, L. S.: Second degree atrioventricular block, Cardiovasc. Res. 1:150, 1967. 12. Moore, N.: Microelectrode studies in concealment of multiple premature atrial responses, Circ. Res. 12:660, 1966. 13. Damato, A. N., and Lau, S. H.: Concealed and supernormal atrioventricular conduction, Circulation 43:967, 1971. 14. Rosen, K. M., Rahimtoola, S. H., and Gunnar, R. M.: Pseudo A-V block secondary to premature nonpropagated His bundle depolarizations: Documentation by His bundle electrocardiography, Circulation 42:367, 1970. 1.5. Langendorf, R., and Pick, A.: Atrioventricular block, type II (Mobitz). Its nature and clinical significance, Circulation X3:819, 1968.