Download Wenckebach Periods in

Wenckebach Periods in
the Bundle Branches
By MAURICIO B. ROSENBAUM, M.D., GERARDo J. NAU, M.D.,
RAUL J. LEVI, M.D., M. SUSANA HALPERN, M.D., MARCELO V. ELIZARI, M.D.,
AND JULIO 0. LAZZARI, M.D.
SUMMARY
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Two cases of intermittent bundle-branch block in which Wenckebach periods could
be directly visualized are reported. The conduction ratios were either 3:2 or 4:3, as
are commonly seen in cases of the Wenckebach phenomenon of atrioventricular (A-V)
conduction. Other groups of beats apparently showing 3:1 and 4:1 bundle-branch
block were interpreted as indicating incompletely concealed Wenckebach periods in the
bundle branches, with actual conduction ratios of 3:2 and 4:3, respectively.
Three prerequisites are necessary for the occurrence of either direct or incompletely
concealed Wenckebach periods in the bundle branches: (1) The opening beat should
be normally conducted (in the affected bundle branch); (2) the second beat should
be conducted with a delay of no more than 0.04 to 0.06 sec; (3) the damaged bundle
branch should not be activated retrogradely in the closure beat.
Wenckebach periods in the bundle branches may be completely concealed if the
conduction delay lasts more than 0.04 to 0.06 sec in the opening beat. In cases of bilateral
bundle-branch block, Wenckebach periods in the bundle branches may be indirectly
visualized through changes in the A-V conduction.
Additional Indexing Words:
Concealed conduction in the bundle branches
Trifascicular blocks
T HE EXISTENCE of Wenckebach periods
in patients with partial A-V block is well
known. However, since Wenckebachl first described the periodic block which follows progressive prolongation of the A-V interval, several authors have pointed out that such a
phenomenon has never been observed in the
main branches of the bundle of His.2
the existence of concealed Wenckebach
riods in the bundle branches.
pe-
Report of Cases
Case 1
The electrocardiograms of a 61-year-old man
with pulmonary abscess and aortic valvular disease showed severe left ventricular hypertrophy,
first degree A-V block, and intermittent left
bundle-branch block (LBBB) (fig. 1). Figure 2
illustrates typical direct Wenckebach periods in
the left bundle branch. The first beat displays a
pattern of complete LBBB, with a QRS interval of
0.16 sec. The QRS interval measured 0.10 sec in
the second beat, 0.11 sec in the third, 0.12 sec in
the fourth, and again, 0.16 sec in the fifth beat.
Beats 2 to 5 constitute a typical Wenckebach period. The sixth beat starts a new period of three
beats (beats 6 to 8). The narrowest and most normal QRS complexes (beats 2, 6, and 9) followed
the QRS complexes having the pattern of complete
LBBB (1, 5, and 8), indicating that conduction
in the left bundle branch failed completely in
In
this paper, two such cases are reported. In
both, groups of beats showing a progressive
increase in the degree of the bundle-branch
block were observed up to the complete bundle-branch block beat that closed the period.
These groups were considered to indicate
direct Wenckebach periods. In addition, other
groups of beats were observed which indicated
From the Services of Cardiology of Salaberry
Hospital and Argerich Hospital, Buenos Aires, Argentina.
Circulation, Volume XL, July 1969
Bilateral bundle-branch block
79
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ROSENBAUM ET AL.
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Case 1. In each lead the first beat is without, and the
second with, LBBB. However, there is some degree of
incomplete LBBB in the "normally" conducted beats.
in the first
The QRS itnterval widens from 0.10
beat to 0.16 sec in the second one.
sec
beats 1, 5, and 8 only, while conduction in the
left bundle branch was delayed but not interrupted in beats 3, 4, and 7. The changes in QRS
duration and configuration occurred without a
change in the heart rate or the P-R interval.
Therefore, figure 2 exhibits two typical direct
Wenckebach periods within the left bundle
branch, with conduction ratios of 4:3 and
3:2, respectively. Forty-four direct Wenckebach
periods of the same kind, with 3:2 and, less frequently, 4:3 conduction, were recorded on the
same patient. In addition, interspersed among the
typical Wenekebach periods, some other types of
QRS grouping occurred, as illustrated in figure 3.
Figure 3 shows three groups of beats. In the
first group, containing four beats (2 to 5), the
initial QRS complex shows a normal* pattern of
*For simplicity, all the beats having the shortest
QRS interval and initiating the Wenckebach periods
will be called "normal." "Complete" means that, although the electrocardiographic pattern looks like
complete LBBB, we cannot be sure that conduction
completely interrupted.
was
intraventricular conduction, while the last three
QRS complexes have a pattern of "complete"*
LBBB. The next two groups (beats 6 to 8 and
9 to 11) include three beats each. In both, the
QRS complex of the first beat is normal. while
the last two have a pattern of "complete" LBBB.
As in figure 2, the normal beats initiating these
periods (beats 2, 6, and 9) always follow a beat
with the "complete" LBBB pattern. This stuggests
that conduction in the left bundle branch was
completely blocked in the preceding beats (beats
1, 5, and 8) only. However, how conduction took
place in beats 3 and 4 of the first period and in
beats 7 and 10 of the last two periods in the left
bundle branch needs clarification. The LBBB configuration of beats 3, 4, 7, and 10 may be explained in one of two ways: either (1) conduction
was completely blocked in the damaged region of
the left bundle branch (during these beats); or
(2) the impulse was conducted in the left bundle
branch with a delay greater than 0.04 to 0.06 sec,
which is the accepted critical time interval"1-13
necessary for the impulse to arrive from the contralateral ventricle and to produce a pattern of
"complete" LBBB. In the first hypothesis, the
periods shown in figure 3 would mean 4:1, 3:1,
and 3:1 block in the left bundle branch; in the
second, these periods would indicate 4:3, 3:2,
and 3:2 conduction, with Wenckebach phenomenon. Two observations lend support to the second
possibility: First, in the same tracings, direct
Wenckebach periods in the left btundle branch,
with the same 4:3 and 3:2 conduction ratios were
observed, as shown in figure 2. Second, in second
degree A-V block, 3:2 conduction of the Wenckebach type is more common thani 3:1 conduction;
and 4:3 conduction of the Wenckebach type is
much more common than 4:1 conduction. Therefore, the three groups of beats shown in figure 3
most likely indicate Wenckebach periods within
the left bundle branch, with conduction ratios of
4:3, 3:2, and 3:2, respectively. We shall refer to
these periods as "incompletely concealed Wenckebach periods."
Figure 4 shows four successive beats with a
pattern of "complete" LBBB, preceded and followed by a normal beat. Since the changes in QRS
pattern are unrelated to changes in cycle duration,
they could indicate another Wenckebach period
in the left bundle branch with a conduction ratio
of 5:4. Again, the normal beat (beat 6) indicates
that the left bundle branch completely failed to
conduct in the preceding beat. A progressive conduction delay may again be assumed, starting
with an initial delay greater than 0.04 to 0.06 sec.
The second half of the strip in figure 4 reveals
2:1 LBBB.
Circulation, Volume XL, July 1969
.
WENCKEBACH PERIODS IN THE BUNDLE BRANCHES
2
1
4
3
5
6
9
8
7
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Case 1. V, and lead
Figure 2
simultaneously recorded, showing
I,
left bundle branch. The conduction
the second one (beats 6 to 8).
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5
4
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11
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9
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two direct Wenckebach periods in the
the first period (beats 2 to 5) and 3:2 in
ratio is 4:3 in
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Figure 3
Case 1. Three groups of beats (beats number 2 to 5, 6 to 8, and 9 to 11) looking, respectively,
as 4:1, 3:1, and 3:1 LBBB. However, these were interpreted as incompletely concealed
Wenckebach periods, with 4:3, 3:2, and 3:2 conduction ratios, respectively.
1
2
3
4
6
5
7
8
9
10
Figure 4
Case 1. Beats number 1 to 5 are interpreted
bach period in the left bundle branch, with
typical 2:1 LBBB.
Case 2
A 72-year-old man with arterial hypertension
had an intermittent right bundle-branch block
(RBBB) (fig. 5). From July 8, 1967 to March
Circulation, Volume XL, July 1969
as
a
forming an incompletely concealed Wencke5:4 conduction ratio. Beats 6 to 10 reveal a
15, 1968, six tracings were obtained, all of which
showed essentially similar findings. Figure 6 exhibits typical direct Wenckebach periods in the
right bundle branch with 4:3 or 3:2 conduction
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Figure 5
Case 2. In every lead, the first beat is without and the second w;ith RBBB. However, there
is definitely some degree of incomplete RBBB in the "normally" conducted beats. The QRS
interval widens from 0.08 to 0.12 sec.
1
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3
2
4
5
6
7
8
9
10
11
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Figure 6
Case 2. Beats number 2 to 5 constitute a ditect Wenckebach period within the right bundle
branch, with a 4:3 conduction ratio. Another direct Wenckebach period with a 3:2 conduction
ratio is formed by beats number 8 to 10. The QRS interval measures 0.08 sec in beat number
2, 0.09 sec in beat number 3, 0.10 sec in beat number 4, and 0.12 sec in beat number 5. Both
Wenckebach periods are linked by a period of 2:1 RBBB.
ratios. Figure 7 shows incompletely concealed
Wenckebach periods, appearing as 3:1 or 4:1
RBBB, but indicating (as in case 1) 3:2 and
4:3 conduction ratios, with Wenckebach phenomenon (beats 2 to 4 and 5 to 8); and in the same
strip, a direct Wenckebach period (beats 9 to 11).
Discussion
In 1925, Scherf and Shookhoffj7 in an experiment using dogs, demonstrated the existence of Wenckebach periods within the bundle branches. After sectioning one branch and
damaging the other only slightly, typical
Wenckebach periods of the A-V conduction
appeared, which undoubtedly were taking
place in the less damaged bundle branch.
They effectively transformed a bifascicular
conduction system into a monofascicular conduction system. Taking advantage of the fact
that the same trick is occasionally performed
by nature, Rosenbaum and Lepeschkin12 were
able to establish, also indirectly, the existence
of Wenckebach periods in the bundle branches
Circulation, Volume XSL, Judy 1969
83
WENCKEBACH PERIODS IN THE BUNDLE BRANCHES
1
2
3
4
7
6
5
8
9
10
11
Figure 7
Case 2. The last three beats constitute a direct Wenckebach period with a 3:2 conduction ratio.
Beats number 2 to 4 form an incompletely concealed Wenchkebach period, with the same 3:2
conduction ratio. Beats number 5 to 8 form another incompletely concealed Wenckebach
period, with a 4:3 conduction ratio.
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Figure 8
Two typical Wenckebach periods with 4:3 and 5:4 conduction ratios, respectively, in a common
case of second degree A-V block. The opening beat starts with an already prolonged P-FR interval (0.28 sec).
of man in clinical cases of "bilateral bundlebranch block." And recently, Rosenbaum's
group'4-16 substantiated, in the same indirect
way, Wenckebach periods in the anterior and
posterior divisions of the left bundle branch,
in clinical and experimental cases of "intraventricular trifascicular block."
In another type of experiment,6 one bundle
branch was slightly compressed, and after
allowing recovery of normal conduction, atrial
flutter was induced in order to increase the
ventricular rate. In this way, the conduction
disturbance in the bundle branch was unmasked, and a progressive increase in the
degree of bundle-branch block was shown to
occur. Holzmann4' 5 reported a similar clinical
observation. A patient with intermittent RBBB
and atrial fibrillation showed, in consecutive
beats, a progressive increase in the degree of
the RBBB, with the last beat of the group
exhibiting the pattern of "complete" RBBB.
However, the next beat did not show normal
conduction-as would be expected for a true
Wenckebach phenomenon.
Segers'7 reported a case showing groups of
three beats; the first beat was normally conducted, the second showed incomplete LBBB,
Circulaton, Volume XL, July 1969
and the third exhibited complete LBBB. These
groups were preceded and followed by a ventricular extrasystole and had characteristic
Wenckebach periods in the left bundle branch
with 3:2 conduction. However, the fact that
the periods were provoked by the ectopic
beats suggests that the post-extrasystolic
pauses were essential for the occurrence of
the normally conducted beats starting each
period. A similar case, in which a Wenckebach
type of progression in the left bundle branch
was observed after post-extrasystolic pauses,
has been reported by Ballarino and Rumolo
(their fig. 32).1'
The two cases reported in this paper are, so
far as we were able to determine, the first examples in which typical direct Wenckebach
periods within the bundle branches were observed in conventional electrocardiographic
tracings, demonstrating that Wenckebach
phenomenon may actually occur in the right
or the left bundle branch, just as in any other
segment of the conduction system subjected
to partial impairment of conduction.3 0, 13 18 2
In both cases, we could also uncover the existence of incompletely concealed Wenckebach
periods. In fact, periods appearing as 3:1 or
84
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4:1 bundle-branch block indicated concealed
Wenckebach periods within the bundle
branches with 3:2 and 4:3 conduction, respectively. It is then possible that cases previously
reported as examples of 3:1 and 4:1 bundlebranch block" really indicate Wenckebach
periods in the bundle branches. It is also
conceivable that apparently complete bundlebranch block may in fact be intermittent, with
completely concealed Wenckebach periods. To
render this more understandable, a parallel
with Wenckebach phenomenon of the A-V
conduction will be helpful. Figure 8 shows typical Wenckebach periods in a case of partial
A-V block. The most rapidly conducted impulses, that is, those- occurring after the pauses,
have a P-R interval of 0.28 sec, indicating a
conduction delay in the A-V junction equal to
or greater than 0.08 sec. Should a similar initial
conduction delay occur within one bundle
branch, the QRS complexes will show the pattern of "complete" bundle-branch block, in
spite of the fact that Wenckebach periods are
actually present under the surface.
The Wenckebach phenomenon is a distinct
form of impaired conduction, which occurs
when impulse propagation is gradually and
progressively slowed until no impulse is propagated. A possible cause for this delayed impulse propagation is a prolonged recovery
time. If one impulse falls on the relative refractory period of the preceding beat, some degree of delayed conduction will occur. In
turn, this delayed conduction determines a
rightward displacement of the corresponding
refractory period, in such a way that the next
impulse (assuming an appropriate and constant rate of stimulation) will fall on an
earlier phase of the recovery curve and will
be conducted with greater delay, until one
beat falls on the absolute refractory period
and is completely blocked. This closes the
period, prompts a longer resting time interval
within the involved region, and allows the
next impulse to be conducted normally or at
least with much less delay. Also, the longer
resting period produces a longer refractory
time, so that the next impulse (after the
normally conducted one) falls again on a
ROSENBAUM ET AL.
relative refractory period, thus perpetuating
the cycle. Within this general set up, two
factors must be further elucidated.
It is well known that in typical Wenckebach
impairment of A-V conduction, the greatest
increment in conduction delay occurs in the
second beat of the period." 5, 23-26 Should this
happen in one bundle branch, the conduction
delay during the second beat of the period
will usually be greater than 0.04 to 0.06 sec.
Under such conditions, the resulting QRS complex will have a pattern of "complete" bundlebranch block. If the next impulse is really
completely blocked, the QRS complex will
again show a similar pattern of complete
bundle-branch block. Therefore, under usual
conditions, as in the customary 3:2 conduction
ratio, a Wenckebach period within one bundle
branch will appear in the electrocardiogram
as 3:1 bundle-branch block (a normal QRS
complex followed by two with "complete"'
bundle-branch block). Accordingly, for Wenckebach phenomenon in one bundle branch to
appear directly in the electrocardiogram, as
in the two cases presented in this paper, the
second beat of the period must have a conduction delay shorter than 0.04 to 0.06 sec.
The second factor is the behavior of the
opening beat (the first beat following the
pause of the Wenckebach period). If the
opening beat regains completely normal conduction in the affected bundle branch, the
Wenckebach period will start with a completely normal QRS complex. If the opening
beat has a conduction delay between 0.01 and
0.04 sec, the first beat of the period will have
a configuration of incomplete bundle-branch
block. This actually occurred in our two cases.
If the conduction delay is greater than 0.04
to 0.06 sec, however, the opening beat, as well
as the following beats, will all show a pattern
of complete bundle-branch block, and the
Wenckebach phenomenon will be completely
concealed. Therefore, another essential condition for the occurrence of direct (or incompletely concealed) Wenckebach periods in the
bundle branches is that the conduction delay
in the first beat of the period be no greater
than 0.04 to 0.06 sec.
Circulation, Volume XL, July 1969
WENCKEBACH PERIODS IN THE BUNDLE BRANCHES
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An even more essential condition for the
existence of Wenckebach phenomenon in one
bundle branch is that in the beat which must
close the period, there should be no retrograde
activation (coming from the contralateral ventricle) of the damaged bundle branch. In fact,
this has been assumed to be the only reason
why the Wenckebach phenomenon in the
bundle branches seems to be so uncommon.3' 10 However, since we do not know how
often this takes place under the above circumstances, it is impossible to tell how important the condition is-as compared to the
other two conditions previously dealt within determining the real frequency or infrequency of Wenckebach phenomenon in the
bundle branches.
From the preceding considerations we may
conclude that for Wenckebach periods in the
bundle branches to become apparent in the
electrocardiogram (provided there is no retrograde activation from the contralateral ventricle), the conduction delay in the first two
beats of the period should be no greater than
0.04 to 0.06 sec. If the two beats fulfill this
requirement, the Wenckebach phenomenon
will be directly visualized in the electrocardiogram. If only the first beat is conducted with
a delay of less than 0.04 sec, the Wenckebach
phenomenon will be incompletely concealed
(disguised as 3:1 or 4:1 bundle-branch block).
If the conduction delay of the first beat is
greater than 0.04 to 0.06 sec, the Wenckebach
phenomenon will be completely concealed.
Accordingly, when considering the concealed
forms (and also the forms precluded because
of retrograde activation of the damaged bundle branch), we can say that Wenckebach
phenomenon has as good a pathophysiologic
chance of occurring in the bundle branches
as in any other segment of the conduction
system. The opinion that Mobitz type I block
may be only characteristic for A-V junctional
tissue27 cannot thus be supported.
References
1. WENCKEBACH, K. F.: Zur Analyse des unregelmassigen Pulses: II. Mitteilung: Ueber den
regelmassig intermittierenden Puls. Klin Med
37: 475, 1899.
Circulation, Volume XL, July 1969
8S
2. GRANT, R. P.: Clinical Electrocardiography. New
York, McGraw-Hill Book Co., 1957.
3. HERRMANN, G. R., AND ASHMAN, R.: Partial
bundle branch block: Theoretical consideration
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4. HOLZMANN, M.: Seltene Abarten von unbestandigen Schenkelblock. Cardiologia 7: 113, 1943.
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ROSENBAUM ET AL.
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Circulation, Volume XL, uldy 1969
Wenckebach Periods in the Bundle Branches
MAURICIO B. ROSENBAUM, GERARDO J. NAU, RAUL J. LEVI, M. SUSANA
HALPERN, MARCELO V. ELIZARI and JULIO O. LAZZARI
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Circulation. 1969;40:79-86
doi: 10.1161/01.CIR.40.1.79
Circulation is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231
Copyright © 1969 American Heart Association, Inc. All rights reserved.
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