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Manifest and Concealed Reentry
A Mechanism of A-V Nodal Wenckebach in Man
By JoHN J. GALLAGHER, M.D., ANTHONY N. DAMATO, M.D.,
P. JACOB VARGHESE, M.D.,
AND
SUN H. LAU, M.D.
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SUMMARY
In five patients, bundle of His electrograms were recorded during right ventricular pacing at various cycle lengths. In all patients, as the cycle length of stimulation was decreased, the pattern of
retrograde conduction proceeded from 1:1 retrograde conduction to retrograde Wenckebach with
or without manifest reentry, to retrograde Wenckebach cycles with concealed reentry. The
requisite condition for reentry was a critical retrograde A-V nodal delay. During retrograde
Wenckebach cycles, reentry could be either concealed or manifest. Concealed reentry resulted in
typical or ordinary Wenckebach cycles on the surface electrocardiogram and manifest reentry resulted in ventricular echo beats. Depending upon the cycle length of stimulation, reentry could
be concealed on the surface electrocardiogram but manifest on the His bundle electrogram recording. Concealed reentry could be manifest by turning off the stimulator at the appropriate
time in the cardiac cycle while manifest reentry could be concealed by changing the cycle length
of stimulation. Reentry with collision of wavefronts within the A-V node or proximal His-Purkinje
conduction system explains why the last ventricular impulse is not conducted to the atria during
ordinary Wenckebach cycles.
Additional Indexing Words:
Critical A-V nodal delay
Ventricular stimulation
His bundle electrograms
Collision of wavefronts
THE A-V nodal Wenckebach phenomenon
(type I second-degree A-V block) is electrocardiographically characterized by a progressive
prolongation of the P-R interval, followed by a
nonconducted atrial impulse.' Previous electrophysiologic studies in man2-4 have demonstrated that
the area of conduction delay and block is proximal
to the bundle of His in most cases. The exact
mechanism for the A-V nodal delay and block is not
well understood. Previous explanations have centered around the concept of decremental conduction.>5 6 Recent animal studies from this laboratory
have demonstrated that block of the nonconducted
beat during retrograde Wenckebach cycles is the
Type I second-degree A-V block
result of manifest and concealed reentry.7 In
addition, it was suggested that manifest and
concealed reentry may be the basis of the
progressive prolongation of conduction seen during
Wenckebach cycles. The present study was undertaken to investigate whether similar phenomena are
present in man.
Methods
Nine men and one woman underwent right heart
catheterization in the postabsorptive, nonsedated state
for evaluation of nondiagnostic chest pain. The patients
were not taking any cardioactive drugs at the time of
the study. The nature of the procedure was explained
and a signed consent obtained. Using a tripolar
electrode catheter introduced percutaneously into a
femoral vein, His bundle recordings (HBE) were
obtained according to methods previously described.8
In addition, a quadripolar electrode catheter was
percutaneously introduced into an antecubital vein and
fluoroscopically positioned against the lateral wall of
the high right atrium, near its junction with the
superior vena cava. The distal pair of electrodes was
connected to a battery-powered pacemaker (Medtronic
no. 5847) which delivered impulses of 2-msec duration
at approximately twice diastolic threshold. The proximal pair of electrodes was used to record a high right
atrial (HRA) electrogram. A bipolar catheter was also
introduced percutaneously into another antecubital vein
From the Cardiopulmonary Laboratory, U. S. Public
Health Service Hospital, Staten Island, New York.
Presented in part at the 21st Annual Scientific Session,
American College of Cardiology, Illinois, March 4, 1972.
Supported in part by the Federal Health Program Service,
USPHS Project Py 72-1 and National Heart and Lung
Projects HE 11829 and HE 12536.
Address for reprints: Anthony N. Damato, M.D.,
Cardiopulmonary Laboratory, USPHS Hospital, Staten
Island, New York 10304.
Received: September 27, 1972; revision accepted for
publication November 29, 1972.
752
Circulation, Volume XLVII, April 1973
753
MANIFEST AND CONCEALED REENTRY
and positioned at the right ventricular apex for
ventricular pacing at a milliamperage _ 1. Care was
taken to insure proper grounding of all equipment.
During all stimulation sequences, the surface electrocardiogram (ECG), intracardiac electrograms, and
time lines generated at intervals of 10 and 100 msec
were displayed on a multichannel switched-beam
oscilloscope and recorded via a universal matching
amplifier onto magnetic tape. Records were subsequently reproduced at paper speeds of 150 mm/sec. All
patients tolerated the procedure without complication.
Results
During ventricular pacing, retrograde conduction
was observed in eight of 10 patients. The criteria
for retrograde conduction and activation of the
atria were similar to those used by Castillo and
Castellanos.9 In five of these eight patients retroDownloaded from http://circ.ahajournals.org/ by guest on June 17, 2017
grade A-V nodal Wenckebach periodicity occurred
at cycle lengths sufficiently slow to permit further
study. The findings in these five patients constitute
the basis of this report.
In all studies, retrograde A-V nodal conduction
time during ventricular pacing was longer than
antegrade A-V nodal conduction time at comparable paced atrial rates. In addition, the Wenckebach phenomenon appeared at slower rates during
ventricular pacing than during atrial pacing. As the
cycle length of ventricular stimulation was de-
CL850
creased, the pattern of retrograde conduction
proceeded from 1:1 retrograde conduction to
retrograde Wenckebach cycles with or without
manifest reentry, to retrograde Wenckebach cycles
with concealed reentry.
Figures 1-4 depict typical responses to decreasing
the cycle length of ventricular s-timulation. In this
patient, reentry occurred whenever retrograde
conduction time exceeded 325 msec. Figure 1
demonstrates that at a paced cycle length of 850
msec, 1:1 retrograde conduction occurred. Decreasing the cycle length to 540 msec, as shown in figure
2, resulted in retrograde Wenckebach cycles.
Manifest reentry, as noted on both the surface
electrocardiogram and HBE recording occurred
following the fourth ventricular beat which was
associated with a retrograde conduction time of 330
msec. The last ventricular stimulus occurred 60
msec after the antegrade His deflection of this
reentrant impulse and contributed little, if at all, to
ventricular depolarization. In figure 3, a further
decrease in the cycle length of stimulation to 460
msec resulted in ordinary 3:2 retrograde Wenckebach cycles in which reentry concealed on the
surface electrocardiogram. However, reentry was
manifest on the HBE recording. The second
V-A 160
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AI
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S
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Figure 1
Ventricular pacing at cycle length (CL) of 850 msec with 1:1 retrograde conduction. The recordings from
top to bottom are standard ECG leads I, II, and III, V1, a high right atrial electrogram (HRA), His bundle
electrogram (HBE), and time. lines (T) generated at 10 and 100 msec. A = atrial electrogram; H = His
bundle electrogram; V = ventricular electrogram; S = stimulus artifact. The first beat is a sinus beat and
the sequence of atrial depolarization is from HRA to the low right atrium. Ventricular pacing results in 1:1
retrograde conduction to the atria with a V-A conduction time of 160 msec. Note that atrial activation
is from the low right atrium to the high right atrium. The above abbreviations will be used for subsequent
figures.
Circulation, Volume XLVII, April 1973
~~~~~~~~~~~~~~~~~~~~~
754
74GALLAGHER ET AL.
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Figure 2
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Retrograde Wenckebach terminated by a manifest reentrant beat (same patient as fig. 1). The panel to the
left depicts single sinus beat with a high-to-low sequence of atrial activation. Ventricular pacing at a CL
of 540 msec results in an increasing V-A conduction time from 280 to 330 msec. The fourth retrograde
impulse reenters within the A-V node and antegradely depolarizes the bundle of His (H) 60 msec prior to
the fifth stimulus artifact (S). Reentry is manifest on both the ECG and HBE tracings.
a
retrograde impulse of each Wenckebach cycle
reentered within the A-V node as evidenced by the
appearance of an antegrade His deflection 25 msec
after the third ventricular stimulus. The reentrant
impulse collided with the retrograde impulse within
the bundle-branch system, thereby resulting in
failure of the third ventricular impulse to propagate
retrogradely to the atria. The reentrant impulse
contributed little if at all to ventricular depolarization.
as
Figure 4 is a recording at the same cycle length
figure 3 and demonstrates how manifest reentry
be produced by turning off the stimulator at the
appropriate time in the Wenckebach cycle. Following the second ventricular beat which was associated with the requisite A-V nodal delay (350 msec)
the stimulator was turned off and manifest reentry
terminated the Wenckebach cycle. Reentry was not
demonstrated when the stimulator was turned off at
earlier points in the Wenckebach cycle, that is, prior
to the point of requisite A-V nodal delay.
Figure 5 is an example of a spontaneous episode
of ventricular tachycardia in which there was an
ordinary 4:3 Wenckebach cycle with concealed
can
CL460
1
V1
l1
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Figure 3
Same patient as figures 1 and 2. Decreasing the CL to 460 msec results in ordianry 3:2 retrograde Wenckebach in which reentry is concealed on the ECG tracings but manifest on the HBE tracing.
Circulation, Volume XLVII, April 1973
7555
MANIFEST AND CONCEALED REENTRY
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Figure 4
Same patient as figures 1-3. Concealed reentry is made manifest by turning off the stimulator at the appropriate time in the cardiac cycle. Same cycle length of stimulation as in figure 3. Following a V-A
conduction time of 350 msec, the stimulator is turned off and reentry occurs. The arrows indicate the
point at which the omitted stimulus would have been delivered.
reentry on the surface electrocardiogram and
manifest reentry on the HBE recording.
Discussion
Reentry within the A-V node is an accepted
electrophysiologic event which has been extensively
studied in both the experimental animal and
man.7' 9-23
The results of this clinical study are in agreement
with our previous experimental observations in
dogs.7 In both studies, it has been demonstrated
that reentry within the A-V node occurred whenever a requisite A-V nodal delay was attained
during the Wendkebach cycle. In this regard our
findings in both man and experimental animals are
in agreement with those of Moe and Mendez who
stated that reciprocal responses can be so readily
induced in normal animal hearts that their occurrence must be considered a normal physiologic
response.10 This reentry can be either manifest or
concealed. Indeed, manifest reentry can be conCirculation, Volume XLVII, April 1973
cealed by changing the cycle length of stimulation,
and concealed reentry can be made manifest by
turning off the stimulator at the appropriate time in
the cardiac cycle. Oftentimes, reentry is concealed
on the surface electrocardiogram (resulting in an
ordinary or typical retrograde Wenckebach cycle)
but manifest on the His bundle electrogram
recording. Reentry in its concealed or manifest form
explains why, during Wenckebach cycles, the last
ventricular impulse fails to retrogradely conduct to
the atria. During ordinary or typical retrograde
Wenckebach cycles there is a collision of the
reentrant impulse and the last ventricular impulse
within the A-V node or proximal His-Purkinje
system. Collision of the two impulses may also
occur within the common bundle itself.7
It should be emphasized that the most important
determinant of A-V nodal reentry is a critical
degree of A-V nodal delay.10-" This fact explains
why reentry was not observed when the stimulator
was turned off at earlier times in the cardiac cycle.
GALLAGHER ET AL.
756
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Spontaneous episode of ventricular tachycardia resulting in 4:3 retrograde Wenckebach cycles terminated
by reentry. Reentry is concealed on the surface electrocardiograms (ordinary Wenckebach) but manifest
on the HBE tracing.
The fact that reentry is responsible for the failure of
the last ventricular impulse of the Wenckebach
cycle to retrogradely conduct to the atria raises the
interesting possibility that an abortive form of
reentry is continuously occurring throughout and
that this abortive reentry may explain the progressive prolongation of the P-R interval.7
Except for quantitative aspects, antegrade and
retrograde A-V nodal conduction are quite similar.13
It, therefore, appears reasonable to extrapolate our
findings during retrograde Wenckebach cycles to
the antegrade counterpart of this phenomenon.
During antegrade Wenckebach cycles, the last
atrial impulse may be blocked in the A-V node by
the reentrant impulse. The fact that antegrade
Wenckebach cycles in which a requisite A-V nodal
delay has been achieved can be terminated by atrial
echo beats lends support to this hypothesis.4 11, 23
However, in both clinical and experimental studies,
echo beats (manifest reentry) are less commonly
seen terminating antegrade Wenckebach cycles
than retrograde Wenckebach cycles. One possible
and as yet unproven explanation for this discrepancy centers about the relationship between antegrade and retrograde A-V nodal conduction times
and the cycle length of stimulation. Since retrograde A-V nodal conduction time is generally
longer than antegrade conduction time, the requisite A-V nodal delay for manifest reentry can be
achieved at longer ventricular cycle lengths relative
to atrial cycle lengths. The shorter atrial cycle
lengths needed to achieve the requisite delay for
reentry favors the possibility that the atrial
pacemaker will depolarize the atria prior to the
arrival of the reentrant impulse. Under these
circumstances collision of atrial and reentrant
impulses will occur in the A-V node and reentry will
be concealed. Furthermore, concealed reentry
during antegrade Wenckebach cycles may be more
common due to the fact that, once the requisite
antegrade A-V nodal delay is achieved, the
reentrant impulse must return to the atria in a
retrograde direction. Since retrograde conduction is
slower than antegrade conduction the possibility
that the atrial pacemaker will capture the atria in
advance of the reentrant impulse is again greater.
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MANIFEST AND CONCEALED REENTRY
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Manifest and Concealed Reentry: A Mechanism of A-V Nodal Wenckebach in Man
JOHN J. GALLAGHER, ANTHONY N. DAMATO, P. JACOB VARGHESE and SUN H. LAU
Circulation. 1973;47:752-757
doi: 10.1161/01.CIR.47.4.752
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