Europace (2003) 5, 231–233
doi:10.1016/S1099–5129(03)00036-9
ISSUE CARDIOGRAM:
Unusual form of AV nodal Wenckebach
block
M. Rivero-Ayerza, D. Kalpakos, M. De Zutter,
P. Geelen and P. Brugada
Cardiovascular Research and Teaching Institute Aalst, Aalst, Belgium
A 73-year-old man had a fast atrioventricular (AV) nodal
pathway accidentally ablated 4 years before, while attempting to ablate a septally located concealed accessory
pathway (AP). After initiation of treatment with betablockers, because of systemic arterial hypertension, the
patient presented to the emergency room complaining of
a markedly diminished exercise tolerance. The 12 lead ECG
showed an interesting AV nodal Wenckebach sequence,
interrupted by P waves retrogradely conducted through the
AP. The mechanisms explaining the ECG are discussed.
(Europace 2003; 5: 231–233)
Ó 2003 The European Society of Cardiology. Published by
Elsevier Ltd. All rights reserved.
Case presentation
dual AV nodal pathways were documented and the AV
node’s Wenckebach point was reached at 800 ms (Fig.
2). During ventricular stimulation the retrograde refractory period of the AP was reached at 300 ms. What
are the mechanisms explaining the ECGs?
A 73 year-old man, presented to the emergency room
(ER) complaining of a markedly diminished exercise
tolerance, 3 weeks after initiation of treatment with a
beta-blocker because of systemic arterial hypertension.
The patient had a fast atrioventricular (AV) nodal pathway accidentally ablated 4 years before, while unsuccessfully attempting to ablate a septally located
concealed accessory pathway (AP). He had remained
asymptomatic ever since. The first ECG, recorded in the
ER (Fig. 1), showed an interesting sequence.
Electrophysiological (EP) investigation using standard techniques was performed. The AH interval was
150 ms and the HV 50 ms. During atrial stimulation no
Manuscript submitted 21 November 2002, and accepted after
revision 29 March 2003.
Correspondence: Pedro Brugada, Cardiovascular Center, OLV
Hospital, Moorselbaan 164, 9300 Aalst, Belgium. Fax: þ32-5372-4185; E-mail: [email protected]
1099–5129/03/000231+03 $30.00/0
Key Words: Fast pathway ablation, AV block, Wenckebach block, concealed accessory pathway.
Discussion
Two interesting EP phenomena are observed in the
present case. First, the mechanism involved in the AV
delay pattern and second, the mechanism of intermittent
retrograde AV conduction. There are many potential
mechanisms that can explain the presented ECGs. First
of all, there is prolongation of the PR interval between
consecutive beats (Fig. 1). Although a higher incidence
of late AV block following fast pathway ablation has
already been described[1,2], this AV interval prolongation could correspond either to an AV Wenckebach
block or to a jump of AV conduction from the fast to
the slow AV nodal pathway. Considering that the P–P
interval is not altered during normal sinus rhythm and
that no dual pathways were documented during EP
Ó 2003 The European Society of Cardiology. Published by Elsevier Ltd. All rights reserved.
232 M. Rivero-Ayerza et al.
Figure 1 ECG recorded in the ER (paper speed 25 mm/s). From top to bottom, leads aVR, aVL and aVF. Progressive
AV delay can be observed between the second and third beat. Note that when PR interval prolongs, retrograde VA
conduction appears.
investigation, the AV delay and later echo beat cannot
be explained by a jump of conduction from the fast to
the slow pathway. The fact that retrograde depolarization of the atrium in the third beat resets the sinus node
and generates a compensatory pause, gives time for the
AV node to recover and the next (delayed) P wave is
normally conducted, instead of being blocked. In this
way the AV Wenckebach sequence is interrupted.
Why are only beats after an AV
conduction delay retrogradely
conducted to the atrium?
This has two potential mechanisms. The first one, is
that the atrium may be refractory after a normally
conducted beat, and only after a prolonged AV delay
the atrium has time to recover and can now be
depolarized retrogradely through the AP.
Europace, Vol. 5, July 2003
The second potential mechanism, is that there is
antegrade AP concealed conduction, and with an AV
delay shorter than the AP’s retrograde refractory period
there is no retrograde conduction of the impulse. While
with an AV delay greater than the AP’s retrograde
refractory period, the AP recovers and can retrogradely
depolarize the atrium.
By carefully analyzing Fig. 2, we see that the
Wenckebach point is reached at 800 ms and that the
first conducted beat has no retrograde conduction.
However, the interval between the retrograde P wave
and the following paced P wave is 280 ms. That means
that the atrial refractory period is less than 280 ms and
that the mechanism of retrograde block during the first
beat of the sequence is not due to atrial refractoriness,
but to concealed antegrade conduction over the AP.
Note that retrograde P wave morphology on the surface
ECG is very helpful to localize the AP, in this case an
inferiorly (negative P wave in leads II, III and aVF) and
septally (positive P wave in aVR and aVL and
isodiphasic in I) located AP.
AV Wenckebach
233
Figure 2 Top: ECG recorded during atrial stimulation (S) at cycle length of 800 ms. A Wenckebach sequence occurs
during atrial pacing. Note that after the second conducted beat, AV conduction is delayed enough to allow retrograde
conduction over the AP. The interval between the retrograde P wave (arrows) and the next paced P wave (280 ms) is
shorter than the refractory period of the AP, confirming that the mechanism responsible for intermittent VA conduction
is concealed antegrade conduction over the AP and not atrial refractoriness. Note the retrograde P wave polarity
suggesting an inferiorly (negative in leads II, III and aVF) and septally (positive in aVR and aVL and isodiphasic in I)
located AP. Bottom: Lewis’ diagram during atrial stimulation showing the mechanism explaining the preceding ECGs.
Paper speed 25 mm/s.
References
[1] Hindricks G, on behalf of the Multicenter European Radiofrequency Survey (MERFS) Investigators. The Multicenter
European Radiofrequency Survey (MERFS)—Complications
of radiofrequency catheter ablation of arrhythmias. Eur Heart J
1993; 14: 1644–53.
[2] Fenelon G, Malacky T, Manios E, Geelen P, Andries E,
Brugada P. Radiofrequency ablation of atrioventricular
node reentrant tachycardia: fast or slow pathway ablation?
In: Farre J, Moro C, eds. Ten Years of Radiofrequency
Catheter Ablation. Armonk, NY: Futura Publishing 1998:
103–14.
Europace, Vol. 5, July 2003