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Teaching Rounds in Cardiac Electrophysiology
Sudden Change From Counterclockwise to Clockwise
Flutter During Cavotricuspid Isthmus Ablation
What Is the Mechanism?
Prabhat Kumar, MBBS; Anil K. Gehi, MD
C
atheter ablation of cavotricuspid isthmus dependent flutter has become a commonly performed procedure with
high success rate and is a prototype of macro–re-entrant
arrhythmia. Although catheter ablation of isthmus-dependent
flutter has become a routine procedure, not infrequently, its
behavior in the electrophysiology laboratory is unusual. We
present one such case highlighting some of the principles of
electrophysiology of re-entrant arrhythmia and atrial flutter.
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block, which may lead to slowing or termination of atrial flutter. Sometimes ablation may lead to unidirectional conduction
block. Unidirectional conduction block may allow atrial flutter only in 1 direction, either counterclockwise or clockwise.
In this case, ablation of cavotricuspid isthmus led to change
from counterclockwise flutter to clockwise flutter. A closer
look at Figure 1 shows that the counterclockwise flutter
breaks, and there is one transition beat before the clockwise
flutter starts. The last beat of the counterclockwise flutter does
not conduct to the first 2 bipoles of the halo catheter (bipoles
1,2 and 3,4), which were located medial to the line of ablation
lesions being created (see the disturbances in the signals on
bipole 5,6 of the halo catheter along which ablation was being
done). This suggests conduction block in the cavotricuspid
isthmus in lateral to septal direction, hence terminating the
counterclockwise flutter circuit. Signal on the bipole 3,4 of
halo catheter during the intervening beat has initial deflection
opposite to that during previously ongoing counterclockwise
flutter, suggesting reversal of direction of activation from septal to lateral. This activation wavefront appears to cross the
isthmus with some delay (wavy arrow from bipoles 1,2 and
3,4 toward bipoles 5,6 and 7,8 on the halo catheter recording,
Figure 2) and activates the lateral wall of the right atrium in
clockwise direction. The delay in conduction is likely because
of the blocked activation wavefront from the transition beat
coming down the lateral right atrial wall toward the cavotricuspid ablation line from the lateral side of the isthmus. In
the subsequent flutter, the reversal of polarity of signal in the
bipoles 3,4 on halo catheter is maintained, which is consistent
with clockwise activation of the atrium in that area.
Continuation of lesion placement along the isthmus led to
termination of this flutter (Figure 3). Termination of clockwise
flutter is clearly because of the development of block in the
septal to lateral direction (clockwise) in the isthmus suggested
by loss of atrial signals in the last beat of the flutter in bipoles
beyond 5,6 on the halo catheter after activation of bipoles 1,2
and 3,4, which also proves that this second atrial tachycardia
was indeed isthmus dependent.
The origin of the transition beat, however, is not clear
and has few possible mechanisms. Electrogram recordings
See Editor’s Perspective p e71
Case Presentation
A 69-year-old woman with history of prior hospital admission for congestive heart failure with preserved left ventricular
systolic function in the setting of atrial tachyarrhythmia presented for atrial flutter ablation. Atrial flutter appeared to be
typical on surface ECG and intracardiac electrogram recordings through 20-electrode halo catheter placed along the tricuspid annulus. Recordings through the halo catheter showed
counterclockwise activation sequence, and entrainment from
the cavotricuspid isthmus confirmed isthmus-dependent flutter. Catheter ablation was done with 8 mm nonirrigated radiofrequency ablation catheter to create a line of block in the
cavotricuspid isthmus from tricuspid annulus to the inferior
vena cava. During the ablation, the activation pattern changed
from counterclockwise to clockwise in direction (Figure 1).
What is the mechanism of this change in activation?
Discussion
Classic atrial flutter involves a macro–re-entrant circuit in the
right atrium around the tricuspid annulus. The cavotricuspid
isthmus, a narrow strip of right atrial tissue between the anatomic boundaries formed by the tricuspid annulus and the inferior vena cava, is a part of the circuit. Catheter-based treatment
of classic atrial flutter involves ablation of cavotricuspid isthmus, creating a line of block in the macro–re-entrant circuit.1,2
Documentation of bidirectional conduction block across the
cavotricuspid isthmus is the end point of the ablation procedure
and leads to freedom from recurrence in >90% of patients.1
Catheter ablation of cavotricuspid isthmus often leads to
delay in conduction across the cavotricuspid isthmus without a
Received February 21, 2013; accepted May 9, 2013.
From the Department of Medicine, Division of Cardiology, University of North Carolina at Chapel Hill.
Correspondence to Anil K. Gehi, MD, Department of Medicine, University of North Carolina at Chapel Hill, Heart and Vascular, 160 Dental Cir, CB
7075, Chapel Hill, NC 27599. E-mail [email protected]
(Circ Arrhythm Electrophysiol. 2013;6:e68-e70.)
© 2013 American Heart Association, Inc.
Circ Arrhythm Electrophysiol is available at http://circep.ahajournals.org
e68
DOI: 10.1161/CIRCEP.113.000380
Kumar and Gehi Reversal of Flutter Activation During Ablation e69
Figure 1. Surface ECG and atrial electrogram recorded through duodecapolar halo
catheter in the left half of the figure suggests
counterclockwise flutter with atrial activation
up the interatrial septum (dashed red arrow)
and down the lateral right atrial wall (solid
blue arrow). The upper 3 channels show
the surface ECG with negative P waves
in leads III and aVF and positive P waves
in V1 typical of counterclockwise flutter
(orange arrows). The right half of the figure
shows reversed activation pattern on the
electrodes of halo catheter with ablation of
cavotricuspid isthmus, suggestive of clockwise flutter with activation up the lateral wall
of the right atrium and down the interatrial
septum. ABL indicates ablation catheter.
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from the halo catheter suggest activation wavefront traveling
down the lateral wall of right atrium toward the cavotricuspid
isthmus ablation line. On the septal side of the ablation, the
wavefront appears to be traveling in the opposite direction
suggested by the reversed deflection pattern on the bipole
right atrium (RA) 3,4 as discussed earlier. This is possible
with an ectopic beat in the high right atrium or a sinus beat.
However, a sinus beat coming in immediately after the flutter
stops is unlikely, which is reaffirmed more strongly by the
delay in initiation of sinus activity seen after the clockwise
flutter finally breaks. The morphology of P wave, although
similar to the sinus P wave (Figure 3), has subtle differences
with longer P-wave duration. Moreover, the coupling interval of this atrial beat with the last counterclockwise flutter
beat is very close to the flutter cycle length, suggesting a
re-entrant mechanism and a link of this beat to the last counterclockwise flutter beat. The likely mechanism in this case
appears to be conduction of the last counterclockwise flutter
beat across the crista terminalis breaking into the midseptal area and activating the septum, upward and downward,
a clockwise lower loop re-entry.3,4 Manifest conduction of
the last beat of counterclockwise flutter across the crista terminalis with minimal delay (255 versus 245 ms measured
at the bipole RA 19,20) likely becomes possible because
of the absence of a competing wavefront of activation after
the development of unidirectional block in the cavotricuspid isthmus. The upward wavefront subsequently travels up
to the high right atrium and then down the lateral wall of
the right atrium. The downward wavefront in turn activates
the lower septum and the cavotricuspid isthmus from the
Figure 2. Top, Change in the activation
pattern with cavotricuspid isthmus ablation. The second atrial beat in the panel
does not conduct across the isthmus to
the first 2 bipoles (right atrium [RA] 1,2 and
RA 3,4) of the halo catheter because of the
development of unidirectional block from
the lateral atrial wall to the septum. The last
counterclockwise flutter beat crosses the
crista terminalis breaking into the midseptal
area and activating the septum, upward
and downward. The upward wavefront
subsequently travels up to the high right
atrium and then down the lateral wall of the
right atrium. The downward activation limb
conducts with a delay across the isthmus
from the septal aspect to the lateral aspect
of right atrium, starting a clockwise flutter. The green arrows show the P waves
corresponding to the single intervening
beat in the upper 3 channels. Bottom, The
unidirectional block from the lateral wall to
septum and conduction across the crista
terminalis around the inferior vena cava
(IVC; dashed blue line) breaking into the
midseptal area and delayed conduction of
its downward wavefront across the isthmus
to the lateral right atrial wall (depicted as
wavy arrow). ABL indicates ablation catheter; CS, coronary sinus; CTI, cavo-tricuspid
isthmus; and His, His bundle.
e70 Circ Arrhythm Electrophysiol October 2013
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Figure 3. Top, Termination of clockwise
atrial flutter with continued ablation of
cavotricuspid isthmus. The upper 3 channels show surface ECG with positive
P wave in leads III and aVF and negative
P wave in V1 typical of clockwise flutter
(green arrows). The activation wavefront of
the last beat of atrial flutter blocks at the
isthmus ablation site with no conduction
of clockwise activation wavefront from the
bipoles right atrium (RA) 1,2 and 3,4 to the
bipoles located on the lateral aspect of
tricuspid annulus. Bottom, The ongoing
clockwise flutter (left) and development of
conduction block across the isthmus from
the septal to the lateral aspect (right) are
shown schematically. IVC indicates inferior
vena cava.
septal side toward the ablation line. The lateral wavefront of
the transition beat reaches the ablation line from the lateral
side slightly earlier and does not conduct because of unidirectional block. However, this concealed activation of the
cavotricuspid isthmus ablation line leads to delay in conduction of the septal to lateral wavefront initiating clockwise
flutter (Figure 2).
This case shows mechanism of termination of atrial flutter
during catheter ablation and shows the importance of bidirectional conduction block in the cavotricuspid isthmus during
the procedure.
Disclosures
None.
References
1. Pérez FJ, Schubert CM, Parvez B, Pathak V, Ellenbogen KA, Wood MA.
Long-term outcomes after catheter ablation of cavo-tricuspid isthmus
dependent atrial flutter: a meta-analysis. Circ Arrhythm Electrophysiol.
2009;2:393–401.
2. Montenero AS, Bruno N, Antonelli A, Mangiameli D, Barbieri L, Andrew
P, Murphy O, O’Connor S, Zumbo F. Long-term efficacy of cryo catheter
ablation for the treatment of atrial flutter: results from a repeat electrophysiologic study. J Am Coll Cardiol. 2005;45:573–580.
3. Zhang S, Younis G, Hariharan R, Ho J, Yang Y, Ip J, Thakur RK, Seger J,
Scheinman MM, Cheng J. Lower loop reentry as a mechanism of clockwise right atrial flutter. Circulation. 2004;109:1630–1635.
4.Cheng J, Cabeen WR Jr, Scheinman MM. Right atrial flutter due to
lower loop reentry: mechanism and anatomic substrates. Circulation.
1999;99:1700–1705.
Key Words: atrial flutter ◼ catheter ablation
Sudden Change From Counterclockwise to Clockwise Flutter During Cavotricuspid
Isthmus Ablation: What Is the Mechanism?
Prabhat Kumar and Anil K. Gehi
Downloaded from http://circep.ahajournals.org/ by guest on April 29, 2017
Circ Arrhythm Electrophysiol. 2013;6:e68-e70
doi: 10.1161/CIRCEP.113.000380
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