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ARRHYTHMIA ROUNDSSection Editor: George J. Klein, M.D.
Three Pauses and Three P Waves: What is the Mechanism?MATTHEW
WRIGHT, M.B.B.S., PH.D., S EBASTIEN KNECHT, M.D.,
SEIICHIRO MATSUO, M.D., KANG-TENG LIM, M.D., M EL `EZE HOCINI,
M.D.,PIERRE JAIS, M.D., and MICHEL HAISSAGUERRE, M.D.
From the Hopital Cardiologique du Haut-Leveque and the
Universite Victor Segalen Bordeaux II, Bordeaux, France
Case Presentation
A 56-year-old man with a 6-year history of symptomaticdrug
refractory idiopathic persistent atrial fibrillation (AF)attended
for catheter ablation. Transthoracic echocardiog-raphy demonstrated
normal biventricular systolic functionwith a dilated left atrium at
58 mm in the parasternal long-axis view. For the
electrophysiological procedure, a de-capolar catheter was placed
into the coronary sinus fromthe right femoral vein, while a
decapolar circumferentialcatheter (Lasso, Biosense Webster, Diamond
Bar, CA, USA)and a quadripolar cooled-tip ablation catheter
(ThermocoolBiosense Webster) were similarly inserted to the left
atriumvia a single transseptal puncture. At the start of the
procedure,left and right AF cycle lengths (AFCL) were measured
fromthe left and right atrial appendages at 124 ms and 125
ms,respectively.
After proximal isolation of all pulmonary
veins,electrogram-based ablation was carried out by targeting
com-plex atrial potentials at the inferior left atrium, the left
inter-atrial septum, the left atrial appendage, and along the
leftatrial roof. This prolonged AFCL to 177 ms in the left
atriumbut only 136 ms in the right atrium, suggesting that the
drivingactivity was emanating from the right atrium.
With ablation of the most rapid right atrial
electrograms,located at the superior vena cava/right atrial
junction, the pa-tient converted to a regular atrial tachycardia
with a cyclelength of 184 ms. Throughout the case, there were a
num-ber of pauses that helped with both mapping and ablation ofthe
atrial tachycardia. How does the pause seen in Figure 1help with
mapping, and what is happening during and afterablation in Figures
2 and 3, respectively?
DiscussionThe electrocardiogram (Fig. 1) shows a consistent
narrow,
positive P wave in V1 with a significant isoelectric
interval.This would suggest that excitation originates close to the
in-
Sebastien Knecht is supported by the Belgian Funds for Cardiac
Surgery.
J Cardiovasc Electrophysiol, Vol. 19, pp. 562-564, May 2008.
Address for correspondence: Matthew Wright, M,B.B.S., Service
deRythmologie, Hopital Cardiologique du Haut-Leveque, Avenue
deMagellan, 33604 Bordeaux-Pessac. Fax: +33-5-57-65-65-09;
E-mail:[email protected]
doi: 10.1111/j.1540-8167.2007.01090.x
teratrial septum, with the contributions from each atria
tend-ing to cancel themselves out. However, interpretation of
thesurface P wave following extensive atrial ablation in
persis-tent AF cases is notoriously difficult. On the surface
elec-trogram and the right atrial intracardiac electrogram thereis
a pause in the tachycardia, yet on the intracardiac
elec-trocardiogram from the left atrial appendage the
tachycardiacontinues without a pause. Additionally, the tachycardia
inthe left atrium is very regular, compared with the right
atrium.These findings localize the source of the tachycardia to the
leftatrium and saves the need for any further mapping within
theright atrium. It appears that the surface P wave reflects
rightatrial activity, given both the timing in relation to the
rightatrial electrogram (EGM) and its absence during the pausein
the right atrium. In contrast, AV conduction appears to berelated
to left atrial activity, with a consistent relationship be-tween
the left atrial EGM and the QRS complex, comparedwith the right
atrial EGM.
Following these observations, the tachycardia was mappedin the
left atrium, and the activation sequence was compat-ible with a
roof-dependent flutter. Ablation was targeted tothe left atrial
roof to complete a roof line. In Figure 2, there isa slowing of the
tachycardia, seen on the surface electrocar-diogram and as measured
from the catheter in the right atrialappendage, but not the left
atrial appendage. The P wave mor-phology changes and becomes wider
with an axis that couldbe compatible with sinus rhythm, while the
right atrial ap-pendage follows the P wave, i.e., is displaced to
the secondhalf of its morphology with a one-to-one relationship.
Whatis also striking is the small contribution to the surface P
wavefrom the left atrium, which can be seen during the pause
fromthe right atrium as a small negative deflection on the
surfaceECG in V1.
Different hypotheses can be raised from these observa-tions: (1)
There is complete dissociation of the left and rightatria, with
restoration of sinus rhythm in the right atrium whilethe left
atrium remains in atrial tachycardia; (2) modificationof
interatrial conduction, Bachmans Bundle resulting in ahigh degree,
but incomplete conduction block from the leftatrium to the right
atrium. Of the two possibilities, the latter ismore likely, as
sinus rhythm would be expected to be regular,whereas here it is
clearly not, suggesting that the right atriumis still being driven
from the left atrial tachycardia.
In Figure 3 there is now a pause measured in the left
atrium,which is not seen in the right atrium. However, inspection
ofthe surface P wave shows this to be a different morphology
tothose in Figures 1 and 2. This occurred at the termination of
