E UROPACE
two groups were present in 45 hearts (90%). In the last 5 cases (10%) there
was also a middle group. Neither a single initial group nor any case without
any initial groups were found. In the examined sections, in 27 hearts (54%) the
superior group appeared as the first, in 23 cases (46%) the inferior group. The
length of each group was measured from the first appearence to the first solid
contact with the second part. The length of the superiorpart oscillated from 0,15
to 2,91 m m (an 0,90&0,6 mm), inferior from 0,ll to 2,41 m m (am. 0,88&0,6
mm)(table 2) and the middle from 0,67 to 2,21 m m (am 1,04&0,7 mm).
Based on OUTstudy we could conclude that the prevalence of at least two
initial zones of the node: superior and inferior one, is constant and occurs in
each examined heart. Our data suggest that the middle group is additional one.
I
P 352
THE SPECIFIC BIMODAL DISTRIBUTION PATTERN IN
RR INTERVAL HISTOGRAM PREDICTS EARLY
RECURRENCE OF ATRIAL FIBRILLATION
FOLLOWING EXTERNAL ELECTRICAL
CARDIOVERSION
X.H. Guo, J.M. Bland, M.M. Gallagher, A.J. Camm. St George’sHospita2
Medical
School,
UK
Background: W e hypothesize that abnormal AV nodal electrophysiological
behaviour as assessed by the presence of a bimodal RR histogram in atria1
fibrillation (AF) may contribute to vulnerability to recurrent AF postexternal
electrical cardioversion (ECV).
Methods: RR interval histograms were constructed from 24hour ECGs
recorded before ECVon 98 patients (68 men, age 65.3&10.3 years) with persistent AF. A 48.hour recording was obtained from each of 20 patients for
evaluating the reproducibility of RR histograms. RR histograms were classified as either unimodal or bimodal, including multi-modal RR histograms, by
3 observers according to predefined criteria. All patients were prospectively
followed-up during ECV, one-week and one-month later.
Results: Out of total 98 patients, 13 (13.2%) patients failed ECV and a total
of 52 (53%) patients were in AF at one-week and 66 (67%) at one-month post
ECV A bimodal RR interval distribution during AF was found in 17 (18%) of
the 98 patients and 8 (47%) of these 17 patients exhibited a speciiicbimodal RR
histogram. Inter- observed identification of bimodality was excellent (k= 0.966,
p<O.OOOl). The reproducibility of bimodality on consecutive days was good
(k= 0.56, p=O.O04). Compared to the patients with non- specific bimodality,
patients with the specific bimodal RR histogram were more likely to have recurrent AF within one-week and one-month (88 vs. 33%, 100 vs. 33%, p=O.Ol,
p=O.O09,respectively) with sensitivity: 78.73%; specificity: 88.100%; positive
predictive accuracy: 88.100% respectively.
Conclusion: A specific bimodal RR histogram is associated with low probability of maintaining sinus rhythm following ECV.
I P 353
P W A V E PARAMETERS IN PACEMAKERBIOTRONIK
AXIOS D ELECTROPHYSIOLOGY
TEST - STUDY IN
BRADYCARDIA-TACHYCARDIA
SYNDROME PATIENTS
M. Rosiak, M. Chudzik, K. Bartuak, .I. Kawinski, H. Bolinska, .I. Ruta.
Institute
of Cardiology,
Medical
of Lodz,
University
Poland
Atria1 fibrillation (AF) is the common arrhythmia observed in patients with
bradycardia-tachycardia syndrome (BTS). Inter&al conduction disturbances
represented by P-wave duration prolongation, and effective refractory period
shortening are proposed as the electrophysiologic substrate for AF. It has
been demonstrated that AAI/DDD pacing reduce supraventricular arrhythmia
(AFISVT) incidence in BTS patients.
Aim: The aim of the study was to document the changes of the P-wave
parameters in BTS patients (pts) after DDD pacemaker @cm) implantation.
Methods: Study population: 7 patients (4 women and 4 men aged 66,8&12,3)
with BTS (AF vs. sinus bradycardia) who hadBiotronikAxiosD
pcm implanted.
All pts were in DDD 60 bpm pacing mode. Pts had measured on l-day (l-d), 2
weeks (2-w) and 3 months (3-m) after implantation the following parameters: 1.
Measured by BiotronikAxios
D pcm electrophysiology program: Paced P-wave
duration (pP), sinus P-wave duration (sP), atria1 effective refractory period
(ERPA); 2. P-wave duration (PWD) from SAECG.
Results (p<O,O5):
Friedman
test
Pd
sPd
ERM
PWD
l-d vs. Z-w
NS
NS
NS
NS
l-d vs. 3-m
0,015s
NS
0,036
NS
Conclusion: In the group of OUTpts treated by DDD 60 bpm pacing we
observed the shortening of pPd and lengthening of ERPA (l-d vs. 3-m) mea-
2003
ERPA
ERR43-m I
P
sued by pcm electrophysiology program. These tendency should be beneficial
in lowering the number of AF episodes. Further studies with larger group and
different pacing rates are necessary to evaluate pacing rate optimal for P-wave
shortening and ERPA lengthening.
IP
354
CHRONAXIE TIMES ARE THE SAME FOR INDUCTION
OF VENTRICULAR FIBRILLATION
AND
DEFIBRILLATION
BUT DIFFERENT FOR STIMULATION
T. Lawo, B. Wenzel, S.M. Wagner, M. Buddensiek, J.H. Fischer, M. Bose,
A. Muegge, B. Lemke. University Hospital Bergmanmheil,
Bochum,
Germany;
University
of Cologne,
Germany;
Biohmik,
Erlangq
Germany
The strength-duration curve for cardiac stimulation is described by the hyperbolic chronaxie-rheobase relationship. Studies on the strength-duration relation
for the defibrillation threshold (DFT) are limited and show conflicting results.
In addition, no such data are available regarding the induction of ventricular
fibrillation (VF) by a T-wave shock. W e therefore assessedthe hypothesis that
the strength-duration curve for VF induction follows a hyperbolic relation with
a chronaxie (&) different from the t, for stimulation but identical to the t, for
defibrillation.
Twelve pigs were implanted with an ICD lead in the right ventricle. Three
single-coil leads served as the common anode. Fairly rectangular monophasic
shocks were applied by a custom made external defibrillator. Pacing thresholds
(via shock coil) were determined at stimulus durations of 0.02-20 ms. The lower
and upper VF induction threshold (LVr, UVT) and the DFT were determined
for different shock durations (0.1-100 ms). Chronaxies were derived from the
strength-duration curves of each single experiment.
The strength-duration curves for the LVT and the UVT followed a hyperbolic
function (r=O.96 for LVT and r=0.78 for UVT. The mean k for stimulation
was 0.22 ms (&0.12 ms, n=12) and was signiiicantly (p<O.OOl, t-test) shorter
than the k for the LVT (2.4&1.7 ms, n=lO), the UVT (2.5&1.3 ms, n=7) and
the DFT (2.2&1.3 ms, n=ll), respectively.
W e conclude, that not only the time constants but also the underlying cellular mechanisms are identical for T-wave induction and defibrillation (“graded
response”) but different from stimulation (“all-or-nothing response”).
I P 355
ORGANIZATION
OF MULTIPLE REENTRANT W A V E
FRONTS DURING ATRIAL FIBRILLATION
BY A PURE
IKR CHANNEL BLOCKER IN CANINE ATRIA
T. Ikeda, A. Kawase, K. Nakazawa, T. Ashihara, T. Namba, T. Yao, S. Yusu,
H. Yoshino. Kyorin University Mitaka, Japan and Japanese Working Group
On Cardiac
Simulation
and Mapping,
To&w, Japan
Background: Effects of II+ channel blocker on wave front dynamics during
atria1 fibrillation (AF) is unknown. This study aimed to assess the effects of
nifekalant, a pure II+ channel blocker on the characteristics of activation waves
during AF using mapping technique.
Methods: W e used an isolated, coronary perfused canine biatrial model
(n=7). The endocardium was mapped using computerized mapping system
(2.mm resolution). AF was induced by an extrastimulus method in the presence
of 5 u M acetylcholine. After coniirming sustained AF, 5 u M nifekalant was
added to the perfusing Tyrode’s solution. Effective refractory period (ERP),
conduction velocity (Cv), and excitable gap (EG) were determined during
AF.
Results: At baseline, multiple nonstationary wave fronts were observed
leading to meandering, breakups, and the generation of new wave fronts. After
perfusing the drug, multiple wave fronts were completely organized into a
single stationary reentrant wave front in all 7 preparations, anchoring to a large
pectinate muscle (5 preparations), to or&x of inferior vena cava (1 preparaEuropace Supplements,
Vol. 4, December 2003
B149