Basic Res Cardiol 100: 365 – 371 (2005)
DOI 10.1007/s00395-005-0533-8 ORIGINAL CONTRIBUTION
Peter Milberg
Nico Reinsch
Nani Osada
Kristina Wasmer
Gerold Mönnig
Jörg Stypmann
Günter Breithardt
Wilhelm Haverkamp
Lars Eckardt
Verapamil prevents torsade de pointes by
reduction of transmural dispersion of
repolarization and suppression of early
afterdepolarizations in an intact heart model
of LQT3

Abstract Background In long QT syndrome (LQTS), prolongation of the
QT-interval is associated with sudden cardiac death resulting from poten-
tially life-threatening polymorphic tachycardia of the torsade de pointes
(TdP) type. Experimental as well as clinical reports support the hypothesis
that calcium channel blockers such as verapamil may be an appropriate ther-
apeutic approach in LQTS. We investigated the electrophysiologic mecha-
nism by which verapamil suppresses TdP, in a recently developed intact heart
model of LQT3. Methods and results In 8 Langendorff-perfused rabbit
hearts, veratridine (0.1 µM), an inhibitor of sodium channel inactivation, led
to a marked increase in QT-interval and simultaneously recorded monopha-
sic ventricular action potentials (MAPs) (p < 0.05) thereby mimicking LQT3.
In bradycardic (AV-blocked) hearts, simultaneous recording of up to eight
epi- and endocardial MAPs demonstrated a significant increase in total dis-
persion of repolarization (56%, p < 0.05) and reverse frequency-dependence.
After lowering potassium concentration, veratridine reproducibly led to early
afterdepolarizations (EADs) and TdP in 6 of 8 (75%) hearts. Additional infu-
sion of verapamil (0.75 µM) suppressed EADs and consecutively TdP in all
hearts. Verapamil significantly shortened endocardial but not epicardial
MAPs which resulted in significant reduction of ventricular transmural dis-
persion of repolarization. Conclusion Verapamil is highly effective in pre-
venting TdP via shortening of endocardial MAPs, reduction of left ventricu-
lar transmural dispersion of repolarization and suppression of EADs in an
intact heart model of LQT3. These data suggest a possible therapeutic role of
verapamil in the treatment of LQT3 patients.

Key words Torsade de pointes – verapamil – long QT syndrome – early
afterdepolarizations – transmural dispersion
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Dr. med. P. Milberg () · N. Reinsch, MS
K. Wasmer, MD · G. Mönnig, MD
J. Stypmann, MD
G. Breithardt, MD, FESC, FACC
W. Haverkamp, MD, FESC · L. Eckardt, MD
Medizinische Klinik und Poliklinik C
Kardiologie und Angiologie
Universitätsklinikum Münster
Albert-Schweitzer Str. 33
48149 Münster, Germany
Tel.: +49-251/8345160
Fax: +49-251/8349943
E-Mail: milbergp@uni-muenster.de
N. Osada, PhD
Department of Medical Informatics and
Biomathematics
University of Münster, Germany
present address:
W. Haverkamp, MD, FESC
Department of Cardiology
Campus Virchow Clinic
Charité – University Medicine Berlin
Berlin, Germany
Received: 21 January 2005
Returned for revision: 15 February 2005
Revision received: 22 February 2005
Accepted: 4 April 2005
Published online: 10 June 2005
Introduction
The long QT syndrome (LQTS) is characterized by pro-
longation of the QT-interval which is associated with
sudden cardiac death resulting from polymorphic tachy-
cardia of the torsade de pointes (TdP) type. More than
250 mutations in seven genes (LQTS 1-7) have been
described. Mutations involve genes encoding potassium
channels (LQT1, 2, 5, and 6, Jervell-Lange-Nielsen (JLN)
1 and 2) and ankyrin B (LQT4), which acts as a targeting
and anchoring molecule for the sodium channel [5]. In
LQT3, SCN5A was found to be the responsible gene [29].
It is located on chromosome 3 and encodes for the car-
diac fast sodium channel. Mutations lead to a persistent
component of a small inward depolarizing ion current
(I
Na
) via continued re-opening of the sodium channel.
This small inward sodium current is sufficient to delay

repolarization and to prolong the QT-interval [30]. We
have recently developed a novel intact heart model of
LQT3 [23] that reproduces the expected electrophysio-
logical alterations using veratridine, an inhibitor of
sodium channel inactivation [11]. We were able to
demonstrate that veratridine reproducibly causes early
afterdepolarizations (EADs) and TdP due to significantly
increased left ventricular transmural dispersion of repo-
larization in bradycardic and hypokalemic hearts. Based
on these experimental data, reduction of transmural dis-
persion of repolarization may be effective in preventing
TdP. This is supported by recent clinical data. The
PAFAC trial (Prevention of Atrial Fibrillation after Car-
dioversion) [10] showed a higher incidence of proar-
rhythmia in patients treated with sotalol (2
160 mg) as
compared to patients taking the combination of quini-
dine (3
160 mg) and verapamil (3
80 mg). As vera-
pamil might therefore have an “antitorsadogenic” poten-
tial, the aim of this study was to investigate the electro-
physiologic effects of verapamil on EADs, TdP and par-
ticularly on transmural dispersion of repolarization in
this intact heart model.
Methods
All experimental protocols were approved by the local
animal care committee and conformed with the Guide for
the Care and Use of Laboratory animals published by the
US National Institutes of Health (NIH Publication No.
852-3, revised 1996).
Preparation of hearts for perfusion
The method has been described previously [6, 8, 21–23].
In summary, male New Zealand white rabbits (n = 8)
weighing 2.5–3.0 kg were anesthetized with sodium
thiopental (200–300 mg iv.). After midsternal incision
and opening of the pericardium, the hearts were removed
and immediately placed in an ice-cold Krebs-Henseleit
solution (composition in mM: CaCl
2
1.80, KCl 4.70,
KH
2
PO
4
1.18, MgSO
4
0.83, NaCl 118, NaHCO
3
24.88, Na-
pyruvate 2.0 and D-glucose 5.55). The aorta was cannu-
lated, the pulmonary artery was incised, and the sponta-
neously beating hearts were retrogradely perfused via
the aorta at constant flow (52 ml/min) with warm (36.8 to
37.2 °C) Krebs-Henseleit solution. Perfusion pressure
was kept stable at 100 mm Hg. The hearts were placed in
a heated, solution-filled tissue bath. After cannulation,
the hearts were given 10 minutes to stabilize. The per-
fusate was equilibrated with 95% O
2
and 5% CO
2
(pH
7.35; 37 °C). The cannulated and perfused hearts were
attached to a vertical Langendorff apparatus (Hugo Sachs
Elektronik, Medical Research Instrumentation, March-
Hugstetten, Germany). A deflated latex balloon was
inserted into the left ventricle and connected to a pres-
sure transducer to control hemodynamic stability. The
atrioventricular (AV) node was ablated by a surgical
tweezers under ECG-control to slow the intrinsic heart
rate. This resulted in complete AV-dissociation with a
ventricular escape rate below 60 beats per minute.
Electrocardiographic and electrophysiologic
measurements
A volume-conducted ECG was recorded by complete
immersion of the heart into a bath of Krebs-Henseleit
solution that had been thermally equilibrated with the
myocardial perfusate. Signals from a simulated
“Einthoven” configuration were amplified by a standard
ECG amplifier (filter settings: 0.1–300 Hz). Monophasic
action potential (MAP) recording and stimulation were
accomplished simultaneously using contact MAP-pacing
catheters (EP Technologies, Mountain View, CA, USA).
The MAP electrograms were amplified and filtered (low
pass 0.1 Hz, high pass 300 Hz). MAPs were analyzed using
a software specifically designed by Franz et al. [9] per-
mitting precise definition of the amplitude and duration
of the digitized signals. QT-interval was analyzed manu-
ally. The recordings were considered reproducible and,
therefore, acceptable for analysis only if they had a stable
baseline amplitude with a variation of less than 20% and
a stable duration (MAP duration at 90% repolarization
(MAP
90
) was reproducible within 4 ms). MAPs were
recorded simultaneously. Seven MAPs were evenly
spread in a circular pattern around the epicardium of
both ventricles (five on the left ventricle, two on the right
ventricle), one MAP was recorded from the left-ventric-
ular endocardium. One of the right-ventricular catheters
was used to pace the heart. Pacing at twice diastolic
threshold was performed for one minute at each cycle
length (CL) from 900 to 300 ms using a programmable
stimulator (Universal Programmable Stimulator, UHS
20, Biotronik, Germany) which delivered square-wave
pulses of 2 ms pulse width. All data were digitized at a rate
of 1 kHz with 12 bit resolution and subsequently stored
on a removable hard disk (BARD LabSystem, Bard Elec-
trophysiology, Murray Hill, Massachusetts, USA).
Experimental protocol
After placing the MAP catheters and achieving complete
AV block, cycle length-dependence was first investigated
under baseline conditions via pacing the hearts at cycle
lengths between 900 and 300 ms. Thereafter, veratridine
366 Basic Research in Cardiology, Vol. 100, No. 4 (2005)
© Steinkopff Verlag 2005