Relationship of Slow Conduction
Detected by Pace-Mapping to Ventricular
Tachycardia Re-Entry Circuit Sites After Infarction
Corinna B. Brunckhorst, MD,* William G. Stevenson, MD,† Kyoko Soejima, MD,†
William H. Maisel, MD, MPH,† Etienne Delacretaz, MD,‡ Peter L. Friedman, MD, P
Shlomo A. Ben-Haim, MD, DS
Zurich and Bern, Switzerland; Boston, Massachusetts; and Haifa, Israel
OBJECTIVES This study sought to characterize the relationship of conduction delays detected by
pace-mapping, evident as a stimulus to QRS interval (S-QRS) delay Ն40 ms, to ventricular
tachycardia (VT) re-entry circuit isthmuses deﬁned by entrainment and ablation.
BACKGROUND Areas of slow conduction and block in old infarcts cause re-entrant VT.
METHODS In 12 patients with VT after infarction, pace-mapping was performed at 890 sites. Stimulus
to QRS intervals were measured and plotted in three-dimensional reconstructions of the left
ventricle. Conduction delay was deﬁned as Ն40 ms and marked delay as Ͼ80 ms. The
locations of conduction delays were compared to the locations of 14 target areas, deﬁned as
the region within a radius of 2 cm of a re-entry circuit isthmus.
RESULTS Pacing captured at 829 sites; 465 (56%) had no S-QRS delay, 364 (44%) had a delay Ն40 ms,
and 127 (15%) had a delay Ͼ80 ms. Sites with delays were clustered in 14 discrete regions,
13 of which overlapped target regions. Only 1 of the 14 target regions was not related to an
area of S-QRS delay. Sites with marked delays Ͼ80 ms were more often in the target (52%)
than sites with delays 40 to 80 ms (29%) (p Ͻ 0.0001).
CONCLUSIONS Identiﬁcation of abnormal conduction during pace-mapping can be used to focus mapping
during induced VT to a discrete region of the infarct. Further study is warranted to determine
if targeting regions of conduction delay may allow ablation of VT during stable sinus rhythm
without mapping during VT. (J Am Coll Cardiol 2003;41:802–9) © 2003 by the American
College of Cardiology Foundation
In many patients with sustained monomorphic ventricular
tachycardia (VT) due to prior myocardial infarction, cath-
eter ablation is complicated by VTs that are unstable for
mapping due to hemodynamic instability, poor reproduc-
ibility for initiation, or spontaneous changes from one VT
to another. Feasibility of ablation of unstable VTs largely
during stable sinus rhythm has been demonstrated (1–3).
Extensive radiofrequency (RF) ablation lines were placed
over low voltage areas, or limited lines were placed through
a target region based on limited assessment of sites during
VT. The infarct regions are typically large. New methods to
guide placement of RF ablation lines during sinus rhythm
are of interest.
Abnormal, slowed conduction through regions of surviv-
ing myocyte bundles is an important substrate causing VT
(4), often associated with critical isthmuses that are desir-
able targets for ablation (5). The isthmus consists of an exit
from which the re-entrant wavefront propagates to the
surrounding more normal myocardium producing the QRS
complex, and a segment that is proximal to the exit.
During sinus rhythm, when pacing is performed from the
mapping catheter located at the exit from the isthmus, the
resulting QRS morphology should theoretically resemble
that of the tachycardia. Analysis of the QRS complex
produced by ventricular pacing during sinus rhythm, known
as “pace-mapping,” is useful for targeting focal VTs, but of
limited utility and potentially misleading for mapping scar-
related VT (6 –8) (Fig. 1). However, pace-mapping also
provides a means of identifying areas of abnormal conduc-
tion from analysis of the interval between the stimulus and
QRS onset. A stimulus to QRS interval (S-QRS) Ն40 ms
is associated with abnormal electrograms and consistent
with slow conduction away from the pacing site (8–11). The
aim of our study was to deﬁne the extent of regions of
S-QRS delays and to assess their proximity to deﬁned VT
re-entry circuit isthmuses. For this purpose, we deﬁned a
potential “target area” as the region within a radius of 2 cm
of a deﬁned re-entry circuit isthmus. Ablation over such an
area has been shown to be feasible (1–3).
Patient population. The study included 12 consecutive
patients (Table 1) who were referred for ablation (all males,
mean age 68 Ϯ 8 years), and who underwent catheter
mapping with an electroanatomic mapping system (Bio-
sense, Tirat Hacarmel, Israel; Cordis Webster, Diamond
Bar, California) with custom software that allowed con-
struction of three-dimensional anatomic maps with plots of
the S-QRS interval during pace-mapping. All patients had
a remote (Ͼ2 months) myocardial infarction, the location of
From the *University of Zurich, Zurich, Switzerland; †Brigham and Women’s
Hospital, Boston, Massachusetts; ‡Swiss Cardiovascular Center, University Hospital,
Bern, Switzerland; §Technion-Israel Institute of Technology, Haifa, Israel.
Manuscript received May 21, 2002; revised manuscript received October 6, 2002,
accepted November 22, 2002.
Journal of the American College of Cardiology Vol. 41, No. 5, 2003
© 2003 by the American College of Cardiology Foundation ISSN 0735-1097/03/$30.00
Published by Elsevier Science Inc. doi:10.1016/S0725-1097(02)02932-7