Sunil Roy T.N., Vikram Sankar, Johnson Francis, Hiroshi Tada, 156
“Tissue Tracking Imaging for Identifying the Origin of Idiopathic Ventricular Arrhythmias:
A New Role of Cardiac Ultrasound in Electrophysiology”
portions of the outflow tract and RF ablation should be attempted at the optimal site of the
outflow tract to cure the OT-VT/PVC. Several non invasive modalities have been used predict
tachycardia focus. However these methods have only modest diagnostic accuracy. Recently,
idiopathic OT-VT/PVC originating from the left ventricular (LV) epicardium (Epi-VT/PVCs)
have been reported.3 Correct identification of the latter type of OT-VT/PVC before the RF
energy applications is important in order to avoid futile RF applications from the left sinus of
Valsalva (LSV) and the ensuing complications.
Several strategies for mapping RVOT VT have been used including activation mapping,
pace mapping, use of basket catheter,4 and non contact mapping systems.5 Precordial R wave
transition, QRS morphology in lead I, R wave duration and R/S amplitude of lead V1 or V2
have been reported as useful indices for differentiating OT-VT/PVCs originating from the right
side from those originating from the left side.6 However some overlap for each index was noted
between these two groups especially in children.7 Activation mapping can be used in sustained
arrhythmias and pace mapping in case where clinical arrhythmia is unstable. Pace mapping and
activation mapping are still the preferred methods to guide ablation in majority of cases of
RVOT-VT as their effectiveness have been well proven. Non contact mapping provides a global
endocardial activation map to guide ablation.8 However RVOT is a complex and narrow three
dimensional structure. There is safety concern of positioning the non contact mapping catheter
in such a narrow area.9
Recently, tissue tracking imaging (TTI) has been demonstrated as a novel non-invasive
modality for identifying the origin of OT-VT/PVCs.10 TTI is an ultrasonographic technique that
measures the myocardial motion amplitude toward the transducer in each region during systole,
identifying regional myocardial displacement on the basis of myocardial velocities using color
Doppler myocardial imaging principles.11 It allows rapid semiquantitative visual assessment of
the systolic distance of the tissue motion along the Doppler axis using a graded color display. In
this technique, the origin of the OT-VT/PVC could be recognized as the site where the earliest
color-coded signal (ECCS) appeared on the myocardium at the onset of the OT-VT/PVC. ECCS
was always found below or at the level of the pulmonary valve in all arrhythmias which could
be ablated from the RVOT whereas the OT-VT/PVCs in which the earliest ventricular activation
was recorded from the LSV had the ECCS in the myocardium above the pulmonary valve, and
some of them in which the ECCS appeared above the pulmonary valve could be ablated from
the LSV. These results indicate that TTI can provide detailed and accurate information on the
arrhythmia origin of OT-VT/PVCs and may be useful for differentiating between an OT-
VT/PVC originating from the LV epicardium remote from the LSV and that from the LSV.12
Tissue tracking imaging is a new ultrasonographic technique that measures longitudinal
myocardial motion amplitude in each region during systole, demonstrating regional myocardial
displacement on the basis of myocardial velocities using color Doppler myocardial imaging
principles.13 Thus, it visualizes the velocity-time integrals (VTI) of different regions in a color,
2D mode online, together with the systolic wall motion. Tissue tracking displays the integral of
the tissue velocity during systole, which equals the distance motion along the Doppler axis
during systole. There are seven colour bands that indicate different distances of motion with a
stepwise increase in the distance of the motion. The site of the arrhythmia origin was defined as
the site at which the earliest colour coded signal (ECCS) appeared in the myocardium during the
first beat of the ventricular tachycardia from all of the obtained images.
In the article by Tada H et al10, TTI was performed in 33 patients with idiopathic
ventricular arrhythmias before radiofrequency catheter ablation. The ECCS during the
arrhythmia was easily identified from the echocardiography by tissue tracking in all patients.
Indian Pacing and Electrophysiology Journal (ISSN 0972-6292), 5(3): 155-159 (2005)