Sunil Roy T.N., Vikram Sankar, Johnson Francis, Hiroshi Tada, 157
“Tissue Tracking Imaging for Identifying the Origin of Idiopathic Ventricular Arrhythmias:
A New Role of Cardiac Ultrasound in Electrophysiology”
The site of the arrhythmia origin, defined as the site where the ECCS appeared on the
myocardium at the onset of the arrhythmia, corresponded to the site of origin as determined on
fluoroscopy during activation mapping in all patients. TTI provided detailed and accurate
information on the arrhythmia origin, especially in the outflow tract and facilitates catheter
ablation of idiopathic ventricular arrhythmias. Radiofrequency energy delivery at the site where
the earliest ventricular activation was recorded abolished 29 arrhythmias. Among the 7
arrhythmias in which ECCS were found in the myocardium above the septum, 5 arrhythmias
were successfully ablated from the left sinus of Valsalva. The distance between the attachment
of the pulmonary valve to the septum and the center of the ECCS (8±4 mm) in these OT-
VT/PVCs with a successful ablation from the LSV was significantly shorter than that in those
with a failed ablation (18±6 mm, p<0.05).12 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.
However some questions remains to be answered before it can be considered as the
modality of choice. Tissue tracking imaging has limitations inherent to tissue Doppler imaging
technique.14 In the cardiac motion there are translational, rotational and deformational
movements. Besides, many tissues near the heart move due to transmitted cardiac motion, vessel
pulsation and respiratory motion. In addition if the initial activation occurs in a plane
perpendicular to interrogating plane, tissue tracking may show tissue displacement starting
from adjacent areas due to tethering movements.15 This issue is further complicated in patients
with regional wall motion abnormalities. We need to further perform the procedure during the
ablation procedure to see whether the ablation site correspond exactly to to the site at which
ECCS were recorded.
Myocardial deformation can be assessed from the B mode images by automated point
wise tracking of speckle patterns. It has the advantage of angle independence and may be
superior to tissue Doppler based techniques for strain estimation.16 Whether speckle tracking
imaging will be useful for identifying breakthrough points of excitation in different arrhythmias
and accessory pathway localization needs to be evaluated. High resolution, high frame rate real
time three dimensional echocardiography with speckle tracking imaging may be the modality for
precise localization of arrhythmias in the future.
Electrical phenomena and its surrogate, the propagation of myocardial contraction, are
three-dimensional events with variable sites of origin and distribution patterns. Next generation
maps must be able to map the full thickness of the atrial and ventricular wall. One major
challenge in clinical electrophysiology is to precisely visualize target cardiac structures and
simultaneously depict electrical events. Using intracardiac ultrasound with high TDI frame rates,
TDI is suitable for displaying more rapid changes in tissue motion related to the onset and
propagation of electrical excitation in the myocardium at a very early stage with high temporal
resolution. This ultrasound imaging technique should have an important impact on the diagnosis
and management of cardiac arrhythmias. Such technology will foster simultaneous single
modality visualization of anatomy, function and electrical events for the purpose of refining the
proper intervention.
References
1. Coggins DL, Lee RJ, Sweeney J, Chein WW, Van Hare G, Epstein L, Gonzalez R, Griffin JC,
Lesh MD, Scheinman MM. Radiofrequency catheter ablation as a cure for idiopathic
Indian Pacing and Electrophysiology Journal (ISSN 0972-6292), 5(3): 155-159 (2005)