Mk. Chung et al., 3-DIMENSIONAL MAPPING OF THE INITIATION OF NONSUSTAINED VENTRICULAR-TACHYCARDIA IN THE HUMAN HEART, Circulation, 95(11), 1997, pp. 2517-2527
Background Elucidation of the electrophysiological mechanisms of nonsu
stained ventricular tachycardia (VT) in humans is required to define t
he relationship between nonsustained VT and sustained VT. This goal re
quires, at least in part, analysis of transmural ventricular activatio
n in patients with both sustained and nonsustained VTs. Methods and Re
sults We analyzed three-dimensional intraoperative cardiac maps of ext
rastimuli and beats during 44 nonsustained VTs and the initiating beat
s of 6 sustained VTs from six patients with healed myocardial infarcts
who were undergoing arrhythmia surgery. The coupling interval, total
activation time, and diastolic interval of each extrastimulus and beat
of nonsustained VT were compared with counterparts during sustained V
T. Sites activated last during extrastimuli initiating nonsustained or
sustained VTs occurred in the same region, and activation times were
comparable. However, the site of earliest activation during the initia
l or subsequent beats of nonsustained VT was discordant from the site
activated earliest during the first and subsequent beats of sustained
VT in 74% of cases. The mean variance in coupling interval, but not to
tal activation time or diastolic interval, was significantly greater f
or VT that terminated before the 10th cycle than for VT that sustained
. When analyzed from the last extrastimulus up to the fifth VT cycle,
the standard deviation of the coupling interval, but not of the total
activation time, was greater for nonsustained than for sustained VTs.
Electrode density was sufficient to define an arrhythmia mechanism for
36 beats of nonsustained VT. Twenty-one (58%) initiated in the subend
ocardium, midmyocardium, or epicardium by a macroreentrant mechanism,
and 15 (42%) initiated in the subendocardium by a focal mechanism. Con
clusions Compared with sustained VT, nonsustained VT initiates at disc
ordant sites, is characterized by oscillations in coupling interval bu
t not in total activation time, and initiates by either a macroreentra
nt or a focal mechanism.