Abstract
BACKGROUND: Elucidation of the electrophysiological mechanisms of
nonsustained ventricular tachycardia (VT) in humans is required to
define the relationship between nonsustained VT and sustained VT.
This goal requires, at least in part, analysis of transmural ventricular
activation in patients with both sustained and nonsustained VTs.
METHODS AND RESULTS: We analyzed three-dimensional intraoperative
cardiac maps of extrastimuli and beats during 44 nonsustained VTs
and the initiating beats 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 VT. 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 initial 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 total activation time or diastolic
interval, was significantly greater for 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 subendocardium,
midmyocardium, or epicardium by a macroreentrant mechanism, and 15
(42\%) initiated in the subendocardium by a focal mechanism. CONCLUSIONS:
Compared with sustained VT, nonsustained VT initiates at discordant
sites, is characterized by oscillations in coupling interval but
not in total activation time, and initiates by either a macroreentrant
or a focal mechanism.
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