4.1 VT termination
In our study, the successful VT termination rate using ATP was 85%,
which is equivalent to those reported in previous
studies.19,20 In cases of faster VT, the rate was
lower since a faster VT has a shorter excitable gap in the reentrant
circuit; hence, it is more difficult for the pacing stimulus to enter
the circuit.21 VT classification, based on the
variability of the VT cycle length, revealed that the successful
termination rate following ATP therapy was 94% in regular VTs and 65%
in irregular VTs with statistical significance. We observed that VTs
with stable cycle length variability are more likely to respond to ATP
therapy.
Spontaneous termination after ATP delivery or without therapy was found
significantly more often in irregular than in regular VTs. Spontaneous
termination after ATP delivery can include purely spontaneous
termination and termination due to overdrive pacing, which is a
characteristic finding of non-reentrant mechanisms.22
Furthermore, no significant differences were found between patients with
ischemic and non-ischemic cardiomyopathies with respect to VT
termination using ATP therapy. Scar-related reentry is the most common
cause of sustained VT in the presence of structural heart
disease.23 In patients with structural heart disease,
myocardial infarction is most commonly associated with a damaged
myocardium, which serves as a substrate for reentrant arrhythmias.
However, scar-related VT also develops in other myocardial diseases,
including dilated cardiomyopathy, sarcoidosis, and arrhythmogenic right
ventricular cardiomyopathy, and after cardiac surgery for congenital
heart disease or valve replacement.17 The scar slows
conduction and increases susceptibility to reentrant arrhythmias.