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.