Main Findings
We evaluated the VT recurrence in patients in whom VT non-inducibility could not be achieved at the end of the RF ablation and the factors attributing to the VT recurrence in ICM and NICM patients.
The main findings of our study were:
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During the follow-up period of 2 years, 65% of the patients in whom VT non-inducibility was not achieved at the end of RF ablation had no recurrence.
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Patients whose LVEF was more than or equal to 35%, and those in whom partial success was achieved as an acute ablation efficacy were independent predictors of fewer VT recurrences in the multivariate analysis.
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Even in patients with VT recurrences, VT ablation could significantly reduce the VT burden.
Endpoint of the VT ablation
It is known whether VT non-inducibility at the end of the VT ablation is less likely to be associated with a VT recurrence6,7, and achieving the combined endpoint of the abolition of the abnormal electrograms and VT non-inducibility further reduces VT recurrence.8,9 In the present study, 20 patients in whom VT non-inducibility was achieved had a small VT recurrence rate of 15%. However, we need to consider the risk of overtreatment at the same time; the enlargement of a scar area by RF ablation may lead to a more depressed cardiac function. There is not enough detailed reporting on the subsequent events in patients with residual VT inducibility at the end of the procedure. In our study, patients having an LVEF ≥ 35% or partial success were independent predictors of VT non-recurrence in patients in whom VT non-inducibility was not achieved. This may indicate that we should try to eliminate the clinical VT as much as possible, and that in this group of patients, inducible residual non-clinical VT is acceptable.
LV dysfunction and VT recurrence
In this study, the recurrence rate was lower in the patients with an LVEF ≥ 35%, even with residual VT inducibility. In a sub-analysis of the AVID (Antiarrhythmics Versus Implantable Defibrillator) trial, the efficacy of ICD therapy was reported to depend on the degree of LV dysfunction in patients with secondary prevention of sudden cardiac death, and in patients with an LVEF < 35%, ICD therapy had an advantage. On the other hand, in patients with an LVEF ≥ 35%, the efficacy of the ICD therapy was equivalent to that of antiarrhythmic drugs.12 Also in a recent trial, Groeneveld et al. reported that in 42 patients with an LVEF > 35% and a hemodynamically non tolerated VT, only 6 patients (14.3%) had VT recurrences, and all were hemodynamically tolerated.13 That suggests that the classification by the degree of LV dysfunction may make sense, and may help determine how aggressively induced VT should be treated.
Patients with an EF < 35% are considered to have more myocardial dysfunction and are more likely to have multiple arrhythmia substrates. Although a more aggressive induction and ablation may be necessary to reduce the VT recurrence rate in them, the dilemma is that patients with such a reduced cardiac function may be more susceptible to hemodynamic compromise and invasive procedures with a prolonged operative time. In the present study, the VT burden was significantly reduced even in the group with an EF < 35%, suggesting that a balanced protocol that ensures safety is desirable.
Importance of a successful ablation of all clinical VT isthmuses
Previous randomized multicenter trials have shown that substate ablation reduces any VT recurrences during the follow-up as compared to targeting only a clinical and stable VT, making substate ablation a basic strategy for VT ablation.14–16 In the present study, the elimination of the clinical VT in addition to a substate ablation was shown to be associated with fewer VT recurrences. Hadjis et al. reported that the identification of the VT isthmus in addition to a substate ablation significantly reduced the recurrence rate (HR 0.21, 95% CI: 0.07–0.63, P < 0.01).17 Cano et al. also reported that a baseline inducibility of greater than 1 VT morphology was an independent predictor of VT recurrence (HR 12.05, 95% CI: 1.60-90.79, P = 0.02) and complete activation mapping was associated with a reduction in the VT recurrence.18
In this study, patients in whom VT non-inducibility could not be achieved at the end of the RF ablation were included, so in many cases, VT was induced with or without hemodynamic stability at the end of the RF ablation. Nevertheless, a successful ablation of all clinical VTs was correlated with non-recurrence, suggesting that the identification of the VT isthmus is important in addition to the basic strategy for a substate ablation.
VT burden reduction
The term "recurrence" has been used to evaluate the outcome of the ablation therapy, however, recently the concept of a VT burden reduction has been proposed.19, 20 The VT burden can be more valuable in terms of the clinical benefit than recurrence as a dichotomous event. In the present study, the VT burden was reduced by 91.1% even in patients in whom VT non-inducibility could not be achieved at the end of RF ablation, and VT ablation significantly reduced the number of VT episodes and shock therapies. Although the design of the current study did not allow us to examine the prevention of mortality, a reduction in the ICD shock therapies may improve the patient survival.21