Evolving patterns of ventricular tachycardia modifying our mapping techniques

The introduction of the implantable cardioverter defibrillator (ICD) and the demonstration of its leading role in the prevention of sudden death over the last 20 years, aside from the indisputable benefits, have caused a negligent attitude of the electrophysiologists towards the use of catheter ablation in patients suffering from recurring ventricular tachycardias (VTs). In the recent years, however, the increasing number of patients surviving potentially lethal ventricular arrhythmia, and the awareness of the negative impact of VT recurrences and shock treatment on survival, is triggering an increasing interest by the Electrophysiological Community towards catheter ablation, as a truly effective treatment strategy.^1–6

Initial studies were focused on mapping of post-myocardial infarction (MI) VTs.^7–12 Extensive knowledge on mechanism of re-entry in this setting was accumulated and proper criteria on activation mapping and pacing manoeuvres were established to identify the effective ablation site aimed to the termination of the index VT and the prevention of its re-inducibility.^7–9 Subsequently, for many years, the prevention of any inducible VT was considered an even more effective endpoint.^10–13 At this point, however, catheter ablation of VT was conceptually a ‘focal’ intervention with an endpoint far different from the complete removal of the arrhythmogenic substrate that was the purpose of anti-arrhythmic surgery.¹⁴

The following factors limit the predictability of this approach: As a consequence, the endpoint for ablation is shifting from the single VT target, to the two-dimensional and three-dimensional assessment of the functional properties of the arrhythmogenic substrate and its modification, which aims to the abolishment of the onset and maintenance of any VT.^16,17 Recent evidences, based on the admission that late potentials during sinus rhythm are found in an area critically involved in re-entry maintenance during VT, are strongly supporting late potential abolition as a feasible, safe, and effective procedural endpoint, as far as the ablation efficacy may be easily assessed by remapping during sinus rhythm after ablation ^18–20 To this point, the analysis of substrate by high-density contact or non-contact mapping techniques in the future may prove to be of great interest.

1. Only in a minority of cases the induced VT is haemodynamically tolerated to allow extensive activation mapping and pacing manoeuvres (<20% in our series).

2. The exact definition the ‘clinical’ form of the target VT is difficult to achieve, since in most instances the intra-cardiac electrograms provided by device interrogation are the only means to document the occurrence of a given VT; VT information of rate criteria is obtained only upon ICD interrogations in a progressively increasing number of patients (45% in year 2010 at our centre).

3. The absence of baseline VT inducibility limits the predictive value of post-ablation inducibility test.

4. Reproducibility of VT induction is related to the induction protocol and post-ablation inducibility predictive value of long-term recurrences is unreliable.^13,15

Among 568 patients admitted for VT ablation in the setting of structural heart disease at our centre, in the last 4 years, the majority were known for coronary artery disease (55%), which has historically been the most studied underlying heart disease; however, the incidence of non-ischaemic substrates is becoming more frequent (idiopathic dilated cardiomyopathy in 27%, arrhythmogenic right ventricular dysplasia/cardiomyopathy in 6%, myocarditis in 4%, valvular heart disease in 3%, hypertrophic cardiomyopathy in 2%). The approach to many different kinds of arrhythmogenic substrates encouraged the evolution of ablation techniques, the development of new  strategies for VT mapping of non-ischaemic substrates, and the need for expert operators.

One of the most important advances that took over during the last years has been the awareness for the need of epicardial mapping and ablation in non-ischaemic and, to a minor extent, post-MI VTs.^21,22 The application of percutaneous epicardial access is, however, rather heterogeneous even among centres with a VT programme, due to the validation and generally low level of confidence of most operators and the perception of as a potentially harmful manoeuvre. The technologies of epicardial access, navigation, and ablation are, at present, equivalent to those used in intra-cardiac access; further developments will be required to refine the epicardial use.

Our experience showed a strong impact of heart failure on long-term morbidity and mortality of patients who underwent VT ablation. Future trends will be linked to peri-procedure and intra-procedure haemodynamic support with intra aortic balloon counterpulsation and extra corporeal membrane oxygenation in cases of cardiogenic shock and left ventricular assist devices implantation, often necessary as temporary or destination therapies in severely decompensated patients.

The growing interest towards VT mapping and ablation is prompting also active involvement in VT research programmes. In this collection of papers we would like to expose clinical and technical experience of some centres deeply involved in VT ablation, with the purpose to state how new technologies impact on procedural success and outcome improvement.

Conflict of interest: P.D.B. has grant cosultancy fee from St Jude Medical, Biosense Webster, Biotronik; Research grant from Biosense Webster, St Jude Medical, Biotronik, Medtronic. F.B. has no conflict of interest to declare.

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