Resumen de Ablation of ventricular tachycardia in patients with structural heart disease:impact of arrhythmic substrate location and presence and abolition of late potentials
Introduction An implantable defibrillator is protection against sudden death, but recurrent ventricular tachycardia (VT) is associated with worse outcomes.1,2 Catheter ablation has an important role in reducing the frequency of VT episodes and in case of electrical storm (ES) catheter ablation has proven to be an effective therapy in the acute setting and in long-term outcome.3,4 The majority of inducible VTs in these patients are unmappable. A variety of alternative substrate-based methods have evolved, to overcome the shortcomings of activation and entrainment mapping.5-9 The purpose of the present studies focused on VT late after myocardial infarct (MI) was to analyze the endo-epicardial electroanatomical mapping (EAM) voltage and morphology characteristics in order to describe the appropriateness of each substrate ablation strategy, the interrelationship of EAM characteristics, their association with clinical data and their prognostic value in a large cohort of post-MI patients undergoing EAM-based catheter ablation for VT.
Previous studies provided the evidence that low voltage area is associated to re-entrant circuit giving rise to ventricular arrhythmia also in non-ischaemic cardiomyopathy (NICM), as it was well established for ischaemic cardiomyopathy (ICM).10-11 This finding sets the rationale for the use of a substrate-based approach for ablation in NICM, as it is the case of ICM. However, although the substrate is the same for NICM and ICM (i.e. scar related to re-entrant circuit), there are many characteristics that differentiate NICM substrate when compared to ICM. The role of VT catheter ablation in patients with NICM has not been analyzed in details as much as in patients with ICM; therefore issues worthy of explanations remain unsolved, such as the optimal ablation strategy, epicardial substrate identification, predictors of recurrence, long-term recurrence. The purpose of our studies is to shed light on these problems, which affect short- and long-term management of patients with NICM. Particular attention required CRT carriers affected by ES as they constituted a sicker population with high risk of haemodynamic impairment.
Theoretical course Ischaemic Population In the first study (Non-Inducibility and Late Potential Abolition: A Novel Combined Prognostic Procedural Endpoint for Catheter Ablation of Post-infarction Ventricular Tachycardia. Silberbauer J, Oloriz T, Maccabelli G, Tsiachris D, Baratto F, Vergara P, Mizuno H, Bisceglia C, Marzi A, Sora N, Guarracini F, Radinovic A, Cireddu M, Sala S, Gulletta S, Paglino G, Mazzone P, Trevisi N, Della Bella P. Circ Arrhythm Electrophysiol. 2014 Jun;7(3):424-35) we described the outcome of VT ablation in a large study (160 patients) of post-ischaemic patients and the role of non-inducibility and late potential abolition as end-points for the procedure. The second study (Electroanatomical Voltage and Morphology Characteristics in Post-Infarction Patients Undergoing Ventricular Tachycardia: A Pragmatic Approach Favoring Late Potentials Abolition. Tsiachris D, Silberbauer J, Maccabelli G, Oloriz T, Baratto F, Mizuno H, Bisceglia C, Vergara P, Marzi A, Sora N, Guarracini F, Radinovic A, Cireddu M, Sala S, Gulletta S, Paglino G, Mazzone P, Trevisi N, Della Bella. Circ Arrhythm Electrophysiol. 2015 Aug;8: 863-873) analyzed 100 patients with drug-refractory VT late after myocardial infarction. It showed the full range of infarct represented by the electoanatomic maps (endo and epicardial), segmented following the 17-segment model. The scar presence and distribution (bipolar and unipolar) and electrogram characteristics (early and late potential) are detailed described and its characteristics correlated with short- and long-term prognosis after VT ablation.
Non-Ischaemic Population Patients are divided accordingly to unipolar scar predominance on EAM into antero-septal (AS) and infero-lateral (IL) scar pattern and further sub-divided into dilated cardiomyopathy (DCM) and early cardiomyopathy (ECM) according to structural (LV dimension) and functional criteria (LVEF cut-off 45%). The first study (Catheter Ablation of Ventricular Arrhythmia in Non-Ischaemic Cardiomyopathy: Anteroseptal versus Inferolateral Scar Sub-Types. Oloriz T, Silberbauer J, Maccabelli G, Mizuno H, Baratto F, Kirubakaran S, Vergara P, Bisceglia C, Santagostino G, Marzi A, Sora N, Roque C, Guarracini F, Tsiachris D, Radinovic A, Cireddu M, Sala S, Gulletta S, Paglino G, Mazzone P, Trevisi N, Della Bella P. Circ Arrhythm Electrophysiol. 2014 Jun;7(3):414- 23.) focused on VT ablation strategy and outcomes, whereas the aim of the second study (The Value of the Twelve-Lead Electrocardiogram in Localizing the Scar in Non-Ischaemic Cardiomyopathy. Oloriz T, Wellens HJJ, Santagostino G, Trevisi N, Silberbauer J, Peretto G, Maccabelli G, Della Bella P. Europace doi: 10.1093/europace/euv360 [Epub ahead of print]) is to correlate the ECG findings with the endo-epicardial voltage maps performed for the purpose of substrate ablation and identify the ECG characteristics that may help to distinguish the scar as anteroseptal or inferolateral.
Cardiac resynchronization therapy and ventricular tachycardia In this study and the corresponding editorial (Electrical Storm Induced by Cardiac Resynchronization Therapy is Determined by Pacing on Epicardial Scar and Can Be Successfully Managed by Catheter Ablation. Roque C, Trevisi N, Silberbauer J, Oloriz T, Mizuno H, Baratto F, Bisceglia C, Sora N, Marzi A, Radinovic A, Guarracini F, Vergara P, Sala S, Paglino G, Gulletta S, Mazzone P, Cireddu M, Maccabelli G, Della Bella P. Circ Arrhythm Electrophysiol. 2014 Dec; 7(6):1064-9. Cardiac Resynchronization Therapy–Induced Proarrhythmia. Understanding Preferential Conduction Within Myocardial Scars. Bradfield JS, Shivkumar, K.) the mechanisms why the cardiac resynchronization therapy may induce electrical storm are presented. Patient population includes consecutive patients undergoing VT ablation with a CRT in place. A detailed description of prevalence, predictors, clinical presentation, management and prognosis is carried out along the study.
Conclusion Ischaemic and non-ischaemic population differ in terms of arrhythmia substrate and VT outcome in the setting of VT ablation. In the ischaemic subgroup, there were 50 (32%) patients with VT recurrences out of 160 patients undergoing first-time ablation. Patients who fulfilled the combined end point of VT non-inducibility and LP abolition compared with inducible patients exhibited a significantly lower incidence of VT recurrence (16.4% versus 47.4%). Only 38 patients (24%) were discharged on amiodarone and a total of 86% on a conventional β-blocker therapy. In contrast, our data regarding non-ischaemic population shows unsatisfactory results for catheter ablation, both in terms of VT recurrence (approximately 50% during a mean follow-up of 1.5 years), which although in line with previous studies, is nevertheless suboptimal, and cardiac death. Notably, it is the scar pattern, not the degree of LV impairment that affects recurrence rates and cardiac death. In particular, The AS scar pattern has the highest VT recurrence and redo procedure rates, evident even in patients with preserved LV function. Overall, epicardial approach was undertaken in 20% of the ischaemic population and 74% of the non-ischaemic population. For post-infarction patients, of utmost importance, our study shows that the size of endocardial bipolar dense scar area is the best predictor of epicardial bipolar DS. Specifically, scar transmurality should be suspected when dense scar area exceeds 10% area of endocardial surface area. In the setting of NICM, AS type, the epicardial approach is not useful because of septal substrate, complex local anatomy, proximal left anterior descending artery, and prominent epicardial fat (ablation was performed in only 14% of these patients; 4 of 28 epicardial maps). This finding sets the rationale to proceed with a first-line epicardial approach in cases where the ECG pattern or imaging suggests an inferolateral pattern, because half of mappable VTs require epicardial ablation and three quarters of patients have epicardial LPs. The ablation of both AS and IL scar pattern is hampered by different technical limits. Fifty percent of IL patients who underwent epicardial procedure had overlying coronary arteries or phrenic nerve in proximity to ablation targets. Therefore, image integration for coronary artery, either with angiography or coronary CT angiography and testing for phrenic nerve capture are mandatory, the latter eventually followed by balloon inflation lifting of phrenic nerve.5,6 AS patients often have a complex, deep intramural substrate characterized by little bipolar scar area, bigger unipolar scar and few LPs. The complex substrate is highlighted by high number of VTs per patients with slight changes in morphology during ablation, suggestive for many exit sites and different isthmi within the scar. Such a deep substrate is hardly targeted with unipolar RF delivery and it is often required high energy RF ablation on both sides of the septum. Although VT termination is frequently observed during the procedure, recurrences are frequent. Importantly, post-ablation programmed stimulation is not a reliable tool to predict recurrence. High recurrence rate is due to the deep intramural scar, which poses difficulties both in the detection of isthmus and prevent the deployment of effective and long lasting lesions because of the limited (<5mm) penetration of unipolar RF energy, even in case of irrigated-tip catheters at high power.
According to the scar distribution in NICM, described in MRI and voltage mapping studies, the majority of patients showed a predominant AS or IL scar pattern. Similarly, post-infarction scars affect the coronary territories of the culprit artery, either anterior, inferior or inferolateral wall. Consequently, most of the candidates for a CRT implant appertain to the AS-DCM group or have a prior anterior or anteroseptal infarction. The scar located in the septum would length the QRS, results in LBBB or advanced AV block. This may explain the low incidence of CRT-induced pro-arrhythmia as the scar need to be very extended involving both the septum, to create the conduction disturbance, and the epicardium, following the hypothesis that an LV lead positioned on epicardial scar could be a determinant of proarrhythmia; or either be secondary to an ablate and pace strategy. This would imply also a sicker population, explaining the high prevalence of heart failure and cardiogenic shock associated to the VT episodes/ES. Besides, the haemodynamic status would be worsened by switching off LV stimulation.
CRT-induced proarrhythmia is an uncommon but life-threatening complication of CRT implantation frequently causing ES and hemodynamic deterioration. In primary prevention, CRT-induced proarrhythmia was defined as VT or ES within 1 month of implantation. In secondary prevention, proarrhythmia was considered positive if there had been no VT in the previous 3 months and ES occurred within 1 month of implantation. From 64 CRT patients undergoing ventricular tachycardia ablation CRT-induced pro-arrhythmia occurred in eight. Half of patients with proarrhythmia presented with acute HF or cardiogenic shock. A relationship between the LV lead position and any-epicardial scar was found in 4 of 5 (80%) patients with proarrhythmia versus 4 of 23 (17%) patients without proarrhythmia (P=0.02). Ablation was performed within epicardial scar, close to the LV lead, and allowed CRT reactivation in all patients.
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