Cardiac Sarcoidosis
From a clinical standpoint, cardiac sarcoidosis (CS) may be difficult to differentiate from other forms of NICM, such as ARVC.78 However, patients with CS typically present with more-extensive LV scar and may have septal involvement (which is rare in ARVC), in addition to worse overall long-term ablation outcomes.58,79
In 2006, Koplan et al. reported a 75 % VT recurrence rate within 6 months of ablation in eight patients with CS treated with catheter ablation for incessant VT.55 Two small observational studies showed long-term VT recurrence rates of 43–44 % over median follow-up periods of 10 and 33 months after ablation.56,57 In another study of eight patients with CS, the clinical VTs were successfully abolished in five (63 %).79 While the authors did not specify the recurrence rate of those with failed ablation, only one (20 %) of the five patients with successful ablation had recurrent VT after 6 months of follow-up.79
The largest study of catheter ablation for VT in patients with CS included 21 patients, who tended to have multiple inducible VTs, which were consistent with scar-related reentry.58 Voltage mapping demonstrated confluent RV and patchy LV scarring with a predilection for the septum, anterior wall and perivalvular regions. While RV epicardial scar is usually overlaid RV endocardial scar, this was not the case with the LV. The rate of complete acute procedural success was relatively poor, and freedom from VT after 1 year after a single procedure was only 25 % (37 % after multiple procedures). Ablation was effective, however, in acutely terminating VT storm in seven (78 %) of the nine patients who were referred for incessant VT.58
Repaired Congenital Heart Disease
Compared with other aetiologies of NICM, long-term outcomes in patients with repaired CHD are quite favourable.66 Smaller reports have shown rates of VT-free survival ranging between 75 and 100 % over long-term follow-up (mean follow-up durations ranging between 16–61 months).59–62 In the largest series to date, Kapel et al. reported outcomes in 34 patients with repaired CHD (82 % with repaired Tetralogy of Fallot) treated with catheter ablation targeting anatomic isthmuses containing reentrant VT circuits.63 During long-term followup (mean 46 months), VT recurred in only 11.7 % of cases (0 % in those with complete procedural success versus 44 % in those without complete success), and one patient with poor cardiac function received an ICD shock for VF after ablation.63
Viral Myocarditis
Arrhythmias including VT often occur during the acute phase of viral myocarditis due to the presence of active inflammation. Later, the long-term sequelae of viral myocarditis including fibrosis and scar may predispose to reentrant VT. Imaging with MRI in patients with viral myocarditis has shown that different viruses tend to have different patterns of myocardial involvement.80 Due to the variability of the scar distribution, pre-procedural imaging (MRI or CT) may be helpful when performing VT ablation in these patients. Using an imaging-guided approach, Maccabelli et al. found that patients with myocarditisrelated VT very frequently have epicardial substrate.65 Long-term (median 23 months) freedom from recurrent VT after ablation in their cohort was 77 %. Dello Russo et al. subsequently studied 20 consecutive patients with biopsy-proven viral myocarditis and VT refractory to AADs referred for catheter ablation.64 During long-term follow-up (median 28 months), 90 % of the patients remained free of sustained VT and only two (10 %) patients died from non-arrhythmic cardiac causes.64
Ongoing Trials
There are multiple major ongoing trials that will further examine the long-term outcomes of VT ablation, and others which have been terminated due to difficult enrolment. Four of these ongoing trials include VT ablation versus Enhanced Drug Therapy (VANISH), the Substrate Targeted Ablation Using the FlexAbility Ablation Catheter System for the Reduction of Ventricular Tachycardia (STAR-VT) trial, PARTITA and the BERLIN study. Additionally, several ongoing studies are analysing effects of sympathetic modulation, including bilateral cardiac sympathetectomy (Cardiac Denervation Surgery for Prevention of Ventricular Tacharrhythmias [PREVENT VT])81 and renal sympathetic denervation (Renal SympathetiC Denervation to Suppress Ventricular Tachyarrhythmias [RESCUE-VT] and Renal Sympathetic Denervation as an Adjunct to Catheter-based VT Ablation [RESET-VT])82,83 as adjunct measures to prevent recurrent VT.
The VANISH trial is a prospective observational trial that is aiming to compare ablation versus aggressive AAD therapy in patients with prior MI who present with recurrent VT.84 Included patients will have prior MI with ICD in place, and must have been treated with at least one appropriate ICD therapy, and have failed at least one AAD. Goal enrolment is 260 patients, and patients will be randomised to either ablation or aggressive AAD therapy (high-dose amiodarone or addition of mexilitine). Duration of follow-up is 5 years, and primary outcome is a composite of appropriate ICD shocks, VT storm and death. Secondary outcome is all-cause mortality. The trial has finished enrolling patients and has an estimated study completion date of March 2016.
STAR-VT is an open-label, prospective randomised trial that aims to examine whether scar-based VT ablation results in superior outcomes compared with routine AAD therapy in patients with monomorphic VT in the setting of ICM or NICM.85 Goal enrolment is 1,453 patients, and inclusion criteria include implantation of a St Jude Medical ICD or cardiac resynchronisation therapy device, ≥1 documented monomorphic VT episode (either spontaneous or induced during electrophysiological study or non-invasive programmed stimulation). Patients will be randomised to either substrate-guided ablation using the FlexAbility Ablation Catheter versus routine drug therapy and followed for 1 year. The primary outcome measure will be freedom from any ICD shock (appropriate or inappropriate) for recurrent sustained VT (>30 s) in one year, and secondary outcome measures include number of cardiovascular-related hospitalisations and emergency room visits. This trial is currently enrolling patients and has an estimated study completion date of May 2021.
The third large ongoing trial is the PARTITA trial, which is a large multicentre European trial aiming to determine whether timing of VT ablation after appropriate ICD shock affects long-term prognosis.86 The estimated enrolment is 590 patients who have ICD for primary or secondary prevention. After enrolment, all patients will remain in Phase A until receiving appropriate ICD shock, at which point they enter Phase B in which they will be randomised to immediate VT ablation after appropriate shock versus waiting until VT storm. Followup duration in Phase B is 2 years, and the primary outcome measure in Phase B will be worsening heart failure hospitalisations or allcause mortality. Secondary outcome measures include cardiovascular mortality, electrical storm or VT recurrence during Phase B. This study is currently recruiting patients, and has an estimated study completion date of September 2018.
The BERLIN study is a prospective randomised controlled trial taking place in Germany, which is aiming to enrol 208 patients with prior MI and LVEF 30–50 % who have an ICD indication and documented VT.87 Patients are randomised to either early ablation (immediately following ICD implantation) versus late ablation (after third ICD shock). Primary endpoints include all-cause mortality and hospital admission secondary to cardiac causes, while the secondary endpoint is time to first ICD shock.
Complications
While catheter ablation is an effective treatment option in the management of VT, it is not without risk. A recent meta-analysis reported overall complication rates in 8–10 % of procedures.88 While the majority of complications are related to vascular access, more serious complications, such as stroke or transient ischaemic attack, pericardial effusion or cardiac tamponade and even death, may rarely occur. Furthermore, since VT ablation procedures may be prolonged and significant amounts of fluids may be given during the procedure (particularly when ablating with irrigated catheters), close monitoring of haemodynamic and fluid status is paramount. Acute periprocedural haemodynamic decompensation occurred in 11 % of patients undergoing VT ablation for scar-related VT in one series.89 As such, patients should be medically optimised prior to the ablation procedure, and prophylactic support with percutaneous LV assist devices may be beneficial to facilitate mapping and ablation in certain high-risk patients.90
Timing and Patient Selection
Since ICD shocks are associated with increased mortality and morbidity, VT ablation should be considered in all patients with SHD and recurrent VT refractory to at least one AAD. Retrospective studies have demonstrated improved VT-free survival with an early ablation approach,2,3 and several prospective clinical trials examining timing of VT ablation are currently ongoing, as described above. VT ablation has been shown to have similar safety and efficacy in elderly patients so older age alone should not be a deterrent.21 The potential risks and benefits must be considered in each particular patient prior to deciding whether to proceed with VT ablation. In all patients with VT who have an appropriate periprocedural risk and in whom VT ablation is likely to be successful, we recommend consideration of ablation early in the course of treatment, especially in those who wish to avoid or are intolerant of AADs.