Currently patients suffering Ventricular Tachycardia (VT) are offered drugs, such as
Amiodarone, Implantable cardioverter defibrillatorf (ICD) implant and catheter ablation.
Although effective drugs have side effects, ICD shocks are painful and catheter ablation is
arduous for patients at high risk of complications. Catheter ablation is currently the gold
standard treatment for recurrent VT despite anti-arrhythmic drugs (AADs).
Catheter ablation (CA) was initially developed in the 1980s following the successful
treatment of VT by surgical resection of myocardial scarring in structural heart disease.
After thorough clinical evaluation and medical stabilization, imaging is performed to
identify culprit areas for ablation and to stratify risk of intervention. Pre procedural
imaging in patients with ICDs in situ involves Echocardiography, Computerized Tomography (CT)
scanning and Positron Emission Tomography (PET) imaging in order to assess cardiac function,
ischemia, inflammation and scarring. If necessary mechanical circulatory support, Left
Ventricular Assist Devices (LVAD) and/ or Extra Corporeal Membrane Oxygenation (ECMO) can be
used to sustain cardiac output during VT induction and mapping.
Radiofrequency (RF) energy delivered via catheter to the arrhythmogenic target results in
local resistive heating and is performed under sedation or anesthesia using multiple
catheters placed in the heart while the patient is anticoagulated. Conventional approaches
involve advancing multiple catheters via Femoral veins and/or arteries under a combination of
fluoroscopic, ultrasound and electroanatomic guidance. Ablation targets include an
arrhythmogenic focus or the critical isthmus of the VT circuit and/ or substrate identified
on preprocedural imaging or low voltage areas, "scar", identified during endocardial mapping.
CA procedures for VT are often long, averaging 5 hours duration reported in clinical trials,
with prolonged procedures being associated with adverse outcomes and 30 day complication
rates, including death, of 7- 13%.
Vulnerable patients requiring circulatory support or at high risk of recurrence and death
following catheter ablation can be identified pre-operatively. Of all patients undergoing CA
for VT, more than a third are "high risk" with a one year risk of death of >20%. Patients
older than 65 with prior catheter ablation and recurrent VT with impaired left ventricular
ejection fraction ≤35% have 90 day VT recurrence rates of 30% and mortality of 20%.
Patients with comorbidities such as Diabetes or COPD and those presenting in VT storm are
also at high risk of hemodynamic compromise and death following Catheter Ablation. Without
prophylactic LVAD placement, patients at high risk of haemodynamic instability (PAINESD score
≥ 15) suffer 30% death at thirty days with 41% VT recurrence post CA. It is these "high risk"
patients that we believe will benefit from a non-invasive RA approach.
Patients undergoing a non-invasive Radio-Ablation (RA) procedure for VT similarly require
medical stabilization and multimodal imaging prior to treatment. Instead of an invasive
catheter-based electrophysiology study (EPS) and ablation, a non-invasive EPS (NIPS) is
performed under light sedation using ECGi mapping. This short procedure, averaging 40
minutes, requiring only the placement of an IV cannula for light sedation, uses the ICD to
stimulate VT which is mapped in real time using the CardioInsight ECGi mapping system.
The multimodal imaging data is digitally fused and then combined with the ECGi data to
identify the VT circuit(s) and to target the arrhythmogenic tissue for radio-ablation. This
analogue process is performed off- line by a committee of Cardiac Imaging and EP
Cardiologists and a Radiation Oncologist. Once the target(s) are identified, the treatment
plan is sent to Medical Physics for alignment on a 4D planning CT performed with breath
holding in the radiotherapy suite. Final treatment targets are reviewed by the local treating
team and discussed with our collaborators in St Louis. Thereafter the patient is booked for a
15 minute out-patient radiotherapy treatment performed on a standard linear accelerator.
Photon radiotherapy, as commonly used in cancer therapeutics across Canada, is guided using a
cone beam onto the cardiac target(s). A single fraction of 25 Gy is delivered painlessly over
15 minutes. Although minor side effects have been reported, serious adverse events are rare
and no ICD related issues have been described. No deleterious effects on cardiac function
(LVEF) have been observed although approximately (5/65? TBC) patients have required a two
week course of oral glucocorticoid therapy for symptomatic inflammation such as pericarditis
or pneumonitis post RA25. All patients are treated with Rivaroxaban 20 mg po as prophylaxis
against thromboembolism for thirty days post RA.
Radioablation is a novel procedure and long-term outcomes remain unknown. Reduction in VT is
reported to be 85-92% up to 6 months post RA and in the ENCORE -VT study 17 of 19 patients
were free from ICD shocks at 6 months. In the only prospective study of RA for VT, patients
reported an improvement in quality of life in 5 of 9 domains remaining unchanged in 4. Long
term safety data continue to be collected but cardiac irradiation <40 Gy has been
historically associated with an approximate 1% excess mortality over years to decades in
those receiving treatment for breast or lung cancer. This is in the context of a total
mortality of 28% over 24 months of follow up in those undergoing CA for recurrent VT in
Canada.