Stereotactic Ablative Radiotherapy for the Treatment of Refractory Ventricular Tachycardia

Principal objectives:

• To determine the safety and efficacy of stereotactic ablative radiotherapy (SABR) for the treatment of VT refractory to conventional therapies.

Background:

VT is an abnormal heart rhythm arising from either of the bottom chambers of the heart (ventricles). Most patients with VT have scarring or fatty deposits in the heart muscle caused by a previous heart attack or a heart muscle problem called a cardiomyopathy. The abnormal heart muscle conducts electricity slowly allowing VT to occur. Most patients with VT have a device called an implantable defibrillator (ICD) fitted to treat VT. The ICD has wires going into the heart from a small generator that is inserted under the skin below the left collar bone. ICDs stop VT by stimulating the heart rapidly or by shocking the heart which is very painful and can stun the heart temporarily, weakening its pumping function. Patients who experience a lot of VT can have more admissions to hospital, worsening heart failure and a poorer quality of life, as well as a higher risk of dying. Consequently, all patients are treated with drugs to prevent VT but these are not always effective. If VT keeps recurring, many patients undergo an invasive procedure called catheter ablation where wires are passed into the heart from the leg and the part of the ventricles causing the VT identified. A high frequency electrical current is then passed down one of the wires making its tip heat up allowing discrete burns (ablation) to be placed on the culprit area, which stops the VT and prevents it from recurring. Performing catheter ablation in such patients is a high risk procedure and the overall complication rate is between 5 - 15% in experienced centres. Some patients have recurrent VT despite catheter ablation or the VT cannot be ablated because the patient is too frail, or the VT causes a significant fall in the blood pressure resulting in cardiac arrest (heart stops beating).

In the last 6 years, several case reports and series have been published showing that radiotherapy using different types of linear accelerator machines (including the Cyberknife) can successfully and safely ablate VT. Most recently, a prospective, randomised trial (ENCORE-VT) has reported a dramatic reduction in VT following radioablation.

This study will therefore assess our ability to perform stereotactic radioablation for VT at St Bartholomew's Hospital. We will determine procedural success and safety. Patients will be assessed 3, 6 and 12 months after the treatment and their burden of VT determined by checking the ICD.

Inclusion criteria

• They are at least 18-85 years old.
• They have recurrent VT (at least three episodes in the preceding six months) requiring therapy from an ICD, that is refractory to conventional treatments - both maximally tolerated doses of anti- arrhythmic drugs and/or conventional catheter ablation.
• They are too frail or do not wish to undergo conventional catheter ablation.
• They have not had previous radiotherapy to the anticipated treatment field.

Exclusion criteria

• They have polymorphic VT or ventricular fibrillation (VF).
• They have inotrope-dependent heart failure or a left ventricular assist device (LVAD) in situ.
• They are unlikely to live more than 12 months irrespective of the VT.
• There is a potentially reversible cause for the VT e.g. critical coronary artery disease or a metabolic problem such as an overactive thyroid gland.
• They are unable to provide informed consent.
• They have had previous radiotherapy to the anticipated treatment field.
• The patient weighs in excess of 170kg (maximum weight capacity of the tables in the imaging department).