Ventricular tachycardia (VT) is an abnormal rhythm arising from the bottom chambers (ventricles) of the heart. The hearts of most patients who develop VT have been previously damaged by a myocardial infarction (heart attack) or other heart muscle diseases (cardiomyopathies). The damage produces scar or fatty deposits that conduct electrical impulses slowly allowing VT to occur. Recurrent episodes of VT can compromise heart function and increase mortality.
VT is prevented by special drugs but these are not always effective and can have many side effects. Most patients with VT will also have a specialised device called an implantable defibrillator (ICD) implanted. The ICD treats VT by either stimulating the heart rapidly or delivering a shock to it. ICDs are very effective but the shocks are painful and have a big impact on quality of life. If VT occurs despite optimal drug treatment, patients undergo an invasive procedure called catheter ablation. Here, wires are passed into the heart from the blood vessels in the leg and the damaged heart muscle causing the VT is identified whilst the heart is in VT. An electrical current is passed down the wire making its tip heat up allowing discrete burns (ablation) to be placed inside the heart. The ablated heart muscle doesn't conduct electricity which stops the VT and prevents it recurring.
Some patients are so frail that ablation cannot be performed safely. A recent clinical trial has shown that VT can be treated in such patients using radiotherapy, which is usually used to treat tumours with high energy radiation. This approach is non-invasive, painless and requires no sedation or anaesthesia.
This study will test whether VT can be successfully treated using stereotactic ablative radiotherapy. This can deliver high dose radiotherapy very precisely, whilst minimising the risk of damage to healthy tissues.
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.
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.
Single group
Stereotactic ablative radiotherapy
RadiationStereotactic ablative radiotherapy will be delivered to a volume of ventricular myocardium responsible for the clinical ventricular tachycardia.
Change in quality of life and cardiac complications as assessed by clinical history, SF-36 questionnaire, electrocardiogram and echocardiography.
The number of serious adverse events at three months after treatment. This will be determined as follows: 1. Clinical history from and examination of the patients assessing for new chest pains, breathlessness or coughing. 2. SF-36 quality of life questionnaire. 3. Echocardiography to assess for pericardial effusion that could indicate radiation-induced pericarditis. 4. Electrocardiogram to assess for pericarditis or myocarditis caused by radiation.
Efficacy endpoint - Cumulative VT burden 6 months before and 6 months after radiotherapy.
There will be a six week blanking period after radiotherapy to allow for ablation effect. The burden of VT will be assessed by interrogating the patient's ICD and assessing the number of episodes of non-sustained and sustained VT as well as the number of ICD therapies delivered.
VT burden
Cumulative VT burden in the second 6 months following radiotherapy. This will be assessed by ICD interrogation as described above.
Survival
Overall survival at 3, 6 and 12 months following radiotherapy.
Cardiac function changes from radiotherapy
Absolute change in numerical left ventricular ejection fraction assessed with echocardiography, at 3, 6 and 12 months.
Radiotherapy impact on ICD function
Deterioration in implantable cardioverter-defibrillator function attributable to radiotherapy at 3, 6 and 12 months. This will be determined by interrogating the ICD and measuring the change in ICD defibrillator lead impedance.
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