This study involves recording electrical signals inside the heart during an ablation procedure. It is thought that by studying these electrical signals in detail the investigators may be able to better identify and treat patients at risk of Ventricular Tachycardia (VT).

VT is where the lower chambers (ventricles) of your heart beat fast and this condition can be life-threatening. An ablation procedure is performed in patients who have VT despite the best treatment available with tablets.

Cardiac ablation involves interrupting the abnormal electrical signals, which cause VT, by applying a type of electrical energy through a catheter. An important part of the ablation procedure is the identification of the exact part of the heart muscle responsible for causing the VT. This typically involves sampling the electrical signals in lots of different areas of the heart, which allows the construction of computer generated 3 dimensional pictures of the structure and the electrical circuits inside the ventricle. Recent research has identified a new method to interpret these electrical signals (called Fibrillatory Factor - FF), which may allow better identification of the area within the ventricle that should be ablated.

A standard VT ablation will often involve us controlling the heart-beat by pacing the heart through 1 of the investigators catheters within the heart. The electrical response to pacing at different heart rates can often provide your doctor with information to help the ablation. This study will involve an additional period of pacing at different heart rates, during which the electrical response is measured in different areas around the ventricle. This will allow us to calculate areas of the ventricle, which the investigators new measure FF would predict to be the source of the VT. In the future this may then allow us to better identify patients who are at risk of VT, and to better locate the area that needs to be ablated.

Inclusion Criteria:

• Age 18 or above, and capable of giving informed consent
• Scheduled for a clinically indicated cardiac ablation for the treatment of ventricular tachycardia

Exclusion Criteria:

• Moderate or severe aortic stenosis or mitral stenosis
• Active infection
• Presence of thrombus, cardiac tumour, interatrial Baffle patch (a specific form of congenital cardiac surgery) or prior septal occluder device
• Subjects who cannot be anticoagulated of infused with heparinized saline
• A history of heparin induced thrombocytopenia
• Pregnant or actively breast feeding