Procedures

Ventricular Tachycardia (VT) occurs most commonly in patients with structural heart disease such as weakened heart muscle (cardiomyopathy) or when scar tissue develops in the heart as a result of myocardial infarction. In this situation the mechanism is usually due to re-entry circuits formed within areas of abnormal scar.

VT can also occur in patients with normal hearts, called “Idiopathic Ventricular Tachycardia” and this accounts for about 10% of all VTs. Idiopathic Ventricular Tachycardia is usually due to a different mechanism than VT seen in the presence of structural heart disease. Idiopathic VT is usually due to a small nest (focus) of overly excitable heart tissue that fires off erratically, like a muscle twitch.

Overall, this form of VT generally has a much better prognosis that VT in the presence of structural heart disease and is not usually associated with a risk of sudden cardiac death. High-risk patients (recurrent syncope and sudden cardiac death survivors) with inherited ion channelopathies predisposing them to VT benefit from the insertion of an implantable cardioverter-defibrillator (ICD).

This form of VT is due to an abnormal nest of cells (a ‘focus’) that fires off erratically to cause either sustained VT or isolated extra beats (called Ventricular Ectopics). Idiopathic VTs can originate from a variety of locations such as the inside surface of the heart (endocardial), deep within the ventricular muscle (mid-myocardial), the outside surface (epicardial) of the heart, in the aortic valve or in the veins surrounding the heart. The most common form of Idiopathic VT is right ventricular outflow tract VT (so called “RV outflow tract -VT”). It accounts for approximately 70% of idiopathic VTs. The right ventricular outflow tract is the top portion of the right ventricle and is situated just below the pulmonary valve. Some idiopathic VTs also form in the aortic valve (aortic cusps) or just beneath the aortic valve in the left ventricle, these are called left ventricular outflow tract VT (LVOT-VT).

There are 2 main treatment options for VT in patients without structural heart disease, medications or catheter ablation. For RVOT VT medications may be prescribed to suppress VT such as beta-blockers (Metoprolol or Atenolol) or calcium channel blockers (Verapamil or Diltiazem), however these medications only have a 25-50% rate of efficacy. Alternate therapy includes anti arrhythmic medications such as Flecainide, Sotalol and Amiodarone can also be trialled if simple beta-blockers or calcium channel blockers are ineffective. Amiodarone, the most effective drug, has many side effects, which can involve toxicity to the vital organs like the liver, thyroid, lungs, eyes, and skin.

Catheter ablation of RVOT-VT now has cure rates approaching 90%, which makes it a preferable option given the young age of patients with RVOT VT. Ablation of other outflow tract sites such as the aortic valve cusps has also been very successful. Catheter ablation is an excellent choice for patients when medications are not effective, tolerated, or preferred.

The aim of this procedure is to target the abnormal focus of the VT by placing a long, thin wire or catheter into the heart chambers through the veins of the leg. When the VT focus is identified, radiofrequency energy is applied to a small area (4 – 5 mm in diameter) to destroy the abnormal tissue. The number of burns required to treat the VT varies among patients.

You may need to stop taking medication that you have been prescribed for you abnormal heart rhythm and anti-coagulation medications will need to be stopped 24 hours prior to your procedure. However, this will be discussed with you prior to your procedure. If this has not been discussed with you, or if you are unsure, please contact the Rhythm and Cardiac Specialists.

You will be required to fast for at least six hours before the study. You will be notified by the hospital the day before your procedure to confirm your admission and fasting times. The clinics nurse will contact you one week prior to your procedure to discuss medications and answer any questions you may have leading up to your procedure.

You will be transferred to the Electrophysiology Laboratory (EP lab) from your ward. Usually before leaving your ward your groin will be shaved. The EP lab has a patient table, X-Ray tube, ECG monitors and various equipment. The staff in the lab will all be dressed in hospital theatre clothes and during the procedure will be wearing hats and masks.

Many ECG monitoring electrodes will be attached to your chest area and patches to your chest and back. These patches may momentarily feel cool on your skin.

A nurse or doctor will insert an intravenous line usually into the back of your hand. This is needed as a reliable way to give you medications during the study without further injections. You will also be given further sedation if and as required. You will also have a blood-pressure cuff attached to your arm that will automatically inflate at various times throughout the procedure.

The procedure is mostly performed under local anaesthetic with sedation for patients with normal hearts. Patients requiring a VT ablation with structural heart disease, such as cardiomyopathy require a general anaesthetic. However, this will be discussed with you prior to your procedure.

If the procedure is performed under local anaesthetic, the doctor will inject the anaesthetic to the area in the groin where the catheters are to be placed. After that, you may feel pressure as the doctor inserts the catheters, but you should not feel pain. If there is any discomfort, you should tell the nursing staff so that more local anaesthetic and sedative medication can be given.

The catheters are inserted through intravenous ports, or sheaths, placed in the veins in the groin and sometimes through a vein on the side of the neck. To access the left ventricle, a catheter can be inserted into the heart via the aorta through an artery in the groin (similar to heart catheterization procedures). Alternatively, a needle may be used to create a small puncture in the wall between the right and left sides of the heart under ultrasound guidance (called transseptal catheterization). If the left ventricle is mapped, a blood thinning medication called Heparin is given intravenously to decrease the risk of stroke during the procedure. The ablation catheter is moved around the ventricle, and a virtual 3-dimensional image of the heart is created with a computer mapping system that acts like a navigation system. The location of the catheter is determined by use of fluoroscopy (X-ray) and a 3D mapping system.

Electrical Mapping of the Heart

The catheters are positioned in your heart using X-Ray guidance. Once the catheters are in place you may feel your heart being stimulated and usually your abnormal heart rhythm will be induced. It is very important that we can induce the VT or the ventricular ectopics at the time of the procedure as we can only map the focus of the VT when it is active. The success of the procedure is determined by the ability to map the VT or ventricular ectopics on the day.

We will routinely use a three-dimensional computer mapping system to guide the ablation procedure. This will help us move the catheters in your heart without the need for X-rays and also help us create an electrical map to localize the focus of the VT. You will be given a form of intravenous adrenaline to stimulate the VT.

When the VT focus has been identified and the abnormal tissue localized, the radiofrequency ablation will be applied to this spot. This may cause a transient warm discomfort in the chest. If the focus of the VT is near the aorta, a coronary angiogram will be performed prior to any ablation to ensure the coronary arteries are not damaged. Radiofrequency ablation procedures for idiopathic VT usually take approximately 2-3 hours.

Afterward, the catheters are removed, but the sheaths are left in until the blood thinner wears off. Typically, this requires the patient to lie still for several hours to prevent bleeding from the puncture sites. Slight discomfort and bruising in the groin area can occur, and some patients experience self-limited mild chest pain resulting from inflammation caused by the ablation lesions. When the procedure is successful, antiarrhythmic medications may be stopped at the discretion of the physician.

A blood test must be taken to determine when the blood thinners have worn off. Once the blood test is within range, the sheaths will then be removed. During this time, it is important to keep your legs straight and your head relaxed on the pillow.

You will stay in hospital overnight and your heart rhythm will be monitored during this time.

The groin area may feel sore and bruised for several weeks after the procedure. You should avoid strenuous physical activity and sports for 2 weeks after the procedure until this has settled. Most people take approximately 1 week off work.

The risk of major complications for VT ablation in patients with normal hearts (Idiopathic VT) is ~3%.

Major risks of the procedure include but are not limited to:

• The risk of major vascular complications (arterio-venous fistula, pseudo aneurysm, dissection) which may require surgery is less than 1 %
• The risk of stroke or transient ischemic attack is less than <1%
• The risk of damage to the heart wall causing bleeding in the sac around the heart (cardiac tamponade) requiring drainage with another catheter or urgent cardiac surgery is less than 1%.
• The risk of death during this procedure is very low < 0.1% (1/1000)
• If the VT focus is close to the coronary artery there is a risk of damaging the coronary artery and causing a heart attack. A coronary angiogram is always performed prior to ablation if the focus is thought to be close to the aortic valve and coronary arteries.
• Damage to a major artery (aorta) or heart valve is extremely rare (These complications may require urgent vascular or open-heart surgery to correct).