Ventricular tachycardia (VT) is an abnormal rapid heart rhythm originating from the lower pumping chambers of the heart (ventricles). The normal heart usually beats between 60 and 100 times per minute, with the atria contracting first, followed by the ventricles in a synchronized fashion. In VT, the ventricles beat at a rapid rate, typically from 120 to 300 beats per minute, and are no longer coordinated with the atria.
VT can also occur in patients with normal hearts, so-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 of 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. 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).
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 (RVOT-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. This form of VT is due to an abnormal nest of cells that fires off erratically to cause either sustained VT or isolated extra beats (called ventricular ectopics). 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 trialed 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 cusps has also been 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 to 5 mm in diameter) to destroy the abnormal tissue. The number of burns required to treat the VT varies among patients.
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 theater 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 usually performed under local anaesthetic with sedative medication rather than under a full general anaesthetic. This will be discussed with you before the 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.
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 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.
You may need to stop taking any medication that you have been prescribed for your abnormal heart rhythm 5 days prior to your procedure. We will discuss this with you. If you are taking anti-coagulation (blood thinning) medication eg warfarin then you will need to stop this for one week prior to your procedure. If this has not been discussed with you, or if you are unsure please call us.
You will be required to fast for at least six hours before the study. If your procedure is in the afternoon you may have a light early breakfast. If your procedure is in the morning, DO NOT EAT OR DRINK AFTER MIDNIGHT, except for sips of water to help you swallow your pills.
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.
The risk of major complications for VT ablation in patients with normal hearts (Idiopathic VT) is <1%.