Ventricular Tachycardia (VT)

Ventricular tachycardia (VT) is a heart rhythm problem where the lower chambers of the heart (or ventricles) beat very rapidly. This can often be very serious because the ventricles are responsible for the majority of the hearts function and it can cause them to beat so rapidly that their ability to pump blood is very poor and this can lead to a cardiac arrest. VT may be caused by a few myocytes (heart cells) that fire off more rapidly than normal but more commonly it occurs due to short circuits in the ventricles that travel through and around regions of scar tissue (1). This scar tissue is usually the result of a previous heart attack or due to a cardiomyopathy (weakness in the hearts muscle).

VT Ablation

Ablation for VT involves passing 2 or 3 catheters up the femoral vein and inferior vena cava to the heart if the VT is coming from the right ventricle or passing a catheter up the femoral artery and aorta if the VT is coming from the left ventricle (rarely other approaches such as accessing the outside of the heart are also needed). To see exactly where the catheter is in the heart an electro-anatomic mapping system (like a GPS) uses a magnetic field across the chest to track the movement of the catheter to the nearest millimetre (see picture 2 below). It is common to pace the heart rapidly to induce (bring on) the patients VT in these ablations so that the critical areas of the heart can be identified and zeroed in on for treatment. Alternatively, if VT is hard to induce at the time of ablation then another approach is to target all of the ‘short circuits’ that can be identified within scarred areas of the heart to reduce the chances of it reoccurring.

Ablation is an important treatment for patients with VT that is causing dizziness or fainting, shortness or breath, chest pain or defibrillator shocks. A number of studies have shown that ablation is superior to medications in treating resistant VT. In the VANISH study, VT ablation was superior to increasing medical therapy at reducing the combined endpoint of mortality, VT storm (>2 episodes of VT in 24 hours) and defibrillator shocks (2). Possible complications of VT ablation in patients with structural heart disease (scar in the heart) include a 1% risk of stroke/TIA, 1% risk of heart attack, 1% risk of bleeding around the heart and 1-2% risk of vascular injury/bleeding in the groin (2). Like all electrophysiology procedures a VT ablation can be performed with local anaesthetic and sedation or general anaesthetic and the average procedure time is 2-4 hours.

References:

1. Jackson N, Gizurarson S, Viswanathan K, et al. Decrement Evoked Potential Mapping: Basis of a Mechanistic Strategy for Ventricular Tachycardia Ablation. Circulation Arrhythmia and electrophysiology Dec 2015;8:1433-1442.
2. Sapp JL, Wells GA, Parkash R, et al. Ventricular Tachycardia Ablation versus Escalation of Antiarrhythmic Drugs. The New England journal of medicine Jul 14 2016;375:111-121.

The diagram above shows a schematic of the four chambers of the heart and the normal conduction system in yellow. In the left ventricle the blue arrows show a ‘short circuit’ through a channel within scar tissue causing ventricular tachycardia (VT). The black shapes represent regions of scar tissue and VT circuits usually travel in and around regions of scar to cause very rapid heart rhythms and sometimes a cardiac arrest. As described above, ablating these channels within areas of scar tissue can be performed to treat patients with VT. Ventricular tachycardia can also be caused by a ‘hot focus’ or a few cells in the heart that fire off more rapidly and more frequently than they should. In the diagram above the purple star in the right ventricle represents a hot focus where electrical activity spreads out from causing VT. This could also be treated by moving a catheter into the heart, across the tricuspid valve and onto the site of the focus to cauterise it.

Above is an image of the left ventricle and aorta created by the Rhythmia® electro-anatomic mapping system. The picture on the left shows the pathway of electrical activation during ventricular tachycardia in blue with arrows (the short circuit). The picture on the right shows the regions of healthy heart muscle in purple and scarred heart muscle in grey (intermediate regions are shown in other colours). Healthy heart muscle records a normal voltage signal through the ablation catheter. Ablation at the site of the black star terminated ventricular tachycardia (VT) in this patient.