Premature ventricular contractions or PVCs are ectopic beats (extra beats) that come from the lower chambers of the heart (the ventricles). A PVC may come from anywhere within the hearts ventricles but some places are more common such as the top of the heart or the ‘outflow tracts’. PVCs can make a persons heart beat feel irregular or can be felt as a ‘pause’ followed by a more ‘forceful’ heart beat due to changes in the time the heart has to fill with blood with each beat. PVCs are a relatively common cause for palpitations and they can often be quite benign but in some people they may cause symptoms such as palpitations, dizziness or shortness of breath. In the setting of very frequent PVCs (usually more than 10,000 a day or ≥10% of total heart beats) they can lead to impairment in the heats ability to pump blood (a cardiomyopathy or worsening of an existing cardiomyopathy). It is common to try an antiarrhythmic medication for patients with frequent PVCs or symptoms from PVCs initially, however, if this is not effective or the medication causes unwanted side effects then an ablation procedure may be recommended.
A PVC Ablation
Ablation for PVCs involves passing 2 or 3 catheters up the femoral vein and inferior vena cava to the heart if the PVC is coming from the right ventricle or passing a catheter up the femoral artery and aorta if the PVC is coming from the left ventricle. To see exactly where the catheter is in the heart an electro-anatomic mapping system uses a magnetic field across the chest to track the movement of the catheter to the nearest millimetre (see picture 2 below). This means if a patient is having a sufficient number of PVCs then by moving the catheter around the heart the exact origin of the PVC can be zeroed in on for ablation. The potential risks from a PVC ablation depend on the region it is coming from but in general the risk of a potentially serious complication such as bleeding around the heart, heart attack or stroke (PVCs from the left side of the heart only) is ≤1% and the risk of bleeding or injury in the groin where the catheters are inserted is 1-2%.
A PVC ablation might take between 1 and 4 hours and is usually performed with local anaesthesia and sedation because general anaesthesia can temporarily suppress the PVCs themselves (put the PVCs to sleep as well). If a patient is having a lot of PVCs at the time of the procedure then it is generally faster and easier to zero in on its precise location. The long term success rates for PVC ablation with a single procedure range between 50-90% and depend on the region of the heart it is coming from and as mentioned the frequency that the PVC is happening on the day of the procedure.
The diagram above shows a schematic of the four chambers of the heart and the normal conduction system in yellow. Premature ventricular contractions (PVCs) are usually caused by a ‘hot focus’ or a few cells in the heart that fire off more rapidly and more frequently than they should. The purple star represents a PVC focus and the electrical activity then spreads out across the heart from there. This could be treated by moving a catheter into the heart, across the tricuspid valve and onto the site of the focus to cauterise it. In the left ventricle the blue arrows show a schematic for a ‘short circuit’ involving some scar tissue from within the heart. These short circuits can cause PVCs as well and may also be targeted by catheter ablation.
Above is a picture of the right ventricular outflow tract (the top portion of the right ventricle just before the pulmonary artery). By carefully moving the ablation catheter around this region of the heart we can zero in on the exact region that a premature ventricular contraction (PVC) is coming from. The earliest region (the exact place the PVC is coming from) is shown in red here and the ablation catheter (also shown) can then be manoeuvred back to this position to perform ablation (cauterization) and terminate this PVC.