Regardless of how good catheter ablation is as a treatment for atrial fibrillation, every treatment approach has its set of potential complications. As with all surgical approaches, complication rates are related to surgical skill, experience and the selected method. Although complication rates are low, some complications are more serious than others.
It is estimated that the overall complication rate for ablation of this type of arrhythmia is 3-5%. The most common complication is injury to the veins at the top of the leg where the catheter is inserted and includes bleeding, bruising or more rarely a more severe injury to blood vessels in this area, which can require injection treatment or in rare cases surgery.
The next most common complication is making a small hole in the wall of the heart, usually whilst performing trans-septal puncture or from the ablation catheter itself perforating the atrial wall. Blood will leak out of the heart if a small hole forms but it can seal itself if blood-thinning drugs are reversed and may require no further intervention, although the procedure is usually abandoned. A drain is inserted under the ribs into the sack around the heart if the bleeding does not stop, (known as a pericardial drain). This is required in approximately 1 in every 50 procedures. This takes pressure off the heart by preventing a build up of blood around it and gives it more time for the hole to seal. Drains can usually be removed after 24 hours and patients can go home 1-2 days later. Sometimes a drain isn’t enough if a hole is created and surgery is required. This may only need a relatively small incision under the ribs but more often than not, the chest must be opened to find the bleeding point and close it off. Ironically this may only need one stitch on the heart itself.
Phrenic nerve injury (or palsy) occurs in up to 5% patients udergoing cryo- or laser balloon ablation. It is much more uncommon with radiofrequency ablation but can occasionally occur, rarely. Phrenic nerve palsy causes breathlessness, which can be severe. It almost always recovers but can take up to 9-12 months in some cases, although the norm would be a few weeks.
Stroke can occur as ablation can cause blood to clot within the left atrium, then travel to the brain and cause damage. The risk of stroke has fallen dramatically with two changes to the procedure over the years. The first is the use of irrigated or cooled radiofrequency catheters. These catheters irrigate the tip of the catheter to keep it cool, meaning the energy dissipates into the atrial tissue rather than the blood. Not only does this cause a deeper lesion to develop (better for creating a permanent barrier around a vein) but it also reduces the risk of clot or char formation on the catheter tip.
The second is a change to the technique so that ablation is performed while patients continue to take warfarin (or other blood thinner) rather than stopping it. In the past warfarin was stopped prior to the procedure because of the perceived risk of bleeding if a perforation occured and patients were asked to inject themselves with a short-acting blood thinner called heparin. This actually increases bleeding and clotting complications and studies showed the advantages of performing ablation with warfarin on board. It is still not clear how safe it is to stop or continue the newer anticoagulant drugs for AF ablation (drugs known as novel oral anticoagulants [NOACs]).
Rare complications include perforation of the oesophagus when advancing the TOE probe, or injury to the oesophagus when ablating the back of the left atrium (which lies over the oesophagus). This is a very severe complication, which patients usually do not recover from. Treatment is early surgery to repair the oesophagus/atrium, but this is a major surgical operation with a very high mortality rate. Fortunately, this complication is thought to only occur in 1 in every 1000 patients.
Other rare complications include pulmonary vein stenosis, which is when the entrance to a pulmonary vein becomes narrowed as an effect of delivering ablation energy adjacent to it. If severe narrowing occurs (i.e. 99% narrowing), this can lead to breathlessness or coughing up blood (haemoptysis). This complication is much rarer now due to greater recognition. Physicians now mostly deliver ablation away from the actual vein entrance unless using baloon-based technologies.
A number of randomised trials have shown that ablation is superior to anti-arrhythmic drugs as a first line treatment for paroxysmal AF. Unlike other arrhythmias however, such as atrial flutter or SVT, ablation is still not usually offered before trying at least one anti-arrhythmic drug first. It is felt that as success rates for paroxysmal AF ablation are not as high as ideal and as complication rates are higher than for these more simple arrhythmias, avoiding a procedure in the first instance is probably best. Whether this changes in the future remains to be seen.