How should new technologies be assessed?
The huge growth in AF ablation, and the complexity of the procedure has led to great interest in the development of new technologies to try and make the procedure quicker, safer and more effective. Whether one technology or technique is superior to another can only be proven in randomised controlled trials. This is a clinical trial where patients suitable for treatment are randomly allocated to receive one of two treatments being tested. The reason that patients must be randomly allocated is to prevent bias (both conscious and subconscious) on the part of the researcher. For example, if a researcher has been involved in developing a new technique they may have a tendency to allocate patients more likely to have a good outcome in that treatment and the more difficult patients in the rival treatment. Randomisation avoids this bias.
How are new technologies assessed?
It may surprise you to know that while new technologies have to undergo rigorous safety testing before being approved for use they do not have to be shown to be superior to existing treatments. Therefore many new technologies have not even been shown to be superior to placebo or medication in randomised trials. The claims made for technologies are often based on uncontrolled series of patients or even theories developed from observation in animal experiments. Therefore when deciding on how you wish your AF ablation to be performed it is important to know not what technology the doctor uses but what their personal results are and how many they have done. If your doctor is not collecting their follow up results in a rigorous manner they don’t really know what their results are, and therefore whether the technology they use actually works. If your doctor does know what their results are then you should be guided by them as to what technique they feel works best for them.
Our experience over the last 20 years has meant that the range of technologies we use at the London AF centre has decreased as we have become more selective of the technologies that work consistently and are safest.
What new technologies are available?
The most common method for AF ablation used today is to perform point-by-point RF ablation to create a wide encirclement of the veins (see catheter ablation).
Multiple randomised trials have shown that this technique is superior to drug therapy and therefore it is reasonable to use this as the gold standard to judge other therapies and techniques by. Alternative approaches have focused on using alternative energy sources, or technologies to make delivery of the RF easier.
We rarely use RF for our first procedure for AF ablation because the applications are precise but limited in size. This makes applying a consistent line of ablation time consuming, technologically difficult and because of this the results are less consistent. We will often use it for repeat procedures where we are looking for limited and focused areas where tissue has recovered its electrical activity after a 1st AF ablation.
The cryo balloon is usually our first choice for AF ablation and has been used in over a million patients around the world over more than 15 years. We therefore have a very good understanding of its success rates and both its short and long-term (none identified to date) risks. It comprises of a balloon on the end of a catheter which is inflated in the left atrium and then pushed up against each of the pulmonary veins in turn. When the balloon is against the vein it is then frozen by passing gas through the catheter. Where the balloon is in contact with the vein it causes freezing of the tissue and cell death. This renders the tissue electrically inert. The damage caused by cryoablation is less traumatic than RF and therefore it is less likely to cause damage to the veins. Unsubstantiated claims that cryo is less likely to cause stroke have never been proven. In addition cryoablation can be associated with damage to the nerve that stimulates the diaphragm (the phrenic nerve) in 1% of patients (this number is probably now dropping because of new technological innovations) but this does not usually cause symptoms and in all published reports has recovered within 12 months. The potential problem with cryoablation is that it only works if the balloon is in contact with the tissue and while the balloon is perfectly circular, the pulmonary veins are not. Modifications of the cryoballoons now mean it is very rare to have to use additional catheters or RF ablation to complete the procedure. Our team performed the first randomised study to demonstrate that cryo ablation is superior to RF ablation in patients with paroxysmal AF https://www.ncbi.nlm.nih.gov/pubmed/26727045 . For this reason, it is our technology of choice for first time paroxysmal AF patients.
PFA or fulguration is a re-designed energy modality that was originally used to perform ablation over 30 years ago. In its current form it offers the same control as radiofrequency but without the need for firm catheter contact with the tissue. This offers the opportunity to design catheters that can perform the pulmonary vein isolation in a few treatment applications. Its advantage over cryoablation is that it may be more cardiac specific and less likely to cause nerve damage. The disadvantage to cryo is that is has been around for much less time and the full long term effects of it are not known. It also may potentially be less effective because it does not appear to reset the heart rate by modifiying the autonomic neural ganglia that control the heart rate that may be one of the mechanisms of success for ablation, particularly in patients with vagally mediated AF (AF that tends to come on with large meals or while patients are in bed).
To see Prof Schilling’s results click here