Freezing the heart is in the news. The STOP-AF trial was presented at ACC, and it sure has generated much excitement about atrial fibrillation ablation. This is a good thing.
However, as is the norm in the era of instantaneous news, the press reports read much differently than reality. The propaganda has an effect. I read one comment from an AF patient, who said he was waiting approval for the Arctic Front balloon before undergoing ablation. Hope his AF isn’t too symptomatic.
Before launching the party favors, here are some musings from the “real world.”
On success rates:
The WSJ, LA Times and Medpage report either 98% success or 70% success rates. These are misleading; the details are important. When using only the cryo-balloon, the pulmonary veins (PVs) were isolated in only 90% of cases. Meaning, in expert hands, one in ten patients had to have a standard RF catheter inserted to complete the PV isolation.
Success in initial PV isolation does not equal successful elimination of AF:
In STOP-AF, the technical success of complete PV isolation with both RF and balloon catheters was 98%. This is the same as we achieve now with radiofrequency catheter ablation, but, and it is a huge but, AF recurrence rates are high. In the study, the successful elimination of AF with a single procedure was only 60% –with two procedures it was 70%. This is about equal to, or slightly lower than what is achieved with present day RF ablation.
Historically, one of the knocks on cryo-ablation is the higher recurrence rate after ablation. In far less complicated ablations, like PSVT or typical atrial flutter, these higher recurrence rates of cryo-ablation therapy have limited its widespread acceptance. STOP-AF’s 40 percent AF recurrence rates speaks to either the impermanence of the PV isolation, or the fact that cryo-balloon isolation is more distal in the vein, thereby missing areas that are presently ablated with the more proximal RF approach.
Herein lies the largest concern. Although, the overall complication rate in STOP-AF was 6%, there are some very concerning specifics. Cryo-ablation is unique in its propensity for injuring the right phrenic nerve. This is really bad. The phrenic nerve innervates the diaphragm which is the primary breathing muscle. Paralysis of it causes shortness of breath, which is one of the same symptoms of AF –the disease one is trying to eliminate. In most, but not all cases, the paralysis resolved after an entire year. Ouch.
The reason for the paralysis can be explained anatomically. The phrenic nerve courses a few millimeters outside the left atrium adjacent to the right sided pulmonary veins. Radiofrequency lesions are never performed inside the veins, rather in the left atrium proper. Therefore, RF lesions do not injure the right phrenic nerve. Six years and hundreds of cases, and I have never seen it.
On the other hand, cryo-balloon isolation of the right sided veins is deeper in the pulmonary vein. This allows for the potential of collateral damage to the nerve, as evidenced by the 29 phrenic nerve injuries (of only 200 cases) in STOP-AF. This, in the hands of experts. When the less experienced masses get hold of the new balloon, the incidence of complications will surely rise.
Trust a cyclist on this one, AF is better than paralysis of the diaphragm.
Every January for the past number of years, I have attended the Boston AF symposium. This same balloon technology was presented many years ago, and the results were similar –including phrenic nerve paralysis. The balloon technology is essentially the same, so I wonder why this data is now generating so much positive press. Could it be that the Arctic Front system is now owned by a fortune 500 medical device company, or that the study was industry funded?
PV isolation is clearly the best ablation strategy for intermittent drug refractory AF, and the cryo-balloon will likely facilitate this presently labor-intensive process. We could use it to isolate the left sided pulmonary veins, and in some cases, the right sided veins may also be amendable. It is clear though, in many cases, an RF catheter may need to be employed in the same procedure. Two catheter technologies in one procedure equates to double the instrument costs, not to mention different sized balloons –each of which will surely be billed separately.
Remember all, this is America, and in our health care system, a new technology from a fortune 500 medical device company will not be cheap. Consider that, even a straight forward SVT ablation is already very expensive. We do PV isolation in 2-3 hours with less than 20 minutes of xray time. The hospital purchasers of equipment will undoubtedly look askance at the marked increase in the cost of adding a second ablation system to complete the job presently done by one. They might even ask about the incidence of phrenic nerve paralysis, or the lack of superiority of success rates compared to RF ablation.
To show superiority of the cryo-balloon, it needs to be compared head to head with RF catheter ablation. We already know PV isolation is superior to medicine in the drug refractory symptomatic AF patient. Also, a future comparative study would have greater clinical relevance if it involved ablators who toil in the “real” world.
Exciting new tools –yes, for sure. But, as is frequently the case, the details are important, and not often elucidated in the immediacy of the press reports.