The trials found that ultralow temperature cryoablation is feasible and shows excellent safety and efficacy. The clinical outcomes for flutter ablation show a 94% success rate at three months.
Ultralow temperature ablation uses near-critical nitrogen. The catheter operates at the near critical point between liquid and vapour for nitrogen, or –196°C. Liquid nitrogen can’t circulate through a small 8-French catheter below the liquid vapour line because evaporation of the liquefied gas results in enormous expansion up to a factor of 200, causing vapour lock, explained lead investigator Tom De Potter (Cardiovascular Center, Onze-Lieve-Vrouw Hospital, Aalst, Belgium).
“If you increase the pressure in the catheter dramatically up to the critical point of nitrogen, this phenomenon disappears. The gas no longer expands from the heating and it allows you to use these ultralow liquid nitrogen temperatures in a percutaneous catheter. This is what this technology does,” he says.
This decreased viscosity allows for a smaller sized catheter to be used than is used in conventional cryoablation. The catheter can also be changed to different shapes, allowing for personalised ablation and a more targeted procedure.
Both trials were two-centre, prospective and observational. Cryocure I looked at typical right atrial flutter in 17 patients and were followed up at three months. The cryocure II trial looked at paroxysmal, long standing persistent atrial fibrillation (AF) in 27 patients who were followed up at 12 months. Oesophageal warming balloons were used for all catheters, and no tamponade, fistula, or mechanical adverse events were reported.
In Cryocure I, bidirectional isthmus block was achieved after a 30-minute waiting period in all 17 patients, with the flutter catheter pouch approach used in 14.
The average ablation time to bidirectional isthmus block was 2.7±3.2 minutes, including a 14-second bonus freeze to the bidirectional isthmus block. The best-case scenario was bidirectional isthmus block real-time isolation in one patient in 14 seconds, De Potter says.
On average, 2.8±3.2 applications were used to reach bidirectional isthmus block with 12±5.0 minutes of X-ray time, resulting in a total procedure time of 85±16.0 minutes, including the 30-minute waiting period.
As for acute safety, there was one transient STsegment elevation, presumed due to right coronary artery spasm that lasted for two minutes with no sequelae on further evaluation.
At three months, 94% of the 17 patients were free of recurrence. Additional electrophysiology studies conducted in three patients for other reasons at three and 12 months confirmed cavotricuspid isthmus block in all.
For Cryocure II, the 27 patients (63% male; mean age, 64 years) had a history of AF for an average of 29 months, and had, on average, a left atrial diameter of 46±6mm. Extreme left atrial diameter was an exclusion criterion.
Pulmonary vein isolation (PVI) ablation was performed in all 27 patients and cavotricuspid isthmus block in seven of the 10 patients with persistent AF. At the discretion of the physician, left atrial posterior wall isolation was also performed in seven patients.
PVI was achieved in 101 of 105 veins (95%), with the procedure aborted after isolation of one of four veins in one patient after the catheter malfunctioned and a replacement was unavailable.
Posterior wall and/or cavotricuspid isthmus block isolation was achieved in all seven patients, adding an additional five minutes of ablation time. The total procedure time averaged 134 minutes.
Among 13 patients treated with PVI only using the first-generation catheter and no cryomapping, there were two cases of phrenic nerve palsy that persisted for some time, but with full recovery.
Among 13 patients treated with PVI with or without linear lesions using the second-generation catheter, there were no complications.