Second-generation cryoballoon ablation for paroxysmal atrial fibrillation: a step forward?

Electrical isolation of the pulmonary veins (PVs) is the established endpoint during ablation of atrial fibrillation (AF) as implemented in the latest European guidelines. 1 Limitations of point-by-point radiofrequency (RF) ablation commonly utilized in combination with a three-dimensional (3D) electroanatomical mapping system led to the development and evaluation of alternative ablation systems and energy sources. The second-generation cryoballoon (CB, Arctic Front Advance, Medtronic, Inc.) is currently the only available ‘single-shot’ ablation tool for pulmonary vein isolation (PVI). Its ‘over-the-wire’ system allows for easy and non-traumatic advancement into the target PV. A spiral mapping catheter (Achieve, Medtronic, Inc.) introduced through the central lumen of the balloon records PV signals and permits live verification of PVI. The cooling system of the first-generation CB consisted of four injection jets in a more proximal balloon position, providing a ring-like zone of maximal cooling along the balloon equator, sparing the distal tip. In clinical use, the first-generation CB demonstrated a high acute success rate combined with a short learning curve. 2 In the Sustained Treatment Of Paroxysmal Atrial Fibrillation (STOP-AF) trial, the acute isolation rate was 97–100% applying a 300 s freeze cycle. 2 The high acute success rate was accompanied by a reasonable safety profile demonstrating an incidence of phrenic nerve (PN) palsy of 6.4%, an incidence of thermal esophageal ulceration of up to 5.2%, and a rate of PV stenosis of 0.9%. 3 However, the long-term single procedure success rate was only 62% and increased to 77% following multiple procedures. 4,5 The addition of two bonus freeze cycles when compared with a single bonus freeze application after successful PVI failed to demonstrate a significant improvement in 1-year clinical outcome. 6 The second-generation CB was introduced to overcome the limitations seen with the first-generation system. Despite an identical outer shape, the balloon incorporates a modified refrigerant injection system with eight injection jets located in a more distal position, providing effective and homogeneous cooling of the complete northern balloon hemisphere including the distal balloon tip. The aforementioned modifications led to the recommended shorter freeze cycle duration of 240 s. Initial studies using the secondgeneration CB demonstrated a high acute success rate with a PVI rate of up to 89% on first attempt. 7 Furthermore, the rate of live verification of PVI increased from 49% using the first-generation CB to 76% using the second-generation system. 8 While the procedural efficacy has increased, Casado-Arroyoetal. 9 reported an unacceptably high rate of PN palsy of 19% using the second-generation CB in their initial series of patients. The concern over a higher rate of PN palsy was not supported by a study from our centre reporting an incidence of 3.5%, which is comparable with the first-generation CB. 10 However, the reported rate of esophageal thermal injury of 12–19% is higher than that for the first-generation CB. 7,11 The first