'Unblinding' the cryoballoon

Abstract

Percutaneous pulmonary vein isolation, with point-by-point elliptical radiofrequency (RF) applications around the pulmonary vein ostia, remains the cornerstone of ablation for atrial fibrillation (AF). 1 The conventional procedure (point-by-point application) is highly dependent on the dexterity and experience of the operator. This implies that large-volume centres have higher success rates, with lower complication rates. 2 Reconnection of pulmonary veins is still the Achilles’ heel of AF ablation. At least one of the veins is reconnected in 50% of the patients undergoing pulmonary vein isolation during a 6-month follow-up. 3 Several limitations of the point-by-point technique can explain the high reconnection rate: non-contiguous lesions can cause tissue oedema, with acute temporary electrophysiological (EP) isolation. When oedema subsides, the vein conduction is unmasked. By this time, the patient is usually out of the EP lab. Longer waiting time, unmasking manoeuvres with drugs (e.g. adenosine, isoprenaline) or new catheter designs to ensure better tissue contact and more effective lesions (e.g. pressure monitoring) have been used, but its utility is still debatable. 4,5 The so-called ‘single-shot’ devices are expected to overcome some of these limitations. They are supposed to enable shorter learning curve, achieving better and safer outcomes, reducing procedure time, radiation exposure, and eliminate the need for three-dimensional mapping. If proved, these devices can allow the expansion of pulmonary vein isolation to a much higher number of centres and patients. 6 Currently available cryoenergy techniques use a cryoballoon to occlude each of the pulmonary veins, theoretically allowing isolation with a single application and assuring continuous lesions (without oedema-related gaps). Distal applications are not always possible, especially when a common ostium is present, increasing the risk of pulmonary vein stenosis and phrenic nerve palsy. In clinical practice, the results with the cryoballoon are not superior to the point-by-point ablation. A recently published systematic review of the cryoballoon trials has shown that in patients with paroxysmal AF, the 1-year freedom from recurrent AF without antiarrhythmic drugs was 73% with a 3-month blanking period and 60% with no blanking period. 7 In many trials, these results could only be achieved with the additional use of an irrigated-tip RF catheter to close gaps in the cryolesion line. It has also been shown that the rate of complications with the use of the cryoballoon is higher than the expected: in the STOP-AF (Sustained Treatment Of Paroxysmal AF) trial phrenic nerve palsy occurred in 11.2%, pulmonary vein stenosis in 3.1%, and cardiac perforation in 1.2%. In regard to the risk of silent cerebral embolism or oesophageal thermal lesion, cryoenergy appears to be non-inferior to the irrigated-tip RF ablation catheter. 8,9 Different experiences among centres may also have impact on the complication and success rates. The currently available cryoballoon system is completely anatomical (‘blind balloon’). To ensure pulmonary vein isolation, an additional circular pulmonary vein mapping catheter has to be used (identical to what is used in the conventional technique). In this issue of the journal, Chierchia et al. 10 compare, for the first time, the use of the ‘blind balloon’ (and a conventional circular mapping catheter) with the Achieve system. The Achieve circular mapping catheter is inserted in the inner lumen of the cryoballoon and placed distally to the catheter. It is used as a supporting guidewire and a circular mapping catheter. Nevertheless, it is important to recognize that the gold standard to assess pulmonary vein isolation is the use of a circular mapping catheter and this new guidewire catheter may not have a similar degree of spatial resolution to record pulmonary vein electrograms as the conventional circular catheter.