Reply to Colli and Romero-Ferrer.

ing of electrical conduction across the ablation lines. With bipolar radiofrequency (RF) clamps, the PV cuff is physically clamped and burned repeatedly in order to achieve 'acute' conduction block. A question for further reflection is: are we achieving block at that moment because of local tissue trauma and inflammation resulting from simultaneous crushing and burning of the PV cuff and is that block durable? Indeed, Benussi et al. [2] have shown previously that despite achieving block acutely with bipolar RF clamps, the veins often recover their ability to conduct (at 3 weeks in 15% of ablated patients). It has been hypothesized that HIFU lesions may take time to scar in and mature. The mode of cell death for this energy source may differ from that of RF and thus may not always be instantaneous. Villamizar et al. [3] have demonstrated that HIFU ablation achieved 100% transmurality. In our experience of using HIFU in 70 cases, we have observed thought-provoking clinical results. The freedom from recurrence of AF after ablation was 82% at 1 month, 90% at 1 year and 100% at 3 years in patients presenting with preoperative parox-ysmal AF and undergoing concomitant open heart cardiac surgery with creation of only a box lesion and no additional ab-lation lines. Those patients were also free from anti-arrhythmic drugs at the time of follow-up. Those impressive results, however, were not observed in patients presenting preoperative-ly with permanent AF, showing a freedom from recurrence of AF of 42% at 1 month, 54% at 1 year and 62% at 3 years. Our experience suggests that in order to achieve good clinical results using the HIFU ablation system it is important to use it in the right patients. In our experience, those patients presented with paroxysmal AF with normal or mildly dilated left atria (area <30 cm 2 ; volume <68 ml). We consider a simple box lesion sufficient to achieve a good postoperative clinical result. In patients with permanent AF, a more complex approach should be applied to treat an evolved histopathological condition of the atria. We believe that the HIFU epicardial ablation system is a high-performing treatment modality creating transmural lesions in the left atrium and yielding good clinical results. Perhaps it is time to revisit the theory of acute conduction block! et al. Reproducibility of left atrial ablation with high-intensity focused ultrasound energy in a calf model. Keywords: Surgical ablation • Atrial …