The upper left panel shows the 28-mm diameter cryoballoon and the octapolar circular catheter, used to measure real-time isolation of the pulmonary veins. In the lower left panel, fluoroscopic image showing the balloon catheter inflated in the ostium of the right superior pulmonary vein of the third case. Contrast retention inside the vein indicates vessel occlusion. Observe the circular catheter inside the vein and the decapolar catheter (arrow) placed in the upper right atrium for phrenic stimulation. In the right panel, intracavitary tracings showing the isolation of the same vein. From top to bottom, surface electrocardiogram (leads I, II, III, aVF, V1 and V6); electrograms recorded inside the vein by the circular catheter (ACH 1, 2 ACH, ACH 3, 4 ACH, ACH 5 and ACH 6); atrial and ventricular electrograms collected by the catheter positioned in the bundle of His (His D and His P); and electrograms of the two pairs of distal electrodes of the decapolar catheter in upper right atrium. Observe the sudden disappearance of the pulmonary vein potentials (arrows) 40 seconds after application of cryoenergy, indicating electrical isolation. The asterisks indicate the spicules of the continuous phrenic nerve stimulation by the catheter in the upper right atrium at 60 bpm cycles. Observe that the stimulation also commands the atria. Tracings at 50 mm/second.