An Achieve catheter lies in the SVC above the balloon and above this a deflectable catheter provides phrenic nerve stimulation. Electrograms from the Achieve show disorganized electrical activity in the SVC, conducted to the heart. Cryotherapy (black arrow) results in isolation of the SVC at 8.2 s (white arrow). The heart reverts to sinus rhythm; rapid activity in the SVC continues. SVC = superior vena cava.