Figure 2.

Electrophysiology study findings. A: Circular mapping catheter (Ls) in the right superior pulmonary vein (RSPV). The first beat is a sinus beat followed by the premature atrial complex (PAC). The RSPV recorded early far-field atrial electrograms (arrow) followed by recording of pulmonary vein potential (arrowhead) during the PAC. This is suggestive of origin of tachycardia in an adjacent chamber—in this case, the right atrium (RA) or the superior vena cava (SVC). B: Circular mapping catheter (Ls) in the SVC. The first beat is a sinus beat showing 2 sets of signals on the Ls catheter. In order to determine the origin of these signals, pacing is performed from the high RA using the ABL catheter (second beat). The first set of signals (arrow) are “pulled into” the pacing spike with capture of the RA, demonstrating that this represents right atrial signal. The remaining electrogram is thus identified as the SVC potential (arrowhead). C: Circular mapping catheter in the SVC. The first beat is a sinus beat followed by a PAC. The right atrium (arrow) is activated first in sinus rhythm, followed by the SVC potential (arrowhead). This relationship is reversed during PAC, with activation of the SVC potential occurring prior to activation of the right atrial signal. The phenomenon of “reversal of the near-field and far-field electrogram” proves that the “chamber of origin” of the PAC is the SVC. The origin of the PAC was mapped to the posterior SVC. D: SVC automaticity (arrows) during ablation at the SVC–right atrial venoatrial junction immediately following isolation of the SVC. Entrance block into the SVC is established at this point.