Isolation of small atrial segment surrounding the atrioventricular node and the His bundle was achieved by sequential radiofrequency ablation. The structures around the Koch triangle in the swine heart are shown here. The relative location of the CS and the IVC is different from that in humans. Please see text for details. The location of the tricuspid annulus is labeled. In this study, the His bundle is mapped first. The atrioventricular node is presumably just proximal and inferior to the His bundle. The small atrial segment surrounding the atrioventricular node and the His bundle is isolated using a series of radiofrequency ablation lesions. The isolation is started with a line crossing the CS–tricuspid isthmus, which is extended superiorly along the anterior edge of the CS. A pacing lead is inserted into the isolated atrial segment surrounded by the ablation lines, the tricuspid annulus, and the atrioventricular node–His bundle. The results of this study are not dependent on the location of the lead implantation (either closer to the AV node or closer to the CS–tricuspid isthmus). The circles labeled as A.B.L.A.T.I.O.N.L.I.N.E. represent the linear ablation lesions. Attain = steerable guiding sheath; AVN = location of the atrioventricular node; CS = coronary sinus; HB = the location of the His bundle; IVC = inferior vena cava.

Complete atrioventricular block created by isolation of a small atrial segment surrounding the atrioventricular node and the His bundle. Complete atrioventricular block emerged on completion of the linear ablation with junctional rhythm at 65 beats/min in the ventricles and sinus rhythm at 95 beats/min in the atria. The recordings from top to bottom are a modified lead II surface electrocardiogram (II), right atrial electrogram (RA), left atrial electrogram (LA), right ventricular electrogram (RV), left ventricular electrogram (LV), recording from pacing lead inserted into the small isolated atrial segment (PACE), and left ventricular pressure (LVP).

After complete atrioventricular block was confirmed, pacing from the isolated atrial segment at a cycle length of 700 ms (86 beats/min) activated both ventricles with a fixed interval between the pacing spike and the ventricular activation. The isolated atrial segment and ventricles were dissociated with both the atria, which were in sinus rhythm at 97 beats/min. The recording format is the same as in Figure 2. HV = interval between His potential and ventricular signal; SV = interval between pacing spike and ventricular signal; other abbreviations as in Figure 2.

The antegrade atrioventricular (AV) conduction and retrograde ventriculoatrial (VA) conduction remained intact after the small atrial segment was isolated. (A) Pacing from the isolated atrial segment at 150 beats/min subsequently activated the ventricles with 1:1 AV conduction. (B) Pacing the left ventricle at 150 beats/min resulted in 1:1 VA conduction. LV = recording from the left ventricle; PACE = recording from pacing lead inserted into the isolated atrial segment; other abbreviations as in Figure 2.

Wenckebach atrioventricular (AV) nodal physiology was reserved after the small atrial segment was isolated. (A) In experiment 4, pacing from the isolated atrial segment at 200 beats/min resulted in Wenckebach AV conduction. (B1) In experiment 5, pacing from the isolated atrial segment at 190 beats/min resulted in constant 1:1 AV conduction. (B2) In the same experiment as B1, pacing from the isolated atrial segment at 200 beats/min resulted in 2:1 AV conduction. LV = recording from the left ventricle; PACE = recording from pacing lead inserted into the isolated atrial segment; RV = recording from the right ventricle.

During pacing at 700 ms (86 beats/min) from the isolated atrial segment, the ventricles were activated after each pacing, with a fixed interval between the pacing spike and the ventricular activation, despite the fact that the right atrium was paced at 200 beats/min (which activated the left atrium as well). This suggests that there was complete conduction block from the right–left atria to the isolated tissue–ventricles. The recording format is the same as Figure 1. LVP = left ventricular pressure; other abbreviations as in Figure 5.