An alternative method of assessing bidirectional block for atrial flutter

The success of cavotricuspid (CTI) ablation depends on the achievement of bidirectional block. Previous investigators have shown that right ventricular (RV) pacing can replace proximal coronary sinus (pCS) pacing in assessing clockwise CTI conduction block.

We sought to assess bidirectional conduction using antegrade (A-V) and retrograde (V-A) conduction times in the absence of coronary sinus (CS) pacing.

Counterclockwise CTI conduction block was evaluated using conduction time to the QRS from 2 pacing sites (immediately lateral and further lateral to the CTI). This was compared to the conduction time to the pCS with pacing from the same 2 lateral points. This was measured prior to ablation in 7 patients and 41 patients following ablation. To evaluate clockwise CTI conduction block we measured the conduction time to the 2 lateral sites during RV pacing and pCS pacing. This was measured in 7 patients prior to ablation and 16 patients following successful ablation.

The abbreviated technique correctly indicated the presence or absence of bidirectional block in all patients. Furthermore, conduction times as assessed by the 2 methods correlated well both before and after creation of bidirectional block (correlation coefficients prior to ablation: clockwise direction r = 0.92, P = 0.0036; counterclockwise direction r = 0.86, P = 0.0132; after ablation: clockwise direction r = 0.82, P = 0.0001; counterclockwise direction r = 0.91, P < 0.0001).

Bidirectional CTI conduction block can be successfully demonstrated using A-V and V-A conduction without the need for CS pacing. Patients need, however, to have intact A-V and V-A AV nodal conduction.