This is a prospective observational study, the purpose of which is to:

1. Characterize response of the AV conduction system to TAVR with various prostheses by recording continuous His bundle electrograms during valve placement.
2. Correlate preprocedure ECG features with changes in AV nodal and infranodal conduction during placement of the valve prosthesis.
3. Correlate changes in AV nodal and infranodal conduction during the procedure with risk of developing AV conduction block after TAVR.
4. Assess the contribution of stressing the conduction system by atrial pacing prior to and following TAVR to prediction of postprocedural heart block.

Assess the correlation between new onset bundle branch block, site and degree of conduction block or delay and subsequent development of high-grade or complete AV block.

Study Population:

Inclusion criteria -all patients undergoing elective TAVR Exclusion criteria -patients with permanent implanted pacemakers or ICDs prior to TAVR

1. Record standard 12-lead ECG prior to procedure.
2. Place standard electrode catheter via a venous sheath prior to TAVR
3. Initially place the catheter in a proximal position with a large atrial electrogram and proximal His electrogram.
4. Record baseline His bundle electrogram. Record baseline AH and HV intervals.
5. Pace the atrium starting at a cycle length 100 ms shorter than the sinus cycle length, progressively reducing the paced cycle length in 20 ms decrements after 3 seconds pacing at each cycle length, while continuously monitoring arterial blood pressure, to A-V block.
6. Advance the distal electrodes while maintaining recording of a His bundle electrogram to a position where stable right ventricular pacing is secured. Record the RV pacing threshold.
7. If a stable right ventricular pacing position together with stable His bundle electrogram cannot be achieved, a second venous temporary pacing wire will be placed.
8. Record presence or absence of retrograde conduction during RV pacing at 4 times pacing threshold.
9. Ensure stable continuous His bundle electrogram recording while the aortic valve prosthesis is deployed.
10. Use the distal electrodes for rapid ventricular pacing at 4 times threshold during deployment of the valve prosthesis.
11. After the prosthesis has been deployed and is deemed stable, just prior to removing the RV catheter, record a final HBE (AH, HBE, SCL) and again pull back catheter to enable atrial capture with proximal electrodes - pace as above to AV block: start starting at a cycle length 100 ms shorter than the sinus cycle length, progressively reducing the paced cycle length in 20 ms decrements after 3 seconds pacing at each cycle length while monitoring continuous arterial blood pressure to A-V block.
12. Record 12-lead ECG after completion of the procedure and daily thereafter until hospital discharge.
13. Standard telemetry monitoring post procedure while hospitalized.
14. Upon hospital discharge place a standard continuous ambulatory ECG monitor for 2 weeks in patients that do not have a pacemaker implanted.

Inclusion Criteria:

• patients undergoing elective TAVR at BIDMC

Exclusion Criteria:

• patients with permanent implanted pacemakers or ICDs prior to TA

Patients with severe aortic stenosis or regurgitation planned to undergo transcatheter aortic valve replacement

Global Results will be published, not individual patient data