Methods
All procedures were conducted at Mayo Clinic, Rochester, MN after review
and approval by the Institutional Animal Care and Use Committee (IACUC).
Animals were fasted overnight, general anesthesia was induced using
ketamine and diazepam and maintained with inhaled Isoflurane.
Anatomic, voltage and activation maps were created using a 64-electrode
INTELLAMAP ORION™ catheter and the RHYTHMIA HDx™ (Boston Scientific
Corporation, Washington, DC) system. Right ventricular (RV) and left
ventricular (LV) maps were created in sinus rhythm and during HB pacing.
HB pacing was achieved using an active-fixation pacing lead (model 3830)
and a deflectable sheath (model C304; Medtronic, Fidley, MN). Pacing
parameters ensured HB pacing by: 1) setting a rate faster than the
animal’s intrinsic heart rate, 2) adjusting output until an isoelectric
interval was noted between pacing spike and QRS, 3) QRS duration less
than 100ms on surface ECG with similar morphology to native QRS. Total
LV and RV activation times were defined as the time difference between
earliest and latest intra-cardiac signals in the corresponding chamber.