IC can be recorded at the HB during permanent HBP in 37% of patients. HBIC is associated with significantly lower pacing thresholds compared to patients in whom HBIC was not recorded. HBIC may be a marker for superior short-term HBP thresholds.

Several studies conducted in the past 10 years have demonstrated the adverse effects of conventional RVA pacing. The Mode Selection Trial (MOST) study included a total of 2,010 patients with sick sinus syndrome who underwent dual-chamber pacemaker implants that were programmed to either a DDD or VVI mode. At three years following implantation, HF hospitalizations were found to have occurred in 12.3% of the VVI group and 10.3% of the DDD group. Of these, 50% were due to new-onset HF. Patients with a greater than 40% ventricular pacing rate in the DDD group and those with a more than 80% pacing rate in the VVI group had a twofold risk of heart failure events [DDD adjusted hazard ratio (HR): 2.60, 95% confidence interval (CI): 1.05-6.47; p < 0.05 and VVI HR: 2.50, 95% CI: 1.44-4.36; p < 0.05]. The similar increase in HF events in patients with both DDD and VVI pacing modes suggests that RVA pacing was independently associated with higher HF events, regardless of atrioventricular (AV) synchrony. 5 A substudy of the MOST trial further demonstrated that the

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