Left ventricular volumes with ventricular inhibited and atrial triggered ventricular pacing

Left ventricular (LV) volumes were assessed with equilibrium radionuclide angiocardiography at rest and during exercise in nine patients with high-degree AV block treated with ventricular inhibited (VVI), which was subsequently changed to atrial triggered ventricular pacing (VAT). The ventricular rates were similar at rest but higher on exercise during treatment with VAT (102 ppm) than with VVI (71 bpm). The LV end-diastolic volume tended to be larger with VAT than with VVI pacing, both at rest (185 vs. 145 ml) and during exercise (220 vs. 162 ml). The LV end-systolic volume also tended to be larger at rest (110 vs. 81 ml) and during exercise (149 vs. 83 ml). The LV ejection fractions were similar at rest but on exercise they decreased to significantly lower levels with VAT (0.35), while remaining unchanged with VVI (0.47). One mechanism for this difference could be an enhanced contractile state in VVI pacing compared with VAT pacing.