Haemodynamic effects of changes in atrioventricular and interventricular delay in cardiac resynchronisation therapy show a consistent pattern: Analysis of shape, magnitude and relative importance of atrioventricular and interventricular delay

Objective: To assess the haemodynamic effect of simultaneously adjusting atrioventricular ( AV) and interventricular (VV) delays. Method: 35 different combinations of AV and VV delay were tested by using digital photoplethysmography (Finometer) with repeated alternations to measure relative change in systolic blood pressure (SBPrel) in 15 patients with cardiac resynchronisation devices for heart failure. Results: Changing AV delay had a larger effect than changing VV delay ( range of SBPrel 21 v 4.2 mm Hg, p < 0.001). Each had a curvilinear effect. The curve of response to AV delay fitted extremely closely to a parabola (average R-2 = 0.99, average residual variance 0.8 mm Hg-2). The response to VV delay was significantly less curved ( quadratic coefficient 67 v 1194 mm Hg/s(2), p = 0.003) and therefore, although the residual variance was equally small ( 0.8 mm Hg2), the R-2 value was 0.7. Reproducibility at two months was good, with the SD of the difference between two measurements of SBPrel being 2.5 mm Hg for AV delay (2% of mean systolic blood pressure) and 1.5 mm Hg for VV delay (1% of mean systolic blood pressure). Conclusions: Changing AV and VV delays results in a curvilinear acute blood pressure response. This shape fits very closely to a parabola, which may be valuable information in developing a streamlined clinical protocol. VV delay adjustment provides an additional, albeit smaller, haemodynamic benefit to AV optimisation.