The impact of short periods of rapid atrial pacing on left and right atrial mechanical function

Objectives: Current techniques to describe atrial function are limited by their load dependency and hence do not accurately reflect intrinsic mechanical properties. To assess the impact of atrial fibrillation on atrial function, combined pressure-volume relationships measured by conductance catheters were used to simultaneously evaluate the right (RA) and left atrium (LA) during rapid atrial pacing (RAP) and after spontaneous conversion to sinus rhythm (SR).

Methods: In 12 anesthetized pigs, combined pressure-volume data of the RA and LA were recorded over a wide range of loading pressures by transient caval occlusion during baseline SR, after the onset of RAP (cycle-length: 70ms), after one hour of RAP, after conversion to SR, and after one hour of recovery. Data were compared using repeated measures ANOVA.

Results: Cardiac output decreased by 16% (p=0.008) with the onset of RAP. Mean LA and RA pressure increased during RAP by 21% and 40% (p<0.001, respectively) and remained elevated during the entire recovery period. RA reservoir function increased during RAP from 51 to 58%, and significantly dropped to 43% right after resumption of SR (p=0.017). Immediately after RAP, a right-shift of LA ESPVR-intercept V₁₀ (24.4±4.9 mL to 28.1±5.2 mL, p=0.005) indicated impaired contractility when compared to baseline. Active LA emptying fraction dropped from 17.6±7.5% to 11.7±3.7% (p<0.001), stroke volume declined by 22% (p=0.038), and maximum ΔP/Δt/P decreased by 22% (p=0.026) right after RAP, while there was only a trend to impaired systolic function in the RA. Active relaxation (minimum ΔP/Δt/P) declined in LA and RA right after RAP (p=0.005, p=0.026, respectively), while stiffness (end-diastolic ΔP/ΔV) increased in the RA (p=0.013) and decreased in the LA (p=0.039) by 14% at 1 hour after RAP.

Conclusion: Bi-atrial pressure-volume relationships revealed a significant impact on systolic function after RAP only in the LA. Diastolic function was impaired in both atria. While the RA reservoir function declined after RAP confirming increased stiffness, the LA stiffness actually decreased. These data suggest that even short periods of AF have a differenzial impact on RA and LA function and that these effects are sustained for one hour after conversion to SR in this model.