Background and goal of study

Postoperative atrial fibrillation (POAF) is commonplace after cardiothoracic surgery. Rate control with betablockers is recommended as a first-line therapy in patients macro-hemodynamically stable. Esmolol is a short-acting β1-selective betablocker whose microcirculatory effects have not been yet investigated. We tested the hypothesis that esmolol could improve the POAF-related microvascular dysfunction. 
Materials and Methods
After approval of the Ethical Committee, we prospectively included 20 cardiothoracic surgical patients with POAF in the Teaching University Hospital Louis Pradel (Lyon, France). Microcirculation was assessed by near-infrared spectroscopy (NIRS) and a vascular occlusion test (VOT) at successive time points: before esmolol infusion, during incremental doses of esmolol (25, 50, 100, and 200 µg/kg/min) and after return to sinus rhythm. Esmolol dose regimen was increased every 45 minutes until heart rate reached a targeted value between 60 and 90 beats/min. NIRS parameters included StO2, StO2 min, StO2 max, ∆StO2, and both desaturation and resaturation speeds. Data before and after cardioversion were compared with a paired Student t test or a Wilcoxon test. A one-way ANOVA for repeated measurements or a Friedman test were used to compare the effects of incremental doses of esmolol.

Results and discussion

StO2 and resaturation speed were significantly improved between POAF and return to sinus rhythm: StO2 64.5 %  3.9 vs. 67.0 %  5.1, p=0.047; and resaturation speed 0.6 %/s (0.45-0.99) vs. 0.7 %/s (0.50-1.03), p=0.02. ∆StO2 was significantly lower after return to sinus rhythm, 8.0  4.5 vs. 6.0  4.5, p=0.026. 
During esmolol infusion, StO2 and resaturation speeds were not statistically different (Figure 1). No significant difference was found at any other time point for StO2 min, StO2 max, ∆StO2 and desaturation speed. On the other hand, mean arterial pressure showed a trend toward a decrease (p = 0.054) whereas pulse pressure had a significant reduction (p < 0.001). Heart rate was lowered as expected (p = 0.031). 

Conclusion

Stable hemodynamic POAF is associated with significant microvascular dysfunction. Rate control with intravenous esmolol showed a not significant trend toward a dose-dependent improvement in POAF-related microvascular dysfunction.

Microvascular effects of esmolol in postoperative atrial fibrillation: a prospective pilot study in cardiac surgery