Microvascular effects of intravenous esmolol in patients with normal cardiac function undergoing postoperative atrial fibrillation: a prospective pilot study in cardiothoracic surgery

BACKGROUND: Postoperative atrial fibrillation (POAF) is commonplace after cardiothoracic surgery. A rate control strategy using short-acting beta blockers is recommended as a first-line therapy in patients without hemodynamic instability. Microcirculatory effects of POAF and esmolol have not yet been investigated. We hypothesized that POAF without hemodynamic instability would induce microvascular dysfunction which could be reversed by intravenous esmolol. METHODS: Twenty-five cardiothoracic surgical patients with POAF were included in the study. Microcirculation was assessed by peripheral near-infrared spectroscopy (NIRS) in association with a vascular occlusion test (VOT) before esmolol infusion, during incremental doses of esmolol (25, 50, 100, and 200 μg/kg/min), and after a return to sinus rhythm. Esmolol was given to control heart rate to between 60 and 90 beats/min. Regional tissue oxygen saturation variables (StO(2), StO(2) min, StO(2) max, and ∆StO(2)) and desaturation/resaturation speeds during VOT were recorded to evaluate the microcirculation. RESULTS: StO(2) and resaturation speed were significantly improved when POAF returned to sinus rhythm (StO(2) 64% ± 6 versus 67% ± 6, P < 0.01; resaturation speed 0.53%/s (0.42–0.97) versus 0.66%/s (0.51–1.04), P = 0.020). ∆StO(2) was significantly decreased after a return to sinus rhythm (7.9% ± 4.8 versus 6.1% ± 4.7, P = 0.026). During esmolol infusion, we found a significant decrease in both heart rate (P < 0.001) and blood pressure (P < 0.001), and a non-significant dose-dependent increase in StO(2) (P = 0.081) and resaturation speed (P = 0.087). CONCLUSION: POAF without hemodynamic instability is associated with significant impairment in the microcirculation which could be partially reversed by intravenous esmolol.