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

Abstract

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 (StO₂, StO₂ min, StO₂ max, and ∆StO₂) and desaturation/resaturation speeds during VOT were recorded to evaluate the microcirculation.

Results: StO₂ and resaturation speed were significantly improved when POAF returned to sinus rhythm (StO₂ 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). ∆StO₂ 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 StO₂ (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.

Keywords: Beta blocker; Esmolol; Microcirculation; Near-infrared spectroscopy; Postoperative atrial fibrillation; Regional oxygen saturation.

Fig. 1

Screen shot of a regular vascular occlusion test (VOT) measured with the O3 Regional oximetry device. Desaturation and resaturation speeds are expressed in %/s. ∆StO₂ is calculated as StO₂ max – StO₂ baseline and expressed in %. StO ₂ tissue oxygen saturation

Fig. 2

Description of the study protocol. Each step lasted 45 min and the dose of esmolol was gradually increased to control ventricular heart rate (HR) between 60 and 90 beats/min. POAF postoperative atrial fibrillation. VOT vascular occlusion test

Fig. 3

Boxplots showing hemodynamic parameters. These parameters were obtained during postoperative atrial fibrillation (POAF) and incremental esmolol dose regimen (25 μg/kg/min (E25), 50 μg/kg/min (E50), 100 μg/kg/min (E100), and 200 μg/kg/min (E200)). Continuous variables were analyzed with a linear mixed-effects model. a Heart rate (HR), (b) mean arterial pressure (MAP), (c) pulse pressure (PP), and (d) arterial oxygen saturation (SpO ₂)

Fig. 4

Boxplots showing microcirculatory parameters. These parameters were obtained by NIRS in combination with a vascular occlusion test during postoperative atrial fibrillation (POAF) and during incremental esmolol dose regimen (25 μg/kg/min (E25), 50 μg/kg/min (E50), 100 μg/kg/min (E100), and 200 μg/kg/min (E200)). Continuous variables were analyzed with a linear mixed-effects model. a Tissue oxygen saturation (StO ₂), (b) resaturation speed, (c) desaturation speed, and (d) variation in StO₂ during reperfusion (DeltaStO ₂)