Supraventricular tachycardia (SVT) is a common arrhythmia in the perioperative period, which is associated with adverse stimulus such as cardiovascular risk factors, emotional tension, hypoxia, CO2 accumulation, hypokalemia, atropine and pain. To treat perioperative SVT, in addition to massage the vagus nerve, the use of antiarrhythmic drugs and other internal medicine classic methods, the cardiovascular protection of anesthetic drugs is also a common adjuvant treatment. Dexmedetomidine which is widely used as an adjuvant to general anesthesia, can excite α2 receptor to produce sedation, analgesia, inhibition of sympathetic activity, stabilization of hemodynamics and other effects.

Dexmedetomidine is approved by FDA for use in operating room anesthesia and intensive care unit sedation in adults. Although dexmedetomidine is not approved for the treatment of arrhythmias, a growing number of evidences indicated dexmedetomidine can serve as a potential treatment for arrhythmias in perioperative patients. Liu et al. confirmed that dexmedetomidine can reduce ventricular rate and improve atrial fibrillation in cardiac surgery patient. Ji et al. showed that dexmedetomidine anesthesia can be effective in lowering cardiovascular and cerebrovascular complications and mortality in patients one year after coronary bypass surgery. A number of retrospective analyses of pediatric patients undergoing cardiac surgery have shown the incidence of perioperative SVT in patients treated with dexmedetomidine sedation is significantly decreased, which prompts that dexmedetomidine has the potential prevention and treatment for tachyarrhythmia. Therefore, the investigators selected dexmedetomidine for sedation in patients with perioperative SVT to explore the effect for treating SVT via its sedation and mechanism of anti-sympatheticon in this study.

Forty patients with SVT of both sexes, aged 35-61 yr, of American Society of Anesthesiologists physical status Ⅰ-Ⅱ, who undergo elective surgery, were randomly divided into two groups (n=30) including dexmedetomidine group (group D) and midazolam group (group M). For comparison of the efficacy of dexmedetomidine and midazolam in the treatment of SVT, the following needs to be done. The patients calm down for 5-10 minutes after getting into the operating room, group D and group M started as a continuous infusion with dexmedetomidine 0.5µg/kg or midazolam 0.06mg/kg using a micro-pump for 10 minutes. The alarm/sedation (OAA/S) score, heart rate (HR), mean arterial pressure (MAP), pulse oxygen saturation (SpO2) and occurrence of SVT were recorded before the infusion (T0), 5 minutes after the infusion (T1), at the end of the infusion (T2), 5 minutes after the end of the infusion (T3) and 10 minutes after the end of the infusion (T4). In two groups, miniature electrocardiograph was used to monitor the frequency domain index of heart rate variability (HRV) in 5 minutes at each time point including normalized low frequency power (LFnorm), normalized high frequency power (HFnorm) and the balance ratio of sympathetic to vagal tone (LF/HF).

Inclusion Criteria:

• Patients with supraventricular tachycardia

Exclusion Criteria:

• Patients who suffered from significant hemodynamic instability, and can not receive dexmedetomidine and midazolam, were thus excluded from the study.
• Patients with other types of arrhythmia, not SVT, abnormal liver and kidney function and anaesthesia-related drug allergy, were excluded from the study.