The parasympathetic tone reduction and sympathetic tone enhancement, which are components of the autonomic nervous system (ANS) activity, increase the likelihood of malignant arrhythmias leading to ventricular fibrillation. Malignant arrhythmias are associated with high mortality and morbidity after coronary artery bypass graft (CABG) surgeries. Heart rate variability (HRV) is a physiological indicator of the effects of ANS activity on heart rate and is associated with a prognostic value for cardiac mortality. Dexmedetomidine has been shown to improve myocardial perfusion, reduce arrhythmia incidence, reduce inflammatory response, and reduce mortality in patients with coronary artery disease. The aim of this study investigate the effects of dexmedetomidine electrophysiologically on cardiac autonomic system by using HRV analysis for the purpose of sedation in patients who were followed up in the intensive care unit after coronary artery bypass graft surgery

Malignant arrhythmias are associated with high mortality and morbidity after coronary artery bypass graft (CABG) operations. Heart rate variability (HRV) is a physiological indicator of the effects of activity on heart ANS rate and has prognostic value for cardiac mortality. Spectral analysis of HRV can provide an assessment of adrenergic and cholinergic system activities during anesthesia. With the "power spectral" analysis of HRV, important clinical information can be obtained about the effects of anesthesia on the autonomic nervous system and the central nervous system. Decrease in HRV has a prognostic value for cardiac-induced mortality. The disease, which is transferred to intensive care unit (ICU) after CABG, is sedated with different medicines until the time of extubation. One commonly used sedative drug is deksmedetomidine, an α2 receptor agonist. Alpha 2 (α2) receptor agonist drugs reduce myocardial oxygen consumption and heart rate with sympatholytic properties. Therefore, deksmedetomidine can be safely and effectively used in patients undergoing cardiac surgery without pro-tachyarrhythmic and / or negative inotropic effects.In this study, it was aimed to investigate electrophysiologic effects of cardiac autonomic system by using HRV analysis in dexmedetomine and midazolam patients who underwent elective CABG and were used for sedation in the postoperative period.

Inclusion Criteria:

• Patients with pre-operative normal sinus rhythm
• Ejection fraction (EF)> 45% on echocardiography (echocardiography) examination
• 25 and 65 years of age will be included.

Exclusion Criteria:

• Atrial fibrillation , atrial flutter, supraventricular tachycardia , AV block, ventricular extrasystole
• Cardiopulmonary bypass have been reported in patients with diabetes mellitus (DM),
• Chronic obstructive pulmonary disease (COPD),
• Previous cerebrovascular event will be excluded from the study.
• Patients receiving high-dose inotropic drug support after surgery (inotropic score of> 10 in the first 24 hours) and
• Patients re-operated for bleeding revision will be removed from the study.

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