Following approval from research and ethics committee, preoperative preparation, and anesthesia inductuion. the baseline heart rate (HR) and blood pressure (BP) will be recorded.~The patients will be divided into three groups according to the type of drug injected.~Group MD (dexmedetomidine Mgso4 group): include (40 ) patients and will receive dexmedetomidine 0.5 µg/kg diluted in 50 mL of normal saline intravenously over 20 minutes, After induction followed by 0.5 µg/kg per hour infusion for 72 hours postoperatively or ready for extubation prior to 72 hour time period (Precedex ; Hospira Worldwide ,Lake Forest, IL).(20) and receiving Magnesium Sulfate (50 mg/kg) bolus administered at the time of Aortic Cross Clamp Release. with continued administration for 72 hours postoperatively at a dose of 30 mg/kg/day.(21) Group D (dexmedetomidine group): include (40 ) patients and will receive the same of dexmedetomidine as MD group in addition to normal saline instead of Magnesium Sulfate .~Group C (control group): include (40 ) patients and will receive normal saline instead of dexmedetomidine and MgSo4 .~after the end of the procedure, inhalational anesthetics will be stopped as well the muscle relaxant. The patient will be transferred to the ICU.~In ICU , the post-operative rhythm was monitored to detect the early incidence of arrythmia~Diagnostic criteria for JET included the following:~Tachycardia with QRS similar to sinus rhythm QRS~A ventricular rate more than 170 beats/min~AV dissociation with or without hemodynamic compromise~A ventricular rate faster than the atrial rate. (8) Early onset postoperative JET was defined as the presence of JET during the first 72 h postoperatively. Continuous ECG monitoring will be used continuously in the PCCU. Standard 12-lead ECG will be registered in all patients preoperatively and at the time of PCCU admission. When JET was detected on the ECG monitor this will be also documented with a standard ECG strip Patients who developed JET and were hemodynamically unstable were managed with mild hypothermia, reduction in inotropes, magnesium, digoxin, and amiodarone.
to study the prophylactic effect of magnesium sulfate , dexmedetomidine or their combination in reduction the incidence of JETS postoperative