Transcutaneous Electrical Nerve Stimulation Improves Vascular Conductance After Coronary Artery Bypass Graft Surgery (TEBCABG)

• Pain Intensity [ Time Frame: 5 day ] [ Designated as safety issue: Yes ]
  A visual analog scale (VAS) for assessing current pain intensity will be used to evaluate pain from 0 to 10, where 0 means no pain and 10 indicates severe pain, being applied on the first and on the 5th day after CABG .
• Opioid Analgesic Amount [ Time Frame: 5 day ] [ Designated as safety issue: Yes ]
  During the first 24 h (immediately, 6, 12 and 24 h) after CABG, the amount of additional analgesic dose (pethidine hydrochloride (HCl) 20 mg, maximum 1 mg/kg/day) was measured for patients in both groups.
• β-Endorphin Analysis [ Time Frame: 5 day ] [ Designated as safety issue: Yes ]
  Ten milliliters of venous blood will be taken by the phlebotomist. 3 ml of which will be stored in ethylenediaminetetraacetic acid (EDTA) for analysis of a differential white cell count. Seven ml of blood will be divided between an EDTA tube and a lithium heparin (LH) gel tube. These blood samples will be centrifuged and frozen until assayed. β-endorphin was measured by sandwich enzyme immunoassay (ELISA) kit (Phoenix Pharmaceuticals, Inc., USA).

• Pain Intensity [ Time Frame: 5 day ] [ Designated as safety issue: Yes ]
  A visual analog scale (VAS) for assessing current pain intensity will be used to evaluate pain from 0 to 10, where 0 means no pain and 10 indicates severe pain, being applied on the first and on the 5th day after CABG .
• Opioid Analgesic Amount [ Time Frame: 5 day ] [ Designated as safety issue: Yes ]
  During the first 24 h (immediately, 6, 12 and 24 h) after CABG, the amount of additional analgesic dose (pethidine HCl 20 mg, maximum 1 mg/kg/day) was measured for patients in both groups.
• β-Endorphin Analysis [ Time Frame: 5 day ] [ Designated as safety issue: Yes ]
  Ten milliliters of venous blood will be taken by the phlebotomist. 3 ml of which will be stored in ethylenediaminetetraacetic acid (EDTA) for analysis of a differential white cell count. Seven ml of blood will be divided between an EDTA tube and a lithium heparin (LH) gel tube. These blood samples will be centrifuged and frozen until assayed. β-endorphin was measured by sandwich enzyme immunoassay (ELISA) kit (Phoenix Pharmaceuticals, Inc., USA).

The investigators will test the hypothesis that transcutaneous electrical nerve stimulation (TENS) may attenuate peripheral vasoconstriction and to improve blood flow redistribution during handgrip exercise in acute myocardial infarction (AMI) patients after Coronary Arterial Bypass Graft Surgery (CABG).

Thirty-eight patients will be randomized to a (4 times/day; 30 min/session) for 5-day program of TENS (n = 20) or to placebo-TENS (P-TENS, n = 18) applied on cervical region (C7-T4). Acute sympathetic stimulation by cold pressor test (CPT), Maximal voluntary contraction (MVC), Femoral blood flow (FBF) and femoral vascular conductance (FVC) will be measured as primary outcome pre and post-CABG, even as the 6-minute walk test (6-MWT), Inspiratory and expiratory muscle strength (PImax and PEmax) and β-endorphin as a secondary clinical parameters. In addition, amount of opioid analgesic and pain intensity also will be measured throughout at first 24 hours after CABG (immediately, 6, 12 and 24 hours).

• Experimental: TENS CABG
  Eligible patients will be randomized to a transcutaneous electrical nerve stimulation program (TENS; n = 20) or to placebo-TENS (P-TENS; n = 18). All patients were followed by their own physicians, received routine nursing assistance, and were visited daily by one of the investigators, but P-TENS group will be not exposed to any specific electrical stimulation or motor physical intervention.
  Intervention: Device: Transcutaneous electrical nerve stimulation
• Placebo Comparator: P-TENS CABG
  Patients will be treated with placebo-TENS (P-TENS) condition for 5 days (4 times/day; 30 min/session) applied on cervical region (C7-T4). P-TENS device underwent modifications in its internal programming: the control capacitor of the time constant was changed and the active time between pulses was modified from 330 milliseconds to 33 seconds, in order to prevent an analgesic effect (33).
  Intervention: Device: Transcutaneous electrical nerve stimulation

Inclusion Criteria:

• a previous history of more than 1 vessel coronary artery disease,
• lifelong abstinence from tobacco, and
• formal indication for CABG, according to established guideline.

Exclusion Criteria:

• Patients older than 70 years of age, with chronic renal failure, or with unstable angina in the 48 h prior to CABG, moderate or severe valve disease, complex cardiac arrhythmias, stroke, and/or inability to exercise the lower limbs.