Drug administration and LL-ES of ARVGP
The HF dogs were anesthetized with an intraperitoneal injection of 3% sodium pentobarbital (30 mg/kg) and then ventilated with room air (DDH-1, NO. 3529 PLA, Henan, China). The right femoral vein was cannulated to infuse normal saline at 100-200 mL/h to replace spontaneous fluid loss. An electrocardiogram lead II was monitored throughout the study. After the chest was opened through a left fourth intercostal thoracotomy, the pericardium was opened and sewn to the chest wall to cradle the heart. A custom electrode with eight metal electrode heads (Henan Huanan Medical Science & Technology Co., Zhengzhou, China) was sewed tightly on the surface of ARVGP to stimulate the neurons. The thirty HF dogs were subsequently divided randomly into control, drug administration, and LL-ES groups, and then the chest was closed. Dogs underwent no treatment in the baseline open chest status. Then different modifications were performed as follows: Dogs in the control group received a placebo (starch,1g,qd ) for 1 w,while dogs in the drug group were administered a mixed powder of drugs including metoprolol(6.25mg,bid), perindopril(2mg,qd), furosemide(20mg,bid),spironolactone(20mg,bid), and digoxin(0.125g,qd) for 1w. Simultaneously, dogs in the LL-ES group underwent 12h (immediate) and 1 w (short-term) of LL-ES ARVGP, which was embedded in the adipose tissues surrounding the root of the aorta and connected to the aorta by the mesangial ligament, as described in our previous study [6]. The lowest voltage level that induced any slowing of the sinus rate or atrial ventricular conduction (measured by the A-V interval) was considered as the threshold. Approximately10% below the threshold was then chosen as the voltage for LL-ES. During LL-ES, the sinus rate and A-V interval were monitored to ensure that the stimulation voltage was below the threshold [7]. The study protocol can be seen in the flow chart (Figure 1).