Influence of sympathetic nerve activity on ventricular arrhythmogenicity in the dog with chronic hypokalemia

pre-operative serum potassium levels and peri-operative outcomes in patients undergoing cardiac surgery

Although potassium is critical for normal electro physiology, the associations between pre-operative serum potassium level and peri-operative adverse events such as arrhythmias in cardiac surgery have not been examined in detail.The objective of this study was to determine the prevalence of abnormal pre-operative serum potassium levels and whether such levels were associated with adverse peri-operative events in 50 patients undergoing coronary artery bypass grafting. Intra-operative and post-operative arrhythmias, the need for cardio-pulmonary resuscitation, cardiac death and death due to any cause prior to discharge from the post-operative intensive care unit were studied. The incidence for adverse outcome was 0.5% for death, 0.5% for cardiac death and 2% for cardio pulmonary resuscitation in patients with hypokalemia (serum potassium level <3.5 meq. L(-1)). Hypokalemia was found to be a predictor of serious peri-operative (OR:2.2; 95% Cl: 1.2-4.1) and post-operative arrhythmias (OR: 1.7;95%Cl: 1.0-2.7).Pre-operative potassium repletion is low cost and low risk treatment measure and the data from this study suggests that screening and repletion be considered in patients scheduled for cardiac surgery.

The effect of patient-controlled intravenous analgesia on postoperative hypokalemia in patients undergoing laparoscopic cholecystectomy

PURPOSE

We investigated whether hypokalemia developed during the postoperative period and whether the use of intravenous patient-controlled analgesia (IV-PCA) could decrease the incidence of postoperative hypokalemia in patients who underwent laparoscopic cholecystectomy.

METHODS

Sixty patients undergoing laparoscopic cholecystectomy were randomly assigned to either IV-PCA (n = 30) or control (n = 30) groups. We measured serum potassium concentration at the outpatient department (T1), at 8:00 a.m. on the day of surgery (T2), at 6 h after the end of surgery (T3), and at 8:00 a.m. on the first (T4), second (T5), and third (T6) postoperative days. Serum potassium concentration, incidence of hypokalemia, mean blood pressure, heart rate, respiratory rate, and the patient-reported visual analogue scale score were compared within each group and between groups at each time point.

RESULTS

Serum potassium concentrations in all patients showed a significant decrease at T2-T4 compared to the preoperative concentration (T1). Serum potassium concentrations at T3 and T4 in the IV-PCA group were significantly higher than those in the control group. Also, the incidence of hypokalemia at T3 and T4 was significantly lower in the IV-PCA group. Mean blood pressure and heart rate were significantly lower in the IV-PCA group than in controls at T3 and T4.

CONCLUSIONS

The results show that hypokalemia developed during the perioperative period and the use of IV-PCA in patients undergoing laparoscopic cholecystectomy effectively decreased the degree and incidence of postoperative hypokalemia on the day of the operation and postoperative day one.

Heterogeneous atrial denervation creates substrate for sustained atrial fibrillation

BACKGROUND

Heterogeneous electrophysiological properties, which may be due in part to autonomic innervation, are important in the maintenance of atrial fibrillation (AF). We hypothesized that heterogeneous sympathetic denervation with phenol would create a milieu for sustained AF.

METHODS AND RESULTS

After the determination of baseline inducibility, 15 dogs underwent atrial epicardial phenol application and 11 underwent a sham procedure. After 2 weeks of recovery, the animals had repeat attempts at inducing AF and effective refractory period (ERP) testing. Epicardial maps were obtained to determine local AF cycle lengths. ERPs were determined at baseline and during sympathetic, vagal, and simultaneous vagal/sympathetic stimulation. Dogs then underwent PET imaging with either a sympathetic ([11C]hydroxyephedrine, HED) or parasympathetic (5-[11C]methoxybenzovesamicol, MOBV) nerve label. None of the animals had sustained AF (>60 minutes) at baseline. None of the sham dogs and 14 of 15 phenol dogs had sustained AF at follow-up. Sites to which phenol was applied had a significantly shorter ERP (136+/-17.6 ms) than those same sites in the sham controls (156+/-19.1 ms) (P=0.01). Although there was no difference in the ERP change with either vagal or sympathetic stimulation alone between phenol and nonphenol sites, the percent decrease in ERP with simultaneous vagal/sympathetic stimulation was greater in the phenol sites (17+/-8%) than in the nonphenol sites (9+/-9%) (P=0.01). There was a significantly increased dispersion of refractoriness (21+/-6.4 ms in the sham versus 58+/-14 ms in the phenol dogs, P=0.01) as well as dispersion of AF cycle length (49+/-10 ms in the sham versus 105+/-12 ms in the phenol dogs, P=0.0001). PET images demonstrated defects of HED uptake in the areas of phenol application, with no defect of MOBV uptake.

CONCLUSIONS

Heterogeneous sympathetic atrial denervation with phenol facilitates sustained AF.