Person:

Shen, Changyu

Background: Purkinje cells (PCs) are important in cardiac arrhythmogenesis. Whether small‐conductance calcium‐activated potassium (SK) channels are present in PCs remains unclear. We tested the hypotheses that subtype 2 SK (SK2) channel proteins and apamin‐sensitive SK currents are abundantly present in PCs. Methods and Results: We studied 25 normal rabbit ventricles, including 13 patch‐clamp studies, 4 for Western blotting, and 8 for immunohistochemical staining. Transmembrane action potentials were recorded in current‐clamp mode using the perforated‐patch technique. For PCs, the apamin (100 nmol/L) significantly prolonged action potential duration measured to 80% repolarization by an average of 10.4 ms (95% CI, 0.11–20.72) (n=9, P=0.047). Voltage‐clamp study showed that apamin‐sensitive SK current density was significantly larger in PCs compared with ventricular myocytes at potentials ≥0 mV. Western blotting of SK2 expression showed that the SK2 protein expression in the midmyocardium was 58% (P=0.028) and the epicardium was 50% (P=0.018) of that in the pseudotendons. Immunostaining of SK2 protein showed that PCs stained stronger than ventricular myocytes. Confocal microscope study showed SK2 protein was distributed to the periphery of the PCs. Conclusions: SK2 proteins are more abundantly present in the PCs than in the ventricular myocytes of normal rabbit ventricles. Apamin‐sensitive SK current is important in ventricular repolarization of normal PCs.

Background: Atrial fibrillation (AF) is a major contributor to the global cardiovascular disease burden. The clinical profile and outcomes of AF patients with valvular heart diseases in sub-Saharan Africa (SSA) have not been adequately described. We assessed clinical features and 12-month outcomes of patients with valvular AF (vAF) in comparison to AF patients without valvular heart disease (nvAF) in western Kenya. Methods: We performed a cohort study with retrospective data gathering to characterize risk factors and prospective data collection to characterize their hospitalization, stroke and mortality rates. Results: The AF patients included 77 with vAF and 69 with nvAF. The mean (SD) age of vAF and nvAF patients were 37.9(14.5) and 69.4(12.3) years, respectively. There were significant differences (p<0.001) between vAF and nvAF patients with respect to female sex (78% vs. 55%), rates of hypertension (29% vs. 73%) and heart failure (10% vs. 49%). vAF patients were more likely to be taking anticoagulation therapy compared to those with nvAF (97% vs. 76%; p<0.01). After 12-months of follow-up, the overall mortality, hospitalization and stroke rates for vAF patients were high, at 10%, 34% and 5% respectively, and were similar to the rates in the nvAF patients (15%, 36%, and 5%, respectively). Conclusion: Despite younger age and few comorbid conditions, patients with vAF in this developing country setting are at high risk for nonfatal and fatal outcomes, and are in need of interventions to improve short and long-term outcomes.