Dexamethasone and cardiac potassium currents in the diabetic rat

Ventricular repolarization disturbances after high dose intravenous methylprednisolone Theraphy

OBJECTIVE

There are no randomized trials evaluating the effects of pulse steroid treatment on cardiac electrophysiologic functions. The data are limited only to case series. In this study, we sought to evaluate the effects of high dose intravenous methylprednisolone therapy on indices of ventricular repolarization.

METHODS

Fifty patients with various autoimmune and inflammatory disorders were enrolled to the study. Electrocardiography (ECG) was obtained 4h before and 12h after the pulse steroid treatment. All ECGs were thoroughly evaluated by an experienced electrophysiologist. Indices of ventricular repolarization including QTc, JT, Tp-Te, Tp-Te/QTc were measured and compared with before and after-treatment ECGs.

RESULTS

There were 36 female and 14 male patients. Mean age was 36±13years. Heart rate was significantly reduced after the therapy (87,16±17,45bpm vs 73,86±17,45 p:0,001). QT interval (361,0±29,91 vs 388,20±42,84 p:0,001) and corrected QT interval (QTc) was significantly prolonged (401,60±19,79 vs 413,72±26,38 p:0,01) after pulse steroid therapy. Also, JT interval (273,0±28,73 vs. 299,60±45,66 p:0,001) and JT interval index (JTI%) was significantly prolonged (118,18±17,54 vs. 110,56±13,92 p:0,01). Tp-e interval was significantly prolonged after high-dose steroid treatment (74,60±13,12 vs. 83,80±13,68 p:0.001). The ratio of Tp-Te to QTc was also significantly increased after pulse steroid therapy (0,18±0,03 vs 0,20±0,03 p:0,009).

CONCLUSION

Our study shows that indices of ventricular repolarization are significantly prolonged after pulse steroid treatment. These findings indicate an increased risk of arrhythmias related to high dose intravenous methylprednisolone therapy.

Three cases of corticosteroid therapy triggering ventricular fibrillation in J-wave syndromes

We describe three cases of J-wave syndrome in which ventricular fibrillation (VF) was probably induced by corticosteroid therapy. The patients involved were being treated with prednisolone for concomitant bronchial asthma. One of the three patients had only one episode of VF during her long follow-up period (14 years). Two patients had hypokalemia during their VF episodes. Corticosteroids have been shown to induce various types of arrhythmia and to modify cardiac potassium channels. We discuss the possible association between corticosteroid therapy and VF in J-wave syndrome based on the cases we have encountered.

LY294002 inhibits glucocorticoid-induced COX-2 gene expression in cardiomyocytes through a phosphatidylinositol 3 kinase-independent mechanism

Glucocorticoids induce COX-2 expression in rat cardiomyocytes. While investigating whether phosphatidylinositol 3 kinase (PI3K) plays a role in corticosterone (CT)-induced COX-2, we found that LY294002 (LY29) but not wortmannin (WM) attenuates CT from inducing COX-2 gene expression. Expression of a dominant-negative mutant of p85 subunit of PI3K failed to inhibit CT from inducing COX-2 expression. CT did not activate PI3K/AKT signaling pathway whereas LY29 and WM decreased the activity of PI3K. LY303511 (LY30), a structural analogue and a negative control for PI3K inhibitory activity of LY29, also suppressed COX-2 induction. These data suggest PI3K-independent mechanisms in regulating CT-induced COX-2 expression. LY29 and LY30 do not inhibit glucocorticoid receptor transactivity. Both compounds have been reported to inhibit Casein Kinase 2 activity and modulate potassium and calcium levels independent of PI3K, while LY29 has been reported to inhibit mammalian Target of Rapamycin (mTOR), and DNA-dependent Protein Kinase (DNA-PK). Inhibitor of Casein Kinase 2 (CK2), mTOR or DNA-PK failed to prevent CT from inducing COX-2 expression. Tetraethylammonium (TEA), a potassium channel blocker, and nimodipine, a calcium channel blocker, both attenuated CT from inducing COX-2 gene expression. CT was found to increase intracellular Ca(2+) concentration, which can be inhibited by LY29, TEA or nimodipine. These data suggest a possible role of calcium instead of PI3K in CT-induced COX-2 expression in cardiomyocytes.