Beta-adrenergic receptor (betaAR) stimulation increases cytosolic Ca(2+) to physiologically augment cardiac contraction, whereas excessive betaAR activation causes adverse cardiac remodeling, including myocardial hypertrophy, dilation and dysfunction, in individuals with myocardial infarction. The Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) is a recently identified downstream element of the betaAR-initiated signaling cascade that is linked to pathological myocardial remodeling and to regulation of key proteins involved in cardiac excitation-contraction coupling. We developed a genetic mouse model of cardiac CaMKII inhibition to test the role of CaMKII in betaAR signaling in vivo. Here we show CaMKII inhibition substantially prevented maladaptive remodeling from excessive betaAR stimulation and myocardial infarction, and induced balanced changes in excitation-contraction coupling that preserved baseline and betaAR-stimulated physiological increases in cardiac function. These findings mark CaMKII as a determinant of clinically important heart disease phenotypes, and suggest CaMKII inhibition can be a highly selective approach for targeting adverse myocardial remodeling linked to betaAR signaling.

Background-Activation of cellular Ca2ϩ signaling molecules appears to be a fundamental step in the progression of cardiomyopathy and arrhythmias. Myocardial overexpression of the constitutively active Ca 2ϩ -dependent phosphatase calcineurin (CAN) causes severe cardiomyopathy marked by left ventricular (LV) dysfunction, arrhythmias, and increased mortality rate, but CAN antagonist drugs primarily reduce hypertrophy without improving LV function or risk of death. Methods and Results-We found that activity and expression of a second Ca

Background-We have shown that the calmodulin inhibitor W-7 suppresses torsade de pointes (TdP) without shortening the QT interval, which is consistent with other findings that QT prolongation, per se, is insufficient to generate TdP. ECGs were analyzed from a well-characterized animal model of TdP to identify more reliable predictors of this life-threatening ventricular arrhythmia. Methods and Results-TdP was induced using methoxamine and clofilium in 12 of 14 rabbits pretreated with vehicle control, whereas pretreatment with W-7 (50 mol/kg), an inhibitor of the intracellular Ca 2ϩ -binding protein calmodulin, significantly suppressed TdP induction (1 of 11 rabbits with TdP, PϽ0.001). W-7 did not affect heart rate, increases in QT intervals, or dispersion compared with measurements in vehicle-treated control animals. However, a progressive and significant increase in the ratio of U-wave to T-wave amplitude (UTA) occurred before TdP onset in control animals, and this was prevented by W-7. Conclusions-Selective suppression of TdP inducibility by W-7, without shortening the duration of cardiac repolarization, allowed identification of the UTA ratio as a new electrocardiographic index for predicting TdP onset. These findings are consistent with the idea that prolonged repolarization is not the proximate cause of arrhythmia initiation, and they suggest that an increased UTA ratio reflects activation of intracellular Ca 2ϩ /calmodulin-dependent processes that are required for triggering TdP in this model.

We describe the case of a 43-year-old male with cardiac sarcoidosis and ventricular tachycardia storm successfully treated with catheter ablation and immunosuppression. Antiarrhythmics alone, and in combination with immusuppressive agents, failed to successfully manage the ventricular tachycardia episodes. Catheter ablation in conjunction with immunosuppression proved to be the most successful treatment strategy. The reported efficacy of catheter ablation for ventricular tachycardia in cardiac sarcoidosis is variable.