Michelle S.C. Khoo

Calmodulin kinase II inhibition protects against structural heart disease

β-Adrenergic receptor (βAR) stimulation increases cytosolic Ca2+ to physiologically augment cardiac contraction, whereas excessive βAR activation causes adverse cardiac remodeling, including myocardial hypertrophy, dilation and dysfunction, in individuals with myocardial infarction. The Ca2+-calmodulin–dependent protein kinase II (CaMKII) is a recently identified downstream element of the βAR-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 βAR signaling in vivo. Here we show CaMKII inhibition substantially prevented maladaptive remodeling from excessive βAR stimulation and myocardial infarction, and induced balanced changes in excitation-contraction coupling that preserved baseline and βAR-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 βAR signaling.

Death, Cardiac Dysfunction, and Arrhythmias Are Increased by Calmodulin Kinase II in Calcineurin Cardiomyopathy

Background— Activation of cellular Ca2+ signaling molecules appears to be a fundamental step in the progression of cardiomyopathy and arrhythmias. Myocardial overexpression of the constitutively active Ca2+-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 Ca2+-activated signaling molecule, calmodulin kinase II (CaMKII), were increased in hearts from CAN transgenic mice and that CaMKII-inhibitory drugs improved LV function and suppressed arrhythmias. We devised a genetic approach to “clamp” CaMKII activity in CAN mice to control levels by interbreeding CAN transgenic mice with mice expressing a specific CaMKII inhibitor in cardiomyocytes. We developed transgenic control mice by interbreeding CAN transgenic mice with mice expressing an inactive version of the CaMKII-inhibitory peptide. CAN mice with CaMKII inhibition had reduced risk of death and increased LV and ventricular myocyte function and were less susceptible to arrhythmias. CaMKII inhibition did not reduce transgenic overexpression of CAN or expression of endogenous CaMKII protein or significantly reduce most measures of cardiac hypertrophy. Conclusions— CaMKII is a downstream signal in CAN cardiomyopathy, and increased CaMKII activity contributes to cardiac dysfunction, arrhythmia susceptibility, and longevity during CAN overexpression.

Temporal changes in ventricular function assessed echocardiographically in conscious and anesthetized mice.

The mouse is an important model system for cardiovascular biology, with echocardiography a critical tool for noninvasive measurement of cardiac morphology and function. The feasibility and short-term temporal consistency of repeated echocardiographic measurements in conscious mice has not been previously evaluated. We performed serial 2-dimensional guided M-mode transthoracic echocardiographic measurements at 5- to 10-minute intervals over 60 minutes in conscious mice and in mice treated with 1 of 3 anesthetic regimens: ketamine and acepromazine (n = 14); pentobarbital (n = 14); and ketamine and xylazine (n = 13). Unanesthetized mice received intraperitoneal saline (n = 6) or no injection (n = 7). In sequentially repeated measurements over 1 hour in conscious mice, none of the measured or derived echocardiographic parameters differed from baseline, whereas all 3 anesthetic regimens produced significant, prolonged, and temporally variable decreases in heart rate and fractional shortening. The relationship between heart rate and fractional shortening was not altered by anesthetic choice. Serial echocardiographic assessments of cardiac function, dimension, and mass can be performed with high reproducibility in conscious mice.

Effect of Obesity on Cardiovascular Disease Risk Factors in African American Women

Obesity is a growing health care concern with implications for cardiovascular disease (CVD). Obesity and CVD morbidity and mortality are highly prevalent among African American women. This pilot study examined the association between obesity and the traditional and emerging CVD risk factors in a sample of African American women. Participants comprised 48 women (27 obese, 21 normal weight) aged 18–45. with no known history of CVD. The women completed demographic and 7-day physical activity recall questionnaires. Height and weight were used to determine body mass index (BMI). Hypertension risk was assessed using the average of two resting blood pressure (BP) measurements. Lipid profile, blood glucose, fibrinogen, high-sensitivity C-reactive protein (hs-CRP), plasminogen activator inhibitor-1 (PAI-1), soluble intercellular adhesion molecule-1 (sICAM-1), and E-selectin (eSel) levels were assessed using fasting blood samples. Laboratory findings were interpreted using the American Diabetes Association (ADA) and Adult Treatment Panel (ATP) III reference guidelines as well as manufacturers’ reference ranges for the novel CVD risk factors. The most common traditional risk factors were physical inactivity (72.9%), positive family history of CVD (58.3%), and obesity (56.3%). Obese individuals had elevated systolic BP (p = .0002), diastolic BP (p = .0007) and HDL-cholesterol (p = .01), triglyceride (p = .02), hs-CRP (p = .002), and fibrinogen (p = .01), when compared with normal-weight women. The findings suggest an association between obesity and higher prevalence of both traditional and emerging CVD risk factors in young African American women.

Migration and infection of a pace-sense lead from an abdominal defibrillator system.

KHOO, M.S.C., et al.: Migration and Infection of a Pace‐Sense Lead from an Abdominal Defibrillator System. A 47‐year‐old man had an ICD system with epicardial and endocardial components and an abdominal generator placed in 1990 following a cardiac arrest. Ten years later his BT10 lead was amputated due to an insulation defect, and he received a new pectoral generator with transvenous leads. A few months later he developed fevers, chills, and bacteremia. Evaluation demonstrated migration of the entire BT10 lead into the right atrium. Complete surgical explantation was required and the bacteremia resolved. This case illustrates the importance of solid anchoring of distal lead components following generator removal and the potential complication of intravascular lead migration.