E. Kevin Heist

Translocation of calmodulin to the nucleus supports CREB phosphorylation in hippocampal neurons

Activation of the transcription factor CREB is thought to be important in the formation of long-term memory in several animal species. The phosphorylation of a serine residue at position 133 of CREB is critical for activation of CREB. This phosphorylation is rapid when driven by brief synaptic activity in hippocampal neurons. It is initiated by a highly local, rise in calcium ion concentration near the cell membrane, but culminates in the activation of a specific calmodulin-dependent kinase known as CaMK IV (ref. 7), which is constitutively present in the neuronal nucleus,. It is unclear how the signal is conveyed from the synapse to the nucleus. We show here that brief bursts of activity cause a swift (∼1 min) translocation of calmodulin from the cytoplasm to the nucleus, and that this translocation is important for the rapid phosphorylation of CREB. Certain Ca2+ entry systems (L-type Ca2+ channels and NMDA receptors) are able to cause mobilization of calmodulin, whereas others (N- and P/Q-type Ca2+ channels) are not. This translocation of calmodulin provides a form of cellular communication that combines the specificity of local Ca2+ signalling with the ability to produce action at a distance.

Enhancement of Cardiac Function and Suppression of Heart Failure Progression By Inhibition of Protein Phosphatase 1

Abnormal calcium cycling, characteristic of experimental and human heart failure, is associated with impaired sarcoplasmic reticulum calcium uptake activity. This reflects decreases in the cAMP-pathway signaling and increases in type 1 phosphatase activity. The increased protein phosphatase 1 activity is partially due to dephosphorylation and inactivation of its inhibitor-1, promoting dephosphorylation of phospholamban and inhibition of the sarcoplasmic reticulum calcium-pump. Indeed, cardiac-specific expression of a constitutively active inhibitor-1 results in selective enhancement of phospholamban phosphorylation and augmented cardiac contractility at the cellular and intact animal levels. Furthermore, the β-adrenergic response is enhanced in the transgenic hearts compared with wild types. On aortic constriction, the hypercontractile cardiac function is maintained, hypertrophy is attenuated and there is no decompensation in the transgenics compared with wild-type controls. Notably, acute adenoviral gene delivery of the active inhibitor-1, completely restores function and partially reverses remodeling, including normalization of the hyperactivated p38, in the setting of pre-existing heart failure. Thus, the inhibitor 1 of the type 1 phosphatase may represent an attractive new therapeutic target.

Pulmonary vein isolation with complex fractionated atrial electrogram ablation for paroxysmal and nonparoxysmal atrial fibrillation: A meta-analysis

BACKGROUND Pulmonary vein isolation (PVI) is recognized as a potentially curative treatment for atrial fibrillation (AF). Ablation of complex fractionated atrial electrograms (CFAEs) in addition to PVI has been advocated as a means to improve procedural outcomes, but the benefit remains unclear. OBJECTIVE This study sought t synthesize the available data testing the incremental benefit of adding CFAE ablation to PVI. METHODS We performed a meta-analysis of controlled studies comparing the effect of PVI with CFAE ablation vs. PVI alone in patients with paroxysmal and nonparoxysmal AF. RESULTS Of the 481 reports identified, 8 studies met our inclusion criteria. There was a statistically significant increase in freedom from atrial tachyarrhythmia (AT) with the addition of CFAE ablation (relative risk [RR] 1.15, P = .03). In the 5 reports of nonparoxysmal AF (3 randomized controlled trials, 1 controlled clinical trial, and 1 trial using matched historical controls), addition of CFAE ablation resulted in a statistically significant increase in freedom from AT (n = 112 of 181 [62%] for PVI+CFAE vs. n = 84 of 179 [47%] for PVI alone; RR 1.32, P = .02). In trials of paroxysmal AF (3 randomized controlled trials and 1 trial using matched historical controls), addition of CFAE ablation did not result in a statistically significant increase in freedom from AT (n = 131 of 166 [79%] for PVI+CFAE vs. n = 122 of 164 [74%] for PVI alone; RR 1.04, P = .52). CONCLUSION In these studies of patients with nonparoxysmal AF, addition of CFAE ablation to PVI results in greater improvement in freedom from AF. No additional benefit of this combined approach was observed in patients with paroxysmal AF.

Assessment of Catheter Tip Contact Force Resulting in Cardiac Perforation in Swine Atria Using Force Sensing Technology

Background— Force sensing is a recently developed technology that allows the determination of the contact force (CF) at the tip of the catheter during electrophysiology procedures. Previous studies suggested that the optimal CF for adequate catheter contact ranges between 10 and 40 g. The aim of this study was to determine the CF needed to cause perforation in the swine atria. Methods and Results— Pericardial access was obtained at the beginning of the study in a swine model to drain pericardial effusions. Electroanatomic maps of the right atrium (RA) and left atrium (LA) were constructed. Ablation was performed using an irrigated-tip radiofrequency catheter equipped with force-sensing technology (30 W, 30 mL/min, for 30 seconds). Perforations of the LA and RA wall were intentionally performed in different locations with and without radiofrequency ablation. CF values preceding each perforation were recorded. A total of 111 cardiac perforations were achieved in 7 pigs. The overall average CF resulting in perforation was 175.8±60.4 g (range, 77 to 376 g). This was significantly lower after 30 seconds of radiofrequency delivery: 151.8±49.9 g versus 197±61.3 g (P=0.00005). The average value of CF resulting in perforation was not statistically different between the RA and the LA (169.6±61.6 g versus 181.7±59.3 g) (P=0.29). Conclusions— Perforation of the atrial wall in a swine model can occur over a wide range of CF values. Perforation can occur with a CF as low as 77 g. Ablation reduces the perforating force by 23%.

The role of Ca2+/calmodulin-dependent protein kinases within the nucleus

Stimulation of cells by Ca(2+)-linked signaling agents increases Ca2+ levels within both the cell cytosol and nucleus. The multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase) family, consisting of CaM kinases I, II and IV, have all been detected within the nucleus and each may serve as a mediator of nuclear Ca2+ signals. Certain isoforms of the large multimeric CaM kinase II are targeted to the nucleus as a result of an alternatively spliced nuclear localization signal. By contrast, CaM kinases I and IV are monomeric and likely gain nuclear access by passive diffusion through nuclear pores. These kinases have activation properties which may allow them to discriminate between Ca2+ signals which differ in their spike frequency, amplitude and duration. In addition, these kinases have the ability to control gene expression through the phosphorylation of key regulatory sites on nuclear transcription factors. CaM kinases may thus serve to decode Ca2+ signals to the nucleus in order to produce a multitude of cellular responses including control of cell cycle, apoptosis and synaptic efficacy.

Remote Magnetic Navigation to Guide Endocardial and Epicardial Catheter Mapping of Scar-Related Ventricular Tachycardia

Background— The present study examines the safety and feasibility of using a remote magnetic navigation system to perform endocardial and epicardial substrate-based mapping and radiofrequency ablation in patients with scar-related ventricular tachycardia (VT). Methods and Results— Using the magnetic navigation system, we performed 27 procedures on 24 consecutive patients with a history of VT related to myocardial infarction, dilated cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, hypertrophic cardiomyopathy, or sarcoidosis. Electroanatomic mapping of the left ventricular, right ventricular, and ventricular epicardial surfaces was constructed in 24, 10, and 12 patients, respectively. Complete-chamber VT activation maps were created in 4 patients. A total of 77 VTs were inducible, of which 21 were targeted during VT with the remotely navigated radiofrequency ablation catheter alone. With a combination of entrainment and activation mapping, 17 of 21 VTs (81%) were successfully terminated in a mean of 8.4±8.2 seconds; for the remainder, irrigated radiofrequency ablation was necessary. The mean fluoroscopy times for endocardial and epicardial mapping were 27±23 seconds (range, 0 to 105 seconds) and 18±18 seconds (range, 0 to 49 seconds), respectively. In concert with a manually navigated irrigated ablation catheter, 75 of 77 VTs (97%) were ultimately ablated. Four patients underwent a second procedure for recurrent VT, 3 with the magnetic navigation system. After 1.2 procedures per patient, VT did not recur during a mean follow-up of 7±3 months (range, 2 to 12 months). Conclusions— The present study demonstrates the safety and feasibility of remote catheter navigation to perform substrate mapping of scar-related VT in a wide range of disease states with a minimal amount of fluoroscopy exposure.

Protein Kinase A Negatively Modulates the Nuclear Accumulation of NF-ATc1 by Priming for Subsequent Phosphorylation by Glycogen Synthase Kinase-3

The nuclear localization and transcriptional activity of the NF-ATc family of transcription factors, essential to many developmental, differentiation, and adaptation processes, are determined by the opposing activities of the phosphatase calcineurin, which promotes nuclear accumulation of NF-ATc, and several kinases, which promote cytoplasmic accumulation. Many reports suggest that protein kinase A (PKA) negatively modulates calcineurin-mediated NF-ATc activation. Here we show that overexpression of PKA causes phosphorylation and cytoplasmic accumulation of NF-ATc1 in direct opposition to calcineurin by phosphorylating Ser-245, Ser-269, and Ser-294 in the conserved serine-proline repeat domain, and that mutation of these serines blocks the effect of PKA. Activation of endogenous PKA is similarly able to promote phosphorylation of these sites on NF-ATc1 in two lymphoid cell lines. We further show that a complete block of NF-ATc1 nuclear localization by PKA requires a second kinase activity that can be supplied by glycogen synthase kinase-3 (GSK-3), and that mutation of either the PKA phosphorylation sites or the upstream GSK-3 sites prevents the effect of PKA. Thus, we propose that PKA functions cooperatively as a priming kinase for further phosphorylation by GSK-3 to oppose calcineurin-mediated nuclear accumulation and transcriptional activity of NF-ATc1 and that, through this mechanism, PKA may be an important modulator of many NF-ATc-dependent processes.

Impact of segmental left ventricle lead position on cardiac resynchronization therapy outcomes

BACKGROUND The optimal pacing site for cardiac resynchronization therapy (CRT) is along the left ventricle (LV) lateral or posterolateral wall. However, little is known about the impact of segmental pacing site on outcomes. OBJECTIVE We assessed the impact of segmental LV lead position on CRT outcomes. METHODS Patients (n = 115) undergoing CRT were followed prospectively. Segmental LV lead position along the longitudinal axis (apical, midventricle, or basal) was determined retrospectively by examining coronary sinus (CS) venograms and chest X-rays. The primary outcome was a combined endpoint of heart failure hospitalization, cardiac transplantation, or all-cause mortality. Secondary outcomes included change in New York Heart Association (NYHA) functional class and degree of LV reverse remodeling. RESULTS Patients were divided into two groups based on LV lead position: apical (n = 25) and basal/midventricle (n = 90). The apical group was older (72.9 +/- 8.9 vs. 66.5 +/- 13.3 years; P = .010) and more likely to have ischemic cardiomyopathy (77% vs. 52%, P <.001). During a mean follow-up of 15.1 +/- 9.0 months, event-free survival was significantly lower in the apical group: 52% vs. 79%, hazard ratio [HR] 2.7 (95% confidence interval [CI] 1.5-5.5, P = .006). The adverse impact of apical lead placement remained significant after adjusting for clinical covariates: HR 2.3 (95% CI 1.1-4.8, P = .03). The apical group also experienced less improvement in NYHA functional class and less LV reverse remodeling. CONCLUSIONS Apical LV lead placement is associated with worse CRT outcomes. Preferential positioning of LV leads in the basal/midventricle segments may improve outcomes.

Left atrial appendage dimensions predict the risk of stroke/TIA in patients with atrial fibrillation.

Risk of Stroke/TIA in Patients With Atrial Fibrillation. Introduction: Most strokes in patients with atrial fibrillation (AF) arise from thrombus formation in left atrial appendage (LAA). Our aim was to identify LAA features associated with a higher stroke risk in patients with AF using magnetic resonance imaging and angiography (MRI/MRA).

Drug-Induced Arrhythmia

Prolongation of the QTc interval has been associated with proarrhythmia resulting from a potentially fatal form of polymorphic ventricular tachycardia called torsades de pointes (TdP). Genetic forms of the long-QT syndrome (LQTS) associated with high arrhythmic risk have been causally related to mutations in ion channels responsible for the cardiac action potential; genetic factors associated with milder degrees of QTc prolongation and arrhythmic risk have also been described. Acquired forms of QTc prolongation and proarrhythmia, particularly related to drug therapy, are frequently related to drug effects on the same ion channels involved in genetic forms of LQTS. As is true for genetic forms of LQTS, there is a wide spectrum of potential drug effects on the QTc interval ranging from trivial to potentially lethal. Drug-induced QTc prolongation is a complicated phenomenon related not just to the properties or dose of a particular drug but also to drug-drug interactions and a variety of patient factors, including age, gender, the presence and severity of underlying heart disease, and genetic predisposition. Additionally, drug effects on other ion channels, including blockade of sodium channels (causing prolongation of the QRS interval rather than the QTc interval), are an important cause of drug-induced proarrhythmia. The purpose of this review is to summarize the available data related to acquired forms of LQTS, with particular focus on drug-related LQTS and proarrhythmia. A brief summary is presented here of genetic LQTS because the relevant genes and proteins form the basis for an understanding of the causes of acquired LQTS, and in any given patient, the QTc is determined by genetic, substrate, and environmental factors. Emphasis is placed on practical strategies for clinicians, with the goal of minimizing the risk of dangerous proarrhythmia related to the use of both cardiac and noncardiac drugs with the potential for QTc prolongation. Genetic …