'Trapped re-entry' as source of acute focal atrial arrhythmias

AIMS

Diseased atria are characterized by functional and structural heterogeneities, adding to abnormal impulse generation and propagation. These heterogeneities are thought to lie at the origin of fractionated electrograms recorded during sinus rhythm (SR) in atrial fibrillation (AF) patients and are assumed to be involved in the onset and perpetuation (e.g. by re-entry) of this disorder. The underlying mechanisms, however, remain incompletely understood. Here, we tested whether regions of dense fibrosis could create an electrically isolated conduction pathway (EICP) in which re-entry could be established via ectopy and local block to become 'trapped'. We also investigated whether this could generate local fractionated electrograms and whether the re-entrant wave could 'escape' and cause a global tachyarrhythmia due to dynamic changes at a connecting isthmus.

METHODS AND RESULTS

To precisely control and explore the geometrical properties of EICPs, we used light-gated depolarizing ion channels and patterned illumination for creating specific non-conducting regions in silico and in vitro. Insight from these studies was used for complementary investigations in virtual human atria with localized fibrosis. We demonstrated that a re-entrant tachyarrhythmia can exist locally within an EICP with SR prevailing in the surrounding tissue and identified conditions under which re-entry could escape from the EICP, thereby converting a local latent arrhythmic source into an active driver with global impact on the heart. In a realistic three-dimensional model of human atria, unipolar epicardial pseudo-electrograms showed fractionation at the site of 'trapped re-entry' in coexistence with regular SR electrograms elsewhere in the atria. Upon escape of the re-entrant wave, acute arrhythmia onset was observed.

CONCLUSIONS

Trapped re-entry as a latent source of arrhythmogenesis can explain the sudden onset of focal arrhythmias, which are able to transgress into AF. Our study might help to improve the effectiveness of ablation of aberrant cardiac electrical signals in clinical practice.

A Brazilian Portuguese translation, cultural adaptation and validation of the Arrhythmia-Specific questionnaire in Tachycardia and Arrhythmia (ASTA) health-related quality of life (HRQOL) scale

INTRODUCTION

The health-related quality of life (HRQOL) of patients with tachyarrhythmia can be negatively influenced by the clinical manifestations. The evaluation of HRQOL with validated instruments can provide valuable information that will contribute to clinical decision-making and treatment. In Brazil, however, there is no available scale that evaluates HRQOL in different types of arrhythmia. The purpose of this study was to adapt the Arrhythmia-Specific Questionnaire in Tachycardia and Arrhythmia-HRQOL scale (ASTA-HRQOL scale) to the Brazilian culture, and to assess the psychometric properties of the adapted questionnaire.

METHODS

The study used a methodological process of cultural adaptation based on international literature guidelines. The analyses were performed with 172 participants, 32 for cultural adaptation and 140 for psychometric validation. Calculation included analysis of reliability by Cronbach's α coefficient, construct validity with convergent validity using the WHOQOL-BREF questionnaire and by the Spearman correlation coefficient, Average Variance Extracted, and assessment of confirmatory factor analysis.

RESULTS

The translation and adaptation processes showed a satisfactory degree of comprehension and applicability (93% reported them to be easy to understand). Confirmatory factor analysis indicated exclusion of one item from the mental scale, but after qualitative analysis the item was retained. The items presented adequate internal consistency (Cronbach's alpha coefficient = 0.88), and an inverse correlation of moderate magnitude with the physical domain (rho = -0.63) and with the mental domain (rho = -0.58) of the WHOQOL-BREF.

CONCLUSIONS

The Brazilian Portuguese version of the ASTA-HRQOL scale, the ASTA-Br-HRQOL scale, can be a valuable tool for use in clinical practice and research.

CONTEMPORARY RADIATION DOSES IN INTERVENTIONAL CARDIOLOGY: A NATIONWIDE STUDY OF PATIENT DOSES IN FINLAND

The amount of interventional procedures such as percutaneous coronary intervention (PCI), transcatheter aortic valve implantation (TAVI), pacemaker implantation (PI) and ablations has increased within the previous decade. Simultaneously, novel fluoroscopy mainframes enable lower radiation doses for patients and operators. Therefore, there is a need to update the existing diagnostic reference levels (DRLs) and propose new ones for common or recently introduced procedures. We sought to assess patient radiation doses in interventional cardiology in a large sample from seven hospitals across Finland between 2014 and 2016. Data were used to set updated national DRLs for coronary angiographies (kerma-air product (KAP) 30 Gycm2) and PCIs (KAP 75 cm2), and novel levels for PIs (KAP 3.5 Gycm2), atrial fibrillation ablation procedures (KAP 25 Gycm2) and TAVI (KAP 90 Gycm2). Tentative KAP values were set for implantations of cardiac resynchronization therapy devices (CRT, KAP 22 Gycm2), electrophysiological treatment of atrioventricular nodal re-entry tachycardia (6 Gycm2) and atrial flutter procedures (KAP 16 Gycm2). The values for TAVI and CRT device implantation are published for the first time on national level. Dose from image acquisition (cine) constitutes the major part of the total dose in coronary and atrial fibrillation ablation procedures. For TAVI, patient weight is a good predictor of patient dose.

Identification of new biophysical markers for pathological ventricular remodelling in tachycardia-induced dilated cardiomyopathy

Our aim was to identify biophysical biomarkers of ventricular remodelling in tachycardia-induced dilated cardiomyopathy (DCM). Our study includes healthy controls (N = 7) and DCM pigs (N = 10). Molecular analysis showed global myocardial metabolic abnormalities, some of them related to myocardial hibernation in failing hearts, supporting the translationality of our model to study cardiac remodelling in dilated cardiomyopathy. Histological analysis showed unorganized and agglomerated collagen accumulation in the dilated ventricles and a higher percentage of fibrosis in the right (RV) than in the left (LV) ventricle (P = .016). The Fourier Transform Infrared Spectroscopy (FTIR) 1st and 2nd indicators, which are markers of the myofiber/collagen ratio, were reduced in dilated hearts, with the 1st indicator reduced by 45% and 53% in the RV and LV, respectively, and the 2nd indicator reduced by 25% in the RV. The 3rd FTIR indicator, a marker of the carbohydrate/lipid ratio, was up-regulated in the right and left dilated ventricles but to a greater extent in the RV (2.60-fold vs 1.61-fold, P = .049). Differential scanning calorimetry (DSC) showed a depression of the freezable water melting point in DCM ventricles - indicating structural changes in the tissue architecture - and lower protein stability. Our results suggest that the 1st, 2nd and 3rd FTIR indicators are useful markers of cardiac remodelling. Moreover, the 2nd and 3rd FITR indicators, which are altered to a greater extent in the right ventricle, are associated with greater fibrosis.

Rapid Electrical Stimulation Increased Cardiac Apoptosis Through Disturbance of Calcium Homeostasis and Mitochondrial Dysfunction in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

BACKGROUND/AIMS

Heart failure induced by tachycardia, the most common arrhythmia, is frequently observed in clinical practice. This study was designed to investigate the underlying mechanisms.

METHODS

Rapid electrical stimulation (RES) at a frequency of 3 Hz was applied on human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) for 7 days, with 8 h/day and 24 h/day set to represent short-term and long-term tachycardia, respectively. Age-matched hiPSC-CMs without electrical stimulation or with slow electrical stimulation (1 Hz) were set as no electrical stimulation (NES) control or low-frequency electrical stimulation (LES) control. Following stimulation, JC-1 staining flow cytometry analysis was performed to examine mitochondrial conditions. Apoptosis in hiPSC-CMs was evaluated using Hoechst staining and Annexin V/propidium iodide (AV/PI) staining flow cytometry analysis. Calcium transients and L-type calcium currents were recorded to evaluate calcium homeostasis. Western blotting and qPCR were performed to evaluate the protein and mRNA expression levels of apoptosis-related genes and calcium homeostasis-regulated genes.

RESULTS

Compared to the controls, hiPSC-CMs following RES presented mitochondrial dysfunction and an increased apoptotic percentage. Amplitudes of calcium transients and L-type calcium currents were significantly decreased in hiPSC-CMs with RES. Molecular analysis demonstrated upregulated expression of Caspase3 and increased Bax/Bcl-2 ratio. Genes related to calcium re-sequence were downregulated, while phosphorylated Ca2+/calmodulin-dependent protein kinase II (CaMKII) was significantly upregulated following RES. There was no significant difference between the NES control and LES control groups in these aspects. Inhibition of CaMKII with 1 µM KN93 partly reversed these adverse effects of RES.

CONCLUSION

RES on hiPSC-CMs disturbed calcium homeostasis, which led to mitochondrial stress, promoted cell apoptosis and caused electrophysiological remodeling in a time-dependent manner. CaMKII played a central role in the damages induced by RES, pharmacological inhibition of CaMKII activity partly reversed the adverse effects of RES on both structural and electrophysiological properties of cells.

Effect of tachycardia on mRNA andf protein expression of the principal components of the lipolytic system in the rat's heart ventricles

There is a convincing piece of evidence showing that most of free fatty acids (FFA) entering cardiomyocytes are first esterified into triacylglycerols (TG) before being oxidized or used for synthesis of complex lipids. The enzyme adipose triglyceride lipase (ATGL) initiates lipolysis of TG by hydrolyzing the first ester bond of the compound. As a result, free fatty acid and diacylglycerol (DG) are released in that process. Finally, DG may be further hydrolyzed by the enzyme hormone sensitive lipase (HSL). The aim of the present study was to examine effect of tachycardia on mRNA and protein expression of ATGL, CGI-58 (an activator of ATGL), G0S2 (an inhibitor of ATGL) and HSL in the left and right ventricle of the rat. The experiments were carried out on male Wistar rats, 240 - 260 grams of body weight. After anesthesia, two electrodes were inserted in the right jugular vein and connected to SC-04 stimulator. The rats were randomly allocated into one of the three groups, namely: control, 30 min and 60 min of the heart stimulation at the rate of 600 times/min. The expressions of ATGL, CGI-58, G0S2 and HSL were evaluated at both gene and protein levels using real-time PCR and Western Blot analysis, respectively. Both 30 and 60 min stimulation reduced ATGL, HSL, CGI-58 and G0S2 mRNA content in the left ventricle. The stimulation had only insignificant impact on ATGL, HSL and CGI-58 transcript levels in the right ventricle. Interestingly, Western Blot analysis showed that the stimulation, regardless of the time, reduced the ATGL and G0S2 protein expression, but did not change the CGI-58 and HSL expression in the left ventricle. Furthermore, in the right ventricle, the protein expressions of ATGL, HSL and G0S2 decreased after stimulation. In conclusion, the obtained results clearly show that tachycardia affects both mRNA and protein expression of particular compounds of the TG lipolytic system in the heart ventricles. Additionally, there are marked differences in the expressions of the examined compounds between the ventricles.

Focal Atrial Tachycardia Arising from the Inferior Vena Cava

The inferior vena cava (IVC) is a rare site of focal atrial tachycardia (AT). Here, we report a 20-year-old woman who underwent catheter ablation for anti-arrhythmic drug-resistant AT originating from the IVC. She had undergone open-heart surgery for patch closure of an atrial septal defect 17 years previously and permanent pacemaker implantation for sinus node dysfunction 6 years previously. The AT focus was at the anterolateral aspect of the IVC-right atrial junction, and it was successfully ablated under three-dimensional electroanatomical-mapping guidance. We suspect that the mechanism of this tachycardia was associated with previous IVC cannulation for open-heart surgery.

Medullary Reticular Neurons Mediate Neuropeptide Y-Induced Metabolic Inhibition and Mastication

Hypothalamic neuropeptide Y (NPY) elicits hunger responses to increase the chances of surviving starvation: an inhibition of metabolism and an increase in feeding. Here we elucidate a key central circuit mechanism through which hypothalamic NPY signals drive these hunger responses. GABAergic neurons in the intermediate and parvicellular reticular nuclei (IRt/PCRt) of the medulla oblongata, which are activated by NPY-triggered neural signaling from the hypothalamus, potentially through the nucleus tractus solitarius, mediate the NPY-induced inhibition of metabolic thermogenesis in brown adipose tissue (BAT) via their innervation of BAT sympathetic premotor neurons. Intriguingly, the GABAergic IRt/PCRt neurons innervating the BAT sympathetic premotor region also innervate the masticatory motor region, and stimulation of the IRt/PCRt elicits mastication and increases feeding as well as inhibits BAT thermogenesis. These results indicate that GABAergic IRt/PCRt neurons mediate hypothalamus-derived hunger signaling by coordinating both autonomic and feeding motor systems to reduce energy expenditure and to promote feeding.

Calcium Imaging in Pluripotent Stem Cell-Derived Cardiac Myocytes

The possibility to generate cardiomyocytes (CMs) from disease-specific induced pluripotent stem cells (iPSCs) is a powerful tool for the investigation of various cardiac diseases in vitro. The pathological course of various cardiac conditions, causatively heterogeneous, often converges into disturbed cellular Ca(2+) cycling. The gigantic Ca(2+) channel of the intracellular Ca(2+) store of CMs, the ryanodine receptor type 2 (RyR2), controls Ca(2+) release and therefore plays a crucial role in Ca(2+) cycling of CMs. In the present protocol we describe ways to measure and analyze global as well as local cellular Ca(2+) release events in CMs derived from a patient carrying a CPVT-causing RyR2 mutation.

Transplantation of adipose tissue-derived stem cells improves cardiac contractile function and electrical stability in a rat myocardial infarction model

The transplantation of adipose tissue-derived stem cells (ADSCs) improves cardiac contractility after myocardial infarction (MI); however, little is known about the electrophysiological consequences of transplantation. The purpose of this study was to clarify whether the transplantation of ADSCs increases or decreases the incidence of ventricular tachyarrhythmias (VT) in a rat model of MI. MI was induced experimentally by permanent occlusion of the left anterior descending artery of Lewis rats. ADSCs were harvested from GFP-transgenic rats, and were cultured until passage four. ADSCs (10×10(6)) resuspended in 100μL saline or pro-survival cocktail (PSC), which enhances cardiac graft survival, were injected directly into syngeneic rat hearts 1week after MI. The recipients of ADSCs suspended in PSC had a larger graft area compared with those receiving ASDCs suspended in saline at 1week post-transplantation (number of graft cells/section: 148.7±10.6 vs. 22.4±3.4, p<0.05, n=5/group). Thereafter, all ADSC recipients were transplanted with ASDCs in PSC. ADSCs were transplanted into infarcted hearts, and the mechanical and electrophysiological functions were assessed. Echocardiography revealed that ADSC recipients had improved contractile function compared with those receiving PSC vehicle (fractional shortening: 21.1±0.9 vs. 14.1±1.2, p<0.05, n≥12/group). Four weeks post-transplantation, VT was induced via in vivo programmed electrical stimulation. The recipients of ADSCs showed a significantly lower incidence of induced VT compared with the control (31.3% vs. 83.3%, p<0.05, n≥12/group). To understand the electrical activity following transplantation, we performed ex vivo optical mapping using a voltage sensitive dye, and found that ADSC transplantation decreased conduction velocity and its dispersion in the peri-infarct area. These results suggest that ADSC transplantation improved cardiac mechanical and electrophysiological functions in subacute MI.

The ER stress-mediated mitochondrial apoptotic pathway and MAPKs modulate tachypacing-induced apoptosis in HL-1 atrial myocytes

Background and Object

Cell apoptosis is a contributing factor in the initiation, progression and relapse of atrial fibrillation (AF), a life-threatening illness accompanied with stroke and heart failure. However, the regulatory cascade of apoptosis is intricate and remains unidentified, especially in the setting of AF. The aim of this study was to explore the roles of endoplasmic reticulum (ER) stress, mitochondrial apoptotic pathway (MAP), mitogen-activated protein kinases (MAPKs), and their cross-talking in tachypacing-induced apoptosis.

Methods and Results

HL-1 cells were cultured in the presence of tachypacing for 24 h to simulate atrial tachycardia remodeling. Results showed that tachypacing reduced cell viability measured by the cell counting kit-8, dissipated mitochondrial membrane potential detected by JC-1 staining and resulted in approximately 50% apoptosis examined by Hoechst staining and annexin V/propidium iodide staining. In addition, the proteins involved in ER stress, MAP and MAPKs were universally up-regulated or activated via phosphorylation, as confirmed by western blotting; and reversely silencing of ER stress, caspase-3 (the ultimate executor of MAP) and MAPKs with specific inhibitors prior to pacing partially alleviated apoptosis. An inhibitor of ER stress was applied to further investigate the responses of mitochondria and MAPKs to ER stress, and results indicated that suppression of ER stress comprehensively but incompletely attenuated the activation of MAP and MAPKs aroused by tachypacing, with the exception of ERK1/2, one branch of MAPKs.

Conclusions

Our study suggested tachypacing-induced apoptosis is regulated by ER stress-mediated MAP and MAPKs. Thus, the above three components are all promising anti-apoptotic targets in AF patients and ER stress appears to play a dominant role due to its comprehensive effects.

Tachycardia-induced silencing of subcellular Ca2+ signaling in atrial myocytes

Atrial fibrillation (AF) is characterized by sustained high atrial activation rates and arrhythmogenic cellular Ca2+ signaling instability; however, it is not clear how a high atrial rate and Ca2+ instability may be related. Here, we characterized subcellular Ca2+ signaling after 5 days of high atrial rates in a rabbit model. While some changes were similar to those in persistent AF, we identified a distinct pattern of stabilized subcellular Ca2+ signaling. Ca2+ sparks, arrhythmogenic Ca2+ waves, sarcoplasmic reticulum (SR) Ca2+ leak, and SR Ca2+ content were largely unaltered. Based on computational analysis, these findings were consistent with a higher Ca2+ leak due to PKA-dependent phosphorylation of SR Ca2+ channels (RyR2s), fewer RyR2s, and smaller RyR2 clusters in the SR. We determined that less Ca2+ release per [Ca2+]i transient, increased Ca2+ buffering strength, shortened action potentials, and reduced L-type Ca2+ current contribute to a stunning reduction of intracellular Na+ concentration following rapid atrial pacing. In both patients with AF and in our rabbit model, this silencing led to failed propagation of the [Ca2+]i signal to the myocyte center. We conclude that sustained high atrial rates alone silence Ca2+ signaling and do not produce Ca2+ signaling instability, consistent with an adaptive molecular and cellular response to atrial tachycardia.

Ictal tachycardia: the head-heart connection

Epileptic seizures can lead to changes in autonomic function affecting the sympathetic, parasympathetic, and enteric nervous systems. Changes in cardiac signals are potential biomarkers that may provide an extra-cerebral indicator of ictal onset in some patients. Heart rate can be measured easily when compared to other biomarkers that are commonly associated with seizures (e.g., long-term EEG), and therefore it has become an interesting parameter to explore for detecting seizures. Understanding the prevalence and magnitude of heart rate changes associated with seizures, as well as the timing of such changes relative to seizure onset, is fundamental to the development and use of cardiac based algorithms for seizure detection. We reviewed 34 articles that reported the prevalence of ictal tachycardia in patients with epilepsy. Scientific literature supports the occurrence of significant increases in heart rate associated with ictal events in a large proportion of patients with epilepsy (82%) using concurrent electroencephalogram (EEG) and electrocardiogram (ECG). The average percentage of seizures associated with significant heart rate changes was similar for generalized (64%) and partial onset seizures (71%). Intra-individual variability was noted in several articles, with the majority of studies reporting significant increase in heart rate during seizures originating from the temporal lobe. Accurate detection of seizures is likely to require an adjustable threshold given the variability in the magnitude of heart rate changes associated with seizures within and across patients.

A quantitative comparison of the behavior of human ventricular cardiac electrophysiology models in tissue

Numerical integration of mathematical models of heart cell electrophysiology provides an important computational tool for studying cardiac arrhythmias, but the abundance of available models complicates selecting an appropriate model. We study the behavior of two recently published models of human ventricular action potentials, the Grandi-Pasqualini-Bers (GPB) and the O'Hara-Virág-Varró-Rudy (OVVR) models, and compare the results with four previously published models and with available experimental and clinical data. We find the shapes and durations of action potentials and calcium transients differ between the GPB and OVVR models, as do the magnitudes and rate-dependent properties of transmembrane currents and the calcium transient. Differences also occur in the steady-state and S1–S2 action potential duration and conduction velocity restitution curves, including a maximum conduction velocity for the OVVR model roughly half that of the GPB model and well below clinical values. Between single cells and tissue, both models exhibit differences in properties, including maximum upstroke velocity, action potential amplitude, and minimum diastolic interval. Compared to experimental data, action potential durations for the GPB and OVVR models agree fairly well (although OVVR epicardial action potentials are shorter), but maximum slopes of steady-state restitution curves are smaller. Although studies show alternans in normal hearts, it occurs only in the OVVR model, and only for a narrow range of cycle lengths. We find initiated spiral waves do not progress to sustained breakup for either model. The dominant spiral wave period of the GPB model falls within clinically relevant values for ventricular tachycardia (VT), but for the OVVR model, the dominant period is longer than periods associated with VT. Our results should facilitate choosing a model to match properties of interest in human cardiac tissue and to replicate arrhythmia behavior more closely. Furthermore, by indicating areas where existing models disagree, our findings suggest avenues for further experimental work.

Permanent junctional reciprocating tachycardia in a dog

A 5-year-old male English Bulldog was presented with a 1-year history of paroxysmal supraventricular tachycardia (SVT) partially responsive to amiodarone. At admission the surface ECG showed sustained runs of a narrow QRS complex tachycardia, with a ventricular cycle length (R-R interval) of 260 ms, alternating with periods of sinus rhythm. Endocardial mapping identified the electrogenic mechanism of the SVT as a circus movement tachycardia with retrograde and decremental conduction along a concealed postero-septal atrioventricular pathway (AP) and anterograde conduction along the atrioventricular node. These characteristics were indicative of a permanent junctional reciprocating tachycardia (PJRT). Radiofrequency catheter ablation of the AP successfully terminated the PJRT, with no recurrence of tachycardia on Holter monitoring at 12 months follow-up.

MicroRNA-1 downregulation increases connexin 43 displacement and induces ventricular tachyarrhythmias in rodent hypertrophic hearts

Downregulation of the muscle-specific microRNA-1 (miR-1) mediates the induction of pathologic cardiac hypertrophy. Dysfunction of the gap junction protein connexin 43 (Cx43), an established miR-1 target, during cardiac hypertrophy leads to ventricular tachyarrhythmias (VT). However, it is still unknown whether miR-1 and Cx43 are interconnected in the pro-arrhythmic context of hypertrophy. Thus, in this study we investigated whether a reduction in the extent of cardiac hypertrophy could limit the pathological electrical remodeling of Cx43 and the onset of VT by modulating miR-1 levels. Wistar male rats underwent mechanical constriction of the ascending aorta to induce pathologic left ventricular hypertrophy (LVH) and afterwards were randomly assigned to receive 10mg/kg valsartan, VAL (LVH+VAL) delivered in the drinking water or placebo (LVH) for 12 weeks. Sham surgery was performed for control groups. Programmed ventricular stimulation reproducibly induced VT in LVH compared to LVH+VAL group. When compared to sham controls, rats from LVH group showed a significant decrease of miR-1 and an increase of Cx43 expression and its ERK1/2-dependent phosphorylation, which displaces Cx43 from the gap junction. Interestingly, VAL administration to rats with aortic banding significantly reduced cardiac hypertrophy and prevented miR-1 down-regulation and Cx43 up-regulation and phosphorylation. Gain- and loss-of-function experiments in neonatal cardiomyocytes (NCMs) in vitro confirmed that Cx43 is a direct target of miR-1. Accordingly, in vitro angiotensin II stimulation reduced miR-1 levels and increased Cx43 expression and phosphorylation compared to un-stimulated NCMs. Finally, in vivo miR-1 cardiac overexpression by an adenoviral vector intra-myocardial injection reduced Cx43 expression and phosphorylation in mice with isoproterenol-induced LVH. In conclusion, miR-1 regulates Cx43 expression and activity in hypertrophic cardiomyocytes in vitro and in vivo. Treatment of pressure overload-induced myocyte hypertrophy reduces the risk of life-threatening VT by normalizing miR-1 expression levels with the consequent stabilization of Cx43 expression and activity within the gap junction.

Left atrial endocardial fibrosis and intra-atrial thrombosis - landmarks of left atrial remodeling in rats with spontaneous atrial tachyarrhythmias

INTRODUCTION

Histological abnormalities are common findings in the left atria (LA) of atrial fibrillation (AF) patients. We aimed to assess LA histological abnormalities in our model of spontaneous atrial tachyarrhythmias in rats.

MATERIALS AND METHODS

LA sampling was performed in 12 spontaneously hypertensive rats (SHRs) and eight age-matched Wistar-Kyoto (WKY) rats. Tissue sections were stained with Masson's trichrome and Hematoxylin-Eosin-Safran and examined with a light microscope. A 0 to 3 scoring system was used to quantify the severity of LA structural abnormalities. LA von Willebrand factor (vWF) content was also assessed using immunohistochemical staining.

RESULTS

In six of the eight SHRs, LA fibrosis, inflammatory infiltrates, and myocyte necrosis of varying grades of severity were observed. The most frequent feature was endocardial fibrosis, which was observed in six SHRs and in none of the WKY rats. Intra-atrial thrombosis was found in three SHRs and in none of the WKY rats. The intensity of vWF-related fluorescence was higher in the atrial endocardium of SHRs compared to age-matched WKY rats.

CONCLUSIONS

Our findings reinforce the role of LA structural abnormalities in atrial arrhythmogenicity. However, two SHRs did not present LA histological abnormalities despite the presence of arrhythmias. This finding suggests that the LA remodeling-atrial tachyarrhythmia relationship could be highly nonlinear and that atrial fibrosis is more likely to be a facilitator of atrial arrhythmogenicity, rather than a prerequisite. We also provide evidence that intra-atrial thrombosis accompanies LA structural remodeling in arrhythmic rats. Increased endocardial platelet adhesion molecule vWF could contribute to this increased thrombogenicity.

Atrial tachyarrhythmia in Rgs5-null mice

AIMS

The aim of this study was to elucidate the effects of regulator of G-protein signaling 5 (Rgs5), a negative regulator of G protein-mediated signaling, on atrial repolarization and tachyarrhythmia (ATA) in mice.

METHODS AND RESULTS

In present study, the incidence of ATA were increased in Rgs5(-/-) Langendorff-perfused mouse hearts during program electrical stimulation (PES) (46.7%, 7 of 15) and burst pacing (26.7%, 4 of 15) compared with wild-type (WT) mice (PES: 7.1%,1 of 14; burst:7.1%,1 of 14) (P<0.05). And the duration of ATA also shown longer in Rgs5(-/-) heart than that in WT, 2 out of 15 hearts exhibited sustained ATA (>30 s) but none of them observed in WT mice. Atrial prolonged repolarization was observed in Rgs5(-/-) hearts including widened P wave in surface ECG recording, increased action potential duration (APD) and atrial effective refractory periods (AERP), all of them showed significant difference with WT mice (P<0.05). At the cellular level, whole-cell patch clamp recorded markedly decreased densities of repolarizing K(+) currents including I(Kur) (at +60 mV: 14.0±2.2 pF/pA) and I(to) (at +60 mV: 16.7±1.3 pA/pF) in Rgs5(-/-) atrial cardiomyocytes, compared to those of WT mice (at +60 mV I(to): 20.4±2.0 pA/pF; I(kur): 17.9±2.0 pF/pA) (P<0.05).

CONCLUSION

These results suggest that Rgs5 is an important regulator of arrhythmogenesis in the mouse atrium and that the enhanced susceptibility to atrial tachyarrhythmias in Rgs5(-/-) mice may contribute to abnormalities of atrial repolarization.

Effects of different small HSPB members on contractile dysfunction and structural changes in a Drosophila melanogaster model for Atrial Fibrillation

The most common clinical tachycardia, Atrial Fibrillation (AF), is a progressive disease, caused by cardiomyocyte remodeling, which finally results in contractile dysfunction and AF persistence. Recently, we identified a protective role of heat shock proteins (HSPs), especially the small HSPB1 member, against tachycardia remodeling in experimental AF models. Our understanding of tachycardia remodeling and anti-remodeling drugs is currently hampered by the lack of suitable (genetic) manipulatable in vivo models for rapid screening of key targets in remodeling. We hypothesized that Drosophila melanogaster can be exploited to study tachycardia remodeling and protective effects of HSPs by drug treatments or by utilizing genetically manipulated small HSP-overexpressing strains. Tachypacing of Drosophila pupae resulted in gradual and significant cardiomyocyte remodeling, demonstrated by reduced contraction rate, increase in arrhythmic episodes and reduction in heart wall shortening, compared to normal paced pupae. Heat shock, or pre-treatment with HSP-inducers GGA and BGP-15, resulted in endogenous HSP overexpression and protection against tachycardia remodeling. DmHSP23 overexpressing Drosophilas were protected against tachycardia remodeling, in contrast to overexpression of other small HSPs (DmHSP27, DmHSP67Bc, DmCG4461, DmCG7409, and DmCG14207). (Ultra)structural evaluation of the tachypaced heart wall revealed loss of sarcomeres and mitochondrial damage which were absent in tachypaced DmHSP23 overexpressing Drosophila. In addition, tachypacing induced a significant increase in calpain activity, which was prevented in tachypaced Drosophila overexpressing DmHSP23. Tachypacing of Drosophila resulted in cardiomyocyte remodeling, which was prevented by general HSP-inducing treatments and overexpression of a single small HSP, DmHSP23. Thus, tachypaced D. melanogaster can be used as an in vivo model system for rapid identification of novel targets to combat AF associated cardiomyocyte remodeling.

Rare mechanical complication of myocardial infarction: isolated right ventricle free wall rupture

Rupture of the left ventricular free wall is a dramatic complication of acute myocardial infarction (MI) and occurs in about ten percent of patients with fatal acute MI. However, there are limited reports about right ventricular free wall rupture due to MI. In this case report, a patient with isolated right ventricular rupture following MI that was visualised with real-time transthoracic echocardiography is discussed for the first time in the literature.

Caudal brainstem processing is sufficient for behavioral, sympathetic, and parasympathetic responses driven by peripheral and hindbrain glucagon-like-peptide-1 receptor stimulation

The effects of peripheral glucagon like peptide-1 receptor (GLP-1R) stimulation on feeding, gastric emptying, and energetic responses involve vagal transmission and central nervous system processing. Despite a lack of studies aimed at determining which central nervous system regions are critical for the GLP-1R response production, hypothalamic/forebrain processing is regarded as essential for these effects. Here the contribution of the caudal brainstem to the control of food intake, core temperature, heart rate, and gastric emptying responses generated by peripheral delivery of the GLP-1R agonist, exendin-4 (Ex-4), was assessed by comparing responses of chronic supracollicular decerebrate (CD) rats to those of pair-fed intact control rats. Responses driven by hindbrain intracerebroventricular (fourth i.c.v) delivery of Ex-4 were also evaluated. Intraperitoneal Ex-4 (1.2 and 3.0 microg/kg) suppressed glucose intake in both CD rats (5.0+/-1.2 and 4.4+/-1.1 ml ingested) and controls (9.4+/-1.5 and 7.7+/-0.8 ml ingested), compared with intakes after vehicle injections (13.1+/-2.5 and 13.2+/-1.7 ml ingested, respectively). Hindbrain ventricular Ex-4 (0.3 microg) also suppressed food intake in CD rats (4.7+/-0.6 ml ingested) and controls (11.0+/-2.9 ml ingested), compared with vehicle intakes (9.3+/-2.1 and 19.3+/-4.3 ml ingested, respectively). Intraperitoneal Ex-4 (0.12, 1.2, 2.4 microg/kg) reduced gastric emptying rates in a dose-related manner similarly for both CD and control rats. Hypothermia followed ip and fourth i.c.v Ex-4 in awake, behaving controls (0.6 and 1.0 C average suppression) and CD rats (1.5 and 2.5 C average suppression). Intraperitoneal Ex-4 triggered tachycardia in both control and CD rats. Results demonstrate that caudal brainstem processing is sufficient for mediating the suppression of intake, core temperature, and gastric emptying rates as well as tachycardia triggered by peripheral GLP-1R activation and also hindbrain-delivered ligand. Contrary to the literature, hypothalamic/forebrain processing and forebrain-caudal brainstem communication is not required for the observed responses.

Mitochondrial dysfunction and redox signaling in atrial tachyarrhythmia

Accumulating evidence links calcium-overload and oxidative stress to atrial remodeling during atrial fibrillation (AF). Furthermore, atrial remodeling appears to increase atrial thrombogeneity, characterized by increased expression of adhesion molecules. The aim of this study was to assess mitochondrial dysfunction and oxidative stress-activated signal transduction (nuclear factor-kappaB [NF-kappa B], lectin-like oxidized low-density lipoprotein receptor [LOX-1], intercellular adhesion molecule-1 [ICAM-1], and hemeoxgenase-1 [HO-1]) in atrial tissue during AF. Ex vivo atrial tissue from patients with and without AF and, additionally, rapid pacing of human atrial tissue slices were used to study mitochondrial structure by electron microscopy and mitochondrial respiration. Furthermore, quantitative reverse transcription polymerase chain reaction (RT-PCR), immunoblot analyses, gel-shift assays, and enzyme-linked immunosorbent assay (ELISA) were applied to measure nuclear amounts of NF-kappa B target gene expression. Using ex vivo atrial tissue samples from patients with AF we demonstrated oxidative stress and impaired mitochondrial structure and respiration, which was accompanied by nuclear accumulation of NF-kappa B and elevated expression levels of the adhesion molecule ICAM-1 and the oxidative stress-induced markers HO-1 and LOX-1. All these changes were reproduced by rapid pacing for 24 hours of human atrial tissue slices. Furthermore, the blockade of calcium inward current with verapamil effectively prevented both the mitochondrial changes and the activation of NF-kappa B signaling and target gene expression. The latter appeared also diminished by the antioxidants apocynin and resveratrol (an inhibitor of NF-kappa B), or the angiotensin II receptor type 1 antagonist, olmesartan. This study demonstrates that calcium inward current via L-type calcium channels contributes to oxidative stress and increased expression of oxidative stress markers and adhesion molecules during cardiac tachyarrhythmia.

Coronary MR angiography at 3T during diastole and systole

PURPOSE

To investigate the impact of end-systolic imaging on quality of right coronary magnetic resonance angiography (MRA) in comparison to diastolic and to study the effect of RR interval variability on image quality.

MATERIALS AND METHODS

The right coronary artery (RCA) of 10 normal volunteers was imaged at 3T using parallel imaging (sensitivity encoding [SENSE]). Navigator-gated three-dimensional (3D) gradient echo was used three times: 1) end-systolic short acquisition (SS): 35-msec window; 2) diastolic short (DS): middiastolic acquisition using 35-msec window; and 3) diastolic long (DL): 75-msec diastolic acquisition window. Vectorcardiogram (VCG) data was used to analyze RR variability. Vessel sharpness, length, and diameter were compared to each other and correlated with RR variability. Blinded qualitative image scores of the images were compared.

RESULTS

Quantitative and qualitative parameters were not significantly different and showed no significant correlation with RR variability.

CONCLUSION

Imaging the RCA at 3T during the end-systolic rest period using SENSE is possible without significant detrimental effect on image quality. Breaking away from the standard of imaging only during diastole can potentially improve image quality in tachycardic patients or used for simultaneous imaging during both periods in a single scan.

Catheter ablation of multiple, surgically created, atrioventricular connections following Fontan Bjork procedure

An increased incidence of Wolff-Parkinson-White (WPW) syndrome with tricuspid atresia has been reported. Although atrioventricular accessory pathways may develop across suture lines after the Fontan-Björk procedure, the presence of multiple acquired accessory pathways has only been described rarely. We report on a case of a female with tricuspid atresia who underwent the Fontan operation at 5 years of age. One year later, she developed a WPW pattern. Narrow complex tachycardias started at the age of 18. An electrophysiological study revealed the presence of three accessory pathway connections at the surgical anastomosis level. All of them were successfully ablated and there were no recurrences.

Tachycardia after pacemaker implantation in a patient with complete atrioventricular block

The atrioventricular (AV) node allows ante- and retrograde conduction between atria and ventricles. It is commonly assumed that these AV nodal conduction properties go hand in hand. However, ante- and retrograde AV conduction can be completely independent from each other in individual patients. We report about a patient with permanent AV block III degrees requiring implantation of a pacemaker. As soon as a dual-chamber device was connected to the implanted leads, a tachycardia started at the maximum tracking rate, which was subsequently reprogrammed from 120 to 170 bpm. Non-invasive electrophysiologic testing showed that this patient demonstrated 1:1 ventriculoatrial (VA) conduction up to 170 bpm leading to endless loop tachycardia (ELT) while the antegrade AV block III degrees persisted. This case impressively illustrates that one has to take into account that patients with antegrade AV block III degrees may still have a high VA conduction capacity leading to ELT. Dual-chamber devices therefore have to be programmed accordingly, activating dedicated reactions after ventricular premature beats and automatic ELT detection and termination algorithms.

Clinical predictors of atrial fibrillation in Brugada syndrome

AIMS

Atrial arrhythmias have been reported in patients with Brugada syndrome. The aim of this study was to evaluate clinical predictors of atrial fibrillation (AF) in Brugada syndrome.

METHODS AND RESULTS

Patients diagnosed with Brugada ECG pattern were enrolled in the study. Type 1, 2, and 3 Brugada ECG pattern was found in 28, 56, and 31 patients, respectively. A total of 85 healthy age and gender-matched subjects were selected as a control group. Mean age, maximum P-wave duration (P(max)), P-wave dispersion (P(disp)), and left atrial dimension were not significantly different between patients and controls. There were no differences between P(max), P(disp), and left atrial dimension of the type 1, 2, and 3 Brugada patients. Spontaneous paroxysmal AF was detected in 15 of 28 type 1 Brugada patients (53%) and none of the type 2 and 3 Brugada patients. All 15 patients with AF had at least one episode of paroxysmal AF and none of the patients showed persistent or chronic AF. All 15 patients who had paroxysmal AF had previous life threatening cardiac events. In contrast, paroxysmal AF did not occur in type 1 Brugada patients without previous life threatening cardiac events. In multiple regression analysis, only the occurrence of previous life threatening cardiac events was a risk factor for paroxysmal AF (P = 0.0001).

CONCLUSION

It is concluded that the most important predictor of AF in Brugada syndrome is the occurrence of previous life threatening cardiac events.

Sympathetic neural activity, sex dimorphism, and postural tachycardia syndrome

OBJECTIVE

To elucidate the mechanisms whereby postural tachycardia syndrome (POTS) patients maintain orthostatic blood pressure and explain the greater prevalence of female cases in POTS cohorts.

METHODS

We investigated muscle sympathetic nerve (MSN) discharge characteristics in 12 female POTS patients and in 9 male and 12 female control subjects using the burst amplitude distribution and the relative contribution of burst frequency and burst amplitude.

RESULTS

At rest, burst distribution was shifted toward larger amplitudes in POTS patients (p < 0.005), consistent with increased sympathetic activity. During hypotension, the distribution shifted toward larger amplitude bursts in control subjects (p < 0.001), whereas it did not change in POTS patients. Total MSN activity increase to hypotension did not differ between subject groups, but the relative contribution of burst frequency change to the total activity increase was greater in POTS patients than in female (p < 0.05) and male (p < 0.001) control subjects. In contrast, the relative contribution of burst amplitude change to total MSN activity increase was greater in male compared with female control subjects (p < 0.05) and POTS patients (p < 0.001).

INTERPRETATION

At rest, the burst amplitude distribution was consistent with increased sympathetic activity in POTS and did not change in response to hypotension. In response to hypotension, burst frequency makes a proportionally greater contribution to the increase in total MSN activity in POTS patients compared with female control subjects, and female compared with male control subjects. These physiological differences in MSN discharge characteristics, in the setting of sympathetic fiber loss associated with POTS, may contribute to the predisposition to and greater prevalence of POTS in female individuals.

Auto-intoxication with flecainide and quinapril: ECG-changes, symptoms and treatment

Flecainide acetate is a sodium channel blocker and a class Ic antiarrhythmic agent with potential life-threatening proarrhythmic and cardioinhibitory properties when taken in overdose. Quinapril is an angiotensin-converting enzyme inhibitor (ACE-inhibitor) and overdose can lead to prolonged hypotension and, less frequently, transient renal impairment. We describe the first published case of intoxication with both drugs. The patient developed a broad-QRS-tachycardia and severe hypotension. Treatment with volume expansion, hypertonic sodium bicarbonate, inotropic support with norepinephrine and insertion of an intra-aortic balloon pump led to complete recovery after 72 hours. We assume that the clinical picture was mainly dictated by flecainide intoxication. Relevant literature data are discussed.

Loss of Vav2 proto-oncogene causes tachycardia and cardiovascular disease in mice

The Vav family is a group of signal transduction molecules that activate Rho/Rac GTPases during cell signaling. Experiments using knockout mice have indicated that the three Vav proteins present in mammals (Vav1, Vav2, and Vav3) are essential for proper signaling responses in hematopoietic cells. However, Vav2 and Vav3 are also highly expressed in nonhematopoietic tissues, suggesting that they may have additional functions outside blood cells. Here, we report that this is the case for Vav2, because the disruption of its locus in mice causes tachycardia, hypertension, and defects in the heart, arterial walls, and kidneys. We also provide physiological and pharmacological evidence demonstrating that the hypertensive condition of Vav2-deficient mice is due to a chronic stimulation of the renin/angiotensin II and sympathetic nervous systems. Together, these results indicate that Vav2 plays crucial roles in the maintenance of cardiovascular homeostasis in mice.

Diversity of the Elevation of Serum Cardiac Troponin I Levels in Patients During Their First Visit to the Emergency Room

BACKGROUND

Although measurement of serum creatine kinase levels, as well as myoglobin levels, has been used for screening patients with acute coronary syndrome (ACS), the specificity of both is low. Measurement of cardiac troponin levels is now extensively used for the diagnosis of ACS because of their superior cardiac specificity. However, troponin levels are reportedly elevated not only in patients with ACS but also in those with other diseases.

METHODS AND RESULTS

The clinical characteristics of 1,023 patients (mean age: 63.5+/-16.3 years; males: 665, females: 358) whose serum cardiac troponin I (cTnI) levels had been measured at the initial visit to the emergency room of Toyota Memorial Hospital between April 2004 and March 2005 were retrospectively analyzed. A positive elevation of cTnI was defined as cTnI > or =0.03 ng/ml. There were 432 patients (42.2%) with positive cTnI levels. The cTnI levels (8.48+/-2.64 ng/ml) in patients with acute myocardial infarction (AMI) were greater than those (0.25+/-0.07 ng/ml) in patients with unstable angina pectoris (AP), as well as those (0.04+/-0.01 ng/ml) in patients with stable AP. In terms of the diagnosis of AMI, the sensitivity was high enough (94.6%), but its specificity was relatively low (61.9%). Furthermore, the differentiation between AMI and unstable AP by the cTnI value alone was impossible. The cTnI levels were elevated in patients with a variety of diseases other than ACS, including heart failure, cardiomyopathies, myocarditis, renal failure, tachyarrhythmias, and pulmonary embolism.

CONCLUSIONS

Elevation of the cTnI level is frequently observed in patients in the emergency room with common diseases other than ACS.

Video-assisted thoracoscopy to treat atrial tachycardia arising from left atrial appendage

A 17-year-old male with tachycardia-induced cardiomyopathy presented with persistent, drug-resistant atrial tachycardia (AT). An electrophysiological study suggested focal abnormal automaticity, and localized the AT origin to the left atrial appendage. Radiofrequency catheter ablation at the site of the earliest endocardial activation during AT failed. A minimally invasive, video-assisted thoracoscopic (VAT) atrial appendectomy terminated the AT and restored left ventricular contractility. The patient remained free of AT and normal left ventricular function was maintained over a 24-month follow-up period. To our knowledge, we are the first to use VAT atrial appendectomy to treat focal AT.

Role of Autonomic Nervous Activity in the Antiarrhythmic Effects of Magnesium Sulfate in a Canine Model of Polymorphic Ventricular Tachyarrhythmia Associated with Prolonged QT Interval

This study was performed to examine the role played by the autonomic nervous system in the antiarrhythmic effects of magnesium sulfate (Mg) in a canine model of polymorphic ventricular tachyarrhythmia facilitated by anthopleurin-A and a slower heart rate induced QT interval prolongation. In 6 experiments, complete atrioventricular block was created to control the heart rate and bradycardia at 800- to 1500-ms cycle lengths was applied for 60 sec before and after drug-induced autonomic block. Transmural unipolar electrograms were recorded from multipolar needle electrodes, and activation-recovery intervals (ARI) were measured. Before drug-induced autonomic block, polymorphic ventricular tachyarrhythmia developed in all 6 experiments during bradycardia before but not after the administration of Mg (0.2 ml/kg intravenous bolus). During drug-induced autonomic block, triggered premature activity decreased without significant changes in underlying dispersion of repolarization and polymorphic ventricular tachyarrhythmia developed during bradycardia in 1 experiment. Administration of Mg during drug-induced autonomic block eliminated premature activity and polymorphic ventricular tachyarrhythmia during bradycardia. The distribution of left ventricular (LV) and right ventricular repolarization and dispersion of transmural repolarization were analyzed before and 60 sec after Mg administration during ventricular pacing at 80 bpm. Mg caused a modest shortening of ARI at all sites before and after drug-induced autonomic block. Since ARI shortening was greater at the mid-myocardial sites than at other LV sites, Mg decreased transmural ARI dispersion from 77 +/- 16 to 46 +/- 21 ms before drug-induced autonomic block and from 79 +/- 7 to 51 +/- 16 ms after drug-induced autonomic block. The antiarrhythmic effects of Mg in this model of long QT syndrome were attributable to its direct pharmacological properties and not to changes in ambient autonomic nervous activity. The blockade of sympathetic activity decreased the incidence of premature events and partially suppressed polymorphic ventricular tachyarrhythmia in this model.

Cardioprotective mechanisms ofPrunus cerasus(sour cherry) seed extract against ischemia-reperfusion-induced damage in isolated rat hearts

The effects of kernel extract obtained from sour cherry ( Prunus cerasus) seed on the postischemic cardiac recovery were studied in isolated working rat hearts. Rats were treated with various daily doses of the extract for 14 days, and hearts were then isolated and subjected to 30 min of global ischemia followed by 120 min of reperfusion. The incidence of ventricular fibrillation (VF) and tachycardia (VT) fell from their control values of 92% and 100% to 50% (not significant) and 58% (not significant), 17% ( P < 0.05), and 25% ( P < 0.05) with the doses of 10 mg/kg and 30 mg/kg of the extract, respectively. Lower concentrations of the extract (1 and 5 mg/kg) failed to significantly reduce the incidence of VF and VT during reperfusion. Sour cherry seed kernel extract (10 and 30 mg/kg) significantly improved the postischemic recovery of cardiac function (coronary flow, aortic flow, and left ventricular developed pressure) during reperfusion. We have also demonstrated that the extract-induced protection in cardiac function significantly reflected in a reduction of infarct size. Immunohistochemistry indicates that a reduction in caspase-3 activity and apoptotic cells by the extract, beside other potential action mechanisms of proanthocyanidin, trans-resveratrol, and flavonoid components of the extract, could be responsible for the cardioprotection in ischemic-reperfused myocardium.

Percutaneous Septal Sinus Shortening

Background— The septal-to-lateral (SL) mitral annular diameter is increased in functional mitral regurgitation (MR). We describe a novel percutaneous technique (the percutaneous septal sinus shortening system) that ameliorates functional MR in an ovine model.

Methods and Results— Sheep underwent rapid right ventricular pacing to obtain moderate to severe functional MR with SL enlargement. The percutaneous septal sinus shortening system was placed via standard interventional techniques consisting of a bridge (suture) element between interatrial septal wall and great cardiac vein anchors. Through progressive tensioning of the bridge element, direct SL shortening was achieved. Sheep underwent short-term (n=19) and long-term (n=4) evaluation after device implantation. In short-term studies, SL diameter decreased an average of 24% (32.5±3.5 to 24.6±2.4 mm; P <0.001), and MR grade significantly improved (2.1±0.6 to 0.4±0.4; P <0.001). Despite continued rapid pacing, chronic device implantation resulted in durable SL shortening (30.4±1.9 mm before implantation to 25.3±0.8 mm at 30 days; P =0.01) and MR reduction (1.8±0.5 before implantation to 0.2±0.1 at 30 days; P =0.01). Increased cardiac output, decreased wedge pressure, and decreased brain natriuretic peptide levels were observed in animals undergoing long-term device implantation.

Conclusions— The percutaneous septal sinus shortening system is effective in ameliorating functional MR in an ovine tachycardia model. The procedure, which uses standard catheter techniques, can be deployed largely under fluoroscopic guidance. The unique bridge element appears durable and allows direct and precise SL shortening to a diameter optimal for MR reduction.

Quetiapine in Overdosage

Data on quetiapine overdosage are only sparsely available in the literature. This study provides additional data on the pharmacokinetics and clinical effects of intoxication with this atypical antipsychotic drug. The authors performed a retrospective analysis of all quetiapine intoxications reported to and screened by the toxicological laboratory of the Central Hospital Pharmacy The Hague between January 1999 and December 2003. Cases with known suggested amount of intake and medical outcome were included. From the patient's medical record and from the toxicological laboratory findings, patient demographic characteristics (gender, age), details of quetiapine intoxication (estimated time of ingestion, estimated amount of ingestion, and coingested drugs) and clinical parameters were obtained. Severity of intoxication was graded by the Poisoning Severity Score (PSS). Individual pharmacokinetic parameter values were calculated using a one-compartment open model and a Bayesian fitting procedure. Out of a total of 21 intoxications with quetiapine, 14 fulfilled the inclusion criteria. The ingested dose ranged from 1200 to 18,000 mg. The blood concentration ranged from 1.1 to 8.8 mg/L with a lag time of 1 to 26.2 hours between time of ingestion and blood sampling at the emergency ward. The most frequent findings were somnolence and tachycardia. The PSS was minor in 6 patients (43%), moderate in 5 patients (36%), and severe in 3 patients (21%). Severity of intoxication was not associated with a higher amount of quetiapine intake. The authors found no correlation between the serum concentration of quetiapine and the amount ingested. Elimination t(1/2) was not prolonged. It can be concluded that quetiapine intoxications appear to proceed mildly. Tachycardia and somnolence were the main clinical symptoms in our case series. No fatalities occurred. The severity of clinical symptoms was not associated with either a high serum concentration or the suggested amount ingested of quetiapine.

Pituitary adenylate cyclase-activating polypeptide: localization and differential influence on isolated hearts from rats and guinea pigs

This study was done to determine if pituitary adenylate cyclase-activating peptide (PACAP)-immunoreactive nerve fibers occur in cardiac muscle as well as intracardiac ganglia of rats and guinea pigs and to clarify the chronotropic actions of PACAP27 in the same species using isolated heart preparations. PACAP nerve fibers were not detected in atrial or ventricular muscle of rat or guinea pig but a few stained nerve fibers occurred in the atrioventricular bundle of the guinea pig. Stained nerve fibers were prominent in intracardiac ganglia of both species. PACAP27 caused a dose-dependent tachycardia in isolated rat hearts (+39 +/- 3 beats/min with 1 nmol, n = 6). Positive and/or negative chronotropic responses were evoked by PACAP27 in guinea pig heart, depending on dose and prior exposure to the peptide. PACAP27 also caused arrhythmias in several guinea pig hearts. Treatment with atropine eliminated or prevented PACAP-evoked bradycardia and arrhythmias, implicating cholinergic neurons in these responses. Positive chronotropic responses to PACAP were unaffected by beta-adrenergic receptor blockade in either species, suggesting that tachycardia resulted from a direct action on the heart. These observations support the conclusion that endogenous PACAP could have a role in regulating parasympathetic input to the heart but through different mechanisms in rats versus guinea pigs. A direct positive chronotropic influence of endogenous PACAP is unlikely since atrial muscle lacks PACAP-immunoreactive nerve fibers.

Usefulness of electroanatomical mapping to differentiate between right ventricular outflow tract tachycardia and arrhythmogenic right ventricular dysplasia

Differentiation between the different right ventricular rhythm disorders and specifically between arrhythmogenic right ventricular dysplasia (ARVD) and right ventricular outflow tract (RVOT) tachycardias has important clinical implications but remains a clinical challenge. We tested the hypothesis that the spatial association of local electrographic parameters may be used to discriminate between these 2 entities. Electroanatomic mapping of the right ventricle was performed in 3 groups: patients who had typical RVOT tachycardia, a control group of patients who had no ventricular arrhythmias, and patients who had a diagnosis of ARVD based on clinical, electrocardiographic, and structural findings. Electroanatomic mapping in the RVOT tachycardia group showed normal electrographic parameters throughout the right ventricle (unipolar electrographic amplitude 9.9 +/- 0.9 mV, duration 55 +/- 1 ms, amplitude/duration 0.193 +/- 0.022) that were no different from those in the control group. In contrast, dysplastic regions in the ARVD group were characterized by significantly lower amplitude (unipolar 3.6 +/- 0.4 mV), prolonged electrographic duration (unipolar 73 +/- 4 ms), and a decreased amplitude/duration ratio (unipolar 0.054 +/- 0.008) compared with the unaffected zones in the same hearts and with all regions in the RVOT and control groups. Thus, endocardial electrographic parameters do not differ between patients who have RVOT and control patients. RVOT tachycardia can be differentiated from ARVD by the absence of abnormal right ventricular electrographic findings. This ability may have important clinical implications and supports the concept of different underlying mechanisms for these 2 entities.

Effects of tachycardia on regional wall motion in acute ischemic canine heart

Tachycardia accompanies the preload reduction. Our aim is to assess the effect of the heart rate change on wall motion in ischemic heart. In 8 dogs with occlusion of left anterior descending artery, we changed the heart rate (heart rate 90, 120, and 150 beats/minute) after using UL-FS49, a selective bradycardic agent, with atrial pacing. Preload was changed by inferior vena caval occlusion at a heart rate of 90 beats/minute. With either an increase in heart rate or an inferior vena caval occlusion, the end-diastolic length was decreased, but the end-diastolic length relationships between the non-ischemic and the ischemic region made different lines from those of the heart rate change and inferior vena caval occlusion. When increasing the heart rate, isovolumetric shortening was unchanged in the non-ischemic region with more expansion in the ischemic region. While inferior vena caval occlusion at a heart rate of 90 beats/minute, isovolumetric shortening was increased in the non-ischemic region, with more expansion in the ischemic region. Both in tachycardia and by the inferior vena caval occlusion, ejectional shortenings decreased in the non-ischemic and ischemic regions. Our results suggest that, in ischemic heart, tachycardia changes both in the end-diastolic length relationship between the non-ischemic and the ischemic region and at the isovolumetric contraction phase. The changes seem to be not only due to the inferior vena caval occlusion, but also due to tachycardia itself.

Prospective evaluation of somatic and autonomic small fibers in selected autonomic neuropathies

BACKGROUND

There are a number of distal and generalized small-fiber neuropathies. The neuropathologic basis is poorly understood as somatic and autonomic C fibers are not usually studied in the same region of the body.

OBJECTIVE

To evaluate prospective somatic and autonomic C-fiber function in 11 healthy control subjects and 38 patients with different clinical patterns of neuropathy.

METHODS

Distal small-fiber neuropathy (DSFN), peripheral neuropathy (PN), diabetic neuropathy (DN), neuropathic postural tachycardia syndrome (POTS), and idiopathic autonomic neuropathy (IAN) were evaluated. Intraepidermal nerve fiber density was used to evaluate distal somatic C fibers. Both quantitative sudomotor axon reflex test and skin norepinephrine content were measured for the biopsy site to assess distal autonomic C-fiber function. Postganglionic sudomotor, adrenergic, and cardiovagal functions were evaluated by autonomic reflex testing and quantified using a Composite Autonomic Severity Scale.

RESULTS

Skin norepinephrine concentration was significantly related to CASS. DN was associated with somatic and autonomic C-fiber impairment with good agreement. POTS was associated with selective distal autonomic deficit. DSFN had combined distal somatic and C-fiber impairment. IAN showed combined and selective distal and generalized autonomic C-fiber impairment. The somatic neuropathies had C-fiber impairment affecting both populations to varying degrees.

CONCLUSION

Although a general agreement exists between the loss of somatic C fibers and autonomic deficits, selective involvement occurs for specific autonomic neuropathies.

[Electrocardiographic recording of long duration (Holter) of 24 hours during idiopathic cardiomyopathy of the peripartum]

The idiopathic myocardiopathy of the peripartum (IMPP) is a frequent disease in the Soudano-Sahelian zone of Africa whose evolution is loaded with many complications hemodynamic, thrombo-embolic and rhythmic. The prevalence and the meaning of the rhythm disorders are unknown. The aims of this prospective study are to measure and to describe the prevalence of the anomalies observed in Holter ECG of 24 hours. It's about a description cross-sectional study realized at the Cardiology Department (CHU Dakar) and 19 patients with IMPP were included, from October 2000 to July 2002. A recording ECG of 24 hours (Holter) was realized on all the patients. The average age was 29.4+/-6.9 years with a low socio-economic level (100%). The diagnosis of IMPP done before childbirth in 4 cases (21%) and the post partum on 15 patients (78.9%). The dyspnea was constant, the chest pain in 12 cases (63.1%) and palpitations in 8 cases (42%). The average rate of hemoglobin was of 10.85+/-2.05 g/dL. The standard electrocardiogram recorded a sinusal tachycardia (68.4%), a cavitary hypertrophy (78.8%), and disorders of the repolarization (47.3%). The cardiac echo-Doppler noted a cavitary dilatation (84.2%), a constant alteration of the left ventricular systolic function with a fraction of average ejection of 29.7+/-10.3%. The anatomy of the valves was normal. The recording Holter ECG of 24 hours recorded a sinusal tachycardia in 17 cases (89.4%), ventricular extrasystoles on 7 patients (36.8%), 4 cases of ventricular tachycardia non-sustained and double ventricular extrasystole on 1 patient, auricular extrasystoles in 4 cases (21%) and 1 case of auriculo-ventricular block of the first degree. The study of heart rate variability founded a mean value of 106 ms.

Costello syndrome and neurological abnormalities

Costello syndrome is a rare but increasingly recognized syndrome of unknown etiology. Neurological abnormalities are not rare in this syndrome and consist of structural and electrophysiological disorders. Ventricular dilatation is observed in more than 40% of cases. Other reported cerebral anomalies are brain atrophy, Chiari malformation and syringomyelia. Although there is insufficient data to propose strict guidelines, it seams reasonnable to have a low threshold for neuroimaging, in general, and particularly when neurologic signs or symptoms are present. Screening including cerebral MRI and EEG should be proposed after a diagnosis of Costello syndrome. The frequency of testing in such children should be guided by neurological follow-up.

Electron microscopic study of intrinsic cardiac ganglia in the adult human

The aim of the present study was to describe in detail the ultrastructure of intrinsic cardiac ganglionic cells in the healthy human as these cells appear to be directly involved in the development of tachycardia, atrioventricular block, ventricular fibrillation, and sudden cardiac death. Tissues examined in this study were obtained from hearts of 10 adult humans of either sex aged 22-80 years at autopsy performed no more than 8 h after death. The examined human intrinsic cardiac nerve cells were in most respects typical autonomic neurons surrounded by a sheath of satellite cells that was either uni- or multilayered. In addition to regular unmyelinated axons, prominent large axon terminals containing lamellated dense bodies, mitochondria and vesicles in the cytoplasm were observed in the ganglion neuropil. Synaptic profiles were more common in the ganglion neuropil than on neuronal somata. According to axon terminal contents, synaptic profiles were of three types. The most common Type 1 synaptic profiles contained a predominance of small clear, with a few larger dense-cored vesicles and mitochondria. Type 2 synaptic profiles, in addition to the same components as in Type 1, had glycogen-like particles. Type 3 vesicle-containing profiles clearly differed from both the previous ones as they were the largest in diameter and included plentifiul large clear pleomorphic or dense-cored vesicles together with small clear and larger dense-cored vesicles, mitochondria, dense and multivesicular bodies. Independently of age of the human, the most frequent neuronal abnormality was an abundant accumulation of inclusions inside of somata and dendrites that, in profile, appeared like circular membranous or fine granular bodies variable in electron density. In addition to inclusions, some neuronal somata and dendrites had strongly swollen mitochondria filled up with granular material in spite of their close association with normal looking ganglionic neurons. Structures resembling an axon growth cone in profile were revealed inside of cardiac ganglia derived from an 80 year old man. In conclusion, the present results provide baseline information on the normal ultrastructure of intracardiac ganglia in healthy humans which may be useful for assessing and interpreting the degree of damage of ganglionic cells both in autonomic and sensory neuropathies of the human heart.

Electronanatomical mapping and ablation of atrial tachycardias with the CARTO system

Variable success rates in the ablation of atrial tachycardias using conventional electrophysiology have been achieved. There is no precise relation between P wave morphology in surface ECG and atrial electrophysiology, and this fact makes it more difficult to locate ectopic atrial foci. The CARTO system creates atrial activation maps that relate an anatomical location to an electrical potential. The aim of this study was to evaluate the efficacy of CARTO guided radiofrequency (RF) ablation of atrial foci. The population consisted of 10 consecutive patients with atrial tachycardia resistant to more than 2 drugs, 7 female, mean age 45 +/- 12 years. CARTO activation maps were constructed based on atrial tachycardia or premature beats. Radiofrequency energy was applied to the earliest activation zone. Immediate success was defined as suppression of ectopic atrial activity. Ectopic foci were located on the ostium of the coronary sinus (3 patients), crista terminalis (1 patient), right atrial appendage (1 patient), interatrial septum (1 patient) and in the pulmonary veins (4 patients). The activation maps contained 85 +/- 35 points. The number of RF applications ranged from 1 to 11 (mean 4). Immediate and 6 month success rate was 90%. We were not able to treat one patient with a focus in the right atrial appendage. No attempt was made to limit procedure or fluoroscopy time in our study. Nonetheless all procedures lasted less than 150 min, and fluoroscopy times were less than 30 minutes.

CONCLUSIONS

The CARTO system precisely located ectopic atrial foci, allowing a high success rate in the ablation of focal atrial tachycardias.

Effect of short-term microgravity and long-term hindlimb unloading on rat cardiac mass and function

The purpose of this study was to test the hypothesis that exposure to short-term microgravity or long-term hindlimb unloading induces cardiac atrophy in male Sprague-Dawley rats. For the microgravity study, rats were subdivided into four groups: preflight (PF, n = 12); flight (Fl, n = 7); flight cage simulation (Sim, n = 6), and vivarium control (Viv, n = 7). Animals in the Fl group were exposed to 7 days of microgravity during the Spacelab 3 mission. Animals in the hindlimb-unloading study were subdivided into three groups: control (Con, n = 20), 7-day hindlimb-unloaded (7HU, n = 10), and 28-day hindlimb-unloaded (28HU, n = 19). Heart mass was unchanged in adult animals exposed to 7 days of actual microgravity (PF 1.33 +/- 0.03 g; Fl 1.32 +/- 0.02 g; Sim 1.28 +/- 0.04 g; Viv 1.35 +/- 0.04 g). Similarly, heart mass was unaltered with hindlimb unloading (Con 1.40 +/- 0.04 g; 7HU 1.35 +/- 0.06 g; 28HU 1.42 +/- 0.03 g). Hindlimb unloading also had no effect on the peak rate of rise in left ventricular pressure, an estimate of myocardial contractility (Con 8,055 +/- 385 mmHg/s; 28HU 8,545 +/- 755 mmHg/s). These data suggest that cardiac atrophy does not occur after short-term exposure to microgravity and that neither short- nor long-term simulated microgravity alters cardiac mass or function.