Modifications of long-term heart rate variability produced in an experimental model of diet-induced metabolic syndrome

Metabolic syndrome (MetS) has been linked to a higher prevalence of cardiac arrhythmias, the most frequent being atrial fibrillation, but the mechanisms are not well understood. One possible underlying mechanism may be an abnormal modulation of autonomic nervous system activity, which can be quantified by analysing heart rate variability (HRV). Our aim was to investigate the modifications of long-term HRV in an experimental model of diet-induced MetS to identify the early changes in HRV and the link between autonomic dysregulation and MetS components. NZW rabbits were randomly assigned to control (n = 10) or MetS (n = 10) groups, fed 28 weeks with high-fat, high-sucrose diet. 24-hour recordings were used to analyse HRV at week 28 using time-domain, frequency-domain and nonlinear analyses. Time-domain analysis showed a decrease in RR interval and triangular index (Ti). In the frequency domain, we found a decrease in the low frequency band. Nonlinear analyses showed a decrease in DFA-α1 and DFA-α2 (detrended fluctuations analysis) and maximum multiscale entropy. The strongest association between HRV parameters and markers of MetS was found between Ti and mean arterial pressure, and Ti and left atrial diameter, which could point towards the initial changes induced by the autonomic imbalance in MetS.

Altered atrial restitution dynamics and refractoriness in metabolic syndrome due to up-regulation of potassium repolarizing currents increases susceptibility to atrial fibrillation

Background

Metabolic alterations, such as Metabolic Syndrome (MS), describe an association of factors including diabetes, hypertension, obesity and dyslipidemia, linked to higher risk and prevalence of overall cardiovascular disease, arrhythmogenesis and sudden cardiac death. Obese and diabetic patients have shown an increased risk for developing atrial fibrillation (AF). However, underlying mechanisms are not understood.

Purpose

To study the effects of MS and obesity remodeling in atrial restitution dynamics, frequency-dependent adaptation, refractoriness and its potential susceptibility to AF.

Methods

Electrophysiological experimental data from High-fat (HF-O, standard rabbit chow with an additional 15% fat) and Hig-fat High-Sucrose Metabolic Syndrome (HFHS-MS, 10% hydrogenated coconut oil and 5% lard, 15% high-sucrose dissolved in water) rabbit models were used to adjust computational models atrial electrophysiology remodeling under each condition. Additionally, isoproterenol and AF conditions were considered to challenge both in-silico models. Validation and sensitivity analysis were performed for each model parameters. Computational simulations in conditions of pacing at different pacing cycle lengths was assessed at 100, 125, 150, 200, 250, 350, 450, 500, 650, 750, 850, 1000 ms. Restitution dynamics were automatically determined and analyzed, as well as restitution slopes and presence of automaticity, early after-depolarizations, alternans and cardiac arrhythmia induction.

Results

Shortening of action potential duration and refractoriness in the left atrium was observed under HFHS-MS. Upstroke velocity, maximum excitability and sodium availability were altered both in HF-O and HFHS-MS. HF-O remodeling showed presence of alternans at high pacing frequencies. Repolarization restitution was shortened in conditions of ISO and MS-AF. Restitution slopes were >1 in HF-O and HFHS-MS, which was correlated to higher susceptibility to AF, and further increased in MS-AF. Under MS-AF, abbreviation in APD in both atria, resulted in increased reentrant frequencies in AF, which was exacerbated under IK1 up-regulation, increasing atrial vulnerability.

Conclusions

HFHS-MS underlies modifications in atrial electrophysiology including shorter refractoriness in HFHS-MS, as well as modifications in atrial excitability, which may be pro-arrhythmic mainly at high frequency rates. This could be explained in part by an up-regulation of outward potassium channels. These results could partially explain increased susceptibility for AF in MS.

Funding Acknowledgement

Type of funding sources: None.

Endurance training increases ventricular refractoriness and wavelength of the cardiac impulse without participation of parasympathetic postganglionic neurons. A study in isolated rabbit heart

Background

Endurance physical training plays a protective role in against ventricular fibrillation (VF), but the exact underlying mechanisms are not completely understood. It is well-known that modifications in myocardial ventricular properties such as refractoriness, conduction velocity and wavelength are key in the initiation and maintenance of VF; furthermore, vagus nerve stimulation has prophylactic effects on malignant arrhythmias and VF. On the other hand, parasympathetic nervous system activity is increased in trained individuals, which in turn affects different ventricular electrophysiological properties. We hypothesized that physical training increases conduction velocity and wavelength, and that these changes are mediated by myocardial cholinergic neurons.

Methods

To test this hypothesis, ten rabbits were submitted to a six-week endurance training protocol and twenty controls were not trained (divided in control group, n=10 and sham group n=10). After training, rabbits were euthanized and their hearts excised, isolated and perfused in a Langendorff system. A pacing electrode and a plaque with 240 recoding electrodes acquiring at 1 KHz were positioned on the left ventricle (LV). Extraestimulus test using four different pacing cycle lengths (90% basal cycle length, 250, 200 and 150 ms) was performed before and after atropine (1μM, control and trained groups) or vehicle (tyrode, sham group) infusion. We studied 1) LV effective refractory period (ERP), 2) LV functional refractory period (FRP), 3) LV conduction velocity (CV), and 4) LV wavelength, determined as LV FRP x CV. Factorial ANOVA (mixed model) was used for statistical analysis (p<0.05).

Results

Before parasympathetic blockade, LV FRP increased in trained animals (Figure, B) whereas no difference was found in LV CV between trained and control animals at any pacing cycle length (Figure, A). In consequence, LV wavelength increased in trained animals (Figure, C). There were no changes in LV ERP, FRP, CV and wavelength when comparisons were made within groups before and after atropine infusion. In sham animals, vehicle infusion or time-course of the experiment did not modify LV FRP, ERP, CV and wavelength.

Conclusion

Physical training increases LV wavelength, which can be one electrophysiological mechanism by which endurance training could protect against VF. Since modifications of ventricular refractoriness and wavelength do not seem dependent of intrinsic parasympathetic nervous system activity, other intrinsic mechanisms could be implied and warrant further research.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Instituto de Salud Carlos III, Generalitat Valenciana

Time and frequency domain analysis of long-term heart rate variability in an experimental model of diet-induced metabolic syndrome

Background

Metabolic syndrome (MetS) is defined as the set of at least three of the following conditions: central obesity, elevation of triglycerides, decreased in high-density lipoproteins, systemic hypertension and glucose intolerance. MetS is linked with a high prevalence of cardiovascular disease, including sudden cardiac death and atrial arrhythmias, which may be a consequence of changes related to the structure, function and autonomic control of the heart. One of the underlying mechanisms responsible could be the alteration of sinus node automaticity. Heart rate variability (HRV) analysis is a useful non-invasive tool for evaluating alterations in neural control of cardiac automaticity.

Purpose

To examine the changes in long-term HRV using time- and frequency- domain analyses in an experimental model of diet-induced MetS which develops all its components.

Methods

Male NZW rabbits were randomly assigned to control (n=10) or MetS group (n=10), fed with high-fat (10% coconut oil and 5% lard) and high sucrose (15% dissolved in water) diet during 28 weeks. At week 28, 24 hour ECG recording was performed (eMotion Faros 180, Mega Electronics®, 1 kHz). We analyzed 60 minutes of RR time series, comparing day (from 8:00 to 19:59 h) and night (from 20:00 to 7:59 h), and quantified the standard parameters of time and frequency domains: 1) Time domain: RR, SDNN, triangular index (Ti), RMSSD and TINN; 2) Frequency domain: very low (VLF), low (LF), high frequency (HF), and LF/HF index. Multivariate analysis of variance (MANOVA, factorial model) was used for statistical analysis (p<0.05).

Results

Time domain analysis showed a decrease in RR interval (p<0.001) and geometrical Ti (p=0.036) in MetS animals (Figure, A-B), indicative of an increased heart rate. The rest of parameters in the time domain (SDNN, RMSSD, TINN) were not modified. Further, in the frequency domain at FFT spectrum, we did find a significant decrease in the LF band (p=0.032) in MetS animals (Figure, C). The rest of the frequency domain parameters (VLF, HF and LF/HF index) remained unchanged.

Conclusion

MetS decreased RR interval duration and triangular index, suggesting an increased sympathetic activity during day and night. Those changes were reflected in LF modifications, and might be attributable to a deficiency in sympathetic-parasympathetic control, which requires adjustments to maintain normal autonomic balance. Collectively, these results could give insight into the autonomic mechanisms that underlie increased atrial arrhythmia susceptibility in MetS.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Generalitat Valenciana, University of Valencia

Simultaneous atrial and ventricular restitution and fibrillation analyses using a low-cost scalable panoramic whole-heart optical mapping configuration for whole-heart imaging of translational models

Introduction

Optical mapping (OM) is the primary method for imaging electrophysiologically relevant parameters from the outer surface of Langendorff-perfused hearts. However, current panoramic OM systems are financially challenging, require multiple sensors to map wide areas of the surface with overlapping regions and missing areas of interest due to the intrinsic shape of the heart. We proposed different panoramic configurations to dynamically characterize atrial and ventricular function during arrhythmia and, in presence of a coronary occlusion.

Methods

We devised both a multi-sensor and a single sensor system integrated with the perfusion circuit comprising sensor elements, a control system for led illumination, electrical stimulation and sensing of physiological variables. Two configurations were tested: A multi-sensor panoramic approach including different camera views and, a precision near-ellipsoidal curved mirror (highly concentrated reflectance in the range 380nm-800nm), with exponential profile and diameter to harbor small to large hearts was used. Twelve-rabbits and two pig hearts were included in the study. OM was performed using di-4 ANDBQPQ near-infrared dye and 5–10uM blebbistatine. Initial camera calibration was done using a fishnet-like pattern and nylon landmarks. We characterized signal-tonoise ratios (SNR) of reconstructed action potentials (AP) and obtained parametric maps of the activation process. A custom-built computational pipeline for accurate motion compensation and AP reconstructions was used. Hearts were stimulated until ventricular fibrillation (VF) was induced with and without presence of a coronary occlusion in the LADartery (LADCO).

Results

High SNRs spatial maps were obtained after AP reconstruction (42.24±4.23dB,stimulated; 23.31±5.24dB,VF) in the most restrictive set-up, the single-sensor near-ellipsoidal configuration. Quantified activation and repolarization dynamic restitution properties were assigned to anatomically labelled scale-invariant areas in the atrium and ventricles during the induction process. Atrial and ventricular restitution dynamics could be reconstructed and analyzed simultaneously. Slower conduction (CT) and higher dispersion in repolarization (DoR) was observed after LADCO in LV (CT: 13.4±5.31ms-vs-22.42±6.82ms,DoR:23.24±4.23ms-vs-38.03±9.17ms,p<0.05). During VF, more heterogeneous activation patterns, enhanced left-to-right VV spectral gradient profiles, and spatially constraint shorter-lived filaments, partially explained the disturbances observed during LADCO. Results obtained with a direct multiple sensor configuration allowed for complete tracking of dominant sources, yet presenting overlapped information.

Conclusion

Hereby results comparing two low-cost configurations for panoramic imaging are presented and validated for the study of cardiac propagation throughout the whole epicardial surface for the study of arrhythmia, drug interventions and cardiovascular disease.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): CIBERcv

CaMKII inhibition reduces electrical activation heterogeneities caused by mechanical stretch in the myocardium

Introduction

Ca2+/calmodulin-dependant protein kinase II (CaMKII) activity in cardiomyocytes plays a crucial role in their contractility. Increased CaMKII signalling has been associated with mechanical stretch, often caused in the border zone of myocardial infarction. CaMKII upregulation causes a mishandling of intracellular calcium, a precursor of multiple pro-arrhythmic mechanisms, such as early afterdepolarisations.

Purpose

In this study, we aim to quantify the effects of KN-93 -a CaMKII inhibitor- on wave dynamics, in order to investigate its effectiveness as an anti-arrhythmic agent.

Methods

An isolated Langendorff model was constructed based on rabbit hearts (n=18) and posteriorly induced to fibrillation. An epicardial multielectrode array (121 electrodes) was used for recording the electrical activity. Mechanical stretch was induced by pushing the anterior myocardial wall from the left-ventricular cavity. Then, a frequency analysis was conducted for the following conditions: before drug infusion, during infusion, during infusion plus stretch, and during infusion post-stretch. Nine hearts represented the untreated group, and the other nine were infused with KN-93 at a concentration of 10 nM (less than 3% of the IC50 value).

Results

Prior to stretch induction, KN-93 caused no effects in the spectral concentration (SC) and average dominant frequency (ADF) calculated on the infused rabbit hearts. Nevertheless, intrasubject measurements revealed statistically significant differences (p<0.05) between hearts infused with KN-93 and the untreated ones when stretch was induced. Changes in SC were milder in the treated than the untreated group (−6% vs −33%). Also, the stretch-induced increase in ADF was more limited in the treated group (+17% vs +40%). Hearts infused with KN-93 shown a higher resistance to stretch-induced electrical abnormalities, potentially due to better regulated intracellular calcium dynamics.

Conclusion

CaMKII inhibitors show cardioprotective potential, even at very low concentrations. Further research is required to investigate the therapeutic use of these compounds in conditions of intracellular calcium mishandling and its concomitant life-threatening consequences, such as heart failure or Torsade de Pointes.

KN-93 reduces stretch-induced changes

Funding Acknowledgement

Type of funding source: Public Institution(s). Main funding source(s): Universitat de València; Generalitat Valenciana - Prometeo; Carlos III, CIBERCV

P1605Increased irregularity and spectral complexity of the intrinsic pacemaker beat-to-beat variability correlates with increased metabolic syndrome components

Background

Metabolic syndrome (MetS) is becoming one of the future potential leading risk factors for heart and cardiovascular disease. MetS relates to a condition associated with at least three metabolic risk factors raising risk for health diseases concomitantly such as diabetes, stroke, hypertension, obesity and dyslipidemia. This can lead to chest pain, heart attack, heart damage and overall higher prevalence of cardiovascular disease, atrial fibrillation and sudden cardiac death. One of the underlying mechanisms of the progressive remodeling in presence of MetS components could be altered automaticity, which would reflect modifications of sinus node activity. These phenomena can be evaluated analyzing the components of heart rate variability (HRV).

Purpose

Our aim was to examine the modifications of sinus node variability in an isolated heart model of diet-induced obesity and MetS.

Methods

Male NZW rabbits were randomly assigned to high-fat (HF, n=8), control (HF-C, n=7), high-fat, high-sucrose (HFHS, n=9), and control (HFHS-C, n=9) groups, fed with their respective diets during 18/28 weeks. After euthanasia their hearts were isolated in a Langendorff system. We recorded 10–15 minutes of spontaneous activity. Short RR time series were analyzed, and standard HRV parameters were determined with special interest in the time-course of spectral, time-frequency and non-linear components. One-way ANOVA, Kruskal-Wallis test and bivariate correlations were used for statistical analysis (p<0.05).

Results

We did find an increase in the complexity and irregularity of intrinsic pacemaker activity as shown by modifications of entropy (ApEn: p=0.011 vs HF, p=0.002 vs HF-C, p=0.019 vs HFHS-C) and the complexity index (CI: p=0.006 vs HF, p=0.047 vs HF-C, p=0.027 vs HFHS-C) in HFHS animals (Figure). Higher dispersion on RR differences distributions was observed in the HFHS group. Time-frequency spectral heterogeneity increased in HFHS group (p=0.002 vs HF, p=0.050 vs HF-X, p=0.027 vs HFHS-C) even though no differences were found in standard time and frequency-domain analyses. High-band and low-band spectral concentration ratios showed decreased organization in HFHS when compared to HF (p=0.002) and controls HFHS-C (p=0.027) and HF-C (p=0.050). Interestingly, animal weight and glucose intolerance were highly correlated with the modifications of intrinsic pacemaker variability.

Modifications of intrinsic IHRV.

Conclusions

Modifications of intrinsic HRV seemed to be reliant on the number of components of MetS present, given that only HFHS group showed significant changes towards an increased complexity and irregularity of intrinsic pacemaker variability.

Acknowledgement/Funding

This work was partially supported by: GV2015-062, CB16/11/00486.

Modifications of mechanoelectric feedback induced by 2,3-butanedione monoxime and Blebbistatin in Langendorff-perfused rabbit hearts

AIM

Myocardial stretching is an arrhythmogenic factor. Optical techniques and mechanical uncouplers are used to study the mechanoelectric feedback. The aim of this study is to determine whether the mechanical uncouplers 2,3-butanedione monoxime and Blebbistatin hinder or modify the electrophysiological effects of acute mechanical stretch.

METHODS

The ventricular fibrillation (VF) modifications induced by acute mechanical stretch were studied in 27 Langendorff-perfused rabbit hearts using epicardial multiple electrodes and mapping techniques under control conditions (n = 9) and during the perfusion of 2,3-butanedione monoxime (15 mM) (n = 9) or Blebbistatin (10 μm) (n = 9).

RESULTS

In the control series, myocardial stretch increased the complexity of the activation maps and the dominant frequency (DF) of VF from 13.1 ± 2.0 Hz to 19.1 ± 3.1 Hz (P < 0.001, 46% increment). At baseline, the activation maps showed less complexity in both the 2,3-butanedione monoxime and Blebbistatin series, and the DF was lower in the 2,3-butanedione monoxime series (11.4 ± 1.2 Hz; P < 0.05). The accelerating effect of mechanical stretch was abolished under 2,3-butanedione monoxime (maximum DF = 11.7 ± 2.4 Hz, 5% increment, ns vs baseline, P < 0.0001 vs. control series) and reduced under Blebbistatin (maximum DF = 12.9 ± 0.7 Hz, 8% increment, P < 0.01 vs. baseline, P < 0.0001 vs. control series). The variations in complexity of the activation maps under stretch were not significant in the 2,3-butanedione monoxime series and were significantly attenuated under Blebbistatin.

CONCLUSION

The accelerating effect and increased complexity of myocardial activation during VF induced by acute mechanical stretch are abolished under the action of 2,3-butanedione monoxime and reduced under the action of Blebbistatin.

Approach to seizures in the neonatal period: a European perspective

In the neonatal period, seizures rank among the most common neurological symptoms, often indicating an underlying serious neurological condition. It is remarkable that although new tools have been incorporated into the diagnosis of neonatal seizures, there is no consensus about the therapeutic approach among different doctors and institutions. Hence, although phenobarbital is still considered the initial drug of choice, the protocols reported in the literature show a great variability in the approach to treatment of refractory seizures. We used a questionnaire to gain information regarding the treatment of seizures in the neonatal period in different European institutions.

CONCLUSION

We conclude that phenobarbital is still the initial drug of choice followed by benzodiazepines, except in preterm infants with a birth weight below 1800 g. In refractory seizures, the use of continuous lidocaine infusion is most common. Of note, clinical studies with newer drugs have been mostly performed in the United States but not in Europe.

[Clinical assessment of peritoneal drainages for necrotizing enterocolitis. A Bayesian approach]

AIM

To assess effectiveness of peritoneal drainages for necrotizing enterocolitis.

MATERIAL AND METHODS

Retrospective cohort study (years 2000 to 2006). Laparotomy or patient's death were considered as failure.

STUDY VARIABLES

sex, gestational age, weight at delivery, Apgar score at minutes 1 and 5, modified Bell score, radiology and ventilatory status.

RESULTS

25 patients were diagnosed with necrotizing enterocolitis and treated with peritoneal drainages. Sample's Bell score was: 13(52%) Ia, 6 (24%) IIa, 5 (20%) IIb, and 1 (4%) IIIa. Mean gestational age was 31.8 (+/- 4.2) weeks, and mean weight 1,564 (+/- 810) g. Patients classified as Bell I presented statistically significat differences compared with Bell II-III as for radiology (unspecific), delivery weight (lower) and ventilatory status (higher mechanical ventilation rates). For the 12 patients with Bell scores II-III, peritoneal drains were enough for 5 cases (41.7%) and failed in 7 (58.3%), who were operated on. Multivariate analysis (logistic regression) was not able to show any conection with collected variables. However, a bayesian analysis using data from similar studies showed that the probability for drainage success rate to be higher than 50% is 99%.

CONCLUSIONS

In our centre, 52% of peritoneal drainages were used in patinets with low clinical suspect for necrotizing enetrocolitis, maybe in relation with their lower body weight and need for ventilatory support. In patients affected with necrotizing enterocolitis, drainages were effective in 41.7%. Although limited for its retrospective nature, our study suggests that peritoneal drainages can be curative in, at least, 50% of patients with necrotizing enterocolitis without pneumoperitoneum and clinical signs of peritonitis.