Arrhythmic Patterns Research Articles

Advanced Cardiac Rhythm Management by Applying Optogenetic Multi-Site Photostimulation in Murine Hearts.

Ventricular tachyarrhythmias are a major cause of mortality and morbidity worldwide. Electrical defibrillation using high-energy electric shocks is currently the only treatment for life-threatening ventricular fibrillation. However, defibrillation may have side-effects, including intolerable pain, tissue damage, and worsening of prognosis, indicating a significant medical need for the development of more gentle cardiac rhythm management strategies. Besides energy-reducing electrical approaches, cardiac optogenetics was introduced as a powerful tool to influence cardiac activity using light-sensitive membrane ion channels and light pulses. In the present study, a robust and valid method for successful photostimulation of Langendorff perfused intact murine hearts will be described based on multi-site pacing applying a 3 x 3 array of micro light-emitting diodes (micro-LED). Simultaneous optical mapping of epicardial membrane voltage waves allows the investigation of the effects of region-specific stimulation and evaluates the newly induced cardiac activity directly on-site. The obtained results show that the efficacy of defibrillation is strongly dependent on the parameters chosen for photostimulation during a cardiac arrhythmia. It will be demonstrated that the illuminated area of the heart plays a crucial role for termination success as well as how the targeted control of cardiac activity during illumination for modifying arrhythmia patterns can be achieved. In summary, this technique provides a possibility to optimize the on-site mechanism manipulation on the way to real-time feedback control of cardiac rhythm and, regarding the region specificity, new approaches in reducing the potential harm to the cardiac system compared to the usage of non-specific electrical shock applications.

B-PO05-014 A RETROSPECTIVE STUDY OF SEASONAL VARIABILITY OF CARDIAC ELECTROPHYSIOLOGY IN THE RABBIT HEART

Rabbits are an important animal model for the study of cardiac electrophysiology and are suitable for analyzing mechanisms of cardiac arrhythmias. Rabbits are known to have seasonal variation in activity, behavior, and breeding; however, there are few data related to seasonal variation in electrophysiological parameters in the rabbit heart. To determine if there is significant seasonal variation in cardiac electrophysiology of the New Zealand White (NZW) rabbit heart. Male NZW rabbit hearts (N = 55) were purchased from an approved vendor and housed on a 12:12 hr light:dark cycle. Hearts were Langendorff-perfused for simultaneous optical mapping of Vm and Ca2+ with voltage-sensitive (RH237) and calcium-sensitive (Rhod2-AM) indicators, respectively. Data were collected from 2012-2016 and retrospectively analyzed. We defined the seasons meteorologically: December-February as winter, March-May as spring, June-August as summer and September-November as autumn. All data were collected while pacing at a constant cycle length of 300 ms. Retrospective data revealed seasonal variability in the action potential duration (APD) and in the calcium transient duration (CaTD). For summer compared to spring and autumn, APD50 (121.1 ± 11 vs. 137 ± 19.8 and vs. 135.3 ± 11.3 ms, p < 0.01 for both) and APD80 (151.1 ± 11.7 vs. 166.4 ± 17.6 and vs. 163.5 ± 11.9 ms, p < 0.01 for both) were significantly shorter, but not different from winter. For summer compared to spring, CaTD50 (123.8 ± 5.5 vs. 137.7 ± 13.2 ms, p < 0.01) and CaTD80 (162.8 ± 6.1 vs. 178.4 ± 16.9 ms, p = 0.11) were shorter. There was not significance difference in Vm-Ca2+ coupling (i.e., CaTD - APD) between seasons. APD and CaTD are significantly shorter in the summer months of isolated rabbit hearts. These data may provide insight into seasonal patterns of arrhythmia in humans, but should also be considered with regard to experimental rigor and reproducibility.

B-PO03-172 PREDICTORS OF IBRUTINIB TREATMENT INTERRUPTION SECONDARY TO ARRHYTHMIAS

Ibrutinib, a tyrosine kinase inhibitor (TKI), used in chronic lymphocytic leukemia, has been associated with increased incidence of atrial fibrillation (AF); with known treatment interruptions due to intractable AF episodes. The details of arrhythmic episodes that are associated with treatment interruptions remain unclear. To determine predictors of ibrutinib treatment interruption secondary to arrhythmias. A retrospective data analysis at a single center using electronic medical records database search tools and individual chart review was conducted to identify consecutive patients who had holter monitors while on ibrutinib therapy. 72 patients who had holter monitors while on ibrutinib therapy were included in analysis. Mean age was 76.9±9.9 years, 25% were female and the average duration of ibrutinib treatment was 32.3±22 months. Ibrutinib treatment was interrupted in n=18 (25%) of patients due to arrhythmias and n=9 (12.5%) were initiated on anti-arrhythmic medications due to arrhythmias secondary to ibrutinib therapy. Interruptions in ibrutinib therapy were associated with >1% PAC burden on holter monitor while on ibrutinib therapy (p=0.002) and a prior history of VT (p=0.005); but not with >1% PVC burden (p=0.285), presence of SVT (p=0.747), AF (p=0.292) or NSVT (p=0.147) on holter monitor. Patients in whom ibrutinib was held for arrhythmias were more likely to be seen by an electrophysiology specialist (p=0.041), along with patients on ibrutinib whose holter monitors showed NSVT (p=0.011). Female patients were referred to a cardiac specialist less than their male counterparts (p=0.051). In this large dataset of holter monitors on patients treated with ibrutinib, interruptions in TKI therapy correlated with certain arrhythmia patterns that could predate intractable arrhythmias and drug cessation in the future; which can help identify patients who may benefit from closer monitoring.

Clinical Phenotype Classification of Atrial Fibrillation Patients Using Cluster Analysis and Associations with Trial-Adjudicated Outcomes.

Background and purpose: Given the great clinical heterogeneity of atrial fibrillation (AF) patients, conventional classification only based on disease subtype or arrhythmia patterns may not adequately characterize this population. We aimed to identify different groups of AF patients who shared common clinical phenotypes using cluster analysis and evaluate the association between identified clusters and clinical outcomes. Methods: We performed a hierarchical cluster analysis in AF patients from AMADEUS and BOREALIS trials. The primary outcome was a composite of stroke/thromboembolism (TE), cardiovascular (CV) death, myocardial infarction, and/or all-cause death. Individual components of the primary outcome and major bleeding were also assessed. Results: We included 3980 AF patients treated with the Vitamin-K Antagonist from the AMADEUS and BOREALIS studies. The analysis identified four clusters in which patients varied significantly among clinical characteristics. Cluster 1 was characterized by patients with low rates of CV risk factors and comorbidities; Cluster 2 was characterized by patients with a high burden of CV risk factors; Cluster 3 consisted of patients with a high burden of CV comorbidities; Cluster 4 was characterized by the highest rates of non-CV comorbidities. After a mean follow-up of 365 (standard deviation 187) days, Cluster 4 had the highest cumulative risk of outcomes. Compared with Cluster 1, Cluster 4 was independently associated with an increased risk for the composite outcome (hazard ratio (HR) 2.43, 95% confidence interval (CI) 1.70–3.46), all-cause death (HR 2.35, 95% CI 1.58–3.49) and major bleeding (HR 2.18, 95% CI 1.19–3.96). Conclusions: Cluster analysis identified four different clinically relevant phenotypes of AF patients that had unique clinical characteristics and different outcomes. Cluster analysis highlights the high degree of heterogeneity in patients with AF, suggesting the need for a phenotype-driven approach to comorbidities, which could provide a more holistic approach to management aimed to improve patients’ outcomes.

Towards non-invasive heart rate monitoring in free-ranging cetaceans: a unipolar suction cup tag measured the heart rate of trained Risso's dolphins.

Heart rate monitoring in free-ranging cetaceans to understand their behavioural ecology and diving physiology is challenging. Here, we developed a simple, non-invasive method to monitor the heart rate of cetaceans in the field using an electrocardiogram-measuring device and a single suction cup equipped with an electrode. The unipolar suction cup was placed on the left lateral body surface behind the pectoral fin of Risso's dolphins (Grampus griseus) and a false killer whale (Pseudorca crassidens) in captivity; their heart rate was successfully monitored. We observed large heart rate oscillations corresponding to respiration in the motionless whales during surfacing (a false killer whale, mean 47 bpm, range 20-75 bpm; Risso's dolphins, mean ± s.d. 61 ± 15 bpm, range 28-120 bpm, n = 4 individuals), which was consistent with the sinus arrhythmia pattern (eupneic tachycardia and apneic bradycardia) observed in other cetaceans. Immediately after respiration, the heart rate rapidly increased to approximately twice that observed prior to the breath. Heart rate then gradually decreased at around 20-50 s and remained relatively constant until the next breath. Furthermore, we successfully monitored the heart rate of a free-swimming Risso's dolphin. The all-in-one suction cup device is feasible for field use without restraining animals and is helpful in further understanding the diving physiology of free-ranging cetaceans. This article is part of the theme issue 'Measuring physiology in free-living animals (Part II)'.

Schlumberger’s Drilling ECG Goes to the Heart of the Matter To Diagnose Abnormal Conditions in Real Time

The trading of technologies is nothing new for the upstream oil and gas and medical communities. The connection makes sense, particularly since both disciplines rely heavily on applied math for diagnoses. It should come as no surprise, then, that a popular paper at the 2021 Virtual SPE/IADC International Drilling Conference proposed a medically inspired approach to prevent catastrophic drilling system failures brought on by downhole shocks (SPE/IADC 204098). The paper describes a “drilling electrocardiogram” that diagnoses “arrhythmic drilling” similarly to how medical electrocardiograms diagnose dangerous vibration anomalies in heart patients. The approach classifies shock wave-forms acquired at 31,250 hertz (Hz) downhole. The shock signals are treated as drilling electrocardiograms (D-ECG) that are processed using clustering algorithms and merged with drilling incidents to identify in real time an arrhythmic signature pattern that can lead to catastrophic failures. A Revelation Justo Matheus, senior control engineer for Schlumberger and lead author of the paper, said that in studying field incidents in which rotary steerable system (RSS) bottomhole assemblies (BHA) had been severely damaged by shocks, the signature patterns reminded him of ECGs (Fig. 1). This led him to medical libraries, which in turn led to a revelation—that throughout the 3 decades that downhole vibration measurements while drilling (MWD) have been studied, only the analysis of the amplitude and root mean square (rms) values of shocks had been the focus. No one had considered frequency for diagnosing downhole shocks. It was this revelation that drove the concept of the D-ECG based on shock waveforms acquired at high frequency in real time to prevent failures of the BHA. What Is “Normal” and What Is Not? Drilling-generated shocks and vibrations affect rate of penetration, directional control, and wellbore quality, making them among the main causes of failures in drilling. “Shocks are present almost all the time,” said Matheus. “The challenge is in knowing which are normal and which are not.” RSS are equipped with measurement devices such as magnetometers, accelerometers, and shock and vibration sensors that obtain statistical information from which whirl, bit bounce, and stick/slip severity are inferred. Often, however, the derived statistics are not sufficient to distinguish between normal drilling vs. abnormal drilling for a location in the wellbore. Recent electronic advances enabled the development of high-resolution drilling dynamic data recorders, extending the sampling frequency from traditional 100 Hz to 1,600 Hz. However, most of these devices are for data recording only. There is no real-time communication with surface and no capability to inform about drilling conditions downhole.

Clinical Indications and Arrhythmic Patterns of 24-h Holter Electrocardiography among Cardiovascular Disease Patients

Background: This study aimed to evaluate the clinical indications and arrhythmic patterns in cardiovascular disease patients who were referred for Holter electrocardiography (ECG) in Dr. Soetomo General Hospital, Surabaya, Indonesia. Methods: A retrospective cross-sectional study was held at Dr. Soetomo General Academic Hospital, Surabaya, Indonesia. Patient's data, including Holter ECG, was obtained from the local Holter Registry between July 2019 and December 2019. Results: A total of 89 patients were included in this study. The mean age was 50.1 ± 16.0 years old, and 48 patients (53.9%) were females. The most common indication was palpitation (39.3%) followed by the history of arrhythmia (14.6%), shortness of breath (13.5%), and chest pain (12.4%). Ventricular ectopic (VE) and supraventricular ectopic (SVE) were the most common arrhythmia in 70.8% and 12.4% of subjects, respectively. About 20.2% of patients had frequent VE, and Lown's Grade 4 was the most prevalent VE accounting for 45.9% of patients among all VE events. A total of 5.6% of patients had episodes of atrial fibrillation. Frequent SVE was found in 4.5% of patients, whereas 5.6% had supraventricular tachycardia. About 3.4% of patients had abnormal atrioventricular conduction, and 4.5% had chronotropic incompetence. Conclusions: Palpitation of unknown etiology was the most common clinical indication for Holter ECG among our patients. The most prevalent arrhythmias were VEs and SVEs, with Lown's Grade 4 being the most prevalent VEs. Holter ECG in patients with that indication was reasonably high diagnostic yield in detecting arrhythmia.

Tunable Q-wavelet based ECG data compression with validation using cardiac arrhythmia patterns

The acquisition of longer electrocardiogram (ECG) signals is an essential step of the recent medical screening and diagnostic procedures. Considering the need of an efficient ECG data management system, this paper presents a novel ECG data compression technique based on the tunable Q-wavelet transform which provides adjustable parameters to achieve good compression performance. The tunable Q-wavelet transform compacts the maximum energy of the signal to fewer transform coefficients. Dead-zone quantization is used to discard the small valued transform coefficients. Further, transform coefficients are rounded-off to nearest integer values and encoded using run-length coding. ECG records of the MIT-BIH arrhythmia database are used to evaluate the performance of the proposed compression technique. The average compression performance obtained in terms of CR, PRD, PRD1, QS, QS1 and SNR are 20.61, 4.43, 6.37, 5.88, 3.46, and 55.93 dB respectively. The proposed technique offers better compression performance than many existing techniques. The proposed technique is also validated using cardiac arrhythmia patterns classification. In the validation phase, tunable Q-wavelet transform based features of 14,878 original cardiac patterns are used to train the support vector machine classifier while testing is performed using features of 26,219 original and reconstructed cardiac patterns separately. It examines the effect of the proposed compression technique on cardiac arrhythmia classification. In the validation part, the overall classification accuracy, sensitivity, and specificity obtained for the proposed compression technique are 98.35%, 95.77%, and 99.19% respectively. It denotes that the proposed technique compresses ECG signal efficiently with preserving diagnostic information very well.

Methods of Signal Analysis for Automatic Diagnosis of Shockable Cardiac Arrhythmias: A Review

Ventricular fibrillation is considered the most common cause of sudden cardiac arrest. The fibrillation, and ventricular tachycardia often preceding it, are cardiac rhythms that may respond to emergency electroshock therapy and return to normal sinus rhythm when diagnosed early after cardiac arrest with the restoration of adequate cardiac pumping function. However, manually checking ECG signals on the existence of a pattern of such arrhythmias is a risky and time-consuming task in stressful situations and practically impossible in the absence of a qualified medical specialist. Therefore, systems of the computer classification of arrhythmias with the function of making a decision on the necessity of electric cardioversion with the parameters of a high-voltage pulse calculated adaptively for each patient are widely used for the automatic diagnosis of such conditions. This paper discusses methods of analyzing the electrocardiographic signal taken from the electrodes of an external automatic or semi-automatic defibrillator in order to make a decision on the necessity for defibrillation, which are applicable in the embedded software of automatic and semiautomatic external defibrillators. The paper includes an overview of applicable filtering techniques as well as subsequent algorithms for extracting, classifying and compressing features for the ECG signal.

Formulation of a New Feature Set to Detect Arrhythmic Cardiac Patterns in ECG

Formulation of a New Feature Set to Detect Arrhythmic Cardiac Patterns in ECG

Awake or dreaming: how brain ‘noise’ tells the difference

Monitoring brain electrical activities helps us discern brain states. But understanding how we sleep is not easy. While deep dreamless sleep brings easily recognized rhythmic electrical waves, light dream sleep shows arrhythmic patterns and looks similar to wakefulness. We discover that the often-ignored background brain ‘noise’ can help distinguish these similar brain states. - submission by Janna D. Lendner

Role of the rabbit whole-heart model for electrophysiologic safety pharmacology of non-cardiovascular drugs.

Plenty of non-cardiovascular drugs alter cardiac electrophysiology and may ultimately lead to life-threatening arrhythmias. In clinical practice, measuring the QT interval as a marker for the repolarization period is the most common tool to assess the electrophysiologic safety of drugs. However, the sole measurement of the QT interval may be insufficient to determine the proarrhythmic risk of non-cardiovascular agents. Several other markers are considered in pre-clinical safety testing to determine potential harm on cardiac electrophysiology. Besides measuring typical electrophysiologic parameters such as repolarization duration, whole-heart models allow the determination of potential predictors for proarrhythmia. Spatial and temporal heterogeneity as well as changes of shape of the action potential can be easily assessed. In addition, provocation manoeuvers (either by electrolyte imbalances or programmed pacing protocols) may induce sustained arrhythmias and thereby determine ventricular vulnerability to arrhythmias. Compared with the human heart, the rabbit heart possesses a similar distribution of ion currents that govern cardiac repolarization, resulting in a rectangular action potential configuration in both species. In addition, similar biophysical properties of rabbit and human cardiac ion channels lead to a comparable pharmacologic response in human and rabbit hearts. Of note, arrhythmia patterns resemble in both species due to the similar effective size of human and rabbit hearts. Thus, the rabbit heart is particularly suitable for testing the electrophysiologic safety of drugs. Several experimental setups have been developed for studying cardiac electrophysiology in rabbits, ranging from single cell to tissue preparations, whole-heart setups, and in vivo models.

The optic lobe–pars intercerebralis axis is involved in circa’bi’dian rhythm of the large black chafer Holotrichia parallela

The large black chafer Holotrichia parallela exhibits ~ 48-h circa'bi'dian rhythm. Although circabidian rhythm is suggested to involve the circadian clock, no physiological studies have been conducted to verify this involvement. We examined the effects of optic lobe or pars intercerebralis removal on the circabidian rhythm. After removing both optic lobes, all beetles lost their circabidian rhythms (N = 25), but all beetles exhibited circabidian rhythm after removing unilateral optic lobe (N = 18). However, 22% of the latter group exhibited day switching. After removal of the pars intercerebralis, 26.3% beetles showed arrhythmic patterns (N = 19). The number of paraldehyde fuchsin-stained pars intercerebralis cells in the arrhythmic group was significantly reduced compared to in the intact and sham-operated groups. The activity in the pars intercerebralis-removed beetles was significantly higher than that in the control groups. The results show that the optic lobe and at least part of the pars intercerebralis are necessary for circabidian rhythm, and bilateral optic lobes are necessary to maintain regularity of the two-day rhythm in H. parallela. This suggests that a neural circuit of circadian clock cells in the optic lobe to pars lateralis might be evolutionally conserved and used also for the generation of circabidian rhythm.

Light and dark rhythms of pupal eclosion and egg hatching in tropical stem borers’ moths

Different traits in insects such as locomotor activity, egg-hatching, emergence from puparia and oviposition follow light and dark rhythms. In noctuid stemborer moths, activity cycles of the adults linked to their reproductive traits concentrate at the first half of the night and some of them are highly species specific. However, little information is available on the light and dark rhythm of egg hatching in noctuid stemborer moths as compared to adult’s activities (emergence, oviposition and mating). The purpose of this study was to compare the light and dark rhythms of pupal eclosion and egg hatching, respectively, for four main species of Afro-tropical noctuid stemborers under 24 h light-dark cycle conditions. In contrast to pupal eclosion, egg-hatching showed to be less controlled by light and dark rhythms. This arrhythmic pattern on egg-hatching compared to pupal eclosion is discussed in terms of interspecific resource utilization within a community of lepidopteran stemborers sharing the same resource.

Developmental patterns of respiratory sinus arrhythmia from toddlerhood to adolescence.

Parasympathetic nervous system functioning as indexed by respiratory sinus arrhythmia (RSA) is widely used as a measure of physiological regulation. We examined developmental patterns of children's resting RSA and RSA reactivity from 2 to 15 years of age, a period of time that is marked by considerable advances in children's regulatory abilities. Physiological data were collected from a community sample of 270 children (116 males) during a resting period and during a frustration laboratory task when the children were 2, 4, 5, 7, 10, and 15 years old. We examined both stability and continuity in resting RSA and RSA reactivity across time. We found stability in resting RSA but not RSA reactivity from toddlerhood to adolescence. Separate multilevel models were used to examine changes in resting RSA and RSA reactivity from Age 2 to Age 15. The rate of change in resting RSA slowed from Age 2 to Age 15 with a plateau around Age 10. A splined growth model indicated that the rate of RSA reactivity increased from Age 2 to Age 7 and a modest slowing and leveling off from Age 7 to Age 15. Understanding the developmental characteristics of RSA across childhood and adolescence is important to understanding the larger constructs of self- and emotion regulation. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Effects of working memory training on cognitive, affective, and biological responses to stress in major depression: A novel cognitive bias modification protocol

BackgroundOver 320 million individuals are living with Major Depressive Disorder (MDD), a leading cause of disability worldwide. Thus, there is a crucial need to identify processes that contribute to the maintenance of depressive episodes. Difficulty removing negative information from working memory (WM) is posited to exacerbate affective, cognitive, and biological dysregulation in Major Depressive Disorder (MDD), but this has not yet been tested empirically. MethodsIn this study we examined whether training depressed individuals to remove negative information from WM (RNI training) would reduce symptoms of depression and levels of rumination, and would be associated with attenuated biological responsivity to stress. Individuals diagnosed with MDD were randomly assigned to complete Real-RNI training or Sham-RNI training for six days. ResultsAcross conditions, participants exhibited significant improvements from pre- to post-training in removing negative information from WM, symptoms of depression, and rumination. Furthermore, participants in the Real-RNI condition showed a more attenuated pattern of cortisol and respiratory sinus arrhythmia (RSA) responses to stress than did participants in the Sham-RNI training condition. LimitationsWe did not assess the long-term effects of training. It will be important for future research to examine whether the documented training-related effects persist across time. ConclusionsThis study is the first to examine the effects of RNI training on clinical symptoms and biological responses to stress in MDD, and it provides experimental evidence that training individuals with depression to remove negative information from WM can help to modulate the heightened biological responses to stress seen in depression.

The Pattern of Cardiac Arrhythmias in Acute ST Elevated Myocardial Infarction and their in-hospital Outcome

Background: Acute myocardial infarction (AMI) is a major cause of death worldwide with arrhythmia being the most common determinant in the post-infarction period. Identification and management of arrhythmias at an early period of acute MI has both short term and long term significance.&#x0D; Objective: The aim of the study is to evaluate the pattern of arrhythmias in acute STEMI in the first 48 hours of hospitalization and their inhospital outcome.&#x0D; Methods: A total of 50 patients with acute STEMI were included in the study after considering the inclusion and exclusion criteria. The patients were observed for the first 48 hours of hospitalization for detection of arrhythmia with baseline ECG at admission and continuous cardiac monitoring in the CCU. The pattern of the arrhythmias during this period &amp; their in-hospital outcome were recorded in predesigned structured data collection sheet.&#x0D; Result: The mean age was 53.38 ± 10.22 years ranging from 29 to 70 years. Most of the patients were male 42(84%). Majority of the patients had anterior wall ( anterior, antero-septal &amp; extensive anterior) myocardial infarction (54%). Sinus tachycardia in isolation was the most common arrhythmia observed in 36.8% of patients followed by sinus bradycardia (22.8%), ventricular tachycardia (19.3%), ventricular ectopic (12.3%),first degree AV block (5.3%), complete heart block and atrial ectopic 1.7% each. Tachyarrhythmias were more common in anterior wall myocardial infarction, whereas bradyarrhythmias were more common in inferior wall myocardial infarction. Among studied patients, 72% had favourable outcome , followed by acute left ventricular failure 10%, cardiogenic shock &amp; lengthening of hospital stay 8% each and death 2%.&#x0D; Conclusion: The commonest arrhythmias encountered were sinus tachycardia followed by sinus bradycardia, ventricular tachycardia, ventricular ectopic, AV block and atrial ectopic. The incidence of mortality was 2%.&#x0D; University Heart Journal Vol. 16, No. 1, Jan 2020; 16-21

Hypoglycaemia and cardiac arrhythmias in diabetes.

Hypoglycaemia remains an inevitable risk in insulin-treated type 1 diabetes and type 2 diabetes and has been associated with multiple adverse outcomes. Whether hypoglycaemia is a cause of fatal cardiac arrhythmias in diabetes, or merely a marker of vulnerability, is still unknown. Since a pivotal report in 1991, hypoglycaemia has been suspected to induce cardiac arrhythmias in patients with type 1 diabetes, the so-called ‘dead-in-bed syndrome’. This suspicion has subsequently been supported by the coexistence of an increased mortality and a three-fold increase in severe hypoglycaemia in patients with type 2 diabetes receiving intensive glucose-lowering treatment in the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial. Studies have investigated the association between hypoglycaemia-induced cardiac arrhythmias. In a rat-model, severe hypoglycaemia resulted in a specific pattern of cardiac arrhythmias including QT-prolongation, ventricular tachycardia, second- and third-degree AV block and ultimately cardiorespiratory arrest. In clinical studies of experimentally induced hypoglycaemia, QTc-prolongation, a risk factor of ventricular arrhythmias, is an almost consistent finding. The extent of QT-prolongation seems to be modified by several factors, including antecedent hypoglycaemia, diabetes duration and cardiac autonomic neuropathy. Observational studies indicate diurnal differences in the pattern of electrocardiographic alterations during hypoglycaemia with larger QTc-prolongations during daytime, whereas the risk of bradyarrhythmias may be increased during sleep. Daytime periods of hypoglycaemia are characterized by shorter duration, increased awareness and a larger increase in catecholamines. The counterregulatory response is reduced during nightly episodes of hypoglycaemia, resulting in prolonged periods of hypoglycaemia with multiple nadirs. An initial sympathetic activity at plasma glucose nadir is replaced by increased vagal activity, which results in bradycardia. Here, we provide an overview of the existing literature exploring potential mechanisms for hypoglycaemia-induced cardiac arrhythmias and studies linking hypoglycaemia to cardiac arrhythmias in patients with diabetes.

Advanced mapping strategies for ablation therapy in adults with congenital heart disease.

Ultra-high density mapping (HDM) is a promising tool in the treatment of patients with complex arrhythmias. In adults with congenital heart disease (CHD), rhythm disorders are among the most common complications but catheter ablation can be challenging due to heterogenous anatomy and complex arrhythmogenic substrates. Here, we describe our initial experience using HDM in conjunction with novel automated annotation algorithms in patients with moderate to great CHD complexity. We studied a series of consecutive adult patients with moderate to great CHD complexity and an indication for catheter ablation due to symptomatic arrhythmia. HDM was conducted using the Rhythmia™ mapping system and a 64-electrode mini-basket catheter for identification of anatomy, voltage, activation pattern and critical areas of arrhythmia for ablation guidance. To investigate novel advanced mapping strategies, postprocedural signal processing using the Lumipoint™ software was applied. In 19 patients (53±3 years; 53% male), 21 consecutive ablation procedures were conducted. Procedures included ablation of atrial fibrillation (n=7; 33%), atrial tachycardia (n=11; 52%), atrioventricular accessory pathway (n=1; 5%), the atrioventricular node (n=1; 5%) and ventricular arrhythmias (n=4; 19%). A total of 23 supraventricular and 8 ventricular arrhythmias were studied with the generation of 56 complete high density maps (atrial n=43; ventricular n=11, coronary sinus n=2) and an average of 12,043±1,679 mapping points. Multiple arrhythmias were observed in n=7 procedures (33% of procedures; range of arrhythmias detected 2-4). A total range of 1-4 critical areas were defined per procedure and treated within a radiofrequency application time of 16 (interquartile range 12-45) minutes. Postprocedural signal processing using Lumipoint™ allowed rapid annotation of fractionated signals within specific windows of interest. This supported identification of a practical critical isthmus in 20 out of 27 completed atrial and ventricular tachycardia activation maps. Our findings suggest that HDM in conjunction with novel automated annotation algorithms provides detailed insights into arrhythmia mechanisms and might facilitate tailored catheter ablation in patients with moderate to great CHD complexity.

Arrhythmias in Patients on Maintenance Dialysis: A Cross-sectional Study

Patients with kidney failure treated with maintenance dialysis experience a high rate of mortality, in part due to sudden cardiac death caused by arrhythmias. The prevalence of arrhythmias, including the subset that are clinically significant, is not well known. This study sought to estimate the prevalence of arrhythmias, characterize the pattern of arrhythmic events in relation to dialysis treatments, and identify associated clinical characteristics. Cross-sectional study. 152 patients with kidney failure treated with maintenance dialysis in Denmark. Dialysis treatment; clinical characteristics; cardiac output and preload defined using echocardiography. Prevalence and pattern of arrhythmias on 48-hour Holter monitoring; odds ratios for arrhythmias. Descriptive analysis of the prevalence of arrhythmias. Pattern of arrhythmias described using a repeated-measures negative binomial regression model. Associations between clinical characteristics and echocardiographic findings with arrhythmias were assessed using logistic regression. Among the 152 patients studied, 83.6% were treated with in-center dialysis; 10.5%, with home hemodialysis; and 5.9%, with peritoneal dialysis. Premature atrial and ventricular complexes were seen in nearly all patients and 41% had paroxysmal supraventricular tachycardia. Clinically significant arrhythmias included persistent atrial fibrillation observed among 8.6% of patients, paroxysmal atrial fibrillation among 3.9%, nonsustained ventricular tachycardia among 19.7%, bradycardia among 4.6%, advanced second-degree atrioventricular block among 1.3%, and third-degree atrioventricular block among 2.6%. Premature ventricular complexes were more common on dialysis days, while tachyarrhythmias were more often observed during dialysis and in the immediate postdialytic period. Older age (OR per 10 years older, 1.53; 95% CI, 1.15-2.03; P=0.003), elevated preload (OR, 4.02; 95% CI, 1.05-15.35; P=0.04), and lower cardiac output (OR per 1L/min greater, 0.66; 95% CI, 0.44-1.00; P=0.05) were independently associated with clinically significant arrhythmias. Arrhythmia monitoring limited to 48 hours; small sample size; heterogeneous nature of the population, risk for residual confounding. Arrhythmias, including clinically significant abnormal rhythms, were common. Tachyarrhythmias were more frequent during dialysis and the immediate postdialytic period. The relevance of these findings to clinical outcomes requires additional study.