Beat-to-Beat Patterning of Sinus Rhythm Reveals Non-linear Rhythm in the Dog Compared to the Human

Use of machine learning and Poincaré density grid in the diagnosis of sinus node dysfunction caused by sinoatrial conduction block in dogs

BACKGROUND

Sinus node dysfunction because of abnormal impulse generation or sinoatrial conduction block causes bradycardia that can be difficult to differentiate from high parasympathetic/low sympathetic modulation (HP/LSM).

HYPOTHESIS

Beat-to-beat relationships of sinus node dysfunction are quantifiably distinguishable by Poincaré plots, machine learning, and 3-dimensional density grid analysis. Moreover, computer modeling establishes sinoatrial conduction block as a mechanism.

ANIMALS

Three groups of dogs were studied with a diagnosis of: (1) balanced autonomic modulation (n = 26), (2) HP/LSM (n = 26), and (3) sinus node dysfunction (n = 21).

METHODS

Heart rate parameters and Poincaré plot data were determined [median (25%-75%)]. Recordings were randomly assigned to training or testing. Supervised machine learning of the training data was evaluated with the testing data. The computer model included impulse rate, exit block probability, and HP/LSM.

RESULTS

Confusion matrices illustrated the effectiveness in diagnosing by both machine learning and Poincaré density grid. Sinus pauses >2 s differentiated (P < .0001) HP/LSM (2340; 583-3947 s) from sinus node dysfunction (8503; 7078-10 050 s), but average heart rate did not. The shortest linear intervals were longer with sinus node dysfunction (315; 278-323 ms) vs HP/LSM (260; 251-292 ms; P = .008), but the longest linear intervals were shorter with sinus node dysfunction (620; 565-698 ms) vs HP/LSM (843; 799-888 ms; P < .0001).

CONCLUSIONS

Number and duration of pauses, not heart rate, differentiated sinus node dysfunction from HP/LSM. Machine learning and Poincaré density grid can accurately identify sinus node dysfunction. Computer modeling supports sinoatrial conduction block as a mechanism of sinus node dysfunction.

Ambulatory electrocardiographic longitudinal monitoring in a canine model for Duchenne muscular dystrophy identifies decreased very low frequency power as a hallmark of impaired heart rate variability

Duchenne muscular dystrophy (DMD) patients exhibit a late left ventricular systolic dysfunction preceded by an occult phase, during which myocardial fibrosis progresses and some early functional impairments can be detected. These latter include electrocardiographic (ECG) and heart rate variability (HRV) abnormalities. This longitudinal study aimed at describing the sequence of ECG and HRV abnormalities, using Holter ECG in the GRMD (Golden retriever muscular dystrophy) dog model, known to develop a DMD-like disease, including cardiomyopathy. Most of the known ECG abnormalities described in DMD patients were also found in GRMD dogs, including increased heart rate, prolonged QT and shortened PR intervals, ventricular arrhythmias, and several of them could be detected months before the decrease of fractional shortening. The HRV was impaired like in DMD patients, one of the earliest evidenced abnormalities being a decrease in the very low frequency (VLF) component of the power spectrum. This decrease was correlated with the further reduction of fractional shortening. Such decreased VLF probably reflects impaired autonomic function and abnormal vasomotor tone. This study provides new insights into the knowledge of the GRMD dog model and DMD cardiomyopathy and emphasizes the interest to monitor the VLF power in DMD patients, still unexplored in this disease, whilst it is highly predictive of deleterious clinical events in many other pathological conditions.

Dog–Owner Relationship, Owner Interpretations and Dog Personality Are Connected with the Emotional Reactivity of Dogs

Simple Summary

The relationship between owner and the dog affects the dog’s attachment behaviors and stress coping. In turn, the quality of the relationship may affect owner’s interpretations about their dog’s behavior. Here, we assessed dogs’ emotional responses from heart rate variability and behavioral changes during five different situations. Dog owners evaluated the emotion (valence and arousal) of their dog after each situation. We found that both negative and positive incidents provoked signs of emotional arousal in dogs. Owners detected the dog’s arousal especially during fear- and stress-evoking situations. The dog–owner relationship did not affect owners’ interpretation of dogs’ emotion. However, the dog–owner relationship was reflected in the dog’s emotional reactions. Close emotional bond with the owner appeared to decrease the arousal of the dogs. Dog owners’ frequent caregiving of their dog was associated with increased attachment behaviors and heightened arousal of dogs. Owners rated the disadvantages of the dog relationship higher for the dogs that were less owner-oriented and less arousable. Dog’s arousal may provoke dog’s need to seek human attention, which in turn may promote the development of emotional bond.

Abstract

We evaluated the effect of the dog–owner relationship on dogs’ emotional reactivity, quantified with heart rate variability (HRV), behavioral changes, physical activity and dog owner interpretations. Twenty nine adult dogs encountered five different emotional situations (i.e., stroking, a feeding toy, separation from the owner, reunion with the owner, a sudden appearance of a novel object). The results showed that both negative and positive situations provoked signs of heightened arousal in dogs. During negative situations, owners’ ratings about the heightened emotional arousal correlated with lower HRV, higher physical activity and more behaviors that typically index arousal and fear. The three factors of The Monash Dog–Owner Relationship Scale (MDORS) were reflected in the dogs’ heart rate variability and behaviors: the Emotional Closeness factor was related to increased HRV (p = 0.009), suggesting this aspect is associated with the secure base effect, and the Shared Activities factor showed a trend toward lower HRV (p = 0.067) along with more owner-directed behaviors reflecting attachment related arousal. In contrast, the Perceived Costs factor was related to higher HRV (p = 0.009) along with less fear and less owner-directed behaviors, which may reflect the dog’s more independent personality. In conclusion, dogs’ emotional reactivity and the dog–owner relationship modulate each other, depending on the aspect of the relationship and dogs’ individual responsivity.

Golden Standard or Obsolete Method? Review of ECG Applications in Clinical and Experimental Context

Cardiovascular system and its functions under both physiological and pathophysiological conditions have been studied for centuries. One of the most important steps in the cardiovascular research was the possibility to record cardiac electrical activity. Since then, numerous modifications and improvements have been introduced; however, an electrocardiogram still represents a golden standard in this field. This paper overviews possibilities of ECG recordings in research and clinical practice, deals with advantages and disadvantages of various approaches, and summarizes possibilities of advanced data analysis. Special emphasis is given to state-of-the-art deep learning techniques intensely expanded in a wide range of clinical applications and offering promising prospects in experimental branches. Since, according to the World Health Organization, cardiovascular diseases are the main cause of death worldwide, studying electrical activity of the heart is still of high importance for both experimental and clinical cardiology.

Vagally Associated Second Degree Atrio-Ventricular Block in a Dog with Severe Azotemia and Evidence of Sympathetic Overdrive

A 14 years old, 6 kg, mix-breed male dog with severe azotemia due to urinary bladder herniation was presented to our Veterinary Teaching Hospital (VTH). Electrocardiography revealed normal heart rate of 100 bpm, evidence of sinus respiratory arrhythmia (SRA) and frequent second degree atrio-ventricular block following peak inspiratory phase suggestive of vagally-induced atrio-ventricular conduction delay. Echocardiographic examination showed mild mitral regurgitation without any other cardiac changes, and systolic (SAP) and diastolic (DAP) blood pressure values were 185/90 mmHg (SAP/DAP). Cardiac troponin I (cTnI) was increased to 7.3 ng/mL, suggesting a myocardial injury. A Holter examination revealed evidence of overall decrease in heart rate variability with evidence of sympathetic overdrive on time and frequency domain as well as when the non-linear Poincaré plot was analyzed. Based on the author's knowledge, this is the first report of a second degree atrio-ventricular block associated with vagal activity in a dog, with evidence of sympathetic overdrive and severe azotemia.

Autonomic modulation of ventricular electrical activity: recent developments and clinical implications

PURPOSE

This review aimed to provide a complete overview of the current stance and recent developments in antiarrhythmic neuromodulatory interventions, focusing on lifethreatening vetricular arrhythmias.

METHODS

Both preclinical studies and clinical studies were assessed to highlight the gaps in knowledge that remain to be answered and the necessary steps required to properly translate these strategies to the clinical setting.

RESULTS

Cardiac autonomic imbalance, characterized by chronic sympathoexcitation and parasympathetic withdrawal, destabilizes cardiac electrophysiology and promotes ventricular arrhythmogenesis. Therefore, neuromodulatory interventions that target the sympatho-vagal imbalance have emerged as promising antiarrhythmic strategies. These strategies are aimed at different parts of the cardiac neuraxis and directly or indirectly restore cardiac autonomic tone. These interventions include pharmacological blockade of sympathetic neurotransmitters and neuropeptides, cardiac sympathetic denervation, thoracic epidural anesthesia, and spinal cord and vagal nerve stimulation.

CONCLUSION

Neuromodulatory strategies have repeatedly been demonstrated to be highly effective and very promising anti-arrhythmic therapies. Nevertheless, there is still much room to gain in our understanding of neurocardiac physiology, refining the current neuromodulatory strategic options and elucidating the chronic effects of many of these strategic options.

Robust neuromorphic coupled oscillators for adaptive pacemakers

Neural coupled oscillators are a useful building block in numerous models and applications. They were analyzed extensively in theoretical studies and more recently in biologically realistic simulations of spiking neural networks. The advent of mixed-signal analog/digital neuromorphic electronic circuits provides new means for implementing neural coupled oscillators on compact, low-power, spiking neural network hardware platforms. However, their implementation on this noisy, low-precision and inhomogeneous computing substrate raises new challenges with regards to stability and controllability. In this work, we present a robust, spiking neural network model of neural coupled oscillators and validate it with an implementation on a mixed-signal neuromorphic processor. We demonstrate its robustness showing how to reliably control and modulate the oscillator's frequency and phase shift, despite the variability of the silicon synapse and neuron properties. We show how this ultra-low power neural processing system can be used to build an adaptive cardiac pacemaker modulating the heart rate with respect to the respiration phases and compare it with surface ECG and respiratory signal recordings from dogs at rest. The implementation of our model in neuromorphic electronic hardware shows its robustness on a highly variable substrate and extends the toolbox for applications requiring rhythmic outputs such as pacemakers.

Lorenz Plot Analysis in Dogs with Sinus Rhythm and Tachyarrhythmias

Simple Summary

The Lorenz plot (LP) is a geometrical method to assess the dynamics of heart rate variability. It consists of a two-dimensional Cartesian coordinate system derived from electrocardiographic monitoring, in which each recorded R-R interval is plotted as a function of the previous R-R interval, and the values of each pair of successive R-R interval define a dot in the plot. The resultant clusters of dots can be evaluated quantitatively and qualitatively, and categorized into distinct geometrical patterns. In humans, several studies have demonstrated that the analysis of LP patterns (LPPs) has the potential to speed-up and improve the accuracy of arrhythmia detection and differentiation, especially in patients with tachyarrhythmias. As data on LP analysis are limited in dogs, this study describes the graphic features of LP derived from Holter recordings obtained in dogs with sinus rhythm and tachyarrhythmias, and analyzes the usefulness of LPP recognition in this species. We sought to evaluate if distinct cardiac rhythms imprint distinct and reproducible LPPs in dogs, as previously described in humans, and if each LLP can be used as a sensitive and specific indicator of a particular cardiac rhythm in this species.

Abstract

The Lorenz plot (LP), a graphical representation of heart rate variability, has been poorly studied in dogs to date. The present study aimed to describe the graphic features of LP in dogs with sinus rhythm (SR) and tachyarrhythmias, and to analyze the usefulness of its pattern recognition. One hundred and nineteen canine Holter recordings were retrospectively evaluated. Cardiac rhythms were classified as: SR; SR with frequent (>100) premature ectopies (atrial, SR-APCs; ventricular, SR-VPCs; atrial and ventricular, SR-APCs-VPCs); atrial fibrillation (AF); and AF with frequent VPCs (AF-VPCs). Lorenz plots were studied qualitatively and quantitatively, and classified by distinct LP patterns (LPPs). Repeatability and reproducibility of LPP classification and diagnostic value were determined. Recordings included: 48 SR, 9 SR-APCs, 35 SR-VPCs, 5 SR-APCs-VPCs, 4 AF, and 18 AF-VPCs. Ten LPPs were identified: comet (n = 12), torpedo (n = 3), Y-shaped (n = 6), diamond (n = 10), diamond with a central silent zone (n = 17), double side-lobe (DSL) (n = 47), triple side-lobe (n = 1), quadruple side-lobe (n = 2), fan (n = 18), and fan with DSL (n = 3). Repeatability and reproducibility of LPP classification were excellent. The DSL pattern was both highly sensitive (91.3%) and specific (94.5%) for SR with frequent premature ectopies, either APCs, or VPCs, or both. The remaining LPPs had lower diagnostic value (high specificity but low sensitivity). Distinct rhythms imprint distinct and reproducible LPPs in dogs. The majority of canine LPPs are specific but insensitive indicators of SR and tachyarrhythmias.

The canine chronic atrioventricular block model in cardiovascular preclinical drug research

Ventricular cardiac arrhythmia is a life threating condition arising from abnormal functioning of many factors in concert. Animal models mirroring human electrophysiology are essential to predict and understand the rare pro- and anti-arrhythmic effects of drugs. This is very well accomplished by the canine chronic atrioventricular block (CAVB) model. Here we summarize canine models for cardiovascular research, and describe the development of the CAVB model from its beginning. Understanding of the structural, contractile and electrical remodelling processes following atrioventricular (AV) block provides insight in the many factors contributing to drug-induced arrhythmia. We also review all safety pharmacology studies, efficacy and mechanistic studies on anti-arrhythmic drugs in CAVB dogs. Finally, we compare pros and cons with other in vivo preclinical animal models. In view of the tremendous amount of data obtained over the last 100 years from the CAVB dog model, it can be considered as man's best friend in preclinical drug research.

Insights into sinus arrhythmia of the dog: Acetylcholine perfusion of canine right atrium results in beat-to-beat patterns that mimic sinus arrhythmia supporting exit block in the sinoatrial conduction pathways

Sinus arrhythmia of the dog is unique because of the pronounced alternating beat-to-beat intervals. The clustering of these short (faster rates) and long (slower rates) intervals is not just influenced by autonomic input from breathing; sinus arrhythmia can persist in the panting or apneic dog. The multiplicity of central and peripheral influences on the sinus node complicates the unraveling of the mechanisms of sinus arrhythmia. Studies of the sinus node suggest that acetylcholine can slow cellular depolarization and block sinoatrial conduction. Electrocardiographic monitoring of the dog supports this notion in that abrupt bifurcation into short and long intervals develop at lower heart rates. We sought to determine whether this phenomenon could be recapitulated in canine atrial preparations perfused with acetylcholine and whether selective pharmacologic blockade of the voltage and calcium clocks could provide insight into its mechanism. Spontaneous beat to beat (A-A) intervals were obtained from monophasic action potential recordings of perfused canine right atrial preparations before and during perfusion with acetylcholine (2-5 μM). The calcium clock was blocked with ryanodine (2-3 μM). The membrane clock was blocked with diltiazem hydrochloride (I_Ca,L blocker; 0.25 μM) and ZD7288 (I_f blocker; 3 μM). Hyperpolarization was hindered by blockade of I_K,Ado/I_K,Ach with tertiapin Q (100 nM) before and during acetylcholine perfusion. Acetylcholine resulted in beat clusters similar to those seen in sinus arrhythmia of the dog. Beat clusters were consistent with intermittent 2:1 and 3:1 sinoatrial conduction block. Tertiapin Q abolished this patterning suggesting a role of I_K,Ado/I_K,ACh in the mechanism of these acetylcholine-induced beat-to-beat patterns.

Optimizing single-chamber pacing in dogs Part 1: Rate determinations, rate interventions and hysteresis

Determining ideal pacing rates to meet physiological needs and optimizing programming to prevent unnecessary right ventricular pacing in dogs requires an understanding of heart rate profiles and applicable pacing technology. The heart rate and rhythm of the dog is complex necessitating investigation of rate requirements of activity and circadian influences. Overlaying this information are a multiplicity of other factors such as age, breed, temperament, cardiovascular disease and underlining rhythm disorders that contribute to the difficulty in making general conclusions. However, all such information permits better implementation of programming options with the goal of better outcomes. In this review (Part 1 of a two-part review) instantaneous heart rate, rolling average heart rate, simple average heart rate, heart rate tachograms, RR interval tachograms (2D, 3D and dynamic), and Poincaré plots (2D, 3D and dynamic) are discussed as they apply to decisions in the determination and examination of pacing rates for dogs programmed in the VVI pacing mode (Ventricular paced, Ventricular sensed, Inhibited pacing). The applicable pacing operations available for three pacemaker companies are reviewed (Abbott, Biotronik/Dextronix, and Medtronic). The programmable options considered include: slowest pacing rate without additional features to extend the pacing interval, sleep/rest rate preferences, hysteresis to lengthen pacing interval following intrinsic beats, and intermittent increases in pacing following abrupt loss of intrinsic rhythm. Recommendations are suggested for follow-up of individual dogs with examination of pacing statistics and Holter monitoring.

Optimizing single-chamber pacing in dogs. Part 2: Rate adaptive pacing

Proper programming of pacemakers for dogs in the rate adaptive mode requires an understanding of the rate requirements for each individual and the interplay of programmable features. The specific advantages and disadvantages of the rate adaptive mode should be considered on a case by case basis. Fundamentally, two components are linked in the implementation of rate adaptive pacing: (1) sensing the need for a change in rate and (2) responding with the appropriate alteration in pacing rate. The programming interaction of these two components are interdependent and affected by the rates programmed. These features may be adjusted manually or automatically. In this review (Part 2 of a two-part review) the considerations required to program each aspect that optimizes the pacing rate profile are reviewed. These include the lower rate, upper sensor rate, activities of daily life rate, sensor threshold, acceleration and deceleration, slope, activities of daily life zone, exertion zone, automatic versus manual adjustments and closed loop stimulation. The programming features of pacemakers manufactured by three companies are summarized (Abbott, formerly St. Jude; Biotronik/Dextronix; Medtronic). Means of assessing the success of pacemaker programing is examined through examples of pacemaker data, Holter analysis, Poincaré plots and tachograms. Finally, the questions and considerations for rate adaptive pacing in dogs that demand investigation are proposed.

Instantaneous and averaged heart rate profiles: Developing strategies for programming pacing rates in dogs

Pacemakers use heart rate histograms (% beats) and sensor indicated rate histograms (% time) to illustrate rate distributions. When programmed to the rate adaptive modes, these data are used to determine the appropriateness of rate response to activity. These histograms are generated from instantaneous heart rate calculations. In humans, such data are compared to known histographic rate profiles. Such rate profiles during 24 h in the dog are not available. Moreover, data representation differ between Holter monitoring and pacemakers making comparisons challenging. The rate distribution in dogs >7-years of age was determined over 24 h using instantaneous and rolling average heart rate. Such data could serve as a guide to programming pacing rates for dogs. Sinus arrhythmia resulted in dissimilar heart rate profiles depending on the method of determining rate. The long intervals of sinus arrhythmia resulted in median values for the percent of time with an instantaneous heart rate of <50 beats/min (bpm) of 15%, whereas a rolling average heart rate of <50 bpm was 0.2%. Based on the cumulative time of the rolling average rate, dogs spent 26.3% of the day between 70-90 bpm with rates <65 bpm and >90 bpm approximating 30% for each. Rates >160 bpm were uncommon (<1%). However, high variability existed between dogs. This study demonstrated the shortcomings of both instantaneous and averaging methods to evaluate heart rate profiles in the dog and that both methods should be incorporated when making pacing rate decisions during programming.

Heart rate variability analysis in horses for the diagnosis of arrhythmias

Heart rate variability (HRV) analysis has been performed on ECG-derived data sets for more than 170 years but is currently undergoing a rapid evolution, thanks to the expansion of the human and veterinary medical technology sector. Traditional HRV analysis was initially performed to identify changes in vago-sympathetic balance, while the most recent focus has expanded to include the use of complex computer algorithms, neural networks and machine learning technology to identify cardiac arrhythmias, particularly atrial fibrillation (AF). Some of these techniques have recently been translated for use in the field of equine cardiology, with particular focus on improving the diagnosis of arrhythmias both at rest and during exercise. This review focuses on understanding the basic HRV variables and important factors to consider when collecting data for use in HRV analysis. In addition, the use of HRV analysis for the diagnosis of arrhythmias is discussed from human, small animal and equine perspectives. Finally, the future of HRV analysis is briefly introduced, including an overview of future developments in this rapidly expanding and exciting field.