Detection of paroxysmal atrial fibrillation preceding persistent atrial fibrillation in a horse using an implantable loop recorder with remote monitoring.

Implantable loop recorders (ILRs) are increasingly used in equine cardiology to detect arrhythmias in the context of collapse, poor performance or monitoring for recurrence of atrial fibrillation (AF). However to date, the ILR has never been reported to be used with a remote monitoring functionality in horses, therefore the arrhythmia is only discovered when a clinician interrogates the ILR using dedicated equipment, which might delay diagnosis and intervention. This case report describes the use of an ILR with remote monitoring functionality in a horse with recurrent AF. The remote monitoring consisted of a transmission device located in the stable allowing daily transmission of arrhythmia recordings and functioning messages to an online server, available for the clinician to evaluate without specialised equipment. The ILR detected an episode of paroxysmal AF approximately three months after implantation. Seven months after implantation, initiation of persistent AF was seen on an episode misclassified by the ILR as bradycardia, and the horse was retired. This report shows the feasibility and benefits of remote monitoring for ILRs in horses, but also the shortcomings of current algorithms to interpret the equine electrocardiogram.

Clinical outcome of idiopathic juvenile ventricular arrhythmias in 25 dogs.

INTRODUCTION/OBJECTIVES: Juvenile ventricular arrhythmias in the absence of structural heart disease have been characterized in a small number of canine breeds with limited long-term follow up. The objective of this study was to describe the clinical outcome of dogs with JVA presenting to a university teaching hospital. ANIMALS, MATERIALS, METHODS: Twenty five dogs, less than two years old with idiopathic ventricular arrhythmias were retrospectively identified via a medical record search. Young dogs with ventricular arrhythmias were excluded if they had structural heart disease, systemic illness, or an abnormal troponin (if performed). Electrocardiographic and Holter monitor data was evaluated for arrhythmia frequency and complexity at the time of diagnosis and over time. Long-term follow up was achieved through client and primary veterinarian contact. RESULTS: Breeds included German Shepherd (eight), Boxer (four), Great Dane (three), mixed breed (two) and one each of the following: Anatolian Shepherd, French Bulldog, golden retriever, Great Pyrenees, Labrador retriever, Shiloh Shepherd, miniature Poodle and Siberian Husky. The average age at diagnosis was 7.9 months (range, 2-22 months). The overall median survival was 10.96 years (range, 1.75-15.66 years). There was an average reduction in the number of ventricular beats by 86.7 % per year (P value -0.0257) based on Holter data. CONCLUSION: In most cases, idiopathic juvenile ventricular arrhythmias had a favorable long-term prognosis with reduced ectopy over time in this case series. Juvenile ventricular arrhythmias remains a diagnosis of exclusion but can be considered in a broader range of dog breeds than previously described.

Comparison of the diagnostic value of a small, single channel, electrocardiogram monitoring patch with a standard 3-lead Holter system over 24 hours in dogs.

INTRODUCTION/OBJECTIVES: The aim of this study was to compare a novel small event recorder device, the Carnation Ambulatory Monitor (CAM), with a standard Holter. ANIMALS: Nineteen adult dogs. MATERIAL AND METHODS: Comparative and explorative study. The two devices were simultaneously applied for approximately 24 h. RESULTS: Analysis time (P=0.013) and percentage of artefacts (P<0.001) were greater for the CAM (110 min [40-264]; and 9% [0-34], respectively) compared to a standard Holter (30 min [18-270]; and 0.3% [0-9], respectively). The total number of beats (P=0.017) and maximum (P=0.02) and mean (P=0.037) heart rates were lower for the CAM (113,806 ± 23,619 beats; 227 ± 35 bpm; and 88 ± 22 bpm, respectively) compared to the standard Holter (131,640 ± 40,037 beats; 260 ± 64 bpm; and 92 ± 26 bpm, respectively). The minimal heart rate (P=0.725), number of pauses (P=0.078), duration of the longest pause (P=0.087), number of ventricular ectopic complexes (P=0.55), ventricular couplets (P=0.186), ventricular triplets (P=0.203), ventricular tachycardia (P=0.05), Lown grade (P=0.233), presence or absence of ventricular bigeminy, trigeminy, supraventricular tachycardia, and atrial fibrillation (P=0.98) did not differ. The CAM missed some relevant events, like complex ventricular arrhythmias, and the Lown grade did not match in 5/19 dogs when comparing the devices. CONCLUSIONS: Cardiac Ambulatory Monitor can be used to record ECG traces in dogs over a prolonged period, allowing to detect arrhythmias. Due to some clinically relevant limitations, including a higher percentage of artefacts, a longer reading time (which precludes quantitative counts of >300ventricular premature complexes), and underestimation of complex ventricular arrhythmias, the CAM appears not suitable for quantitative arrhythmia analysis in dogs.

A pilot study of patch Holter electrocardiograph recordings in healthy cats.

Background: A patch Holter electrocardiograph (P-Holter) is cordless, making it lightweight, unlike the conventional Holter electrocardiograph (C-Holter). A P-Holter can also take continuous measurements for up to 14 days without replacing the battery or SD card. Aim: To compare the performance of the P-Holter and the C-Holter in healthy cats. Additionally, we aimed to investigate whether multiday recordings with the P-Holter decrease sympathetic nerve activity or improve the accuracy of arrhythmia detection. Methods: Five healthy domestic short-haired cats were used for this study. Both a P-Holter and C-Holter were used on the first day, but only the P-Holter was used on days 2-6. The evaluated variables were the analyzable time of both Holter types, heart rate (HR), HR variability (HRV), and the number of arrhythmia occurrences. Results: For two out of the five cats, measurement of P-Holter was interrupted. Eventually, continuous recordings using the P-Holters were able to be collected from all individuals for 6 days. The 24 hours analyzable time from the P-Holter and C-Holter was almost identical (p = 0.94). The 24 hours mean HR did not differ across Holter types (p = 0.67). In addition, the timing of the occurrences of arrhythmias was almost identical to the P-Holter and C-Holter. Results of HRV suggested that sympathetic nerve activity was likely to decrease and vagal nerve activity was likely to increase after 4-5 days of measurement, compared to the second day of measurement (p < 0.05). When only the P-Holter was installed, the number of arrhythmia occurrences was similar on days 2-6. Conclusion: In this study, the P-Holter may be as useful as the C-Holter in cats with suspected intermittent arrhythmias, although the P-Holters were placed on cats without a clinical indication. However, cats may have individual differences in their adaptation to the device. P-Holter recordings taken for more than 4-5 days may allow the cat to acclimate to the device and reduce sympathetic nerve activity. The accuracy of arrhythmia detection across multiday P-Holter recordings requires further investigation using clinical cases.

Validation of heart rate spot-check protocol to measure circadian variation and heart rate in healthy dogs and dogs with atrial fibrillation.

INTRODUCTION: Alternatives for out-of-clinic heart rate (HR) measurement are required to optimise the management of atrial fibrillation (AF) in dogs. Additionally, the presence of circadian variation (CV) in HR in pet dogs remains unknown. We aimed to identify the number and duration of spot-checks required for an accurate estimation of 24-hour HR in canine AF. Circadian variation in HR was examined in healthy dogs and dogs with AF, and spot-check-derived HR was compared with a CV-derived gold standard. MATERIALS AND METHODS: Ambulatory electrocardiogram data from healthy dogs and dogs with AF were retrospectively analysed. Heart rate was calculated from the entire recording and pre-defined periods (spot-checks) of one hour to 30 and 60 s in duration. Circadian variation in HR was determined by cosinor analysis. Bias and limits of agreement of means and median HR with mesor HR were determined by correlation and Bland-Altman analysis. RESULTS: Circadian variation in HR was identified not only in 18/22 healthy dogs and 14/21 AF dogs but only on ambulatory electrocardiogram recordings. Four-hourly spot-checks provided the most accurate estimate of mesor HR in healthy dogs (bias of the median over 30 s 7.70, limits of agreement 7.48), whereas, in dogs with AF, four, six and eight-hourly spot-checks provided reliable estimates of mesor HR (bias within -1.29 and -29.5). CONCLUSIONS: Four, six and eight-hourly HR spot-checks can estimate 24-hourly HR in dogs with AF. There was CV in HR in most healthy pet dogs and dogs with AF. Spot-check protocols cannot identify CV in HR.

The next heartbeat: Creating dynamic and histographic Poincaré plots for the assessment of cardiac rhythms.

The rhythm of the heart is not a stationary phenomenon, and therefore, incorporation of the dynamic Poincaré plot and tachogram provides additional diagnostic information to complement and expand waveform (P-QRST) analyses from the electrocardiogram. Although pattern assessment of the Poincaré plot and tachogram can provide an appraisal for normal and abnormal rhythms and serve as a potential means for machine-learned rhythm diagnoses, time-selected windows of beat-to-beat variability permit more detailed examination. As such, expanded criteria for rhythm diagnoses, identification of arrhythmic triggers, global appreciation of rhythm changes, and recognition of patterns that provoke mechanistic questions may be gleaned from the use of the methods reviewed in this report. More specifically, these methods demonstrate that limitations exist in the reliance on traditional measures of heart rate variability in the dog due to the non-linear beat-to-beat rhythm of sinus arrhythmia in the species. Behavior of arrhythmias based on coupling intervals, repeating patterns, preceding triggers of beat-to-beat variability, and circumstantial evidence of atrioventricular nodal conduction during atrial flutter and fibrillation are a few examples of discovery founded in these techniques. The open access website, The Next Heartbeat (https://thenextheartbeat.com/), permits anyone to implement these methods in the assessment of long-term electrocardiographic examinations (Holter monitoring) so that, as yet to be revealed, features of the beating heart through time may be discovered.

Ambulatory electrocardiography, heart rate variability, and pharmacologic stress testing in cats with subclinical hypertrophic cardiomyopathy.

The utility of ambulatory electrocardiography (AECG) to evaluate cats with subclinical hypertrophic cardiomyopathy (HCM) for arrhythmias and heart rate variability (HRV) is not well defined but may provide information regarding risk stratification. This prospective study used AECG to evaluate ectopy and HRV in subclinical HCM cats compared to healthy controls and is the first to implement a pharmacologic cardiac stress test. Twenty-three purpose-bred, Maine coon cross cats (16 HCM, 7 control) underwent 48-h of continuous AECG. Terbutaline (0.2-0.3 mg/kg) was administered orally at 24 and 36 h. Heart rate, ectopy frequency and complexity and HRV parameters, including standard deviation of normal R-R intervals (SDNN), were compared pre-terbutaline and post-terbutaline and across phenotype, genotype and sex. Genotype for an HCM-causative mutation was significantly associated with the frequency of supraventricular (P = 0.033) and ventricular (P = 0.026) ectopy across all cats. Seven HCM cats and zero healthy cats had a sinus arrhythmia. Mean heart rate was significantly higher post-terbutaline (p < 0.0001). HCM cats had significantly greater HRV compared to controls (SDNN: p = 0.0006). Male cats had significantly higher HRV (SDNN: p = 0.0001) and lower mean heart rates (p = 0.0001). HRV decreased post-terbutaline (SDNN: p = 0.0008) and changes in HRV observed between sexes were attenuated by terbutaline.

Presumptive vagally-mediated atrial flutter in a dog.

An asymptomatic nine-year-old Dobermann Pinscher underwent a screening for dilated cardiomyopathy. Echocardiography revealed left ventricular eccentric hypertrophy and systolic dysfunction; the rest of the echocardiographic parameters were within normal limits. Holter monitoring demonstrated sinus rhythm as the dominant cardiac rhythm during the first hours of the recording. Then, during a period of physiologically enhanced vagal tone (sleep), spontaneous development of atrial flutter (AFL) associated with variable ventricular response was documented. Alternation between AFL and paroxysmal atrial fibrillation was also observed. Subsequently, during a period of physiological increase of sympathetic tone (physical activity/excitement), spontaneous conversion of AFL to sinus rhythm occurred. In light of these findings, a presumptive diagnosis of vagal AFL was made. The images here described allow us to study the onset, behavior and termination of this intriguing electrocardiographic entity.

Screening for dilated cardiomyopathy in dogs.

BACKGROUND: Dilated cardiomyopathy (DCM) is the most common cardiac disease in large breed dogs. The disease can start with arrhythmias or with systolic dysfunction of the myocardium. OBJECTIVE: To describe screening methods for DCM in various breeds and provide a new, modified staging system. RECOMMENDATIONS: Screening for occult DCM should start at three years of age and use Holter monitoring in Boxers and Dobermans and might be useful also in other breeds. Single ventricular premature complexes (VPCs) can be detected in many healthy dogs, but healthy animals typically have <50 VPCs in 24 h and demonstrate minimal complexity most often occurring only as single ectopic beats. In general, >100 VPCs in 24 h was recommended as the cut-off value for establishing a diagnosis of DCM. However, there are breed-specific recommendations related to Holter recording diagnosis of DCM in Dobermans and Boxers. Yearly screening over the life of a dog is recommended, as a one-time screening is not sufficient to rule out the future development of DCM. Several echocardiographic methods such as M-mode derived measurements, the measurement of the left ventricular (LV) volume by Simpson's method of discs (SMOD), and E-point to septal separation (EPSS) are recommended for screening purposes. The value of additional tests such as cardiac biomarkers (troponin I and N-terminal pro-B-type natriuretic peptide) as well as a 5-min resting electrocardiogram (ECG) or newer echocardiographic methods such as strain measurements is discussed. CONCLUSION: This review suggests some guidelines for screening for DCM in various breeds.

Heart rhythm characterization during sudden cardiac death in dogs.

INTRODUCTION/OBJECTIVES: Inherited or acquired arrhythmic disorders and cardiac disease have been associated with sudden cardiac death (SCD) in dogs. The electrical mechanism related to death in most of these cases is unknown. This retrospective study aimed to describe arrhythmic events in dogs that experienced SCD during Holter monitoring. ANIMALS, MATERIALS AND METHODS: Nineteen client-owned dogs that experienced SCD during Holter examination were included. Clinical records from a Holter service database were reviewed, and both the rhythm preceding death and the dominant rhythm causing SCD were analysed. Clinical data, Holter diaries and echocardiographic diagnosis were also evaluated. RESULTS: Structural heart disease was identified in 12/19 dogs (dilated cardiomyopathy in five dogs, arrhythmogenic right ventricular cardiomyopathy in four dogs, myxomatous mitral valve disease in two dogs, and suspected myocarditis in one dog), five of which had concurrent congestive heart failure. Sudden cardiac death was related to ventricular premature complexes or monomorphic ventricular tachycardia degenerating into ventricular fibrillation in 42% of dogs, polymorphic ventricular tachycardia, or torsade de pointes-like inducing ventricular fibrillation in 21%, and asystole or presumptive agonal pulseless electrical activity triggered by malignant bradyarrhythmias in 37%. CONCLUSIONS: The most common rhythm associated with SCD in our population of dogs was ventricular tachycardia leading to ventricular fibrillation, although bradyarrhythmia-related SCD, possibly related to inappropriate vagal reflexes, was also a notable cause.

Comparison of in-hospital continuous electrocardiography versus recordable Holter monitoring in dogs with ventricular arrhythmias.

OBJECTIVE: Determine the agreement between nonrecordable continuous ECG and Holter monitoring at estimating arrhythmia severity in hospitalized dogs. DESIGN: Prospective, observational, cohort study. SETTING: University teaching hospital. ANIMALS: Ten dogs. INTERVENTIONS: Heart rates and rhythms were simultaneously monitored using nonrecordable cage-side continuous ECG and Holter monitoring. Continuous ECG was assessed by ICU technicians for 1 min every hour, and heart rate and rhythm were recorded. A modified Lown score was used to grade arrhythmia severity (Grade 0 = sinus; Grade 1 = single ventricular premature complexes; Grade 2 = accelerated idioventricular; Grade 3 = bigeminy/trigeminy; Grade 4 = couplets/triplets; Grade 5 = ventricular tachycardia or R on T). Holter data were analyzed by a board-certified cardiologist, and arrhythmia grade was assigned to the same 1-min time period reported by ICU technicians. A 1-h arrhythmia grade was also determined from Holter data and was reported as the highest grade noted during the previous hour. Cohen's weighted kappa analysis was used to compare the agreement of ICU and Holter grade during the same 1-min time period and to compare 1-min Holter grade with the prior hour Holter grade. MEASUREMENTS AND MAIN RESULTS: Weak agreement was found between ICU-reported grade and Holter grade (κ = 0.40), as well as weak agreement between 1-min Holter grade and hour Holter grade (κ = 0.39). CONCLUSIONS: Results of this study indicate that arrhythmia grades assessed by ICU technicians and hourly 1-min observations weakly agree with recordable Holter monitoring in hospitalized dogs with ventricular arrhythmias.

Holter monitoring in dogs: 24 h vs. 48 h.

Holter monitoring has an important role in the diagnosis of cardiac arrhythmias in dogs with underlying heart disease or clinical signs such as intermittent weakness/ collapse or exercise intolerance, and in the assessment of antiarrhythmic treatment efficacy. A typical recording lasts for 24 h, although 48 h or any number of days up to 7 are possible, especially when investigating clinical signs that may not happen during the first 24 h. The objective of this study was to review retrospectively a large number of 48 h Holter recordings obtained from dogs to assess the possible incremental diagnostic yield of the second 24 h period in comparison to the first 24 h. Three hundred and fifty four 48 h Holter recordings were included in the study for analysis. A 48 h Holter recording contributed to a 14.5% increase in the likelihood of documenting the cardiac rhythm during an event of interest; a 24 h recording increased the diagnostic yield from 32.2% to 46.7%. When the recordings were grouped according to the most important rhythm abnormalities (supraventricular arrhythmias group, ventricular arrhythmias group, bradyarrhythmias group, no arrhythmias group), the 48 h Holter monitor contributed to a 5% increase in the likelihood of identifying a relevant cardiac rhythm abnormality, increasing the diagnostic yield from 58% to 63%. This benefit occurred mostly in dogs with iterative or paroxysmal supraventricular arrhythmias. In dogs with bradyarrhythmias or ventricular arrhythmias, an additional 24 h of analysis was useful in only a limited number of cases.

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.

Evaluating heart electrical activities and cardiac arrhythmias of Holstein cows during ageing by short-term electrocardiography in comparison with 24-hour holter-monitoring.

Short-term electrocardiography is one of the most suitable tools to study the electrical activity of the heart, but the use of a tool such as a Holter-monitor with the ability to assess the long-term of the heart electrical activity, can provide more accurate information about these activities by comparing the results. It is possible to understand the superiority of each over the other and the resulting differences. Therefore, 60 female Holstein cows in 10 age groups, including 1 day, 1, 3, 6 months, 1, 2, 3, 4, 6 and 8 years were included in the study (6 heads in each age group). Electrocardiography (for 5 min) and Holter-monitoring (for 24 hr) were performed from the entire study population. The Q, R and T amplitudes in electrocardiography were significantly higher than those in Holter-monitoring. The P, R and T durations and P-R, R-R, Q-T and S-T intervals at all ages were significantly longer in the Holter-monitoring than in the electrocardiographic method. The heart rate of animals was significantly lower in the 24-hr Holter-monitoring than in the short-term electrocardiography. The trend of changes of all parameters was significant during ageing. Cardiac arrhythmias included sinus arrhythmia and sino-atrial block, which were the most common cardiac arrhythmias in the 24-hr Holter-monitoring. It appears that long-term Holter-monitoring is a more reliable method than short-term electrocardiography to assess cardiac arrhythmias. Additionally, the indicators of electrical activity of the heart (waves) in the Holter-monitoring method are significantly different from short-term electrocardiography, which is probably due to the collection of information over a long period and in non-stressful situations. Furthermore, it appears that the use of the 24-hr Holter-monitoring method is preferable to the short-term electrocardiography method to evaluate the electrical activity of the heart of cows at all ages.

Evaluation of a novel ambulatory electrocardiogram monitor (the Carnation Ambulatory Monitor) for use in horses.

INTRODUCTION: Short-term electrocardiogram (ECG) examinations of horses may not detect paroxysmal arrhythmias. Twenty-four hour Holter equipment can be unwieldy and inconvenient for long-term use. This study evaluated a novel long-term ECG patch recorder, the Carnation Ambulatory Monitor (CAM) in horses, determining ideal placement, practicality, durability and performance. ANIMALS: Twenty-one adult mixed-breed horses. METHODS: Prospective observational study. Three horses had ECG patches fitted at selected sites (phase 1); the two most promising sites were used for further wear testing (phase 2) and the best site was chosen for a trial in 18 horses (phase 3), 16 of which had presented for evaluation of cardiac disease. In phase 1, the CAM was compared with a standard telemetric ECG. The CAM ECGs were analysed using proprietary software. RESULTS: The most promising sites for CAM placement were the ventral midline caudal to the xiphisternum and left thorax caudal to the girth. The ventral midline was chosen for further evaluation. The CAM provided reliable and generally excellent ECG quality at rest (median quality score 4.5/5, range 3-5), over extended periods, allowing detection of arrhythmias. The ECG quality was poor during exercise (median quality score 1, range 1-5), except in three horses. In 15/17 placements in the standing horse, greater than 85% of the potential recording time was achieved. CONCLUSIONS: The CAM is a convenient and well-tolerated device for evaluating equine cardiac rhythm at rest over long periods. Further evaluation of the ideal placement site during exercise may increase its diagnostic utility.

Assessment of heart rate turbulence in dogs with myxomatous mitral valve disease.

BACKGROUND: Myxomatous mitral valve degeneration (MMVD) is the most common heart disease affecting small dogs, it reduces cardiac output resulting in compensatory adaptation of the autonomic nervous system. Chronically, it leads to reduced heart rate variability (HRV) which is an accurate marker for autonomic balance. More than two decades ago in human medicine an indicator of autonomic balance that happens after a premature ventricular beat, it was described as heart rate turbulence (HRT). In humans with ischemic heart disease, the absence of HRT has proven to be a more accurate and an independent indicator of mortality than known HRV parameters. Currently, there are very few studies of HRT in dogs and it is still not tested in small dogs within different stages of myxomatous mitral valve disease. AIM: The aim of this study was to assess the HRT indicators, onset and slope, in small dogs with myxomatous mitral valve disease and to statistically test it. METHODS: Dogs under 25 kg had electrocardiogram and echocardiography performed and, in some patients, holter monitoring was carried out. Data were divided into groups B1, B2, C, and D for mean comparison with analysis of variance and Tukey test. In addition, receiver operating characteristic (ROC) curve for differentiating among symptomatic and asymptomatic dogs and for differentiating between remodeled and non-remodeled hearts. The Pearson was executed after correlations of turbulence onset (TO) and turbulence slope (TS) with commonly used echocardiographic parameters. RESULTS: Variance analyses held significant differences in TO and TS between stages B1 from stages C and D, while B2 held similarity to the other groups. In the receiver operating curve was found a very good area under the curve for differentiating among symptomatic and asymptomatic dogs and remodeled and non-remodeled dogs. Few echocardiography parameters held weak correlation with TO while others held weak to moderate correlation with TS. CONCLUSION: In dogs with MMVD and without other diseases, HRT is a feasible indicator for autonomic balance. Our result suggests HRT changes as the MMVD progresses and congestive heart failure is present. More studies with HRT are needed. The number of ventricular premature contractions (VPCs) may be the strongest limitation for the technique.

Detection of atrial fibrillation with implantable loop recorders in horses.

BACKGROUND: Cardiac arrhythmias in horses are diagnosed by auscultation or electrocardiogram (ECG), which results in a low sensitivity for detecting arrhythmias that occur sporadically. Implantable loop recorders (ILRs) are small ECG devices placed subcutaneously, to automatically detect arrhythmias in human patients. OBJECTIVES: To test ILRs ability to detect atrial fibrillation (AF) in horses. Furthermore, we hypothesised that anatomical location of the implant site might influence signal quality. Signal quality was evaluated both during exercise and over time. STUDY DESIGN: Experimental study. METHODS: In five Standardbred mares, eleven ILRs were implanted subcutaneously in up to three different positions (Front: pectoral region, Left-6: sixth left intercostal space and Ventral: xiphoid region) and AF induced. The R- and T-wave amplitudes were measured in all positions over time during AF. AF burden automatically registered by the ILRs over a 2-month period was compared with selected Holter ECG recordings. RESULTS: All three positions had stable R- and T-wave amplitudes during the study period and were of sufficient quality to allow AF detection at rest. The position Left-6 showed significantly higher R- and T-wave amplitudes compared with the other positions. During submaximal exercise only the Left-6 position was able to record ECG signals of diagnostic quality. No position yielded diagnostic signals at maximum exercise due to artefacts. MAIN LIMITATIONS: Few horses and ILRs included and no spontaneous AF episodes were studied. CONCLUSIONS: This preliminary study indicates that ILRs can be used for AF detection in horses, but the anatomical location is important for optimal ECG quality. Despite insufficient quality during exercise, ILRs were suitable for AF detection at rest. Therefore, the ILR may be a valuable diagnostic tool for detecting paroxysmal AF in horses.

Visual representations of canine cardiac arrhythmias with Lorenz (Poincaré) plots.

OBJECTIVE: To characterize the patterns associated with Lorenz plots (LPs) or Poincaré plots derived from the Holter recordings of dogs with various cardiac rhythms. ANIMALS: 77 dogs with 24-hour Holter recordings. PROCEDURES: A 1-hour period from the Holter recordings from each of 20 dogs without arrhythmias and from each of 57 dogs with arrhythmias (10 each with supraventricular premature complexes, complex supraventricular ectopy, ventricular premature complexes, complex ventricular ectopy, and atrial fibrillation, and 7 with high-grade second-degree atrioventricular block) were used to generate the LPs. Patterns depicted in the LPs were described. RESULTS: Arrhythmia-free Holter recordings yielded LPs with a Y-shaped pattern and variable silent zones. Recordings with single premature complexes yielded LPs with double side and triple side lobes. Complex ectopy was denoted by dots clustered in the lower left corner of the LPs. The LPs of recordings with atrial fibrillation had fan patterns consistent with a nonlinear relationship between atrial electrical impulses and atrioventricular nodal conduction. The recordings with atrioventricular block yielded LPs with island patterns consistent with variable atrioventricular nodal conduction. CONCLUSIONS AND CLINICAL RELEVANCE: Distinct LP patterns were identified for common cardiac rhythms of dogs, supportive of nonrandom mechanisms as the cause of most rhythms. Visual interpretation of an LP generated from a Holter recording may aid in determining the arrhythmia type and understanding the arrhythmia's mechanism in dogs and other species.

Twenty-four-hour ambulatory (Holter) electrocardiographic findings in 13 cats with non-hypertrophic cardiomyopathy.

Detection and characterisation of cardiac arrhythmias in cats with hypertrophic cardiomyopathy (HCM) has already been documented in various studies. However, similar studies have not been reported for other forms of feline cardiomyopathy. The clinical records of 13 client-owned cats diagnosed with restrictive cardiomyopathy (RCM), arrhythmogenic right ventricular cardiomyopathy (ARVC) and non-specific cardiomyopathy (NSCM) that underwent Holter recording at the time of diagnosis were reviewed retrospectively. Eight cats had signs of congestive heart failure at presentation, one cat had a history of recurrent syncope and the remaining four cats were asymptomatic. The average heart rate was 138 ± 22 (range 97-181) beats per minute (bpm) with the lowest value (97 bpm) recorded in a cat with third degree atrioventricular block (3-AVB) and the highest value (181 bpm) observed in a cat with atrial fibrillation (AF). The median number of ventricular ectopic beats (VEB) over 24 h was 2031 (338-8305), mostly represented by single isolated VPCs (803, 123-2221). Cardiac pauses were observed in three cats, with the longest pause lasting more than 6 s. A survival analysis was not performed due to the small number of cats and limited follow-up information. Holter recording revealed cardiac arrhythmias in all 13 cats, while 8/13 cats (61.5%) had an unremarkable resting electrocardiogram (ECG). The average daily heart rate in these cats did not appear affected by the presence of heart failure, although periods of sinus arrhythmia were absent in all individuals.

Heart rhythm characterisation during unexplained transient loss of consciousness in dogs.

The identification of the heart rhythm during an episode of transient loss of consciousness (TLOC) is considered the reference standard method to elucidate the underlying aetiology. This study aimed to characterise heart rhythm in dogs during TLOC using Holter and external loop recorder monitoring. We retrospectively reviewed 24-h Holter monitoring and external loop recorder tracings from 8084 dogs. Heart rhythms from dogs that experienced TLOC during the recording was analysed to identify rhythm disturbances that occurred during episodes of TLOC. Electrocardiograms (ECGs) were subsequently categorised into Type 1 (ventricular arrest), Type 2 (sinus bradycardia), Type 3 (no/slight rhythm variations), and Type 4 (tachycardia). Transient LOC was documented in 92 dogs over 230 episodes of TLOC. Percentage of cases with ECGs compatible with each classification were as follows: 72.1%, Type 1; 6.1%, Type 2; 20.9%, Type 3; and 0.9%, Type 4. Cardiac rhythm during the TLOC could have been a consequence of a neurocardiogenic mechanism in 46.7% cases, while intrinsic rhythm disturbances of the sinus node or of the atrioventricular node were diagnosed in 31.5% cases. In two cases, tachycardia was the possible cause of the TLOC. ECG patterns in dogs presenting with multiple TLOC episodes were completely reproducible during each episode. TLOC in dogs was primarily caused by ventricular arrest. Most dogs with TLOC had electrocardiographic finding suggestive of a reflex or neurally-mediated syncope, but one third had an ECG more suggestive of a conduction disorder. Distinguishing these two entities could help inform diagnostic, therapeutic, and prognostic plans.