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: The purpose of this study was 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 to 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 h analyzable time from the P-Holter and C-Holter was almost identical (p = 0.94). The 24 h 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 to 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 to 6. Conclusion: In this study, the P-Holter may be as useful as the C-Holter in cats with suspected intermittent arrhythmias, although these 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 to 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.

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.

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.

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.

Effect of a lactate-guided conditioning program on heart rate variability obtained using 24-Holter electrocardiography in Beagle dogs

The dogs’ responses to training exercise are seldom monitored using physiological variables, and cardiac autonomic regulation (CAR) is a relevant determinant of endurance-training adaptation. There are studies in the literature establishing that regular exercise could interfere with CAR in dogs, measured by heart rate and vagal-derived indexes of heart-rate-variability (HRV). However, few studies were found using a prescribed training program based on the lactate threshold (LT) to determine HRV by a 24-h Holter analysis. The purpose of this study was to test whether an endurance-training program (ETP) guided individually by LT raises time-domain measures of HRV in healthy Beagle dogs. Twenty dogs were assigned to two groups: control (C) and trained (T). The dogs from group T underwent an incremental exercise test (IET) to determine their LT. Both LT and velocity corresponding to the LT (VLT) was determined by visual inspection. T group performed an eight-week endurance-training program consisting of treadmill runs set to 70–80% of the VLT. Next, dogs from the group T have submitted to IET again. The maximal velocities (Vmax) at which achieved by the trained dogs in both IETs were determined. The group S did not undergo IETs or ETP. HRV was determined by the 24-hour-Holter at rest, before and on the 2°, 4°, 6° and 8° training weeks. To examine the HR impact on HRV, standard HRV variables were normalized to prevailing HR. VLT and Vmax rose in group T, indicating an improvement of dogs’ aerobic and anaerobic capacity. The normalized standard HRV indexes were relatively attenuated since these variables had a reduction in the degree of correlation concerning an average HR. The ETP resulted in decreased resting heart rate and increased time-domain indices, highlighting the log-transformed square root of the mean sum of the squared differences between R–R intervals (Ln rMSSD). The lactate-guided endurance-training program could lead to better parasympathetic cardiac modulation in Beagle dogs.

Selected cardiac abnormalities in Trypanosoma cruzi serologically positive, discordant, and negative working dogs along the Texas-Mexico border

BACKGROUND

Chagas disease is increasingly recognized in the southern U.S., where triatomine vectors transmit Trypanosoma cruzi among wildlife and domestic dogs with occasional vector spillover to humans. As in humans, clinical outcome in dogs is variable, ranging from acute death to asymptomatic infections or chronic heart disease. In order to characterize cardiac manifestations of T. cruzi infections, we tracked a cohort of naturally-infected dogs and a matched cohort of uninfected dogs. We hypothesized that selected measures of cardiac disease (abnormal rate, abnormal rhythm, and elevated cardiac troponin I (cTnI; a biomarker of cardiac injury)) would occur more commonly in infected than uninfected dogs matched by age, breed, sex and location. In addition to the clearly positive and negative dogs, we specifically tracked dogs with discordant test results across three independent serological assays to gather clinical data that might elucidate the infection status of these animals and inform the utility of the different testing approaches.

RESULTS

We placed an ambulatory ECG monitor (Holter) on 48 government working dogs and analyzed 39 successful recordings that met length and quality criteria from 17 T. cruzi-infected, 18 uninfected dogs and 4 dogs with discordant results. Overall, 76.5% of positive, 100.0% of discordant, and 11.1% of negative dogs showed > 1 ECG abnormality (p < 0.0001), and positive and discordant dogs had a higher mean number of different types of ECG abnormalities than negative dogs (p < 0.001-0.014). The most common cardiac abnormalities included supraventricular and ventricular arrhythmias and atrioventricular block. Positive dogs had higher serum concentrations of cTnI than both negative dogs (p = 0.044) and discordant dogs (p = 0.06). Based on dog handler reports, nearly all (4/5; 80%) dogs with reported performance decline or fatigue were T. cruzi-infected dogs.

CONCLUSIONS

Further understanding cardiac manifestations in dogs naturally infected with T. cruzi is critical for prognostication, establishing a baseline for drug and vaccine studies, and better understanding of zoonotic risk.

Effects of peripherally administered urotensin II and arginine vasotocin on the QT interval of the electrocardiogram in trout

The QT interval of the electrocardiogram (ECG) is a measure of the duration of the ventricular depolarization and repolarization. In fish as in human, the QT interval is positively correlated with the RR interval of the ECG, a measure of the cardiac cycle length. Urotensin II (UII) is a neuropeptide that has been highly conserved from fish to human, and UII and its receptor (UT) are expressed in cardiovascular tissues including the heart. Although UII exerts potent cardiovascular actions, its possible effects on the QT interval have never been investigated. The goal of the present study was to provide insight into the potential effect of UII on the QT interval in an established in vivo trout model. To this end, the effects of UII on dorsal aortic blood pressure (PDA), RR, QT intervals and corrected QT (QTc) for RR interval, were investigated after intra-arterial (IA) injection of 5, 50 and 100 pmol UII. The effects of UII were compared to those of two structurally UII-related peptides (URPs), URP1 and URP2, and to those of arginine vasotocin (AVT), homolog of the mammalian arginine vasopressin. IA injection of vehicle or 5 pmol UII had no effect on the various parameters. At the 50-pmol dose, UII evoked its usual increase in PDA with a peak value observed 15 min after the injection (+22% from baseline, P<0.001). This hypertensive effect of UII was accompanied by a significant increase in the RR interval (+18%, P<0.001), i.e. a bradycardia, and these effects remained constant until the end of the recording. The highest dose of UII evoked similar hypertensive and bradycardic effects. Of interest, the QT interval did not change during the bradycardic action of UII (50 and 100 pmol) but the QTc interval significantly decreased. In trout pre-treated with urantide, a peptidic antagonist of UT, the hypertensive and bradycardic actions of 50 pmol UII were reduced 3-fold and no change occurred in the QT and QTc intervals. In trout pre-treated with blockers of the autonomic nervous system, the hypertensive effect of UII was maintained but no change appeared in RR, QT and QTc intervals. IA injections of 50 pmol URPs were without action on the preceding parameters. IA administration of 50 pmol AVT provoked quite similar increase in PDA, and elevation of the RR interval to those evoked by IA injection of UII but, in contrast to UII, AVT injection induced a highly significant and sustained prolongation of the QT interval compared to baseline (+7%, P<0.001) without change in QTc. Our results are indicative of a lack of QT interval change during UII-evoked bradycardia but not after AVT-induced bradycardia and suggest for the first time that some compensatory mechanism specific for the UII peptide is working to stabilize the QT interval. Further research is needed to elucidate the mechanism involved in this action of UII. The potential for UII to prevent detrimental prolongation of cardiac ventricular repolarization might be questioned.

Use of an Implantable Loop Recorder in a Chimpanzee (Pan troglodytes) to Monitor Cardiac Arrhythmias and Assess the Effects of Acupuncture and Laser Therapy

Cardiovascular disease is a leading cause of death in captive chimpanzees and is often associated with myocardial fibrosis, which increases the risk of cardiac arrhythmias. In this case report, we present a 36-y-old male chimpanzee (Pan troglodytes) diagnosed with frequent ventricular premature complexes (VPC). We placed a subcutaneous implantable loop recorder for continual ECG monitoring to assess his arrhythmias without the confounding effects of anesthetics. During his initial treatment with the antiarrhythmia medication amiodarone, he developed thrombocytopenia, and the drug was discontinued. After reviewing other potential therapies for the treatment of cardiac arrhythmias, we elected to try acupuncture and laser therapy in view of the positive results and the lack of adverse side effects reported in humans. We used 2 well-known cardiac acupuncture sites on the wrist, PC6 (pericardium 6) and HT7 (heart 7), and evaluated the results of the therapy by using the ECG recordings from the implantable loop recorder. Although periodic increases in the animal's excitement level introduced confounding variables that caused some variation in the data, acupuncture and laser therapy appeared to decrease the mean number of VPC/min in this chimpanzee.

[Comparison of different electrocardiographic techniques for the detection of arrhythmias in horses]

OBJECTIVE

The aim of the study was to extend the range of the electrocardiographic examination in horses, evaluating the practicability of special electrocardiographic techniques (exercise- and Holter-ECG) and comparing these with more common techniques (resting-ECG) in equine medicine.

MATERIAL AND METHODS

Electrocardiographic examination (resting-ECG for 1 minute, exercise-ECG and Holter-ECG) was performed in 20 horses without any clinical or echocardiographic findings and in 80 patients with abnormal findings (valvular regurgitation and/or atrial fibrillation).

RESULTS

In comparison with the resting-ECG, the exercise-ECG demonstrated more atrial and ventricular premature beats, while the Holter-ECG had a higher detection rate of 2nd degree atrioventricular or sinuatrial blocks, and of ventricular and atrial premature depolarisations (p < 0.001). In comparison to the exercise-ECG, the Holter-ECG registered more 2nd degree atrioventricular blocks (p < 0.001) and ventricular (p < 0.001) or atrial premature contractions (p < 0.01). Atrial fibrillation was detected in every recorded ECG-type, but Holter-ECG provided additional information. Three of 16 horses with atrial fibrillation had R-on-T-episodes during Holter-monitoring. In addition to more common findings in the ECG, Holter-monitoring detected a 2nd degree atrioventricular block associated with an adjacent ventricular escape beat in a horse without any clinical or echocardiographic findings. An accelerated idioventricular rhythm was identified in a horse without any clinical or echocardiographic findings and in a horse with mitral valve insufficiency.

CONCLUSION AND CLINICAL RELEVANCE

The Holter-ECG is a useful tool in the evaluation of heart disease and could supply additional information when compared to the usual diagnostic electrocardiographic procedures used in horses. Exercise-ECG should not be replaced by Holter-ECG, however, Holter-EGC can provide additional diagnostic value.

Simultaneous pulmonary and systemic blood pressure and ECG Interval measurement in conscious, freely moving rats

Here we evaluated the ability of a new, dual blood-pressure telemetry transmitter to simultaneously measure pulmonary and systemic blood pressure and the electrocardiogram in rats. The transmitter was implanted in normotensive and monocrotaline-induced pulmonary hypertensive Wistar rats, with sensing catheters placed in the pulmonary artery (channel 1) and descending aorta (channel 2). Biopotential electrodes were positioned to record an apex-based lead II electrocardiogram. Pulmonary and systemic arterial blood pressure and electrocardiographic waveforms were recorded between 2 and 12 wk after implantation of the transmitter. During this period, pulmonary arterial pressure progressively increased in monocrotaline-treated compared with saline-treated rats. The pharmacologic response of rats to reference compounds was measured by using the transmitter to validate the technique and to evaluate the ability of the device to transmit changes in blood pressure and the electrocardiogram. Validation against 2 Millar high-fidelity blood-pressure catheters confirmed the accuracy of the blood pressure data recorded with the transmitter. In addition, local tolerance of the associated catheters was confirmed by histologic examination.

[Holter monitoring of primates]

Validation of the Holter harness developed for cardiac monitoring of caged rhesus-macaques attested to usability of the technique for studying the cardiac rhythm variability in primates.

"Zone of avoidance": RR interval distribution in tachograms, histograms, and Poincaré plots of a Boxer dog

The RR intervals of sinus and ventricular beats were determined by analysis of a 24-h ambulatory electrocardiogram in a Boxer before and after treatment with sotalol. These RR intervals were plotted using tachograms, histograms, and Poincaré plots. The tachogram demonstrated a 'band' wherein a range of RR intervals was infrequent, the histogram did not take the form of a single Gaussian distribution of RR intervals, and the Poincaré plot showed nonhomogeneous beat-to-beat variability. This type of patterning was described as a "zone of avoidance" potentially caused by the clustering of beats within specific ranges. Treatment with sotalol enhanced the "zone of avoidance". Further investigation is needed to understand the mechanism for this observation as well as any clinical implications.

Endurance exercise is associated with increased plasma cardiac troponin I in horses

REASON FOR PERFORMING STUDY

Information is lacking regarding the influence of long distance exercise on the systemic concentration of cardiac troponin I (cTnI) in horses.

OBJECTIVES

To determine if the concentration of cTnI in horses competing in 80 and 160 km endurance races increases with exercise duration and if cTnI concentrations can be correlated with performance data.

METHODS

Blood samples for the measurement of cTnI and 3 min electrocardiogram recordings were obtained from horses prior to, during and after completion of 80 and 160 km endurance races at 3 ride sites during the 2004 and 2005 American Endurance Ride Conference competition seasons.

RESULTS

Full data sets were obtained from 100 of the 118 horses. Endurance exercise was associated with a significant increase in cTnI over baseline in both distance groups. Failure to finish competition (poor performance) was also associated with an increased cTnI concentration over baseline at the time of elimination when data from both distances were combined. Other than one horse that developed paroxysmal atrial fibrillation, no arrhythmias were noted on the 3 minute ECG recordings that were obtained after endurance exercise in either distance group.

CONCLUSIONS

Systemic concentrations of cTnI increase in endurance horses competing in both 80 and 160 km distances. Although final cTnI concentrations were significantly increased over their baseline values in horses that failed to finish competition, the degree of increase was not greater than the increase over baseline seen in the horses that successfully completed competition. The clinical significance of increased cTnI in exercising horses could not be ascertained from the results of this study.

POTENTIAL RELEVANCE

These data indicate that cardiac stress may occur in horses associated with endurance exercise. Future studies utilising echocardiograpy to assess cardiac function in horses with increased cTnI are warranted.

Influence of antiarrhythmia therapy on survival times of 19 clinically healthy Doberman pinschers with dilated cardiomyopathy that experienced syncope, ventricular tachycardia, and sudden death (1985-1998)

Overtly healthy Doberman pinschers, having moderate to severe myocardial failure secondary to dilated cardiomyopathy, which experienced ventricular tachycardia, syncope or collapse, and sudden death were studied to determine the effect of antiarrhythmic medication on their clinical outcome. Antiarrhythmia drug therapy may have retarded sudden death in 13 treated dogs compared to the six dogs not administered antiarrhythmia drugs.

Atrial myocarditis as a cause of sinus arrest in a dog

A 10-year-old male cairn terrier cross was presented with a history of myxomatous mitral valve disease diagnosed six months previously and with a four-week history of intermittent collapse. On 24 hour electrocardiograph (Holter) analysis, periods of no discernable electrical cardiac activity, which coincided with three collapsing episodes, were identified. Unfortunately, on re-presentation for removal of the Holter monitor, the dog collapsed and died. A post-mortem examination was conducted, and histology of the right and left atrium showed evidence of myocarditis. This is the first reported case, to our knowledge, of collapse because of electrical asystole in a dog with atrial myocarditis.

Prevalence of perioperative arrhythmias in 50 young, healthy dogs

The objective of this study was to assess the type and frequency of cardiac dysrhythmias occurring after routine ovariohysterectomy or orchidectomy in young, healthy dogs by using 2 anesthetic protocols (group I: propofol and isoflurane; group II: thiopental and halothane). Fifty dogs under 2 years of age, judged to be clinically normal by physical examination and standard electrocardiography, were evaluated by using 24-hour ambulatory electrocardiography. The most common dysrhythmias in the postoperative period were 2nd degree atrioventricular block (44%), ventricular premature complexes (44%), and atrial premature complexes (32%). For study purposes, more than 100 ventricular or atrial premature complexes per 24 hours, or any occurrence of R-on-T phenomenon, ventricular or atrial tachycardia were classified as clinically significant arrhythmias. Significant arrhythmias were observed in 9 dogs in the postoperative period, 5 of which were in group I and 4 in group II. All of these dogs were under 1 year of age. The R-on-T phenomenon occurred in 4 dogs in group II and 1 dog in group I. Results from this study show that significant arrhythmias, including R-on-T phenomenon, can occur in the perioperative period in young, healthy dogs undergoing routine surgeries with both protocols used.

Practical application of holter monitoring in dogs and cats

Holter monitoring is a valuable noninvasive tool for the monitoring of the cardiac rhythm over a prolonged period during normal daily activities. The advent of this diagnostic test has demonstrated that the incidence of serious arrhythmias is much greater than previously determined using routine electrocardiography. A resting electrocardiogram is typically recorded for several seconds to several minutes and is likely to miss or underestimate the underlying arrhythmia. This article will present the clinical indications, equipment, technical application, and assessment of holter monitoring.

Clinical, echocardiographic, and electrocardiographic abnormalities in Boxers with cardiomyopathy and left ventricular systolic dysfunction: 48 cases (1985-2003)

OBJECTIVE

To identify clinical, echocardiographic, and electrocardiographic abnormalities in Boxers with cardiomyopathy and echocardiographic evidence of left ventricular systolic dysfunction.

DESIGN

Retrospective study.

ANIMALS

48 mature Boxers.

PROCEDURE

Medical records were reviewed for information on age; sex; physical examination findings; and results of electrocardiography, 24-hour ambulatory electrocardiography, thoracic radiography, and echocardiography.

RESULTS

Mean age of the dogs was 6 years (range, 1 to 11 years). Twenty (42%) dogs had a systolic murmur, and 9 (19%) had ascites. Congestive heart failure was diagnosed in 24 (50%) dogs. Seventeen (35%) dogs had a history of syncope. Mean fractional shortening was 14.4% (range, 1% to 23%). Mean left ventricular systolic and diastolic diameters were 4.5 cm (range, 3 to 6.3 cm) and 5.3 cm (range, 3.9 to 7.4 cm), respectively. Twenty-eight (58%) dogs had a sinus rhythm with ventricular premature complexes (VPCs), and 20 had supraventricular arrhythmias (15 with atrial fibrillation and 5 with sinus rhythm and atrial premature complexes). Sixteen of the dogs with supraventricular arrhythmias also had occasional VPCs. Morphology of the VPCs seen on lead II ECGs was consistent with left bundle branch block in 25 dogs, right bundle branch block in 8, and both in 11.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that Boxers with cardiomyopathy and left ventricular dysfunction frequently have arrhythmias of supraventricular or ventricular origin. Whether ventricular dysfunction was preceded by electrical disturbances could not be determined from these data, and the natural history of myocardial disease in Boxers requires further study.

Results of 24-hour ambulatory electrocardiography in dogs undergoing ovariohysterectomy following premedication with medetomidine or acepromazine

OBJECTIVE

To investigate heart rate characteristics in dogs undergoing ovariohysterectomy following premedication with medetomidine or acepromazine.

DESIGN

Clinical trial.

ANIMALS

43 client-owned dogs.

PROCEDURE

24-hour ambulatory electrocardiography was performed beginning approximately 1 hour prior to administration of premedications. Dogs were premedicated with medetomidine and butorphanol (n = 21) or acepromazine and butorphanol (22) and, approximately 85 minutes later, were anesthetized with propofol and isoflurane. Electrocardiographic recordings were examined to determine heart rate, cardiac conduction disturbances (ventricular premature complexes and atrioventricular block), and indices of heart rate variability (HRV).

RESULTS

Minimum heart rate during the 24-hour recording period was significantly lower among dogs given medetomidine than among dogs given acepromazine, but during the postoperative period, heart rate increased in all dogs as they became physically active. Intraoperative time domain HRV indices were lower and the low frequency-to-high frequency ratio was higher among dogs given acepromazine than among dogs given medetomidine; however, significant differences between groups were no longer seen by 6 hours after surgery. There was no significant difference between groups with regard to the number of ventricular premature complexes or to values of scaling exponent alpha2 (a nonlinear measure of HRV).

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that there are greater enhancements in vagally related heart rate indices in medetomidine-treated dogs that may persist until 6 hours after surgery. Despite the low heart rates, dogs given medetomidine showed expected responses to surgery and positional stimuli, and the 2 preanesthetic protocols may not result in different prevalences of ventricular premature complexes.

Incidence of post-anaesthetic arrhythmias in dogs

OBJECTIVES

To assess the use of Holter monitoring for evaluating the incidence of post-anaesthetic cardiac arrhythmias and associated anaesthetic risk for two different anaesthetic protocols.

METHODS

Patients undergoing orthopaedic surgery were randomly divided into two groups with different anaesthetic regimens (group A, isoflurane n = 30; group B, propofol n = 30). Two 24-hour Holter recordings were performed for each patient: the first directly following anaesthesia and the second, as a comparison, on the fifth postoperative day.

RESULTS

Although all dogs were healthy on pre-anaesthetic cardiac evaluation, 56 dogs showed arrhythmias in the two 24-hour (Holter) electrocardiograms performed. However, the number of arrhythmias recorded was low in most cases (less than 10 supraventricular extrasystoles and less than 100 ventricular extrasystoles). One patient in group A showed 94 supraventricular extrasystoles during the second monitoring period. Three patients in each group developed more than 100 ventricular extrasystoles during both Holter recordings. There were no statistically significant differences between the two anaesthetic regimens or between the two recordings in both groups.

CLINICAL SIGNIFICANCE

The two anaesthetic protocols investigated in this study did not induce an increased incidence of severe arrhythmias in healthy dogs in the post-anaesthetic phase.

Use of signal-averaged electrocardiography in the evaluation of arrhythmogenic right ventricular cardiomyopathy in Boxers

OBJECTIVE

To assess signal-averaged electrocardiography (SAECG) for evaluation of Boxers with arrhythmogenic right ventricular cardiomyopathy (ARVC) and identify dogs at risk for sudden death (SD) or death related to congestive heart failure (CHF).

DESIGN

Prospective study.

ANIMALS

94 Boxers with ARVC and 49 clinically normal non-Boxers (controls).

PROCEDURE

Boxers were screened for ARVC, and severity was estimated by use of echocardiography, 24-hour ambulatory ECG, and SAECG. Statistical evaluation was performed to identify significant differences in SAECG variables relative to clinical outcome, frequency of ventricular arrhythmias, and systolic function. Sensitivity, specificity, and positive and negative predictive values were evaluated for each SAECG variable for occurrence of SD or death related to CHF. Late potentials were also evaluated as a predictor of cardiac-related death.

RESULTS

Differences were detected in SAECG variables on the basis of clinical outcome, systolic function, and frequency of ventricular arrhythmias. More severely affected dogs had significantly more abnormal SAECG findings. The presence of late potentials, defined as 2 abnormal root mean square values (of 4), was associated with high sensitivity, specificity, and negative predictive value for cardiac-related SD or death secondary to CHF CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that SAECG is a useful noninvasive diagnostic test to evaluate dogs affected with ARVC and identify individuals at risk for cardiac-related death.

Assessment of heart rate variability in Boxers with arrhythmogenic right ventricular cardiomyopathy

OBJECTIVE

To assess heart rate variability (HRV) in Boxers with arrhythmogenic right ventricular cardiomyopathy (ARVC), assess the ability of HRV analysis to identify differences in Boxers on the basis of severity of their arrhythmia, and evaluate the use of HRV to determine whether persistently high sympathetic tone is present in these dogs.

DESIGN

Prospective study.

ANIMALS

24 Boxers with ARVC and 10 clinically normal non-Boxer dogs.

PROCEDURE

Boxers were categorized as dogs with congestive heart failure (CHF), dogs with < or = 2 ventricular premature complexes (VPCs)/24 h (designated unaffected), or dogs with > 1,000 VPCs/24 h (designated affected). Ambulatory electrocardiography (24 hours) was performed in each dog. Recordings were analyzed for HRV variables at a commercial laboratory; differences in HRV variables among groups were compared with 1-way ANOVA.

RESULTS

Compared with control non-Boxer dogs and Boxers without CHF (affected and unaffected Boxers), HRV was reduced in Boxers with CHF. No differences in HRV variables were detected between affected and unaffected Boxers. Inconsistent differences were identified between the control dogs and Boxers without CHF that had various degrees of arrhythmias.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that persistently high sympathetic tone is not a consistent feature of ARVC. Differences in some HRV variables between Boxers without CHF and control dogs suggest that Boxers may have different autonomic control of heart rate, compared with that of clinically normal non-Boxer dogs. The usefulness of HRV analysis appears limited to Boxers with ARVC that have systolic dysfunction and CHF.

Evaluation of spontaneous variability in the frequency of ventricular arrhythmias in Boxers with arrhythmogenic right ventricular cardiomyopathy

OBJECTIVE

To evaluate spontaneous variability in the frequency of ventricular arrhythmias and assess the influence of day of ECG recording and day of week on arrhythmia frequency in Boxers affected with arrhythmogenic right ventricular cardiomyopathy (ARVC).

DESIGN

Prospective study.

ANIMALS

10 Boxers with ARVC with prior ambulatory ECG recordings that included > or = 500 ventricular premature complexes/24 h.

PROCEDURE

Consecutive 24-hour ambulatory ECG recordings were obtained during a 7-day period in each dog. The number of ventricular premature complexes and grade of the arrhythmia were obtained from each recording. For each dog, the number of ventricular premature complexes for each recording was evaluated to identify any differences relative to the day of recording (recording 1 to 7) and day of the week (Monday through Sunday).

RESULTS

Spontaneous variability accounted for as much as 80% of the change in frequency of ventricular premature complexes in dogs with frequent arrhythmias; this value was almost 100% in dogs with less frequent arrhythmias. Grade of arrhythmia was less variable but was also inversely related to frequency of arrhythmia. No significant differences in frequency values were identified among days of recording or among days of the week.

CONCLUSIONS AND CLINICAL RELEVANCE

Changes of < or = 80% in the frequency of ventricular arrhythmias may be within the limit of spontaneous variability in dogs with ARVC. This degree of variability should be considered in evaluations of ambulatory ECG recordings, particularly in the assessment of the efficacy of antiarrhythmic drugs.

The relationship of resting S-T segment depression to the severity of subvalvular aortic stenosis and the presence of ventricular premature complexes in the dog

Electrocardiograms (ECG) from 35 dogs with subvalvular aortic stenosis (SAS) with a left ventricular outflow tract pressure gradient (PG) of > or =50 mm Hg were retrospectively evaluated for S-T segment depression (STD, > or =0.2 mV in lead II). Pressure gradient, age, heart rate (HR), and number of ventricular premature complexes (VPCs) on a 24-hour ambulatory ECG for dogs with STD were not significantly different from those for dogs without STD. The S-T segment deviation did not correlate significantly with PG, age, HR, or VPCs. The significance of STD in the dog with SAS remains uncertain. Long-term prospective studies are needed to fully understand this observation.

Validation of a cardiac monitor for measuring heart rate variability in adult female pigs: accuracy, artefacts and editing

Autonomic regulation of cardiac activity during stress has not been clearly defined in farm animals. In part, this is due to the limited availability of affordable ambulatory cardiac monitors capable of accurately monitoring and storing large amounts of data that meet the criteria necessary for heart rate variability analysis. Our objectives were to measure the accuracy of a 24-h Polar RR monitor using gold standard ECG, to examine and categorise any occurring anomalies and to ascertain their impact on the outcome of heart rate variability analysis. Five 1-year-old female pigs (gilts) were socially isolated from their pen mates and cardiac activity was simultaneously measured using two systems, a 24-h Polar RR Recorder and a Telemetric ECG system. The Polar data were manually assessed both against and in isolation of the ECG data to identify anomalous beats, which were then assigned to one of five identified error categories. The anomalies in the Polar data were corrected and statistical comparisons were performed among the three data sets to evaluate the effects of anomalies on heart rate variability analysis. Bland-Altman analysis was used to measure the level of agreement among the ECG, Uncorrected Polar and Corrected Polar data. No anomalies or ectopies were found in the ECG data but 46 anomalies (0.81% of total interbeat intervals [IBI]) were found in the Polar Uncorrected data. Manual identification and editing procedures reduced this error to 0.018%. Most mean heart rate and IBI parameters were unaffected by error (P>.05). Standard deviation (S.D.) and root mean square of successive differences (RMSSD) were 45% and 50% higher when anomalies were present in the data. Artefacts affected the magnitude of the frequency domain indices and overestimated total and parasympathetic activity and underestimated sympathetic activity. The mean difference between ECG and Uncorrected Polar data was 1.36 ms (limits of agreement -69.03 to 71.74 ms). This was greatly improved to 0.36 ms (limits of agreement -5.37 to 6.10 ms) after editing. Overall, even a small proportion of error biased the outcome of heart rate variability analysis. This bias was greatly reduced by correcting the anomalous beats. Bland-Altman analysis demonstrated that when there was error present in the Polar data, it could not be used interchangeably with the ECG data. However, if there were no anomalies present in the data or if they were classified and corrected using the approach in this study, then the two systems could be used interchangeably.

[Comparison of the influence of different anesthetic protocols in the development of post-anesthetic arrhythmia in the dog]

Post-anesthetic holter monitoring was performed in 2 patient groups in order to compare the incidence of cardiac arrhythmias as a result of different anesthetic protocols. The 2 groups differed in their anesthetic protocol. Both groups received levomethadone as pre-anesthetic. The dogs in group A (n = 30) additionally received diazepam, the dogs in group B (n = 30) received propofol instead. Anesthesia was maintained by isoflurane in group A and a propofol constant rate infusion in group B. In each patient 2 holter monitorings were performed. The first recording began directly after anesthesia. As a comparison a second recording was performed on the 5th post-operative day. The recorded number of arrhythmias was low and no statistical difference was demonstrated between the 2 patient groups.

Assessment of an ECG event recorder in healthy dogs in a hospital environment

Ambulatory electrocardiography techniques are superior to standard electrocardiography in evaluating rhythm disturbances in dogs with episodic weakness or collapse. Disadvantages include cumbersome equipment, short recording periods and an inherent delay in trace analysis. A small programmable cardiac event recorder with combined automatic and owner-triggered recording capability was evaluated in 13 healthy dogs in a hospital environment. The unit was well tolerated and produced diagnostic recordings directly to a personal computer, with useful information about continuous heart rate. It detects premature complexes, pauses and bradycardias according to programmed detection thresholds. These events were counted frequently but trace review revealed concerns regarding specificity. Recordings were often triggered by sinus arrhythmia, sinus tachycardia and unclassifiable rate changes rather than by clinically significant arrhythmias. Correct detection of ventricular ectopic complexes, a single supraventricular premature complex, sinus arrest and second-degree atrioventricular block occurred in individual dogs. Visual review of all automatically recorded events was essential and significantly increased the time required for event recording analysis. Manual recordings might be more useful and the overall results suggest that further studies are warranted to evaluate the system in clinical cases in the home environment.

Effects of initial handling and training on autonomic nervous function in young Thoroughbreds

OBJECTIVE

To determine the effects of initial handling and training on autonomic nervous functions in young Thoroughbreds.

ANIMALS

63 healthy Thoroughbreds.

PROCEDURE

All horses were trained to be handled and initially ridden in September of the yearling year and then trained until the following April by conventional training regimens. To obtain the heart rate (HR), electrocardiograms were recorded in the stable before initial handling and training and following 7 months of training; variations in HR were then evaluated from the power spectrum in terms of the low frequency (LF; 0.01 to 0.07 Hz) power and high frequency (HF; 0.07 to 0.6 Hz) power as indices of autonomic nervous activity. To evaluate the fitness, the V200 (velocity at HR of 200 beat/min), which is reflective of the aerobic capacity of the horse, was measured.

RESULTS

Mean (+/- SE) resting HR decreased significantly from 41.5 +/- 0.8 to 38.7 +/- 0.4 beat/min following 7 months of training. The LF power of horses increased significantly from 1,037 +/- 128 milliseconds2 in September of the yearling year to 2,944 +/- 223 milliseconds2 in the following April. Similarly, the HF power increased significantly from 326 +/- 30 milliseconds2 to 576 +/- 39 milliseconds2 at the corresponding time points. The V200 increased significantly following training.

CONCLUSIONS AND CLINICAL RELEVANCE

Increases in LF and HF powers indicate that parasympathetic nervous activity increases in horses by 7 months of training. The decrease in resting HR may be dependent on the training-induced increase of parasympathetic nervous activity in Thoroughbreds.

Syncope associated with paroxysmal atrioventricular block an ventricular standstill in a cat

A four-and-a-half-year-old neutered male shorthair cat was presented with a three-week history of episodic fainting. Twenty-four hour electrocardiographic (Holter) recording revealed frequent prolonged episodes of complete atrioventricular (AV) block with ventricular standstill. The fainting episodes coincided with the longest periods of ventricular inactivity. A permanent transjugular pacemaker was placed to prevent further life-threatening episodes of syncope. Three months after discharge, the patient was re-presented with sudden onset dyspnoea associated with chylothorax and electrocardiography showed a third degree (complete) AV block. The pacemaker was reprogrammed in view of the third degree AV block and the chylous effusion was successfully treated by repeated thoracocentesis and long-term diuresis. However, the patient's general condition deteriorated progressively and the cat was euthanased five and a half months after implantation of the pacemaker.

Correlations among time and frequency measures of heart rate variability recorded by use of a Holter monitor in overtly healthy Doberman pinschers with and without echocardiographic evidence of dilated cardiomyopathy

OBJECTIVE

To determine correlations between time-domain and frequency-domain variables of heart rate variability (HRV) derived from 24-hour recordings obtained by use of an ambulatory electrocardiographic recorder (Holter monitor).

ANIMALS

59 overtly healthy Doberman Pinschers (41 without echocardiographic evidence of cardiomyopathy and 18 with precongestive heart failure attributable to cardiomyopathy).

PROCEDURE

The HRV was analyzed from 24-hour recordings. Variables were calculated from the entire 24-hour recording as well as 4 user-selected time epochs. Comparisons were made for total power to SD of normal beat-to-normal-beat (NN) intervals (SDNN), ultra-low frequency power to SD of the means of NN intervals, low-frequency power and very-low-frequency power to mean of the SD of NN intervals, and high-frequency (HF) power to the root mean square successive difference of NN intervals (RMSSD) and percentage of NN intervals that varied from the previous NN interval by > 50 milliseconds (PNN50).

RESULTS

58 of 66 (88%) comparisons revealed significant values, indicating that relationships between variables were not random (r > 0.7 in 41 of 66 [62%)) comparisons). Strong correlations (r > 0.8) were found between the square root of total power and SDNN and between HF power and RMSSD.

CONCLUSIONS AND CLINICAL RELEVANCE

Time-domain surrogates for variables of frequency-domain analysis variables that correlated in the dogs reported here are the same ones that reportedly correlate in humans. When 24-hour recordings obtained by use of a Holter monitor are used to calculate HRV, SDNN and total power as well as RMSSD and HF power are interchangeable.

Effect of severity of myocardial failure on heart rate variability in Doberman pinschers with and without echocardiographic evidence of dilated cardiomyopathy

OBJECTIVE

To determine whether heart rate variability (HRV) is reduced in Doberman Pinschers with dilated cardiomyopathy.

DESIGN

Case series.

ANIMALS

62 overtly healthy Doberman pinschers.

PROCEDURE

Heart rate variability was analyzed in time and frequency domains from data obtained during 24-hour ambulatory electrocardiographic Holter recordings in 41 overtly healthy Doberman pinschers with normal echocardiograms and 21 overtly healthy Doberman pinschers with abnormal echocardiograms.

RESULTS

Heart rate variability usually was greater during night versus day, and 2 dogs with the most severe myocardial failure had reduced HRV.

CONCLUSIONS AND CLINICAL RELEVANCE

Reduced HRV was detected only in Doberman Pinschers with the most severe myocardial failure. Thus, HRV in less severely affected dogs is not reduced, or the normal sinus arrhythmia of dogs renders HRV relatively insensitive. Analysis of HRV did not provide additional information relative to the severity of left ventricular dysfunction or risk of sudden death from that which could be derived from echocardiography, analysis of Holter recordings, and signal-averaged electrocardiography.

Results of ambulatory electrocardiography in overtly healthy Doberman Pinschers with equivocal echocardiographic evidence of dilated cardiomyopathy

OBJECTIVE

To determine results of ambulatory electrocardiography in and outcome of overtly healthy Doberman Pinschers with equivocal echocardiographic evidence of dilated cardiomyopathy.

DESIGN

Case series.

ANIMALS

44 overtly healthy (25 male, 19 female) Doberman Pinschers.

PROCEDURE

24-hour ambulatory electrocardiographic (Holter) recordings with > 90% scan quality obtained the same day that echocardiography was performed were reviewed.

RESULTS

Holter recordings from 42 of 44 (95%) dogs contained ventricular premature complexes (VPC). Fifteen of 44 (34%) dogs had > 100 VPC, 9 (20%) had > 500 VPC, and 5 (11%) had > 1,000 VPC. Nonsustained (< 30 seconds) ventricular tachycardia was detected in 4 dogs. Eighteen of 27 (67%) dogs with > 100 VPC, any couplets or triplets of VPC, or ventricular tachycardia developed dilated cardiomyopathy within 1 year, compared with 8 of 17 (47%) dogs with < 100 VPC, no couplets or triplets of VPC, and no ventricular tachycardia. Of the 18 dogs that did not develop dilated cardiomyopathy within 1 year, 11 (61%) did so within 3 years.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that a high percentage of Doberman Pinschers with equivocal echocardiographic evidence of dilated cardiomyopathy will be found to have VPC during 24-hour ambulatory electrocardiography and that most will develop echocardiographic abnormalities indicative of cardiomyopathy.

Correlation of QT dispersion with indices used to evaluate the severity of familial ventricular arrhythmias in Boxers

OBJECTIVE

To measure QT interval duration and QT dispersion in Boxers and to determine whether QT variables correlate with indices of disease severity in Boxers with familial ventricular arrhythmias, including the number of ventricular premature complexes per day, arrhythmia grade, and fractional shortening.

ANIMALS

25 Boxers were evaluated by ECG and echocardiography.

PROCEDURE

The QT interval duration was measured from 12-lead ECG and corrected for heart rate (QTc), using Fridericia's formula. The QT and QTc were calculated for each lead, from which QT and QTc dispersion were determined. Echocardiography and 24-hour ambulatory ECG were performed to evaluate for familial ventricular arrhythmias. Total number of ventricular premature complexes, arrhythmia grade, and fractional shortening were determined and used as indices of disease severity.

RESULTS

There was no correlation between any QT variable and total number of ventricular premature complexes, arrhythmia grade, or fractional shortening. No difference between QT dispersion and QTc dispersion was identified, and correction for heart rate did not affect the results.

CONCLUSIONS AND CLINICAL RELEVANCE

QT interval duration and dispersion did not correlate with indices of disease severity for familial ventricular arrhythmias. Heart rate correction of the QT interval did not appear to be necessary for QT dispersion calculation in this group of dogs. QT dispersion does not appear to be a useful noninvasive diagnostic tool in the evaluation of familial ventricular arrhythmias of Boxers. Identification of affected individuals at risk for sudden death remains a challenge in the management of this disease.

Use of ambulatory electrocardiography for detection of ventricular premature complexes in healthy dogs

OBJECTIVE

To evaluate the use of 24-hour ambulatory electrocardiography (AECG) for the detection of ventricular premature complexes (VPC) in healthy dogs.

DESIGN

Case series.

ANIMALS

50 healthy mature dogs.

PROCEDURE

A 24-hour AECG was performed on each dog and evaluated for the presence of VPC.

RESULTS

Fifty dogs weighing between 18.2 to 40.9 kg (40 and 90 lb) representing 13 breeds were evaluated; there were 4 sexually intact females, 21 spayed females, 4 sexually intact males, and 21 castrated males. Ages ranged from 1 to 12 years. Thirty-four dogs had no VPC; 16 dogs had between 1 and 24 VPC. The grade of arrhythmia ranged from 1 to 4, with 4 dogs having an arrhythmia with a grade > 1. Significant differences were not detected between the group of dogs with VPC and those without VPC with regard to sex, age, and minimum, maximum, or mean heart rate.

CONCLUSIONS AND CLINICAL RELEVANCE

We conclude that healthy mature dogs have infrequent VPC, as detected by use of 24-hour AECG. The presence of numerous or sequential VPC may be suggestive of cardiac or systemic disease and may indicate the need for thorough clinical evaluation.

Comparison of in-hospital versus 24-hour ambulatory electrocardiography for detection of ventricular premature complexes in mature Boxers

OBJECTIVE

To evaluate the use of in-hospital electrocardiography (ECG) for detection of ventricular premature complexes (VPC), compared with 24-hour ambulatory ECG.

DESIGN

Original study.

ANIMALS

188 Boxers > 9 months old; 31 had a history of syncope, and 157 were healthy (no history of syncope).

PROCEDURE

In-hospital ECG was performed on all Boxers for at least 2 minutes. Within 7 days after the in-hospital ECG was completed, 24-hour ambulatory ECG was performed.

RESULTS

The specificity of in-hospital ECG was 100% for the detection of at least 50 VPC in a 24-hour period in dogs with syncope and 93% in healthy dogs. In-hospital ECG had poor sensitivity, although sensitivity increased as the number of VPC per 24 hours increased.

CONCLUSIONS AND CLINICAL RELEVANCE

Use of in-hospital ECG is highly specific for detection of at least 50 VPC during a 24-hour period. However, in-hospital ECG is insensitive, and a lack of VPC does not suggest that the dog does not have a substantial number of VPC during that same period. The use of in-hospital ECG appears to be inadequate for screening purposes and therapeutic evaluations in mature Boxers with ventricular arrhythmic disease.

Electrocardiographic findings in dogs with motor vehicle-related trauma

Motor vehicle-related injury is the most common form of trauma incurred by dogs, and cardiac arrhythmias are a well-recognized complication. Although posttraumatic arrhythmias are often observed, little is known regarding their frequency. This study utilized continuous ambulatory electrocardiography (i.e., Holter monitoring) to describe the cardiac rhythm disturbances in 30 dogs sustaining trauma in motor vehicle accidents. Ventricular ectopy was identified by Holter monitoring in 29 of 30 dogs, although the initial electrocardiogram (EKG) only documented ventricular ectopic complexes (VECs) in four dogs. Ventricular ectopy was infrequent in most dogs (i.e., 62% of the dogs had less than 100 VECs per day for the entire study), but 16% developed frequent arrhythmias (greater than 4,000 VECs per day). In all cases, the VECs were observed within 24 hours of injury. Forty-three percent of dogs had at least one episode of ventricular tachycardia, including several dogs that had an overall infrequent rate of VECs (i.e., less than 100 or 100 to 1,000 VECs per day). Although baseline EKGs are useful in identifying arrhythmias in most dogs, the length of the recording should be increased to improve the likelihood of observing an abnormal EKG event. Most importantly, additional EKGs should be obtained or continuous EKG monitoring should be performed in dogs that display clinical signs that could be attributed to ventricular arrhythmias.

Spectral analysis of circadian rhythms in heart rate variability of dogs

OBJECTIVE

To determine characteristics of power spectral analysis of heart rate variability (HRV) during a 24-hour period in dogs and to evaluate the effects of vagal and sympathetic tone on HRV ANIMALS: 16 healthy adult Beagles.

PROCEDURE

Power spectral analysis of HRV was conducted, using 24-hour ambulatory ECG recordings. Circadian rhythms were evaluated in terms of absolute units of low-frequency (LF) and high-frequency (HF) powers, their ratio (LF:HF), and their adjusted (normalized) units (LF[norm] and HF[norm]). Three or 4 dogs were used for simultaneous measurement of heart rate and respiratory waveform as well as to evaluate treatment (propranolol, atropine, or both) administered to cause blockade of the autonomic nervous system.

RESULTS

Values for LF and HF powers, LF:HF, LF(norm), and HF(norm) had obvious rhythmicity in clinically normal dogs. The HF power of HRV in dogs was extremely high, compared with that of other species, and HF peaks corresponded to peaks obtained from respiratory waveforms. Blockade of the autonomic nervous system documented that HRV in dogs was mostly attributable to vagal activity.

CONCLUSION AND CLINICAL RELEVANCE

We determined characteristics of power spectral analysis of HRV in dogs, including circadian rhythm of the autonomic nervous system. Power spectral analysis of HRV may provide a useful noninvasive technique for assessing the effect of drugs on activity of the autonomic nervous system in dogs.

Results of ambulatory electrocardiography in overtly healthy Doberman Pinschers with echocardiographic abnormalities

OBJECTIVE

To identify, by means of 24-hour ambulatory electrocardiography, electrocardiographic abnormalities in overtly healthy Doberman Pinschers in which results of echocardiography were abnormal.

DESIGN

Clinical case series.

ANIMALS

56 (35 male, 21 female) overtly healthy Doberman Pinschers with echocardiographic evidence of cardiomyopathy on initial examination that subsequently died of cardiomyopathy.

PROCEDURE

Twenty-four-hour ambulatory electrocardiographic (Holter) recordings obtained at the time of initial examination were reviewed. For all dogs, scan quality was > 90%.

RESULTS

Initial Holter recordings of all 56 dogs contained ventricular premature contractions (VPC). Thirty-six (65%) dogs had > 1,000 VPC/24 h, 17 (31%) had > 5,000 VPC/24 h, and 11 (19%) had > 10,000 VPC/24 h. Fifty-four (96%) dogs had couplets of VPC, 37 (66%) had triplets of VPC, and 36 (64%) had episodes of nonsustained (< 30 seconds) ventricular tachycardia. Number of VPC/24 h during the initial Holter recordings was positively correlated with numbers of couplets and triplets of VPC and number of ventricular escape beats and negatively correlated with left ventricular fractional shortening. Twenty-eight dogs died suddenly prior to the putative onset of congestive heart failure.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that along with echocardiography, 24-hour ambulatory electrocardiography can be used to help identify overtly healthy Doberman Pinschers with cardiomyopathy.

Heart rate variability in Doberman Pinschers with and without echocardiographic evidence of dilated cardiomyopathy

OBJECTIVE

To characterize the salient variables of the time-domain analysis of heart rate variability (HRV) in clinically normal Doberman Pinschers and to compare those variables with those of Doberman Pinschers with cardiomyopathy and mild to moderate myocardial failure.

ANIMALS

46 Doberman Pinschers.

PROCEDURE

HRV was analyzed in the time-domain from 24-hour Holter recordings obtained from 28 Doberman Pinschers with normal echocardiograms and 18 Doberman Pinschers with echocardiograms consistent with mild to moderate myocardial failure.

RESULTS

Significant differences in HRV variables between the 2 groups of dogs were not detected. The HRV was greater during the nighttime (12 AM to 6 AM), compared with the 24-hour day and an 18-hour (6 AM to 12 AM) period.

CONCLUSIONS AND CLINICAL RELEVANCE

HRV of dogs with mild to moderate myocardial failure was not different from that of clinically normal dogs, because there were no disturbances of autonomic balance, baroreceptor function, and other factors that influence HRV in the dogs with cardiomyopathy, or the sensitivity of time-domain analysis was overwhelmed by normal sinus arrhythmia. The techniques now used to study HRV have important limitations, especially in dogs, and better noninvasive tests of autonomic function are needed.

D0870, an antifungal agent, induces reverse use-dependent QT prolongation in dogs

We previously reported that D0870 induced QT prolongation and sudden death due to torsades de pointes (TdP) in dogs and that catecholamines played an important part in the development of the sudden death. In the present study, we analyzed in detail the ambulatory electrocardiographic recordings obtained from the just-mentioned study to elucidate the mechanism of the onset of TdPs and conducted an in vitro study using isolated canine Purkinje fibers to assess the effect of D0870 on repolarization. The hearts with TdPs observed before the sudden death showed a higher sinus rate for 5 and 10 sec before the onset, a shorter coupling interval, and a higher ventricular tachycardia rate compared with those having the non-sustained TdPs. These findings suggest that D0870-induced fatal TdPs may be provoked by a triggered activity developed from delayed after depolarizations. In contrast, as the pause-dependent, non-sustained TdPs in bradycardia showed a typical "short-long-short" sequence, they may be developed from early afterdepolarization . Moreover, the results of the in vitro study supported our contention that D0870 induced QT prolongation in a reverse use-dependent manner in vivo and suggested that it may inhibit not only rapidly activating delayed rectifier potassium current (Ik(r)) but also L-type Ca current (I(ca-L)).

Effects of a canine Elizabethan collar on ambulatory electrocardiogram recorded by a Holter recording system and spontaneous activities measured continuously by an accelerometer in Beagle dogs

Ambulatory electrocardiogram (ECG) has been recorded in dogs wearing a jacket to protect a Holter recording system, but the jacket was often damaged by dogs. We compared ECG recorded by a Holter recording system and spontaneous activity measured by an accelerometer in Beagle dogs with or without an Elizabethan collar. There were few significant differences in mean values (per hr) of the heart rate and the amount of spontaneous activity between dogs with or without the Elizabethan collar. Mean values (per 23 hr) of them had no significant difference between them. We concluded that the Elizabethan collar did not have any effect on ambulatory ECG and canine movements and was effective to protect the recording apparatus.

Association between results of ambulatory electrocardiography and development of cardiomyopathy during long-term follow-up of Doberman pinschers

OBJECTIVE

To characterize ambulatory electrocardiographic results of overtly healthy Doberman Pinschers and determine associations between those results and development of dilated cardiomyopathy.

DESIGN

Cohort study.

ANIMALS

114 (58 male, 56 female) overtly healthy Doberman Pinschers without echocardiographic evidence of cardiac disease on initial examination.

PROCEDURE

Echocardiograms and 24-hour ambulatory electrocardiograms (Holter recordings) were obtained initially and at variable intervals. The status (live vs dead) of all dogs was known at least 2 years and as long as 10 years after initial examination (mean [+/- SD] follow-up time, 4.33 +/- 1.84 years). Associations between development of dilated cardiomyopathy and number of ventricular premature contractions (VPC), age, and sex were determined.

RESULTS

55 dogs (48%) did not have VPC on initial Holter recordings, and only 8 dogs had > 50 VPC/24 hours. The likelihood that a dog would have VPC was associated with increasing age and being male. At least 1 VPC/24 hours, and in particular, > 50 VPC/24 hours or > or = 1 couplet or triplet of VPC/24 hours, were predictive of subsequent development of dilated cardiomyopathy. Fifty-four dogs (47%) developed dilated cardiomyopathy; 12 were still alive at the end of the study, and 42 had died. Twenty-five of these 42 dogs died after the onset of congestive heart failure (CHF), 15 died suddenly before the onset of overt CHF, and 2 died of noncardiac causes. More males developed dilated cardiomyopathy than females, and dogs that died suddenly were approximately 1 year younger than those that developed CHF.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of high-quality Holter recordings may be used to identify overtly healthy Doberman Pinschers that are at a high risk for dilated cardiomyopathy.

Duration of the QT interval in healthy cats

OBJECTIVE

To develop a clinically useful model for predicting QT interval duration as a function of heart rate in healthy cats.

ANIMALS

20 healthy cats.

PROCEDURE

For all cats, results of a physical examination, electrocardiography, and echocardiography were normal. Twenty-four hour heart rate and rhythm data were collected by means of ambulatory electrocardiography. Hourly ECG segments were obtained from the 24-hour recordings. Mean heart rate and the mean of 5 QT interval measurements were calculated for each of 479 usable ECG segments. Analysis of covariance was used to develop models to describe variability in QT interval duration.

RESULTS

Prediction equations (R2 = 0.81) including terms for heart rate, (heart rate)2, age group (1 to 4 vs 8 to 14 years old), and their interactions were developed. Sex, individual cat, and time of day were of little value in predicting QT interval duration. A simplified prediction equation without age group (R2 = 0.71) also was developed and had better predictive ability than reported correction formulas for QT interval duration.

CONCLUSIONS AND CLINICAL RELEVANCE

Prediction equations with 95% prediction intervals for expected QT interval duration in healthy cats were generated. Abnormal QT interval duration can be associated with cardiac electrical instability, yet QT interval duration is greatly influenced by heart rate. Results of the present study provide reference ranges for expected QT interval duration as a function of heart rate in healthy cats.