Spectral analysis of heart rate variability in dogs with mild mitral regurgitation

MITRAL REGURGITATION IN SADDLE-BILLED STORKS (EPHIPPIORHYNCHUS SENEGALENSIS) IN HUMAN CARE: DIAGNOSIS, ECHOCARDIOGRAPHIC MEASUREMENTS, AND MANAGEMENT

The asymptomatic and slow progressive nature of cardiopathies represents a risk to the welfare of avian species in human care. Diagnosis and treatment of cardiac disease in birds pose a challenge due to unique anatomic and physiologic characteristics. Comprehensive cardiac assessments with diagnostic tools such as echocardiography, color-Doppler, the biomarker cardiac troponin I (cTn1), and cholesterol serum concentrations have been utilized in different bird species with varying success. Saddle-billed storks (Ephippiorhynchus senegalensis) have been maintained in human care for over 80 yrs and several institutions have noted heart murmurs and cardiomegaly. Despite these findings, peer-reviewed literature describing cardiopathies is lacking for this species. This case series documents the identification of mitral valve regurgitation in saddle-billed storks in a breeding center. Transcoelomic echocardiography using a ventromedial approach with a two-chambered view and color Doppler was utilized. Echocardiographic measurements were taken and compared 1 yr later in most of the birds. There was left atrial enlargement and worsened mitral regurgitation in one geriatric patient, and no progression of the disease in two young birds. Serum samples showed that cTn1 had different concentrations depending on the severity of the disease, whereas cholesterol was within reference range for all birds. Treatment with digoxin and pimobendan was recommended in one bird, serum concentrations of digoxin were tested in a 6-mon span, results were within therapeutic range, and there were no overt adverse effects. There was a suspected genetic component in this population, as four of the five birds with confirmed mitral regurgitation were related.

Impact of a combination of pimobendan, furosemide, and enalapril on heart rate variability in naturally occurring, symptomatic, myxomatous mitral valve degeneration dogs

BACKGROUND

Pimobendan, diuretics, and an angiotensin-converting enzyme inhibitor (ACEi) are widely used for the management of chronic valvular heart disease in dogs; however, the effects of that combination on heart rate variability (HRV) are unknown. The purpose of this study was to assess the HRV of symptomatic myxomatous mitral valve degeneration (MMVD) dogs in response to therapy with a combination of pimobendan, diuretics, and ACEi.

RESULTS

MMVD stage C (n = 17) dogs were enrolled and a 1-hour Holter recording together with echocardiography, blood pressure measurement, and blood chemistry profiles were obtained before and 1, 3, and 6 months after oral treatment with pimobendan (0.25 mg/kg), enalapril (0.5 mg/kg), and furosemide (2 mg/kg) twice daily. The results revealed that MMVD stage C dogs at the baseline had lower values of time-domain indices, low frequency (LF), high frequency (HF), and total power, as well as higher value of LF/HF. Triple therapy significantly increases these parameters in MMVD stage C dogs (P < 0.05). A positive moderate correlation was observed between time domain parameters and a left ventricular internal diastole diameter normalized to body weight (P < 0.05).

CONCLUSIONS

It can be concluded that MMVD stage C dogs possess low HRV due to either the withdrawal of parasympathetic tone or enhanced sympathetic activation, and a combination therapy was shown to enhance cardiac autonomic modulation inferred from the increased heart rate variability. Therefore, a combination therapy may be useful for restoring normal autonomic nervous system activity in dogs with MMVD stage C.

Heart rate variability for small animal veterinarians - A concise debate

This manuscript aims to provide a simple and concise discussion on heart rate variability (HRV) for small animal veterinarians. Despite the fact that heart rate variability analysis techniques have been used for quite a long time in medical sciences, it seems to be not completely understood by a large fraction of veterinarian professionals, thereby, reducing the possible benefits to patients that could arise from such information. The analysis of the R-R intervals enables the veterinarian to evaluate autonomic sympathetic and parasympathetic modulation of the heart, composing the so-called cardiac autonomic balance. Several pathophysiological states lead to profound changes in autonomic balance, especially in the cardiovascular system. Therefore, heart rate variability methods remain a valuable and powerful tool for the diagnosis and prognosis of cardiovascular diseases.

Heart Rate and Heart Rate Variability of Rhesus Macaques (Macaca mulatta) Affected by Left Ventricular Hypertrophy

Hypertrophic cardiomyopathy (HCM) is frequently associated with sudden cardiac death, presumably due to the development of malignant arrhythmias. The risk of sudden cardiac death due to HCM has been reported to be predicted by assessing electrocardiographic (ECG) changes including frequencies and complexities of arrhythmias as well as heart rate variability (HRV) as an assessment of autonomic balance. Sudden cardiac death in association with naturally-occurring left ventricular hypertrophy (LVH) has been reported in a colony of rhesus macaques and is under investigation as a potential non-human primate model of human HCM. In the present study, 10 rhesus macaques with LVH and 10 without the signs of LVH confirmed by an echocardiographic examination were recruited for assessing ECG and HRV parameters. ECG morphology on 10-s, 6-lead ECG analysis, and the frequency and complexity of arrhythmias as well as HRV on 20-h ambulatory ECG Holter analyses were assessed. On the standard 10-s 6-lead ECG analysis, P wave and QRS complex duration as well as the QRS complex amplitude were significantly increased in the LVH-affected rhesus macaques compared to control rhesus macaques. Analysis of 20-h Holter monitoring revealed no statistically significant differences in the frequency or the complexity of arrhythmias between the LVH and the control groups. Several HRV parameters were smaller in the LVH group than the control group throughout the majority of Holter recordings showing periods of reduced variability, however, no statistically significant differences were achieved across groups and/or time points. These findings indicate that ECG analysis and Holter monitoring of rhesus macaques are feasible and that ECG morphological changes in association with LVH could be used as a possible component of an antemortem screening tool. The rhesus macaques of this study did not reveal clear indications of risk for sudden cardiac death. Further studies are necessary to determine the etiology of sudden cardiac death due in LVH affected rhesus macaques and identify if any parameters of arrhythmia assessment or HRV can be used to predict the development of sudden cardiac death.

Sildenafil improves heart rate variability in dogs with asymptomatic myxomatous mitral valve degeneration

Myxomatous mitral valve degeneration (MMVD) causes an imbalance of sympathovagal activity resulted in poor cardiac outcomes. Phosphodiesterase-5 inhibitors have been revealed cardioprotective effect in patients with heart diseases. This study aimed to 1) compare the heart rate variability (HRV) between asymptomatic MMVD and healthy dogs and 2) assess long-term effects of sildenafil and enalapril on time- and frequency-domains analyzes. Thirty-four dogs with MMVD stage B1 or B2 and thirteen healthy dogs were recruited into the study. MMVD dogs were divided into 3 subgroups: control (n=13), sildenafil (n=12) and enalapril (n=9). HRV was analyzed from 1-hr Holter recording at baseline (D0) in all dogs and at 30, 90 and 180 days after treatment. The results showed that MMVD dogs had significant higher heart rate (HR), systemic blood pressures, the ratio of low to high frequency (LF/HF) and had significant decreased standard deviation of all normal to normal RR intervals (SDNN) and the percentage of the number of normal-to-normal sinus RR intervals with differences >50 msec computed over the entire recording (pNN50) when compared with healthy dogs (P<0.05). Neither time nor frequency domain parameters were different among subgroups of MMVD dogs at D0. After treatment with sildenafil for 90 days, both time- and frequency-domain parameters were significantly increased when compared with control and enalapril groups. This study demonstrated that sildenafil improves HRV in asymptomatic MMVD dogs suggesting that sildenafil should be used in the MMVD dogs to restore the sympathovagal balance.

Clinical severity score system in dogs with degenerative mitral valve disease

BACKGROUND

Several risk factors already have been determined for dogs with degenerative mitral valve disease (DMVD). Risk factors often have been considered in isolation and have not always taken into account additional information provided by the history and physical examination (PE).

HYPOTHESIS/OBJECTIVES

Data obtained from history and PE of dogs with DMVD provide prognostic information and can be used for risk stratification.

ANIMALS

Client-owned dogs (n = 244) with DMVD recruited from first opinion practice.

METHODS

Prospective longitudinal follow-up of dogs with DMVD. History and PE data were obtained at 6-month intervals and analyzed with time-dependent Cox models to derive relative risk of cardiac death. Independent hazard ratios were used to derive a clinical severity score (CSS), the prognostic value of which was evaluated by analyzing the median survival times for different risk groups and ROC analysis. Analysis of the progression of CSS over time also was undertaken.

RESULTS

History of cough, exercise intolerance, decreased appetite, breathlessness (difficulty breathing) and syncope with PE findings of heart murmur intensity louder than III/VI and absence of respiratory sinus arrhythmia were independently associated with outcome and allowed development of the CSS. Clinical severity score distinguished groups of dogs with significantly different outcomes.

CONCLUSIONS AND CLINICAL IMPORTANCE

Routinely obtained clinical findings allow risk stratification of dogs with DMVD. Results of ancillary diagnostic tests may be complementary to history and PE findings and always should be interpreted in conjunction with these findings.

Short-term follow-up of exercise training program and beta-blocker treatment on quality of life in dogs with naturally acquired chronic mitral valve disease

This study aimed to evaluate the effects of carvedilol treatment and a regimen of supervised aerobic exercise training on quality of life and other clinical, echocardiographic, and biochemical variables in a group of client-owned dogs with chronic mitral valve disease (CMVD). Ten healthy dogs (control) and 36 CMVD dogs were studied, with the latter group divided into 3 subgroups. In addition to conventional treatment (benazepril, 0.3-0.5 mg/kg once a day, and digoxin, 0.0055 mg/kg twice daily), 13 dogs received exercise training (subgroup I; 10.3 ± 2.1 years), 10 dogs received carvedilol (0.3 mg/kg twice daily) and exercise training (subgroup II; 10.8 ± 1.7 years), and 13 dogs received only carvedilol (subgroup III; 10.9 ± 2.1 years). All drugs were administered orally. Clinical, laboratory, and Doppler echocardiographic variables were evaluated at baseline and after 3 and 6 months. Exercise training was conducted from months 3-6. The mean speed rate during training increased for both subgroups I and II (ANOVA, P>0.001), indicating improvement in physical conditioning at the end of the exercise period. Quality of life and functional class was improved for all subgroups at the end of the study. The N-terminal pro-brain natriuretic peptide (NT-proBNP) level increased in subgroup I from baseline to 3 months, but remained stable after training introduction (from 3 to 6 months). For subgroups II and III, NT-proBNP levels remained stable during the entire study. No difference was observed for the other variables between the three evaluation periods. The combination of carvedilol or exercise training with conventional treatment in CMVD dogs led to improvements in quality of life and functional class. Therefore, light walking in CMVD dogs must be encouraged.

Heart rate variability parameters of myxomatous mitral valve disease in dogs with and without heart failure obtained using 24-hour Holter electrocardiography

Time-domain heart rate variability (HRV) parameters and the correlation between echocardiography and Holter examinations in dogs with myxomatous mitral valve disease (MMVD) were determined. Holter examination was also performed at different time frames: an entire 24-hour period, a four-hour period during sleep, and a four-hour period while awake. Ten healthy (control group) and 28 MMVD dogs, 15 with and 13 without heart failure, were evaluated. The SDANN (sd of the mean normal RR intervals for all five-minute segments during 24-hour Holter) and pNN(50) (percentage of differences between adjacent normal RR intervals that are >50 ms computed over 24-hour Holter) variables were significantly lower in the dogs with MMVD heart failure. The differences in HRV between the groups were only detected during the 24-hour evaluation period (P<0.05). There were high correlations (canonical analysis) between Holter and echocardiography examinations when considering pNN(50), SDANN, and LA/AO (left atrial to aortic root ratio) (r=0.92; P<0.05), indicating that both are important in evaluating MMVD dogs. SDANN and pNN(50) are measures of parasympathetic control of the heart, and thus, it is possible to infer that the MMVD dogs exhibit parasympathetic withdrawal during the development of heart failure.

Pharmacologic management of myxomatous mitral valve disease in dogs

Myxomatous mitral valve disease (MMVD) causing mitral regurgitation is the most important disease of the heart in small animal cardiovascular medicine. Because MMVD is an example of a chronic disease that progresses from mild to severe over years, treatment strategies change with the stage of the disease. In this review the treatment options are compared and contrasted as they are discussed relative to the recently published ACVIM consensus statement regarding the treatment of MMVD. Results from clinical trials and evidence-based medicine are likely to provide significant improvements in the management of MMVD in the coming decades.

Heart rate, heart rate variability, and arrhythmias in dogs with myxomatous mitral valve disease

BACKGROUND

Autonomic modulation of heart rhythm is thought to influence the pathophysiology of myxomatous mitral valve disease (MMVD).

HYPOTHESES

(1) Holter-derived variables reflecting autonomic modulation of heart rhythm change with MMVD severity in Cavalier King Charles Spaniels (CKCS); (2) Holter-derived variables can identify MMVD severity in CKCS; and (3) Holter-derived variables in CKCS in congestive heart failure (CHF) secondary to MMVD differ from those in dogs of other breeds in CHF.

ANIMALS

Ninety privately owned dogs: 70 CKCS with variable MMVD severity and 20 non-CKCS in CHF secondary to MMVD.

METHODS

Dogs were prospectively recruited and divided into 5 MMVD severity groups based on history, breed, and physical and echocardiographic examination findings. Holter-derived variables included heart rate variability (HRV), heart rate (HR), and arrhythmia evaluated from 24-hour Holter recordings.

RESULTS

In CKCS, 18 of 26 HRV (all P < .0002) and 3 of 9 arrhythmia (all P < .0004) variables decreased with increasing MMVD, whereas minimum and mean HR (all P < .0001) increased with increasing MMVD severity. An arrhythmia variable representing sinus arrhythmia ("premature normals") (P < .0001) and the HRV variable triangular index (TI) (P < .0001) could distinguish CKCS with moderate or severe mitral regurgitation from CKCS in CHF in specific intervals. Among dogs in CHF, Holter-derived variables did not differ among breeds.

CONCLUSIONS AND CLINICAL IMPORTANCE

In CKCS, Holter-derived variables changed with MMVD severity. "Premature normals" and TI showed diagnostic potential. Breed differences were not seen among dogs in CHF secondary to MMVD.

Pharmacokinetics of nicorandil in dogs with mild mitral regurgitation

The aim of this study was to examine the pharmacokinetics of nicorandil, a hybrid of an adenosine triphosphate-sensitive potassium channel opener and a nitrate, and to estimate its clinical doses in dogs with mild mitral valve regurgitation (MR). Nicorandil (0.1, 0.3, and 1.0 mg/kg) was administered orally to normal dogs and those with experimentally-induced MR, and its plasma concentrations were analyzed using high-performance liquid chromatography. Plasma concentrations increased dose-dependently after the administration of nicorandil, and were not different between normal dogs and those with MR. Similar to the effective plasma values obtained in cardiac disease in humans, the findings of this pharmacokinetic study may indicate that a dose of 0.3-1.0 mg/kg has the same effectiveness in dogs with cardiac dysfunction.

Evaluation of the effect of topical application of lavender oil on autonomic nerve activity in dogs

OBJECTIVE

To investigate the effect of topical application of undiluted lavender oil on sympathovagal activity in dogs.

ANIMALS

5 healthy adult male Beagles.

PROCEDURES

An ambulatory ECG monitor (Holter recorder) was placed on each dog (day0), and 48-hour ECGs were recorded, beginning at 8:00 the next day (day 1). Lavender oil (0.18 mL) or saline (0.9% NaCl) solution (0.18 mL) was topically applied to the inner pinnas of both ears of all dogs at 8:30, 12:00, 15:30, and 19:00 on day 2. Each trial was duplicated in each dog, with an interval of 3 to 4 days between trials. Spectral indices of heart rate variability, power in the high-frequency range, and the ratio of low-frequency to high-frequency power were calculated as an indirect estimate of autonomic nerve activity.

RESULTS

When dogs were treated with lavender oil, the mean heart rate was significantly lower during the period of 19:00 to 22:30 on day 2, compared with the mean heart rate during the same period when dogs were treated with saline solution. On the other hand, high-frequency power during the period of 15:30 to 19:00 was significantly higher when dogs were treated with lavender oil, compared with the high-frequency power during the same period when dogs were treated with saline solution.

CONCLUSIONS AND CLINICAL RELEVANCE

The study revealed some evidence that topical application of lavender oil affected vagal activity in dogs. However, whether such an effect exists and whether lavender oil has a calming effect on dogs remains equivocal and requires additional investigation.

Modulation of the tissue reninangiotensin-aldosterone system in dogs with chronic mild regurgitation through the mitral valve

OBJECTIVE

To investigate whether the tissue and plasma renin-angiotensin-aldosterone system (RAAS) is activated in dogs with mild regurgitation through the mitral valve and determine the contribution of chymase and angiotensin-converting enzyme (ACE) to the activation of the RAAS and potential production of angiotensin II during the chronic stage of mild mitral valve regurgitation.

ANIMALS

5 Beagles with experimentally induced mild mitral valve regurgitation and 6 clinically normal (control) Beagles.

PROCEDURES

Tissue ACE and chymase-like activities and plasma RAAS were measured and the RAAS evaluated approximately 1,000 days after experimental induction of mitral valve regurgitation in the 5 dogs.

RESULTS

Dogs with experimentally induced mitral valve regurgitation did not have clinical signs of the condition, although echocardiography revealed substantial eccentric hyper- trophy. On the basis of these findings, dogs with mitral valve regurgitation were classified as International Small Animal Cardiac Health Council class Ib. Plasma activity of renin and plasma concentrations of angiotensin I, angiotensin II, and aldosterone were not significantly different between dogs with mitral valve regurgitation and clinically normal dogs. Tissue ACE activity was significantly increased and chymase-like activity significantly decreased in dogs with mitral valve regurgitation, compared with values in clinically normal dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

The tissue RAAS was modulated without changes in the plasma RAAS in dogs with mild mitral valve regurgitation during the chronic stage of the condition. An ACE-dependent pathway may be a major route for production of angiotensin II during this stage of the condition.

Correlation between activation of the sympathetic nervous system estimated by plasma concentrations of norepinephrine and Doppler echocardiographic variables in dogs with acquired heart disease

OBJECTIVE

To evaluate correlations between plasma concentrations of norepinephrine and Doppler echocardiographic variables for dogs with degenerative mitral valve disease (DMVD) or dilatative cardiomyopathy (DCM) to better understand the time course and magnitude of sympathetic activation in dogs with heart failure (HF).

ANIMALS

15 healthy dogs, 15 dogs with DMVD, and 15 dogs with DCM.

PROCEDURES

Dogs were positioned in lateral recumbency with minimal restraint for at least 20 minutes. Plasma samples were obtained and assayed by use of high-performance liquid chromatography. Concentrations were correlated with HF classification and with the main Doppler echocardiographic variables for each group.

RESULTS

Mean +/- SD norepinephrine concentration was significantly higher in dogs with DMVD (494.4 +/- 204.8 pg/mL) or DCM (655.7 +/- 652.5 pg/mL) than in healthy dogs (205.8 +/- 78.9 pg/mL), but concentrations did not differ significantly between the 2 groups with HF. Correlations were not detected between norepinephrine and heart rate or any M-mode echocardiographic variables evaluated, except for fractional shortening (FS) in DCM dogs. In that group, norepinephrine was inversely correlated with FS values. In DMVD dogs, no significant correlation was found between norepinephrine and the left atrium-to-aortic root ratio or mitral regurgitation.

CONCLUSIONS AND CLINICAL RELEVANCE

A proportional inverse correlation exists between norepinephrine and FS values in dogs with DCM. However, norepinephrine concentration was not correlated with the evaluated echocardiographic variables in dogs with DMVD. Sympathetic antagonists should be evaluated as a treatment option because of the increased plasma concentrations of norepinephrine detected in dogs with HF.

Heart rate and heart rate variability of healthy cats in home and hospital environments

To investigate heart rate and its variability, a telemetry device was affixed to 16 healthy, young cats. Prior to inclusion in the study, cats were subject to echocardiographic examination. The heart rate (HR) when cats were restrained for echocardiography (HR(r)) was calculated from 4-5 consecutive RR intervals obtained from a simultaneously recorded electrocardiogram. Electrocardiographic data were then acquired by telemetry in a quiet room in the veterinary hospital (VTH) and later, in the owner's home (home). The ambulatory data were digitally sampled and the RR interval tachogram from a 4 min epoch subject to Fast Fourier Transform to yield measures of heart rate variability (HRV). Sinus arrhythmia was often observed in resting cats. Heart rates (bpm) expressed as mean (+/-SD) were: HRr: 187 (+/-25), HRVTH: 150 (+/-23), HR(home): 132 (+/-19); each of these rates was significantly different from the others. Significant differences in profiles of HRV suggested that sympathetic tone was higher (and parasympathetic tone lower) when cats were in the hospital.