Prevalence of iatrogenic heart murmurs in a population of apparently healthy cats.

OBJECTIVES: To determine the prevalence of iatrogenic heart murmurs in a population of apparently healthy cats and to investigate factors that may predispose cats to iatrogenic murmurs. MATERIALS AND METHODS: Apparently healthy cats presenting for routine examinations were prospectively enrolled. Following a physical examination to confirm there were no abnormalities, a cardiac examination was performed before and during a provocative manoeuvre performed independently by two clinicians. The provocative manoeuvre was performed on the right side of the chest wall by applying gentle pressure with a stethoscope to ascertain whether a murmur became audible, graded using a modified descriptive scale (soft/moderate). The cat's heart rate before and during the provocative manoeuvre and their age, sex, body condition score and bodyweight were recorded. RESULTS: One hundred and six cats were prospectively enrolled. The average prevalence of iatrogenic murmurs was 28.2% with good interobserver agreement recorded on both the presence (kappa 0.67 and 0.62) and grade of the murmur (kappa 0.6 and 0.53). A significant association was noted between age and body condition score, with iatrogenic murmurs more likely in cats with increasing age and decreasing body condition score. There was no association between heart rate and the presence of an iatrogenic murmur. CLINICAL SIGNIFICANCE: Iatrogenic murmurs are a common finding in cats with increasing prevalence noted in older and lean cats. Iatrogenic murmurs should therefore be considered as a differential diagnosis in a cat when an audible soft systolic right-sided murmur occurs with gentle pressure application to the chest wall during auscultation.

The predictive value of clinical, radiographic, echocardiographic variables and cardiac biomarkers for assessing risk of the onset of heart failure or cardiac death in dogs with preclinical myxomatous mitral valve disease enrolled in the DELAY study.

OBJECTIVES: To identify the predictive value on time to onset of heart failure (HF) or cardiac death of clinical, radiographic, and echocardiographic variables, as well as cardiac biomarkers N-terminal pro brain natriuretic peptide (NT-proBNP) and cardiac troponin I in dogs with preclinical myxomatous mitral valve disease (MMVD). ANIMALS: One hundred sixty-eight dogs with preclinical MMVD and left atrium to aortic root ratio ≥1.6 (LA:Ao) and normalized left ventricular end-diastolic diameter ≥1.7 were included. METHODS: Prospective, randomized, multicenter, single-blinded, placebo-controlled study. Clinical, radiographic, echocardiographic variables and plasma cardiac biomarkers concentrations were compared at different time points. Using receiving operating curves analysis, best cutoff for selected variables was identified and the risk to develop the study endpoint at six-month intervals was calculated. RESULTS: Left atrial to aortic root ratio >2.1 (hazard ratio [HR] 3.2, 95% confidence interval [95% CI] 1.9-5.6), normalized left ventricular end-diastolic diameter > 1.9 (HR: 6.3; 95% CI: 3.3-11.8), early transmitral peak velocity (E peak) > 1 m/sec (HR: 3.9; 95% CI: 2.3-6.7), and NT-proBNP > 1500 ρmol/L (HR: 5.7; 95% CI: 3.3-9.5) were associated with increased risk of HF or cardiac death. The best fit model to predict the risk to reach the endpoint was represented by the plasma NT-proBNP concentrations adjusted for LA:Ao and E peak. CONCLUSIONS: Logistic and survival models including echocardiographic variables and NT-proBNP can be used to identify dogs with preclinical MMVD at higher risk to develop HF or cardiac death.

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.

Evaluation of N-terminal prohormone of brain natriuretic peptide and cardiac troponin-I levels in cats with systolic anterior motion of the mitral valve in the absence of left ventricular hypertrophy.

OBJECTIVES: To identify the prevalence of systolic anterior motion of the mitral valve (SAM) in apparently healthy cats in the absence of left ventricular hypertrophy (LVH) and examine the relationship between specific cardiac biomarker concentrations and echocardiographic parameters in these individuals. ANIMALS: eighty client-owned cats. MATERIALS AND METHODS: retrospective study; inclusion criteria were the presence of SAM on conscious echocardiography and concurrent measurement of plasma N-terminal prohormone of brain natriuretic peptide (NT-proBNP) and serum cardiac troponin-I (cTnI). Cats were excluded if they had LVH, left atrial enlargement or systemic disease. The percentages of cats with NT-proBNP and cTnI concentrations above the normal reference range were calculated. The correlation between each biomarker concentration and left ventricular myocardial wall thickness, left atrial size and maximum left ventricular outflow tract velocity was evaluated. RESULTS: Thirty-four of 80 patients with SAM showed no evidence of cardiac remodelling (LVH or left atrial enlargement). Of these patients, 30 of 34 had elevated NT-proBNP, and cTnI was elevated in 13 of 27 (48.1%) cats where this biomarker was measured in association with the NT-proBNP assay. A positive correlation was observed between concentration of plasma NT-proBNP and maximum left ventricular outflow tract velocity (rs = 0.67, p<0.0001). No significant correlations were found between the concentration of biomarkers and the remaining echocardiographic parameters. CONCLUSIONS: SAM is frequently observed in cats even in the absence of cardiac remodelling, and these individuals often demonstrate elevated plasma NT-proBNP and serum cTnI concentrations. Plasma NT-proBNP elevation is correlated with the severity of the left ventricular outflow obstruction caused by SAM.

Long-term biological variability and the generation of a new reference interval for plasma N-terminal pro-B-type natriuretic peptide in Labrador retrievers.

OBJECTIVES: First, to investigate the biological variability of N-terminal pro-B-type natriuretic peptide (NT-proBNP) in healthy Labrador retrievers and compare this with current laboratory recommendations for dilated cardiomyopathy screening. Second, to calculate a breed-specific reference interval and validate it in a retrospective cohort. MATERIALS AND METHODS: Plasma NT-proBNP was measured in 51 clinically healthy Labrador retrievers at 0, 2, 4, 6 and 8 weeks. Coefficient of variation for individual dogs over time, the coefficient of variation for the group at each time point and the index of individuality were calculated. A reference interval was derived and tested on a clinical dataset available from four UK cardiology referral centres. RESULTS: Median NT-proBNP was 865 pmol/L (315 to 2064 pmol/L). Mean individual coefficient of variation was 19% (95% CI: 16 to 21%) and group coefficient of variation was 43% (95% CI: 41 to 46%), with index of individuality at 0.44. The breed-specific reference interval was 275 to 2100 pmol/L. In the validation group, 93% of NT-proBNP measurements from healthy dogs were within the reference interval. NT-proBNP measurements exceeded the reference interval in 82% of dogs with dilated cardiomyopathy. The upper bound of the reference interval (2100 pmol/L) had a positive predictive value of 90% and a negative predictive value of 87% for identification of dilated cardiomyopathy in this population. CLINICAL SIGNIFICANCE: Breed-specific reference intervals might improve the diagnostic accuracy of NT-proBNP measurement. Applying the currently recommended general cut-off value to Labradors is likely to result in frequent false positives and diagnosis would be improved by application of the new breed-specific reference interval calculated here.

DELay of Appearance of sYmptoms of Canine Degenerative Mitral Valve Disease Treated with Spironolactone and Benazepril: the DELAY Study.

INTRODUCTION: Efficacy of renin-angiotensin-aldosterone system (RAAS) blockade using angiotensin-converting enzyme inhibitors (ACEi) in dogs with preclinical myxomatous mitral valve disease (MMVD) is controversial. HYPOTHESIS: Administration of spironolactone (2-4 mg q 24 h) and benazepril (0.25-0.5 mg q 24 h) in dogs with preclinical MMVD, not receiving any other cardiac medications, delays the onset of heart failure (HF) and cardiac-related death. Moreover, it reduces the progression of the disease as indicated by echocardiographic parameters and level of cardiac biomarkers N-terminal pro brain natriuretic peptide (NT-proBNP) and cardiac troponin I (cTnI). ANIMALS: 184 dogs with pre-clinical MMVD and left atrium-to-aortic root ratio (LA:Ao) ≥1.6 and normalized left ventricular end-diastolic diameter (LVEDDn) ≥1.7. METHODS: This is a prospective, randomized, multicenter, single-blinded, placebo-controlled study. Primary outcome variable was time-to-onset of first occurrence of HF or cardiac death. Secondary end points included effect of treatment on progression of the disease based on echocardiographic and radiographic parameters, as well as variations of NT-proBNP and cTnI concentrations. RESULTS: The median time to primary end point was 902 days (95% confidence interval (CI) 682-not available) for the treatment group and 1139 days (95% CI 732-NA) for the control group (p = 0.45). Vertebral heart score (p = 0.05), LA:Ao (p < 0.001), LVEDDn (p < 0.001), trans-mitral E peak velocity (p = 0.011), and NT-proBNP (p = 0.037) were lower at the end of study in the treatment group. CONCLUSIONS: This study failed in demonstrating that combined administration of spironolactone and benazepril delays onset of HF in dogs with preclinical MMVD. However, such treatment induces beneficial effects on cardiac remodeling and these results could be of clinical relevance.

Coughing in dogs: what is the evidence for and against a cardiac cough?

Cough has been historically reported as a major clinical sign of cardiogenic pulmonary oedema in dogs. However, recent evidence appears to contradict the traditional dogmatic approach that linked cough to congestive heart failure in dogs. Here we use a question-based format to introduce and discuss the modern evidence regarding "cardiac cough" and the interpretation of this important but often misleading clinical sign.

Sleeping and resting respiratory rates in dogs and cats with medically-controlled left-sided congestive heart failure.

Sleeping and resting respiratory rates (SRR and RRR, respectively) are commonly used to monitor dogs and cats with left-sided cardiac disease and to identify animals with left-sided congestive heart failure (L-CHF). Dogs and cats with subclinical heart disease have SRRmean values <30 breaths/min. However, little is known about SRR and RRR in dogs and cats with CHF that is well controlled with medical therapy. In this study, SRR and RRR were measured by the owners of 51 dogs and 22 cats with stable, well-controlled CHF. Median canine SRRmean was 20 breaths/min (7-39 breaths/min); eight dogs were ≥25 breaths/min and one dog only was ≥30 breaths/min. Canine SRRmean was unrelated to pulmonary hypertension or diuretic dose. Median feline SRRmean was 20 breaths/min (13-31 breaths/min); four cats were ≥25 breaths/min and only one cat was ≥30 breaths/min. Feline SRRmean was unrelated to diuretic dose. SRR remained stable during collection in both species with little day-to-day variability. The median canine RRRmean was 24 breaths/min (12-44 breaths/min), 17 were ≥25 breaths/min, seven were ≥30 breaths/min, two were >40 breaths/min. Median feline RRRmean was 24 breaths/min (15-45 breaths/min); five cats had RRRmean ≥25 breaths/min; one had ≥30 breaths/min, and two had ≥40 breaths/min. These data suggest that most dogs and cats with CHF that is medically well-controlled and stable have SRRmean and RRRmean <30 breaths/min at home. Clinicians can use these data to help determine how best to control CHF in dogs and cats.

Management of acute heart failure in cats.

Acute heart failure in cats represents a complex clinical situation in feline practice and this review has been designed to focus on the description of acute heart failure in cats, the diagnostic approach and clinical management of acutely decompensated feline cardiac patients. The authors acknowledge the lack of scientific evidence regarding many treatments used for heart disease in cats, and hence their approach may differ from recommendations given by other cardiologists. Every individual cardiac cat is also different, and it is important that all treatments are carefully tailored to the individual. Therefore this review provides generic advice based on the authors' personal experience but should not provide prescriptive guidelines on when to use particular drugs and doses and readers are encouraged to seek the latest information when managing these challenging cases.

Murmur intensity in small-breed dogs with myxomatous mitral valve disease reflects disease severity.

OBJECTIVES: To determine whether murmur intensity in small-breed dogs with myxomatous mitral valve disease reflects clinical and echocardiographic disease severity. METHODS: Retrospective multi-investigator study. Records of adult dogs Ä20 kg with myxomatous mitral valve disease were examined. Murmur intensity and location were recorded and compared with echocardiographic variables and functional disease status. Murmur intensities in consecutive categories were compared for prevalences of congestive heart failure, pulmonary hypertension and cardiac remodelling. RESULTS: 578 dogs [107 with "soft" (30 Grade I/VI and 77 II/VI), 161 with "moderate" (Grade III/VI), 160 with "loud" (Grade IV/VI) and 150 with "thrilling" (Grade V/VI or VI/VI) murmurs] were studied. No dogs with soft murmurs had congestive heart failure, and 90% had no remodelling. However, 56% of dogs with "moderate", 29% of dogs with "loud" and 8% of dogs with "thrilling" murmurs and subclinical myxomatous mitral valve disease also had no remodelling. Probability of a dog having congestive heart failure or pulmonary hypertension increased with increasing murmur intensity. CLINICAL SIGNIFICANCE: A 4-level murmur grading scheme separated clinically meaningful outcomes in small-breed dogs with myxomatous mitral valve disease. Soft murmurs in small-breed dogs are strongly indicative of subclinical heart disease. Thrilling murmurs are associated with more severe disease. Other murmurs are less informative on an individual basis.

Purring in cats during auscultation: how common is it, and can we stop it?

OBJECTIVES: When cats purr during examination it is difficult to perform auscultation. The objective of this study was to determine the prevalence of purring in cats during examination, and identify interventions that could be used to stop purring. METHODS: Cats seen at a first opinion clinic were enrolled in the study and their purring status recorded. Thirty of the purring cats were exposed to up to three different interventions in an attempt to stop purring in a randomised controlled trial including blowing at the ear, use of an ethanol-based aerosol near the cat and proximity to a running tap. RESULTS: The 30 cats in the trial were subjected to a total of 54 attempts to stop purring, proximity to a running tap caused 17 of 21 (81%) cats to stop purring, blowing at the cat's ears worked in 2 of 15 (13%) cats, spraying an aerosol close to the cat was effective in 9 of 18 (50%) cases. In 2 cats (7%), none of the interventions interrupted purring. CLINICAL SIGNIFICANCE: This study provides evidence that placing a purring cat near a running tap and in proximity to the discharge of an ethanol-based aerosol are effective measures to stop purring in order to allow auscultation.

Risk factors for coughing in dogs with naturally acquired myxomatous mitral valve disease.

BACKGROUND: Cough often is reported as the primary clinical sign of congestive heart failure (CHF) in dogs with chronic degenerative myxomatous mitral valve disease (MMVD). Concurrent airway disease and compression of the left mainstem bronchus by a large left atrium also have been proposed as potential causes of coughing in these patients. OBJECTIVES: To investigate the association between the presence of coughing and different potential causes of cough, including CHF, abnormal radiographic airway pattern, and cardiomegaly in dogs affected by naturally acquired MMVD. ANIMALS: Two hundred six client-owned dogs. METHODS: Retrospective analysis performed on medical records of dogs affected by MMVD that underwent full cardiac evaluation, including echocardiographic examination and thoracic radiography. RESULTS: Univariate analyses showed that CHF is not a predictor of coughing (OR = 1.369; 0.723, 2.594), whereas abnormal radiographic airway pattern (OR = 3.650; 2.051, 6.496) and increased left atrial size observed radiographically (OR = 3.637; 1.904, 6.950) or echocardiographically (OR = 2.553; 1.436, 4.539) were significantly associated with coughing in dogs with MMVD. The same risk factors were significant in multivariate analyses. CONCLUSIONS AND CLINICAL IMPORTANCE: This study indicates that CHF is not significantly associated with coughing in dogs with MMVD. Instead, abnormal radiographic airway pattern and left atrial enlargement are associated with coughing in these patients. This important finding should be taken into account when considering diagnosis and clinical management of CHF in these dogs.

Lack of correlation between canine heart rate and body size in veterinary clinical practice.

OBJECTIVES: An association between heart rate (HR) and bodyweight has been reported in dogs and it is common belief that small breeds of dog exhibit higher HR than large breeds. The first aim of this study was to test the null hypothesis that, in veterinary clinical practice, bodyweight does not affect HR measured in healthy dogs. A second objective of this investigation was to assess whether other variables, such as gender, breed morphology, age and demeanour, may have a significant effect on dog's HR measured in a clinical setting. METHODS: The investigation was performed via two different studies: a retrospective analysis performed on 243 electrocardiogram recordings and a prospective study based on 153 standardised clinical examinations. RESULTS: The two separate studies did not show any significant correlation between HR and bodyweight (P=0.5705 and P=0.4682, respectively). Subject's breed morphology and gender did not appear to affect HR measured under these circumstances. However, dogs under the age of one year seem to have significantly higher HRs than older dogs (P < 0.05). Finally, subject's demeanour was also found to have a significant influence on HR; lower values were recorded in relaxed dogs, and higher rates were documented in excited, nervous dogs (P < 0.05). CLINICAL SIGNIFICANCE: Normal HR could be erroneously interpreted as bradycardia or tachycardia if bodyweight was to be considered a determinant factor. Instead, HR in healthy dogs undergoing routine clinical examination is related to their demeanour or age, if younger than 12 months, but does not appear to be related to bodyweight.

An intestinal neuroendocrine tumour associated with paroxysmal ventricular tachycardia and melaena in a 10-year-old boxer.

A 10-year-old female neutered boxer was presented with a five-week history of episodic collapse and melaena. Twenty-four-hour electrocardiograph (Holter) analysis revealed the collapsing episodes to coincide with episodes of paroxysmal ventricular tachycardia. Investigation of the dog's melaena revealed a gastric ulcer which was treated medically and an ileocaecal mass which was surgically excised. Histopathological examination of the mass was consistent with a neuroendocrine (carcinoid) tumour. The patient's recovery after surgery was unremarkable. At six-week follow-up, there had been no further episodes of melaena or collapse and repeat Holter analysis did not show any significant abnormalities. In this dog the gastric ulceration and paroxysmal ventricular tachycardia could be attributed to a paraneoplastic syndrome as a result of circulating vasoactive substances released by the tumour; this is supported by the evidence that all clinical signs resolved after surgical excision of the mass and the dog was clinically well 18 months after surgery.

A pilot study to assess the feasibility of a submaximal exercise test to measure individual response to cardiac medication in dogs with acquired heart failure.

Exercise testing is not commonly used in canine medicine because of several limitations. The aim of this study was to investigate the suitability of a treadmill test to measure the exercise capacity of untrained canine cardiac patients and to measure some biological parameters that might reflect the tolerance of dogs with heart failure to submaximal exercise. The exercise capacity of seven dogs with naturally occurring heart failure was evaluated before the institution of cardiac medication and 7 days after the beginning of the study. An additional re-examination was requested after 28 days. The exercise test was performed on a motorized treadmill at three different speeds (0.5 m/s, 1.0 m/s and 1.5 m/s). The following parameters were measured at the end of each stage and after 20 min recovery: heart rate, rectal temperature, glucose, lactate, aspartate aminotransferase, creatine kinase, PvO(2), PvCO(2), pH, haematocrit, bicarbonate, sodium, potassium and chloride. Serum cardiac troponin-I was also measured at the beginning of the test and at the end of the recovery period. Owners' perception reflected the ability of their dogs to exercise on the treadmill. Lactate level increased noticeably with the intensity of the exercise test, and its variation coincided with different exercise tolerance observed by the owners. Heart rate seemed to follow a similar trend in the few dogs presented in sinus rhythm. None of the remaining parameters appeared to be sensitive indicators of activity level in the dogs used in this study. The treadmill exercise test in dogs with acquired heart failure is feasible and might provide useful information for assessing individual response to cardiac medication. Lactate and heart rate seemed to reflect individual levels of exercise tolerance, although further studies are necessary to confirm the reliability and repeatability of this test.

Original investigation of right-to-left shunting patent ductus arteriosus in an Irish setter puppy.

A six-month-old, entire female, Irish setter was presented with a two-month history of progressive hindlimb weakness and collapse on exercise. Thoracic auscultation revealed a soft systolic murmur and a split second heart sound. Differential cyanosis and polycythaemia were not observed. Right-to-left shunting patent ductus arteriosus (r-PDA) was confirmed on contrast echocardiography ("bubble study") and selective right ventricular angiography. Comparison of blood gases from the metatarsal and auricular artery confirmed the presence of differential hypoxia. This technique is not known to have been described previously in the diagnostic investigation of r-PDA in dogs.

Congestive heart failure caused by intracardiac tumours in two dogs.

Congestive heart failure is a common presentation in small animal practice. Cardiac tumours are an unusual cause of congestive heart failure and, when they occur, usually cause clinical signs associated with pericardial effusion and cardiac tamponade. This case report outlines the clinical and histological findings in two dogs presented with clinical signs of congestive heart failure caused by obstruction of blood flow by intracavitary cardiac tumours. Case 1 showed signs of left-sided heart failure caused by osteosarcoma within the left atrial lumen, and case 2 presented with clinical signs of right-sided heart failure due to haemangiosarcoma occupying the right atrial and ventricular lumens. This case report provides further evidence for the inclusion of intracardiac neoplasia in the differential diagnosis for dogs with clinical signs of congestive heart failure.

Electrocardiographic parameters of normal alpacas (Lama pacos).

The electrocardiographic parameters of 40 healthy alpacas (Lama pacos) were recorded with a base-apex lead system to establish the normal resting electrocardiographic parameters in this species. The following parameters were measured: heart rate and rhythm, QRS and T morphology, ST segment position, P amplitude and duration, QRS duration and PQ and QT intervals. The heart rate varied between 50 and 110 bpm, with a mean (sd) of 80 (17.8) bpm, and no significant differences were observed between males and females or between alpacas of different ages. Sinus arrhythmia was observed in 35 of the animals, and a regular sinus rhythm was recorded in the other five. The QRS morphology was variable, with an 'rS' pattern observed in 29 animals, 'RS' in six, 'Rs' in three and 'QS' in the other two. A variable morphology was also observed for the T wave, which was positive in 27 animals, negative in seven and biphasic in the other six. All the electrocardiographic parameters were normally distributed and no significant differences were observed between the sexes, except that the amplitude of the P wave was higher in males. The PQ interval was significantly shorter in animals less than six months old.

Effect of body position on feline electrocardiographic recordings.

The aim of this study was to determine whether changes in body position alter feline electrocardiographic parameters. Forty-seven cats referred to the Feline Unit of the University of Bristol had electrocardiograms (ECGs) recorded. Only cats presenting in sinus rhythm were included in the study (n = 41). ECGs were recorded either as part of the investigation for potential cardiac disease (n = 38) or as a preanesthetic screen (n = 3). Standard 6-lead ECGs (leads I, II, III, aVR, aVL, and aVF) were recorded in 3 different recumbent positions in the 41 cats. Recordings were 1st made in right lateral (RL) recumbency, followed by sternal (ST) and then left lateral (LL) recumbency. Measurements were taken of the amplitude and duration of P waves and QRS complexes and duration of PQ and QT intervals from lead II was taken in the 3 different positions. Mean electrical axis (MEA) also was calculated. Repeated measures analysis of variance was performed and identified a significant difference in R wave amplitudes (P = .009) and MEA (P = .037) among the 3 different body positions. Two-tailed paired t-tests demonstrated that the R wave amplitude differed significantly both in ST (P = .025) and LL recumbency (P = .009). The mean R wave amplitude was reduced in both ST and LL recumbency when compared with RL recumbency. The MEA only was significantly different in LL recumbency (P = .037). ST and LL recumbencies should not be used for recording ECGs in cats if amplitudes and MEA are to be compared with standard references.

Use of a multi-stage exercise test to assess the responsiveness of rate-adaptive pacemakers in dogs.

OBJECTIVES: To assess the ventricular rate response of rate-adaptive (VVIR) pacemakers in dogs using a multi-stage exercise test. METHODS: The rate-responsiveness of VVIR pacemakers was assessed in seven dogs with complete atrioventricular (AV) block and implanted with various models of pulse generators (six motion sensors and one automatic dual-sensor rate-response pacemaker). Response activity was assessed with a multi-stage exercise test on a treadmill. Atrial and ventricular rate were analysed retrospectively at the end of the test and the AV ratio was calculated after each minute of exercise. RESULTS: During exercise, the mean (sd) AV ratio recorded in all paced dogs was 1.7 (0.5) (expected physiological ratio 1.0), although a variety of individual performances was observed. A poor response (AV ratio 2.8 [0.2]) was obtained with the automatic dual-sensor pacemaker, suggesting that this type of rate-responsive device may not be indicated for implantation in dogs with complete AV block. The overall AV ratio for the six dogs implanted with motion sensors was 1.4 (0.2), showing a better performance of these pacemakers during exercise. CLINICAL SIGNIFICANCE: This multi-stage exercise test represents an easy and repeatable method for assessing the accuracy of rate-responsive sensors and offers valuable information for the correct setting of VVIR pacemakers in dogs.