Cardiomyopathy prevalence in 780 apparently healthy cats in rehoming centres (the CatScan study)
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Journal of Veterinary Cardiology (2015) 17, S244eS257
www.elsevier.com/locate/jvc
Cardiomyopathy prevalence in 780
apparently healthy cats in rehoming
centres (the CatScan study)
Jessie Rose Payne, BVetMed, PhD ,
David Charles Brodbelt, MA, VetMB, PhD ,
Virginia Luis Fuentes, MA, VetMB, PhD*
Clinical Science and Services, Royal Veterinary College, Hawkshead Lane, North
Mymms, Hatfield, Hertfordshire, AL9 7TA, United Kingdom
Received 11 December 2014; received in revised form 26 March 2015; accepted 30 March 2015
KEYWORDS Abstract Objectives: Hypertrophic cardiomyopathy (HCM) appears to be common
HCM; in cats and, based on pilot data, a prevalence of 15% has been hypothesized. The
Feline; objectives were to screen a large population of apparently healthy adult cats for
Screening; cardiac disease, and identify factors associated with a diagnosis of HCM.
Echocardiography; Animals: A total of 1007 apparently healthy cats 6 months of age.
Shelter Methods: In this prospective, cross-sectional study, the inclusion criteria were: appar-
ently healthy cats, aged 6 months, available for rehoming over a 17-month period
from two rehoming centres. Hypertensive or hyperthyroid cats were excluded. Body
weight, body condition score, auscultation, systolic blood pressure and two-
dimensional (2-D) echocardiography were evaluated. Cats with left ventricular end-
diastolic wall thickness 6 mm on 2-D echocardiography were considered to have HCM.
Results: Complete data were obtained in 780 cats. Heart murmur prevalence was
40.8% (95% confidence interval (CI) 37.3e44.3%), 70.4% of which were considered func-
tional. The prevalence of HCM was 14.7% (95% CI 12.3e17.4%), congenital disease 0.5%
(95% CI 0.1e1.3%), and other cardiomyopathies 0.1% (95% CI 0.0e0.7%). The HCM pre-
valence increased with age. The positive predictive value of a heart murmur for indi-
cating HCM was 17.9e42.6% (higher in old cats), and the negative predictive value
was 90.2e100% (higher in young cats). The factors associated with a diagnosis of
HCM in binary logistic regression models were male sex, increased age, increased body
Some of the results from this study were presented at the Veterinary Cardiovascular Society Autumn meeting 2013, Loughborough, UK
and at the ACVIM Forum 2014 (Nashville, Tennessee).
* Corresponding author.
E-mail address: vluisfuentes@rvc.ac.uk (V. Luis Fuentes).
http://dx.doi.org/10.1016/j.jvc.2015.03.008
1760-2734/ª 2015 Elsevier B.V. All rights reserved.
Cardiomyopathy prevalence in healthy cats S245
condition score and a heart murmur (particularly grade III/VI or louder).
Conclusions: Hypertrophic cardiomyopathy is common in apparently healthy cats, in
contrast with other cardiomyopathies. Heart murmurs are also common, and are often
functional.
ª 2015 Elsevier B.V. All rights reserved.
certainty, but two recent studies have suggested
that prevalence is higher than in humans
Abbreviations (14e16%),5,6 although the sample size was less
than 200 cats in both studies, and neither study
2-D two-dimensional randomly selected subjects.
BCS body condition score Echocardiography remains the principal test
CVs coefficients of variation for diagnosing HCM in people7,8 and cats.9 In
FS% measurement of LV fractional short- people, an HCM phenotype is most often defined
ening by a maximum end-diastolic LV wall thickness
HCM hypertrophic cardiomyopathy (LVWd) that exceeds an arbitrary cut-off value.10
IQR interquartile range In cats, an LVWd 6 mm is most commonly cited
IVSd end-diastolic interventricular septum as defining HCM, either as the maximum meas-
thickness urement in any region10e14 or measured in >50%
LA:Ao ratio of diastolic left atrial diameter of a segment.5,9 As with people,10 there is a grey
to aortic root diameter measured on area of uncertainty, which in cats may be
the last frame prior to aortic valve between an LVWd of 5.5 mm and 6.0 mm.6 One
opening group of investigators have suggested that a
LAD diameter of the left atrium measured normal LVWd in cats should be
S246 J.R. Payne et al.
and although cats of any age can be diagnosed estimated age) and medical history. For statistical
with HCM, it is often initially diagnosed in young- analyses, cats were categorized as juvenile (6e12
to-middle-aged cats.2,9,24,25 So far, the effect of months), young adult (1e3 years), adult (3e9
age on HCM prevalence in cats has not been years) and senior (9 years or older). Cats were
evaluated. Males are generally over-represented excluded if they: had any current illness identified
in human27 and feline2,24,25,28 HCM populations, or known pre-existing systemic disease; had a
despite the fact that genetic mutations that cause systolic blood pressure (SBP) 180 mmHg29 or were
HCM in people and in Maine Coon and Ragdoll cats being medically managed for hypertension; had
are evenly distributed between males and hyperthyroidism (as diagnosed by the rehoming
females. centre or on blood samples collected as part of the
Based on previous work and the work of oth- study); had been diagnosed with diabetes mellitus
ers,5,6,22 it was hypothesized that in a population by the rehoming centre; were azotemic in the
of apparently healthy cats, the prevalence of cats presence of polyuria and polydipsia; were preg-
with a heart murmur would be around 33% and the nant or nursing queens; had already been selected
prevalence of cats with HCM would be around 15% for a new home; or were too aggressive or too
(using the most commonly used LVWd cut-off of nervous to allow handling.
6.0 mm). It was hypothesized that older age, Cats meeting the inclusion criteria were aus-
male sex and the presence of a heart murmur cultatedb in their pens and underwent echo-
would be associated with an increased likelihood cardiography in a separate room. Prior to
of diagnosing HCM. echocardiography, cats were allowed to acclima-
The main aims of this study were to estimate tise to the new room until calm (or for up to
the prevalence of heart murmurs and HCM in a 10 min), and were then weighed. Body condition
group of apparently healthy cats and to evaluate score (BCS) was assessed on a scale of 1e9 by the
the risk factors for the diagnosis of HCM in this same observer.30 The cats were then auscultated a
population. second time, SBP was measured, and echo-
cardiography was performed. After the echo-
cardiographic examination, cats were auscultated
Animals, materials and methods for a third time and were returned to their pens.
Presence/absence of a heart murmur, point of
This study was approved by the Royal Veterinary maximal heart murmur intensity, minimum/max-
College (RVC) ethics and welfare committee (URN imum heart murmur intensity, and heart rate were
2010 1004). Prior to data acquisition for the main noted at each auscultation.31 The presence of a
study, inter-observer repeatability was analysed in third heart sound or arrhythmia was also recorded.
a group of 17 apparently healthy cats, which If a cat purred loudly throughout all three auscul-
included normal cats and cats with HCM. Each cat tation periods such that it was impossible to hear
separately underwent echocardiography and in a the heart sounds, attempts were made during the
randomized order by two trained observers (JRP third auscultation period to stop purring. Methods,
and VLF), and each observer then measured her in order attempted, included: knocking on the
own studies. underside of the table; turning on a nearby source
Two rehoming centres for catsa agreed to take of running water; or holding rubbing alcohol under
part in the cross-sectional study (‘CatScan’). the cat’s nose.32 Ambient noise was minimal in all
Between October 2011 and February 2013, all areas in which the cats were auscultated, with
apparently healthy cats believed to be aged 6 only quiet talking or sometimes low-level music in
months were considered eligible for inclusion and housing areas, and complete silence in the echo-
were screened by one investigator (JRP). This cardiography room. Cats were classed as having a
investigator was not a board-certified cardiologist, heart murmur even if not detected during all
but she received 2 years of training (October auscultation periods and the maximum heart
2009eSeptember 2011) from a board-certified murmur grade was considered to be the maximum
cardiologist (VLF) prior to data collection. In detected on any auscultation period. Likewise,
order to prevent cats being screened more than cats were considered to have a third heart sound
once, the cat identification number allocated by or arrhythmia even if these findings were inter-
the rehoming centre was noted. Records were mittent. Indirect SBP assessment was performed as
reviewed to determine age (or if unknown, recommended by the ACVIM Consensus
a
Battersea Dogs & Cats Home’s central London branch and b
Harvey Elite Stethoscope with paediatric diaphragm,
Cats Protection’s National Cat Centre. Welch Allyn, Skaneateles Falls, NY, USA.
Cardiomyopathy prevalence in healthy cats S247 Statement29 using a Doppler sphygmomanometer were used only for measurement of LV fractional technique,c noting cuff size, limb used, cat posi- shortening (FS%). tion and cat demeanour. The LA size was assessed using two separate Following SBP assessment, coat hair was clipped methods: using 2-D images from a right parasternal from the right axillary area and the cat restrained short-axis view to calculate the ratio of diastolic in a position that was well tolerated. The positions LA diameter to aortic root diameter (LA:Ao) attempted (in order of preference) were right measured on the last frame prior to aortic valve lateral recumbency on a purpose-built table top; opening35 and using a right parasternal long-axis on the lap of the echocardiographer; or with the four-chamber view to measure the diameter of cat sitting or standing on the echocardiography the left atrium measured parallel with the mitral table and lightly restrained. If adequate quality annulus in the last frame before mitral valve echocardiographic images could not be obtained opening (LAD).36,37 At least three measurements from any of these positions, the cat was excluded were made of each variable, recording an average from the study. value for each. The presence or absence of systolic An echocardiography machined with a 7.5 MHz anterior motion of the mitral valve (SAM) was transducer was used to obtain two-dimensional (2- assessed on a 2-D right parasternal long-axis LV D) and M-mode images from right parasternal outflow view, using cine loop played back at views. Loops were recorded of the right para- reduced speed. The ECG leads were not routinely sternal long-axis four-chamber view, the right attached during the echocardiographic examina- parasternal long-axis LV outflow (‘5-chamber’) tion unless an arrhythmia was detected on aus- view, the right parasternal short-axis view at the cultation or was apparent during SBP assessment or level of the papillary muscles and the right para- echocardiography. sternal short-axis view at the level of the aortic At the completion of the study, medical records valve. M-mode images were guided from 2-D kept by the rehoming centre were re-assessed to images of the right parasternal short-axis view at check whether cats had been subsequently diag- the level of the papillary muscles.33 nosed with a condition considered to be an Measurements were made from recorded images. exclusion criterion. All LV wall thickness measurements were made from 2-D images. Maximal LVWd was measured on the first Statistical analysis frame after mitral valve closure on images where the mitral valve was visible and at the time point in the Statistical analysis was performed using commer- cardiac cycle of greatest LV internal diameter on cially available software.e Normality of continuous images where the mitral valve was not visible. A data was assessed graphically. Normally distributed leading-edge-to-trailing-edge method of measure- data were presented as mean standard deviation ment was used, being careful to exclude the peri- (SD) and non-normally distributed data were pre- cardium, false tendons or papillary muscles, but sented as median (interquartile range, IQR: 25th including the endocardial borders.34 At least three percentilee75th percentile), where appropriate. measurements were made of the thickest region Power calculationsf were performed based on identified for each view of the end-diastolic inter- pilot data6 and a preliminary estimate of HCM ventricular septum (IVSd) and left ventricular free prevalence of 15% was used to calculate that 196 wall (LVFWd), recording the largest repeatable screened cats were required to estimate the value. The maximum left ventricular wall thickness prevalence of HCM in the study population with a measurement of either the IVSd or LVFWd was also precision of 5.0% (confidence level 95%, power recorded (LVWd). Hypertrophic cardiomyopathy 80%) and that 783 screened cats would be needed was defined as LVWd 6 mm; equivocal was defined to estimate the prevalence with a precision of as LVWd 5.5e5.9 mm; and normal was defined as 2.5% (confidence level 95%, power 80%).
S248 J.R. Payne et al. LAD and LA:Ao). Bias and 95% limits of agreement excluded for either being too aggressive (n ¼ 93, were calculated for each variable. 9.2%) or too nervous to handle (n ¼ 134, 13.3%). When comparing cats with and without a diag- Age, body weight and BCS were non-normally nosis of HCM, the ManneWhitney U test was used distributed, while heart rate was normally dis- to compare continuous, non-normally distributed tributed. The median and modal age group cat- data and the Student’s independent t-test for egory in the CatScan population was 1e3 years continuous, normally distributed data. The Fish- (36.1%), with 14.9% of the cats aged 6e12 months, er’s exact and Pearson Chi-squared tests were 35.8% aged 3e9 years and 13.1% aged >9 years. A used, as appropriate, to compare categorical data. total of 70% of the cats were
Cardiomyopathy prevalence in healthy cats S249
Figure 1 Age of CatScan population cats (n ¼ 780).
HCM. Auscultated arrhythmias included seven cats a heart murmur was present compared with an
that had one or more pauses during examination, auscultation period in which no heart murmur was
none of which showed evidence of any arrhythmia heard (200 37 bpm, p < 0.001).
when an electrocardiogram (ECG) was performed. Hypertension was ruled out as a cause for LV
Two other cats had ventricular premature com- hypertrophy in all cats and the veterinarians in the
plexes and one cat had atrial premature com- rehoming centres ruled out hyperthyroidism and
plexes confirmed on ECG. Three of the 10 cats with diabetes on a case-by-case basis. Median (IQR) SBP
arrhythmias were diagnosed with HCM. for the group was 120.6 (110.4e132.4) mmHg.
The proportion of cats with identified heart Thyroxine concentrations (total T4) were meas-
murmurs increased with the number of ausculta- ured in 216 (27.7%) cats and were within normal
tions performed. Of those with a detected heart limits for all cats.
murmur, the heart murmur was present during all End-diastolic LV wall thickness showed a bimo-
auscultation periods in the majority of cats (Fig. 2). dal pattern (Fig. 3). Using the current cut-off of
Taking into account all auscultations, mean heart 6 mm, the prevalence of HCM in the 780 cats was
rate was 203 35 bpm. The heart rate was higher 14.7% (95% CI 12.3e17.4%). Twenty-five cats (3.2%)
(208 32 bpm) during an auscultation period when were classed as equivocal for HCM, 635 cats
(81.4%) were classified as normal, and five (0.6%)
had other cardiac diagnoses: peritoneal pericardial
Table 2 Auscultation data for all CatScan pop- diaphragmatic hernia (n ¼ 2), ventricular septal
ulation cats, all data reported as number (%). defect (n ¼ 1), supravalvular mitral stenosis
n (%) (n ¼ 1), and unclassified cardiomyopathy (UCM,
Number auscultated 780 n ¼ 1). This gave prevalence for congenital disease
Heart murmur present 318 (40.8%) as 0.5% (95% CI 0.1e1.3%) and 0.1% (95% CI
Grade I/VI 49 (15.4%) 0.0e0.7%) for other cardiomyopathies.
Grade II/VI 165 (51.9%) Forty-five (5.8%) cats had systolic anterior motion
Grade III/VI 99 (31.1%) of the mitral valve (SAM). Of these, 41 (91.1%) had
Grade IV/VI 4 (1.3%) HCM, two (4.4%) were equivocal and two (4.4%) had
Grade V/VI 1 (0.3%) normal LV wall thickness (LVWd of 5.3 mm and
Variable heart murmur grade 290 (91.2%)
5.4 mm, respectively) (Table 3). The proportion of
Third heart sound present 3 (0.4%)
Arrhythmia present 10 (1.3%)
cats with a heart murmur was higher (p < 0.001) in
the cats with SAM (42/45, 93.3%) than in the catsS250 J.R. Payne et al.
Figure 2 Number of cats with a heart murmur detected according to number of times auscultated.
without SAM (276/735, 37.6%). Cats with SAM had higher median FS% values (48% (IQR 43e53)) than
greater median maximal LV wall thickness (LVWd those without SAM (43% (IQR 39e47), p < 0.001) and
6.6 mm (IQR 6.2e7.3)) compared with cats without had greater median LAD (15.0 mm (IQR 13.9e15.8))
SAM (LVWd 4.7 mm (IQR 4.2e5.1), p < 0.001), had than those without SAM (14.1 mm (IQR 13.3e15.1),
Figure 3 Maximum left ventricular wall thickness of 780 cats.
Table 3 Echocardiographic features of screened cats.
Normal Equivocal HCM
N 635 25 115
LVWd (mm) 4.6 (4.2e4.9) 5.8 (5.7e5.9) 6.3 (6.2e6.6)
LAD (mm) 14.1 (13.3e15.0) 14.8 (13.8e16.3) 14.7 (13.4e15.8)
LA:Ao (end-diastole) 1.19 (1.12e1.25) 1.15 (1.08e1.19) 1.16 (1.09e1.26)
FS% 42 (39e47) 45 (40e50) 47 (41e51)
SAM 2 (0.3%) 2 (8.0%) 41 (35.7%)Cardiomyopathy prevalence in healthy cats S251
Table 4 Univariate comparisons of cats with and without HCM (cats without HCM include those considered
normal, equivocal or other cardiac disease).
HCM (n ¼ 115) No HCM (n ¼ 665) p-Value
Age 5e7 years 1e3 yearsS252 J.R. Payne et al.
Table 5 Heart murmur and HCM prevalence, sensitivity, specificity, positive and negative predictive values of
using a heart murmur to detect HCM.
Juvenile: 6e12 Young adult: 1e3 years Adult: 3e9 years Senior: 9 years
months (n ¼ 116) (n ¼ 283) (n ¼ 279) (n ¼ 102)
Heart murmur 24.1% 37.5% 44.1% 59.8%
prevalence
HCM prevalence 4.3% 9.9% 18.6% 29.4%
Sensitivity 100.0% 92.9% 71.1% 86.7%
Specificity 79.3% 68.6% 62.1% 51.4%
PPV 17.9% 24.5% 30.1% 42.6%
NPV 100.0% 98.9% 90.4% 90.2%
investigating prevalence of HCM, with a suggested distribution of end-diastolic wall thicknesses seen
prevalence of 14e16%.5,6 Of the 780 cats that in this population of cats showed a bimodal pat-
underwent echocardiography in the present tern, with the likely cut-off being between
study, 115 cats were diagnosed with HCM com- 5.5 mm and 6.0 mm. If a lower cut-off were to be
pared with five cats with other cardiac abnor- used, the prevalence of HCM diagnosis would be
malities, only one of which was another higher. It is difficult to determine whether all of
myocardial disease (UCM). Although HCM is these cats truly have HCM. From this analysis it
acknowledged to be the most common type of was not possible to determine whether cut-off
cardiomyopathy in cats, most previous studies values for LV wall thickness should be variable
have reported the prevalence in referral-centre to take account of additional factors such as age,
populations,2 and the present study suggests weight and body condition score, or whether
that other forms of cardiomyopathy (e.g. alternative factors such as obesity might alter
restrictive cardiomyopathy, dilated cardiomyop- expression of LV hypertrophy in cats with HCM, as
athy, arrhythmogenic right ventricular cardiomy- has been proposed in people.41 Multi-faceted
opathy) are substantially less common than HCM longitudinal studies with pathologic, genomic
in the general cat population. and outcome components might be needed to
The phenotype of HCM is very variable among resolve this.
people with a positive HCM genotype.11 In the The presence of a heart murmur (in particular, a
absence of a gold standard for the diagnosis of grade III/VI or louder heart murmur), being male,
HCM, an arbitrary LVWd cut-off is generally clin- increasing age group and being overweight were
ically used to define HCM in people and cats. found to be risk factors for diagnosis of HCM. Heart
Although a variety of cut-off values for LVWd have murmurs were extremely common, and increased
been used to define HCM in cats, the present in prevalence with increasing age. Most heart
study used maximum wall thickness 6 mm on any murmurs were of low intensity (III/VI) and
2-D image,12e14 as this is widely used and is likely dynamic. The PPV of a heart murmur for identify-
to provide a conservative estimate of HCM prev- ing HCM was very low, though it increased with
alence. Despite this, the HCM prevalence in the age. Conversely, the NPV was very high, especially
study was 14.7%, which is much higher than that in young cats. As PPV and NPV are influenced by
reported in people.3,4 Visual assessment of the prevalence, these values are only applicable whenCardiomyopathy prevalence in healthy cats S253 Figure 4 Multivariable binary logistic regression model of factors associated with a diagnosis of HCM (115 cats with HCM out of 780 cats). Juvenile ¼ 6e12 months, Young adult ¼ 1e3 years, Adult ¼ 3e9 years, Senior ¼ 9 years. BCS e Body condition score (underweight 4/9, ideal ¼ 5/9, overweight 6/9). populations of similar prevalence are assessed. The with the MYBPC3 mutation, an abnormal phenotype prevalence of heart murmurs in cats in this pop- develops earlier in males than in females,26 and this ulation (40.8%) was higher than has previously been has also been reported in Maine Coons with HCM.12 It reported, with previous reports suggesting a prev- is possible that there are multiple factors influenc- alence of 15.5e33.7%.5,6,22 In the present study, ing the expression of LVH in HCM that have not yet however, the prevalence was calculated over been identified; these could include modifying multiple auscultation periods. Repeated ausculta- genes or environmental factors. The cats in the tion has been shown to increase the overall prev- present study were diagnosed with HCM in all age alence of heart murmurs, both in this population groups, but HCM prevalence increased with and a previous study6; this is possibly due to the increasing age, suggesting that there is a similar variable nature of heart murmurs in cats. The age-related increase in expression of an abnormal majority (70.4%) of heart murmurs were considered phenotype, as seen in people.26 to be functional. This is a higher proportion of It was not anticipated that an increased body functional heart murmurs than in previous condition score would be associated with LV reports.5,6 Functional heart murmurs are also hypertrophy in this population. Obesity has common in people, particularly in children and recently been proposed to be an environmental young adults.42,43 In people, functional heart factor associated with increased LV mass in human murmurs are often heard in states associated with HCM patients, although no increase in maximum increased cardiac output such as fever, hyper- LVWd was identified.41 Being overweight has only thyroidism, hypertension, anaemia and exercise.31 recently been suggested as a risk factor for HCM in Dynamic right ventricular outflow obstruction has cats.45 Dogs with obesity have been shown to have been reported as a cause of systolic heart murmurs increased maximum LVWd compared with lean in cats23 both with and without structural abnor- control dogs,46 and obese people have been shown malities,5 but the presence or absence of this was to have increased LV mass and increased LVWd not routinely recorded in this population. The compared with those without obesity.47,48 There mean heart rate was significantly higher when a are many structural and functional cardiac changes heart murmur was present than in auscultation associated with obesity in people, which may var- periods in which there was no heart murmur, iously be due to the presence of metabolic although the difference was arguably clinically syndrome, a pro-inflammatory state, or athero- insignificant. sclerotic changes, amongst other factors. In addi- Males were more likely than females to be diag- tion, obese individuals may have increased nosed with HCM. This had previously been found in a ventricular stiffness in the face of an expanded number of other studies of cats,2,24,25,28 and a central blood volume and increased cardiac out- smaller male bias has been described in people.27 put, which might create a state of volume overload No gender bias is expected with a classic Mende- that could result in eccentric hypertrophy.47 There lian pattern of inheritance, as described for HCM in may be similar pathophysiological processes both people and cats.12,44 In human HCM patients involved in obese cats.49 In the absence of a gold
S254 J.R. Payne et al.
standard test for HCM, it is impossible to deter- been reported to be familial in other pedigree
mine whether the cardiac changes seen in this breeds12,58,59,h,i,j and in some non-pedigree
population of cats associated with being over- cats,60,61 the true prevalence of sarcomeric
weight represent true HCM or whether they are mutations in cats with HCM is unknown. If there is
load-related LVH. a genetic basis for most HCM in cats, it is possible
Third heart sounds were uncommon and all that the prevalence might be high if selection
three cats with a third heart sound in this study pressures against HCM are weak. Natural selection
had HCM and were 9 years old. Without phono- may not have a large effect on HCM prevalence, as
cardiography it is difficult to determine whether most affected cats in the present study had rela-
these third heart sounds were gallop sounds or tively mild changes and would be considered to be
systolic clicks. The predictive value of a third heart at low risk of a cardiac death.
sound should be further investigated in an older
population of cats. The presence of a third heart
sound was not predictive of HCM in the multi- Limitations
variable model, possibly because few cats with
HCM had a third heart sound. There were a number of limitations in this study.
Arrhythmias were also very uncommon in this Cats were selected from rehoming centres, and
population. Most of the arrhythmias described in although this is more representative of the general
this population consisted of single pauses on aus- population than cats presented to referral hospi-
cultation or during blood pressure assessment and tals, it is possible that other unknown bias factors
were not documented during ECG recordings, may be present in cats given up for rehoming. This
which makes it difficult to categorize them, study represents a snapshot of the cats that came
although premature complexes of either atrial or through the rehoming centres during the 17
ventricular origin were suspected. There was no months of the study and no cause and effect con-
association between arrhythmias and the presence clusions can be drawn.
of LV hypertrophy (Table 4). Ventricular premature As many cats were strays, ages were estimated
complexes have been found in people that are free if unknown. This opened up a potential for inac-
of cardiac disease,50 and while a study investigat- curacy, although every effort was made to provide
ing prognostic indicators suggested that cats with a realistic estimate, and using age categories may
HCM and arrhythmias have a poorer outcome than have minimized this risk. Although over 100 cats
those without arrhythmias,51 the specific prog- were aged 9 years, generally this was a young
nostic implications of ventricular or supra- population. As these data show an increasing
ventricular arrhythmias in cats without structural prevalence of HCM with age, the reported preva-
heart disease is unknown. lence of HCM may be an underestimate with
Systolic anterior motion was found in cats respect to the general UK cat population. The
considered to be normal, equivocal, and affected proportion of overweight and obese cats may not
with HCM, although it was rare in normal and be reflective of the general population of owned
equivocal cats. As has previously been reported,52 cats. The incidence of obesity in cats is reported to
cats with HCM and SAM had greater LVWd than be >35% and is thought to be increasing with
those without SAM, and there was no difference in time,62 whereas only 10.5% were considered
measures of left atrial size. Very few cats had left overweight in this population. It may not be pos-
atrial enlargement. As left atrial enlargement is sible to extrapolate the finding of this study to
considered to be an important risk factor for pedigree cats, as very few were included in the
cardiac death in cats with HCM, one might spec- population. Not all cats had total thyroid hormone
ulate that only a small proportion of the cats in levels measured, although this was assessed on a
this study were at imminent risk of life-
threatening complications of their disease, but h
longitudinal studies would be required to confirm Martin L, VandeWoude S, Boon J, Brown D. Left ventricular
hypertrophy in a closed colony of Persian cats. J Vet Intern Med.
this. 1994;8:143.
If the current diagnostic criteria for diagnosing i
Meurs K, Kittleson MD, Towbin J, Ware W. Familial systolic
HCM are appropriate, then HCM is extremely anterior motion of the mitral valve and/or hypertrophic car-
common in cats compared with other spe- diomyopathy is apparently inherited in as an autosomal domi-
cies,3,4,49,53e55 and the reasons for this are nant trait in a family of American Shorthair cats. J Vet Intern
Med. 1997;11:138.
unclear. Although causative mutations in myosin- j
Putcuyps I, Coopman F, Van de Werf G. Inherited hypertrophic
binding protein C have been identified in Maine cardiomyopathy in British Shorthair cats. J Vet Intern Med.
Coon56 and Ragdoll57 cats with HCM, and HCM has 2003;17:439e40.Cardiomyopathy prevalence in healthy cats S255
case-by-case basis, so it is less likely that any Conflicts of interest
hyperthyroid cat was erroneously included. Fol-
lowing screening, no cat was excluded for ill health The authors have no conflict of interest to declare
reasons. It is possible that systemic disease was with regard to this study.
present but missed in some screened cats, and
undetected pyrexia or anaemia was not ruled out
as a cause of heart murmurs, as the examination Acknowledgements
did not include assessment of temperature or of a
complete blood count. However, cats with ill The authors gratefully acknowledge the Everts Luff
health were often housed separately and this may feline endowment and IDEXX Laboratories for
have reduced the prevalence of systemic disease financial support for Dr Payne’s PhD studies. They
in the screened population. It was not possible to are indebted to the staff and volunteers at Bat-
auscultate all cats during all time periods. Some tersea Dogs & Cats Home and Cats Protection’s
cats only underwent auscultation once while oth- National Cat Centre, and would also like to thank
ers underwent auscultation three times, which the individuals who adopted the cats that were
limited some of the interpretation of the varia- seen as part of the screening program.
bility of heart murmurs between auscultation
periods. Neither ECGs nor ambulatory ECG mon-
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