Date Published: June 18, 2008
Publisher: BioMed Central
Author(s): Suzanne Gundler, Anna Tidholm, Jens Häggström.
Maine coon cats have a familial disposition for developing hypertrophic cardiomyopathy (HCM) with evidence of an autosomal dominant mode of inheritance . The current mode to diagnose HCM is by use of echocardiography. However, definite reference criteria have not been established. The objective of the study was to determine the prevalence of echocardigraphic changes consistent with hypertrophic cardiomyopathy in Swedish Maine coon cats, and to compare echocardiographic measurements with previously published reference values.
All cats over the age of 8 months owned by breeders living in Stockholm, listed on the website of the Maine Coon breeders in Sweden by February 2001, were invited to participate in the study. Physical examination and M-mode and 2D echocardiographic examinations were performed in all cats.
Examinations of 42 asymptomatic Maine coon cats (10 males and 32 females) were performed. The age of the cats ranged from 0,7 to 9,3 years with a mean of 4,8 ± 2,3 years. Four cats (9,5%) had a diastolic interventricular septal (IVSd) or left ventricular free wall (LVPWd) thickness exceeding 6,0 mm. In 3 of these cats the hypertrophy was segmental. Two cats (4,8%) had systolic anterior motion (SAM) of the mitral valve without concomitant hypertrophy. Five cats (11,9%) had IVSd or LVPWd exceeding 5,0 mm but less than 6,0 mm.
Depending on the reference values used, the prevalence of HCM in this study varied from 9,5% to 26,2%. Our study suggests that the left ventricular wall thickness of a normal cat is 5,0 mm or less, rather than 6,0 mm, previously used by most cardiologists. Appropriate echocardiographic reference values for Maine coon cats, and diagnostic criteria for HCM need to be further investigated.
Primary HCM is characterised by concentric myocardial hypertrophy, i.e. increased wall thickness with normal or decreased chamber inner dimensions, primarily of the left ventricle, in the absence of other cardiac, systemic or metabolic abnormalities which may cause myocardial hypertrophy [2,3]. This disease has also been labeled idiopathic HCM, but because some of the underlying causes for HCM have been identified [1,4], primary HCM may be a more appropriate name.
Cats over the age of 8 months, owned by breeders listed on the website of Maine coon cat breeders in Sweden, living in Stockholm, as defined by area code number, by february 2001 were invited to participate in the study. Nine out of ten invited breeders accepted the invitation, and 42 out of 45 possible cats participated in the examinations. Out of these cats, 30 were closely related (mother, father, daughter, son, sister, brother, half sister or half brother) to one or more of the other cats examined in this study. Exclusion criteria consisted of echocardiographic signs of heart disease, other than HCM. None of the invited cats was excluded from the study.
Screening programs of apparently healthy animals involve the hazard of over- or underestimating the prevalence of the investigated disease. Therefore, the choice of reference values is a pertinent issue, which merits special attention. There is discrepancy between diagnostic echocardiographic values for HCM used by different cardiologists. Most reports consider an end diastolic thickness at any location of the left ventricular wall of > 6 mm [5,17-19] or ≥ 6 mm [1,5,20] diagnostic of HCM, but reference value of > 5,5 mm  and separate values for the interventricular septum of >6 mm and of the free wall of > 5,5 mm  is also used.
Irrespective of the reference values used, the prevalence of echocardiographic findings consistent with HCM in this population of asymptomatic cats was high.
The authors declare that they have no competing interests.
SG participated in the design of the study, carried out the clinical and echocardiographical examinations and drafted the manuscript.