Acta Veterinaria Scandinavica 2008, 50:22 http://www.actavetscand.com/content/50/1/22 thick or when severe papillary muscle hypertrophy was present. Cats with moderate papillary muscle hypertrophy or SAM without hypertrophy of left ventricular wall or the septum were suspected of having the disease [1]. Assess- ment of the left atrium was made on M-mode as well as on 2D image. When measuring on 2D we used the method later described by Hansson et al [14]. Statistical methods All statistical calculations were performed by use of a com- puterized statistical program [15]. To compensate between differences in body weight between the cats, body surface area (BSA) was used to investigate associa- tions between body size and echocardiographic measure- ments. Body surface area was calculated according to the formula: BSA (m2) = (10,4xBW (2/3))/100 [16]. Statistical methods included linear regression between body weight and IVSd and LVWd. Outliers were identified using Jack- nife distances. Values are given as mean ± 2 standard devi- ations. Results Clinical examination The 42 cats were examined in groups at six different occa- sions. None of the cats had any history or clinical signs of significant organ or systemic disease. Thirty-two cats were females (eight castrated), and ten were males (eight cas- trated). One cat was pregnant. The age of the cats varied between 0,7 and 9,3 years (mean 4,8 ± 2,3 years). The body weight for all cats ranged from 3,0 to 8,2 kg (mean 4,9 ± 1,3 kg). The bodyweight of the female cats ranged from 3,0 to 7,0 kg (mean 4,4 ± 0,88 kg) and of the male cats from 4,5 to 8,2 kg (mean 6,5 ± 1,32 kg). One cat had a low grade systolic murmur, II-III/VI, This cat was preg- nant (49 days from mating) at the time of initial examina- tion when the murmur was heard. On reexamination, 545 days post partum, no murmur could be detected. None of the examined cats had relatives with confirmed HCM. Echocardiographic findings According to the criteria specified above, 4 cats (9,5%) in the present study were diagnosed with HCM. One of them (a male, 4 years old) had hypertrophy of the entire left ventricular wall, but the basal part of septum was most thickened, (IVSd 9,3 mm, LVFWd 6,4 mm). The papillary muscles were moderatly hypertrophied in this cat, but the left atrium was not dilated. The other 3 cats diagnosed with HCM (1 male, 9 years of age and 2 females, 11 months and 8 years and 4 months old) had regional hypertrophy of the basilar septum (IVSd 7,3; 7,0 and 6,9 mm, respectively) but normal dimensions of the free wall. The male cat in this group, also had moderately hypertro- phied papillary muscles. IFViSgdurceor1related to body weight IVSd correlated to body weight. Described by outlier analysis in 42 nonsedated asymptomatic Maine coon cats. Two more cats (1 male and 1 female) had wall dimen- sions < 6,0 mm, but were suspected of having HCM because of SAM. The measurement of the basilar part of interventricular septum of one of these cats was border- line (5,9 mm). Five cats (2 males and 3 females) had septal dimensions greater than 5,0 mm but less than 6,0 mm. One of them had SAM, as mentioned above, but none had hypertrophy of the papillary muscles. (Table 1). One cat had a free wall of 5,6 mm but septal dimension less than 5,0 mm. Nine cats out of ten with left ventricular wall thickness of > 5,0 mm had asymmetric hypertrophy as defined by IVSd/LVWd ≥ 1,1. The IVSd and LVWd were both significantly correlated to body weight (P < 0,05) with a correlation coefficient of 0,46. Outlier analysis showed that eight cats had IVSd dimensions outside of the Jacknife distance (Figure 1). Discussion Screening programs of apparently healthy animals involve the hazard of over- or underestimating the preva- lence 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 car- diologists. Most reports consider an end diastolic thick- ness at any location of the left ventricular wall of > 6 mm [5,17-19] or ≥ 6 mm [1,5,20] diagnostic of HCM, but ref- Page 3 of 6 (page number not for citation purposes)