Acta Veterinaria Scandinavica 2008, 50:22 http://www.actavetscand.com/content/50/1/22 Table 1: Data from clinical and echocardiographical examination Age, body weight, mean ± SD and range values for M-mode and 2D echocardiographic parameters in 42 nonsedated, asymtomatic Maine coon cats. Variable Age (Yrs) Body weight (kg) IVSd (mm) LVIDd (mm) LVWd (mm) IVSs (mm) LVIDs (mm) LVWs (mm) FS (%) AO-M-mode (mm) LA-M-mode (mm) LA/AO-M-mode AO-2D (mm) LA-2D (mm) LA/AO-2D Mean 4.8 4.9 4.3 14.8 4.1 6.4 8.7 6.2 41.8 8.9 11.6 1.3 9.0 11.1 1.3 SD 2.3 1.3 1.2 2.5 0.8 1.6 2.4 1.4 9.9 1.6 2.0 0.3 1.5 1.6 0.2 Range 0.7–9.3 3,0–8.2 2.3–8.1 8.4–20,0 2.9–6.2 3.8–12.3 3.0–14.4 3.9–10.5 25–73 6.6–14.3 8.2–16.6 0.8–1.9 6.4–13.1 7.9–15.2 0.9–2.2 IVSd = Interventricular septal end-diastolic diameter LVIDd = Left ventricular inner end-diastolic diameter LVWd = Left ventricular posterior wall end-diastolic diameter IVSs = Inter ventricular septal systolic diameter LVIDs = Left ventricular inner systolic diameter LVWs = Left ventricular posterior wall systolic diameter FS = Fractional shortening AO-M-mode = Aortic end-diastolic diameter measured on M-mode LA-M-mode = Left atrial end-systolic diameter measured on M-mode AO-2D = Aortic end-diastolic diameter measured on 2D LA-2D = Left atrial end-diastolic diameter measured on 2D erence value of > 5,5 mm [21] and separate values for the interventricular septum of >6 mm and of the free wall of > 5,5 mm [22] is also used. Assessment of papillary muscle hypertrophy and SAM are subjective, and the inter-operator variability between studies must be considered. It may be expected that the use of screening program will increase the estimated prev- alence of HCM. Reexamination of cats with equivocal results is of importance in screening programs. Echocardiographic reference values for dogs are modified according to body weight, and there are also breed specific references. For adult cats, most cardiologists use reference values irrespective of breed and body size. In Maine coon cats, especially male cats with lean body weights of 8–9 kg, there is reason to question whether reference values should be different from normal sized cats. A recent report on M-mode measurements in healthy adult Maine coon cats compared to normal domestic cats concludes that mean values of aortic root (Ao), four dif- ferent systolic measurements (LVIDs, IVSs, LVPWs, LADs) and left ventricular end diastolic diameter (LVIDd) were significantly greater in Maine coon cats compared to domestic cats in general [23]. The diagnostically impor- tant dimensions of interventricular septum (IVSd) and left ventricular posterior wall (LVPWd) were however not sig- nificantly different from previously reported values for domestic cats. Maine coon cats with echocardiographic parameters consistent with, or suggestive of, a diagnosis of HCM were excluded from the study, but it is not reported what criteria where considered diagnostic. In our study, the cats with abnormal wall thickness were identified using outlier analysis (jackknife distances). We believe that this approach may be more appropriate to establish normal reference range because all cats are included in the initial analysis, and the identification of potentially abnormal cats was not dependant on previously estab- lished reference ranges. No cat in our study had LVIDd above normal reference for domestic cats [5,23]. Mean weight for cats in Drourrs study was 5,5 ± 1,33 kg compared to 4,9 ± 1,3 kg in our study. This difference is probably due to a greater percent- age of male cats (44%) compared to our study (24%), which also affects the measurements for all adult Maine coons, male and female together. Using specific reference values according to gender seems appropriate for Maine coon cats. In HCM the hypertrophy may be symmetrical (septum and free wall equally effected) or asymmetrical (the sep- tum more hypertrophied than the free wall or vice versa) Asymmetrical septal hypertrophy in cats has been defined by one author as septal to free wall thickness ratio ≥ 1,1 [6]. Reports in the literature differ on whether the most common form of HCM among cats is symmetrical or asymmetrical hypertrophy. These differences may to some degree depend on different definitions of asymmetrical septal hypertrophy and methods of measuring the ven- tricular wall, and determining the ratio between dimen- sion of septum and free wall, but may also be caused by different phenotypic expressions between different popu- lations of cats. In our study, all cats but one who had hypertrophy of the left ventricular wall, had more promi- nent hypertrophy of septum than of the free wall. That dif- fers from reported findings in a colony of Maine coon cats with familial HCM [1], where Kittleson reported that wall thickening is often localized primarily to the papillary muscles and the posteriolateral free wall, between the papillary muscles. This differs from the human form of familial HCM wich mostly affects the interventricular sep- tum [24], and other reports of feline HCM where asym- metrical septal hypertrophy or symmetric ventricular hypertrophy is the most common form [2,5,19,25-27]. Whether or not this disparity is caused by mutations in different genes, is presently not known. Page 4 of 6 (page number not for citation purposes)