What is the recommended HCM screening protocol for Maine Coons including echocardiographic criteria?

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Maine Coon HCM screening combines genetic testing with serial echocardiography, as genetic tests alone do not identify all affected cats. Echocardiography remains the only viable means to breed screen cats regardless of genotype, because known disease-causing mutations such as A31P do not account for all cases of hypertrophic cardiomyopathy (HCM) in the breed. 5 Genetic testing for the A31P mutation in cardiac myosin binding protein C (MYBPC3) stratifies cardiac death risk but does not replace echocardiographic phenotyping. Cats homozygous for A31P have an 80% prevalence of HCM and a 48% rate of cardiac death during follow-up, compared to significantly lower rates in heterozygous and wild-type cats. 3 Heterozygous cats do not always show left ventricular (LV) hypertrophy, but the prevalence of hypertrophy increases with age, making serial echocardiographic monitoring essential in this genotype group. 4 Echocardiographic diagnosis of HCM is based on subjective impression supported by measurements — measurements alone are not diagnostic. Assessment of cardiac chamber size and wall thickness should be interpreted alongside the overall echocardiographic picture and other supportive findings. 5 Body weight-normalized measurements are recommended because heart size in normal cats is dependent on body weight, and allometric scaling is the most accurate normalization method. 5 Speckle tracking echocardiography adds diagnostic value in preclinical and equivocal cases. The combination of LV mass, mitral annular plane systolic excursion of the free wall (MAPSE FW), and LV internal diameter in diastole (LVIDd) shows the best association with an HCM diagnosis. This combined model is particularly useful when hypertrophy is not obvious, such as in equivocal cases or cats with a family history of HCM. 4 Longitudinal strain and MAPSE alongside LV mass are additional tools that can aid identification of HCM or improve monitoring beyond wall thickness alone. 4 ProANP (atrial natriuret