Background: The cardiac myosin binding protein C gene is mutated in Maine Coon (MC) cats with familial hypertrophic cardiomyopathy.
Hypotheses: Early diastolic mitral annular velocity is incrementally reduced from normal cats to MC cats with only an abnormal genotype to MC cats with abnormal genotype and hypertrophy.
Animals:Group 1 consisted of 6 normal domestic shorthair cats, group 2 of 6 MC cats with abnormal genotype but no hypertrophy, and group 3 of 15 MC cats with hypertrophy and abnormal genotype.
Methods:The genotype and echocardiographic phenotype of cats were determined, and the cats were divided into the 3 groups. Tissue Doppler imaging (TDI) of the lateral mitral annulus from the left apical 4-chamber view was performed. Five nonconsecutive measurements of early diastolic mitral annular velocity (EM) or summated early and late diastolic velocity (EAsum) and heart rate were averaged.
Results:There was an ordered reduction in Em-EAsum as group number increased (group 1, range 9.7–14.7 cm/s; group 2, range 7.5–13.2 cm/s; group 3, range 4.5–14.1 cm/s; P= .001). Using the lower prediction limit for normal Em-EAsum, the proportion of cats with normal Em-EAsum decreased as the group number increased (P= .001). However, Em-EAsum was reduced in only 3 of 6 cats in group 2.
Conclusion: The incremental reduction of Em-EAsum as group severity increased indicates that diastolic dysfunction is an early abnormality that occurs before hypertrophy development. TDI measurement of Em or EAsum of the lateral mitral annulus is an insensitive screening test for identification of phenotypically normal, genotypically affected cats.