RESULTS

The baseline characteristics of the study animals

In the present study, forty cats were included (22 males, 18 females), with a mean age of 4.91 ± 2.68 years. Scottish Fold (n = 13) and domestic short hair (n = 7) were the most frequently represented breeds, followed by Persian (n = 6). The remaining cats included Maine Coon (n = 5), British Shorthair (n = 3), and mixed breeds (n = 6). Because of the small number of cats in some breed categories, breed-based comparisons were not performed. Mean LV fractional shortening was 43.60 ± 5.9%. The enrolled animals consisted of 40 cats, divided into three groups: Healthy controls (Group 1, n = 15) with no clinical or echocardiographic evidence of heart disease. HCM phenotype with a normal LA/AO ratio (Group 2, n = 13), increased myocardial thickening without LA enlargement. Hypertrophic phenotype (Group 3, n = 12) with myocardial hypertrophy and LA dilation. The most prevalent breeds among cats were Scottish fold (n = 12; 30%), domestic shorthair (n = 7; 17.5%), Persian (n = 6; 15%), Maine Coon (n = 5; 12.5%), British shorthair (n = 3; 7.5%), mixed breeds (n = 6; 15%), and other breeds (n = 1; 2.5%). Other breeds had fewer than two cats. As reported in Table 1.

Parameters | Group 1 (N = 15) | Group 2 (N = 13) | Group 3 (N = 12) | p-value
Age (years) | 5.06 ± 2.27 | 3.65 ± 1.89 | 6.08 ± 3.25 | 0.0768
Body weight (kg) | 3.74 ± 1.22 | 4.46 ± 2.03 | 5.15 ± 1.10 | 0.1039
Male (number (%)) | 5/15 (33.33%) | 6/13 (46.15%) | 11/12 (91.66%) | -
Blood pressure (mmHg) | 138.04 ± 15.34 | 128.34 ± 20.34 | 137.50 ± 5.88 | 0.410
Heart rate (bpm) | 180.93 ± 31.35 | 183.00 ± 29.87 | 154.02 ± 31.21 | 0.0597

Echocardiographic parameters of the study animals

The echocardiographic parameters of all cats are summarized in Table 2. There were no significant differences among groups in aortic diameter (AO), interventricular septal thickness in diastole (IVSd), LVPWd, left ventricular internal dimension in systole (LVIDs), or fractional shortening (FS) (p > 0.05 for all). In contrast, cats in Group 3 demonstrated significantly increased LA diameter, LA/AO ratio, and LA volume compared with healthy controls (Group 1) (p < 0.05), accompanied by a corresponding decrease in LVGLS (p < 0.0001). Furthermore, interventricular septal thickness in systole (IVSs) and left ventricular posterior wall thickness in systole (LVPWs) were markedly higher in Group 3 relative to Group 1 (p < 0.05), consistent with a hypertrophic myocardial phenotype.

Strain analysis

Figures 1–4 show strain echocardiography in healthy cats and cats with HCM. Healthy cats (Group 1) exhibit steep, tightly clustered strain–volume relationships, indicating normal myocardial deformation and preserved ventricular–atrial coupling. Cats with hypertrophic phenotypes and left atrium enlargement (Group 3) show flatter, right-shifted strain–volume curves, consistent with reduced myocardial strain amplitude and progressive chamber dilatation. Figures 1D and 1H show a transition from higher, more uniform, and predominantly positive myocardial work in healthy cats to lower, heterogeneous, and partially negative myocardial work in cats with HCM.

The reference intervals for feline LVGLS are approximately –21% to –37%. Quantitatively, Group 3 cats exhibited significantly lower strain-curve slopes and ratios than controls (p < 0.05), indicating impaired relaxation despite preserved or mildly reduced chamber volumes. The flattened and right-shifted strain–volume curves in Group 3 cats, compared with steep and clustered patterns in healthy cats, indicate impaired deformation-volume coupling. RVLS remained relatively preserved across groups. The correlation between RVLS and LVGLS was modest and not statistically significant (r = 0.26, p = 0.17). This observation is now presented as a notable finding suggesting limited biventricular involvement in early or moderate disease stages.

The Correlations between Echocardiographic Parameters

Spearman correlation analysis between strain parameters and conventional echocardiographic indices is presented in Figure 5. LVGLS showed a moderate positive correlation with radial strain (r = 0.46) and FS (r = 0.34), indicating that myocardial longitudinal deformation is moderately associated with circumferential and radial contractility as well as global systolic performance. Conversely, LVGLS demonstrated weak or negligible correlations with interventricular septal thickness in systole (IVSs), LVPWs, and mitral inflow E/A ratio (r = –0.01, 0.06, and –0.24, respectively), suggesting that strain-derived systolic indices are relatively independent of wall thickness and diastolic filling patterns. Right ventricular strain (RVS) correlated weakly with LVGLS (r = 0.22) and FS (r = 0.35), while LARS demonstrated mild to moderate inverse correlations with indices of left ventricular hypertrophy, including IVSs (r = –0.43) and LVPWs (r = –0.46). These findings imply that increasing wall thickness is associated with reduced atrial compliance and reservoir function. However, LARS did not correlate with conventional diastolic indices (E/A ratio, r = 0.05). Collectively, these correlations highlight the complementary relationship between deformation parameters and conventional echocardiographic measures, underscoring the utility of strain imaging in assessing subclinical myocardial and atrial dysfunction in feline cardiomyopathy.

Parameters | Group 1 (N = 15) | Group 2 (N = 13) | Group 3 (N = 12) | p-value
LA (cm) | 1.17 ± 0.15* | 1.19 ± 0.19 | 1.55 ± 0.55* | 0.0223
LA/AO ratio | 1.40 ± 0.12** | 1.40 ± 0.09## | 1.85 ± 0.48**## | 0.0003
MPA/AO ratio | 0.98 ± 0.04 | 1.0 ± 0.08 | 1.06 ± 0.22 | 0.4403
IVSd (cm) | 0.47 ± 0.11 | 0.53 ± 0.15 | 0.61 ± 0.18 | 0.0688
LVPWd (cm) | 0.49 ± 0.11 | 0.51 ± 0.10 | 0.59 ± 0.13 | 0.0591
LVIDd (cm) | 1.35 ± 0.27 | 1.34 ± 0.23 | 1.52 ± 0.24 | 0.1617
IVSs (cm) | 0.57 ± 0.11** | 0.64 ± 0.17 | 0.78 ± 0.16** | 0.0054
LVPWs (cm) | 0.50 ± 0.11** | 0.59 ± 0.15 | 0.69 ± 0.15** | 0.0047
LVIDs (cm) | 0.83 ± 0.23 | 0.77 ± 0.16 | 0.86 ± 0.15 | 0.4895
LV FS (%) | 38.24 ± 6.98 | 44.07 ± 7.60 | 43.69 ± 5.92 | 0.0694
MV E/A ratio | 0.93 ± 0.15 | 0.90 ± 0.19 | 0.89 ± 0.21 | 0.8185
TAPSE (cm) | 0.44 ± 0.12 | 0.34 ± 0.10 | 0.41 ± 0.11 | 0.1907
LA volume (ml) | 1.0 ± 0.29* | 1.37 ± 0.86 | 1.89 ± 0.76* | 0.0148
LA FS (%) | 54.25 ± 11.27 | 49.59 ± 13.10 | 41.50 ± 13.11 | 0.0706
LARS (%) | 32.79 ± 11.09* | 24.35 ± 7.19 | 20.28 ± 4.67* | 0.0405
LV GLS-AV (%) | –22.09 ± 3.39**† | –14.24 ± 4.62† | –11.95 ± 4.93** | <0.0001
RV LS-AV (%) | –19.55 ± 4.15 | –17.38 ± 5.70 | –15.42 ± 2.84 | 0.2674
Circumferential Strain (%) | –27.92 ± 5.97† | –18.62 ± 7.56† | –24.17 ± 2.62 | 0.0155