Page 63 - Feline Cardiology

58 Section B: Diagnostic Testing

Table 7.1. Normal feline M-mode echocardiographic measurements

Parameter Moïse et al. Jacobs and Fox et al. Koffas et al. Chetboul Adin and Drourr et al.
Knight(a) 1.40 ± 0.13 1.49 ± 0.22 et al. Diley-Poston (Maine coon)

1.54 ± 0.16
1.51 ± 0.21
1.89 ± 0.23
1.59 ± 0.19
LVIDd (cm)
1.85 ± 0.21
Diagnostic Testing LVIDs (cm) 0.69 ± 0.22 0.80 ± 0.14 ±0.81 ± 0.16 0.83 ± 0.22 0.81 ± 0.18 0.75 ± 0.19 0.89 ± 0.2
0.94 ± 0.11
0.95 ± 0.11
–
0.95 ± 0.15
0.95 ± 0.14
Ao (cm)
1.12 ± 0.13
1.21 ± 0.18
1.03 ± 0.14
1.23 ± 0.14
LA (cm)
–
1.37 ± 0.17
1.13 ± 0.17
1.20 ± 0.19
1.23 ± 0.16
1.29 ± 0.23
0.9 ± 0.1
1.10 ± 0.18
LA/Ao
–
1.30 ± 0.17
0.4 ± 0.07
IVSd (cm)
0.38 ± 0.09
0.43 ± 0.07
0.41 ± 0.07
0.46 ± 0.05
0.33 ± 0.06
0.35 ± 0.08
LVFWd (cm) 0.50 ± 0.07 0.31 ± 0.04 0.36 ± 0.05 0.38 ± 0.08 0.46 ± 0.06 0.45 ± 0.08 0.43 ± 0.06
IVSs (cm) 0.76 ± 0.12 0.58 ± 0.06 – 0.64 ± 0.12 0.74 ± 0.13 – 0.75 ± 0.13
LVFWs (cm) 0.78 ± 0.10 0.68 ± 0.07 – 0.68 ± 0.11 0.75 ± 0.11 – 0.8 ± 0.11
EPSS (cm) 0.04 ± 0.07 0.02 ± 0.09 – – – – –
RVDd (cm) 0.54 ± 0.10 0.60 ± 0.15 0.50 ± 0.21 – 0.3 ± 0.14 – –
HR (bpm) 182 ± 22 194 ± 23 245 ± 36 150 ± 26 184 ± 33 – –
Body weight (kg) 4.3 ± 0.05 – 3.88 ± 1.17 4.56 ± 0.8 4.6 ± 1.2 – 5.5 ± 1.33
Age (yr) – 4.11 ± 1.05 3.36 ± 3.15 6.9 ± 3.5 3.1 ± 2.4 4.7 ± 3.7 –
LVIDd = left ventricular internal dimension during diastole; LVIDs = left ventricular internal dimension during systole; Ao = aortic
diameter; LA = left atrial diameter; IVSd = interventricular septum diameter during diastole; LVFWd = left ventricular free wall
diameter during diastole; IVSs = interventricular septum diameter during systole; LVFWs = left ventricular free wall diameter during
systole; EPSS = E point to septal separation; RVDd = right ventricular internal diameter during diastole; HR = heart rate.
normovolemic cat and suggests the presence of HCM or (excitement, hyperthyroidism, medications, sedatives/
secondary left ventricular hypertrophy (i.e., systemic anesthetics, etc.), intravascular volume (hydration
hypertension). Some clinicians use a more stringent status), blood viscosity (anemia, polycythemia), and
classification and define left ventricular hypertrophy as blood pressure. The left ventricular shortening fraction
being when the walls measure greater than 0.55 cm in (SF% or FS%) is the most commonly used echocardio-
thickness (Wagner et al. 2010). Breed-specific differ- graphic index of systolic function in veterinary medicine.
ences do not appear to be significant in cats compared It is calculated using the equation: SF% = [(LVIDd-
to dogs because there is much less body size variation LVIDs)/LVIDd] × 100. In this formula, LVIDd is the left
between breeds; however, one group has reported several ventricular internal dimension during diastole and the
M-mode echocardiographic parameters for Maine coon LVIDs is the left ventricular internal dimension during
cats (Drourr et al. 2005). Not surprisingly, the normal systole. The SF% increases with improved contractility,
cardiac dimensions are increased in this breed of physi- increased preload, or decreased afterload. The normal
cally large cats compared to the smaller feline breeds range in cats is 35–55%. Hypertrophic cardiomyopathy
(Table 7.1). After measurements are completed, the patients are said to have an elevated SF% due to a smaller
heart should be assessed subjectively in real time for ventricular luminal diameter, but many cases with mild
abnormalities in chamber size, wall thickness and hypertrophy and/or regional, nondiffuse hypertrophy
motion, valve morphology and valve. may have a normal SF%. Therefore, SF% cannot be
Systolic dysfunction, the hallmark of dilated cardio- used for ruling in or ruling out hypertrophic cardiomy-
myopathy, is now observed relatively uncommonly in opathy. The end-systolic dimension is also a marker
cats, a species that most frequently develops diastolic of systolic function, which correlates in an inverse
abnormalities. However, it is also important to evaluate pattern with systolic function; intuitively, as LV systolic
systolic function by echocardiography. Systolic perfor- function decreases, LV end-systolic diameter increases.
mance can be assessed by several different echocardio- Additionally, the EPSS dimension increases with
graphic measurements, all of which are affected by reduced systolic function. Normally there is no or very
loading conditions. This means that echocardiographic little separation; however, as the left ventricular ejection
measurements must be interpreted with consideration fraction—which is the 3-dimensional equivalent of
given to factors that may increase or decrease heart rate SF%—decreases, the EPSS increases.