Cardiomyopathies are a heterogeneous group of disorders that result in structural and functional impairment of cardiac muscle and represent the most common cause of acquired heart disease in cats.1 The World Health Organization has specified hypertrophic, restrictive, dilated, arrhythmogenic right ventricular, and unclassified cardiomyopathies as basic categories of idiopathic heart muscle disease, and all of these have been described in cats.1–7 Diagnosis of cardiomyopathy is made primarily on the basis of measurements of atrial and ventricular size, myocardial thickness, and systolic function by use of standard 2-D and M-mode echocardiography. Conventional Doppler modes provide additional information on diastolic and systolic function based on peak mitral flow velocities during diastole and dynamic abnormalities, such as obstructions of the ventricular outflow tract. However, similar to the situation in human patients, these conventional echocardiographic and Doppler ultrasonographic abnormalities do not appear to be early markers of cardiomyopathy.
A novel ultrasonographic method known as TDI8 is able to detect early myocardial dysfunction for several pathologic conditions, such as hypertrophic and dilated cardiomyopathy in humans,9,10 dogs,11–13 and rabbits.14 This technique also appears promising for the accurate analysis of myocardial function in cats and has already been validated for use in this species.15 However, prospective studies in large populations of healthy cats are required to establish the reference ranges of TDI values for radial and longitudinal motions of the left ventricle.
Therefore, the primary objective of the study reported here was to describe and analyze radial and longitudinal velocities of the annulus of the left atrioventricular valve and LVFW in a large population of healthy cats by use of quantitative 2-D color TDI. Another objective was to study the effects of breed, body weight, sex, and age of cat on these TDI variables. Finally, we intended to determine reference ranges for these myocardial and annular variables.
Materials and Methods
Animals—The study population consisted of healthy cats of various breeds and origins (client-owned pets or breeding animals) that had not been administered medications and did not have a history of heart or respiratory tract disease. Owner consent was obtained for each cat before it was enrolled in the study. The procedures used in this experiment were approved by the Animal Use and Care Committee of the National Veterinary School of Alfort.
All cats were assessed as healthy on the basis of results of a complete physical examination, systemic arterial blood pressure measurement, ECG, and serum biochemical analyses (glucose and creatinine concentrations). In addition, plasma total thyroxine concentrations were measured for cats > 6 years old. Cats with hyperglycemia (reference range, 80 to 120 mg/dL), high serum creatinine concentrations (reference range, 0.5 to 1.5 mg/dL), and high plasma total thyroxine concentrations (reference range, 10 to 50 nmol/L), as well as cats with systemic systolic arterial hypertension (defined as > 160 mm Hg in unstressed catsa), were excluded from the study. Systolic arterial blood pressure was measured indirectly on awake cats by investigators (CCS, VG, and APN) who used a standard Doppler method.b
Conventional echocardiographic and Doppler examinations—Standard transthoracic echocardiography with continuous ECG monitoring was performed by one of the investigators (VC) by use of an ultrasonographic unitc equipped with a 7.5- to 10-MHz phased-array transducer. All conventional ultrasonographic examinations were conducted on awake cats that were gently restrained in a standing position, as described and validated in another study.16 A mean of 3 measurements was obtained for each variable on 3 consecutive cardiac cycles on the same frame. Ventricular measurements were obtained from the right parasternal location (short-axis view) by use of a 2-D–guided M-mode,17 which was in accordance with the recommendations of the American Society of Echocardiography.18 Measurements of the aorta and diameter of the left atrium were obtained by use of a 2-D method.19 Conventional echocardiographic variables were compared with results reported in other studies.2,20 Finally, maximal velocities of aortic and pulmonary flow during systole and maximal velocities of mitral flow during early and late diastole were determined by use of pulsed-wave Doppler techniques. Velocities of aortic and pulmonary flow were recorded by use of the left apical 5-chamber view and right parasternal short-axis view at the level of the aortic valve, respectively. Velocities of mitral flow were determined by use of the left apical 4-chamber view.
Color TDI—The 2-D color TDI examinations were performed in awake cats in a standing position with continuous ECG monitoring by 1 investigator (VC) and by use of the same ultrasonographic unitc used for standard echocardiography. Investigator performance in terms of repeatability and reproducibility has been documented in awake cats.15 Receiving gain of the gray scale was set to optimize clarity of the endocardial and epicardial boundaries of the LVFW during each examination. Off-line measurements of segmental myocardial velocities were obtained from color Doppler images of the LVFW. Real-time color Doppler images were superimposed on the gray scale with a frame rate ≥100 frames/s. Doppler receiving gain was adjusted to maintain optimal color of the myocardium, and Doppler velocity range was set as low as possible to avoid aliasing artifact.
Digital images were obtained, stored, and reviewed later by use of an off-line measuring system.d A 2 × 2-mm sample was used, and a tissue velocity pattern was displayed for each sample location. Three measurements of each myocardial velocity were obtained on 3 consecutive cardiac cycles on the same frame, and the mean value was calculated and used for analysis. Mean heart rate was calculated by use of ECG monitoring during each radial and longitudinal TDI examination from the same 3 cardiac cycles used for the velocity measurements.
Quantification of radial velocities of the left ventricle—Velocities of the LVFW resulting from radial motion of the left ventricle were measured by use of the right parasternal ventricular short-axis view between the 2 papillary muscles, as described elsewhere.15 Measurements were obtained for endocardial and epicardial segments of the LVFW. Simultaneous velocity patterns for the endocardial and epicardial segments were obtained during off-line analysis. Radial velocities of the myocardium were determined during systole, early diastole, and late diastole. Radial MVGs, which were defined as the difference between endocardial and epicardial velocities, were calculated for each phase of the cardiac cycle.21
Quantification of longitudinal velocities of the annulus of the left atrioventricular valve and left ventricle—Velocities of the LVFW that resulted from longitudinal motion of the left ventricle were measured by use of the standard left apical 4-chamber view, as described elsewhere.15 Measurements were obtained for 3 segments (the annulus of the left atrioventricular valve and 2 myocardial segments of the internal midportions of the LVFW [ie, basal and apical segments]). Concurrent velocity patterns for the annular, basal, and apical segments were obtained during off-line analysis. Longitudinal velocities of the annular and myocardial segments were determined during systole, early diastole, and late diastole. Longitudinal MVGs, which were defined as the difference between basal and apical velocities, were then calculated for each phase of the cardiac cycle.21 The value for Em:Ea was also calculated.
Statistical analysis—Data were expressed as mean ± SD. Statistical analyses were performed by use of computer software.e For radial motion, Student paired t tests were used to compare endocardial and epicardial velocities. For longitudinal motion, annular, basal, and apical velocities were compared by use of a repeated-measures ANOVA followed, when necessary, by a post hoc Student t test.
General linear modeling is a statistical method that allows description, explanation, and prediction of the variation of a quantitative variable with respect to quantitative and qualitative variables. It is considered as an extension of the ANOVA.22 The following general linear model was used to study the effect of breed, age, body weight, and sex of cat on echocardiographic and TDI variables:
where Yikjl is the TDI variable of a cat of breedi, agej, body weightk, and sexl; ϵijkl is the residual term of the model; and μis the mean general effect. Reference ranges for TDI variables were established for the 2 predominant breeds of cats and were considered as the mean ± 2 SD.
The Pearson product moment correlation was used to detect correlations between heart rate, age, or body weight and the various velocities (endocardial, epicardial, annular, basal, and apical). The Pearson product moment correlation was also used to detect the correlation between fractional shortening and annular and myocardial velocities during systole for radial and longitudinal motions. Values of P < 0.05 were considered significant.
Results
Animals—One hundred healthy cats of 6 breeds were used in the study (Table 1). Maine Coon (n = 51) and domestic shorthair (31) cats were the 2 predominant breeds represented. Results for standard echocardiographic and Doppler variables for the entire population and for the 2 predominant breeds represented were summarized (Table 2). For the entire population of 100 healthy cats, mean ± SD heart rate and systolic blood pressure were 184 ± 33 beats/min (range, 100 to 261 beats/min) and 139 ± 12 mm Hg (range, 110 to 159 mm Hg), respectively.
Characteristics of 100 healthy cats in which cardiac indices were evaluated by use of TDI.
| Breed | No. of cats | Male | Female | Age (y)* | Body weight (kg)* | ||
|---|---|---|---|---|---|---|---|
| Sexually intact | Castrated | Sexually intact | Castrated | ||||
| Entire population | 100 | 21 | 9 | 51 | 19 | 3.1 ± 2.4 | 4.6 ± 1.2 |
| (0.3–12.0) | (1.0–8.0) | ||||||
| Maine Coon | 51 | 15 | 0 | 36 | 0 | 2.5 ± 1.6 | 5.0 ± 1.2 |
| (0.7–6.5) | (3.0–8.0) | ||||||
| Domestic shorthair | 31 | 3 | 8 | 7 | 13 | 4.4 ± 3.3 | 4.0 ± 1.2 |
| (0.3–12.0) | (1.0–6.5) | ||||||
| Sphynx | 6 | 1 | 0 | 5 | 0 | 1.6 ± 0.9 | 3.4 ± 0.8 |
| (0.7–3.0) | (2.8–5.0) | ||||||
| Chartreux | 6 | 0 | 0 | 0 | 6 | 3.0 ± 1.5 | 4.5 ± 0.7 |
| (1.5–5.5) | (3.5–5.4) | ||||||
| Norwegian | 5 | 2 | 0 | 3 | 0 | 3.3 ± 1.8 | 5.0 ± 0.9 |
| (1.5–6.0) | (4.3–6.4) | ||||||
| British shorthair | 1 | 0 | 1 | 0 | 0 | 1.8 | 6.4 |
Values reported are mean SD (range), except for the British shorthair breed because there was only 1 cat for that breed.
Mean ± SD, minimum, and maximum values for conventional echocardiography and Doppler variables in a population of 100 healthy cats and mean ± SD, minimum, and maximum values and reference ranges* for the 2 predominant breeds (Maine Coon and domestic shorthair cats).
| Variable | Factors with a significant effect† | Entire population (n = 100) | Maine Coon cats (51) | Domestic shorthair cats (31) | |||||
|---|---|---|---|---|---|---|---|---|---|
| Mean ± SD | Minimum–maximum | Mean ± SD | Minimum maximum | Reference range | Mean ± SD | Minimum–maximum | Reference range | ||
| Morphologic characteristics | |||||||||
| Diameter of left atrium: diameter of aorta | NS | 0.9 ± 0.1 | 0.5–1.2 | 0.9 ± 0.1 | 0.5–1.2 | 0.7–1.2 | 0.9 ± 0.1 | 0.7–1.2 | 0.6–1.1 |
| Diameter of left ventricle (mm) | |||||||||
| During diastole | Breed, BW‡ | 15.9 ± 2.3 | 9.7–21.2 | 17.1 ± 1.8 | 13.3–21.2 | 13.6–20.6 | 14.2 ± 2.1 | 9.7–19.4 | 10.1–18.4 |
| During systole | NS | 8.1 ± 1.8 | 4.1–12.7 | 8.8 ± 1.5 | 4.2–12.7 | 5.8–11.7 | 7.2 ± 1.8 | 4.5–11.2 | 3.5–10.8 |
| LVFW (mm) | |||||||||
| During diastole | Breed, BW‡ | 4.3 ± 0.7 | 2.4–5.8 | 4.5 ± 0.6 | 3.8–5.8 | 3.3–5.8 | 3.9 ± 0.6 | 2.4–5.0 | 2.7–5.2 |
| During systole | NS | 7.5 ± 1.1 | 4.2–10.3 | 7.8 ± 1.1 | 4.2–10.0 | 5.5–10.0 | 7.1 ± 1.0 | 5.2–9.0 | 5.1–9.1 |
| Interventricular septum (mm) | |||||||||
| During diastole | Breed§ | 4.6 ± 0.6 | 2.9–5.9 | 4.5 ± 0.7 | 2.9–5.9 | 3.2–5.9 | 4.5 ± 0.6 | 3.2–5.3 | 3.4–5.6 |
| During systole | BW§ | 7.4 ± 1.3 | 4.6–12.1 | 7.7 ± 1.2 | 4.8–12.1 | 5.3–10.0 | 6.9 ± 1.0 | 4.6–8.7 | 5.0–8.8 |
| Interventricular subaortic septum during diastole (mm) | Sex§ | 4.1 ± 0.8 | 2.3–5.7 | 4.1 ± 0.8 | 2.6–5.7 | 2.5–5.7 | 3.9 ± 0.8 | 2.3–5.7 | 1.6–3.8 |
| Diameter of right ventricle during diastole (mm) | Breed, BW and sex§ | 3.0 ± 1.4 | 0.5–6.7 | 2.8 ± 1.2 | 0.8–5.5 | 0.5–5.2 | 3.5 ± 1.5 | 0.9–6.7 | 0.5–6.6 |
| Thickness of right myocardial wall during systole (mm) | NS | 2.7 ± 0.8 | 1.2–4.9 | 2.8 ± 0.9 | 1.2–4.9 | 1.0–4.5 | 2.7 ± 0.6 | 1.3–3.7 | 1.6–3.8 |
| Systolic function | |||||||||
| Fractional shortening (%) | NS | 49 ± 7 | 33–66 | 48 ± 5 | 36–60 | 38–59 | 49 ± 10 | 33–66 | 29–69 |
| Maximal ejection velocity during systole (m/s) | |||||||||
| Aorta | NS | 1.1 ± 0.2 | 0.8–1.9 | 1.1 ± 0.2 | 0.8–1.9 | 0.7–1.6 | 1.1 ± 0.2 | 0.8–1.5 | 0.7–1.4 |
| Pulmonary artery | Breed‡ | 0.9 ± 0.2 | 0.5–1.6 | 1.0 ± 0.2 | 0.7–1.6 | 0.5–1.4 | 0.8 ± 0.2 | 0.5–1.2 | 0.5–1.1 |
| Doppler variables during diastole | |||||||||
| Cats with separate mitral E and A waves∥ | |||||||||
| Mitral E wave (m/s) | Breed§ | 0.7 ± 0.1 | 0.5–1.1 | 0.7 ± 0.1 | 0.5–1.0 | 0.5–0.9 | 0.7 ± 0.1 | 0.5–1.0 | 0.4–0.9 |
| Mitral A wave (m/s) | NS | 0.5 ± 0.1 | 0.3–0.9 | 0.5 ± 0.1 | 0.3–0.8 | 0.3–0.8 | 0.5 ± 0.1 | 0.3–0.7 | 0.3–0.7 |
| Mitral E wave:A wave | NS | 1.5 ± 0.3 | 1.1–2.9 | 1.5 ± 0.4 | 1.1–2.9 | 0.7–2.2 | 1.4 ± 0.3 | 1.1–2.4 | 0.9–2.0 |
| Cats with fusion of mitral E and | NE | ||||||||
| A waves (m/s)¶ | 0.9 ± 0.1 | 0.7–1.1 | 0.8 ± 0.1 | 0.7–0.9 | NE | 1.0 ± 0.1 | 1.0–1.1 | NE | |
| Temporal | |||||||||
| Isovolumic relaxation time (ms) | Breed§ | 43 ± 9 | 34–56 | 55 ± 11 | 38–88 | 34–76 | 50 ± 11 | 29–80 | 29–71 |
| Heart rate during examination (beats/min) | NS | 184 ± 33 | 100–261 | 183 ± 35 | 113–252 | 113–251 | 187 ± 30 | 100–243 | 127–247 |
Reference ranges were calculated as mean ± 2 SD.
Factors (age, body weight, sex, or breed) that had a significant effect on the corresponding variable.
Significant effect at a value of P = 0.01.
Significant effect at a value of P < 0.05.
Represents results for 89 cats in the entire population, 44 Maine Coon cats, and 29 domestic shorthair cats.
Represents results for the wave resulting from fusion of the mitral E and A waves for 11 cats in the entire population, 7 Maine Coon cats, and 2 domestic shorthair cats.
General description of left ventricular motion—All velocity patterns included 1 positive wave (S wave) and 2 negative waves (E and A waves; Figure 1). Velocity patterns also included 2 isovolumic phases (isovolumic contraction phase [end of the A wave to the beginning of the S wave] and isovolumic relaxation phase [end of the S wave to the beginning of the E wave]). Fusion of the E wave and A wave into a single negative diastolic wave was observed in 8 radial TDI examinations and 10 longitudinal TDI examinations. Observed maximal heart rate that permitted identification of the E wave and A wave was 210 beats/min for both the radial and longitudinal motions.
Representative Doppler and ECG recordings of radial (A) and longitudinal (B) velocity patterns obtained for 2 healthy domestic shorthair cats. The radial velocity patterns were obtained by use of the right parasternal short-axis view, and the longitudinal velocity patterns were obtained by use of the left apical 4chamber view. In panel A, simultaneous Doppler recording of the velocities in the endocardium (yellow line) and epicardium (green line) reveals that the endocardial segment is moving more rapidly than the epicardial segment in systole and diastole. In panel B, simultaneous Doppler recording of the velocities in the annulus of the left atrioventricular valve (yellow line) and 2 myocardial segments of the LVFW (basal [green line] and apical [red line]) reveals that the annulus and basal segment are moving more rapidly than the apical segment in systole and diastole. Peak mean velocity of the LVFW is indicated during systole (S wave), early diastole (E wave), and late diastole (A wave).
Citation: American Journal of Veterinary Research 67, 2; 10.2460/ajvr.67.2.250
Radial motion of the left ventricle—Myocardial velocities in the population of 100 cats were significantly higher in the endocardial segments, compared with velocities for the epicardial segments, during systole (P < 0.001), early diastole (P = 0.01), and late diastole (P < 0.001), thus defining significant intramyocardial gradients between the inner and outer layers of the LVFW (Table 3). Mean ± SD radial MVG was 2.2 ± 0.7, 3.3 ± 1.3, and 1.8 ± 0.7 cm/s during systole, early diastole, and late diastole, respectively. The highest radial velocities were recorded during early diastole in the endocardial layers, and the lowest velocities were recorded during late diastole in the epicardial layers.
Mean ± SD, minimum, and maximum values of TDI variables for radial motion in a population of 100 healthy cats and mean ± SD, minimum, and maximum values and reference ranges* for the 2 predominant breeds (Maine Coon and domestic shorthair cats).
| Variable | Factors with a significant effect† | Entire population (n = 100) | Maine Coon cats (51) | Domestic shorthair cats (31) | |||||
|---|---|---|---|---|---|---|---|---|---|
| Mean ± SD | Minimum–maximum | Mean ± SD | Minimum maximum | Reference range | Mean ± SD | Minimum–maximum | Reference range | ||
| Radial velocities and gradient during systole (cm/s) | |||||||||
| S wave | |||||||||
| Endocardium | Breed and sex‡ | 4.7 ± 1.1 | 3.0–8.1 | 5.1 ± 1.1 | 3.3–8.8 | 2.8–7.3 | 4.4 ± 0.9 | 3.2–6.6 | 2.7–6.2 |
| Epicardium | Breed‡ | 2.5 ± 0.9 | 1.1–5.6 | 2.8 ± 0.9 | 1.2–5.6 | 1.0–4.6 | 2.2 ± 0.8 | 1.2–4.9 | 0.5–3.9 |
| Gradient between endocardium and epicardium | Age‡ | 2.2 ± 0.7 | 0.8–3.6 | 2.3 ± 0.8 | 1.0–4.3 | 0.7–3.9 | 2.2 ± 0.6 | 1.1–3.8 | 1.1–3.4 |
| Radial velocities and gradient during diastole | |||||||||
| Cats with separate E and A waves§ | |||||||||
| E wave (cm/s) | |||||||||
| Endocardium | Breed∥ | 5.7 ± 1.5 | 3.5–10.8 | 5.9 ± 1.4 | 3.9–10.4 | 3.0–8.8 | 5.1 ± 1.0 | 3.5–7.0 | 3.0–7.1 |
| Epicardium | NS | 2.4 ± 1.0 | 0.5–4.3 | 2.7 ± 1.0 | 0.5–5.6 | 0.7–4.6 | 1.9 ± 0.7 | 0.8–4.0 | 0.5–3.4 |
| A wave (cm/s) | |||||||||
| Endocardium | NS | 3.0 ± 1.0 | 0.9–5.0 | 3.0 ± 1.0 | 1.3–5.0 | 1.1–5.0 | 3.0 ± 0.9 | 1.2–4.6 | 1.2–4.8 |
| Epicardium | Breed‡ | 1.2 ± 0.6 | 0.2–3.2 | 1.3 ± 0.6 | 0.3–2.8 | NE | 1.0 ± 0.6 | 0.2–2.2 | NE |
| E wave: A wave | |||||||||
| Endocardium | Breed¶ | 2.1 ± 1.2 | 1.1–10.2 | 2.2 ± 0.9 | 1.1–4.5 | NE | 1.8 ± 0.6 | 1.2–4.2 | NE |
| Epicardium | NS | 2.5 ± 1.8 | 1.0–13.0 | 2.4 ± 1.9 | 1.0–13.0 | NE | 2.3 ± 1.2 | 1.1–5.3 | NE |
| Gradient between endocardium and epicardium (cm/s) | |||||||||
| E wave | Breed∥ | 3.3 ± 1.3 | 1.1–8.4 | 3.3 ± 1.1 | 1.1–6.2 | 1.0–5.5 | 3.2 ± 0.8 | 1.8–4.8 | 1.5–4.8 |
| A wave | NS | 1.8 ± 0.7 | 0.2–3.5 | 1.7 ± 0.8 | 0.2–3.4 | 0.2–3.2 | 2.0 ± 0.6 | 0.8–3.5 | 0.8–3.1 |
| Cats with fusion of E and A waves (cm/s)# | |||||||||
| Endocardium | NS | 6.3 ± 1.2 | 5.4–8.7 | 6.1 ± 1.2 | 5.4–8.7 | NE | NA | NA | NA |
| Epicardium | NS | 2.6 ± 0.7 | 1.9–3.8 | 2.7 ± 0.7 | 1.9–3.8 | NE | NA | NA | NA |
| Gradient between endocardium and epicardium | NS | 3.7 ± 1.3 | 2.2–6.0 | 3.4 ± 1.2 | 2.2–6.0 | NE | NA | NA | NA |
| Temporal | |||||||||
| Isovolumic contraction time (ms) | |||||||||
| Endocardium | Breed¶ | 40 ± 10 | 24–73 | 38 ± 9 | 24–64 | 20–57 | 41 ± 7 | 28–54 | 27–54 |
| Epicardium | Breed¶ | 40 ± 10 | 24–73 | 38 ± 9 | 24–64 | 20–57 | 41 ± 7 | 28–54 | 27–54 |
| Isovolumic relaxation time (ms) | |||||||||
| Endocardium | Age‡ | 45 ± 10 | 21–75 | 45 ± 9 | 28–71 | 27–64 | 48 ± 12 | 21–75 | 24–72 |
| Epicardium | NS | 45 ± 10 | 21–75 | 45 ± 9 | 28–71 | 27–64 | 48 ± 12 | 21–75 | 24–72 |
| Heart rate during examination (beats/min) | NS | 174 ± 25 | 122–242 | 172 ± 24 | 123–226 | 125–219 | 175 ± 17 | 139–210 | 142–208 |
Significant effect at a value of P < 0.05.
Represents results for only 92 cats in the entire population, 44 Maine Coon cats, and 31 domestic shorthair cats.
Significant effect at a value of P < 0.001.
Significant effect at a value of P = 0.01.
Represents results for the wave resulting from fusion of the E and A waves for 8 cats in the entire population and 7 Maine Coon cats; none of the domestic shorthair cats had fusion of the E and A waves for this variable.
For the 92 cats in which there was no fusion of the E and A waves, the E wave was consistently higher than the A wave, with a mean E wave-to-A wave ratio of 2.1 and 2.5 for the endocardium and epicardium, respectively. A positive correlation was observed between heart rate and 3 of 6 radial velocities (Table 4). Age was negatively correlated and body weight was positively correlated with 1 radial myocardial velocity. Significant positive correlations were observed between fractional shortening and endocardial (r, 0.37) and epicardial (r, 0.24) velocities during systole.
Correlations between heart rate, age, or body weight and TDI variables for radial and longitudinal motions.
| Correlation variable | Heart rate | Age | Body weight |
|---|---|---|---|
| Radial motion | |||
| S wave | |||
| Endocardium | r, 0.24* | NS | NS |
| Epicardium | NS | r, –0.23* | NS |
| E wave | |||
| Endocardium | r, 0.21* | NS | NS |
| Epicardium | NS | NS | r, 0.21* |
| A wave | |||
| Endocardium | NS | NS | NS |
| Epicardium | r, 0.21* | NS | NS |
| Longitudinal motion | |||
| S wave | |||
| Annular segment | r, 0.23* | NS | r, 0.29* |
| Basal segment | r, 0.21* | NS | r, 0.28* |
| Apical segment | NS | NS | r, 0.30* |
| E wave | |||
| Annular segment | NS | NS | NS |
| Basal segment | NS | NS | NS |
| Apical segment | NS | NS | NS |
| A wave | |||
| Annular segment | NS | NS | NS |
| Basal segment | NS | NS | NS |
| Apical segment | NS | NS | r, 0.27* |
For TDI variables during systole, the entire population of 100 cats was used. For TDI variables during diastole, correlation was assessed in cats in which there were separate E and A waves (92cats for the radial motion and 90 cats for the longitudinal motion).
Significant at a value of P < 0.05.
Longitudinal motion of the left ventricle—Myocardial velocities for the entire population of 100 cats were significantly (P < 0.001) higher in the basal segment, compared with velocities in the apical segment, during both systole and diastole, thus defining a significant intramyocardial gradient in the LVFW from the base to the apex (Table 5). Mean ± SD longitudinal MVG was 2.7 ± 0.8, 3.1 ± 1.4, and 2.1 ± 0.9 cm/s during systole, early diastole, and late diastole, respectively. The highest longitudinal velocities were recorded during early diastole in the basal segment, and the lowest velocities were recorded during late diastole in the apical segment. Basal and annular velocities were similar, except for a significant difference during early diastole.
Mean ± SD, minimum, and maximum values of TDI variables for longitudinal motion in a population of 100 healthy cats and mean ± SD, minimum, and maximum values and reference ranges* for the 2 predominant breeds (Maine Coon and domestic short-hair cats.
| Variable | Factors with a significant effect† | Entire population (n = 100) | Maine Coon cats (51) | Domestic shorthair cats (31) | |||||
|---|---|---|---|---|---|---|---|---|---|
| Mean ± SD | Minimum–maximum | Mean ± SD | Minimum maximum | Reference range | Mean ± SD | Minimum–maximum | Reference range | ||
| Longitudinal velocities and gradients during systole (cm/s) | |||||||||
| S wave | |||||||||
| Annular segment | NS | 4.4 ± 1.3 | 2.2–8.4 | 4.8 ± 1.4 | 2.4–8.4 | 2.0–7.7 | 3.9 ± 1.0 | 2.2–6.7 | 1.9–5.9 |
| Basal segment | NS | 4.5 ± 1.2 | 2.4–8.4 | 4.8 ± 1.3 | 2.4–8.4 | 2.1–7.4 | 4.1 ± 1.0 | 2.5–6.0 | 2.1–6.2 |
| Apical segment | NS | 1.7 ± 0.9 | 0.2–4.5 | 1.9 ± 1.1 | 0.1–4.5 | 0.0–4.0 | 1.5 ± 0.5 | 0.8–3.0 | 0.5–2.6 |
| Gradient between basal and apical segments | NS | 2.7 ± 0.8 | 1.2–5.5 | 2.9 ± 0.9 | 1.3–5.5 | 1.1–4.6 | 2.6 ± 0.7 | 1.2–4.0 | 1.3–3.9 |
| Longitudinal velocities and gradients during diastole | |||||||||
| Cats with separate E and A waves‡ | |||||||||
| E wave (cm/s) | |||||||||
| Annular segment | NS | 5.5 ± 1.6 | 2.6–10.2 | 5.5 ± 1.6 | 2.6–9.9 | 2.4–8.7 | 5.3 ± 1.7 | 3.0–10.2 | 1.8–8.7 |
| Basal segment | NS | 5.8 ± 1.6 | 2.8–9.9 | 5.6 ± 1.5 | 2.8–9.9 | 2.6–8.7 | 5.7 ± 1.9 | 3.2–9.8 | 2.0–9.5 |
| Apical segment | Body weight§ | 2.7 ± 1.2 | 0.5–5.6 | 2.6 ± 1.2 | 0.5–5.6 | 0.2–5.0 | 2.7 ± 1.2 | 0.5–5.6 | 0.3–5.1 |
| A wave (cm/s) | |||||||||
| Annular segment | NS | 2.9 ± 1.3 | 0.3–5.8 | 3.2 ± 1.3 | 0.9–5.5 | 0.7–5.7 | 2.6 ± 1.5 | 0.3–5.8 | 0.0–5.5 |
| Basal segment | NS | 2.9 ± 1.0 | 1.1–5.5 | 3.1 ± 1.0 | 1.3–5.5 | 1.1–5.2 | 2.9 ± 1.1 | 1.3–4.7 | 0.7–5.0 |
| Apical segment | Body weight§ | 0.8 ± 0.6 | 0.2–3.7 | 1.0 ±0.6 | 0.2–3.7 | 0.0–2.3 | 0.7 ± 0.5 | 0.2–1.9 | 0.0–1.7 |
| E wave: A wave | |||||||||
| Annular segment | NS | 2.2 ± 1.1 | 1.0–6.6 | 1.9 ± 0.7 | 1.0–4.6 | NE | 2.5 ± 1.5 | 1.0–6.6 | NE |
| Basal segment | Breed§ | 2.2 ± 0.9 | 1.1–5.8 | 1.9 ± 0.7 | 1.1–4.5 | NE | 2.2 ± 1.0 | 1.4–5.8 | NE |
| Apical segment | Breed§ | 4.3 ± 3.0 | 1.1–17.5 | 3.2 ± 2.0 | 1.1–11.0 | NE | 5.0 ± 3.9 | 1.4–17.5 | NE |
| Gradient between basal and apical segments (cm/s) | |||||||||
| E wave | Breed§ | 3.1 ± 1.4 | 0.3–7.3 | 3.0 ± 1.4 | 1.0–6.4 | 0.3–5.8 | 3.1 ± 1.5 | 0.3–7.3 | 0.0–6.1 |
| A wave | NS | 2.1 ± 0.9 | 0.2–4.4 | 2.2 ± 0.9 | 0.5–4.4 | 0.3–4.0 | 2.1 ± 1.0 | 0.2–4.3 | 0.0–4.2 |
| Cats with fusion of the E and A waves (cm/s)∥ | |||||||||
| Annular segment | NS | 7.6 ± 3.2 | 4.2–11.6 | 6.9 ± 3.1 | 4.2–11.6 | 0.7–13.0 | NA | NA | NA |
| Basal segment | NS | 7.8 ± 3.0 | 4.3–11.7 | 7.4 ± 2.6 | 5.2–11.7 | 2.1–12.7 | NA | NA | NA |
| Apical segment | NS | 2.3 ± 1.5 | 0.3–4.7 | 2.6 ± 1.6 | 0.5–4.7 | 0.0–9.0 | NA | NA | NA |
| Gradient between basal and apical segments | NS | 5.5 ± 2.7 | 2.9–10.5 | 4.8 ± 2.1 | 3.0–8.3 | 0.5–9.0 | NA | NA | NA |
| Temporal | |||||||||
| Isovolumic contraction time (ms) | |||||||||
| Basal segment | NS | 36 ± 9 | 21–71 | 37 ± 10 | 21–71 | 17–56 | 36 ± 8 | 21–52 | 19–52 |
| Apical segment | NS | 36 ± 9 | 21–71 | 37 ± 10 | 21–71 | 17–56 | 36 ± 8 | 21–52 | 19–52 |
| Isovolumic relaxation time (ms) | |||||||||
| Basal segment | NS | 55 ± 12 | 28–90 | 54 ± 11 | 36–88 | 33–75 | 58 ± 12 | 39–90 | 33–82 |
| Apical segment | NS | 55 ± 12 | 28–90 | 54 ± 11 | 36–88 | 33–75 | 58 ± 12 | 39–90 | 33–82 |
| Heart rate during examination (beats/min) | Breed¶ | 173 ± 28 | 105–253 | 170 ± 27 | 125–250 | 116–225 | 173 ± 20 | 105–212 | 134–212 |
Represents results for only 90 cats in the entire population, 46 Maine Coon cats, and 31 domestic shorthair cats.
Significant effect at a value of P < 0.05.
Represents results for the wave resulting from fusion of the E and A waves for 10 cats in the entire population and 5 Maine Coon cats; none of the domestic shorthair cats had fusion of the E and A waves for this variable.
Significant effect at a value of P = 0.01.
For the 90 cats in which fusion of the E wave and A wave was not observed, the E wave was consistently higher than the A wave, with a mean E wave-to-A wave ratio of 2.2 and 4.3 for the basal and apical segments, respectively. Mean ± SD value for Em:Ea was 14.1 ± 3.8 (range, 7.3 to 23.5) in these 90 cats. In the 46 Maine Coon cats in which there was no fusion of the E and A waves, mean Em:Ea was 14.3 ± 3.8 (range, 9.1 to 23.5), with a reference range of 6.8 to 21.8. For the 31 domestic shorthair cats in which there was no fusion of the E and A waves, mean Em:Ea was 14.0 ± 4.3 (range, 7.3 to 23.3), with a reference range of 5.4 to 22.6; these results were similar to those for Maine Coon cats.
A positive correlation was observed between heart rate and 2 longitudinal velocities during systole (in the annular and basal segments; Table 4). Body weight was positively correlated with 3 longitudinal velocities during systole and apical velocity during late diastole. No significant correlation was observed between age and any of the longitudinal velocities, whereas fractional shortening was significantly correlated during systole with annular (r, 0.21), basal (r, 0.22), and apical (r, 0.26) velocities.
Effects of breed, age, body weight, and sex on echocardiographic, Doppler, and TDI variables—Analyses were conducted to detect effects of breed, age, body weight, and sex on conventional echocardiographic, Doppler, and radial and longitudinal TDI variables for the overall population of 100 cats (Tables 2, 3, and 5). Age of cat did not have an effect on any of the 18 conventional echocardiographic or Doppler variables, and sex of cat had an effect on only 2 variables. Similarly, age and sex had an effect on only 3 of 18 radial TDI variables and no effect on any of 23 longitudinal TDI variables. Conversely, breed and body weight had a significant effect on 8 of 18 conventional echocardiographic and Doppler variables. The effect of breed was predominant for 10 radial and 5 longitudinal TDI variables for which a significant effect was detected and included 8 of 10 and 3 of 5 of those variables, respectively (ie, 8/18 radial TDI variables and 3/15 longitudinal diastolic variables). Therefore, we decided to specifically assess the reference ranges for conventional echocardiographic, Doppler, and TDI variables in those 2 breeds that represented the largest number of cats (ie, Maine Coon and domestic shorthair cats), rather than for the entire population of 100 cats. In contrast to its effect on conventional echocardiographic and Doppler variables, body weight had no significant effect on any radial TDI variables and influenced only 2 of 23 longitudinal TDI variables.
Discussion
The main objective of the study reported here was to precisely document velocity patterns of the LVFW for short- and long-axis views and motion of the annulus of the left atrioventricular valve during the entire cardiac cycle in healthy cats and determine reference ranges for these novel ultrasonographic variables. A study15 involving one of the investigators (VC) and the same TDI technique revealed that radial and longitudinal motions of the left ventricle could be quantified by use of TDI in awake cats. That validation study revealed that the repeatability and reproducibility of TDI measurements for all variables, except in the apical myocardium in which the highest coefficients of variation were recorded, were similar to or slightly higher than those for routine echocardiography. The lowest within-day and between-day values for the coefficient of variation were observed in the endocardial segments (8.2% and 6.5% for velocities during systole and early diastole, respectively) and basal segment during early diastole (5.5%). Therefore, the data reported here complete the validation of the TDI technique in cats and, to our knowledge, for the first time provide accurate information on the 2-D color TDI variables in a large population of healthy cats and reference ranges for 2 breeds (Maine Coon and domestic shorthair cats).
Two views were used for the TDI examination in our study. The right parasternal ventricular short-axis view was used to analyze the radial motion of the LVFW, and the left apical 4-chamber view was used to evaluate the longitudinal velocities of the LVFW and annulus of the left atrioventricular valve. Velocities of the LVFW provide information on regional myocardial function resulting from circular and longitudinal myocardial fibers for radial and longitudinal motions, respectively,23 whereas velocities of the annulus of the left atrioventricular valve provide information on global function of the left ventricle in the long-axis view.24–26 It has been reported in humans, with regard to fatality attributable to cardiac disease, that the predictive power for velocity of the annulus of the left atrioventricular valve measured by TDI in early diastole is higher than the predictive power for clinical data and standard echocardiographic measurements. For example, in a study27 involving human patients with various cardiac diseases, the TDI variables, especially Ea and Em:Ea as calculated in the study reported here, were the most powerful predictors of death attributable to cardiac disease during the subsequent 2 years, and the velocities of the annulus of the left atrioventricular valve during systole and diastole were all significantly lower in the nonsurvivors, compared with velocities for the survivors. Early velocity of the annulus of the left atrioventricular valve is a relatively preload-independent variable for determination of left ventricular relaxation,28,29 and the value for Em:Ea can be used to estimate filling pressure of the left ventricle.30–32 Therefore, we can assert that analysis of the longitudinal velocities of the annulus of the left atrioventricular valve associated with the assessment of radial and longitudinal velocities of the LVFW in various segments, as performed in the TDI study reported here, allows relatively complete exploration of left ventricular function.
The TDI radial and longitudinal velocity patterns in the study reported here were similar to those described in healthy awake dogs,33 except that there was fusion of the E and A waves in cats with high heart rates (> 210 beats/min). This wave fusion was not observed in any of 100 healthy awake dogs, probably because the highest heart rate recorded in the dogs was 171 beats/min.
Similar to results in dogs,33 analysis of our data, as expected, clearly revealed that LVFW segments move with differing velocities. There are higher velocities in the endocardium than the epicardium and in the basal myocardial segment than in the apical myocardial segments, thus defining transmural myocardial gradients. These myocardial gradients were calculated, and reference ranges were defined for Maine Coon and domestic shorthair cats. These TDI variables are of particular interest because one of the main limitations of the TDI interest because one of the main limitations of the TDI technique in evaluation of regional myocardial velocities is that velocity values are composed of the intrinsic myocardial velocity added to the whole translational cardiac velocity. Because MVGs are obtained by calculating the difference between the velocities of 2 myocardial segments, the whole translational cardiac motion is canceled, and MVGs are unaffected by the value for the whole translational cardiac velocity.34
Analysis of our results indicated that a positive correlation exists between heart rate and 5 of 15 radial and longitudinal velocities, which is similar to results reported in a validation study of the TDI technique in cats15 and in a population of dogs.33 Another TDI study35 performed on cats by use of the color M-mode technique revealed that heart rate influenced (negatively or positively) some myocardial velocities and velocity gradients to a variable extent and that heart rate was not a significant independent predictor of myocardial indices for any stage of the cardiac cycle. The discrepancy between that study and the study reported here may have been attributable to the fact that fewer cats (n = 18) were used in the former study.
Many studies have indicated the influence of aging on myocardial properties, and TDI studies performed in healthy human subjects have revealed that the velocity patterns of the LVFW differ with age. Age-related TDI changes in the LVFW include an increase of the peak MVG and peak velocity during late diastole and, conversely, a decrease of these indices during the rapid ventricular filling associated with a decrease in myocardial velocities during systole.24,36 This reflects the dominant role of contraction of the left atrium during left ventricular filling and alteration of myocardial properties during systole with increasing age. Results similar to those described in humans were obtained in another study35 performed on cats in which a positive association was detected between age and MVG during late diastole and between age and late LVFW velocities; conversely, a negative association was detected between age and LVFW velocities during systole and between age and LVFW velocities during early diastole.
Similarly, in the study reported here, the S wave was negatively correlated with age in the epicardium, but no association was observed between age and the other 14 velocities for the annulus of the left atrioventricular valve or myocardial segments. Moreover, no effect of age was observed on any longitudinal TDI variables (age affected only 2 radial TDI variables). This lack of a significant effect of age may have been attributable to the fact that 90% of the cats in the study were < 6 years old, which may represent 1 limitation of our study. The only way to correctly document the effect of age on TDI variables would have been to study a population of older healthy cats or to perform a longitudinal TDI study over several years by use of the cats that were included in the study reported here.
A significant but moderate correlation was detected between fractional shortening and all myocardial velocities during systole. This agrees with data obtained from healthy humans, which indicate that a moderate correlation exists between the left ventricular ejection fraction and TDI indices during systole.24
By use of the general linear model, we detected an overall effect of breed on standard echocardiographic and Doppler variables. The breed-dependent response of conventional echocardiographic and Doppler variables has been reported in dogs33,37 but not in cats, and we believe we have determined this for the first time in the study reported here. Similarly, in the entire population of 100 cats, an effect of breed was evident for several TDI variables, similar to results reported in dogs.33 This breed effect implies that reference ranges must be determined for each breed. However, too few cats of the Sphynx (n = 6), Chartreux (6), Norwegian (5), and British shorthair (1) breeds were included in our study. Therefore, TDI reference ranges were only determined for Maine Coon (51) and domestic shorthair (31) cats.
Similar to results reported for dogs,33 the effect of body weight was observed for only 2 of 41 TDI variables, whereas it affected 5 of 11 conventional echocardiographic variables. This was in contrast to the effects seen for breed.
Within the whole population of cats, an effect of sex was detected for 1 TDI (S wave in the endocardium) and 2 conventional echocardiographic variables. However, it is difficult to interpret the meaning of this effect because most of the cats (70%) were females.
The major limitation of our study was that interventricular septal velocities were not recorded and therefore synchrony of the left ventricle could not be analyzed. Such data would have provided more information on normal function of the left ventricle in cats by use of TDI. Moreover, lack of old and geriatric cats and a preponderance of females (particularly because male cats are more commonly affected by hypertrophic cardiomyopathy1,2,5) are additional limitations of our study.
To our knowledge, the study reported here describes for the first time the motion of the left ventricular myocardium and annulus of the left atrioventricular valve in a large population of healthy cats and reveals the heterogeneous ranges of velocity, depending on the site of measurement and breed. The reference ranges provided here are novel indices of myocardial function in cats. They should contribute to the noninvasive assessment of heart dynamics in cats and be used to complete or complement conventional routine echocardiographic examination. Sensitivity, specificity, and clinical relevance of these novel myocardial indices need to be investigated in large populations of animals with cardiac diseases.
| 2-D | 2-Dimensional |
| TDI | Tissue Doppler imaging |
| LVFW | Left ventricular free wall |
| MVG | Myocardial velocity gradient |
| Em | Peak velocity of mitral inflow during early diastole |
| Ea | Peak velocity of the annulus of the left atrioventricular valve |
| S wave | Positive wave during systole of a Doppler recording of cardiac velocity patterns |
| E wave | Negative wave during early diastole of a Doppler recording of cardiac velocity patterns |
| A wave | Negative wave during late diastole of a Doppler recording of cardiac velocity patterns |
Stepien RL. Blood pressure measurement: equipment, methodology and clinical recommendations (abstr), in Proceedings. 22nd Am Coll Vet Intern Med Forum 2004;605–607.
811-BL, Parks Medical Electronics Inc, Aloha, Ore.
Vivid 5, General Electric Medical System, Waukesha, Wis.
Echo Pac 5.4 software for Vivid 5, GE-Vingmed Ultrasound, Waukesha, Wis.
Systat, version 10.0, SPSS Inc, Chicago, Ill.
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