Disease
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Key to abbreviations
2D-STE Two-dimensional speckle tracking echocardiography AAT Aortic outflow acceleration time
AGp Aortic outflow peak velocity pressure gradient AVp Aortic outflow peak velocity
BW Body weight
CS Peak circumferential strain
CSg Global peak circumferential strain CSR Peak circumferential systolic strain rate CSR-A Peak circumferential late diastolic strain rate
CSR-Ag Global peak circumferential late diastolic strain rate CSR-E Peak circumferential early diastolic strain rate
CSR-Eg Global peak circumferential early diastolic strain rate CSRg Global peak circumferential systolic strain rate EFM Ejection fraction derived from m-mode
EFste Ejection fraction derived from speckle tracking echocardiography EPSS E point to septal separation
ESVI End systolic volume index FAC Fractional area change FS Fractional shortening
HR Heart rate
IVRT Isovolumic relaxation time
IVS% Percentage thickening of the interventricular septum IVSd Interventricular septal thickness in end diastole LA/Ao The ratio of left atrium and aortic diameter LS Peak longitudinal strain
LSg Global peak longitudinal strain LSR Peak longitudinal systolic strain rate LSR-A Peak longitudinal late diastolic strain rate
LSR-Ag Global peak longitudinal late diastolic strain rate LSR-E Peak longitudinal early diastolic strain rate
LSR-Eg Global peak longitudinal early diastolic strain rate LSRg Global peak longitudinal systolic strain rate LVDd Left ventricular dimension in end-diastole LVDs Left ventricular dimension in end-systole
LVFW% Percentage thickening of the left ventricular free wall LVFWd Left ventricular free wall thickness in end-diastole
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LVFWs Left ventricular free wall thickness in end-systole LVMI Left ventricular mass index
MAvp Peak late mitral inflow velocity ME/A Early and late mitral inflow ratio MEVp Peak early mitral inflow velocity
PEP:ET Pre-ejection time period and ejection time ratio PVp Pulmonary outflow peak velocity
QP-Ao Difference between pulmonary pre-ejection time and aortic pre-ejection time
RS Peak radial strain
RSg Global peak radial strain RSR Peak radial systolic strain rate RSR-A Peak radial late diastolic strain rate
RSR-Ag Global peak radial late diastolic strain rate RSR-E Peak radial early diastolic strain rate
RSR-Eg Global peak radial early diastolic strain rate RSRg Global peak radial systolic strain rate
RT-cε Range of the 6 segment time to peak circumferential strain RT-lε Range of the 6 segment time to peak longitudinal strain RT-rε Range of the 6 segment time to peak radial strain RT-ε Range of the 6 segment time to peak strain
SDT-cε Standard deviation of the 6 segment time to peak circumferential strain SDT-lε Standard deviation of the 6 segment time to peak longitudinal strain SDT-rε Standard deviation of the 6 segment time to peak radial strain SDT-ε Standard deviation of the 6 segment time to peak strain Sg Global peak strain
SH-cε Circumferential segmental heterogeneity SH-lε Longitudinal segmental heterogeneity SH-rε Radial segmental heterogeneity
SH-ε Segmental heterogeneity SR Peak systolic strain rate SR-A Peak late diastolic strain rate
SR-Ag Global peak late diastolic strain rate SR-E Peak early diastolic strain rate
SR-Eg Global peak early diastolic strain rate SRg Global peak strain rate
SV Stroke volume
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TAVp Peak late tricuspid inflow velocity TE/A Early and late tricuspid inflow ratio Tei index Myocardial performance index TEVp Peak early tricuspid inflow velocity TH-ε Transmural heterogeneity
Vcf Velocity of circumferential fiber shortening
ε Langarian strain
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Comparison between Conventional and Two-Dimensional Speckle Tracking Echocardiography in Clinically Healthy Cats and Cats Affected with Lower Respiratory Tract Disease
Yueh-Lun Hsu, Hui-Pi Huang
Department of Veterinary Medicine, National Taiwan University, Taipei, Taiwan Abstract
Feline lower respiratory tract disease (LRTD), also known as asthma, is a syndrome characterized by acute bronchoconstriction, the clinical sigh of which is similar to cardiac failure. The aim of this study was to analysis left ventricular deformation change by application 2D-STE in cat with LRTD.
Fifty-six cats were included in this study. These cats were further categorized to clinically healthy control (n=34) and LRTD (n=22). Physical examinations, blood pressure measurement, routine blood examinations, chest radiographs, conventional echocardiography and 2D-STE were carried out in all cats in both groups.
Indices of conventional echocardiography were not different between two groups, but impaired systolic and diastolic function was detected in LRTD based on using circumferential/longitudinal strain of 2D-STE. Decreased transmural heterogeneity and ejection fraction/fractional area change those were derived from 2D-STE were also found. No difference of synchrony and heterogeneity were detected between two groups.
The deformation changes mainly affected the segments of left ventricle free wall.
In the cats with LRTD, no change of stroke volume and end diastolic dimension were detected, no pulmonary to tricuspid regurgitation were identified either. These
findings suggested that even in a very mild degree of lower respiratory tract disease the function of left ventricle could be affected.
Key words: cat, left ventricle, lower respiratory tract disease, two-dimensional speckle tracking echocardiography
_____________________________________________________________________
Part of the study was presented as an abstract in the 21th European College of Veterinary Internal Medicine Congress, Seville, Spain. Sep. 8-10, 2011.
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Introduction
The impact of respiratory diseases on cardiac function has been intensively discussed in past fifty years in human patients. Changes in the volume or pressure of right ventricular may affect the condition of systole and diastole in left ventricle via pericardium and interventricular septum (ventricular interdependence) [1-5].
Feline lower respiratory tract disease (LRTD), also known as asthma, is a syndrome characterized by acute bronchoconstriction that can lead to cough and respiratory distress [6]. These clinical signs are also consistent with left sided heart failure in cats [7]. Study regarding cardiac function in association with respiratory diseases in cats is very limited. The aims of this study were to assess cardiac function and myocardial deformation in cats with lower respiratory tract using different modalities of echocardiography.
Material and Method Animals
Fifty-six client-owned cats admitted to the National Taiwan University
Veterinary Hospital during 2010-2012 were included for this perspective study. These cats were further categorized into groups of clinically healthy control and LRTD. All cats underwent a complete physical examination, blood pressure measurements, routine blood work (complete blood counts and biochemical profiles) examinations, chest radiography, conventional echocardiography, and two-dimensional
speckle-tracking echocardiography (2D-STE).
Clinically healthy cats (control)
Among these 56 cats, 34 that were clinically healthy cats for annual wellness recheck and without history of respiratory signs were deemed as healthy controls in
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this study. The mean age was 3.1 ± 2.2 years (range 6 months to 8 years old), with a mean body weight of 4.3 ± 1.3 kg; 18 were males, and 16 were females. Breeds represented in this group were 19 Domestic Short-hairs, 6 American Short-hairs, 7 Persians, 1 Bengal cat and 1 British Blue.
Cats with lower respiratory tract disease (LRTD)
The remaining 22 cats that were presented with intermittent to continuous respiratory signs (cough, respiratory distress and open mouth breathing) were categorized into LRTD group. The inclusion criteria of LRTD in this group were based on clinical signs, chest radiographs [8, 9], and results of provocative barometric whole-body plethysmography test. The mean age of this group was 5.0 ± 3.4 (range of 5 month to 12 years). A mean body weight was 4.5 ± 0.9 kg, 12 were males, and 10 were females. The represented breeds were 12 Domestic short-hairs, 3 each of Persians and Himalayas, 2 American short-hairs, and 1 each of English short-haired and Siamese crossed bred
Clinical evaluation
Conventional echocardiography
Ultrasound examinations were performed without sedation with gentle restrain in lateral recumbency [10].
Indices of left ventricle was including left ventricular diastolic dimension
(LVDd), left ventricular systolic dimension (LVDs), the ratio of Left atrium and aortic diameter (LA/Ao), interventricular septal thickness in diastole (IVSd), left ventricular free wall thickness in diastole (LVFWd), and left ventricular mass index (LVMI) were obtained from the standard views [11, 12].
Parameters of left ventricular systolic function were derived from M-mode, including end-posterior E point to septal separation (EPSS), percentage thickening of
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the interventricular septum (IVS%), percentage thickening of the left ventricular free wall(LVFW%), fractional shortening (FS), ejection fraction by M-mode (EFM);
parameters were derived from pulse-wave Doppler including velocity of
circumferential fiber shortening (Vcf), the ratio of pre-ejection period an ejectiontime (PEP:ET), Aortic outflow acceleration time (AAT), including aortic outflow peak velocity (AVp), aortic outflow peak velocity pressure gradient (AGp), pulmonary outflow peak velocity (PVp), stroke volume (SV), and derived from B mode, including end systolic volume index (ESVI) were obtained from the standard views [12-21].
Parameters of left ventricular diastolic function were including mitral early and late diastolic inflow velocity (MEVp, MAVp), and tricuspid early and late diastolic inflow velocity (TEVp, TAVp), the ratio between MEVp and MAVp (ME/A), the ratio between TEVp and TAVp (TE/A), isovolumic relaxation time (IVRT), and myocardial performance index (Tei index) were obtained from the standard views [14, 22, 23].
Interventricular synchrony, the difference between pulmonary pre-ejection time and aortic pre-ejection time (QP-Ao) was obtained from standard views [24].
Two-dimensional speckle tracking echocardiography Measurement regional strain and strain rate
Indices of left ventricular longitudinal and circumferential/radial/longitudinal strain and strain rates were obtained using right parasternal apical 4-chamber and short axis views, respectively. All images were acquired in cine loops of 3 cardiac cycles recorded at frame rate of 54-111 frames per seconds, saved in digital format, and analyzed by off-line software (XStrainTM software for MyLabTM50 X Vision).
In quantification of strain and strain, 6 segments (cranio-septum, cranial, lateral, caudal, ventral, and septal) of endocardium and another 6 segments of epicardium for
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epicardial circumferential strain were semi-automatically selected by Aided Heart Segmentation (AHS) for analysis; 6 segments (craniao-septum, cranial, lateral, caudal, ventral, and septal) across endocardium to epicardium were semi-automatically
selected by AHS for radial strain analysis. In left ventricular longitudinal strain and strain rate, 6 segments (basal-septal, mid-septal, apical-septal, apical-lateral,
mid-lateral, basal-lateral) of endocardium were semi-automatically automatically selected by the AHS tool for analysis. Left ventricular ejection volume (EFste) and fraction area change (FAC) were also calculated by modified Simpson’s rule.
The STE indices included in this study were circumferential/radial/longitudinal systolic peak strain (CS/RS/LS), circumferential/radial/longitudinal systolic peak strain rate (CRS/RSR/LSR), circumferential/radial/longitudinal peak early diastolic strain rate (CSR-E/RSR-E/LSR-E) and circumferential/radial/longitudinal peak late diastolic strain rate (CSR-A/RSR-A/LSR-A). The STE off-line analysis was performed by 1 examiner (YLH)
The images without adequate visualization of one or more segments of the endocardium were excluded from this study.
Measurement of synchrony and heterogeneity
Interventricular synchrony, defined as time difference between mean pulmonary and aortic pre-ejection periods (QP-Ao), was calculated based on conventional pulse wave-Doppler. Intraventricular synchrony, defined as the standard deviation of the six segments time to reach peak strain (SDT-ε) at longitudinal (SDT-lε), circumferential (SDT-cε) and radial (SDT- rε) directions, and the range of the six segments time to peak strain (RT-ε) at longitudinal (RT-lε), circumferential (RT-cε) and radial (RT-rε) directions were also calculated. Segmental heterogeneity (SH-ε), defined as the range of the peak strain of the six segments, and transmural heterogeneity (TH-ε), defined as
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the difference strain between endocardium and epicardium were also calculated
Statistical analysis
Continuous data are presented as mean ± SD. Normality was assessed by using Kolmogorov-Smirnov test. Group data of conventional echocardiography (LVMI, IVSd, LFFWd, LVDd, LVDs, LA/Ao; EPSS, IVS%, LVFW%, FS, EFM ; PEP:ET, AAT, AVp, AGp, PVp SV, mitral inflow, tricuspid inflow, IVRT and Tei index; Vcf ) and STE (strain, SR, FAC, EFste)were compared using 2-tailed independent Student t- test. In the event of cohorts of variables without a normal distribution, comparisons were done with Mann-Whitney U test. P<0.05 were considered to be statistically significant.
Results
The demographic information of control and LRTD is listed at Table 1. Gender (P=0.906) and age (P=0.054) were not different between these two groups, heart rate was significantly higher in LRTD (P<0.005, Table 4-6).
Indices of conventional echocardiography
Differences of left ventricular indices, including LVMI, IVSd, LVFWd, LVDd, LVDs and LA/Ao were all not significant (Table 2). Indices derived from M-mode (EPSS, IVS%, LVFW%, FS and EFM), and from pulse-wave Doppler (PEP: ET, AAT, AVp, AGp, PVp SV, mitral inflow, tricuspid inflow, IVRT and Tei index) and Vcf were not different between these 2 groups (Table 3).
Indices derived from myocardial strain
Global CS, CSRg, and CSR-Eg were significantly decreased in LRTD group (Table 4). Global radial strain and strain rate were not different between control and
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LRTD (Table 5). Global LS and LSRg were significantly decreased in LRTD group (Table 6).
EFste and FAC
The EFste and FAC derived from speckle tracking echocardiography were significantly decreased in LRTD (Table 7).
Synchrony and heterogeneity
Indices of ventricular synchrony were not different between control and LRTD (Table 8). Segmental heterogeneity was not different between control and LRTD (Table 8). Circumferential transmural heterogeneity was significantly decreased in LRTD (P=0.034, Table 8).
Discussion
Left sided heart failure and LRTD share similar clinical signs, cough and
respiratory distress. These two conditions cannot be discriminated by the heart rate or absence of cardiac murmurs. Absence of murmur is prevalent in cats with clinical signs of heart failure [25-28]. In this study, indices derived from conventional
echocardiography in control and LRTD were not different. This finding suggests that echocardiography may distinguish LRTD from left sided heart failure if results of physical examination or chest radiographs are not conclusive. Indices of
echocardiography are normal in coughing cats are highly unlikely to be affected with cardiac disease.
Although no difference of indices derived from conventional echocardiography was found between control and LRTD, significantly decreased left ventricular strain in circumferential and longitudinal systole and significantly decreased circumferential
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early diastole were found in this study. Decreased transmural heterogeneity was also found in cats with LRTD. Changes in the volume or pressure of right ventricular may influence the condition of systole and diastole in left ventricle via the pericardium and interventricular septum. In this study, decreasing systolic function in terms of reduces EFste / FAC, also reflected the decreasing transmural heterogeneity in cats with LRTD[29]. The decreasing pattern of our finding was different comparing with the human patients suffering from pulmonary disorders/hypertension [30-32]. Ventricular interdependence has been exhibited in human patients with pulmonary hypertension [33]. Interventricular septum plays an important role in ventricular interdependence.
Impact of pressure gradient between right and left ventricles, pulmonary hypertension resulted from chronic hypoxia and volume expansion of right ventricle may indirectly affect compliance of interventricular septum and left ventricular deformation [2, 3, 5, 33-35]. Left ventricular dyssynchrony may develop eventually [36]. However, in this study no ventricular dyssynchrony and segmental heterogeneity was detected in LRTD. The affected segments were mainly on the free wall of left ventricle. The mechanism of the discrepancies was not clear. Nevertheless, no pulmonary or tricuspid regurgitation was detected in our cases. In addition, the end diastole
dimension and stroke volume were not different from the control. This suggested that pulmonary hypertension had not yet developed in these cases. Impact of pressure or volume right ventricle on the interventricular septum and left ventricle might be subtle at this stage. Only decreased myocardial strain and EFste/FAC derived from strain were detected. These findings supported that the LS of left ventricle has decreased before decreasing systolic function right ventricle has developed in asthma patients [32].
Longitudinal study is needed to clarify the impact of decreasing strain and strain
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rate in LRTD group and further provide prognostic and diagnostic value in clinical application.
Conclusion
Impaired systolic and diastolic function of left ventricle was developed as mild as the secondary pulmonary hypertension and ventricular interdependence could not be detected by the conventional echocardiography.
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