Tissue Doppler Imaging and Two-Dimensional Speckle Tracking of Left Ventricular Function in Healthy Horses After Clenbuterol Application

The cardiac effects of high dosages of the ß²-adrenergic agent clenbuterol have been the focus of several histological, biochemical and echocardiographic studies in the past. Possible effects of a therapeutic dosage on myocardial contractility and velocities have not been evaluated using tissue Doppler imaging (TDI) and two-dimensional speckle tracking (2DST) in equine medicine. Twenty-five healthy horses were treated over 14 days with clenbuterol in a normal dosage (0.8 μg/kg every 12 hours). Before and after the treatment, an echocardiographic examination was performed using B-mode, M-mode, color flow Doppler, and tissue Doppler imaging (TDI). In all horses, the radial and circumferential myocardial functions were recorded in the right parasternal short-axis view (SAX). Pulsed-wave (PW) and color TDI were used for evaluation of peak and mean myocardial velocities; myocardial deformation was documented in 2DST. An improvement of diastolic function after clenbuterol treatment was demonstrated by a significant increase of the early diastolic radial wall motion velocity (E_m) in all myocardial sections except the right ventricular free wall (RVFW) in TDI, as well as an increase of the E/A quotient in the left ventricular free wall (LVFW) and the interventricular septum (IVS). Shortened time intervals, in particular in the LVFW and a tendency of increase of all deformation parameters showed improved relaxation characteristics of the cardiac muscle after treatment. The results can be interpreted as beginning physiologic cardiac hypertrophy due to clenbuterol treatment. No signs of increased rigidity or reduced compliance of the heart muscle could be found at the applied dosage. This study demonstrates the sensitivity of TDI and 2DST in equine cardiology to detect myocardial remodeling before the appearance of obvious findings in conventional echocardiographic techniques. This technique can be used to detect pharmacologic effects on myocardial function.     

Quantitative Analysis of Stress Echocardiograms in Healthy Horses with 2‐Dimensional (2D) Echocardiography,Anatomical M‐Mode,Tissue Doppler Imaging,and 2D Speckle Tracking

Background: Stress echocardiography is used to diagnose myocardial dysfunction in horses, but current methods are not well standardized. The influence of heart rate (HR) on measurements is largely unknown. Objectives: To investigate the use of 2‐dimensional echocardiography (2DE), anatomical M‐mode (AMM), tissue Doppler imaging (TDI), and 2D speckle tracking (2DST) at rest and after exercise for quantification of regional and global left‐ventricular (LV) function. Animals: Five athletic Warmblood horses; 11.6 ± 3.6 years; 529 ± 48 kg. Methods: Prospective study. Three separate echocardiographic examinations were performed before (baseline) and over 5 minutes after treadmill exercise with 2DE (1st, short‐axis view; 2nd, long‐axis view) and pulsed‐wave TDI (3rd examination). Offline analyses were performed at baseline and after exercise at HR 120, 110, 100, 90, and 80 minute^?1. Global and segmental measurements were compared by analysis of variance. Results: Quantitative analyses of stress echocardiograms were feasible in all horses. None of the AMM indices changed significantly after exercise. Stroke volume and ejection fraction by 2DE and strain by 2DST decreased, whereas strain rate by 2DST increased significantly at HR > 100 minute^?1. TDI analyses were technically difficult and provided little additional information. Conclusions and Clinical Importance: Volumetric indices by 2DE and strain and strain rate by 2DST are applicable for quantitative assessment of stress echocardiograms. In healthy horses, they are significantly altered at a HR > 100 minute^?1 and need to be evaluated in view of the instantaneous HR. Further investigations are needed to define the clinical value of stress echocardiography in horses with cardiac disease.     

Evaluation of Right Ventricular Myocardial Function in Healthy Horses With Recurrent Airway Obstruction Using Tissue Doppler Imaging

It has been described in humans that chronic obstructive bronchitis leads to pathologic changes, especially in the right ventricular myocardium due to hypoxia, which can be assessed by tissue Doppler imaging (TDI). In our study, different TDI techniques, that is, pulsed-wave TDI and color TDI, were evaluated for applicability in different scan planes (apical long-axis view and short-axis view) for the analysis of right ventricular myocardial function in six healthy horses (control) and six horses affected with recurrent airway obstruction (RAO) (RAO group). Tissue Doppler imaging was applicable to all scan planes described. Myocardial movement directions in general and the absolute values of TDI parameters were assessable. Significantly reduced early diastolic filling velocities (E), elevated late diastolic filling velocities (A), thereby decreased E/A quotient, prolonged electromechanical coupling periods between electrocardiograph Q-wave and maximal velocities, and compensatory elevated systolic strain as well as diminished displacement could be observed in horses with RAO compared with the control group. To conclude, equine right ventricular myocardial function is assessable by TDI. Significant changes of right ventricular myocardial function could be demonstrated by TDI in horses with RAO compared with matched healthy controls. The hypothesis that RAO potentially leads to right ventricular dysfunction detectable by TDI before conventional echocardiography changes are evident is supported by this explorative study.     

Assessment of regional systolic and diastolic myocardial function using tissue Doppler and strain imaging in dogs with dilated cardiomyopathy

BACKGROUND: Tissue Doppler Imaging (TDI) or strain (St) imaging could provide sensitive indices for early detection and treatment follow-up of canine dilated cardiomyopathy (DCM). Analysis of TDI and St features in dogs with overt DCM is a prerequisite before using these new criteria in prospective screenings of predisposed families or in clinical trials. HYPOTHESIS: Radial and longitudinal right and left myocardial motion, assessed by TDI and St variables, is altered in dogs with DCM. ANIMALS: Case records for 26 dogs; 14 with DCM and 12 healthy controls of comparable age and weight were reviewed. METHODS: A retrospective analysis was conducted of conventional echocardiography, 2-dimensional color TDI, and St imaging data. RESULTS: The DCM group was characterized by decreases in radial and longitudinal systolic velocity gradients of the left ventricular free wall (LVFW), radial and longitudinal absolute values of peak systolic St of the LVFW, and longitudinal systolic right ventricular (RV) velocities (all P < .001 versus control) associated with longitudinal postsystolic contraction waves in 7/14 dogs. Early diastolic LVFW velocities also were decreased for longitudinal (P < .01) and radial (P < .05) motions. All radial LVFW, longitudinal basal LVFW, and RV systolic velocities were negatively correlated with heart rate (P < .01). CONCLUSIONS AND CLINICAL IMPORTANCE: LV contractility along both the short and long axes is impaired in dogs with spontaneous DCM, as is systolic RV and diastolic LVFW function. These myocardial alterations are associated with an inverse force-frequency relationship. Studies now are needed to determine the comparative sensitivity of TDI and St variables for the early detection of canine DCM.     

Tissue Doppler assessment of diastolic and systolic alterations of radial and longitudinal left ventricular motions in Golden Retrievers during the preclinical phase of cardiomyopathy associated with muscular dystrophy

OBJECTIVE: To quantify radial and longitudinal left ventricular free wall (LVFW) velocities in dogs during the preclinical phase of Golden Retriever muscular dystrophy (GRMD)-associated cardiomyopathy by use of tissue Doppler imaging (TDI). ANIMALS: 9 dogs with GRMD and 6 healthy control dogs. PROCEDURE: All dogs (< 3 years old) were examined via conventional echocardiography and 2-dimensional color TDI. Myocardial velocities in the LVFW were recorded from right parasternal ventricular short-axis (radial motion) and left apical 4-chamber (longitudinal motion) views. Cardiac assessments via TDI included maximal systolic and early and late diastolic LVFW velocities in the endocardial and epicardial layers (for radial motion) and in the basal and apical segments (for longitudinal motion) (for longitudinal motion), RESULTS:-No notable ventricular dilatation or alteration of inotropism was detected in dogs with GRMD via conventional echocardiography. Compared with healthy dogs, endocardial velocities were significantly decreased in dogs with GRMD, resulting in marked decreases in radial myocardial velocity gradients during systole and early and late diastole. Similarly, basal and apical velocities were significantly decreased in systole and the former also in early diastole, resulting in significant decreases in the 2 corresponding longitudinal myocardial velocity gradients. The radial epicardial and longitudinal late diastolic velocities were comparable in the 2 groups. CONCLUSION AND CLINICAL RELEVANCE: Results indicated that GRMD-associated cardiomyopathy in dogs is associated with early marked dysfunction of both radial and longitudinal LVFW motions. These combined regional myocardial abnormalities might be useful criteria for detection of dilated cardiomyopathy at the preclinical stage of the disease in dogs.     

Assessment of repeatability, reproducibility, and effect of anesthesia on determination of radial and longitudinal left ventricular velocities via tissue Doppler imaging in dogs

OBJECTIVE: To determine left ventricular free wall (LVFW) motions and assess their intra- and interday variability via tissue Doppler imaging (TDI) in healthy awake and anesthetized dogs. ANIMALS: 6 healthy adult Beagles. PROCEDURE: n the first part of the study, 72 TDI examinations (36 radial and 36 longitudinal) were performed by the same observer on 4 days during a 2-week period in all dogs. In the second part, 3 dogs were anesthetized with isoflurane and vecuronium. Two measurements of each TDI parameter were made on 2 consecutive cardiac cycles when ventilation was transiently stopped. The TDI parameters included maximal systolic, early, and late diastolic LVFW velocities. RESULTS: The LVFW velocities were significantly higher in the endocardial than in the epicardial layers and also significantly higher in the basal than in the mid-segments in systole, late diastole, and early diastole. The intraday coefficients of variation (CVs) for systole were 16.4% and 22%, and the interday CV values were 11.2% and 16.4% in the endocardial and epicardial layers, respectively. Isoflurane anesthesia significantly improved the intraday CV but induced a decrease in LVFW velocities, except late diastolic in endocardial layers and early diastolic in epicardial layers. CONCLUSIONS AND CLINICAL RELEVANCE: Left ventricular motion can be adequately quantified in dogs and can provide new noninvasive indices of myocardial function. General anesthesia improved repeatability of the procedure but cannot be recommended because it induces a decrease in myocardial velocities.     

Use of quantitative two-dimensional color tissue Doppler imaging for assessment of left ventricular radial and longitudinal myocardial velocities in dogs

OBJECTIVE: To determine left ventricular free wall (LVFW) radial and longitudinal myocardial contraction velocities in healthy dogs via quantitative 2-dimensional color tissue Doppler imaging (TDI). ANIMALS: 100 dogs. PROCEDURE: TDI was used by a single trained observer to measure radial and longitudinal myocardial movement in the LVFW. Radial myocardial velocities were recorded in segments in the endocardial and epicardial layers of the LVFW, and longitudinal velocities were recorded in segments at 3 levels (basal, middle, apical) of the LVFW. RESULTS: LVFW velocities were higher in the endocardial layers than in the epicardial layers. Left ventricular free wall velocities were higher in the basal segments than in the middle and apical segments. Radial myocardial velocity gradients, defined as the difference between endocardial and epicardial velocities, were (mean +/- SD) 2.5 +/- 0.8 cm/s, 3.8 +/- 1.5 cm/s, and 2.3 +/- 0.9 cm/s in systole, early diastole, and late diastole, respectively. Longitudinal myocardial velocity gradients, defined as the difference between basal and apical velocities, were 5.9 +/- 2.2 cm/s, 6.9 +/- 2.5 cm/s, and 4.9 +/- 1.7 cm/s in systole, early diastole, and late diastole, respectively. A breed effect was detected for several systolic and diastolic TDI variables. In all segments, systolic velocities were independent of fractional shortening. CONCLUSIONS AND CLINICAL RELEVANCE: LVFW myocardial velocities decreased from the endocardium to the epicardium and from base to apex, thus revealing intramyocardial radial and longitudinal velocity gradients. These indices could enhance conventional echocardiographic analysis of left ventricular function in dogs. Breed-specific reference intervals should be defined.     

Systolic and diastolic myocardial dysfunction in cats with hypertrophic cardiomyopathy or systemic hypertension

BACKGROUND: Hypertrophic cardiomyopathy (HCM) and chronic systemic hypertension (SHT) can both lead to left-ventricular hypertrophy (LVH) in cats. Assessment of LVH-associated myocardial dysfunction could provide new insights in the understanding of the pathophysiology of these diseases. HYPOTHESIS: Quantification of left-ventricular free-wall (LVFW) motion using tissue Doppler imaging (TDI) could permit differentiation of feline HCM from SHT-related LVH (LVH-SHT). ANIMALS: A total of 108 cats of different breeds were enrolled in this study: 35 cats with HCM, 17 with concentric LVH and SHT, and 56 healthy cats as a control group. METHODS: All cats were examined by conventional echocardiography and 2-dimensional color TDI. RESULTS: Radial and longitudinal diastolic LVFW velocities were similarly altered in cats with HCM and LVH-SHT, compared to controls. Systolic velocities were also lower in the groups with hypertrophy than in the controls, for longitudinal but not radial motion. To determine whether these diastolic and systolic alterations could also be observed in cats without LVFW hypertrophy, we performed a subgroup analysis in cats with a normal M-mode examination, that is, with only a localized subaortic interventricular septum hypertrophy. A significant radial and longitudinal diastolic dysfunction was still observed in both the HCM and LVH-SHT groups compared to controls, and systolic dysfunction was detected in the longitudinal motion. CONCLUSIONS: LVFW motion is similarly altered in cats with HCM and LVH-SHT. This dysfunction occurs independently of the presence of myocardial hypertrophy, demonstrating that TDI is capable of detecting systolic and diastolic segmental functional changes in nonhypertrophied wall segments in cats with HCM and SHT.     

Echocardiographic and tissue Doppler imaging alterations associated with spontaneous canine systemic hypertension

Background: Feline systemic arterial hypertension (SHT) is associated with a wide spectrum of left ventricular (LV) geometric patterns as well as diastolic, and to a lesser extent, systolic myocardial dysfunction. However, little is known about SHT‐related cardiac changes in dogs. Hypothesis: SHT in dogs is responsible for morphological and functional cardiac alterations. Animals: Thirty dogs with spontaneous untreated SHT and 28 age‐ and body weight‐matched healthy dogs as controls. Methods: Prospective observational study. Conventional echocardiography and 2‐dimensional color tissue Doppler imaging were performed in SHT dogs by trained observers and compared with controls. Results: Forty‐seven percent of SHT dogs (14/30) had diffuse concentric hypertrophy. None had left atrial dilatation and 10/30 (33%) had aortic insufficiency (AoI) associated with proximal aortic dilatation. Longitudinal diastolic left ventricular free wall (LVFW) motion was altered in all SHT dogs at the base (early to late diastolic wave ratio, E/A = 0.5 ± 0.1 versus 1.3 ± 0.3 for controls, P < .0001) and the apex (E/A = 1.6 ± 1.7 versus 3.9 ± 3.1, P < .05). Longitudinal motion of the interventricular septum at the base (E/A = 0.7 ± 0.4 versus 1.1 ± 0.1, P < .01) and radial LVFW motion in the subendocardium (E/A = 0.9 ± 0.5 versus 1.6 ± 0.3, P < .01) were also altered in dogs with SHT. Longitudinal LVFW systolic velocities and gradients were also significantly decreased (P < .05) in SHT dogs. Conclusion and Clinical Importance: As in SHT in cats, SHT in dogs is associated with myocardial dysfunction independently of the presence of myocardial hypertrophy. However, unlike feline SHT, it results in a homogeneous LV geometric pattern with a relatively high prevalence of AoI.     

Influence of valvular insufficiency and recurrent airway obstruction on haemodynamics and therapy in warmblood horses with atrial fibrillation

The aim of this study was to investigate the potential haemodynamic effects of valvular insufficiency and recurrent airway obstruction (RAO) in horses with atrial fibrillation (AF). Therefore in ten healthy horses (group 1) and 40 horses with AF a clinical examination, a lung examination, echocardiography and right heart catheterization for measurement of intracardic and pulmonary pressures were performed. According to the clinical findings the horses with AF were subdivided into 4 groups (group 2: AF; group 3: AF/valvular insufficiency; group 4: AF/RAO; group 5: AF/valvular insufficiency/RAO). Most of the horses of group 3 and 5 suffered from two valvular insufficiencies (mitral and tricuspid valve insufficiency: n=11, mitral and aortic valve insufficiency: n=2). The remaining horses showed a single mitral (n=6), tricuspid (n=2) or aortic valve insufficiency (n=1) or more than two valvular insufficiencies (n=4). In group 2 right ventricular mean pressure (RVPm) was higher than in group 1 and 4 (P<0.025); diastolic right ventricular pressure was higher than in group 1; PWP was higher than in group 1 and group 4; PDP was lower compared to group1. Compared to group1 in group 3 left atrial diameter (LA) was greater; the PAPs was higher and the PDP lower (P<0.05). In group 4 RVPm and PWP was lower compared to group 2. In group 5 LA, fractional shortening and diastolic left ventricular diameter were greater, PWP and PAPs were higher and PDP lower compared to group1. Twenty six of the 40 horses with AF (65%) were treated. Successful cardioversion to sinus rhythm occurred in 15 horses (58%). Therapy was successful in 50% of the treated horses of group 2 and 3, in 67% of the treated horses of group 4 and in 63% of the treated horses in group 5. In conclusion the presence of valvular insufficiency or RAO influences the haemodynamics of horses with AF.     

Tissue Doppler imaging for detection of radial and longitudinal myocardial dysfunction in a family of cats affected by dystrophin-deficient hypertrophic muscular dystrophy

Diagnosis of feline hypertrophic cardiomyopathy currently is based on the presence of myocardial hypertrophy detected using conventional echocardiography. The accuracy of tissue Doppler imaging (TDI) for earlier detection of the disease has never been described. The objective of this sudy was to quantify left ventricular free wall (LVFW) velocities in cats with hypertrophic muscular dystrophy (HFMD) during preclinical cardiomyopathy using TDI. The study animals included 22 healthy controls and 7 cats belonging to a family of cats with HFMD (2 affected adult males, 2 heterozygous adult females, one 2.5-month-old affected male kitten, and 2 phenotypically normal female kittens from the same litter). All cats were examined via conventional echocardiography and 2-dimensional color TDI. No LVFW hypertrophy was detected in the 2 carriers or in the affected kitten when using conventional echocardiography and histologic examination, respectively. The LVFW also was normal for 1 affected male and at the upper limit of normal for the 2nd male. Conversely, LVFW dysfunction was detected in all affected and carrier cats with HFMD when using TDI. TDI consistently detects LVFW dysfunction in cats with HFMD despite the absence of myocardial hypertrophy. Therefore, TDI appears more sensitive than conventional echocardiography in detecting regional myocardial abnormalities.     

Pulsed tissue Doppler imaging in normal cats and cats with hypertrophic cardiomyopathy

Myocardial motion was quantified in normal cats (n = 25) and cats with hypertrophic cardiomyopathy (HCM) (n = 23) using the pulsed tissue Doppler imaging (TDI) technique. A physiologic nonuniformity was documented in the myocardial motion of normal cats, which was detected as higher early diastolic velocities, acceleration, and deceleration in the interventricular septum compared with the left ventricular free wall (LVFW). HCM cats exhibited lower early diastolic velocities, acceleration, and deceleration and also prolonged isovolumic relaxation time compared with normal cats. These differences were detected mainly along the longitudinal axis of the heart. A cutoff value of E' in the LVFW along the longitudinal axis >7.2 cm/s discriminated normal from HCM cats with a sensitivity of 92% and a specificity of 87%. The physiologic nonuniformity of myocardial motion during diastole was lost in affected cats. Systolic impairment (decreased late-systolic velocities in most segments along the longitudinal axis and decreased early systolic acceleration in both mitral annular sites) was evident in HCM cats irrespective of the presence of left ventricular outflow tract obstruction and congestive heart failure. Postsystolic thickening was recorded in the LVFW along the longitudinal axis only in affected cats (n = 6) and was another finding indicative of systolic impairment in the HCM of this species. This study identified both diastolic and systolic impairment in cats with HCM compared with normal cats. The study also documents the normal physiologic nonhomogeneity in myocardial motion in cats and the subsequent loss of this feature in the HCM diseased state.     

Reference range values of regional left ventricular myocardial velocities and time intervals assessed by tissue Doppler imaging in young nonsedated Maine Coon cats

OBJECTIVE: To describe and analyze the left ventricular free wall (LVFW) radial and longitudinal motions in a population of healthy Maine Coon cats by use of quantitative 2-dimensional color tissue Doppler imaging (TDI). ANIMALS: 23 healthy young Maine Coon cats (mean +/- SD: age, 2.1 +/- 0.9 years; weight, 5.0 +/- 1.0 kg). PROCEDURE: TDI was performed by the same trained observer (VC) on all cats. Radial LVFW velocities were recorded in endocardial and epicardial LVFW segments, and longitudinal velocities were recorded in the mitral annulus and in basal and apical LVFW segments. Isovolumic contraction and relaxation times were calculated in each myocardial segment, and the coefficients of variation (CVs; %) were determined for each TDI parameter. RESULTS: LVFW velocities were significantly higher in the endocardial layers than in the epicardial layers and also significantly higher in the basal than in the apical segments. Annular velocities were significantly higher than basal myocardial velocities in systole and early diastole. Coefficient of variation values were lower for radial velocities, particularly in systole, and were also lower for time intervals (16% to 22%) than for myocardial velocities (19% to 62%). CONCLUSIONS AND CLINICAL RELEVANCE: Because Maine Coon cats are predisposed to an inherited hypertrophic cardiomyopathy, which is a common cause of death in this breed, TDI could provide a useful tool for early detection of the disease. Tissue Doppler imaging indices may complete the conventional analysis of the left ventricular function in Maine Coon cats. However, the usefulness of TDI indices in the early detection of myocardial dysfunction needs to be clarified.     

Ultrasonographic assessment of regional radial and longitudinal systolic function in healthy awake dogs

BACKGROUND: Strain (St) and strain rate (SR) imaging are new ultrasound modalities based on tissue Doppler imaging (TDI) that allow quantitative assessment of segmental myocardial contraction or stretching and rate of deformation, respectively. HYPOTHESIS: Regional peak systolic St and SR could allow repeatable and reproducible assessment of systolic function of the right (RVW) and left (LVFW) myocardial walls in dogs. ANIMALS: Six healthy Beagle dogs were used to determine the repeatability and reproducibility of regional peak systolic St and SR in the RVW and LVFW (Study 1). These variables were also assessed in 30 healthy dogs of several breeds (Study 2). METHODS: Longitudinal peak systolic St and SR were recorded in 2 segments (basal and apical) of the RVW and LVFW. Radial peak systolic St and SR of the LVFW were also assessed. RESULTS: All within- and most (7/10) between-day coefficients of variation were <15%. Absolute values of the longitudinal deformation indices were significantly higher (P < .001) in the RVW (St = -39.5 +/- 5.5% and SR = -5.2 +/- 0.8 s(-1) at the base; St = -36.3 +/- 4.3% and SR = -4.7 +/- 1.1 s(-1) at the apex) than in the LVFW. Absolute values were also higher for the radial (St = 62.9 +/- 10.4% and SR = 5.8 +/- 1.1 s(-1), P < .001) than for the longitudinal LFVW motions. CONCLUSIONS AND CLINICAL IMPORTANCE: St and SR imaging is a repeatable and reproducible method for assessing systolic myocardial function. The combination of these indices with conventional echocardiographic variables may be useful for screening canine myocardial diseases.     

Abnormalities in lung surfactant in horses clinically affected with recurrent airway obstruction (RAO)

Background: Abnormalities in lung surfactant are well described in human respiratory diseases including asthma, but are poorly described in horses. Hypothesis: Lung surfactant is abnormal in horses with clinical signs of recurrent airway obstruction (RAO). Animals: Six healthy horses and 5 horses with RAO. Methods: Bronchoalveolar lavage fluid (BALF) was obtained from all horses by standard procedures. Cell‐free BALF was separated into crude surfactant pellets (CSP) and supernatant via ultracentrifugation. Phospholipid and protein content was analyzed from both of these fractions. Phospholipid composition of CSP was determined using high‐performance liquid chromatography with an evaporative light scatter detector. Surface tension of CSP was measured with a pulsating bubble surfactometer. Results: Compared with healthy horses, surfactant from RAO‐affected horses was characterized by significantly decreased phospholipid content in total surfactant (median; range: 23.2; 14.7–62.2 μg/mL BALF versus 172; 111–267 μg/mL BALF, P= .0062) and CSP (20.2; 6.4–48.9 μL/mL BALF versus 155; 94.4–248 μg/mL BALF, P= .0062), and a significantly lower percentage of phosphatidylglycerol (PG) (4.5; 3.6–5.6% versus 6.6; 4.1–7.6%, P= .028). Furthermore, the ratio between the percentages of phosphatidylcholine and PG was significantly higher in RAO‐affected horses than in healthy horses (20.9; 16.6: 25.9 versus 13.9; 11.8–22.8, P= .045). Conclusions and Clinical Importance: This study demonstrates that surfactant from RAO‐affected horses is abnormal. Further studies are needed to determine if these abnormalities are related to an increased tendency for bronchoconstriction and to a decreased ability to clear airway mucus in RAO‐affected horses.     

Effect of Restricted Pasture Access on Pasture Dry Matter Intake Rate,Dietary Energy Intake,and Fecal pH in Horses

Eight mature horses were used in a 4 × 4 Latin square design to determine the effect of restricted pasture access on dry matter intake rate (DMIR), energy intake, and fecal pH. Horses were randomly assigned to one of four groups (HGRPs), each containing two horses. HGRPs were randomly assigned to one of four treatments consisting of 3, 6, 9, or 24 hours of pasture access, for a period of 7 days. Treatments were switched every 7 days. The 3- and 6-hour groups were fed free choice mature grass hay while not grazing. Daily pasture dry matter intake (DMI) for each HGRP was estimated by calculating the difference between initial herbage mass of the grazing cell before grazing and residual herbage mass after 7 days of grazing. Total dry matter intake was the sum of pasture and hay DMI for the 3- and 6-hour treatments. Fecal pH was measured on day 7 of each period. Response variables were analyzed using analysis of variance for Latin square design. Restricting pasture access decreased mean pasture DMI (P = .02), pasture dietary energy (DE) (P = .02), and fecal pH (P < .001), but increased DMIR (P = .02). Mean total dry matter intake was not different (P = .16) among treatments. In conclusion, restricting pasture access accelerates pasture DMIR and decreases fecal pH, and although restricting pasture access decreases DE intake from pasture, it did not result in a decrease in total DE intake for horses having ad libitum access to hay.     

Comparative efficacy of inhaled albuterol between two hand-held delivery devices in horses with recurrent airway obstruction

Reasons for performing study: Studies investigating the clinical efficacy of albuterol administered with the same propellant and commercially available delivery devices in horses with recurrent airway obstruction (RAO) are not currently available. Objectives: To determine the efficacy of aerosolised albuterol administered to horses with RAO by means of 2 commercially available, hand‐held delivery devices. Methods: Ten horses with RAO were kept in a dusty environment and fed mouldy hay to induce airway obstruction. Lung mechanics were measured before and after the procedure. ΔP_max was measured 5 min after administration of 180 µg of albuterol from a pressurised metered dose inhaler, using an aerosol delivery device chosen randomly. This process was repeated every 5 min until maximal bronchodilation was achieved. After a 24 h washout period, lung mechanics data were again collected using the other aerosol delivery device. Results: Aerosolised albuterol induced a significant and rapid bronchodilation in the horses using both aerosol delivery devices. No statistically significant difference in pulmonary function was observed in response to albuterol therapy between the 2 devices. The dose required to achieve 50% of maximal bronchodilation was not statistically different between the 2 devices (173.35 ± 78.35 µg with Device 1 and 228.49 ± 144.99 µg with Device 2, P = 0.26). The decrease in lung resistance tended to be more pronounced after albuterol administration with Device 1 (P = 0.066). Conclusions: Aerosolised albuterol is an effective bronchodilator in horses with recurrent airway obstruction. There is no statistically significant difference between the 2 commercially available aerosol delivery devices in terms of efficacy. Potential relevance: Aerosolised albuterol is effectively delivered using currently available devices leading to maximal bronchodilation in horses with RAO at an average dose of 540 µg.     

Myocardial Function of Horses Under Sedation with Romifidine Using Two-Dimensional Speckle Tracking

Two-dimensional speckle tracking echocardiography (2DST) provides the assessment of the left ventricle deformation parameters strain (St) and strain rate (SR). The objective of this study was to evaluate St and SR under the influence of romifidine in healthy horses and horses affected with heart disease. The study subjects were 45 privately owned horses. Valvular insufficiencies were identified by color Doppler in 21 out of 45 horses. Dimensional changes were identified in 13 of these 21 horses. These dimensional changes included dilatations of the left ventricle (130 ± 8.95 mm) and/or the left atrium (141 ± 4.8 mm). The other 24 horses were without echocardiographic findings and had normal heart dimensions. Based on clinical signs, echo-, and electrocardiographic examinations, 24 horses were categorized as group 1 (healthy), 13 as group 2 (heart disease without dimensional changes), and 8 as group 3 (heart disease with dimensional changes). The radial St and SR were assessed in the left ventricular free wall and the interventricular septum using 2DST. After application of romifidine, a significant reduction of St and the systolic peak of SR were found in all three groups. Group 3 showed the most significant reduction of these parameters (41.5%). The reduction of St and SR under romifidine showed a reduced myocardial function, which is more obvious in horses with cardiac dilatation. It can be assumed that heart disease with myocardial dilatation leads to decreasing myocardial function, which becomes more obvious after romifidine application and of clinical importance in horses with severe heart disease and cardiac dilatation.     

Peak mean myocardial velocities and velocity gradients measured by color M-mode tissue Doppler imaging in healthy cats

We sought to assess the feasibility of recording the myocardial velocity gradients (MVGs) and mean myocardial velocities (MMVs) measured by color M-mode tissue Doppler imaging (TDI) in the free wall of unsedated normal cats (n = 18) with a 7.4-MHz probe equipped to record TDI images. The peak MVG and MMV values during the different phases of the cardiac cycle corresponded to certain color velocity patterns occurring in the left ventricular free wall (LVFW). Biphasic shifts were recorded in the tracings of both the MVG and MMV during early diastole (E1 and E2) as well as during the isovolumic relaxation (IVR) and isovolumic contraction (IVC) phases. Stepwise regression analysis showed that age was the only significant predictor for the peak MVG values during the 2nd phase of early diastole (E2) (r = -0.79, r2 = 0.63, and P < .001). The peak late diastolic MVG values were associated positively with age (r = 0.50, r2 = 0.25, and P < .05). The peak MMV values showed a negative association with age during E2 (r = -0.71, r2 = 0.50, and P < .001) as well as during early systole (Se) (r = -0.55, r2 = 0.30, and P < .05) and late systole (SI) (r = -0.62, r2 = 0.39, and P < .01). A positive association was found between age and the peak MMV values during late diastole (r = 0.54, r2 =- 0.29, and P < .05). The MVG values showed cyclic variations consistent with wall thickness changes. The accuracy of velocity determination and the spatial resolution of the system used were validated with a phantom. To our knowledge, this study is the 1st report of the application of this technique to the myocardium of cats,providing insights into the physiology of myocardial motion. It provides reference ranges of the peak MVG and MMV values for future studies of feline myocardial diseases.     

The Effect of Aerosolized and Intravenously Administered Clenbuterol and Aerosolized Fluticasone Propionate on Horses Challenged with Aspergillus fumigatus Antigen

β-Agonists have been shown to display anti-inflammatory properties in several experimental models. The aim of this study was to investigate the anti-inflammatory properties of clenbuterol (CB), administered either intravenously or by aerosol, in comparison with fluticasone propionate (FP) in recurrent airway obstruction (RAO)-susceptible horses. Eight horses, of which five were known to be susceptible to RAO, underwent an inhalation challenge with Aspergillus fumigatus (AF) antigen and were treated with CB intravenously, CB by aerosol, or FP by aerosol. Twenty-four hours after the challenge, bronchoalveolar lavage was performed, the total and differential cell counts were assessed, and cytokines were measured in isolated alveolar macrophages. After challenge with AF, RAO-susceptible horses showed an increase in total cell count, based on an increase in macrophages and lymphocytes, which was inhibited by treatment with intravenous CB, aerosolized CB and aerosolized FP. Neutrophil ratios were decreased when treated with aerosolized CB and FP. Expression of interleukin (IL)-1β and IL −8 was significantly increased after AF challenge .Interleukin −1β was significantly decreased following treatment with intravenous CB, aerosolized CB and aerosolized FP, whereas only FP decreased the expression of IL-8. These data suggest that the anti-inflammatory property of CB provide new opportunities in the therapeutic intervention of early inflammation in RAO.