Sofie Ven

Cardiac Troponin I as Compared to Troponin T for the Detection of Myocardial Damage in Horses

Background Different cardiac troponin I (cTnI) assays give different results. Only 1 manufacturer has marketed troponin T (cTnT) assays. Therefore, cTnT often is preferred for detection of myocardial infarction in human patients. Studies of cTnT in horses are limited. Objectives To compare a cTnI and a high‐sensitive cTnT assay (hs‐cTnT) in horses. Animals Cardiac troponin I and cTnT were determined in 35 healthy horses (group 1), 23 horses suspected to have primary myocardial damage (group 2a), and 41 horses with secondary myocardial damage caused by structural heart disease (group 2b). Methods All cTnI samples were analyzed at laboratory A (limit of detection [LOD]: 0.03 ng/mL), whereas cTnT samples were analyzed at 2 laboratories with the same hs‐cTnT assay (laboratory B, LOD: 10.0 pg/mL; laboratory C, LOD: 4.0 pg/mL). Results The median cTnI concentration in group 2a (0.90 ng/mL; range, 0.03–58.27 ng/mL) was significantly higher (P < .001) than in group 1 (0.03 ng/mL; range, 0.03–0.09 ng/mL) or group 2b (0.05 ng/mL; range, 0.03–30.92 ng/mL), and the optimal cut‐off for detection of primary myocardial damage was 0.095 ng/mL (sensitivity: 90.5%, specificity: 100%). Using an LOD of 10.0 pg/mL for all cTnT samples, a cut‐off value of 10.5 pg/mL was found, but sensitivity was low (42.9%). When only samples analyzed at laboratory C (n = 58) were included, a cut‐off of 6.6 pg/mL was found (sensitivity: 81%, specificity: 100%). Conclusions and Clinical Importance Despite large quantitative differences, cTnI and cTnT are both useful for detection of myocardial damage in horses.

Evaluation of assays for troponin I in healthy horses and horses with cardiac disease

Cardiac troponin I (cTnI) is a marker for detection of myocardial damage in horses. Many cTnI assays exist and medical studies have shown that the clinical performance of assays differs. The aim of this study was to compare two different cTnI assays in horses. Serum samples were taken from 23 healthy horses (group 1) and 72 horses with cardiac disease (group 2). Cardiac troponin I was determined using assay 1 in laboratory A (limit of detection, LOD, 0.03 ng/mL) and assay 2 in laboratories B and C (LOD 0.01 ng/mL). In group 1, a median cTnI concentration of <0.03 (<0.03-0.04) ng/mL and <0.01 (<0.01-0.15) ng/mL was found with assays 1 and 2, respectively. A higher median value was demonstrated in group 2 for both assays (assay 1: 0.11 ng/mL, range 0.03-58.27 ng/mL, P < 0.001; assay 2: 0.02 ng/mL, range 0.01-22.87 ng/mL, P = 0.044). Although a significant correlation between assays existed, large mean differences that could be important for clinical interpretation of test results were found. A small mean difference was found between laboratories B and C. A significant optimal (P < 0.001) cut-off value for detection of cardiac disease could only be determined for assay 1 (0.035 ng/mL, sensitivity 70%, specificity 91%). Assay 1 performed better for detection of cardiac disease in horses in this study.

Pharmacokinetics of intravenously and orally administered sotalol hydrochloride in horses and effects on surface electrocardiogram and left ventricular systolic function

Arrhythmias are common in horses. Some, such as frequent atrial or ventricular premature beats, may require long-term anti-arrhythmic therapy. In humans and small animals, sotalol hydrochloride (STL) is often used for chronic oral anti-arrhythmic therapy. STL prolongs repolarization and the effective refractory period in all cardiac tissues. No information on STL pharmacokinetics or pharmacodynamics in horses is available and the aim of this study was to evaluate the pharmacokinetics of intravenously (IV) and orally (PO) administered STL and the effects on surface electrocardiogram and left ventricular systolic function. Six healthy horses were given 1 mg STL/kg bodyweight either IV or PO. Blood samples to determine plasma STL concentrations were taken before and at several time points after STL administration. Electrocardiography and echocardiography were performed at different time points before and after IV STL administration. Mean peak plasma concentrations after IV and PO administration of STL were 1624 ng/mL and 317 ng/mL, respectively. The oral bioavailability was intermediate (48%) with maximal absorption after 0.94 h, a moderate distribution and a mean elimination half-life of 15.24 h. After IV administration, there was a significant increase in QT interval, but no significant changes in other electrocardiographic and echocardiographic parameters. Transient transpiration was observed after IV administration, but no adverse effects were noted after a single oral dose of 1 mg/kg STL in any of the horses. It was concluded that STL has an intermediate oral bioavailability in the horse and might be useful in the treatment of equine arrhythmias.

Right atrial and right ventricular ultrasound-guided biopsy technique in standing horses.

REASONS FOR PERFORMING STUDY Endomyocardial biopsies could be a valuable tool in equine cardiology for diagnosing myocardial disease, which is probably underdiagnosed in horses because of lack of specific diagnostic measures and limitations of currently available diagnostic methods. OBJECTIVES To describe a technique for serial right atrial and right ventricular endomyocardial biopsy in standing horses using a percutaneous approach through the jugular vein. STUDY DESIGN Prospective study. METHODS Biopsy was performed in 10 healthy standing horses sedated with detomidine, under continuous electrocardiography monitoring. A 10 cm (n = 6), 45 cm (n = 1) or 98 cm (n = 3) introducer sheath was inserted into the right jugular vein. Under echocardiographic guidance, a biopsy forceps was introduced through the sheath into the right ventricle and right atrium and endomyocardial biopsies were acquired. RESULTS In all horses, 3 right ventricular biopsies were obtained from the right ventricular apex and 3 right atrial biopsies were obtained from the dorsal right atrial wall near the tuberculum intervenosum. The presence of myocardial tissue was confirmed by histology. All horses showed atrial and ventricular premature depolarisations associated with acquisition of the biopsies. In 9 horses, the arrhythmia disappeared after retraction of the forceps and introducer sheath. In one horse, ventricular premature depolarisations disappeared only after 8 h. No other complications were observed. CONCLUSIONS Endomyocardial biopsy of the right atrium and right ventricle could be performed in standing horses using a percutaneous approach through the jugular vein and was not associated with complications other than temporary arrhythmias. This technique may be useful for research purposes or as a diagnostic tool, although further research is needed to establish the safety of the technique in clinical patients with myocardial disease.

Analytical validation of a high-sensitivity cardiac troponin T assay in horses

Although cardiac troponin T (cTnT) assays have been used to detect myocardial damage in horses, a cTnT assay has not been analytically validated, to our knowledge. The aims of this study were to estimate the precision of a high-sensitivity cTnT assay in horses and determine the effect of hemolysis on the measured cTnT concentration. Serum samples from horses were mixed in 3 different pools. Pool 1 consisted of samples from 3 healthy horses, pool 2 from 6 horses with heart failure or atypical myopathy, and pool 3 from 10 horses with atypical myopathy. The within- and between-run coefficients of variation were determined for each pool. Pools 2 and 3 were diluted to estimate linearity. To study the influence of sample hemolysis, serum was collected from 4 horses with a high cTnT concentration, in which hemolysis was mechanically induced. In addition, ethylenediamine tetra-acetic acid blood tubes were collected from 3 other horses, from which hemolysate was prepared and added to plasma at different concentrations. The within- and between-run coefficients of variation of all pools were <10%, and a good linearity was found. Three out of 4 hemolyzed serum samples had a decreased serum cTnT concentration. Plasma samples with a high hemolysis index showed a negative interference, resulting in a lower cTnT concentration. Results of the high-sensitivity cTnT assay were highly reproducible. Because samples from horses with musculoskeletal damage were included, further studies should test the possible cross-reactivity between troponin T of musculoskeletal and cardiac origin before the assay can be used in equine clinical practice.

Assessing aortic regurgitation severity from 2D, M-mode and pulsed wave Doppler echocardiographic measurements in horses.

Aortic regurgitation (AR) in horses can lead to left ventricular (LV) eccentric hypertrophy, ventricular arrhythmia and heart failure. Objective quantification of the severity of regurgitation is difficult. The aim of this study was to evaluate dimensional measurements, systolic time intervals and blood flow velocities, acquired by standard 2D, M-mode and pulsed wave Doppler echocardiography, for quantification of AR. Echocardiography was performed in 32 healthy horses and 35 horses with AR that were subdivided in three groups (mild, moderate or severe AR). From the recorded images LV, left atrial and aortic dimensions, systolic time intervals and aortic blood flow velocities were measured. Diastolic run-off in the aorta (AoDiastDecr) was calculated as the difference in aortic diameter between early diastole and late diastole. Stroke volume (SV) was calculated from pulsed wave Doppler measurements, by the bullet method (SVbullet) and by the area-length method. Pre-ejection period (PEP) and ejection time (LVET) were determined from the M-mode images. Horses with AR showed enlargement of the LV, left atrium and aorta compared to the control group. The SV, the AoDiastDecr and the rate of AoDiastDecr were significantly larger than controls. PEP decreased significantly in horses with AR, whereas LVET did not change. PEP and the newly defined variable AoDiastDecr proved to be easy to measure parameters that provided a good indication of AR severity. There was increased SV in horses with AR using all three methods, but SVbullet was superior for the detection of increased AR severity.

Influence of detomidine on atrial fibrillation cycle length measured by intracardiac electrogram recording and by colour tissue Doppler imaging in horses

REASONS FOR PERFORMING STUDY Shortening of atrial fibrillation cycle length (AFCL) is a marker of atrial electrical remodelling due to atrial fibrillation (AF). OBJECTIVES To investigate the effect of administration of detomidine on AFCL measured invasively from an intra-atrial electrogram (AFCLEGM) and noninvasively by tissue Doppler imaging (AFCLTDI). We hypothesised that detomidine would have no effect on AFCL but would improve the ease of TDI measurements and facilitate noninvasive AFCL determination. STUDY DESIGN Prospective clinical study. METHODS Measurements were performed before and after i.v. administration of 7.5 μg/kg bwt detomidine in 33 episodes of AF in 32 horses (582 ± 64 kg bwt, 10 ± 3 years old) referred for electrical cardioversion. The AFCLEGM was measured from a right atrial intracardiac electrogram. The AFCLTDI was measured from atrial colour tissue velocity curves in 5 atrial wall regions. Mean AFCLEGM and AFCLTDI without and with sedation were compared using a repeated-measures linear mixed model with Bonferroni correction for multiple comparisons and calculation of the Bland-Altman mean bias and limits of agreement between AFCLEGM and AFCLTDI. RESULTS The mean AFCL was significantly increased after sedation, but this increase was very small (mean difference +4 ms). For AFCLTDI measurements, sedation significantly improved the quality of the atrial myocardial velocity curves and the number of AF cycles that could be measured per cardiac cycle. The Bland-Altman bias between AFCLEGM without sedation and AFCLTDI with sedation ranged from -18 to +15 ms depending on wall region. Bland-Altman limits of agreement were similar between AFCLEGM without sedation and AFCLTDI without and with sedation. Therefore, noninvasive AFCLTDI measurements with sedation can be used to estimate the atrial fibrillatory rate. CONCLUSIONS Sedation facilitates noninvasive AFCL measurements but causes a slight increase in AFCL. Noninvasive AFCL measurements can be used as an indicator of atrial electrical remodelling, to study AF pathophysiology and to investigate the effect of anti-arrhythmic drugs.

Heart rate variability parameters in horses distinguish atrial fibrillation from sinus rhythm before and after successful electrical cardioversion

BACKGROUND Atrial fibrillation (AF) is the most common pathological arrhythmia in horses. After successful treatment, recurrence is common. Heart rate monitors are easily applicable in horses and some devices offer basic heart rate variability (HRV) calculations. If HRV can be used to distinguish between AF and sinus rhythm (SR), this could become a monitoring tool for horses at risk for recurrence of AF. OBJECTIVES The purpose of this study was to assess whether in horses AF (before cardioversion) and SR (after cardioversion) can be differentiated based upon HRV parameters. STUDY DESIGN Cohort study with internal controls. METHODS Six HRV parameters were determined in 20 horses, both in AF and in SR, at rest (2- and 5-min and 1- and 4-h recordings) and during exercise (walk and trot, 2-min recordings). Time-domain (standard deviation of the NN intervals, root mean squared successive differences in NN intervals and triangular index), frequency domain (low/high frequency ratio) and nonlinear parameters (standard deviation of the Poincaré plot [SD]1 and SD2) were used. Statistical analysis was done using paired Wilcoxon signed rank tests and receiver operating characteristic curves. RESULTS HRV was higher during AF compared to SR. Results for the detection of AF were good (area under the receiver operating characteristic curve [AUC] 0.8-1) for most HRV parameters. Root mean squared successive differences in NN intervals and SD1 yielded the best results (AUC 0.9-1). Sensitivity and specificity were high for all parameters at all recordings, but highest during exercise. Although AUCs improved with longer recordings, short recordings were also good (AUC 0.8-1) for the detection of AF. In horses with frequent second degree atrioventricular block, HRV at rest is increased and recordings at walk or trot are recommended. MAIN LIMITATIONS Animals served as their own controls and there was no long-term follow-up to identify AF recurrence. CONCLUSIONS AF (before cardioversion) and SR (after cardioversion) could be distinguished with HRV. This technique has promise as a monitoring tool in horses at risk for AF development.

Atrial natriuretic peptide vs. N-terminal-pro-atrial natriuretic peptide for the detection of left atrial dilatation in horses.

REASONS FOR PERFORMING STUDY Studies on the use of atrial natriuretic peptide (ANP) as a biomarker for left atrial dilatation in horses have produced variable results. Few have been performed, and the results may have been influenced by ANP instability, differences in sampling protocol and changes in the assay over time. N-Terminal proANP (NT-proANP) is a more stable molecule and might be a good alternative for clinical use. OBJECTIVES To compare ANP and NT-proANP in terms of the detection of left atrial dilatation and to determine the influence of sample storage at temperatures of -80 and -20°C. STUDY DESIGN Prospective clinical study. METHODS Atrial natriuretic peptide and NT-proANP concentrations were compared between healthy horses (Group 1, n = 20), horses with mitral valve regurgitation and a normal atrial size (Group 2, n = 11) and horses with mitral valve regurgitation associated with left atrial dilatation (Group 3, n = 16). The ANP concentration was measured with an equine enzyme-linked immunosorbent assay and the NT-proANP concentration with an enzyme-linked immunosorbent assay developed for use in human patients. Samples were stored at -20 and -80°C and analysed within 7 months. RESULTS The NT-proANP concentrations were not significantly different between the groups. Horses in Group 3 had a significantly higher ANP concentration (median 366 pg/ml; interquartile range [IQR] 74-2000 pg/ml) compared with horses in Group 1 (median 31 pg/ml; IQR 31-333 pg/ml) or Group 2 (median 31 pg/ml; IQR 31-1152 pg/ml; P = 0.02). The ANP cut-off value for detection of left atrial dilatation was 52 pg/ml (sensitivity 81%; specificity 84%) for sample storage at -80°C, and 44 pg/ml (sensitivity 69%; specificity 84%) for storage at -20°C. A larger decrease in ANP (45 ± 126 pg/ml) than in NT-proANP (10 ± 31 pg/ml) was found associated with sample storage at -20 instead of -80°C. CONCLUSIONS Atrial natriuretic peptide, but not NT-proANP, can be used to detect left atrial dilatation in horses. Atrial natriuretic peptide is less stable than NT-proANP when samples are stored at -20°C. Atrial natriuretic peptide is a more suitable biomarker of left atrial dilatation in horses than NT-proANP.

Atrial Premature Depolarization-Induced Changes in QRS and T Wave Morphology on Resting Electrocardiograms in Horses.

Background The electrocardiographic differentiation between atrial (APDs) and ventricular (VPDs) premature depolarizations is important. P wave prematurity and normal QRS and T wave morphology generally are used as discriminating criteria for APDs. Hypothesis/Objectives The aim of this study was to determine whether P, Q, R, S, and T wave amplitude, PQ interval, QRS and P wave duration and P and T wave morphology differ between APDs and sinus beats. To determine the relationship between the RR coupling interval and the change in S wave amplitude between sinus beats and APDs. Methods Case–control study. From a modified base‐apex configuration of 30 horses with APDs at rest, sinus beat and APD associated preceding RR interval, P, PQ and QRS duration and P, R, S, and T wave amplitudes were measured. Linear mixed models and logistic regression were used to determine the effect of APDs on the ECG variables studied. Results In comparison to sinus beats, APDs were associated with a significant (P < .001) change in P amplitude (−0.03 ± 0.01 mV) and increase in S (0.20 ± 0.02 mV) and T (0.08 ± 0.03 mV) amplitude. PQ (−20.3 ± 5.2 ms) and RR (−519 ± 14 ms) interval and P duration (−21.1 ± 3.0 ms) decreased (P < .001). APDs were significantly associated with a singular positive P wave (OR: 11.0, P < .001) and were more likely to have a monophasic positive T wave (OR: 9.2, P < .001). A smaller RR coupling interval was associated with an increased relative difference in S amplitude (P < .01). Conclusions Atrial premature depolarizations may lead to changes in QRS and T wave morphology. Knowledge of these changes is important to avoid interpreting certain APDs as VPDs.