Gunther van Loon

Cardiac changes in horses with atypical myopathy.

BACKGROUND Atypical myopathy (AM) is an acute, fatal rhabdomyolysis in grazing horses that mainly affects skeletal muscles. Postmortem examinations have shown that myocardial damage also occurs. Limited information is available on the effect of AM on cardiac function in affected and surviving horses. OBJECTIVES To describe electrocardiographic and echocardiographic changes associated with AM in the acute stage of the disease and after follow-up. ANIMALS Horses (n = 12) diagnosed with AM in which cardiac ultrasound examination and ECG recording were available. METHODS All horses underwent clinical examinations, serum biochemistry, electrocardiography, and echocardiography. Four surviving horses underwent the same examinations after 2-10 weeks. RESULTS All but 1 horse had increased cardiac troponin I concentrations and 10 horses had ventricular premature depolarizations (VPDs). All horses had prolonged corrected QT (QT(cf) ) intervals on the day of admission and abnormal myocardial wall motion on echocardiography. One of the surviving horses still had VPDs and prolonged QT(cf) at follow-up after 10 weeks. CONCLUSIONS AND CLINICAL IMPORTANCE The AM results in characteristic electrocardiographic and echocardiographic changes and may be associated with increased cardiac troponin I concentrations and VPDs. In survivors, abnormal cardiac function still may be found at follow-up after 10 weeks. Additional research in a larger group of horses is necessary to identify the long-term effects of AM on cardiac function.

Effects of an adapted intravenous amiodarone treatment protocol in horses with atrial fibrillation

REASON FOR PERFORMING STUDY Good results have been obtained with a human amiodarone (AD) i.v. protocol in horses with chronic atrial fibrillation (AF) and a pharmacokinetic study is required for a specific i.v. amiodarone treatment protocol for horses. OBJECTIVES To study the efficacy of this pharmacokinetic based i.v. AD protocol in horses with chronic AF. METHODS Six horses with chronic AF were treated with an adapted AD infusion protocol. The protocol consisted of 2 phases with a loading dose followed by a maintenance infusion. In the first phase, horses received an infusion of 6.52 mg AD/kg bwt/h for 1 h followed by 1.1 mg/kg bwt/h for 47 h. In the second phase, horses received a second loading dose of 3.74 mg AD/kg bwt/h for 1 h followed by 1.31 mg/kg bwt/h for 47 h. Clinical signs were monitored, a surface ECG and an intra-atrial electrogram were recorded. AD treatment was discontinued when conversion or any side effects were observed. RESULTS Three of the 6 horses cardioverted successfully without side effects. The other 3 horses did not convert and showed adverse effects, including diarrhoea. In the latter, there were no important circulatory problems, but the diarrhoea continued for 10-14 days. The third horse had to be subjected to euthanasia because a concomitant Salmonella infection worsened the clinical signs. CONCLUSION The applied treatment protocol based upon pharmacokinetic data achieved clinically relevant concentrations of AD and desethylamiodarone. POTENTIAL RELEVANCE Intravenous AD has the potential to be an alternative pharmacological treatment for AF in horses, although AD may lead to adverse drug effects, particularly with cumulative dosing.

Acute Respiratory Failure Caused by Leptospira spp. in 5 Foals

A lthough clinical disease in horses is uncommon, serological surveys show that equine exposure to leptospires is very common. In some populations, up to 80% of the animals have leptospiral antibodies. In Europe, Leptospira interrogans serovar bratislava, copenhageni, and patoc are the presumed host-adapted serovars of horses. Clinical leptospirosis in horses is primarily associated with recurrent uveitis, abortions, stillbirth, neonatal disease, hemolysis, renal disease, and liver disease. Unlike cases in humans or small animals, respiratory signs caused by alveolar hemorrhage have not been associated with leptospirosis. The present report describes 5 cases of foals with respiratory distress caused by leptospirosis.

Long-term follow-up of atrial function after cardioversion of atrial fibrillation in horses

Atrial fibrillation (AF) causes atrial electrical and contractile remodelling in horses. The aim of this study was to quantify left atrial (LA) contractile function and its time course of recovery after cardioversion of naturally-occurring AF in horses. The study population included 42 AF horses which were successfully treated using transvenous electrical cardioversion TVEC (n=39) or quinidine sulfate (n=3), with trivial or mild mitral regurgitation present in 25 horses. Thirty-seven healthy horses were used as controls. AF duration was estimated based on the history and previous examinations. Echocardiography was performed during general anaesthesia after TVEC (day 0) and on days 1, 2, 6 and then 7 weeks after cardioversion. The two-dimensional (2D) echocardiographic measurements included LA diameter, area and ejection phase indices such as fractional shortening. Atrial TDI measurements included peak myocardial velocity during atrial contraction (A), time to onset A, time to peak A and duration of A. During follow-up after cardioversion, atrial contractile function measured by 2D echocardiography and TDI gradually improved. At 7 weeks following cardioversion, TDI-based myocardial velocities returned to reference values. However, AF horses still showed significantly larger atrial dimensions, lower 2D ejection phase indices and prolonged TDI-based conduction time compared to the control group. In conclusion, AF-induced atrial contractile dysfunction gradually improves in the weeks following cardioversion, but at 7 weeks post-cardioversion, significant differences remain compared to healthy controls.

Tissue Doppler imaging and 2-dimensional speckle tracking of left ventricular function in horses exposed to lasalocid.

BACKGROUND Tissue Doppler imaging (TDI) and 2-dimensional speckle tracking (2DST) can quantify left ventricular (LV) function in horses. OBJECTIVES To evaluate LV function by TDI and 2DST in horses with myocardial dysfunction after accidental ionophore intoxication. ANIMALS Sixty-seven horses exposed to lasalocid in feed. METHODS Prospective study. Horses were included in the study if a full cardiac examination was performed, consisting of determination of cardiac troponin I (cTnI), electrocardiography, and echocardiography. By TDI, radial systolic velocity and strain were measured. By 2DST, circumferential (SC) and radial (SR) strain at papillary muscle and chordal level and longitudinal (SL) strain were measured. RESULTS Twenty horses showed signs of myocardial injury. Forty-nine examinations were performed on these horses between day 30 and 490 after suspected onset of exposure. Five horses had increased cTnI and ventricular tachycardia and 15 had increased cTnI without ventricular tachycardia. Horses with mild myocardial damage showed few significant differences compared with a control group. Horses with severe myocardial damage showed severely decreased TDI, 2DST and fractional shortening measurements (P < .05), indicating impaired LV function. Long-term follow-up of 2 surviving horses demonstrated full recovery in 1 horse and permanent myocardial fibrosis in the other. The lowest measurements per horse (n = 20) for all TDI measurements, SL, SR at chordal level, and FS correlated significantly with maximal cTnI (P < .05). Over all examinations (n = 49), TDI and 2DST measurements correlated well with FS (P < .05). CONCLUSIONS AND CLINICAL IMPORTANCE The TDI and 2DST measurements allowed accurate detection and quantification of LV dysfunction in horses exposed to lasalocid.

Human and equine cardiovascular endocrinology: beware to compare

Cardiac biomarkers such as troponins and natriuretic peptides are routinely used in human medicine for the evaluation of myocardial damage and heart failure. Recently, these markers have also been introduced in veterinary medicine. Comparison between human and equine cardiac biomarker studies show important species differences, which can partly be explained by variations in physiology or pathophysiology. Most important are physiological differences in heart rate, cardiovascular response to exercise, food and water intake, and molecular elimination in plasma. Pathological differences are even more prominent. In humans, troponins and natriuretic peptides are mostly used for the diagnosis of acute coronary syndromes and heart failure. These cardiac entities, however, are rare in horses. In this species, cardiac biomarkers are rather proposed for the assessment of valvular or myocardial disease. In conclusion, these species differences corroborate that extrapolation of cardiac biomarker data should always be performed with caution and species-specific data should be applied whenever possible.

Evaluation of tissue Doppler imaging for regional quantification of radial left ventricular wall motion in healthy horses

OBJECTIVE To compare the feasibility and repeatability of tissue Doppler imaging (TDI) for quantification of radial left ventricular (LV) velocity and deformation from different imaging planes and to correlate cardiac event timing data obtained by TDI to M-mode and pulsed-wave Doppler-derived time intervals in horses. ANIMALS 10 healthy adult horses. PROCEDURES Repeated echocardiography was performed by 2 observers from right and left parasternal short-axis views at papillary muscle and chordal levels. The TDI measurements of systolic and diastolic velocity, strain rate, strain peak values, and timing were performed in 8 LV wall segments (LV free wall and interventricular septum from right parasternal views; left and right region of LV wall from left parasternal views). The inter- and intraobserver within- and between-day variability and measurement variability were assessed. The correlation between TDI-based measurements and M-mode and pulsed-wave Doppler-based time measurements was calculated. RESULTS TDI measurements of velocity, strain rate, and strain were feasible in each horse, although deformation could often not be measured in the LV free wall. Systolic and diastolic time intervals could be determined with low to moderate variability, whereas peak amplitude variability ranged from low to high. The TDI-based time measurements were significantly correlated to M-mode and pulsed-wave Doppler measurements. CONCLUSIONS AND CLINICAL RELEVANCE TDI measurements of radial LV velocity and deformation were feasible with low to moderate variability in 8 LV segments. These measurements can be used for evaluating LV function in further clinical studies.

Temporary transvenous atrial pacing in horses: threshold determination

The purpose of this study was to perform temporary atrial pacing and to determine the atrial strength-duration (S-D) curve which displays the minimal pulse intensity necessary to achieve atrial capture. In 7 horses, atrial pacing was applied using a temporary pacing catheter and a pacemaker as electrical pulse generator. Using the stimulus reduction method, 3 approaches for atrial threshold determination were used. With the fixed pulse width method, at several pulse widths, the corresponding minimal amplitudes to achieve capture were determined, describing an S-D curve. With the fixed amplitude method, the corresponding threshold pulse widths were determined at several fixed amplitudes. The third method proved to be the best and was a combination of both aforementioned methods to determine 2 points of the S-D curve. From these 2 points the whole S-D curve was calculated using a mathematical equation. Temporary pacing can be used to terminate atrial flutter, to induce atrial arrhythmias or to obtain more information about the electrophysiological properties of the heart, such as the atrial refractory period, atrial vulnerability and atrioventricular conduction.

Atropine reduces dobutamine‐induced side effects in ponies undergoing a pharmacological stress protocol

REASONS FOR PERFORMING STUDY High-dose dobutamine stress echocardiography has been shown to be cardiotoxic and arrhythmogenic in horses. However, the test may have benefit in practice as a pharmacological challenge of exercise without the treadmill being required. OBJECTIVES To investigate the effect of low-dose dobutamine on cardiac performance in ponies previously treated with atropine, in order to develop a pharmacological protocol that allows examination of the equine heart under stimulation. METHODS In 13 healthy Shetland ponies, heart rate (HR), stroke index (SI) and cardiac index (CI) were calculated from pulsed-wave Doppler ultrasound measurements performed at rest and during incremental steps of dobutamine infusion. Group 1 (n = 7) received dobutamine infusion at 2 microg/kg bwt/min for 5 mins followed by incremental rates of 5 microg/kg bwt/min every 5 mins, from 5 to 40 microg/kg bwt/min. Group 2 (n = 6) received dobutamine infusion in incremental rates of 1 microg/kg bwt/min, every 5 mins, from 2 microg/kg bwt/min to 5 microg/kg bwt/min, after premedication with 2 injections of 25 microg/kg bwt of atropine 5 mins apart. RESULTS The increase in CI during the pharmacological challenge was higher in Group 2 and reached about 2.5 times the resting value. This increase in CI was mediated by a significant increase in HR in both groups, while SI significantly decreased in Group 1 and did not change significantly in Group 2. Ponies of Group 1, but not those of Group 2, showed excessive restlessness and cardiac arrhythmias during the pharmacological challenge and a high intragroup variability in cardiac response. CONCLUSIONS The results of this study suggest that a low dose of dobutamine in ponies previously given atropine could be a helpful pharmacological protocol to perform stress echocardiography in equids. POTENTIAL RELEVANCE Further studies should evaluate left ventricular wall motion in horses undergoing low-dose dobutamine protocol after pretreatment with atropine.

Cardiovascular responses to transvenous electrical cardioversion of atrial fibrillation in anaesthetized horses.

OBJECTIVE To examine the influence of direct current shock application in anaesthetized horses with atrial fibrillation (AF) and to study the effects of cardioversion to sinus rhythm (SR). STUDY DESIGN Prospective clinical study. ANIMALS Eight horses successfully treated for AF (transvenous electrical cardioversion after amiodarone pre-treatment). METHODS Cardioversion catheters and a pacing catheter were placed under sedation [detomidine 10 microg kg(-1) intravenously (IV)]. After additional sedation (5-10 microg kg(-1) detomidine, 0.1 mg kg(-1) methadone IV), anaesthesia was induced with ketamine, 2.2 mg kg(-1) and midazolam, 0.06 mg kg(-1) (IV) in a sling and maintained with isoflurane in oxygen. Flunixin meglumine, 1.1 mg kg(-1), was administered IV. Shocks were delivered as biphasic truncated exponential waves, synchronized with the R-wave of the electrocardiogram. Monitoring included pulse oximetry, electrocardiography, capnography, inhalational anaesthetic agent concentration, arterial blood pressure, LiDCO and PulseCO cardiac index (CI) and arterial blood gases. Values before and after the first unsuccessful shock and before and after cardioversion to SR were compared. RESULTS Values before the first shock were comparable to reported values in healthy, isoflurane anaesthetized horses. Reliable CI measurements could not be obtained using the PulseCO technique. Intermittent positive pressure ventilation was required in most horses (bradypnea and/or PaCO(2) >8 kPa, 60 mmHg), while dobutamine was administered in two horses (0.3-0.5 microg kg(-1) minute(-1)). After the 1st unsuccessful shock application, systolic arterial pressure (SAP) was decreased (p = 0.025), other recorded values were not influenced (CI measurements not available for this analysis). SR was associated with increases in CI (p = 0.039) and stroke index (p = 0.002) and a decrease in SAP (p = 0.030). CONCLUSIONS AND CLINICAL RELEVANCE Despite the presence of AF, cardiovascular function was well maintained during anaesthesia and was not affected by shock application. Cardiac index and stroke index increased and SAP decreased after cardioversion.