Standardised exercise testing in 17 reining horses: Musculoskeletal, respiratory, cardiac and clinicopathological findings

Evaluation of Cardiac Arrhythmias before, during, and after Treadmill Exercise Testing in Poorly Performing Standardbred Racehorses

The incidence of significant arrhythmias in sport horses and knowledge about their exact influence on athletic performance need to be clarified. The aims of the present study are to report the prevalence of cardiac arrhythmias during maximal treadmill exercise in poorly performing Standardbreds, and to investigate the possible relationship of demographic, cardiac and performance indices on premature complexes (PCs). Electrocardiographic Holter recordings before, during and after treadmill exercise testing of 158 poorly performing Standardbreds were analyzed retrospectively. Fifty horses did not have any type of arrhythmia. One hundred and eight horses had at least one type of arrhythmia, such as sinus arrhythmia (8.2%), sinoatrial block (3.2%), second-degree atrioventricular block (33.5%), supraventricular PCs (7.6%), and ventricular PCs (48.1%). A multiple regression analysis showed weak evidence that the occurrence of premature complexes decreases as the minimum heart rate increases, and a tendency for these arrhythmias to increase with increasing age and maximum lactate concentration. Our results suggest that PCs are frequent in poorly performing Standardbred racehorses, but further studies are necessary to clarify their role and clinical significance.

Retrospective analysis of lameness localisation in Western Performance Horses: A ten-year review

BACKGROUND

Similar to other high-level athletic disciplines, the western performance horse experiences a variety of orthopaedic conditions as a result of rigorous sport-specific physical demands. While musculoskeletal injury rates have been quantified in other equine disciplines, these data are lacking for the western performance athlete.

OBJECTIVES

To identify the most common anatomical regions of lameness in western performance horses being evaluated at the nation's largest sanctioned shows over a 10-year study period.

STUDY DESIGN

Retrospective review of clinical records.

METHODS

Records of diagnostic analgesia of western performance horses competing at nationally sanctioned shows were retrospectively reviewed over a 10-year period to identify affected limb(s) and lameness localisation patterns.

RESULTS

A total of 2267 lameness examinations on 2512 horses were included. The average lameness grade was 2.21/5 with 1504/2267 (56%) cases being primarily forelimb in origin while 1173/2267 (44%) were hindlimb related. Forelimb lameness localised to the distal limb in 40% of cases. The proximal metatarsus/distal tarsus was an identified source of lameness in 16% of cases, followed by the stifle in 9% of cases. All-around western performance horses most commonly presented with a single hindlimb lameness (315/1188, 26.5%) in contrast to reining horses that presented with a single forelimb lameness (135/616, 22%).

DISCUSSION

Determining the source of lameness through diagnostic analgesia remains challenging, but the continued assessment of response to diagnostic analgesia may help characterise discipline-specific injuries in western performance horses.

MAIN LIMITATIONS

Retrospective review of subjective responses to diagnostic analgesia.

CONCLUSIONS

The distal forelimb and distal tarsus/proximal metatarsus were the two most common anatomical regions of lameness based on response to diagnostic analgesia.

Hypercapnia and hyperlactatemia were positively associated with higher-grade arrhythmias during peak exercise in horses during poor performance evaluation on a high-speed treadmill

Cardiac arrhythmias are common in horses during exercise, especially immediately post-exercise. The objectives of this study were to: (1) describe the frequency and type of cardiac arrhythmias detected in horses during incremental high-speed treadmill exercise testing (ITET); (2) determine if arterial blood gas (ABG) changes at peak and immediately post-exercise were associated with arrhythmias; and (3) determine whether upper or lower airway disease was associated with exercising cardiac arrhythmias. Horses (n = 368) presenting for an ITET underwent resting and exercising upper airway endoscopy, resting, exercising and post-exercise electrocardiography, resting and post-exercise echocardiography and exercising ABG. Arrhythmias were graded by the most severe arrhythmia present. Grade 1 arrhythmias were defined as one or two atrial (APCs) or ventricular premature complexes (VPCs), or one APC and one VPC, detected in 6.9% at peak and 16% at 0-2 min post exercise.. Grade 2 arrhythmias were >2 APCs or VPCs, or both, detected in 5.8% at peak and 16.6% at 0-2 min post exercise. Grade 3 included complex arrhythmias (couplets, triplets, R on T, multiform complexes or paroxysmal atrial or ventricular tachycardia), detected in 4.4% at peak and 7.3% at 0-2 min post exercise. Both partial pressure of arterial CO₂ (PaCO₂; P = 0.008) and lactate (P = 0.031) were significantly associated with arrhythmias occurring at peak exercise, but not immediately post-exercise. As PaCO₂ and lactate increased, arrhythmia severity increased. Blood pH was significantly associated with grades 2 and 3 arrhythmias at 0-2 min post ITET (OR = 0.0002; P < 0.001). There was no significant association between grades 2 and 3 cardiac arrhythmias, inflammatory airway disease (IAD), or exercise-induced pulmonary hemorrhage (EIPH). When adjusted for lactate concentration (P = 0.06), higher PaCO₂ concentrations in horses with and without exercising upper respiratory tract (URT) obstruction were associated with higher likelihood of grades 2 and 3 arrhythmias (P < 0.01). This study demonstrated that at peak exercise, with severe hypercapnia and hyperlactatemia, there was increased risk for grades 2 or 3 cardiac arrhythmias and, as the PaCO₂ and lactate values increased further, the severity of those arrhythmias increased.

Cardiovascular Response to Exercise and Training, Exercise Testing in Horses

The physiology of exercise and training is fascinating, and hundreds of interesting studies have given insight into its mechanisms. Exercise testing is a useful clinical tool that can help veterinarians assess poor performance, fitness, and performance potential and prevent injuries. The clinically applicable aspects of cardiovascular adaptions to training and exercise testing are highlighted in this review. Different exercise tests should be used to evaluate horses performing in different disciplines and levels. Exercise tests that simultaneously assess several body systems can be beneficial when assessing poor performance, because this is often a multifactorial problem with signs not detectable at rest.

Assessment of the Cardiovascular System in Horses During Prepurchase and Insurance Examinations

Arrhythmias detected on prepurchase examination should be confirmed with an ECG. Exercising ECG determines if the arrhythmia is overdriven during exercise or is a safety concern. An echocardiogram is needed in all horses with a grade 3/6 or louder mid to late systolic, holosystolic, or pansystolic murmur or any holodiastolic decrescendo murmur to identify the cardiac abnormality and its hemodynamic impact. Most horses with arrhythmias and murmurs have a normal performance career and life expectancy and are insurable. Risks for sudden death and congestive heart failure associated with the common murmurs and arrhythmias are identified, because these horses cannot be insured.