Evaluation of poor performance in the equine athlete (Proceedings)

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Common sources of poor performance: lameness, upper airway, lower airway, cardiac, myopathy, or any combination of the above.

Common sources of poor performance

• Lameness

• Upper airway

• Lower airway

• Cardiac

• Myopathy

• Or any combination of the above

Incidences of causes of poor performance

• Morris EA et al (EVJ 1991;23:169-174)

o 275 racehorses

o 84% had more than one problem

o 40% dx with airway obstruction

• Martin BB et al (JAVMA 2000:216(4):554-558)

o Definitive diagnosis only in 73.5%

o 43% dynamic airway obstruction

o 22% clinically important arrhythmias

o 15% had concurrent airway obstruction

o 7% rhabdomyolyis

o 10% lameness

o 36% subclinical myopathy

• Wilsher S et al (EVJ 2006:38(2) 113-118)

o Musculoskeletal problems

• 55% of 2 year olds

• 45% of 3 year olds

• Sore shins the most common problem (29%, 12%)

o Respiratory problems

• 16% of 2 year olds

• 13% of 3 year olds

• IAD the most common problem (13%, 8%)

• Inflammatory airway disease

o 22-50% incidence

o Neutrophilic inflammation in bronchi, bronchioles, and trachea

o Tracheal mucus accumulation

o BAL

• total nucleated cells

• Total and % neutrophils

• Total and % lymphocytes

• Mast cells

• Eosinophils

o TTW = neutrophilic inflammation

o Associated with EIPH, environmental exposure to respiratory irritants, specific bacteria

Diagnostics for poor performance

• Field diagnostics

• High speed treadmill exam

Upper airway

• Resting endoscopy

• Nasal occlusion

o Achieves pharyngeal and tracheal pressures consistent with maximal exercise (Holcombe SJ et al AJVR 1996 Sep;57(9):1258-60)

• Treadmill endoscopy

• Field exercising endoscopy

• Evaluation of poor performance

Lower airway

• Disorders include:

o Inflammatory Airway Disease (IAD)

o Exercise Induced Pulmonary Hemorrhage (EIPH)

• Diagnostics

o Bronchoalveolar lavage

• 100-250 ml of sterile fluids drawn up into 60cc syringes

• 50 ml mepivacaine

• Pass blind or endoscopically guided

• Infuse mepivacaine as passing tube

• Pass until wedged

• Inflate cuff

• Infuse fluids

• Draw back until no further recovered (expect 40-60% retrieval)

o Transtracheal wash

• Endoscopic guided:

• Teflon tubing passed through biopsy channel in endoscope (use guarded catheter if culture desired)

• Infuse 100 ml sterile fluids

• Aspirate for retrieval of fluids and sample

• Percutaneously

• Mid-cervical region between tracheal rings

• Aseptic preparation

o Malikides et al recommends using both to evaluate the entirety of the lower airway (Aust Vet J 2003 81:685-7)

o Pre and post exercise?

• TTW values shown to be different pre and post-exercise (Malikides et al Aust Vet J 2007 85(10):414-419)

o Endoscopic tracheal mucus scores

o IAD associated with presence of specific bacteria so culture may be important. (Wood JLN et al J Clin Microbiol 2005;43:120-126)

o Cytology

• Total nucleated cell counts (normal = < 300 cells/µL)

• % macrophages ( normal = 30-60%)

• % lymphocytes (normal = 30-70%)

• % neutrophils and appearance (normal = < 5% non-degenerate)

• Mast cells (normal = occasional)

• Eosinophils (normal = occasional)

• Mucus

• Hemosiderophages

o Arterial blood gases during exercise

• Cannot be taken alone as a reflection of total airway function

• PaO2, SaO2

• Evaluation of oxygen exchange that can be compromised by both upper and lower airway disease

o Other bloodwork

• Lactate

• Marked increases indicate poor conditioning

Cardiac

• Echocardiography

o Performed within 3 minutes of maximal exercise while HR still > 100 bpm

• Right and left ventricular diameter (end diastole and systole)

• Interventricular septal wall thickness

• Left ventricular free wall thickness

• Fractional shortening

• Aortic root diameter

• Diameter of left atrial appendage

• Ejection time

• Septal to E-point separation

o Electrocardiography

• Obtained at rest and throughout test with Holter monitor or telemetry

• Evaluated for clinical significant arrhythmias

• Atrial or ventricular premature depolarization

• Ventricular tachycardia

Myopathy

• Obtain pre and post-exercise (30 min to 4 hours) CK

• May observe clinical rhabdomyolysis following exercise

• Sub-clinical myopathy = CK > 1,000 U/L

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