Diagnostic approach to equine cardiology

Why is it hard to assess cardiac function at rest

• Low resting heart rate (30-40)

• Horses hide CV dx at rest

• Large heart, big change in heart rate (HR) (highest 240) and stroke volume (SV) with exercise and training

• Massive cardiac reserve

• High vagal tone → related arrhythmias & cardiac abnormalities common in horses

• Often mild or no signs of cardiac disease in early stages or at rest/low level exercise

How does cardiac disease present in horses?

• History of poor performance (depends on use)

• Clinical signs of cardiac failure (rare)

• Systemic illness → secondary heart disease

• Often incidental finding in pre-purchase examination and vaccination

What do you need to do if you find a cardiac murmur/arhythmia in a vetting?

• Interpret findings according to use of the horse (more significant in athletes)

• Many have no effect on performance on life expectancy

What can cardiac condition affect?

• Athletic performance

• Risk of collapse (→ human injury)

• Resale value

• Risk of developing CHF (death)

What is being shown in this ECG of a horse?

• Atrial fibrillation (bigger horses more likely to have)

• Irregularly irregular pattern

• No p wave —> fibrillating baseline

• Low HR at rest, but cannot be ridden (don’t exercise)

What can be used to investigate the CV system?

• History / signalment

• Clinical Examination / Auscultation (be aware of gut sounds caused by colon, resp sounds, background noise etc.)

• +/- Ancillary techniques

  • ECG +/- exercise and 24-hour

  • Echocardiography (Ultrasound)

  • Clinical pathology

  • Exercise testing

How would you determine the effect of a heart condition when exercising?

Strava trace and ECG attached then exercise the horse

What useful things can we find out when taking a history?

• Include performance history

• Current fitness level

• History of any concurrent disease especially respiratory noise, EIPH etc.

What disease in other bodily systems can cause a cardiac abnormality?

What do we assess about the pulse?

Peripheral arterial pulses —> facial

• Regular —> timing and strength

• Strength —> diff between diastolic and systolic

• Easy to occlude

• How turgid the artery is

• Palpate while auscultating

What can severe backflow from the aortic valve (severe aortic valve regurg) cause?

Bounding 'hyperdynamic' pulse

What does a high jugular pulse tell us about systemic pressure?

• Jugular pulse should not be observed more than one third of the jugular

• Increased pressure in the right side of the heart

What do we assess in the cv system?

• Heart Rate

• Peripheral oedema

  • Ventral oedema - inc hydrostatic pressure

• Mucous membranes

  • Colour

  • CRT

• Hydration status

• Peripheral perfusion

What is being shown here?

Build up of blood in veins (increased BP) due to right sided CHF

What do we listen for in cardiac auscultation?

• Heart Rate:

  • Physiological tachycardia:

    • Exercise, temperature, stress

  • Pathological tachycardia

    • Metabolic, compensation for reduced stroke volume, reduced ABP (arterial blood pressure)

• Rhythm

  • Regular

  • Regularly irregular

  • Irregularly irregular

• Pulse

  • Quality

  • Deficits

• Murmurs

What is the process of auscultating the heart?

• Quiet environment

• Take time

• Let horse settle

• Get into the rhythm

• Pull leg forward —> opens up cardiac window

• Feel for the apex beat (i.e. most prominent beat = @ mitral valve) then move dorsally or cranially

Where do you put your stethoscope on the left and right side?

Pull leg forward, stick stethoscope bell right under triceps just dorsal to point of elbow (harder on right)

What valves are you listening to on the right and left side?

Left

Right

What is the dorsal view of the valves?

Can hear the aortic on the right also

Describe the basic heart sounds

• Depolarisation, systole (contraction) —> AV valves shut, semi-lunar valves open

• Repolarisation, diastole (relaxation) —> AV valves open, semi-lunar valves shut

What are the features of the S1 heart sound?

• Ventricles contract

• Shutting of AV valves (Mitral/tricuspid)

• “ LUB “

What are the features of the S2 heart sound?

• Ventricles relax

• Shutting of Semilunar valves (Aortic/Pulmonic)

• “ DUP “

What are the other common heart sounds in horses?

• S4: ATRIAL CONTRACTION (Just before S1) = more common

• S3: END OF RAPID VENTRICULAR FILLING (Just after S2) = usually seen in fit young horses i.e. only sometimes heard

How do the heart sounds fit with the ECG?

Where in the heart are the different heart sounds loudest?

How does the duration of systole and diastole differ between different heart rates?

Resting heart rates —> Systole much shorter than diastole (long pause)

Higher heart rates —> more equal

What are examples of peripheral pulses you can take on the limbs?

What is the main cardiac biomarker we test for?

• Cardiac Troponin (I or T —> I most commonly used)

  • marker of muscle damage in the heart (myocardial dx)

  • Mild increases in response to endurance/sprint racing

• Minimal use of natriuretic peptides in horses

When would we use an ECG on horses?

• Suspected non-physiological arrhythmia on auscultation

• Chamber dilation on echocardiography

• Poor performance

• Monitoring of patients with CVS compromise e.g. systemically ill, under anesthesia

What do the different waves represent on an ECG and how does the normal complex differ in a horse?

Downward QRS complex

Describe the match up of the P QRS T waves to horse heart sounds

Where do you place the ECG leads?

• Base —> apex trace (Only cross the heart in one direction)

• The closer leads are to MEA, the larger amplitude deflection you get on your ECG trace

  

(lellow left, red right)

What is the usefulness of a Telemetric and 24 hour ECG?

• No wires between horse and machine

• Exercise, continuous assessment, or treatment monitoring

• Detection of arrhythmias that may be missed on auscultation (can watch remotely)

How does the electrode placement differ in exercising ECGs?

• Can get electrical interference due to muscular activitiy beneath electrodes during exercise

What is measured in exercising ECG?

R-R interval —> normal? getting shorter / longer?

What are the features of echocardiography in horses?

• Standard image planes

• Use of Doppler

• M mode technique

(similar to dogs/cats)