Common Equine Cardiovascular Conditions PDF

Common Equine Cardiovascular Conditions ANDY DURHAM BSC.BVSC.CERTEP.DEIM.DIPECEIM.MRCVS Learning Objectives Following this lecture students should be able to  Understand the common causes of heart murmurs in horses  Understand which heart murmurs are clinically concerning and which are n...

Common Equine Cardiovascular Conditions ANDY DURHAM BSC.BVSC.CERTEP.DEIM.DIPECEIM.MRCVS Learning Objectives Following this lecture students should be able to  Understand the common causes of heart murmurs in horses  Understand which heart murmurs are clinically concerning and which are not  Understand the importance of valvular regurgitation and ventricular septal defect in relation to prognosis and performance  Differentiate between common dysrhythmias in horses  Understand which dysrhythmias are clinically concerning and which are not  Recognise the clinical presentation and diagnosis of atrial fibrillation in horses Heart Murmurs  A heart murmur is an abnormal noise that is heard during the cardiac cycle  They are generally caused by turbulent (rather than laminar) flow of blood  They are detected by auscultation and assessed further (if necessary) with ultrasound (echocardiography)  They MAY OR MAY NOT be associated with underlying cardiac disease: 1. Some murmurs occur in an entirely normal heart and are of no consequence (“physiologic”, “functional”, “flow” murmurs) 2. Some murmurs are associated with cardiac abnormalities i. Some have no significant effect on cardiac output ii. Some do affect cardiac output (“pathologic” murmurs)  Equine murmurs – general rules  valvular murmurs in horses are generally due to regurgitation rather than stenosis  pulmonary valve murmurs are very rare  tricuspid valve (RAV) murmurs are rarely significant Therefore:  potentially significant valvular murmurs tend to be caused by mitral (LAV) and/or aortic valve regurgitation  the 3rd potentially significant murmur to consider is ventricular septal defect (VSD)  3 potentially significant murmurs  valvular murmurs in horses are due to regurgitation rather than stenosis  pulmonary valve murmurs are very rare  tricuspid valve (RAV) murmurs are rarely significant Therefore:  potentially significant valvular murmurs tend to be caused by mitral (LAV) and/or aortic valve regurgitation  the 3rd potentially significant murmur to consider is ventricular septal defect (VSD)  Auscultation: 3 pairs of mumurs MURMUR UNIMPORTANT POTENTIALLY IMPORTANT LEFT systolic Aortic ejection Mitral insufficiency LEFT diastolic Ventricular filling Aortic insufficiency Right systolic Tricuspid insufficiency VSD LEFT systolic 2. Mitral regurgitation throughout systole grade 1-5/5 PMI: often low radiates caudosorsally 1. Aortic flow usually short (early systole) Ao grade 1-3/5 M PMI: high, under triceps localised LEFT systolic 2. Mitral regurgitation throughout systole grade 1-5/5 PMI: often low radiates caudosorsally 1. Aortic flow usually short (early systole) grade 1-3/5 PMI: high, under triceps localised Mitral Insufficiency – clinical significance Unpredictable:  Mild regurgitation  not uncommon in successful performance horses  often remain stable with no impact on performance  May (or may not):  progress to left sided congestive heart failure?  cause respiratory signs?  develop atrial fibrillation?  cause collapse – pulmonary artery rupture? LV  Re-evaluate annually LA  Monitor resting heart rate  Should have echocardiography LEFT diastolic 2. Aortic regurgitation throughout diastole 1-5/5 high, under triceps radiates caudoventrally 1. Ventricular filling early diastole (squeak) Ao 1-2/5 M low, towards apex localised The Liphook Equine Hospital LEFT diastolic 2. Aortic regurgitation throughout diastole 1-5/5 high, under triceps radiates caudoventrally 1. Ventricular filling early diastole (squeak) 1-2/5 low, towards apex localised Aortic Insufficiency – clinical significance usually older horses RV usually clinically insignificant RA usually self limiting via increased LV contractility Ao bounding pulses reflect severe regurgitation volume overload may lead to mitral stretching and regurgitation susceptible to exercise induced ventricular arrhythmias (VPCs) should have echocardiography and ECG Aortic Insufficiency – clinical significance usually older horses usually clinically insignificant Prognosis poorer if: usually self limiting via increased ◦ Young contractility ◦ Multiple murmurs bounding pulses reflect severe ◦ VPCs (collapse/sudden death?) regurgitation ◦ Hyperkinetic pulses volume overload may lead to mitral ◦ Pulse pressure > 60 mmHg regurgitation susceptible to exercise induced ventricular arrhythmias RIGHT systolic 2. Ventricular septal defect throughout systole 3-5/5 low, near sternum 1. Tricuspid regurgitation throughout systole Tr VSD 1-5/5 high under triceps The Liphook Equine Hospital RIGHT systolic 2. Ventricular septal defect throughout systole 3-5/5 low, near sternum Both sound the same and can be differentiated based on: position (VSD low; TI high) echocardiography 1. Tricuspid regurgitation throughout systole 1-5/5 high under triceps Ventricular Septal Defect – clinical significance usually immediately below aortic/tricuspid valves flow generally left to right small defects ( 4 months – poor success and higher recurrence rate Atrial Fibrillation – medical treatment 1. Quinidine sulphate 22 mg/kg q 2h for up to 5 or 6 doses 2. not an entirely safe treatment! 3. monitor ECG continuously 4. do not move the horse (low blood pressure) 5. leave stomach tube in place 6. watch ECG for widening of QRS by >25% 7. after 5-6 doses give q 6h? 8. Lots of side effects – diarrhoea, depression, hives, (death!)….. Atrial Fibrillation – transvenous electrocardioversion (TVEC) at a few specialist centres higher success than quinidine  Summary points Murmurs: Short murmurs usually not significant Murmurs lasting throughout systole or diastole often are of potential significance (except tricuspid) Normal resting heart rate is reassuring only 3 common and potentially significant murmurs L pan/holo-systolic mitral regurgitation L pan/holo-diastolic aortic regurgitation R pan/holo-systolic VSD  Summary points Dysrhythmias: The vast majority of dysrhythmias in horses are either 2nd degree AV block (common) or atrial fibrillation (occasional) Regularly irregular “dropped beats” is very common and indicates innocuous 2nd degree AV block Random, irregular irregularity suggests atrial fibrillation which is a problem for athletic horses Other rare causes of dysrhythmia can also be identified on ECG  Further reading Reef et al (2014) Recommendations for management of equine athletes with cardiovascular abnormalities. Journal of Veterinary Internal Medicine. 28(3):749-61. Cardiology of the horse, Marr and Bowen Chapter 6 Electrophysiology and arrhythmogenesis Chapter 13 Dysrhythmias: assessment and medical management Chapter 16 Cardiac murmurs: valvular regurgitation and insufficiency