MMVD Flashcards
How do diuretics affect the (a) lungs and (b) heart?
(a) reduce cardiogenic pulmonary oedema
(b) reduce preload
What stage heart disease do you start frusemide?
Stage C (Heart failure)
What is a mid-moderate frusemide dose?
1-3mg/kg q8-12h
What dose of frusemide would you use in severe/refractory heart failure?
4mg/kg q8h
What is a potential serious side effect when starting frusemide therapy?
XS volume depletion and reduction in CO if circulating V decreases XS or if patient is dependent on high ventricular filling pressure to maintain CO (HCM, pericardial effusion) –> severe fall in CO –> Hypotension –> azotaemia
What electrolyte abnormality can occur dt frusemide tx?
hypokalaemia
How do venodilators effect the heart?
Cause relaxation in systemic and pulmonary veins –> increase capacity –> reducing preload
How do arteriodilators effect the heart?
Reduce afterload - thus reduce workload
(dt reduction of SNS and peripheral vasoconstriction mediated by RAAS and SNA)
What is a ‘balanced’ vasodilator?
it has both arterio and venodilator properties ie. Pimobendan
When is pimobendan indicated?
Stage B2 onwards
What is the IV dose of pimobendan in dogs?
0.15mg/kg IV (once then switch to PO)
What is the oral dose of pimobendan in dogs?
0.1-0.3mg/kg PO q12h (one hour before food)
When is pimobendan contraindicated?
hypertrophic cardiomyopathy or aortic stenosis
Why is pimobendan known as an ‘inodilator’
i. Increases binding affinity of calcium to cardiac troponin C
ii. inhibits cardiac phosphodiesterase (PDE) III -> reduces breakdown of cAMP –> increases myocardial contraction (and subsequent relaxation)
What vessels does Sildenafil act on?
predominantly veins (venodilator)
When do you start ACE inhibitors?
Stages C onwards
List 4 ACE inhibitors
- Benazepril
- Ramipril
- Imidapril
- Enalapril
What is the MOA of ACE inhibitors?
- Blocks conversion of angiotensin I –> angiotensin II
- -> decreases plasma aldosterone –> mild arteriolar/venous dilation –> Less Na+/H2O retention
- –> reduces pathologic remodelling/fibrosis
Dose of benazepril
0.25-0.5mg/kg q24h
What is the MOA of nitrates?
releases nitric oxide which causes vascular smooth muscle relaxation
When are nitrates indicated?
In acute, severe heart failure
Contrast administration of nitroprusside and nitroglycerin
Nitroprusside IV CRI (rapid acting, v. potent) in ECC
Nitroglycerin percutaneous ointment
MOA of sildenafil
Phosphodiesterase V inhibitor –> acts predominantly on pulmonary arterial vasculature –> reduces pulmonary arteriolar resistance
Indication of use of sildenafil
Treats pulmonary hypertension
i. Heartworm/severe lung disease
ii. Late stage MMVD
What is the oral dose of sildenafil?
0.25mg/kg q12h to 2mg/kg q8h
Start at low end and titrate upwards
Inotrope indications
i. Primary myocardial dysfunction (DCM)
ii. Secondary myocardial dysfunction (eg. myocardial exhaustion) in late MMVD/ severe arrhythmia causing rapid and prolonged contraction
What is the MOA of dobutamine?
Sympathomimetic direct acting on B1 receptors. –> increases force of ventricular contraction + rate of myocardial relaxation
When do you use dobutamine in heart disease?
IV by CRI (ECC) as rescue drug in acute heart failure.
Describe the pathology of MMVD
i. Affects mitral and tricuspid valve leaflets and chordae tendinae: pathology alters valve motion and closure
ii. Valve thickening, prolapse, annular dilation, mitral (and tricuspid) regurgitation
Compare the typical onset of MMVD in a toy poodle vs. a dalmation
typically smaller breeds have a slow progression through stages A–> D where in larger sized dogs they have a more rapid progression and onset of CHF.
List 5 more serious, later stage complications of chronic MMVD
i. chordae tendinae may rupture
ii. arrhythmias esp. supraventricular: atrial premature contractions, atrial fibrillation, syncope may become freq. w/ these arrhythmias
iii. cardiac cachexia develops in some cases
iv. atrium may rupture –> haemopericardium (sudden deterioration)
v. myocardial exhaustion
Actions taken at Stage A
simple recognise that some dogs such as CKCS/small breeds have a high risk of MMVD
No treatment
Actions taken at Stage B1
- thoracic rads +/or refer for echo: VHS<10.5 follow up rads q12m 10.5-11.4 q6-12m - measure BP for baseline - advise O to observe for disease progression (RR>30bpm sleeping)
No medications
Actions taken at B2
Pimobendan 0.25mg/kg q12h PO
+ all B1 actions if not already done
Actions taken at stable Stage C
Full cardiac evaluation (Echo)
Pimobendan 0.25mg/kg POq12h + frusemide 1-3mg/kg PO q12h
(+/- anti-arrhythmic if indicated)
List 3 anti-arrhythmics
Digoxin
Sotalol
Beta-blockers
Actions taken at acute Stage C presenting as an emergency
i. Oxygen
ii. Frusemide 2mg/kg IV –> then 2mg/kg IM/IV q1h until RR/RE good
iii. Pimobendan 0.15mg/kg IV
iv. Absolute rest
v. Anxiolytics (butorphanol, buprenorphine)
vi. Stabilise before rads.
Actions taken at progressing Stage C
Pimobendan + frusemide (as w/ C)
+ ACE inhibtor - Benazepril 0.25-0.5mg/kg PO q24h
+ Diet: low salt, prevent cachexia
Actions taken at Stage D
Meds (4) Pimobendan 0.25-0.3mg/kg PO q12h Frusemide >4mg/kg PO q12h Benazpril 0.25-0.5mg/kg PO q24h Spironolactone 1mg/kg q12h PO Diet: low salt \+/- anti-arrythmics \+/- drain effusions (pleural +/-ascites)
Actions taken at acute stage D CHF
i. O2
ii. Frusemide 2mg/kg IV q1h OR 0.66-1mg/kg/h CRI
iii. Pimobendan 0.25mg/kg PO or IV
iv. Drain effusions (pleural/ascites)
v. Buprenorphine 0.0075-0.01mg/kg + ACP 0.01-0.03mg/kg IV/IM (anxiolytic)
vi. Dobutamine 2.5-10ug/kg CRI (myocardial failure)
vii. Nitroprusside CRI (poorly responsive oedema)
viii. allow free access to water
3 signs of MMVD cardiac remodelling on rads
i. Straight cd. border (enlarged LV)
ii. Increased sternal contact (enlarged RV)
iii. Large left atrial wedge
