Name the 4 groups of positive inotropic drugs and name an example of each.
Cardiac glycosides (i.e. Digoxin) Methylxanthines (i.e. Theophylline) Catecholamines (i.e. Adrenaline) Inodilators (i.e. Pimobendan)
Name the 3 types of vasodilators.
Afterload reducers (arteriodilators)
Preload reducers (venodilators)
Dual effect (preload & after load reducers)
Vasodilators reduce what in the treatment of CHF?
Cardiac load
Name the 3 types of dual effect vasodilators and an example of each.
Alpha blockers (i.e. Prasozin) Angiotensin-converting enzyme (ACE) inhibitors (i.e. Benazepril) Calcium-channel blocking drugs (i.e. Amlodipine/Diltiazem)
Example of an afterload reducer vasodilator?
Hydralazine
Example of an preload reducer vasodilator?
Nitrates (nitroglycerine)
How do afterload reducers help treat congestive heart failure (MOA)?
Reduce blood flow impedance (i.e. aortic flow & pressure) Increase forward stroke volume Decrease myocardial O2 demand Decrease regurgitant flow in i.e. mitral valve insufficiency
What vasodilator drug decreases regurgitant flow caused by valvular insufficiencies to treat CHF?
Afterload reducers, i.e. hydralazine
How do preload reducers help treat congestive heart failure (MOA)?
Dilate systemic veins ā reduce venous return ā reduce LV filling pressure ā reduce preload
Name 4 catecholamines which are used in the treatment of hypotension.
Adrenaline Isoproterenol Dopamine Dobutamine
Administration of catecholamines in the treatment of hypotension?
I/V (due to short half-life) Single bolus/continuous infusion
T/F: Dobutamine is used in the treatment of hypotension in shock AND improving renal perfusion in renal failure.
False, dopamine (dobutamine has no effect on kidney)
Catecholamines: side effects?
Arrthymogenic esp. in conditions of hypoxia or acidosis
Catecholamines should not be administered with what general anaesthetic agent and why?
Halothane (sensitises the heart to catecholamines)
Catecholamine administration is contra-indicated if what other positive inotropic drug is currently prescribed to a patient?
Cardiac glycosides
What are the 2 most important vasodilator drugs used in the treatment of cardiac failure and other forms of cardiac insufficiency?
ACE inhibitors (i.e. Benazepril) Ca-channel blockers (i.e. Amlodipine, diltiazem)
Define inodilator.
Agent with inotropic effects that also causes vasodilation, leadings to decreased systemic and/or pulmonary vascular resistance (INOTROPY + VASODILATION)
Give an example of an inodilator.
Pimobendan
Pimobendan: MOA?
Positive inotrope via Ca sensitisation of cardiac muscle (via inhibition of phosphodiesterase III and increase sensitivity to intracellular Ca)
Peripheral vasodilator (arterial & venous)
Pimobendan: Clinical indications?
Dog with CHF (dilated cardiomyopathy/DCM)
Dog with chronic mitral valve insufficiency
T/F: Greater survival times are observed in CHF dogs treated with ACE inhibitors and furosemide vs. those of dogs treated with pimobendan.
FALSE, greater survival times seen with treatment with pimobendan
ACE inhibitors: list the different classes and drugs in each.
Class 1: Captopril Class 2: Enalapril / Benazepril Class 3: Lisinopril
Explain how heart failure stimulates the RAA axis and results in the production of angiotensin II.
Heart failure: decreased renal perfusion ā renin release Renin acts on angiotensinogen ā angiotensin I ACE (angiotensin-converting enzyme) acts on angiotensin I ā angiotensin II
Effects of angiotensin II?
Potent vasoconstrictor Aldosterone release (Na reabsorption, water retention) ADH release (water reabsorption in collecting ducts)
How does high angiotensin II increase preload?
Fluid retention and reabsorption due to ADH & aldosterone
How does high angiotensin II increase afterload?
Vasoconstrictor effects
How do ACE inhibitors decrease afterload and preload to treat CHF?
Reduce angiotensin II concentrations
Vasodilation = decrease afterload
Diuresis (less ADH, aldosterone) = decrease fluid retention = decrease preload
Anti-hypertensive effects of ACE inhibitors are potentiated by what?
Low-Na diet
ACE inhibitors: MOA?
Heart failure: ā renal perfusion, ā“ renin release Angiotensin I + ACE ā angiotensin II
Potent vasoconstrictor
Aldosterone release: Na reabsorption & water retention
ADH release: Water reabsorption in collecting ducts
ACE inhibitors: reduce amount of angiotensin II ā“ Vasodilation ā decrease bp/afterload ā“ Diuresis ā decrease fluid retention/preload
ACE inhibitors: Clinical uses?
Congestive heart failure
ACE inhibitors are usually administered concurrently with which other 2 drugs in the treatment of CHF?
Furosemide Diuretics
ACE inhibitors: side effects?
Hypotension Azotemia Increased risk of hyperkalaemia Increased risk of kidney failure (if pre-existing renal disease)
Calcium channel blockers: MOA?
Suppresses Ca2+ influx through plasma membrane channels in cardiac tissues/vascular smooth muscle ā“ Decrease intracellular Ca2+ concentrations = Decreased contractility = Vasodilation = Lower myocardial O2 demand = Slow AV demand = Lower impedance to LV ejection
Name the 2 most commonly used calcium channel blocker drugs?
Amlodipine Diltiazem
Calcium channel blockers: Clinical indications?
Diltiazem: hypertrophic cardiomyopathy in cats
What drug is used to specifically treat hypertrophic cardiomyopathy in cats?
Diltiazem (Ca-channel blocker)
Example of anti-arrhythmic drug in Class IA?
Quinidine
Example of anti-arrhythmic drug in Class IB?
Lignocaine
Class I of anti-arrhythmic drugs: MOA?
Blocks fast inward sodium currents of myocardial cells IA: Quinidine IB: Lignocaine
Class II of anti-arrhythmic drugs: MOA? Example?
Block Ī²-adrenoreceptors i.e. Propanolol
Class III of anti-arrhythmic drugs: MOA? Example?
Block K channel = prolong repol and extend refractor periods i.e. Amiodarone
Class IV of anti-arrhythmic drugs: MOA? Example?
Block Ca channel i.e. Amlodipine, diltiazem
Quinidine is used to treat what in horses?
Atrial fibrillation
Treatment procedure of using quinidine in horses to treat atrial fibrillation?
Test dose: 20 mg/kg dissolved in water by stomach tube (to test sensitivity to SE) Starting next day: 20 mg/kg dissolved in water every 2 hrs until rhythm returns to sinus rhythm Once arrthymia stops: Continue treatment for 2-3 days at 20 mg/kg twice daily DO ECG BEFORE EACH ADMINISTRATION TO SEE IF SINUS RHYTHM PRESENT
Oral dose safer
Urgent treatment? Can give I/V as infusion + I/V fluids simultaneously to overcome hypotensive effects