Cardiovascular Flashcards
What treatment options exist to manage a bradyarrythmia such as “Sick Sinus Syndrome”?
Medical management is usually unrewarding
Test dose of atropine, if responsive, try propantolene orally
Usually requires pacemaker surgery
Name the basic mechanism for the four different classes of antiarrhythmics.
Class I: sodium-channel blockade
Class II: Beta blockade
Class III: potassium-channel blockade
Class IV: calcium-channel blockade
Why do excessively high heart rates have a deleterious impact on cardiac output?
They do not allow for adequate ventricular filling
What drug is most commonly used to manage atrial fibrillation when there is underlying myocardial disease?
Digoxin
What drug is most commonly used to convert idiopathic atrial fibrillation to a normal sinus rhythm, and what are its main toxicities?
Amiodarone
High incidence of side-effects including hepatotoxicity
What is the initial drug of choice in treating nearly all PVCs during hospitalization?
Lidocaine
What is an “escape beat” on an ECG and how does its presence impact the use of antiarrhythmics?
An escape beat is depolarization that occurs after a long pause that can help rescue the heart from complete standstill
Ventricular antiarrhythmics can cause cardiac arrest
Is lidocaine useful to treat ventricular arrhythmias, supraventricular arrhythmias, or both?
Ventricular arrhythmias
Is procainamide or mexiletine useful to treat ventricular arrhythmias, supraventricular arrhythmias, or both?
Ventricular arrhythmias
Is solatlol useful to treat ventricular arrhythmias, supraventricular arrhythmias, or both?
Both
Is amidoraone useful to treat ventricular arrhythmias, supraventricular arrhythmias, or both?
Both
Name the therapeutic goals in the management of hypertrophic cardiomyopathy (HCM) and what drugs we commonly use to accomplish these.
Treat underlying cause Decrease LA (and LV) pressure: Oxygen, Furosemide, low dose opioid (butorphanol) Relax cardiac muscle (positive lusitropy): Diltiazem (calcium channel blocker) Slow HR (negative chronotropy): Dilatiazem, beta 1 blocker (atenolol), nonselective beta blockers
Contrast the merits of diltiazem versus atenolol use in HCM.
Atenolol decreases the effects of catecholamine in hyperthyroidism and is give every 12 hours. The benefit of dilatiazem over atenolol has been questioned. Dilatiazem is given every 8 hours.
In early congestive heart failure (systolic heart failure) physiologic changes occur that allow “compensated” heart failure to exist. Explain those physiologic changes and how eventually overexaggerated responses lead to decompensated heart failure.
Heart failure –> reduced CO –> reduced BP –> reduced renal perfusion with activation of RAAS and activation of sympathetic nervous system –> salt and water retention and systemic arteriolar vasoconstriction
Salt water retention–> excessive preload
Systemic arteriolar vasoconstriction –> increased total peripheral resistance –> excess afterload
What are the therapeutic goals in the management of CHF (systolic heart failure)?
Decrease preload Decrease afterload Increase force of contraction Slow HR Decrease pulmonary edema
What drugs decrease preload?
Nitrates (Nitroglycerine, Nitroprusside)
Diuretics (Furosemide, Torsemide, Thiazides, Postassium-sparing (sprinolactone, triamterene, amiloride), Aldactazide (sprinolactone and hydrochlorothiazide))
What drugs decrease afterload?
Amlodipine
Hydralazine
What drugs increase the force of contration?
Dobutamine
Dopamine
Pimobendan
Digitalis glycosides (Oubain, Digitoxin, Digoxin)
Does nitroglycerine alter preload, afterload, or both?
Decreases preload
Does nitroprusside alter preload, afterload, or both?
Affects both
Do diuretics alter preload, afterload, or both?
Decrease preload
Does amlodipine alter preload, afterload, or both?
Decrease afterload
Does hydralazine alter preload, afterload, or both?
Decrease afterload
Do ACE inhibitors alter preload, afterload, or both?
Both
Do angiotensin II receptor antagonists alter preload, afterload, or both?
Both
Salt (sodium) restriction has historically been a method used in heart failure to reduce preload. What disadvantages might it however pose?
Palatability problems
Many cardiologists now feel that sodium restriction may activate RAAS too early especially if diuretics are used
Does nitroglycerin decrease afterload, preload, or both?
Preload
Furosemide decreases preload. What additional benefit does it provide when pulmonary edema is present?
Causes the release of vasodilatory prostaglandins in the lungs to lower pulmonary arterial pressure to help diminish pulmonary edema
For what group of cardiac drugs does tachyphylaxis limit the duration of their usefulness?
Nitrates
Why are hydrochlorothiazide or spironolactone seldom used as a sole diuretic in congestive heart failure (CHF), yet are commonly used as adjunct diuretics with furosemide, especially when pulmonary edema occurs despite furosemide therapy.
They cause weak diuresis, so it is often combined with furosemide in refractory cases
Explain how an Angiotensin converting enzyme (ACE) inhibitor, by virtue of inhibiting conversion of angiotensin 1 to angiotensin 2, has a beneficial effect in CHF.
It causes less vasoconstriction (both arteriolar (afterload) and venous (preload)) and it decreases aldosterone which will decrease sodium retention
How might NSAIDs interfere with ACE inhibitors?
NSAIDs may inhibit vasodilatory PG thereby decreasing GFR and/or inhibit the release of natriuretic PGs causing increased sodium retention
When might benazepril be preferred over enalapril as an ACE inhibitor?
In renal failure patients because enalapril can affect the kidney
Describe how renal function and body weight impact the dosing of digoxin
Renal function affects digoxin elimination
Dose on lean body weight
What benefit besides inotropy does digoxin provide in CHF?
Sensitizes baroreceptors –> increased parasympathomimetic effect –> slows conduction at AV node –> slowing of HR
Which electrolyte abnormality predisposes to digoxin toxicity?
Hypokalemia
Pimobendan is an oral inotrope. What other beneficial effect does it have?
It is also a vasodilator, decreasing afterload and preload
Absorption is enhanced and consistent in an acid stomach
What receptors are stimulated by dobutamine?
Selective stimulates a subset of beta1 receptors. Some beta 2 activity occurs
What are the clinical indications for dobutamine?
Target to raise systolic BP to 100-120 mmHg
What is a dobutmaine holiday?
Accumulates in cardiac muscle so that residual inotropy occurs after infusion
What are the receptors stimulated by dopamine?
Low doses stimulate beta1 and dopamine receptors
What is the dopamine therapeutic window?
Higher doses stimulate alpha receptors resulting in an increase in peripheral vascular resistance
Why are opioids often beneficial in pulmonary edema other than for sedation?
Morphine decreases preload by splanchnic vasodilation
Desensitizes CO2 receptors
What drug is used for left atrial enlargement with mild clinical signs?
Enalapril
What drug is used for left ventricular enlargement with systolic impairment?
Pimobendan/digoxin
What drug is used for atrial fibrillation with a high heart rate?
Digoxin and diltiazem
What drug is used for early pulmonary edema?
Furosemide
What drug is used for refractory pulmonary edema?
Chlorothiazide or spironolactone to furosemide
What drug is used for PVCs?
Procainamide or sotolol
How do pulmonary vessels differ in their response to hypoxia versus other vessels in the body?
Pulmonary vessels undergo vasoconstriction
What is considered the vasodilator of choice in the management of pulmonary hypertension?
Oxygen
Which breed of dog may be more prone to digoxin toxicity?
Dobermans
What drugs are used as vasopressors?
Dobutamine Epinephrine Norepinephrine Vasopressin Dopamine Phenylephrine Ephiderine
How does dobutamine works as a vasopressor?
Acts to raise blood pressure by increasing CO. Not a vasoconstrictor
How does epinephrine works as a vasopressor?
Stimulates the heart and vasoconstricts
How does norepinephrine works as a vasopressor?
Stimulates alpha1 and beta1 receptors with modest activity on beta2 receptors. Causes vasoconstriction and cardiac stimulation
How does vasopressin works as a vasopressor?
Causes vasoconstriction without cardiac stimulation
How does dopamine works as a vasopressor?
High dose: alpha1 receptor stimulation causes vasoconstriction
How does phenylephrine works as a vasopressor?
Causes vasoconstriction without cardiac stimulation
How does ephiderine works as a vasopressor?
Causes indirect effect by the release of norepinephrine at the postsynaptic alpha and beta receptors
Why are vasopressors used only after more conservative measures have failed to adequately raise blood pressure?
Vasoconstricting vasopressors may decrease perfusion to some tissue
What is the rationale for using epinephrine IV for cardiac asystole?
Stimulates the heart and vasoconstricts
Encourages preload to return to the heart during preload
What is the rationale for using epinephrine IM for anaphylaxis?
Raises BP while avoiding ventricular fibrillation
Beta2 are in muscle blood vessels- so it causes rapid onset IM and avoids cardiac effects.
What is the rationale for using epinephrine SQ for acute bronchoconstriction without hypotension?
Reverses bronchocontrction
Blood vessels are primarily alpha1 receptors. So you get slower absorption, less risk of cardiac effects
Discuss the preference of amlodipine versus enalapril in the management of hypertension in the dog versus cat.
Dog: enalopril first, add amlodipine if necessary
Cat: Amlodipine first, enolapril or beta-blocker may be combine with amlodipine in refractory cases
How do aspirin and clopidogrel have their anticoagulant effect?
Aspirin: inhibits platelet function by its effects on thromboxane
Clopidogrel: Inhibits platelet function by irreversibly inhibiting ADP receptors on the platelet membrane
Why is low molecular weight heparin often preferred over regular unfractionated heparin? What clotting factors are affected?
Low molecular weight heparins inactivate factor Xa activity but not thrombin activity and are less likely to cause accidental hemorrhage unlike unfractioned heparin
It inactivates factor Xa activity, but not thrombin activity
Why is warfarin not used therapeutically as an anticoagulant in animals?
The small therapeutic index makes it difficult to adjust the dose for the anticoagulant effect without causing bleeding
What ophthalmic indication is tPA used for?
Hyphema (blood in anterior chamber). Injected into anterior chamber to decrease risk of glaucoma
What is “reperfusion injury” as it relates to tPA use?
We hoped that tPA, as a thrombolytic, would break down saddle thrombus in cats. While it did, the cats died from reperfusion injury due to the thrombus having cut off blood supply to the hind limbs for so long. Also, those that did survive the reperfusion injury ended up with a saddle thrombus again.
What evidence supports the use of acepromazine in laminitis?
Shown to increase blood flow to laminae in healthy horses through vasodilation
What evidence supports the use of nitroglycerine in laminitis?
Shown to increase blood flow to laminae in healthy horses through vasodilation
Limited and conflicting evidence for use
What evidence supports the use of isoxsuprine in laminitis?
Peripheral vasodilator; unclear mechanism involving either beta receptor stimulation or alpha receptor antagonism
Limited and conflicting evidence for use
What evidence supports the use of DMSO in laminitis?
Given IV early in laminitis as anti-inflammatory and mild platelet inhibitor
Limited and conflicting evidence for use
What evidence supports the use of pentoxyfylline in laminitis?
Increases flexibility of the RBC membrane leading to increased flow through narrow vessels
Limited and conflicting evidence for use
