Cardiology Flashcards
What does the T-wave indicate?
Ventricular repolarization
Ventricles relax
How many seconds is each small square on ECG paper @ 25mm/sec?
0.04 seconds
How many seconds is each large square on ECG paper @ 25mm/sec?
0.2 seconds
What conditions make up Tetralogy of Fallot
Pulmonic stenosis, ventricular septal defect, right ventricular hypertrophy, overriding aorta
What do Beta Blockers do?
Antagonize sympathetic nervous system
Slow HR, decrease cardiac oxygen demand, control of some arrhythmias
What are some adverse effects of beta blockers?
Excessive bradycardia, worsening heart failure, bronchospasm, hypotension, depression, mask hypoglycemia
What is the flow of blood through the cardiovascular system? Starting with deoxygenated blood returning from body.
Deoxygenated blood moves from vena cava to right atrium
Through the tricuspid valve into right ventricle
Out pulmonary semilunar valve to pulmonary artery
Blood oxygenated in pulmonary circulation
Return to left atrium via pulmonary veins
Through bicuspid valve to left ventricle
Through aortic semilunar valve to aorta
Deliver oxygen via systemic circulation
Preload
Volume of blood in left ventricle before contraction
Afterload
Resistance to left ventricle ejection
Normal CVP
0-5 cm H2O
0-3mmHg
Normal Systolic BP
100-160mmHg
Normal diastolic BP
60-110mmHg
Normal MAP
80-120mmHg
Pathway of cardiac conduction
Sinoatrial Node (SA) Atrioventricular Node (AV) Bundle of His Bundle Branches Purkinjie Fibers
Clinical signs associated with right sided heart failure
Weakness, syncope, exercise intolerance, pallor, jugular distention, large liver/spleen, tachypnea, peritoneal and/or pleural effusion
Clinical signs associated with left sided heart failure
Weakness, collapse, coughing, orthopnea, pulmonary edema, hemoptysis
Pulmonary edema exclusively from left sided heart failure
Milrinone and amrinone
Phosphodiesterase-3 inhibitor
Inotrope and arteriolar dilator
For decompensated systolic failure
Increase contractility, decrease preload and afterload
May cause hypotension and tachyarrhythmia
Dobutamine
Sympathomimetic amine
Stimulates B-adrenergic receptors and increase calcium availability
Increase contractility and stroke volume
Increase cardiac output
Increase myocardial O2 demand and cardiac workload
Blood pressure and heart rate - normal to slightly increased
Injectable pimobendan
Dopamine
Sympathomimetic amine
Precursor of norepinephrine
Has dose dependent effects
Low - Arterial vasodilation
Mid - systemic arteriolar vasoconstriction
High - Significant vasoconstriction
Do not use with beta blockers
Causes tissue necrosis and sloughing if extravasated
Stimulates beta adrenergic receptors and calcium availability
Positive Inotropes
Sympatomimetic amines, phosphodiesterase inhibitors, Ca sensitizers, digitalis glycosides
Increase strength of contraction and cardiac output
Thiazide Diuretics
Hydrochlorothiazide
Act in proximal portion of distal convoluted tubule
Inhibits Na resorption and increase K excretion
Potassium Sparing Diuretics
Spirinolactone
May increase potassium concentration
Inhibits action of aldosterone on distal tubular cells
Loop diuretics
Act on ascending Loop of Henle
Furosemide, torsemide
Decrease reabsorption of Na and Cl
Increase excretion of K, H2O, Cl, Ca, Mg, H
Possible decrease in kidney function, electrolyte disturbances, dehydration
Digitalis glycosides
Digoxin, digitoxin
Digitoxin only for dogs
Increase cardiac performance, decrease fluid retention, decrease heart rate, stop supraventricular tachyarrhymias
TOXIC - require serum monitoring, higher risk when combined with diazepam, anticholenergics, tetracycline, erythromycin
Pimobendan
Calcium sensitizer
Positive inotrope, Ca sensitization, vasodilaton
Platelet aggregation inhibitor
Monitor HR and rhythm
Sildenafil
Phosphodiesterase inhibitor
Inotrope and arteriolar dilator
5-Phosphodiesterase inhibition
What is special about the AV node?
Decremental conduction
More frequent stimulation leads to slower conduction
Depolarization
Systole, contraction, Na ions move into the cell
Repolarization
Diastole, relaxation, K ions move out of the cell
What does the P-wave indicate?
Atrial depolarization
Tricuspid & bicuspid valves open
Blood moving into ventricles
What does the QRS complex indicate?
Depolarization (Q- septal, R - ventricular, S - Purkinje)
Tricuspid and bicuspid valves close
Ventricular contraction
Pacemaker of the heart
SA node
Diltiazem
Ca Channel blocker
Non-Dihydropyridine
Negative inotrope
Vasodilator and negative chronotrope
Use for AFib, supraventricular tachycardia, HCM
Has GI side effects, cardiac blocking effects, CNS effects, peripheral and pulmonary edema, liver effects
DO NOT USE IN KIDNEY DYSFUNCTION
Amlodipine
Calcium Channel Blocker Blocks Ca channels from moving Ca across barrier Used for systemic hypertension Do not use in renal disease Monitor blood pressure, vomiting Arteriolar vasodilator Dihydropyridine
ACE Inhibitors
Vasodilators
Decrease angiotensin II levels, allows for artery and venodilaton
Increase renal sodium and water excretion
Hypertension, valve disease, DCM, HCM
Enalapril, benazepril
Side effects - vomiting, diarrhea, hypotension, renal dysfucntion, hyperkalemia
Nitroglycerin
Vasodilators
Venodilator
Decrease preload
Monitor blood pressure, heart rate, sodium
Hydralazine
Vasodilator
Arteriolar vasodilator
Decreases afterload
Use in DCM, mitral valve regurgitation, intracardiac shunting
Nitroprusside
Vasodilator Arteriolar and venodilator (Combination vasodilator) Decreases afterload Decrease preload May cause decreased BP and increased HR Administration via CRI
Patent Ductus Arteriosus
Normally shuts 3-4 days after birth. If patent, flow of blood between aorta and pulmonary artery occurs. Blood moves from aorta to pulmonary artery (left to right shunt)
Congenital defect
Right side of heart carries _________ blood
Systemic
Left side of heart carries _________ blood
Pulmonary
Treatment for patent ductus arteriosus
Requires surgery - either coil or ligation
Stabilization with oxygen and diuretics and digoxin if needed
Which arrhythmia can be present in patent ductus arteriosis? Why?
AFib. Due to enlargement of left atrium from volume overload
Ventricular Septal Defect
Congenital defect
Hole in interventicular septum
Effect depends on size of defect and direction of flow
Small defect may have no effect
USUALLY - left to right shunting of blood (higher left sided pressure)
Treatment for ventricular septal defect
Palliative medical therapy - ACE inhibitors, symptomatic care
SURGERY REQURIED
What is the most common congenital cardiac defect in cats?
Ventricular septal defect
What is the most common congenital cardiac defect in dogs?
Patent ductus arteriosus
Tricuspid valve dysplasia
Congenital malformation of tricuspid valve caused by pathologic lesion to the valve
Usually leads to tricuspid regurgitation and right sided heart failure
Treatment for tricuspid valve dysplasia
Reduce preload - diuretics and ACE inhibitors
May need antiarrhythmics long term (CCBs, digoxin)
If ascites present may require abdominocentesis
Surgery possible
Mitral valve dysplasia
Can be from various causes - leaflet deformity adhering to adjacent structures, cleft leaflet, inappropraite length of chordae tendonae, abnormal valve annuls, or fibrous ring/membrane above valve
Often causes volume overload, dilation, hypertrophy of left atrium and ventricle - left sided heart failure
Treatment for mitral valve dysplasia
ACE inhibitors (reduce preload), diuretics and/or digitalis if needed
Tetraology of Fallot
Pulmonic stenosis, VSD, secondary right ventricular hypertrophy, overriding aorta
Treatment for tetraology of Fallot
Palliative medical management, surgery required
Pulmonic stenosis
Right ventricular outflow obstruction, more common in small breeds
Clinical signs of right sided heart failure
Feline hypertrophic cardiomyopathy
Disorder of myocardium with left ventricular hypertrophy and impaired myocardial relaxation
Decreased diastolic function
Leads to left atrial enlargement
What are some consequences of feline hypertrophic cardiomyopathy
Circulatory stasis, thormboembolism, pulmonary congestion and edema, pleural effusion
What are treatment options for feline hypertrophic cardiomyopathy?
Increase diastolic function, decrease myocardial ischemia, decrease circulatory congestion and hypoxemia Calcium channel blockers - diltiazem Furosemide for congestion Vasodilators (nitroglycerin) ACE inhibitor
Canine dilated cardiomyopathy
Decreased myocardial contractility leading to end systolic ventricular volume increasing, increased chamber volume
What are treatment goals for canine DCM?
Decrease preload, decrease afterload, improve contractility
Loop diuretics, vasodilator, dobutamine in emergency
Calcium channel blockers and beta blockers contraindicated
Which drug classes are contraindicated in DCM? Why?
Calcium channel blockers, beta blockers
Negative inotropes
Degenerative valvular disease
Most common cardiac disease in dogs
Mitral valve regurgitation or tricuspid valve regurgitation
What is the treatment for degenerative valvular disease
ACE inhibitors for vasodilation
Calcium channel blockers
Diuretics in case of edema
Infective endocarditis
Bacteria colonization of heart valves
Heartworm disease
Result of infection with Dirofilaria immitis
Potential complications of heartworm disease
Caval syndrome, obstruction of pulmonary circulation (leads to pulmonary hypertension), death, PTE
What is the treatment for heartworm disease
Doxycycline, immitacide, crate rest
Caval Syndrome
Large number of adult heartworms lodged in cranial and caudal vena cava and right atrium
ECG - undulating baseline with no normal p waves
Irregularly irregular R-R intervals
Normal - wide QRS complexes
Atrial fibrillation
Treatment for atrial fibrillation
Cardioversion, digoxin, calcium channel blockers
ECG - Tachycardia, rhythm is regular and extremely fast, p waves may be regular or irregular but often hard to locate, can be continuous or paroxysmal
Supraventricular tachycardia
Treatment for supraventricular tachycardia
Vagal maneuver, or calcium channel blocker, beta blocker, digoxin, diltiazem
ECG - Pause between two normal complexes >2x normal R-R interval
Sinus arrest
May be normal in brachycephalic dogs
ECG - Absence of P waves, wide bizarre QRS complexes, and bradycardia
Atrial standstill
What causes atrial standstill?
Hyperkalemia >7.5mEq/L
Addison’s disease, anuric/oliguric renal failure, DKA, metabolic acidosis, UO, ruptured bladder
Treatment of atrial standstill
IV dextrose, +/- insulin, IV bicabonate, calcium gluconate
ECG - Prolonged P-R interval, normal rate and rhythm
First degree AV block
What are some causes for first degree AV block?
Digitalis - most common
Any drug that delays AV conduction, hyperkalemia, increased vagal tone, myocarditis, doxorubicin, cardiomyopathies
ECG - Progressively prolonging P-R interval until dropped beat occurs, after several prolonged beats P wave with no QRS
Second Degree AV block - Mobitz type 1 (Wenckebach)
ECG - Consistent PR intervals, intermittent p wave with no QRS
Second degree AV block - Mobitz type 2
Which type of second degree AV block is more serious?
Type 2
More likely to progress to third degree, more likely to cause reduced cardiac output
What causes second degree AV block type 1?
Increased vagal tone, fibrosis, some drug/electrolyte imbalances
ECG - Consistent P-P interval, consistent R-R interval, irregular P-R interval
Third degree AV block
Atria and ventricles acting independently of one antoher
ECG - Bidirectional saw toothed atrial complexes, tachycardia
Atrial fluttter
ECG - Premature P waves, QRS normal or abnormal
Atrial premature complexes
Sick sinus syndrome
Any combination of sinus bradycardia, sinus arrest, SA block, vary/alternating brady/tachycardia, SA/AV conduction issues
What breeds are predisposed to sick sinus syndrome?
Mini schnauzer, cocker spaniel, dachshunds, pugs, west highland terriers
Usually older females
What is the treatment for sick sinus syndrome
Check atropine response -
If atropine responsive isoproteronol
If not atropine responsive, pacemaker required
Heart rate is controlled by?
Sympathetic nervous system
Heart failure
Inability to meet metabolic needs of peripheral tissues or instances when heart can only do so in presence of increased venous filling pressures
Describe renin-angiotensin-aldosterone system
Inability of the heart to provide normal renal perfusion leads to decreased renal blood flow and Na delivery to distal portion of nephron which induces renin release
Renin converts angiotensinogen into angiotensin I
Angiotensin I is converted to angiotensin II by ACE in pulmonary vasculature
Angiotensin II used in responses that promote cardiac injury and heart failure (renal sodium and water retention, production of aldosterone, thirst, vasoconstriction)
RAAS activation causes retention of fluid and myocardial and vascular remodeling
What causes renin release?
Decreased renal blood flow and Na delivery to distal portion of nephron
What does renin do in the body?
Converts angiotensinogen to angiotensin I
What is the significance of angiotensin I?
Converted into angiotensin II by angiotensin converting enzyme (ACE) in pulmonary vasculature
What is the role of angiotensin II in the body?
causes renal sodium and water retention, production of aldosterone, myocardial apoptosis, cardiac and vascular remodeling/fibrosis, thirst, vasoconstriction
How is angiotensin II produced?
Both by being converted from angiotensin I into angiotensin II by ACE
AND by independent generation - can be elevated despite ACE inhibitor therapy
What is the role of aldosterone in the RAAS system
Contributes to further retention of water and sodium in the body
What are the main effector molecules of the sympathetic nervous system?
Epinephrine and norepinephrine
What is the purpose of the sympathetic nervous system?
Evolutionary response to stress
Increase HR, CO, blood flow increase to stress-response organs (skeletal muscle)
What is the natriuretic peptide system?
Two hormones produced by myocardial tissue - induce natriuresis, diuresis, and vasodilation
Atrial natriuretic peptide and b-type natriuretic peptide (ANP & BNP)
Produced in response to stretch or stress of myocardial tissue
Counter regulatory system to RAAS and SNS
What is endothelin 1?
Vasoconstrictor produced by vascular endothelial cells in response to stress, angiotensin II, and other cytokines
Alters Ca cycling in muscles
What is arginine vasopressin?
Antiduretic hormone
Increases reabsorption of free water in renal collecting duct
What happens in a normal heart if preload increases?
Cardiac contraction increases
What can happen in a diseased heart if preload increases too much?
Cardiac contraction does not improve - excess preload leads to CHF
Poor contractility leads to low output heart failure
Generally, what are causes of diastolic heart dysfunction?
Primary impairments of ventricular filling, relaxation, compliance, or secondary to pericardial disease
What are the four clinical stages for grading heart failure?
Class A - overtly healthy animals at risk for developing heart disease (Dobermans >4 yrs, adult Maine Coons)
Class B - Diagnostic evidence of heart disease without clinical signs
- Asymptomatic
-Class B1 - No radiographic or echocardiographic changes
-Class B2 - Radiographic or echocardiographic changes
Class C - Cardiac remodeling and current or historical signs of heart failure
Class D - Severe and debilitating signs of heart failure -even at rest
Most dogs and cats develop (low output or congestive failure)?
Congestive failure
Congestive heart failure clinical signs
Pulmonary edema, effusion, ascities, increased RR/RE, coughing, activity intolerance, abdominal distention
Low output heart failure clinical signs
Weakness, depression, cardiogenic shock, syncope, hypotension, hypothermia, oliguria/anuria, lactic acidosis
How is low output heart failure treated
Positive inotropes
Causes of left sided heart failure in dogs
Degenerative mitral valve disease, DCM, patent ductus arteriosus
Causes of left sided heart failure in cats
Hypertrophic and restrictive cardiomyopathy
Pleural effusion
Causes of right sided heart failure in dogs
DCM, degenerative or congenital tricuspid valve disease, pulmonary hypertension
Causes of right sided heart failure in cats
Rare. Even if ascites, usually non-cardiac in origin
Forward flow failure with hypoperfusion
Cardiogenic shock
Cardiac output
Stroke volume x heart rate = cardiac output
Stroke volume
Preload x afterload x contractility
Clinical signs of cardiogenic shock
Altered mentation, pale MM, prolonged CRT, cool extremities, tachycardia
Which metabolic abnormality is often seen on blood gas results of a patient in cardiogenic shock?
Metabolic acidosis, often compensated with respiratory alkalosis
Due to poor cellular oxygenation leading to anaerobic metabolism
One possible cause of increased A-a gradient in cardiogenic shock?
Pulmonary edema
Radiographic signs of CHF
Enlarged pulmonary veins, alveolar or interstitial pattern in perihilar region of dogs
Cats patchy lung pattern and pleural effusion
What is the most common cause of cardiogenic shock from systolic dysfunction?
Dilated cardiomyopathy
What dog breeds are predisposed to DCM?
Boxer, Great Dane, Labrador, Cocker Spaniel, Doberman
Is DCM a failure of flow or contractility?
Flow. Forward failure. Decreased myocardial contractility leads to decreased stroke volume
What is the treatment for cardiogenic shock when caused by DCM?
Maximize CO by increasing SV
Monitor preload closely, diuretics for left sided failure, positive inotropes (dobutamine), Phosphodiesterase inhibitors (amrinone, pimobendan), cardiac glycossides
What can happen with the heart in sepsis to cause cardiogenic shock
Decreased ejection fraction caused by decreased contractility, biventricular dilation, and reduced ventricular compliance
When does myocardial dysfunction peak in sepsis?
Within days of onset
When does myocardial dysfunction resolve in sepsis?
Within 7-10 days of resolution
Endomyocarditis
Rare condition in cats - occurs within several days of routine anesthetic procedure
Cardiac dysfunction, hypotension, pulmonary edema, and interstitial pneumonia
Mechanical failure of the heart in dogs and cats
Rare. Possible chordae tendonae rupture. May have reduction of forward flow from left ventricular outflow obstruction (aortic stenosis or HCM)
Diastolic failure occurs due to?
Inadequate ventricular filling (decreased preload)
When is a fluid bolus warranted in a patient with cardiogenic shock?
If cardiogenic shock due to cardiac tamponade
What causes cardiogenic shock in cardiac tamponade?
Decreased diastolic filling leading to decreased SV and CO
Inability to continue to compensate with tachycardia leads to severe hypotension and cardiovascular collapse
What is the most commonly diagnosed feline cardiac disease?
Hypertrophic cardiomyopathy
What type of flow failure happens in HCM?
Backward flow failure
How does HCM cause cardiogenic shock
Decreased end-diastolic ventricular volume - leads to decreased SV and CO
What is the most common tachyarrhythmia to cause cardiogenic shock?
Supraventricular tachycardia
Which are the most common bradyarrhythmias to cause cardiogenic shock?
Second or third-degree AV block and severe sick sinus syndrome
Systolic heart failure
Defect in pumping or contractile function of heart
Diastolic heart failure
Defect in filling or relaxation function of heart
Forward heart failure
Decreased CO results in inadequate delivery of blood to arterial system. Leads to reduced organ perfusion, accumulation of plasma volume, and ECF.
Backward heart failure
Elevated filling pressures - causes increased pressure in left atrium and pulmonary vasculature. Elevated capillary hydrostatic pressure, pulmonary edema, if right sided heart disease may lead to ascites
Primary causes of ventricular (systolic) failure
DCM, arrhythmogenic right ventricular cardiomyopathy
What other cardiac diseases may cause ventricular failure?
Chronic volume or pressure overload, congenital disease like PDA or VSD, or chronic valve disease
What are possible extracardiac causes of ventricular failure?
Sepsis, cardiotoxic drugs, nutritional deficiency, myocarditits
Which disease processes may cause true myocardial infarction in animals?
In hypercoagulable or hyperfibrinolytic states. End-stage feline or canine cardiomyopathy
What are clinical signs consistent with ventricular failure?
May be consistent with right, left, or both side heart failure
Dobutamine has what effect?
Positive inotrope with peripheral vasodilation
Dopamine has what effect?
Low dose - positive inotrope with peripheral vasodilation, higher doses peripheral vasoconstriction
Treatment goals for ventricular failure
Support contractility, relieve congestion, suppressing arrhythmia, maximize cardiac output
What type of heart diseases do cats usually get?
Myocardial diseases. Rare for valve, pericardial, or conduction disease
Hypertrophic cardiomyopathy
Primary heart muscle disease in which ventricular hypertrophy develops without cause
Restrictive cardiomyopathy
Ventricular filing impaired in absence of myocardial hypertrophy or pericardial disease
Atrial enlargement associated with ventricle that has normal or near normal appearance
Diastolic dysfunction
Happens when there is impaired myocardial relaxation and poor chamber compliance
Alters pressure volume relationship leading to high diastolic pressure with normal to low ventricular volume
What is the predominant pathophysiologic mechanism responsible for signs in HCM and RCM?
diastolic dysfunction
What is systolic anterior motion of mitral valve? Why is it significant?
Systolic anterior motion (SAM)
Occurs in 65% of cats with HCM
Movement of mitral leaflets leading to dynamic left ventricular outflow tract obstruction and concurrent mitral valve regurgitation
Associated with asymptomatic status in cats, most important cause of heart murmur in cats with HCM
What is important about gallop rhythms in cats?
It is a more specific than a murmur for diagnosing cardiac disease
Feline hypertrophic cardiomyopathy usually results in dilation of which chamber?
Left atrium - due to diastolic dysfunction and mitral valve regurgitation
If a feline patient has respiratory signs and a normal left atrial size, what is the cause of the respiratory signs?
Difficult to say without more information but NOT due to cardiomyopathy
What causes pseudohypertrophy?
Dehydration - causes temporary thickening of cardiac wall due to low volume within chambers
Feline aortic thromboembolism often lodges where?
Usually lodges at aortic trifurcation
Is FATE caused solely from arterial occlusion?
No, likely other vasoactive mediators released from thrombus decrease blood flow through collateral circulation and contribute to development of ischemia
What is the role of furosemide or nitroglycerin in treatment of congestive heart failure?
Reduces preload but does not improve cardiac performance
What are treatment goals for long-term management of feline chronic heart failure?
Slow heat rate, speed myocardial relaxation
What types of cardiomyopathies are most common in dogs?
Dilated cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy
Hypertrophy cardiomyopathy has been reported
What type of dog is arrhythmogenic cardiomyopathy reported in?
Boxers
What dog breeds most commonly get dilated cardiomyopathy
Dobermans, dalmatians, Portuguese water dog, cocker spaniel, giant breeds
What breed of dog gets pediatric onset dilated cardiomyopathy?
Portuguese water dogs
Do dogs with DCM have a significant heart murmur?
Often no, usually low grade (I-III/VI)
What might be auscultated on a dog with DCM?
Low grade murmur along with A-Fib or APCs or VPCs, tachycardia
What medications are used for long-term treatment of DCM?
Diuretics PRN, ACE inhibitors, Digoxin, Pimobendan, pimobendan
How many VPCs daily warrants treatment of ARVC?
> 500-1000
