Cardio (Continued) Flashcards
What is the origin of the normal cardiac electrical impulse?
Sinoartial node located in the right atrium which contains pacemaker cells
Do pacemaker cells (P cells) need to be stimulated to depolarize?
No, can spontaneously depolarize
What part of the heart do Purkinje fibers conduct electrical impulses to?
Ventricles
What generates the electrical field through which impulses travel through the heart?
Ion fluxes across cell membranes
List the four ECG electrode colors and their corresponding correct placement
Red-left hind
Green-right hind
Black-left front
White-right front
What is an electrocardiogram?
A graphical record of the average electrical potential produced by the heart during the cardiac cycle
What occurs when a electrical impulse moves towards the positive pole, or negative pole?
Positive-upward deflection on the ECG
Negative-downward deflection
Baseline=isoelectric
List the three most common standard ECG leads:
I: right front (-), left front (+)
II: right front (-), left hind (+)
III: left front (-), left hind (+)
List what each waveform of the ECG represents in the cardiac cycle
P wave: atrial depolarization
QRS complex: ventricular depolarization (R wave left ventricle, S wave right ventricle)
T wave: ventricular repolarization
What do the PR, QT, and RR intervals indicate?
PR: atrial depolarization and conduction through the AV node
QT: ventricular depolarization and repolarization
RR: time between ventricular depolarizations
T/F: RR intervals should be consistent
True
There shouldn’t be more than a 10% variation in RR intervals in order to be considered normal
What are the two most common paper speeds for ECG?
25mm/sec
50mm/sec
What are the two most common amplitudes for ECG?
10mm/mv
5mm/mv
What is the normal heart rate for dogs and cats?
Dog: 70-160 (big doggos), 80-180 (little yippers), up to 220 in puppers
Cat: 140-240 (hospital setting), 100-120 (home setting)
What is the normal PR interval in dogs/cats?
60-130 in dogs
50-90 in cats
What is the normal QRS duration in dogs and cats?
Under 60 in dogs
Under 40 in cats
what does a “wide” QRS waveform mean?
Prolonged duration
In dogs, greater than 60ms, in cats greater than 40ms
What is required for normal sinus rhythm?
Consecutive sinus complexes, consistent RR and PR intervals, normal heart rate
What is the most commonly used lead for determining heart rhythm, conduction disturbances, and chamber enlargement?
Lead II with the patient in right lateral recumbency
What is considered a heart rhythm?
Three or more consecutive QRS complexes with the same morphology (there can be more than one rhythm present)
What do we look for in our general assessment (step one)of interpreting an ECG?
What is our paper speed/amplitude?
Does the HR seem slow, fast, or normal?
Do the QRS complexes have the same morphology?
Does the rhythm appear to be regular or irregular?
Are there any artifacts?
How do we calculate the heart rate (step two) from an ECG?
Count all QRS complexes that occur in 30 large boxes and multiply by 10 for 25mm/s paper and 20 for 50mm/s paper (this method is good for arrhythmias)
Count the number of small boxes in one RR interval, and divide 1500 by that # if paper speed is 25mm/s, or 3000 divided by the # of small boxes for 50mm/s (this method is only good for patients with a regular rhythm)
What do we do during step three of our ECG interpretation?
Measure RR intervals
If irregular, determine whether is is regularly irregular, or irregularly irregular
What do we do during step four of our ECG interpretation?
Examine P, QRS, and T’s by amplitude and duration
We should be using lead II with the patient in right lateral recumbency
What does abnormally high amplitude or duration indicate for P-QRS-T waves?
High amplitude=chamber enlargement (P wave; right atria, R wave; left ventricle, S wave; right ventricle)
Long duration=chamber enlargement, bundle branch block, or ectopic ventricular impulse
What is the mean electrical axis?
The average direction of the electrical potential generated during a cardiac cycle
Testing for this is not routinely done, can be used to indicate chamber enlargement or conduction abnormalities
What do we do during step 5 of our ECG evaluation?
Identify ectopic complexes (most commonly seen presentation is a wide QRS complex)
What do we do during step six of our ECG evaluation?
Identify pauses
What is a respiratory sinus arrhythmia?
HR accelerates during inspiration and decelerates during expiration, caused by parasympathetic tone dominating over sympathetic tone
Normal and common in calm dogs at the clinic, abnormal in cats at the clinic but normal at home
Can be exaggerated in patients with certain respiratory diseases (brachycephalic airway syndrome)
What is a wandering pacemaker?
Variation in the site of electrical impulse generation
What we see in the ECG: variation of P wave amplitude, consistent PR interval, commonly respiratory sinus arrhythmia rhythm
Can be normal in calm dogs at the clinic, rare in cats
Why do arrhythmias occur?
The heart itself is diseased
Extra-cardiac disease is affecting the heart’s electrical activity/blood supply (gastric dilatation-volvulus)
What three mechanisms cause arrhythmias?
Disturbances of impulse formation
Disorders of impulse transmission
Complex (both)
What occurs when cardiac excitability is increased in intermittent or sustained frequencies?
Intermittent increase causes premature heart beats
Sustained increase causes tachycardia
What occurs when cardiac excitability is decreased for an intermittent or sustained period?
Intermittent decrease: sinus pause (lack of sinus complexes)
Sustained decrease: bradycardia or asystole
What is the primary or secondary cause of sinus bradycardia?
Primary: disease or dysfunction of the sinus node
Secondary: increased fatal (parasympathetic) tone
Secondary is more common than primary
We will see long RR intervals
What are some pathologic and non-pathologic causes of high Vaal (parasympathetic) tone?
Respiratory, GI, neurologic, ophthalmic diseases, drugs/toxins, hypothermia
Sleep/rest, athleticism, brachycephalic
Define sinus tachycardia
A sinus rhythm with an abnormally high heart rate (short RR intervals)
What are the primary and secondary causes of sinus tachycardia?
Primary: disease of the sinus node (sick sinus syndrome)
Secondary: increased sympathetic tone
Secondary is more common than primary
What are some causes of high sympathetic tone? How can we test if the sympathetic response is appropriate?
Hypotension, hypoxia, anemia, pain, fear/excitement, drugs/toxins
Dose with Fentanyl to check if the response is appropriate
What is supraventricular premature complex?
Premature depolarization generated by an ectopic impulse located ABOVE the ventricles (atrial is most common)
Affects P wave
What are some ECG signs of supraventricular premature complex?
Premature P-QRS-T (P may not be visible)
Narrow QRS, or QRS associated with a P’ (has a different morphology from P)
Pauses after QRS
What are some causes of supraventricular premature complex?
Atrial dilation, atrial tumor, systemic/metabolic disease, drugs (mostly sympathomimetics, old age
Define supraventricular tachycardia
Any pathologic tachycardia originating above the ventricles
List the ECG criteria for supraventricular tachycardia
Three or more consecutive supraventricular premature complexes with an abnormally high rate
P’ waves instead of P waves
Generally has a normal rhythm
Can be sustained or paroxysmal
Define atrial fibrillation
Chaotic and very rapid atrial impulses (400-1200 per minute)
Large surface area affected in order for this to occur
List the ECG criteria for atrial fibrillation
Irregularly irregular RR
No P wave
Narrow QRS
List some causes of atrial fibrillation
Usually secondary to atrial dilation
General anesthesia, GI disease, post-pericardiocentesis
Primary (lone) AFib associated with no structural disease (giant/large breed dogs because they have larger hearts with more surface area)
Define atrial flutter and list the ECG criteria for it
Organized and rapid atrial impulse (280-400 per minute)
No P waves, flutter waves (saw tooth appearance), narrow QRS, regular or irregular RR intervals
How can we differentiate sinus tachycardia from supraventricular tachycardia/atrial flutter?
Sinus tachycardia is usually the response to pathology, while SVT/ A-flutter is usually the pathology itself and we will usually see flutter waves associated with A-flutter
If still not sure, can perform vagal maneuver to slow down the HR to allow visualization of P/flutter waves
What can we do to perform the vagal maneuver?
Apply ocular pressure, or carotid sinus massage
May fail to work, may need to use drugs instead
Define ventricular premature complex
Premature depolarization generated by an ectopic focus located in the ventricular tissue
What are some causes of ventricular premature complex?
Cardiomyopathy (most common)
Various non-cardiac causes
List the ECG criteria form ventricular premature complex
Premature and wide QRS
Often followed by a pause
Can be positive, negative, or biphasic
What’s the difference between a ventricular premature complex from the left/right ventricle?
VPC from the left ventricle will be negative
VPC from the right ventricle will be positive
Define ventricular tachycardia and list the ECG criteria
Tachycardia originating from the ventricle
Three or more consecutive VPC’s with an abnormally high rate
(Bottom line from her Lab Retriever brothers story: if heart rate is ever too fast or slow, do an ECG to avoid embarrassing yourself)
Define ventricular fibrillation
Chaotic/disorganized/rapid ventricular impulses
Fatal rhythm
Ventricular tachycardia can deteriorate into this
What arrhythmia is considered a “sheep in wolf’s clothing”?
Accelerated idioventricular rhythm
Has all the characteristics as VT except it isn’t fast
Stable rhythm, normally caused by a non-cardiac cause
What are the three main disorders of impulse conduction?
Atrioventricular block, bundle branch block, atrial standstill
Define first degree AV block and list its ECG criteria and causes
Conduction in the AV node is delayed, not hemodynamically significant
Prolonged PR interval
Caused by high vagal tone, drugs/toxins
Define second degree AV block, list its ECG criteria, and types
Conduction through the AV node is stopped (transiently)
Some P waves do not have QRS after them
Two types: Mobitz type I, Mobitz type II
Define second degree AV block Mobitz types I, and II
Mobitz type I: prolongation of the PR interval prior to the block (look for a P without a QRS after it)
Mobitz type II: no prolongation of PR interval prior to the block, can be low or high grade (low grade is better for your patient, the number of conducted P’s is greater than unconducted), (high grade is bad, number of unconducted P’s is greater than conducted P’s, causes bradycardia
Define third degree AV block and list its ECG criteria
Conduction through the AV node is stopped permanently
P’s without QRS’s, PR intervals not consistent, QRS’s are preceded by a pause
Presence of “escape beats”
Escape beats help keep our patient alive! Occur when the ventricles don’t receive atrial impulses for an extended period of time, will depolarize from latent pacemaker cells in junctions
List the causes of first through third degree AV blocks
First degree and Mobitz type I AV blocks are caused by high vagal tone and drugs
Second degree Mobitz type II and third degree AV blocks are caused by structural disease of the AV node
What is a bundle branch block?
Delays in conduction or a lack of conduction in the left/right bundle branch
We’ll see wide QRS complexes (negative for right, positive for left), will have sinus rhythm
What are the causes of bundle branch blocks?
Left BBB: structural
Right: idiopathic, structural
Transient: fast sinus tachycardia or SVT
Define atrial standstill and list the ECG criteria
Absence of atrial depolarization
No P waves (and no flutter or fibrillation waves), normal QRS
What are the causes of atrial standstill and which dog breed is predisposed to this?
Hyperkalemia, atrial myopathy
Springer Spaniel
What is sick sinus syndrome and what breeds of dog are predisposed?
Complex idiopathic disturbance of conductive tissue resulting in sinus bradycardia/sinus arrest with or without SVT/VT, or first/second degree AV block
Normal SA node cells are replaced by fibrous/fibrofatty tissue
Miniature Schnauzer, West Highland Terrier, Dachshund, Cocker Spaniel
List the main electrolyte derangements and their effects
Hypokalemia: prolongs repolarization
Hyperkalemia: shortened repolarization, can be mild-moderate-severe
Hypomagnesemia: VPC, VT, AIVR (not commonly tested for, should request it)
Hypocalcemia: common in patients that have recently given birth, lowers AP threshold
Hypercalcemia: raises AP threshold
What is a Holter Monitor?
Records ECG continuously for 24-48 hours, allows us to see intermittent arrhythmias easier
What kind of arrhythmias cause clinical signs?
Arrhythmias that are hemodynamically significant (cause low blood pressure and hypo perfusion)
What three things do we observe during our distance cardiovascular exam?
Respiration-rate and effort, posture, mucous membrane color
Ambulation-abdominal distention (right sided CHF), can they walk?
Mentation-dullness
(RAM)
What should normal mucous membranes look like?
Moist, pink, CRT less than or equal to 2 seconds
What abnormality are we looking for in our patients during our cardio exam?
Systemic hypertension can cause hyphema, retinal hemorrhage/detachment, edema, vision loss in 50% of patients
What abnormality can be seen in cardio patients associated with the jugular vein?
Distension of the vein, pulsation higher than the distal third even when standing with the head erect
These are more difficult to assess in cats
Why do we inspect the thorax of our patient with them in a standing position?
If the patient is laying down, artifacts are more likely to be heard
What is the apex beat and where can we locate it?
The apex beat is where heart sound are the loudest at the mitral valve region, calculate HR here
Locate it by palpation on the left side of the animal around the fifth intercostal space on the ventral third of the abdomen
Should simultaneously palpate femoral pulses to make sure they match (differences in HR and PR)
What do the S1/S2, and S3/S4 sounds indicate?
S1/S2 are systolic sounds in both small and large animals, S1 occurs at the onset of systole, S2 at the end of systole
S3/S4 are diastolic sounds (LA only)
What side of the stethoscope should we use to listen to S1/S2 sounds?
Diaphragm
T/F: The louder the murmur, the bigger the defect
False! The higher the velocity, the louder the murmur. Loudness or softness of sound is not always correlated with the severity of disease
What is the sound of a heart murmur produced by?
Turbulent blood flow within the cardiac chambers and/or great vessels
Remember, a murmur is a physical exam finding, not a diagnosis
Describe the difference between a grade I, III, and VI heart murmur
I: very faint, focal only
III: readily heard, radiates on same side as the point of maximum intensity
VI: palpable thrill and is audible with the stethoscope lifted off the chest
What is the most common timing in the cardiac cycle for murmurs to occur?
Systolic
To-and-fro is common in animals with fast HR’s
When we report a murmur, what information should we include about it?
Grade, location, timing
What heart sounds produce a “gallop”? Which side of the stethoscope should we use to listen to this?
Diastolic (S3/S4)
Bell of the stethoscope
How can we differentiate between a “gallop” and a systolic “click”?
Use both sides of the stethoscope, clicks are high frequency and are best heard with the diaphragm, gallops are low frequency and are best heard with the bell
When might we hear a split S1 or split S2 heart sound in a healthy patient?
Can occur in healthy, large breed dogs
What are some causes of increased intensity heart sounds?
Thin animal, hyperdynamic states (fever, anemia, hyperthyroidism)
What are some causes of decreased intensity heart sounds?
Pericardial/pleural effusion, intrathoracic mass, poor left ventricular contractility, obesity
How many lung fields are there in dogs/cats for pulmonary auscultation?
Dogs: 3-4 dorsally, 2-3 ventrally
Cats: 2-3 dorsally, 2 ventrally
Auscult each field for 1-2 breaths
What can we hear if we auscultate an animal with severe pulmonary edema?
Crackles and wheezes on inspiration/expiration
Might not hear it if edema is mild
What might we hear on auscultation of an animal with pleural effusion?
Muffled/absent lung sounds, especially ventrally
Heart sounds may also be muffled
Can also occur in cats with L/R CHF, dogs with R CHF
What do we have to keep in mind when performing auscultation on cats?
Heart position is more ventral, they have pliable chests (if you press too hard, you’ll create a transient murmur)
Be aware of purring, intermittent gallops/murmurs are not uncommon
What might we suspect in a normal body condition cat with an absent femoral pulse?
Feline distal aortic thromboembolism (saddle thrombus)
Other clinical signs of this include cyanotic/pale nail beds/paws, neuro deficits of both hind limbs, rectal hypothermia
Always painful, but cats conceal it well
Why do we look at the abdomen during our cardio physical exam?
Looking for evidence of right-sided heart failure (distention, fluid wave, cranial organomegally)
Ascites might be accompanied with loose stool
What main criteria are we looking for when differentiating a pendulous abdomen with obesity?
Obesity should be diffuse
Describe the abbreviated cardio exam we give to dyspneic patients
Observation for only 15-30 seconds
Auscultation and pulse palpation 15-30 seconds
Assess vital signs
Make a tentative diagnosis and initiate therapy
Perform a complete exam once the patient has stabilized
(Bonus tips) handle gently and minimize stress, only separate from family if medically necessary
What are clinical signs of arrhythmias associated with? What are they?
Low cardiac output, anxiety/discomfort
Collapse/syncope, weakness, lethargy, exercise intolerance, tachypnea, hyporexia/vomiting, restlessness, excessive panting
T/F: patients can be hypoperfused while still having a normal blood pressure
True
What are the anti-arrhythmic drug classes?
Class I: blocks sodium channels (membrane stabilizers)
Class II: blocks beta-adrenergic receptors
Class III: blocks potassium channels
Class IV: blocks calcium channels
“Stretch Before Playing Catch” “SBPC”
What are your main class I anti-arrhythmic drugs?
Lidocaine, mexiletine, procainamide, quinidine
Sodium channel blockers
What are your main class II anti-arrhythmic drugs?
Esmolol, atenolol, propranolol, metoprolol
Beta-adrenergic receptor blockers
What are your main class III anti-arrhythmic drugs?
Amiodarone, sotalol (also has a beta blocker effect)
Potassium channel blockers
What are your main class IV anti-arrhythmic drugs?
Diltiazem, verapamil
Calcium channel blockers
What are digitalis glycosides (digoxin) used for in anti-arrhythmic therapy?
Increases vagal tone in the SA and AV nodes
What is our drug of choice for treating supraventricular tachycardia (SVT)? How do we administer it?
Diltiazem
Oral in stable patients, IV then oral in unstable patients
Secondary choices include digoxin, sotalol
At what point in the cardiac cycle would we administer electrical cardioversion if indicated? (When do we shock the poor suckers?)
Defibrillate before the T wave, not at the T wave
Is anti-arrhythmic therapy usually indicated for cases of supraventricular premature complex?
No, it isn’t usually necessary
If frequent or sustained though (over 1000 VPC’s in 24 hours), may use Diltiazem, must investigate and treat underlaying cause (best idea)
What’s our treatment of choice for ventricular tachycardia?
Lidocaine IV if patient is hemodynamically unstable, followed by oral Mexiletine or Sotalol
Always investigate and treat underlaying cause if possible!
What’s the correct emergency Lidocaine dosage for dogs/cats?
2mg/kg dogs
0.2mg/kg cats
What’s an atropine response test and what do positive and negative results mean?
Used to differentiate bradyarrhythmias caused by high vagal tone from structural heart disease
Perform and record ECG, administer 0.04mg/kg atropine, wait 20 minutes, recheck ECG
Positive means high vagal tone
Negative means that we’re gonna have a bad time
How do we treat low vs. high grade Atrioventricular blocks?
Low grade: no treatment necessary, look for cause of high vagal tone
High grade: pacemaker, in emergencies while awaiting pacemaker implantation, dopamine or dobutamine therapy to increase ventricular escape rate
What is our treatment of choice for sick sinus syndrome?
Don’t always need treatment, but can treat with a pacemaker
What must we rule out before treating atrial standstill?
Hyperkalemia
T/F: ECGs in patients with pacemakers look different
True
What are ECG artifacts? How can we avoid them?
Waveforms that are not created by the heart
Make patient comfortable, don’t have patient come into contact with metal, shave fur if using adhesive pads, use enough gel/alcohol on electrodes
