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