ECG Flashcards
Which node initiates a current of depolarization?
- SA node
What occurs during P wave?
- Atrial muscle depolarization
What occurs during PR interval?
- Conduction from SA through AV node
What happens during QRS wave?
- Ventricular muscle depolarization
What happens during QT interval?
- Time it takes for ventricular muscle to depolarize and repolarize
What happens during T wave?
- Ventricular muscle repolarization
What is a lead?
- Evaluation of the electrical field from different aspects of the body
- Different from a lead wire or electrode on the body
How many leads are there?
- 6!
- All 6 leads calculate your mean axis
Which lead is most commonly used for measurements?
- Lead II
- Moving from base to apex, right to left
Positive deflection vs negative deflection on an ECG
- Toward the positive electrode, a positive deflection is observed in that lead
- Away from the positive electrode, a negative deflection occurs
Polarity of QRS
- Normally a large positive on lead II, due to large muscle mass of the left heart
- If QRS is negative and leads are in correct position, means that there is right ventricular enlargement
Mean electrical axis
- QRS in all six leads is used to calculate actual # degree of axis
- Also gives information about ventricular enlargement
Is lead II QRS normally positive or negative in dogs and cats?
- POSITIVE
What is ECG BEST for evaluating (2 main things)
- Heart rate
2. Heart RHYTHM and conduction
What can ECG tell you about cardiac chamber enlargement?
- It can tell you about cardiac enlargement
- Specific but NOT VERY SENSITIVE
- If you see a change, it exists; if you don’t see changes, doesn’t mean that they don’t exist
ECG and CHF or quality of cardiac muscle contraction
- CAN NOT tell you about presence of CHF or quality of cardiac muscle contraction
What are two primary reasons to obtain an ECG in practice?
- Diagnose an arrhythmia detected on physical examination
- Search for an arrhythmic cause of syncope/collapse
Other reasons to obtain an ECG?
- Assess cardiac size (knowing that a normal ECG does not exclude cardiac enlargement)
- Assess/monitor a critical patient post-HBC or GDV
- Individualize therapy for heart failure patients (monitor HR, rhythm)
- Monitor effectiveness of anti-arrhythmic therapy
- Evaluate patients with suspected drug toxicity (digoxin, etc.)
- Screen for electrolyte abnormalities (hyperkalemia, etc.)
- Look for supportive evidence of other disease processes
What might you see with pericardial effusion on ECG?
- Low-voltage complexes, electrical alternans
What might you see with hypothyroidism on ECG?
- Low-voltage complexes
What might you see with hypoadrenocorticism on ECG?
- Bradycardia, spiked T wave, flat P wave
Types of ECG equipment
- Standard vs rhythm monitoring
Which type of ECG can you measure complexes with?
- Standard/in hospital/diagnostic
Rhythm monitoring (surgical) ECG use
- Not diagnostic
- Rhythm and heart rate machine
- SHOULD NOT USE FOR CARDIAC CHAMBER ENLARGEMENT
Ambulatory monitor definition
- Portable device that records ECG while the animal is in home surroundings (AKA Holter monitor)
Ambulatory monitor indication
- Evaluating collapsing patients for intermittent arrhythmia or monitor response to anti-arrhythmic therapy
What are the four steps of ECG interpretation?
- Evaluate ECG for artifacts, quality and calibrations
- Determine heart rate
- Name the cardiac rhythm
- Evaluate the P-QRS-T complex configurations and morphologies
Standard calibration for ECG complex height
- 1 cm (10mm) = 1 mV
ECG complex width
- Duration can indicate cardiac chamber enlargement
- Complex duration - horizontal axis or paper speed
What speed are P-QRS-T measurements typically made at?
- 50mm/sec
- 1 small box = 0.02 sec
Why quality and calibrations?
- Values are measured for duration and amplitude of P wave and R wave
- Measurements indicate heart enlargement or electrical conduction abnormalities
Dogs normal HR on ECG
- 60-160 BPM
- Can be as low as 120 in the home environment
Cats normal HR on ECG
- 140-220 BPM
- Can be as low as mid 20s to 30s for sleeping dogs
Other reference ranges for ECG
- P wave (max)
- PQ interval
- QRS (width)
- R wave (max)
- ST segment
- T wave (max)
- QT interval
SEE SLIDES and also ask if this is important?
What can happen with artifacts?
- Affect ability to interpret the electrocardiogram by basking the real ECG or appearing similar to an arrhythmia
- Common examples: Purring, respiration movement, motion, muscle twitches
How many boxes to count for HR at 50 mm/sec?
- 30 boxes for 3 sec, then multiply by 20
- Bic pen is exactly 3 seconds on 50 mm/sec speed
How many boxes to count for HR at 25 mm/sec?
- 15 boxes is 3 seconds
Normal horse heart rate
- 28-40 BPM
Normal cow heart rate
- 70-90 BPM
2 normal rhythms in dogs
- Sinus rhythm
- Sinus arrhythmia
Sinus rhythm characteristics
- Normal P wave
- Normal heart rate
- Normal, similar shaped P wave for every QRS
- Normal, similar shaped QRS for every P wave
- Regular, very little variation in P-P interval (<10%)
Sinus arrhythmia characteristics
- Irregular rhythm originating from the SA node, but normal in many species
- Defined by normal heart rate
- Normal shaped P wave (some variation in height okay; “wandering” pacemaker of vagal tone)
- Normal QRS for every P wave
- Pattern of increasing and decreasing heart rate that is regularly irregular
What is the cause of a sinus arrhythmia?
- Pronounced vagal tone
- SOMETIMES associated with respiration
What are the normal rhythms in cats?
- JUST ONE
- Sinus rhythm or sinus tachycardia
Normal rhythms in bovines
- Sinus rhythm
- Sinus bradycardia may be associated with a lack of food intake
Normal rhythms in equines
- Normal sinus rhythm
- Sinus arrhythmia
- Second degree atrioventricular block (vagal tone species)
Morphology of complex assessment
- Are complex measures within normal range for amplitude and duration?
- Do P waves look different?
- Do QRS waves look different?
Normal variations in ECG
- In some animals, Q wave may not be present or S wave may not be visible
- T wave can be small, positive, negative, or biphasic
Normal P wave, deep S wave rule out
- Right ventricular enlargement
- HIS bundle branch block
Big T wave meaning
- Hyperkalemia
- Maybe if you have ventricular depolarization abnormalities and expect to see repolarization abnormalities
Meaning of Tall P wave
- Right atrial enlargement in dogs
- Right or left atrial enlargement in cats
- Sinus tachycardia in dogs
Meaning of Tall R wave***
- Left ventricular enlargement
Meaning of Wide P wave
- Left atrial enlargement in dogs and cats
- Pseudo abnormality
Absent p wave meaning
- Hyperkalemia
- Atrial standstill
- SIlent atrium or atrial fibrillation
P height variation
- Wandering pacemaker (normal finding with sinus arrhythmia), atrial or junctional premature beats
Meaning of shortened PR interval
- High sympathetic tone
Meaning of prolonged PR interval
- First degree AV block
Meaning of deep Q wave
- normal variation in deep-chested dogs; biventricular enlargement potentially
Meaning of wide QRS
- Ventricular enlargement; intraventricular conduction disturbance
Meaning of small QRS
- Normal variation; pericardial or pleural effusion; pneumothorax, hypothyroidism, obesity
Meaning of large T wave
- Myocardial hypoxia, interventricular conduction disturbance, bradycardia, ventricular enlargement, hyperkalemia
Meaning of small T wave
- Same as for small QRS, normal for cats
Meaning of dep S wave
- Normal variation; right ventricular enlargement; left ventricular hypertrophy (in leads II, III, and aVE? ONLY)
Ectopic beat definition
- Complex with abnormal shape may come from a different location of the heart (not from sinus node)
Where can ectopic beats come from?
- Atria or ventricle
Premature vs escape beats
- Premature is earlier than expected
- Escape is later than expected
Supraventricular complex appearance
- QRS looks similar, but P wave looks different (or in junctional, are absent)
- Timing will usually be early
- QRS is the same!
Ventricular complex appearance
- Wide and bizarre
- Nothing like a sinus rhythm
- Look to sinus beats to see if there is chamber enlargement
How do you differentiate escape beats and premature beats?
- Escape and premature beats can look morphologically the same
- Differentiated by timing (early or late) compared to preceding complexes
What four things to assess with morphology of complexes that appear different from the rest?
- Which beat is it?
- Is it ventricular or supraventricular?
- Is it premature or delayed?
- What would you call it?
