Cardio: ECG Flashcards
What can an ECG tell you (9)?
1) Heart rate (atrial and ventricular)
2) Rhythm
3) Conduction pattern
4) Chamber enlargement (less than rads, echo)
5) Myocardial condition (inflammation, necrosis, epicardial dz)
6) Electrolyte abnormalities
7) Effusions (pericardial, pleural)
8) Drug toxicities or effects
9) Sympathetic or parasympathetic tone alterations
Reasons to perform an ECG (9)
1) Congenital heart disease in younger dogs
2) Valvular disease (Ex: Cavalier spaniel)
3) Myocardial disease (Ex: Dobermans)
4) Monitor drug therapy or suspected drug toxicity (Ex: digoxin, anti-arrhythmics)
5) Evalulate arrhythmias
6) Evaluate syncope or weakness
7) Pre-anesthetic or anesthetic monitoring
8) Electrolyte screening (Ex: post parathyroidectomy)
Four prep steps in performing an ECG
1) RIGHT lateral recumbency
2) Electrodes above the elbows and stifles
3) Alcohol to couple signals to electrodes
4) Light restraint
Sequence of electrical activation in the heart
1) Starts in the sinus node (SA) = pacemakers that initiate electrical impulses
2) ATRIAL DEPOLARIZATION
3) Impulse slowed by the AV node = specialized conduction tissue that separates the atria from ventricles
4) Conduct via the Bundle of His
5) Conduct via Purkinji fibers for VENTRICULAR DEPOLARIZATION
What does an ECG tell you (and not tell you) about the heart?
Only explains the ELECTRICAL ACTIVITY of the heart, says nothing about the mechanical functionality
What is the P wave?
Atrial depolarization
What is the QRS complex?
Ventricular depolarization
What is the T wave?
> Ventricular repolarization
- Can be negative or positive
What is the PR/PQ interval?
> AV nodal conduction
- Time needed for conduction from the the SA node through the AV node to the ventricular myocardium
What is the Q wave?
First negative deflection before a positive deflection
What is the R wave?
The first positive deflection in the QRS complex
What is the S wave?
Negative deflection after the positive deflection
What is the ST segment?
- Duration of phase 2 of the AP during repolarization
- No change in electrical charge = equal to baseline (PR) = isoelectric
What is the QT segment?
> Ventricular systole
- Time of ventricular depolarization and repolarization
Difference between paper speed on the ECG and writings?
- Quicker = things are farther apart
- Slower = things are written closer together
Which lead sees the largest QRS deflection?
Lead II = where we do our ECG measurements from
What is the calibration of the ECG?
> “Sensitivity” = 10 mm = 1 mV
- Usually increased with cats = 2x –> 1 mV = 1 cm
- Usually decreased with dogs = 1/2x –> 1 mV = 1/2 cm
How do you determine the HR from the ECG?
[Each box = 1 mm]
1) Count 25 or 50 mm (depending on speed) = equals one second
2) Count the number of QRS complexes for 3 seconds
3) Multiply those QRS complexes x 20s
Does size of the dog (animal) affect the HR on the ECG?
NO - all dogs should have similar heart rates
Normal heart rate for a dog
70-140 bpm
Normal heart rate for a cat
160-220 bpm
WHAT IS A SINUS RHYTHM?
Upright P waves, in lead II, at a rate the sinus node can fire
What is the mean electrical axis and what is normal for the MEA?
> Defines the orientation of the average wave of ventricular depolarization
- Normal = left (of the animal) and towards the feet
How do we calculate the mean electrical axis (MEA)?
1) Measure the positive boxes from baseline (PR) to the top of the QRS
2) Measure the negative boxes below baseline of the QRS
3) Add them together for your lead total (on each perpendicular lead)
4) Connect the point where the two leads intersect
5) Draw a line from the belly button to that point = MEA
Two reasons for right axis ECG deviation
1) Right ventricular enlargement
2) Conduction disturbance, particularly in the right bundle branch
Two reasons for left axis ECG deviation
1) Left ventricular enlargement
2) Conduction disturbance, particular in the left bundle branch
What does tall P waves indicate?
- “P pulmonale” = right sided pulmonic valve
|»_space; Right atrial enlargement
What does wide P waves indicate?
- “P mitrale” = left sided mitral valve
» Left atrial enlargement - Takes a longer time to depolarize = wider waves
What does tall and wide P waves indicate?
Biatrial enlargement
What does tall or wide QRS complexes indicate?
> > Left ventricular enlargement
- Either due to dilation or hypertrophy
What do we see with right ventricular enlargement?
> Usually only seen with severe disease (needs to overcome the large left ventricular mass)
- See S waves in leads I, II, III, and aVF
- Right axis shifts
Four differentials for a wide QRS complex
1) Bundle branch block
2) Ventricular espace (late) complexes
3) Ventricular premature (early) complexes
4) Ventricular enlargement
What can cause bundle branch blocks?
> > Result from damage to the bundle branches from STRETCHING
- Hypertrophy
- Infiltrative diseases
- Infarction
- Idiopathic degeneration
- Surgical manipulation
- Congenital heart disease
- Acquired heart disease
*Need to distinguish from ventricular ectopic beats (VPC’s and escape beats)
Axis deviation (which direction) with right bundle blocks
Right axis deviation = slower depolarization on the right side because it doesn’t go through the normal right sided His-Purkinje fibers
Consequences on the ECG with right bundle blocks
- Right axis deviation
- WIDE and NEGATIVE QRS complex in leads I, II, and aVF
- NORMAL P wave and PR interval –> differentiate between right bundle block and VPC’s
+/- Abnormal T wave (abnormal depolarization may affect the repolarization)
How do you differentiate between VPC and ectopic beats AND right bundle blocks?
Right bundle blocks conduct through the His-Purkinje system = normal P wave and PR interval
Consequences on the ECG with left bundle blocks
- WIDE and POSITIVE QRS in leads I, II, III, and aVF
- NORMAL P wave and PR interval
Two types of ventricular ectropy
- Premature (VPC’s) ventricular complexes
- Escape (late) ventricular complexes
What is a sign of ventricular ectopy on an ECG?
- WIDE and BIZARRE QRS complexes
- NOT associated with P waves (didn’t originate from the SA node)
Three reasons for wide and bizarre QRS complexes
1) Premature (VPC’s)
2) Escape (late) ventricular complexes
3) Bundle blocks
Four causes of depression of the ST segment
1) Myocardial ischemia (endocardial)
2) Acute infarction
3) Hyper/hypokalemia
4) Trauma
> > Never returns to PQ baseline
*Worry about ischemic heart disease
Four causes of elevation of the ST segment
1) Myocardial hypoxia, esp EPIDCARDIAL
2) Pericarditis
3) Myocardial infarction (transmural)
4) Trauma
Two reasons for abnormal T waves
1) Abnormal ventricular depolarization or conduction –> abnormal repolarization
2) Hyperkalemia, looks tented or spiked
Reasons for prolonged QT intervals
- Varies with HR
- Hypocalcemia
- Hypokalemia
- Hypomagnesemia
Reasons for shortened QT interval
- Varies with HR
- Hypercalcemia
- Hyperkalemia
Cause of short/attenuated or low-voltage QRS complexes (4)
> “Insulator” that decreases the QRS voltage (in the way)
1) Pericardial effusion
2) Pleural effusion
3) Hypothyroidism
4) Obesity
Causes of arrhythmias
1) Primary cardiac disease
2) Sepsis
3) Drugs and toxins
4) Medical = metabolic, electrolyte, neoplastic
5) Hypoxia
6) Autonomic tone, Ex: vagal or sympathetic tone
Sinus bradycardic rates for dogs and cats
- Dogs < 60-70 bpm
- Cats < 140 bpm
*Can be normal in a dog = parasympathetically driven
ECG signs of a wandering pacemaker
> High vagal tone
- See different P wave morphologies, depending on where the SA node fires
- Still upright P waves
Sinus tachycardic rates for dogs
- Dogs > 140 bpm
- Still upright P waves
- Normal sinus rhythym
Sinus arrest - ECG
> Two RR intervals without anything happening = NO P waves
- No sinus node activity
**Junctional escape complexes - ECG
> Junction = AV node = SUPRAVENTRICULAR
- Escape complex = comes in late
- Doesn’t originate from the SA node = no P waves
- COMPENSATORY from the ventricular His-Purkinje system = upright and narrow
**Ventricular escape complexes - ECG
- Normal sinus rhythm = sinus tachycardia, upright P waves
- Ventricles are not seeing the AV node signals = not conducting SA nodes through the AV node
- Jumping in late
Atrial premature complexes - ECG
- Premature and abnormal atrial depolarization
- Jumps in early before the next scheduled P wave
- SA node is firing + something else extra fires in the left atria
- Normal conduction through His-Purkinje (normal/upright QRS complex)
Ventricular premature complexes - ECG
> Wide and bizarre QRS = slowly conducted
- Something abnormal fires in the ventricular system that’s not a part of the His-Purkinje
+/- Abnormal T waves
Ventricular bigeminy - ECG
Specific type of ventricular premature complex where the wide and bizarre QRS occurs every other normal QRS (jumps in before the next scheduled P wave)
Atrial tachycardia - ECG
- Atrial cells (not SA node) are generating impulses
- Normal, upright P waves
- Jump in early = type of APC?
» Three or more in a row = atrial tach
*Will feel pulse deficits = heart doesn’t have time to fill
Atrial fibrillation - ECG
> Occurs supraventricular, above the AV node
- NO P WAVES
- Irregular rhythm = hundreds of atrial impulses hit the AV node and only a few get through to the ventricles
- Normal upright and narrow QRS (goes through His-Purkinje)
- Tachycardic = as many of the atrial impulses as possible get through (240 of 500)
Ventricular tachycardia - ECG
> Three or more VPC’s occurring in a row
- Wide and bizarre - not going through the normal His-Purkinje system
- Originating from somewhere else in the ventricles
Paroxysm - ECG
Sustained run of tachycardia (sp v-tach)
Ventricular fibrillation - ECG
No organized depolarization in the ventricles = FATAL if left untreated
1st degree AV block - ECG
> Involving AV nodal conduction time
- Too long of PQ interval
- “Lazy gatekeeper” - signals getting through to the ventricles, but the AV node is lazy
2nd degree AV block - ECG
> Involving the AV nodal conduction time
- AV node is functioning some of the time = some of the impulse conduct to the ventricles and some don’t
- “Sleepy” gatekeeper
3rd degree AV block - ECG
- “Dead gatekeeper”
- No conduction between the atria and ventricles
- Sinus node keeps firing, but ventricles need to create a compensatory escape complex
- Slow (compared to faster premature VPC’s)
Right bundle branch block - ECG
- Wide, bizarre, and NEGATIVE QRS
- Preceded by a normal P wave
- Doesn’t require treatment (unlike VPC’s or v-tach)
Left bundle branch block - ECG
- Wide, bizarre, and POSITIVE QRS
- Preceded by a normal P wave
Atrial standstill - ECG
Atria are paralyzed = no atrial depolarization = missing a P wave
