Electrocardiogram Flashcards
What cardiac and extra cardiac abnormalities cause abnormal rhythm?
-stress
-fever
-toxicity (nutritional or pharmacological)
-low or high blood pressure
-hyperthyroid
-hypothyroid
-anemia
-heart failure
-shock
Consequences of arrhythmia
-dizziness
-syncope
-fatigue
-chest
-pain
-sudden cardiac death
-cardiac remodeling over time
Beats per lifetime
-larger animals often live longer but they also have low heart rates
-In general all animals seemed to fall within the same amount of beats/lifetime just takes different species different amounts of time to get there
P wave
-atria depolarize (contraction)
QRS wave
-ventricles depolarize
T wave
-ventricles repolarize (relax)
RR interval
-used to measure the heart rate (1 cardiac cycle)
PR interval
-time for atria to depolarize and excitation to travel to purkinje fibers
PR segment
-time between atrial and ventricular depolarization
QT interval
-time required for ventricles to depolarize and repolarize
ST interval
-time from the end of ventricular depolarization until repolarization is complete
ST segment
-time between ventricular depolarization and repolarization (time when ventricles are contracting)
Rules of ECG interpretation
1.a wave of depolarization travelling towards a positive electrode is a positive deflection in ECG trace
2. a wave of depolarization travelling away from a positive electrode is a negative deflection in the ECG trace
3. a wave of repolarization travelling towards a positive electrode is a negative deflection in ECG trace
4.A wave of repolarization traveling away from a positive electrode is a positive deflection in ECG trace
5. a wave of de- or repolarization traveling perpendicular to an electrode axis does not produce a deflection in ECG trace
6. a deflection amplitude depends on the position of the positive electrode relative to the mean electrical vector
7. the voltage amplitude is related directly to the mass of the tissue experiencing de- or repolarization
Einthoven’s Triangle
-Electrodes in shape of upside down triangle (RA, LA, LL)
-Lead I goes from RA (negative) to LA (positive)
-Lead II goes from RA (negative) to LL (positive)
-Lead III goes from LA (negative) to LL (positive)
Placing electrodes
-white to right
-smoke over fire
-green is ground
RA
-negative both directions
LA
-positive top
-negative bottom
LL
-positive both directions
Summation of leads
-Lead II= Lead I + Lead II
What degree angles are the leads at?
-Lead I at 0
-Lead II at +60 degrees
-Lead III at +120 degrees
-aVR at -150 degrees
-aVL at -30 degrees
-aVF at 90 +90 degrees
Mean Electrical Axis (MEA)
-sum of the electrical vectors during ventricular depolarization
Lower Mean Electrical Axis
-left axis deviations
Greater Mean Electrical Axis
-right axis deviations
Reasons for axis deviation
-can be pathological and include left ventricular hypertrophy, conduction deficits, and infarcted tissue
Estimated Mean electrical axis steps
1.find the biphasic wave (the deflection during the QRS)
2.find the perpendicular wave to the biphasic
3. Determine whether the perpendicular wave is positive or negative, and whatever one it is will be the estimate
Ventricular depolarization sequence from Lead II standpoint
-impulses conducted down left and right branches of both sides of septum causes septum to depolarize (from left to right). Occurs slightly away from positive electrode resulting in small negative deflection = Q wave
-impulse travels towards the apex of heart, resulting in heading directly at positive electrode producing a tall positive reflection = R wave
-impulse then moves and depolarizes the free wall of the left ventricle (endocardial to epicardial surface) resulting in vector towards positive electrode and a small positive
-impulse at base of left ventricular free wall causing depolarization towards negative electrode= S wave
Ventricular depolarization from other aspects of heart
-all the other leads are recording the same depolarizations as lead II but they will record something slightly different
Cardiac excitement patterns in species
-differs between species, depending on position of heart in the body
-need to place leads in different places depending on species
-ECG reflections vary across species and each animal
T wave variations in different species
-positive T wave in primates, swine, sheep
-negative, positive, biphasic T wave in cats and dogs
-negative T waves that become positive T waves in horses during locomotion
Electrode placement in horses
-RA electrode on right neck
-LA and LL on left side over the apex of heart
**Lead I and Lead II can be chosen to record ECG
Why do waves have different names in horse ECG?
-because the Traditional “Q wave” which is usually negative does not exist. Their first wave is the positive deflection of the R wave. Therefore they have an RS wave instead of a QRS wave
Intervals of Horse
-PR intervals
-RS duration/interval
-RT interval
-SS interval instead of RR interval help determine heart rate
Brady/tachycardia
-ECG abnormality
-altered autonomic control
-slow or fast heart rate
Sinus bradycardia
-from a reduced SA node firing due to excess vagal stimulation or damage to SA node. Block or damage results in AV node taking over and controlling heart rate resulting in slow heart rate
Sinus tachycardia
-from an excessive sympathetic nerve stimulation of SA node or high circulating concentrations of catecholamines resulting in increased heart rate
AV conduction blocks
-can occur during excessive vagal stimulation or removal of normal sympathetic influences on AV node
SA blocks
-results in missed beats
-AV node rhythm occurring during the block period
First degree A-V heart block
-prolonged P-R interval
-Signal sent from SA node to AV node is blocked resulting in excessive slowing down and larger distance between P wave and QRS complex
Second degree A-V block
-Atrial contraction occurs and then there is the occasional failure of the ventricles to receive the excitatory signals. Results in dropped beat!
Complete AV block
-results in orphaned P waves with no QRS to go with them
Premature AV node contraction
-Normally ventricles repolarize and fill with blood, eject blood, and then relax. But when a premature beat occurs, the contraction occurs before they have the chance to fill with blood
Axis deviations
-common ECG abnormalities
-due to abnormal position of heart, hypertrophy, left bundle branch block, congenital heart defect, hyperkalemia, pneumothorax, pulmonary stenosis/hypertension, Wolff-Parkinson-White syndrome
Increased voltage (mV)
-common ECG abnormality
-hypertrophy
Decreased voltage (mV)
–common ECG abnormality
-from decreased muscle mass, excess pericardial fluid, pulmonary emphysema
Prolonged QRS
-common ECG abnormality
-from hypertrophy, blocks in bundle branches or purkinje fibers
SA or AV block
-common ECG abnormality
-caused by ischemia, inflammation of SA/AV node, excessive vagal tone (autonomic imbalance)
Elevated or depressed ST segments
-common ECG abnormality
Premature ventricular contractions (PVC)
-common ECG abnormality
-caused by anemia, low blood oxygen levels, heart disease, high blood pressure, chronic sympatho-excitation
Irregular heart beats and the brain
-each irregular beat will impact blood flow to the brain
-can play a role in accelerated cognitive decline
Prevalence of arrythmias in dogs
-~60%
-most have atrial fibrillation, premature ventricular contraction or AV blocks
-sounds like dryer ball in dryer (hoping around)
Cardioversion
-low energy shocks used to restore sinus rhythm
-delivered synchronously with heart rhythm
-often used for atrial fibrillation
Defibrillation
-higher energy shocks used to restore sinus rhythm
-delivered only for lethal arrythmias or dysrhythmias
**no rhythm then CPR needed
