Electrocardiogram Flashcards
Standard Calibration of ECG Recording
2 Speeds:
1) 50 mm/sec - 1mm = 0.02 sec
2) 25 mm/sec - 1mm = 0.04 sec
Lead Placement
1) Place patient in R LATERAL RECUMBANCY
2) Attach electrodes on skin just proxiaml (above) to elbows and stifles
3) Wet electrodes with alcohol
Ground Lead
R Leg
3 Bipolar Limb Leads
Lead I = RA to LA
Lead II = RA to LL
Lead III = LA to LL
NEGATIVE TO POSITIVE
Augmented Unipolar Limb Leads
Lead aVR = LA & LL to RA
Lead aVL = RA & LL to LA
Lead aVF = RA & LA to LL
NEGATIVE (2) TO POSITIVE
Chest Leads
Unipolar Precordial Chest Limbs
Record electrical activity from dorsal and ventral surface of heart
RA, LA, and LL are connected to for a zero reference at center of heart
ECG measures voltage from heart to the selected electrode on chest
Axis of Leads
Einthoven’s Triangle
Lead I = 0 Degrees Lead II = 60 Degrees Lead III = 120 Degrees Lead aVR = 210/ -150 Degrees Lead aVL = -30 Degrees Lead aVF = 90 Degrees
Determination of POS or NEG Waves
1) Direction of Wave
2) Depolarization or Repolarization
3) Amount of Tissue
4) Axis of Lead
Depolarization Waves
1) Impulses from the heart that travels towards the positive electrode produce and upward deflection on the ECG
2) Towards negative = downward deflection
3) Electrical forces are equal = Isoelectrc trace
Impulse = PERP to a lead
Cancel each other out
4) No electrical activity = baseline trace
Tissue is FULLY REPOLARIZED OR DEPOLARIZED
P Wave
Atrial Depolarization
Impulse originates at SA Node and spreads over atria
Electric vector = downward and to the left
Upward Deflection in ECG Tracing = Leads 1 and aVF
QRS Wave
Direction of wave and amount of tissue depolarizing changes as the impulse travels through the heart = positive and negative deflections
Dep in 3 diff directions: Septal, Apical, Late Ventricular
Septal Depolarization
1st part of QRS Wave
After a brief delay at AV Node, impulse travels through common bundle of His and right and left bundle branches, then it enters the interventricular septum
R AND DOWNWARD = small negative deflection in lead I (Q Wave) and small upward deflection in Lead aVF (R wave)
NOT A LOT OF CURRENT = not a lot of tissue
Apical Depolarization
2nd Part of QRS Wave
Impulse continues causing apical (apex) vent dep
L AND DOWNWARD = large positive deflection in lead I (R Wave) AND extends R wave in lead aVF
MORE CURRENT
Late Ventricular Depolarization
3rd Part of QRS Wave
Depolarization over ventricles = points back up
Base of Heart
L and UPWARD = Upward deflection in Lead I (extending R Wave) AND downward deflection in Lead aVF (S Wave)
T Wave
Ventricular Repolarization - Rep of one cell does not cause rep of next cell
Cells rep based on length of action pot
Epicardium (near apex) rep first first = same direction as dep
Then Endocardium
SO T wave in same direction as major wave (R) as QRS
WIDE WAVE
Tracing
P Wave
Baseline = Atria fully dep and Ventricles fully Rep
QRS Wave
Baseline = Ventricles dully Dep and Atria fully Rep (ST Segment)
T Wave
Baseline = Atria and Ventricle fully Rep
P-Q / P-R Interval
From Beginning of atrial electrical excitation to the beginning of ventricular electrical excitation
P-R if no Q is present
0.16 sec
Q-T Interval
Length of time of contraction of ventricles
0.35 sec
Determining Heartrate from an ECG
Heart Rate = reciprocal of the time interval between 2 heartbeats (2 R to Rs)
50 mm/sec = beats per 3 marks (3 sec) x 20
25 mm/sec = beats between 2 marks (3 sec) x 20
Mean QRS Vector
+59 Degrees
What part of the Atrial system is repolarized first?
Ventricular Sytem?
SA Node (rep vector direction is opp of dep vector)
Epicardium near the apex
The rest of the Epicardium
The Endocardium
vector is same direction as dep vector
During most of vent dep, direction of electrical potential is from ——– to ———
Base to Apex of the heart
Mean Electrical Axis
Average Direction of Ventricular Dep (Base to Apex)
Normal Range = +40 - +100 Degrees
Average Normal = +59 Degrees
Mean Electrical Axis - Shifts to the Left
1) After Deep Expiration
2) Lying Down
3) Obesity (Diaphragm pushes against heart
MEA - Shifts to the Right
1) End of deep inspiration
2) Standing up
3) Tall, Lanky People (heart hangs downward)
MEA - Hypertrophy of One Ventricle
Shift of MEA to the same side at the hypertrophied ventricle
MEA - Bundle Branch Block
Block of one side of purkinje branches = the other side ventricle depolarizes faster
Left Block = Left shift of axis
Right Block = Right shift of axis
Determiningg MEA
1) Look for largest net deflection of QRS
2) If QRS has UPWARD DEFLECTION = MEA is toward positive electrode of lead
If QRS has DOWNWARD DEFLECTION = MEA is toward negative electrode of lead
3) Look at lead perpendicular to this
4) Adjust MEA based of isoelectric lead:
If more pos = adjust towards pos electrode of PERP LEAD
If more neg = adjust toward neg electrode of PERP LEAD
If isoelectric = NO ADJUSTMENT
If any lead is isoelectric =
MEA is in the perpendicular direction (DO NOT NEED ISOELECTRIC DEFLECTION FOR MEA TO EXIST)
Methodical Approach to the ECG
1) Identify waves (P, QRS, T, PR Interval) and evaluate DURATION and AMPLITUDE
2) MEA
3) Det Heartrate - Det normal or abnormal (Bradycardia/Tachycardia)
Reciprocal of time between 2 R-R Intervals
4) Is rhythm reg or irreg? Look at R-R INTERVALS
5) Are there P wavs? QRS complexes?
6) Is there a P wave for every QRS complex?
7) Is there a QRS complex for each P wave?
8) Are the Ps and QRSs consistently related?
9) Do all the Ps and QRSs look alike?
Normal ECG Values
1) Heart Rate = 70-160 bpm (60-140 bpm for giant breeds; up to 180 for toy breeds; up to 220 for puppies)
2) Normal rhythms = Normal sinus rhythm, Sinus arythmias, and Wandering pacemaker
3) P Wave = Width (max) = 0.04 sec
Height (max) = 0.4 mV
4) P-R Interval = 0.06 - 0.13 sec
5) QRS Complex = Width (max) = 0.05 sec
Height (max) = 3.0 mV (large)
2.5 mV (small)
6) T Wave = positive, negative, or biphasic
7) Electrical Axis = +40 - +100 Degrees
Right Atrial Enlargement
INCREASED P WAVE AMPLITUDE
Associated Conditions: Chronic respiratory disease, congenital heart defects, interatrial septal defect
Left Atrial Enlargement
INCREASED P WAVE DURATION (P mitrale)
NOTCHING of P waves = due to superimposition of asynchronous right and left atrial conduction (not lined up)
Associated Conditions: Mitral valve insufficiency, aoritc stenosis, ventricular septal defect, patent ductus arteriosis
Conditions that cause shifts in axis, abnormal voltages and duration of QRS Complexs
Excessive generation of electrical potential in a particular direction
More time required for depolarization wave to travel through muscle
R and L Ventricle Enlargements
Right Ventricular Enargement
ECG = Large S waves in I, II, and aVF
MEA of 100 Degrees and Clockwise
Possible Causes = pulmonary stenosis, intraventricular septal defect, heart worm disease, and inc pulmonary vascular resistance
Left Ventricular Enlargement
Dilation or Hypertrophy
ECG = abnormalities not always observed bc L side of heart is already bigger than R
Associated Conditions - aortic stenosis, mitral insufficiency, and hypertension
Left Bundle Branch Block
DELAY or BLOCK of conduction in left branch bundle
At MAIN BRANCH or at level of the ANT or POST FASCICLES
ECG:
1) QRS Complex > 0.08 sec
2) Wide pos deflection in I, II, III and aVF AND inverted inverted in aVR and aVL
3) L Bundle Branch must be differentiated form L ventricular enlargement (thoracic radiography)
Can OCCUR simultaneously w/ L ventricle hypertrophy
R Bundle Branch Block
DELAY or BLOCK of conduction in left branch bundle
At MAIN BRANCH or at level of the ANT or POST FASCICLES
ECG:
1) QRS > 0.08 sec
2) R axis deviation
3) Large S waves in I, II, III and avF
4) Must be differentiated from R vent enlargement with thoracic radiography
