Electrocardiogram

Question 1

Standard Calibration of ECG Recording

Answer 1

2 Speeds:

1) 50 mm/sec - 1mm = 0.02 sec
2) 25 mm/sec - 1mm = 0.04 sec

Question 2

Lead Placement

Answer 2

1) Place patient in R LATERAL RECUMBANCY
2) Attach electrodes on skin just proxiaml (above) to elbows and stifles
3) Wet electrodes with alcohol

Question 3

Ground Lead

Answer 3

R Leg

Question 4

3 Bipolar Limb Leads

Answer 4

Lead I = RA to LA
Lead II = RA to LL
Lead III = LA to LL

NEGATIVE TO POSITIVE

Question 5

Augmented Unipolar Limb Leads

Answer 5

Lead aVR = LA & LL to RA
Lead aVL = RA & LL to LA
Lead aVF = RA & LA to LL

NEGATIVE (2) TO POSITIVE

Question 6

Chest Leads

Answer 6

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

Question 7

Axis of Leads

Answer 7

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

Question 8

Determination of POS or NEG Waves

Answer 8

1) Direction of Wave
2) Depolarization or Repolarization
3) Amount of Tissue
4) Axis of Lead

Question 9

Depolarization Waves

Answer 9

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

Question 10

P Wave

Answer 10

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

Question 11

QRS Wave

Answer 11

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

Question 12

Septal Depolarization

Answer 12

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

Question 13

Apical Depolarization

Answer 13

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

Question 14

Late Ventricular Depolarization

Answer 14

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)

Question 15

T Wave

Answer 15

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

Question 16

Tracing

Answer 16

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

Question 17

P-Q / P-R Interval

Answer 17

From Beginning of atrial electrical excitation to the beginning of ventricular electrical excitation

P-R if no Q is present

0.16 sec

Question 18

Q-T Interval

Answer 18

Length of time of contraction of ventricles

0.35 sec

Question 19

Determining Heartrate from an ECG

Answer 19

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

Question 20

Mean QRS Vector

Answer 20

+59 Degrees

Question 21

What part of the Atrial system is repolarized first?

Ventricular Sytem?

Answer 21

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

Question 22

During most of vent dep, direction of electrical potential is from ——– to ———

Answer 22

Base to Apex of the heart

Question 23

Mean Electrical Axis

Answer 23

Average Direction of Ventricular Dep (Base to Apex)

Normal Range = +40 - +100 Degrees
Average Normal = +59 Degrees

Question 24

Mean Electrical Axis - Shifts to the Left

Answer 24

1) After Deep Expiration
2) Lying Down
3) Obesity (Diaphragm pushes against heart

Question 25

MEA - Shifts to the Right

Answer 25

1) End of deep inspiration 2) Standing up 3) Tall, Lanky People (heart hangs downward)

Question 26

MEA - Hypertrophy of One Ventricle

Answer 26

Shift of MEA to the same side at the hypertrophied ventricle

Question 27

MEA - Bundle Branch Block

Answer 27

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

Question 28

Determiningg MEA

Answer 28

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

Question 29

If any lead is isoelectric =

Answer 29

MEA is in the perpendicular direction (DO NOT NEED ISOELECTRIC DEFLECTION FOR MEA TO EXIST)

Question 30

Methodical Approach to the ECG

Answer 30

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?

Question 31

Normal ECG Values

Answer 31

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

Question 32

Right Atrial Enlargement

Answer 32

INCREASED P WAVE AMPLITUDE Associated Conditions: Chronic respiratory disease, congenital heart defects, interatrial septal defect

Question 33

Left Atrial Enlargement

Answer 33

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

Question 34

Conditions that cause shifts in axis, abnormal voltages and duration of QRS Complexs

Answer 34

Excessive generation of electrical potential in a particular direction More time required for depolarization wave to travel through muscle R and L Ventricle Enlargements

Question 35

Right Ventricular Enargement

Answer 35

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

Question 36

Left Ventricular Enlargement

Answer 36

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

Question 37

Left Bundle Branch Block

Answer 37

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

Question 38

R Bundle Branch Block

Answer 38

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