Exam 2 – Cardio Ch 11 Flashcards
LOOK AT NORMAL EKG
LOOK AT NORMAL EKG
Describe P wave
Depolarization of atria
0.3 seconds
Immediately precedes contraction
What is the P wave caused by?
Electrical potentials generated when atria depolarizes before atrial contraction begins
Describe R wave
Ventricles depolarize
More muscle, more electrical activity
What does more electrical activity look like on an EKG?
Higher peak
Describe T wave
Ventricles repolarizing
Where is atria repolarization?
Hidden somewhere in QRS due to greater electrical activity in ventricles
Cannot be seen on electrocardiogram
Atria remain contracted until it is repolarized
What does the QRS complex precede?
Ventricular contraction
How long do ventricles remain contracted?
Until a few milliseconds after the end of the T repolarization
What causes QRS complex?
Potential generated when ventricular depolarizes before contraction
What should always accompany a QRS complex?
A P wave
What are the depolarization waves?
P wave
QRS complex waves
Describe P-Q or P-R interval
Duration of time between beginning of P wave and beginning of QRS wave
This represents the time between the beginning of the atrial contraction and the beginning of ventricular contraction
Describe Q-T interval
Duration of time from the beginning of Q wave to the end of the T wave
Approximates the time of ventricular contraction
How can the heart rate be determined?
With the reciprocal of the time interval between each heartbeat or calculated using paper speed # of complexes/25mm or 50mm/sec x 60
LOOK AT STANDARDIZED EKG’S
LOOK AT STANDARDIZED EKG’S
LOOK AT DEPOLARIZATION AND REPOLARIZATION WAVES
LOOK AT DEPOLARIZATION AND REPOLARIZATION WAVES
When is no potential recorded?
When ventricular muscle is either completely depolarized or repolarized
What does Bipolar limb leads mean?
EKG is recorded from two electrodes on the body
Electrodes are located on different sides of the heart (ie limbs)
Describe Lead I
The negative terminal of the electrocardiogram is connected to the right arm, and the positive terminal is connected to the left arm
Describe Lead II
The negative terminal of the electrocardiogram is connected to the right arm, and the positive terminal is connected to the left leg
Describe Lead III
The negative terminal is connected to the left arm, and the positive terminal is connected to the left leg
What are other types of EKG leads?
Chest leads
Augmented unipolar limb leads
How many chest leads are there?
V1-V6
V2 in 4th interspace
V4-V6 in 5th
V3 between V2 and V4
What are chest leads very sensitive to?
Potential changes underneath electrode
relatively minute abnormalities in ventricles, particularly in the anterior ventricle wall, can cause marked changes in EKG recorded from individual chest leads
What is the flow of electrical currents in the chest around the heart?
Ventricular depolarization starts at the ventricular septum and the endocardial surfaces of the heart
The average current flows positively from base of heart to apex
At the very end of depolarization the current reverses from 1/100 second and flows toward the outer walls of the ventricles near the base (S wave)
How is the QRS in chest leads V1 and V2?
Mainly negative because chest electrode in these leads is nearer to the base of heart
Base of heart is direction of electronegativity during most of ventricular depolarization
How is the QRS in chest leads V4-V6?
Mainly positive because chest electrodes in these leads in nearer the apex of the heart
Apex is direction of electropositivity during most of depolarization
What is the mean vector through?
Partially depolarized heart
What does Einthoven’s Law state?
Electrical potential of any limb equals the sum of the other two
+ and - signs of leads must be observed
If lead I is 1mV, lead III is 0.5 mv, what is lead II?
1.5mV
What is augmented unipolar limb leads?
Two of the limbs are connected through electrical resistances to negative terminal of EKG and third limb is connected to positive terminal
What is aVR in augmented unipolar limb leads?
Positive terminal is attached to right arm
What is aVL in augmented unipolar limb leads?
Positive terminal is attached to left arm
What is aVF in augmented unipolar limb leads?
Positive terminal is attached to left foot
What is the R-R interval?
0.83 seconds
Heart rate calculation
(60 sec)/(0.83 sec) = 72 beats/min
What is the normal heart rate in dogs?
60-180
What is the normal heart rate in cats?
180-220
What is the width and height of the P wave in dogs?
W: 0.04 sec
H: 0.4 mV
What is the width and height of the P wave in cats?
W: 0.04 sec
H: 0.2 mV
What is the P-R interval in dogs? Cats?
- 06-0.15 sec
0. 05-0.09 sec
What is the width and height of the QRS interval in dogs?
W: 0.06 sec
H: less than 3 mV
What is the width and height of the QRS interval in cats?
W: 0.04 sec
H: less than 0.9 mV
What is the QT interval in dogs?
0.15 to 0.25 sec depending on heart rate
What is the QT interval in cats?
0.07 to 0.2 sec depending on heart rate
What is the ST segment in dogs?
No more than 0.2 mV elevation or depression
What is the ST segment in cats?
No depression or elevation
What is the T wave in dogs and cats?
Positive, negative, or biphasic
What are the 5 steps to an interpretation of an ECG strip?
- Heart rate
- Heart rhythm
- P P-wave
- PR interval
- QRS complex
Traditionally, what does every P wave have?
QRS complex
How do you know if the SA node is firing?
P waves are present
What is a reasonable rate for SA node?
More than 45-60
How can you tell if the SA node is calling the shots?
If some or all of the P waves have a QRS
When does a dog have bradycardia? Tachycardia?
Heart rate of less than 70 bpm
Heart rate of more than 140 bpm
When does a cat have bradycardia? Tachycardia?
Heart rate of less that 160 bpm
Heart rate of more than 220 bpm
