Med Surg Exam 3- Chapter 26
What is a lead?
A viewpoint of the electrical activity. It is like an eye of a camera, w/ a narrow peripheral field of vision, looking only at the electrical activity right in front of it.
HR is influenced by what?
The Autonomic Nervous System
P wave
Atrial depolarization
What is measured on the horizontal axis of the graph?
time & rate
List the waveforms of an ECG
-P wave -QRS complex -T wave -possibly a U wave -segments & intervals: PR interval, ST segment, QT interval
Characteristics of Normal Sinus Rhythm
-V & A rate- 60-100 bpm -V & A rhythm- regular -QRS shape & duration- usually normal, but may be regularly abnormal -P wave- normal & consistent shape, always in front of the QRS complex -PR Interval- consistent interval b/w 0.12-0.20 seconds -P:QRS ratio- 1:1
The P wave is normally how long/tall?
0.11 seconds or less; 2.5 mm or less in height.
The QRS complex is normally less than _______ seconds in duration.
0.12
In adults, the PR interval normally ranges from ......?
0.12 - 0.20 seconds in duration
How long is the QT interval, normally?
0.32-0.40 seconds in duration if the HR is 65-95 bpm.
What is the formula to determine rhythm?
1,500/ # of boxes b/w 2 P waves (atrial) or 2 R waves (ventricular)
the atrial kick accounts for how much of the volume ejected during ventricular contraction?
1/3
For a standard 12-lead ECG, how many electrodes are placed on the body?
10
ECG papers are usually marked at ____-second intervals.
3
A 1-minute rhythm strip contains how many large & small boxes?
300 large, 1,500 small.
There are how many boxes in 1 large box or 1 second?
5
Standard 12-lead ECG: ____ electrodes on the ____________ & ____ on the ________________.
6 on the chest; 4 on the limbs
At what rate does the electrical impulse occur in the adult?
60-100 times/min
What do the following stand for? aVR, aVL, aVF.
Augmented voltage right arm, augmented voltage left arm, augmented voltage left leg/foot
The limb electrodes are placed on areas that are not ________ & do not have significant ____________.
Bony; movement
The electrical stimulation of the cardiac muscle cells causes them to ___________.
Contract
The electrical stimulation is called ____________ & the mechanical contraction is called ________________.
Depolarization; systole
True or false: conduction is the process in which the electrical impulse quickly travels from the AV node through the atria to the SA node.
FALSE: it travels from the SA node, through the atria, to the AV node.
PP interval
From the beginning of 1 P wave to the beginning of the next P wave.
What should be done to the skin before placing electrodes on the body for an ECG?
Gently abrading the skin w/ a clean dry gauze pad helps to expose the inner conductive layer of the epidermis, which will reduce skin impedance.
What leads do the limb electrodes provide?
I, II, III, aVR, aVL, aVF
Treatment of torsades
IV Magnesium sulfate
What is the drug of choice for a pt with impaired cardiac fxn or AMI
IV amiodarone
A standard 12-lead ECG reflects the electrical activity primaily in the...?
Left ventricle
Which electrodes provide the first 6 leads?
Limb
RR interval
Measured from 1 QRS complex to the next QRS complex.
Is atrial repolarization visible on ECGs?
NO
Electrical relaxation is called ____________ & mechanical relaxation is called ______________.
Repolarization; diastole
The electrical impulse that stimulates & paces the cardiac muscle normally origintes in the ___________________.
SA Node
Electrical conduction that begins in the SA node generates a __________________________.
Sinus Rhythm
When obtaining a 12-lead ECG, which type of muscle activity can easily interfere with the reading?
Skeletal muscle
Where is V5 placed?
The same level as V4, anterior axillary line.
The # & placement site of the electrodes depend on....?
The type of ECG being obtained
The chest electrodes provide the V or precordial leads, which are....?
V1-V6
The RR interval is used to determine _____________ rate & rhythm.
Ventricular
QRS Complex
Ventricular depolarization
Atrial repolarization occurs at the same time as...?
Ventricular repolarization
T wave
Ventricular repolarization
When does a normal sinus rhythm occur?
When the electrical impulse starts at a regular rate & rhythm in the SA node & travels through the normal conduction pathway
Torsades de pointes
a lethal ventricular dysrhythmia; prolonged QT interval. Common causes: CNS disease, certain meds: Cipro, Zithromax, Haldol, Lithium, Methadone, low potassium.
What is measured on the vertical axis?
amplitude or voltage
The PP interval is used to determine _____________ rate & rhythm.
atrial
How is the HR determined from the ECG when the rhythm is irregular?
count the # of RR intervals or # of QRS complexes in a 6-second strip & multiply by 10.
When a wave is taller than ____ mm in height, what kind of letters are used?
capital (Q,R,S)
Where is V3 placed?
diagonally b/w 2 & 4
ST Segment
early ventricular repolarization
The U wave is rare, but sometimes appears in patients with ________________.
hypokalemia, HTN, heart disease.
The Q wave is the first __________________ deflection after the P wave.
negative
The S wave is the first ________________ deflection after the R wave.
negative
The R wave is the first ________________ deflection after the P wave.
positive
U Wave
repolarization of the Purkinje fibers
Where is V6 placed?
same level as 4 & 5, midaxillary line.
When a wave is less than ____ mm in height, what kind of letters are used?
small (q,r,s)
Where is V2 placed?
the 4th intercostal space, left sternal border
Where is V1 placed?
the 4th intercostal space, right sternal border
Where is V4 placed?
the 5th intercostal space, left midclavicular line
QT Interval
the total time for ventricular depolarization & repolarization
What is the atrial kick?
when the structure of the AV node slows the electrical impulse, giving the atria time to contract & fill the ventricles w/ blood.