EKG basics Flashcards
each small square
- 04 sec duration
0. 1 mV amp
5 small squares
make 1 large box
- 2 sec duration
- 5 mV amp
P wave meaning and duration
initiation of impulse in SA node, depolarization of RA and LA, impulse passing through AV junction
Duration: 0.06 to 0.10 seconds
amplitude 0.5-2.5
PR interval
from start of P wave to start of QRS complex
denotes depolarization of heart from SA node through atria, AV node and His-Purkinje system
duration: 0.12-0.2 sec
PR segment
isoelectric line bw end of P wave and start of QRS complex
QRS complex
normal duration: 0.06 - 0.11 sec
ST seg
isoelectric line following QRS to beginning to T wave
T wave
ventricular repolarization; slightly asymmetrical
J point
where QRS complex meets ST segment
QT interval
onset QRS to end of T wave
measures time of ventricular depolarization and repolarization
Normal duration 0.36-0.44 sec
varies depending on HR (slower HR, longer QT)
Bipolar leads (*note: all move - to +)
Lead I: RA to LA
Lead II: RA to LL
Lead III: LA to LL
*bipolar bc record difference bw positive and negative electrode; use 3rd electrode called ground
Unipolar leads
*use 1 + electrode and reference point (center of heart); waveforms enhanced by machine bc small
*augmented limb leads: aVR, aVL, aVF
aVR: augmented vector right
aVL: augmented vector left
aVF: augmented vector foot
*precordial leads (“chest” or V leads)
V1-6 horizontal plane, all +; V4-6 on same plane
specifics of augmented leads
aVR: RA + views base of heart -atria and great vessels
aVL: LA + views lateral wall of left ventricle
aVF: LL + views inferior wall of left ventricle
Precordial leads
provide anterior and lateral views of heart
Leads that view anterior surface of heart
V1-4
Leads that view lateral surface
Lead I, aVL, V5-6
Leads that view inferior surface of heart
Lead II, III; aVF
5 step process for analyzing ECG
Rate, regularity/rhythm, P waves, QRS complex, PR interval
Normal sinus rhythm
rate: 60-100
rhythm: regular
P wave: upright and round, 1:1 ratio with QRS
QRS: narrow, 0.06-0.11 sec duration
PR interval: 0.12-0.2 sec
T wave: upright and slightly asymmetrical
methods for calculating HR
- # QRS complexes in 6 sec interval x10 (fast and easy but not as accurate) *15 large boxes in 3 sec
- R to R wave 300, 150, 100, 75, 60, 50 method (quick, decent accuracy, can’t use with irregular rhythms)
- 1500/# small sq bw two consecutive R waves (most accurate)
- Rate calculator: R to R wave (easy but not always available, doesn’t work for irregular rhythms)
Methods for determining rhythm
- Caliper
- Paper and Pen
- Counting small squares
Types of Irregular rhythms
- occasional or very
- slightly: “wandering atrial pacemaker” HB initiated from different sites in atria changing appearance of P waves
- sudden acceleration in HR: paroxysmal tachycardia (ectopic site from above ventricles fires rapidly taking over as pacemaker)
- Patterned/cyclical: ex = sinus dysrhythmia, 2nd deg AV block, type I
- Totally: no pattern i.e. a fibrillation
- Variable conduction ratio: not all impulses conducted through AV node –> more P waves than QRS i.e. a flutter
Tall peaked sinus P waves
may indicated increased RA pressure and RA dilation
> 2.5 amp = RAE, p pulmonale
notched, wide, or biphasic sinus P waves
seen in LA presure and LA dilation
width > 0.10 sec suggests LAE, p mitrale
Premature atrial complex
P wave of early beat differs in appearance from underlying rhythm; continuously change in appearance
Peaked, notched or larger than normal T waves
happens in rapid rates such as atrial tachycardia, P wave likely buried in T wave due to short P-P interval
Flutter waves
seen instead of normal P waves when atria fire rapidly from one site 250-350 BPM - more P than QRS
“saw toothed” pattern
“F” waves or Flutter
Fibrillatory “f” waves
absence of discernable P waves and chaotic looking baseline due to atria firing >350 bpm
*only some atrial impulses conducted through AV node
Inverted P waves
when P wave arises from lower RA near AV node, in LA or in AV junction –> retrograde depolarization of atria
- may immediately precede, occur during or follow QRS complex
- associated with dysrhythmias that originate from AV junction
More P than QRS
indicates impulse initiated in SA node or atria but was blocked and didn’t reach ventricles
QRS configurations
- can be more than one R and/or S but just one Q
* second is R’ or S’.. if small it is r or s
QRS complex should appear normal if
- Rhythm initiated from site above ventricles
- Normal conduction from Bundle of His –> r and L bundle branches –> purkinje
- Normal depolarization of ventricles has occurred
Production and pacemaker sites for abnormal QRS complexes
due to abnormal depolarization of ventricles
*pacemaker site can be: SA node, ectopic pacemaker in the atria, AV junction, bundle branches, Purkinje network, or ventricular myocardium
Various possible causes of abnormal QRS complexes
- ventricular hypertrophy
- intraventricular conduction disturbance
- aberrant ventricular conduction
- ventricular pre-excitation
- ventricular ectopic or escape pacemaker
- ventricular pacing by cardiac pacemaker
Tall QRS complexes
usually caused by:
- hypertrophy of one or both ventricles
- abnormal pacemaker
- aberrantly conducted beat
Low voltage QRS complexes
seen in: obese pt, hypothyroid pt, pericardial effusion
wide bizarre QRS complexes (supraventricular origin)
result form intraventricular conduction defect; usually R or L bundle branch block
Aberrant Conduction
when electrical impulses reach bundle branch while still in refractory after conducting previous electrical impulse –> causes impulse to travel down unaffected bundle branch first followed by stimulation of other bundle branch
Abnormal PR interval classifications
- shorter than 0.12 sec
- longer than .2 sec
- absent
- vary
when do shorter PR intervals occur
when impulse originates in atria close to AV junction or in AV junction
*can occur when impulse arises from supraventricular site but travels through abnormal accessory pathways (ie bundle of kent) to ventricles –> premature ventricular depolarization called pre-excitation, delta waves
Longer PR intervals
occur when delay in impulse conduction through AV node (ex: 1st deg AV block)
when do varying PR intervals occur
In wandering atrial pacemaker, pacemaker site moves from beat to beat causing P waves to appear different and PR intervals to vary
common cause of varying PR intervals
2nd deg AV block, Type I: has PR intervals that are progressively longer until QRS complex is dropped and cycle repeats
when do absent PR intervals occur?
- a flutter
- a fib
- ventricular dysrhythmias
- 3rd deg AV heart block (PR interval not measurable, atria and ventricles beating independently of each other)
