EKG- Class 1 Flashcards
phases of cardiac pacemaker cell
phase 4: Na influx If channels
phase 0: Ca influx
phase 3: K efflux
difference between cardiac muscle and pacemaker cell AP voltages:
muscle cell: -90 to +10
pacemaker cell: -60 to +10
Q wave
first negative deflection
R wave
first positive defection
S wave
second negative deflection
PR interval
beginning of P to beginning of QRS
120-200msec (3-5boxes)
QTc is corrected with ___ and ___ dependent
HR; sex
causes of prolonged QTc:
drugs, genetics, metabolic disturbances (dangerous!)
which is longer, segment or interval?
interval is always longer
U wave
uncommon; after T wave; indicates purkinje fibers
intrinsic pacemaker rhythms:
SA node: 60-100
AV node: 45-50
His: 40-45
Ventr cells/purkinje: 20-40
which His bundle has ant/post divisions?
left
which type of heart block is considered an escape rhythm?
third degree (bc rhythm not driven by SA node)
limb leads:
I, II, III, aVR, aVL, aVF
limb lead for forces going to the upper right
heart
aVR
limb lead for forces moving to left lateral heart
aVL
limb lead for forces moving to inferior heart
aVF
electrical trend of precordial leads:
V1/2: negative, V3/4: isoelectric, V5/6: positive
Degrees of Limb Leads I-III (when calculating axis)
I: 0
II: +60
III: + 120
Degrees of Augmented Limb leads
aVL: -30
aVF: +90
aVR: -150
Heart Rate Box intervals:
300/150/100, 75/60/50, 43/37
leads used in rule of thumbs
I and aVF (both should be positive)
If lead I is + and aVF is negative, which lead should be used to check if true left axis deviation?
lead II (if negative, true LAD)
LAD axis:
-30 to -90
RAD axis:
+90 to +180
no mans land axis:
-90 to +180
what does an equiphasic lead mean?
depolarization occurs perpendicular to the lead
Causes of Right axis deviation:
lateral MI COPD pumonary embolus Right ventricular hypertrophy nl in kids/tall thin adults (athletes) dextrocardia
Causes of Left axis deviation:
LBBB
inferior MI
artificial pacing
left ventricular hypertrophy
