Axis and BBB Flashcards
The QRS complex is indicative of what within the heart?
deolarization of the ventricles
What is the normal order of depolarization within the heart?
septum (L to R)
Main portion of ventricle (largest vector)
Basilar/bottom portion of ventricle
What leads are in the frontal plane?
limb leads
What leads are in the transverse (coronal) plane?
precordial leads
What is amplitude affected by?
the size and direction of vectors in relation to lead
What happens to amplitude with hypertrophy?
There is more heart, thus more vector, thus more amp
What happens to amplitude with infarct?
Dead hear cells, thus less heart, less of a vector and thus decreased amp
What are the criteria for low voltage?
<10mm in all precordial leads
What is a big determinant in voltage?
the amount and location of fluid and fat
How is voltage affected with a pericardial effusion?
decreased
What is the normal duration of QRS?
<.12 sec, 3 small boxes
How do we measure QRS?
measure it in several different leads and use the widest one
What are some causes of wide QRS?
hyperkalemia (wide and peaked T waves) medications ventricular tachy idioventricular rhythms WPW BBB and IVCD ventricular premature contractions aberrrantly conducted complexes pacemaker
Where is QRS notching most common?
precodial leads
What is QRS notching usually indicative of?
generally a/w benign causes of ST elevation
early repol
pericarditis
What is an Osborn Wave?
large deflection at the end of QRS complex (much larger than benign notching)
Where do we see Osborn waves?
Severe hypothermia
How do we determine if a Q wave is benign or pathologic?
based on size
What can cause a slight variation in the depth of a Q wave with respiration
obeses, pregnant or ascites
What are the characteristics of a pathological Q wave?
> 1/3 total height of QRS
0.04 seconds wide (one small box)
Look at regional pattern (inferior, anterior, lateral)
What is normal transitional pattern?
mostly neg to mostly pos in precordial leads
Where is the transition zone?
V3-V4
What happens if the transition zone is before V3?
axis is rotated counterclockwise = early rotation
What happens if the transition zone is after V4?
axis is rotated clockwise = late rotation
How do we measure the QT interval?
beginning of QRS to the end of T wave
What is a normal QT interval?
less than 1/2 R-R interval
What are multiple variables that affect QT interval?
age, HR, meds, etc
What is indicative of a prolonged QT?
Torsades
What is the definition of the electrical axis?
sum of all vectors of individual ventricular myocytes
What is the normal average direction of the hearts electrical axis?
down and to the left
What can axis be helpful in diagnosing?
L or R ventricularhypertrophy Hemiblock pulmonary embolism dextrocardia lead misplacement
What is the most common mistake with lead misplacement? What happens?
interchanging R and L arm leads; will see negative P and QRS in lead II and positive P and QRS in aVR (opposite of normal)
What else can cause a negative P and QRS in lead II and positive P and QRS in aVR (opposite of normal)?
dextrocardia
What is the hexiaxial system?
represented by circle with limb leads enclosed, each limb having a positive and negative pole
What is each “spoke” seperated by in the hexiaxial system?
30 deg
What are the degree markers for each of the leads?
I 0 II 60 III 120 aVL -30 aVF 90 aVR -150
What is an isoelectric lead?
each lead has a corresponding isoelectric lead, found at 90 deg from lead; or at line dividing +/- halves of lead
What leads are used to calculate axis?
I and aVF (isoelectric)
What is normal axis?
0-90 deg
What is the axis for LAD?
(-1)-(-90) deg
What is the axis for RAD?
91-180
What is the axis for Indeterminate?
extreme LAD or RAD (-91)-(180)
What are the characteristics of I and aVF in a normal axis?
both pos
T/F: if one lead is isoelectric, then the axis is parallel to that lead.
false perpendicular
What are causes of RAD?
normal variant in adolescents and children RV hypertrophy L posterior hemiblock dextrocardia pulmonary pathology
What are causes of LAD?
normal variant with agin
left anterior hemiblock
When is LAD pathologic?
if lead II is negative, this makes axis more neg than -30
What is a LAF?
left anterior fasicle; thin bundle of fibers that innervate anterior and lateral walls of LV
What is a LPF?
left posterior fasicle; bundle that fans out and innervates inferior and posterior walls of LV
Which fascicle is easier to block?
LAF
What is LAH?
Left anterior hemiblock; creates a late unopposed vector point UP and LEFT
Between -30 and -90 (= pathologic LAD)
What are other characteristics of LAH?
if QR complex or tall R wave in lead I; rS complex in lead III
What is LPH?
Left posterior hemiblock; creates a late and unopposed verctor DOWN and RIGHT
Axis 90 and 180
What are other characteristics of LPH?
rS in lead I and qR in lead III
diagnosis of exclusion
What are bifascicular blocks
RBBB with LAH or LPH
What is the impulse in a BBB?
impulse is conducted until it is blocked at either R or L BB (cell to cell transmission is slow and chaotic)
What are characteristics of a BBB?
wide QRS and flipped T wave (opposite of QRS) = discordance
Characteristics of RBBB?
wide QRS
RSR’ pattern in lead V1 - rabbit ears
Deep S wave in leads 1 and V6
What else can be seen in a RBBB in replace of RSR’?
QR’ - found with old anteroseptal infarct in lead V1
Characteristics of LBBB?
wide QRS
broad R waves in lead 1 and V6 - all positive
broad S waves in V1 - all negative
What is the clinical significance of LBBB?
very difficult to diagnose infarction in presence of LBB
What is LBBB until proven otherwise?
NEW LBBB IS CAD UNTIL PROVEN OTHERWISE
What leads do we use to diagnose BBB?
I, V1, V6
What are the characteristics of IVCD?
intraventricular conduction delay; wide QRS but not BBB- “mixed”
What is commonly associated with IVCD?
hyperkalemia
What is discordance?
T wave in opp direction of last wave of QRS
What is concordance?
T wave in same direction of last wave of QRS
