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How is axis determined in RBBB?
Look at the initial 60-80 ms (should be normal unless LAFB or LPFB is present)
What is the duration of LBBB and RBBB?
120 ms (greater than or equal to)
What are the five criteria for RBBB?
1. duration 120 ms or greater; 2. R' in V1 or V2 (R' > R); 3. delayed onset of intrinsicoid deflection (beginning of QRS to peak of R > 0.05 seconds in V1 and V2; 4. secondary ST/T wave changes in V1 and V2; 5. wide slurred S in I, V5, and V6
Does RBBB interfere with the diagnosis of MI or LVH?
What are the criteria for incomplete RBBB?
RBBB morphology with QRS duration between 90-120 ms
What is the QRS axis in LAFB?
-45 --> -90 degrees
100 --> 180 degrees
Why is there left axis deviation in LAFB?
The impulse reaches the LV via the LPF (inserts in the inferoseptal wall); initial impulse is downward and rightward (r wave inferiorly) then the wave heads leftward and upwards (deep S inferiorly, large R left leads); takes 20 ms longer (QRS widening and delayed R peak in AVL)
Is the septum depolarized R-->L or L--> R?
The left bundle arborizes earliest, therefore impulses reach the left side of the septum first
What are the criteria for LAFB?
Axis -45 --> -90 degrees; qR in I and AVL; rS in III; QRS duration 80-100 ms; no other causes of LAD
What are the "other" causes of LAD in LAFB?
LVH, inferior MI, emphysema, ostium primum ASD, LBBB
What false positive diagnosis can result from LAFB?
Which false negative?
LVH based on voltage criteria in I and avL
What part of the heart is activated by the left anterior fascicle?
anterior and lateral walls of the LV
What are the criteria for LPFB?
RAD, QRS duration 80-100 ms, no other factors causing RAD
What are the "other" causes of RAD in LPFB?
RVH, verticle heart, emphysema, lateral wall MI, dextrocardia, lead reversal, WPW
Why is there right axis deviation in LPFB?
The impulse reaches the LV via the LAF (inserts in the upper, lateral wall); initial impulse is upward and leftward (endo --> epi) (r waves in left leads and q waves inferiorly); the wave then heads downward and rightward (tall R waves inferiorly and deep S waves in I and avL); takes 20 ms longer (wider QRS) and reaches the inferior leads late (delayed R peak in AVF)
Why is isolated LAFB more common than isolated LPFB?
The LPF is shorter, thicker, and received blood from two arteries (RCA and LAD)
What are the 5 criteria for LBBB?
1. QRS > 120 ms; 2. delayed onset of intrinsicoid deflection in leads I, V5, V6; 3. broad monophasic R waves in I, V5, V6; 4. secondary ST / T wave changes; 5. rS or QS in right precordial leads
How do you determine axis in LBBB?
Can LVH and LBBB be coded simultaneously?
What is the criteria for incomplete LBBB?
LBBB morphology with QRS duration 90-120 seconds
What is the diagnosis? QRS > 110 ms without LBBB or RBBB morphology?
Nonspecific intraventricular conduction disturbance
ECG definition of ischemia?
ST depression, T waves usually inverted, no q waves
ST segment elevation; no q waves
abnormal Q waves, ST elevated or depressed; T waves inverted, normal, or upright and symmetrically peaked
What is the ST elevation criteria in the leads V1-V3?
All the others?
What Q waves are abnormal in V1-V3?
The other leads (except AVR)
any q wave
> 30 ms, > 1 mm depth in 2 contiguous leads
What is the definition of acute MI?
Abnormal Q waves, ST elevation; hyperacute T waves very early
Abnormal Q waves, isoelectric ST segments, ischemic (usually inverted) T waves
Abnormal Q waves, isoelectric ST segments, normal T waves
Anterolateral MI, recent or acute:
Abnormal Q waves with significant ST elevation in leads V4-V6
I and avL
II, III, avF
Posterior MI, age recent or acute
Age indeterminate or old
R wave in V1 > 40 ms with R/S > 1 and significant ST depression
without ST depression
Normal variant, early repol
ST segment elevation at the J point, Concave upward, distinct notch and slur of the downstroke of the R wave, no ST depression
Nonspecific ST and/or T wave abnormalities
< 1 mm ST depression or elevation, and/or T wave flat or slightly inverted
ST and/or T wave suggesting ischemia
ST: horizontal or downsloping ST segments with or without T wave inversion
T: Biphasic T waves with or without ST depression; symmetrically or deeply inverted T waves
ST and/or T waves suggesting injury
ST segment elevation; T waves invert before ST segments resolve; ST depression in the noninfarct leads is common
Prolonged QT interval
QTC > 440 ms or > 50% of the RR
In which lead is the QT segment measured?
Longest QT interval with a distinct T wave termination
Prominent U wave
> 1.5 mm
How is ST segment elevation produced?
MI causes destruction of the dielectric property of the cell membrane which allows free motion of ions. This depresses the baseline; the ST segments are actually not moved because during early repolarization there is not much movement of ions
What rhythms can result from digitalis toxicity?
Atrial tachycardia with block, AF with complete heart block, 2nd or 3rd degree AV block, 3rd degree AV block with accelerated junctional rhythm or AIVR, SVT with alternating bundle branch block
What electrolyte abnormalities exacerbate dig toxicity?
hypokalemia, hypomagnesemia, hypercalcemia