11/1 EKG - Saluja Flashcards
EKG basics
what is it showing
electrodes vs leads
graph of voltage (potential diff) vs time as recorded by 12 leads
→ 3D view of depolarization/repolarization occuring over time
10 electrodes are placed on body (6 precordial, 4 limb)
12 leads are displayed on the EKG (avF, avL, avR, I, II, III, V1-V6)
- bipolar leads (derived from 2 electrodes) : I, II, III
- unipolar leads (derived from an electrode & Wilson’s Central Terminal) : V1-V6, aVL, aVR, aVF
- WCT = (RA+LA+LL)/3
terminology
wave
segment
interval
wave: deviation from baseline
segment: piece of baseline
interval: segment AND wave(s)
naming QRS waves
FIRST POSITIVE DEFLECTION : R wave
if there’s a NEGATIVE DEFLECTION PRECEDING POSITIVE DEFLECTION : Q wave
NEGATIVE DEFLECTION PRECEDED BY POSITIVE DEFLECTION : S wave
P waves
sinus duration < 0.12s in Lead II
sinus amplitude < 2.5-3mm in Lead II
PR interval
normal duration: 0.12-0.20s (3-5 small boxes)
- prolonged PR: > 0.20s
- short PR: < 0.12s
QRS complex
normal duration: < 0.12s
- normal conduction down His-Purkinje tissue and through ventricles
wide QRS: > 0.12s
- abnormal conduction in His-Purkinje or in ventricles
- ex. bundle branch block or IVCD (interventricular conduction delay)
QT interval
normal
- < 440ms for men
- < 460ms for women
need to correct for HR
- Bazzet Correction (QTc) = QT interval/root(RR interval)
EKG reading algorithm
- rate
- measure RR interval (300/BIGboxes)
- impulse formation and conduction (rhythm)
- SA node is the pacemaker; overdrive-suppresses all other foci
- hierarchy: sinus node - jx/fascicles - ventricular myocardium
- axis
- remember angles! average axis of depol is approx 60degrees
- intervals
- hypertrophy and enlargement
- ST segment and T wave analysis
axis specifics
normal
LAD
RAD
extreme RAD
normal axis (-30 to 90): QRS I+, II+
LAD (-30 to -90): QRS I+, II- (-30→-90)
RAD: QRS I-, aVF+
extreme RAD: QRS I-, aVF-
causes of axis deviation
things that cause deviation:
- extra depol in the direction of the deviation (hypertrophy)
- loss of depol in the direction opposite the deviation (infarction)
- issue with pattern of depol due to fascicular block
LAD
- MI
- left anterior fascicular block
- LV enlargement
RAD
- left posterior fascicular block
- RV enlargement
His-Purkinje system basics
what happens if you block the system somewhere?
Bundle of His splits off into…
- R common bundle
- L common bundle
- anterior hemifascicle
- posterior hemifascicle
what happens if you block the system somewhere?
impulse is still conveyed BUT conveyed by cell-to-cell conduction! →→ slow
- arrive at the end of the QRS in the direction of the block
- ex. in RBBB → terminal forces go toward the right, and the waves look slurred
RBBB characteristics
- terminal impulses (conducted by cell-to-cell transmission) arrive on right side at end of QRS
- **NO CHANGES SEEN IN SEPTAL DEPOL i.e. very first part of QRS is unchanged in RBBB
- septum is innervated by branches coming off proximal left common bundle
V1: large, broad positive deflection at end of wide QRS
I, V6: negative slurred deflection at end of wide QRS
- wide because you have slow conduction (> 120ms)
- characteristic pos/neg deflection indicating that terminal impulses are in the right side of the heart
LBBB characteristics
*ALTERED SEPTAL DEPOL → don’t see Q waves
- very beginning of QRS complex is altered
terminal impulses seen on the L side of the heart
wide QRS (> 120ms)
I, V6: positive slurred deflections
V1: negative slurred deflections
fascicular blocks
what do the anterior and posterior hemifascicles supply?
will initial depol be affected? why/why not?
- left anterior hemifascicle supplies superior/leftwards part of LV
- left posterior hemifascicle supplies inferior/medial part of LV
initial septal depol NOT affected because hemifascicles are distal to the proximal L common bundle, which is the source of septal depol
LAFB
left anterior fascicular block
initial depol normal
late forces are UPWARDS, LEFTWARDS
- overall QRS < 120ms
over 100ms; a little wider than normal but not WIDE)
- septal (nonpatho) Q waves intact in I, aVL
absent in LBBB
- RS in II, III, aVF
- precordial axis is less than -45 degrees
- frontal axis is more posterior (poor R-wave progression)
LPFB
left posterior fascicular block
- initial depol normal
- late forces are DOWNWARDS, RIGHTWARDS
- overall QRS < 120ms
* over 100ms; a little wider than normal but not WIDE - septal (nonpatho) Q waves intact in I, aVL
* absent in LBBB - rS in I, qR in III
- precordial axis rightwards: 90-180 degrees
- frontal axis is more posterior (poor R-wave progression)
LVH
Sokolow-Lyons criteria:
- sum of amplitudes of S wave in V1 + R wave in V5 or V6 is 35mm or more
- AVL: R wave is 11mm or more
STEMI
evolution of it
key markers of infarction
ST elevation MI
- elevation followed by Q wave development
- as infarct completes, ST segment comes back to normal and Q wave persists, but T wave becomes inverted
- over even longer time, T wave might come back up to normal, and you’re left with a Q wave
key:
Q wave = infarctED
- wider or deeper than expected
- wider than 40ms and/or deeper than 1/3(R wave height)
ST segment deviation = infarctING
ST depression
typically indicative of subendocardial infarction
- downsloping ST : most common
- upsloping ST
- horizontal ST
