CVPR 04-03-14 08-09am 12-Lead ECG Interpretation - Horwitz Flashcards
Lead I – polarity & sign
bipolar w/ positive electrode at the left arm and the negative electrode at the right arm
Lead II - polarity & sign
Bipolar w/ positive in the left leg and negative in the right arm
Lead III - polarity & sign
Bipolar w/ positive in left leg and negative in left arm.
Augemented leads (aVR, aVL, aVF) – polarity & plane
unipolar & share frontal plane of the heart with the bipolar leads
aVR lead –type/polarity of lead & signs
unipolar augmented lead; positive in the right arm
aVL lead –type/polarity of lead & signs
unipolar augmented lead; positive in the left arm
aVF lead –type/polarity of lead & signs
unipolar augmented lead; is positive in the left leg
Chest (precordial) leads – locations & polarity/plane
Placed on the front of the chest right of the sterna border in the aortic region (V1), left of the sternal border in pulmonic region + two below (V2, V3, V4), and then two in the axillary region (V5 &6) – see picture….. Unipolar leads that reflect changes in the horizontal plane
Leads V1 & V2 – proximity to what heart structures & thus what defects they detect
“Right chest leads” = monitor the RV….They are close to the right ventricle - increased voltage from RV hypertrophy is seen there…. Also, they are close to the septum – septal infarcts are most evident in these leads
Leads V5 & V6 – proximity to what heart structures & thus what defects they detect
“Left heart leads” = monitor the LV…. They are close to the left ventricle, esp. its anterolateral portion - increased voltage from LV hypertrophy & changes from anterolateral infarcts are most evident in these leads
Left ventricular depolarization
B/c of its greater muscle mass, the dominant producer of voltage is the LV…. Normal depolarization of the ventricles goes from Rt to Lt & downward from the Rt arm towards the Lt leg….Lead aVR (+ in Rt arm) is NEGATIVE since all forces are away from it leftward & downward….. Leads I & II are POSITIVE b/c forces are going towards their positive electrodes on the left arm & left leg, respectively….. V1 & V2 are mostly negative b/c predominant forces are away from the right ventricle.
Normal QRS Axis– degrees & when positive (in what leads)
The normal QRS axis shows the mean direction of the depolarization (LV dominates, so it is mostly leftward & dominant)….. The normal axis ranges from straight downward +90 degrees (perpendicular to Lead I) to leftward slightly above the horizontal +30 degrees (Lead II), as seen in the normal 12 lead tracing….. Positive in both leads I & II
Right Axis Deviation (RAD) – degrees & when positive (in what leads)
From +90 degrees to +180 degrees….. negative in lead I and positive in lead II
Right Axis Deviation (RAD) – degrees & when positive (in what leads)
From -30 degrees to -90 degrees….. positive in lead I and negative in lead II
Indeterminate axis – degrees & when positive (in what leads)
From -90 to +180 degrees …negative in both leads I & II
Bundle branch blocks/Ectopic ventricular beat - QRS effects
Conduction of the QRS is outside the specialized conduction system and the QRS is wide
Right bundle block & QRS
W/right bundle block, there are late forces to the right ventricle (must go through slower contractile myocytes b/c bundle is blocked) —> delay widens QRS = tall late positive deflection (an R prime) in V1 & V2 (rt sided leads) and a negative deflection (wide S) wave in I and V6 (away from these left sided leads) [see ppt]
Left bundle block & QRS
W/ left bundle block, there is high voltage generated in the left ventricle —> QRS is widened and all forces are away from V1 towards V6…. Wide S wave in V1, Wide R wave in V6 (possibly notched)
Left bundle block in the fascicles (Hemiblock)
Distal blocks in the left bundle cause QRS Axis shifts (w/out widening QRS significantly): 1. Blocks in the left anterior fascicle cause left axis deviation (LAD)….. 2. Left posterior fascicle block causes right axis deviation (RAD) [see pic in slides]
Left ventricular hypertrophy – 12 lead effects
LV hypertrophy causes large positive deflections = tall R waves in V5 & V6 (lt. sided leads) and deep negative deflections (S waves) in V1 (rt. sided lead)….. Often, a negative T wave
Right ventricular hypertrophy – 12 lead ECG effects
In RV hypertrophy, there is high voltage in V1 and V2…. Any time the R wave is greater than the S wave in V1, it’s right ventricular hypertrophy
Sizable Q wave development in 12 lead ECG
If a sizable Q wave (1+ small box wide, or atleast 0.04s) is seen in at least two adjacent leads = due to transmural necrosis (infarcts usually involve only the LV)….. Often looks like you’ve lost part of the R wave b/c the Q is big…..When Q waves develop in leads which would normally be positive they give information on localization of the infarct: 1. Inferior lead (II,III, aVF) Q’s are due to inferior infarcts…… 2. Leads V1-V4 Q’s are due to anterior wall infarcts….. 3. Leads I, aVL & anterolateral leads (V5,V6) are associated with lateral wall infarcts.
Acute pericarditis on ECG
Diffuse ST elevation (in almost all leads; in aVR appears as ST depression) <== once pericarditis occurs, it is in every part of the pericardium
P - Tall (>2.5 mm in inferior lead)
RA enlargement
P – wide & notched, w/late negativity in V1
LA enlargement
QRS – wide (>/= 0.12 s)
Bundle branch block
Large late R’ in V1 + late S in V6
RBBB
Wide QS in V1 + Wide R in V6
LBBB
Right axis shift
RV hypertrophy, posterior hemiblock
Left axis shift
LV hypertrophy, anterior hemiblock
High voltage
Ventricular hypertrophy
R>S in V1
RV hypertrophy
Large R w/ ST-T changes in V5/V6, S in V1/V2
LV hypertrophy
Q waves
Infarct if in 2 related leads, 25% of R wave, or 0.04 s wide
ST elevation
Injury if localized….. Pericarditis if diffuse
ST depression
Ischemia or subendocardial infarct
T inversion
Ischemia or secondary hypertrophy or bundle block
Long QT
Electrolyte imbalance, Drug effect
