CVPR 04-03-14 08-09am 12-Lead ECG Interpretation - Horwitz

Question 1

Lead I – polarity & sign

Answer 1

bipolar w/ positive electrode at the left arm and the negative electrode at the right arm

Question 2

Lead II - polarity & sign

Answer 2

Bipolar w/ positive in the left leg and negative in the right arm

Question 3

Lead III - polarity & sign

Answer 3

Bipolar w/ positive in left leg and negative in left arm.

Question 4

Augemented leads (aVR, aVL, aVF) – polarity & plane

Answer 4

unipolar & share frontal plane of the heart with the bipolar leads

Question 5

aVR lead –type/polarity of lead & signs

Answer 5

unipolar augmented lead; positive in the right arm

Question 6

aVL lead –type/polarity of lead & signs

Answer 6

unipolar augmented lead; positive in the left arm

Question 7

aVF lead –type/polarity of lead & signs

Answer 7

unipolar augmented lead; is positive in the left leg

Question 8

Chest (precordial) leads – locations & polarity/plane

Answer 8

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

Question 9

Leads V1 & V2 – proximity to what heart structures & thus what defects they detect

Answer 9

“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

Question 10

Leads V5 & V6 – proximity to what heart structures & thus what defects they detect

Answer 10

“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

Question 11

Left ventricular depolarization

Answer 11

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.

Question 12

Normal QRS Axis– degrees & when positive (in what leads)

Answer 12

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

Question 13

Right Axis Deviation (RAD) – degrees & when positive (in what leads)

Answer 13

From +90 degrees to +180 degrees….. negative in lead I and positive in lead II

Question 14

Right Axis Deviation (RAD) – degrees & when positive (in what leads)

Answer 14

From -30 degrees to -90 degrees….. positive in lead I and negative in lead II

Question 15

Indeterminate axis – degrees & when positive (in what leads)

Answer 15

From -90 to +180 degrees …negative in both leads I & II

Question 16

Bundle branch blocks/Ectopic ventricular beat - QRS effects

Answer 16

Conduction of the QRS is outside the specialized conduction system and the QRS is wide

Question 17

Right bundle block & QRS

Answer 17

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]

Question 18

Left bundle block & QRS

Answer 18

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)

Question 19

Left bundle block in the fascicles (Hemiblock)

Answer 19

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]

Question 20

Left ventricular hypertrophy – 12 lead effects

Answer 20

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

Question 21

Right ventricular hypertrophy – 12 lead ECG effects

Answer 21

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

Question 22

Sizable Q wave development in 12 lead ECG

Answer 22

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.

Question 23

Acute pericarditis on ECG

Answer 23

Diffuse ST elevation (in almost all leads; in aVR appears as ST depression) <== once pericarditis occurs, it is in every part of the pericardium

Question 24

P - Tall (>2.5 mm in inferior lead)

Answer 24

RA enlargement

Question 25

P – wide & notched, w/late negativity in V1

Answer 25

LA enlargement

Question 26

QRS – wide (>/= 0.12 s)

Answer 26

Bundle branch block

Question 27

Large late R’ in V1 + late S in V6

Answer 27

RBBB

Question 28

Wide QS in V1 + Wide R in V6

Answer 28

LBBB

Question 29

Right axis shift

Answer 29

RV hypertrophy, posterior hemiblock

Question 30

Left axis shift

Answer 30

LV hypertrophy, anterior hemiblock

Question 31

High voltage

Answer 31

Ventricular hypertrophy

Question 32

R>S in V1

Answer 32

RV hypertrophy

Question 33

Large R w/ ST-T changes in V5/V6, S in V1/V2

Answer 33

LV hypertrophy

Question 34

Q waves

Answer 34

Infarct if in 2 related leads, 25% of R wave, or 0.04 s wide

Question 35

ST elevation

Answer 35

Injury if localized….. Pericarditis if diffuse

Question 36

ST depression

Answer 36

Ischemia or subendocardial infarct

Question 37

T inversion

Answer 37

Ischemia or secondary hypertrophy or bundle block

Question 38

Long QT

Answer 38

Electrolyte imbalance, Drug effect