2. EMS Rounds
12-Lead EKG Basics, etc.
Part I: 12-lead EKG basics
Part II: Correlation with anatomy and infarction
Part III: Interesting cases with associated EKGs
Peter Graves, MD
August, 2012
3. Goals
• NOT a comprehensive 12-lead review…
• Part I: Basic 12-lead interpretation
techniques
• Part II:
– Review coronary artery anatomy
– Correlate with 12-lead EKG findings
– Review infarct patterns on 12-lead EKG
• BREAK
• Part III:
– See interesting EKGs that you need to
recognize
– A few interesting cases with EKG findings
6. What use is a 12-lead EKG
anyway?
• A 10 second snapshot of the heart
– Electrical activity and direction
– Heart rate and regularity
– Physical orientation in the body
– Disease states
• Cardiac
– Acute (e.g. arrhythmia, MI)
– Chronic (e.g. LVH)
• Non-cardiac
– Acute (e.g. brain hemorrhage)
– Chronic (e.g. COPD)
• Each lead gives a snapshot from a
different point of view
7. Using a systematic approach is
key
• Rate
• Rhythm
• Axis
• Intervals
• Chamber hypertrophy
• Ischemia/infarct patterns
8. Rate
• 10 seconds of EKG
– Each large box is 10 seconds/50 = 0.2 sec
– Each small box is 0.2 seconds/5 = 0.04 sec
0.04 sec
0.2 sec
1 sec 10 sec
9. Rate
• Easy way
– # of QRS complexes and multiply by 6 = heart rate
• Harder way: “300, 150, 100, 75, 60, 50, …”
– each large box = 0.2 sec = 1/300 min
0.04 sec
0.2 sec
1 sec 10 sec
10. Rhythm (too many to cover
here…)
• Is it regular or not?
• Irregular
– Irregularly irregular
• No p waves = Atrial fibrillation
• “Sawtooth” p waves = Atrial flutter (may
also be regular if conduction is non-
variable)
• 3 different p waves = MAT
– Regularly irregular (grouped beating)
• 2nd degree heart blocks
• Regular
– Everything else…
11. Axis
• The EKG axis gives us information
about the direction of the electrical
current flowing through the heart
– May also relate to the physical orientation in
the chest
• The limb leads (I, II, III) provide
information about the heart in the
frontal plane
• The Augmented Voltage leads
(avR, avL, avF) also reflect information
about the heart in the frontal plane, but
are computed averages of the other 3
limb leads
14. Correlation of Anatomy and
EKG – Precordial leads
• The 6 precordial leads give information
about the heart in the axial (horizontal)
plane
• We don’t generally talk about axis in
the axial plane
• From V1-V6, the precordial leads
provide information about the heart
from right to left anatomically
– V1-V2 = Right side of heart (RV)
– V3-V4 = Anterior wall (septum, LV)
– V5-V6 = Lateral wall (LV)
• Depending on individual anatomy there
is a great deal of overlap
17. Intervals
• Remember – each small box is 0.04 sec
• PR interval = start of p to start of QRS
– 0.12 - 0.2 sec, longer = 1st degree AV block
• QRS interval = start of QRS to end of
QRS
– Max 0.1 sec, longer = lots of things
(IVCD/BBB, drug fx, accessory pathway,
etc.)
• QT interval = start of QRS to end of T
– Max varies by gender, generally upper limit
of normal is 0.42 sec. Abnormal males >0.45
sec., females >0.47 sec
– If longer, risk of sudden death by “R on T
phenomenon” causing VF/VT
18.
19.
20. Part II: EKG Correlation with
Anatomy and Infarction
21. Case
• You are called to the scene of a minor
MVA. The occupants appear
uninjured, and the passenger tells you
that her husband, the driver, suddenly
clutched his chest before veering off of
the road into a mailbox. He is a 54 y/o
male with h/o HTN, high
cholesterol, and diabetes and appears
semi-conscious, diaphoretic, and pale.
His BP is 86/54, HR 75, RR 24, and pOx
88%
22. Case
• You extricate him from the vehicle with
c-spine precautions and get him in the
rig. He appears uninjured, but
complains of severe chest pain and is
obviously dyspneic. You start an
IV, O2, and obtain a 12-lead EKG while
en route to the hospital.
24. Case Question
• You decide to
– A) Drive like hell
– B) Give ASA and maybe some MSO4
– C) Give him 2 sublingual nitros
– D) Get him to the nearest
hospital, preferably somewhere with a cath
lab
– E) A, B, and D
25. Case Question
• You decide to
– A) Drive like hell
– B) Give ASA and maybe some MSO4
– C) Give him 2 sublingual nitros
– D) Get him to the nearest
hospital, preferably somewhere with a cath
lab
– E) A, B, and D
29. Coronary Artery Anatomy
• R and L coronary arteries arise
independently from individual ostia at
the level of the aortic valve cusps
• L mainstem divides into LAD and LCx
arteries
30. Coronary Artery Anatomy
• LAD: Anterior LV, anterior 2/3 of
septum, apex
• LCx: Lateral LV and posterior LV walls
• Rarely, PDA arises from LCx and
supplies posterior septum (“L
dominant”)
• Sinus node (40%)
• AV node (10%)
31. Coronary Artery Anatomy
• RCA
– RV
– PDA (posterior 1/3 of septum), “R dominant”
– Inferior wall of LV and RV
– Part of posterior LV via PDA
– Sinus node (60%)
– AV node (90%)
32.
33.
34. Acute Coronary Syndromes
and EKG Findings
• Depending on the cardiac anatomy
(which vessel), and where the infarct
is, we see different 12-lead EKG
findings
– Inferior (usually RCA): II, II, avF
– Interventricular Septum (LAD, perforating
branches): V1, V2
– Anterolateral (proximal LAD): V2-V6
– Anterior (usually mid-LAD): V3, V4
– Lateral (usually further down LAD or
branches): V5, V6, often also I, avL
– High lateral wall (L Cx): 1, avL
38. Acute Inferior Wall MI
(II, III, avF)
• Usually due to RCA occlusion
• EKG changes in II, III, avF (ST elevation)
• May be associated with posterior/RV
infarcts due to shared blood supply
• Often associated with arrhythmias due
to nodal involvement
40. Acute Posterior Wall MI (V1-V2)
• EKG changes in V1, V2 (tall R waves;
“early transition”, ST
depressions, upright T waves)
• Due to usual etiology of RCA
occlusion, often associated with
inferior MI
• Increased morbidity/mortality
compared with isolated IMI
• Consider R sided (look for ST elevation
in rV4) or POSTERIOR leads (V7,8,9,…)
– continue placing leads around to
posterior CW under axilla until you
reach the spine
