Systematic
Approach to 12
Lead EKG
Interpretation
Maureen Knechtel MPAS, PA-C
Wellmont CVA Heart Institute
Objectives
1.
2.
3.
4.
Establish a concise approach to EKG
interpretation
Gain confidence in the ability to
correctly and thoroughly interpret an
EKG
Use EKG findings to guide clinical
management
Know when to refer based on EKG
findings
Disclosure Statement of
Financial Interest
I, Maureen Knechtel, do not have a
financial interest/arrangement or
affiliation with one or more organizations
that could be perceived as a real or
apparent conflict of interest in the
context of the subject of this
presentation.
Follow a System
Rate
Rhythm
Axis
Infarction
Block
Rate
Rate
Large box = 200
ms
Find R wave on
thick line
Count to next
thick line to
estimate HR
Rate
If less than 40 bpm, divide rhythm strip in 2
and multiply number of QRS complexes by 10
Rhythm: Regular or Irregular
Axis
Lead I: QRS positive = axis points to
Lead aVF: positive: axis in lower left quadrant: axis
normal
Lead aVF: negative: axis in upper left quadrant: left
axis deviation
Axis quadrants: defined by intersection of leads
I and aVF
Normal: 0 to +90
Right Axis Deviation: +90 to +180
Left Axis Deviation: -1 to -90
Axis
Lead I: QRS negative = axis points to
Lead aVF: positive: axis in the lower right quadrant:
right axis deviation
Lead aVF: negative: axis indeterminate
Axis
Axis
Causes of Axis Deviation
Left Axis
Inferior MI
LVH
Obesity
LBBB
LAFB
Ischemia and Infarction
Right Axis
Lateral MI
RVH
Tall, thin frame
COPD
RBBB
LPFB
Ischemia and Infarction
EKG Leads
Myocardial
Distribution
Reciprocal
Changes
(Injury Pattern)
RCA
II, III, aVF
Inferior Wall
Lateral Leads
LAD
V1-V4
Anterior Wall
Inferior Leads
Left Circumflex
I, aVL, V5-V6 Lateral Wall
Ischemia
Diminished blood flow causes a delay in the
depolarization and repolarization pattern
T wave inversion, ST depression
Injury
ST segment elevation
Define in millimeters from baseline
2 mm = clinically significant
Infarct
Q waves = no depolarization, scar tissue
Inferior Leads
Reciprocal Changes
Posterior Ischemia
Coronary Blood Supply and
the Conduction System
Block
Coronary Artery Conduction System
Right Coronary
SA Node, AV Node
Left Anterior
Descending
Right Bundle
Branch
Left Bundle Branch
Left Circumflex
SA Node (less
common)
AV Node (less
common)
Inferior wall MI can be
complicated by sinus
arrest or complete heart
block
Anterior infarction can be
complicated by new
bundle branch block or
complete heart block
LAD supplies
interventricular septum
1st Degree AVB
2nd Degree AVB (Type 1 and 2)
3rd Degree
RBBB
LBBB
First Degree AVB
2nd Degree Type I
2nd Degree Type II
3rd Degree AV Block
RBBB
RBBB
QRS > 120 ms
Findings due to slow, rightward
spread of ventricular depolarization
from LV
Can occur in structurally normal heart or any
condition that affects R heart
R wave: LV activation
V6: RS
R wave: LV activation
S wave: RV activation
LBBB
QRS > 120 ms
Findings due to slow, leftward spread of
ventricular depolarization from RV
More likely associated with structural
heart disease
V1: QS
Q: RV activation
S: LV activation
V6: Tall R wave, +/R wave: RV activation
LBBB
Ischemia and LBBB
LBBB affects early and late phases
of ventricular depolarization
LBBB is reflected by Q waves, ST
segment and T wave changes
These are the same findings that
can be present in ischemia and
infarction
ST Elevation Discordant with QRS
Ischemia and BBB
ST elevation > 1mm in leads with a
positive QRS complex (QRS
concordant with ST segment)
ST elevation > 5 mm in leads with a
negative QRS complex (QRS
discordant with ST segment)
ST depression > 1 mm in V1 to V3
Obtain serial EKGs if you are
suspicious of an acute event
Obtain serial EKGs if you are
suspicious of an acute event
Left Hemiblock
Diagnose by:
Axis deviation
QRS patterns
QRS duration
may be normal
LAFB
Left Anterior Fascicle
Anterolateral LV
Delay in electrical activation shifts
general axis towards left
Left axis deviation -30 or more
negative
QRS negative inferior: rS
QRS positive lateral: qR
LAFB
LPFB
LPFB
Left Posterior Fascicle
Inferoseptal portion of LV
Delay in electrical activation shifts axis
towards right
Right axis deviation +120 or more
positive
QRS negative lateral: rS
QRS positive inferior: qR
Prolonged QTc
QT > ½ the R-R Interval
Examine drug list:
Antipsychotics
Antidepressants: SSRIs
Antibiotics: fluoroquinolones and
macrolides
Antifungals
Antiarrhythmics
www.torsades.org
QTc prolongation
Summary
Always follow a pattern in order to
correctly and efficiently interpret a 12
lead EKG
Examine the EKG leads as groups
Use EKG clues to guide clinical
management and refer when high risk
findings are present