Title: EKG Basics
1EKG Basics
2What is an EKG?
- The electrocardiogram (EKG) is a representation
of the electrical events of the cardiac cycle. - Each event has a distinctive waveform, the study
of which can lead to greater insight into a
patients cardiac pathophysiology.
3Rules of ECG
- Wave of depolarization traveling towards
apositive electrode causes an upward deflection
on the ECG - Wave of depolarization traveling away from a
positive electrode causes a downward deflection
on the ECG
4Resting Myocardial Cell
Na
K
Ca
K
Na
Ca
K
K
K
K
K
K
Na
Ca
Na
Ca
Na
Ca
Na
Ca
Na
Ca
Ca
5Characteristics of ECG Recordings
- Duration
- Amplitude
- Configuration
6Time and voltage
Amplitude
Duration
7(No Transcript)
8Configuration
Negative
Positive
9Outline
- Review of the conduction system
- EKG waveforms and intervals
- EKG leads
- Determining heart rate
- Determining QRS axis
10The Normal Conduction System
11What types of pathology can we identify and study
from EKGs?
- Arrhythmias
- Myocardial ischemia and infarction
- Pericarditis
- Chamber hypertrophy
- Electrolyte disturbances (i.e. hyperkalemia,
hypokalemia) - Drug toxicity (i.e. digoxin and drugs which
prolong the QT interval)
12Waveforms and Intervals
13Atrial Depolarization
- P wave small, round deflection on the ECG
- Right atrial component
- Left atrial component
- Normal amplitude ? 0.25 mV (2.5 mm)
- Normal duration 0.04 0.12 msec
- AV node conduction pause
14(No Transcript)
15Ventricular Depolarization
- Includes
- Bundle of His
- Bundle Branches
- Right
- Left
- Septal
- Anterior
- Posterior
- Terminal Purkinjie fibers
16Ventricular Depolarization
- Ventricular Waves
- Q wave first downward deflection after P wave
- Rwave first upward deflection after Q wave
- R wave any second upward deflection
- S wave first downward deflection after the R
wave - QRS duration 0.06 to 0.12 msec
- QRS configurations
17(No Transcript)
18Ventricular Repolarization
- T wave
- small to moderate size positive deflection wave
after the QRS complex, - Height is 1/3 to 2/3 that of the corresponding R
wave - U wave
- Septal repolariztion (not always seen on ECG)
19Segments and Intervals
- Segment strait line between waves
- Interval wave plus a segment
- PR interval 0.12 0.20 msec
- QRS Interval (Duration)
- ST segment end of ventricular depolarization to
start of vent. repolariztion - QT interval ventricular cycle, 40 of each
cardiac cycle
20EKG Leads
- Leads are electrodes which measure the difference
in electrical potential between either
- 1. Two different points on the body (bipolar
leads) - 2. One point on the body and a virtual reference
point with zero electrical potential, located in
the center of the heart (unipolar leads)
21EKG Leads
- The standard EKG has 12 leads
3 Standard Limb Leads 3 Augmented Limb Leads 6
Precordial Leads
The axis of a particular lead represents the
viewpoint from which it looks at the heart.
22Standard Limb Leads
23Standard Limb Leads
24Augmented Limb Leads
25All Limb Leads
26Precordial Leads
Adapted from www.numed.co.uk/electrodepl.html
27Precordial Leads
28Summary of Leads
29Arrangement of Leads on the EKG
30Anatomic Groups(Septum)
31Anatomic Groups(Anterior Wall)
32Anatomic Groups(Lateral Wall)
33Anatomic Groups(Inferior Wall)
34Anatomic Groups(Summary)
35Determining the Heart Rate
- 2 Beat Rule
- Rule of 300
- 10 Second Rule
- 6 (3 x 2) Second Rule
36(No Transcript)
37Calculation
- Distance between Ventricular beats 20 mm
- Time of one ventricular beat
- 20 X 0.04 0.80 sec
- Heart Rate
- 60 / 0.80 75 beats/min
38Rule of 300
- Take the number of big boxes between
neighboring QRS complexes, and divide this into
300. The result will be approximately equal to
the rate - Although fast, this method only works for regular
rhythms.
39What is the heart rate?
www.uptodate.com
(300 / 6) 50 bpm
40What is the heart rate?
www.uptodate.com
(300 / 4) 75 bpm
41What is the heart rate?
(300 / 1.5) 200 bpm
42The Rule of 300
- It may be easiest to memorize the following table
4310 Second Rule
- As most EKGs record 10 seconds of rhythm per
page, one can simply count the number of beats
present on the EKG and multiply by 6 to get the
number of beats per 60 seconds. - This method works well for irregular rhythms.
44What is the heart rate?
The Alan E. Lindsay ECG Learning Center
http//medstat.med.utah.edu/kw/ecg/
33 x 6 198 bpm
45Six Second Rule
- Count the number of beats per 3
- Repeat again
- Add the two
- Multiply by 10
46The QRS Axis
- The QRS axis represents the net overall direction
of the hearts electrical activity. - Abnormalities of axis can hint at
- Ventricular enlargement
- Conduction blocks (i.e. hemiblocks)
47The QRS Axis
By near-consensus, the normal QRS axis is defined
as ranging from -30 to 90. -30 to -90 is
referred to as a left axis deviation (LAD) 90
to 180 is referred to as a right axis deviation
(RAD)
48Determining the Axis
- The Quadrant Approach
- The Equiphasic Approach
49Determining the Axis
Predominantly Positive
Predominantly Negative
Equiphasic
50The Quadrant Approach
- 1. Examine the QRS complex in leads I and aVF to
determine if they are predominantly positive or
predominantly negative. The combination should
place the axis into one of the 4 quadrants below.
51The Quadrant Approach
- 2. In the event that LAD is present, examine lead
II to determine if this deviation is pathologic.
If the QRS in II is predominantly positive, the
LAD is non-pathologic (in other words, the axis
is normal). If it is predominantly negative, it
is pathologic.
52Quadrant Approach Example 1
The Alan E. Lindsay ECG Learning Center
http//medstat.med.utah.edu/kw/ecg/
Negative in I, positive in aVF ? RAD
53Quadrant Approach Example 2
The Alan E. Lindsay ECG Learning Center
http//medstat.med.utah.edu/kw/ecg/
Positive in I, negative in aVF ?
Predominantly positive in II ? Normal Axis
(non-pathologic LAD)
54The Equiphasic Approach
- 1. Determine which lead contains the most
equiphasic QRS complex. The fact that the QRS
complex in this lead is equally positive and
negative indicates that the net electrical vector
(i.e. overall QRS axis) is perpendicular to the
axis of this particular lead. - 2. Examine the QRS complex in whichever lead lies
90 away from the lead identified in step 1. If
the QRS complex in this second lead is
predominantly positive, than the axis of this
lead is approximately the same as the net QRS
axis. If the QRS complex is predominantly
negative, than the net QRS axis lies 180 from
the axis of this lead.
55Equiphasic Approach Example 1
The Alan E. Lindsay ECG Learning Center
http//medstat.med.utah.edu/kw/ecg/
Equiphasic in aVF ? Predominantly positive in I ?
QRS axis 0
56Equiphasic Approach Example 2
The Alan E. Lindsay ECG Learning Center
http//medstat.med.utah.edu/kw/ecg/
Equiphasic in II ? Predominantly negative in aVL
? QRS axis 150