LAB #3 - 12 Lead ECG Lab – KINE 4315 - Resting and Exercise Electrocardiography
The Electrodes and Leads
The six limb leads…three standard and three augmented
View heart in frontal plane (up, down, left, right)
Standard leads and angle of orientation Augmented leads and angle of orientation:
I: RA (-), LA (+); 0°
aVL: LA (+), all others negative; -30°
II: RA (-), LL (+); 60° most looked at lead
aVR: RA (+), all others negative; -150°
III: LA (-), LL (+); 120°
aVF: LL and RL (+), all others negative; 90°
LEAD PLACEMENT:
Right Arm (RA) Right deltoid fossa, midclavicular
Left Arm (LA) Left deltoid fossa, midclavicular
Right Leg (RL) Right anterior axillary, midclavicular line
Left Leg (LL) Left anterior axillary, midclavicular line
The six precordial leads (chest leads) view the heart in a horizontal plane (anterior/posterior).
Each chest electrode is + and the rest of the body is neutral or a “ground”
V1 and V2 lie directly over the right ventricle
V3 and V4 are over the interventricular septum
V5 and V6 are over the left ventricle
LEAD PLACEMENT:
Right Arm (RA) Right deltoid fossa, midclavicular
Left Arm (LA) Left deltoid fossa, midclavicular
Right Leg (RL) Right anterior axillary, midclavicular line, to the right of the umbilicus
Left Leg (LL) Left anterior axillary, midclavicular line, to the left of the umbilicus
V1 4th interspace, just to the right of the sternum
V2 4th interspace, just to the left of the sternum
V3 Midway between V2 and V4
V4 5th interspace left midclavicular line
V5 Left anterior axillary line on the same level as V4
V6 Left midaxillary line on the same level as V4 and V6
Skin Preparation for ECG – This is an essential step for recording high quality ECGs during
exercise. Failure to prepare the skin properly and consistently for an exercise test will result in an
ECG signal that cannot be continuously monitored or accurately interpreted because of artifact.
1. Have the patient disrobe to the waist and lie down face up on the prep table. (Women should
wear a sports bra for this step).
2. Shaving may be required for men over the sites for the electrode placement. Place the shaver in
the biohazard container when you are finished.
3. Identify the general areas to be used for electrode placement (consider marking each electrode
location with an ‘X’ using a felt-tip pen).
4. Rub the skin with an abrasive pad such as sandpaper to remove the outer layer of the dead skin.
The area should be red, but do not press too hard, as you will cause pain, remove the skin and/or
cause bleeding.
5. Use an alcohol swab to remove any excess oils before marking the spot.
6. Electrode Application - The electrode gel at center of electrode should be placed directly over
the area abraded. Smooth the adhesive part of the electrode with your finger to insure proper
adhesion to the skin. Do NOT press on the center of the electrode.
7. Attach the lead wires from the ECG recorder to the patient electrodes. Caution: be sure to
connect the lead wires to the proper electrodes.
ECG Quick Reference Guide
P wave: atrial depolarization
Normal P wave = 0.04 sec. P wave should be upright.
QRS Complex: ventricular depolarization
Normal QRS = 0.08-0.12 sec = amplitude depends on situation
T wave: ventricular repolarization
Normal T wave = 1/3 -1/2 amplitude of QRS complex. T wave should be upright and not inverted
PR interval: measures the time from the start of atrial depolarization to the start of
ventricular depolarization. Normal: 0.12-0.20 seconds or 3-5 boxes.
ST segment: records the time from the end of ventricular depolarization to the start of
ventricular repolarization. Normal: Should be at the baseline or isoelectric line.
QT interval: measures the time from the start of ventricular depolarization to the end of
ventricular repolarization
Rate, Rhythm, Axis
Rate can be determined by counting the number of small boxes between two R waves and dividing
them into 1500. Or a standard counting system can be used by labeling the number of large boxes
between two R waves. See below:
Rhythm refers to whether the strip is normal or has deviations. An abnormal ECG is called an
arrhythmia. It may or may not be clinically significant. Several basic things to look for when
evaluating rhythm.
1) Does every QRS have a P wave and is the P wave normal.
2) Is the QRS complex normal. Normal duration of the QRS is .08-.12 seconds or 2-3 boxes.
3) Is the rhythm regular or irregular. Meaning is the space between each R wave the same. Deviations
can be caused by slightly heavy breathing but most often due to a AV node conduction delay problem.
Axis
The term axis refers to the direction of the mean electrical vector, representing the average direction of
current flow. Normally the axis lies between 0-90 degrees showing the dominance of the left ventricle
over the right ventricle. An abnormal or deviated axis is usually applied to left or right ventricular
hypertrophy.
Three things happen to a wave on the ECG when a chamber hypertrophies
1) The chamber may take longer to depolarize. Therefore the ECG wave will increase in duration.
2) The chamber may generate more current and thus a larger voltage. Therefore the wave may
increase in amplitude.
3) The mean electrical vector (or the electrical axis) of the ECG may shift or deviate.
Basic determination of axis is based on the QRS complex. If the QRS is predominately positive when
the height of the complex above the isoelectric line is greater than that below. The converse is true
when a QRS is negative.
Lead I (0°)
+
+
Normal Axis
aVF (90°)
+
+
Left Axis Deviation
Axis
Left axis deviation
Right axis deviation
Extreme right axis deviation!!!
Normal
Assignment:
Prep one other student. Run a 12 lead supine ECG. Depending on the size of the lab you may work in
groups of 4. Everyone should to prep another member of the class and evaluate their ECG. THIS IS
NOT A GROUP PROJECT.
Evaluate the rate, rhythm and the axis. Determine lengths as normal or abnormal when evaluating the P
and T waves, QRS complexes, and PR intervals. Determine rate by either hand method. Show your
work.
Determine if there is any artifact? What do you think the cause of the artifact is?
Use the data sheet provided. Turn in your EKG strips with the data sheet. Save this information for the
practical.
LAB #3: EKG
Name:_______________________________
Subject’s name:________________________
Lying:
Rate:________________________________
Rhythm:_____________________________
Pwave:________________________
PR interval length:_______________
QRS width:_____________________
T wave:________________________
Axis:________________________________
Artifact:______________________________
Date:___________________________