Download ECG Lab

ECG Lab
Electrocardiography- electrical changes that
accompany the cardiac cycle
Today you will use Bio Pac to record an
electrocardiogram (ECG) and:
▫ Analyze the results by measuring and calculating
the amplitudes of the deflections, time intervals,
and segments.
▫ Determine heart rate.
Cardiac Cell Types
• Contractile myocardial cells (99% of cardiac
muscle) are responsible for the mechanical
pumping of the heart.
• Autorhythmic cells (1% of cardiac muscle
tissue) of the conduction system are responsible
for electrical stimulation of the myocardial cells.
These cells spontaneously depolarize.
Intrinsic Conduction System
SA node = 70 BPM
AV node = 50 BPM
AV Bundle (Bundle
of His) = 35 BPM
Bundle branches =
35 BPM
Purkinje Fibers =
30 BPM
Action Potential in Autorhythmic Cells
Action Potential of
Contractile Myocardial Cells
Electrocardiogram
Deflections of the ECG:
• P wave: atrial depolarization from SA node toward the ventricles
• QRS complex: ventricular depolarization. Atrial repolarization
also occurs during this phase but is masked by the large QRS
• T wave: ventricular repolarization
Time Intervals and Segments of the ECG:
• P-R interval: interval between the activation of the SA node and
AV node
• P-R segment: interval between atrial depolarization and
ventricular depolarization
• S-T segment: interval between end of S wave and start of T wave
• R-R interval: interval of time between successive cycles
Electrode Placement
• A lead is an arrangement of electrodes used in recording
the electrical changes in the heart during a cardiac cycle.
• Bipolar Limb Leads: records changes in electrical
potential between two electrodes placed on two limbs.
▫ Lead I: Right arm (-) and Left arm (+)
▫ Lead II: Right arm (-) and Left leg (+)
▫ Lead III: Left arm (-) and Left leg (+)
Electrode Placement
• Unipolar Limb Leads: records changes in electrical
potential in reference to a single exploratory (+)
electrode placed on the limbs.
▫ aVR: Right arm(+) and Left arm/Left leg(-)
▫ aVL: Left arm(+) and Right arm/Left leg(-)
▫ aVF: Left leg(+) and Left arm/Right arm(-)
Electrode Placement
• Unipolar Chest Leads: : records changes in electrical
potential in reference to a single exploratory (+)
electrode placed on an intercostal space.
▫ V1 - V6 which are placed on various intercostal spaces
Abnormalities of the ECG
• Enlarged Q wave = myocardial infarction
• Enlarged P wave = enlargement of atria
• Lengthened P-R interval = scarring or inflammation
of the heart muscle (as in rheumatic fever)
• Enlarged R = enlarged ventricles
• Enlarged ST segment = acute myocardial infarctions
• Flattened T wave = heart muscle is “ischemic”
Experimental Procedure
• Each group needs a 3-lead cable, 3 electrode
pads, and alcohol swab.
• Clean the anterior surface of right wrist and
the medial aspect of both ankles.
• Start the software by clicking on the “ECG” file
on the desktop.
• Record a resting ECG for approximately 15
seconds.
• Measure the duration of the indicated waves,
segments and intervals and record the time
values in the first column (“Resting”) on the
data sheet.
Measurements
• Sample selection for measuring P wave duration
(Delta T) and amplitude (P-P)
Measurements
• Sample selection for measuring P-R Interval
duration (Delta T).
Calculation for Heart Rate
• Given paper speed: 2.5cm
1 sec
2.5cm = 1.5cm
1 sec
x sec
Measured R-R: 1.5cm
2.5x = 1.5
2.5x = 1.5
2.5
2.5
x= 0.6 sec
1 beat x 60 sec = 60beats
0.6 sec
1 min
0.6 min
= 100beats/ min
Experimental Procedure
Extending Your Knowledge
• Have your subject perform another activity,
record an ECG, measure and record your data in
the column labeled “Activity ”.
• Run a Lead I and Lead III ECG
ECG practice measurements