F513 ECG I II print v7.pptx
From Iusmphysiology
- continued here from 20110113 Lecture 10 notes on 01/14/11 at 11AM.
[edit] ELECTROCARDIOGRAM (EKG or ECG) I, II
[edit] References
- Boron, W.F., and E.L. Boulpaep. (“B&B”) Medical Physiology. Philadelphia: Saunders, 2005. Relevant reading – B&B, Lederer, Chapter 20, Cardiac Electrophysiology and the Electrocardiogram
- Scheidt, S. Basic Electrocardiography: ECG. West Caldwell, NJ: CIBA-GEIGY, 1986 (yes, 1986)
- Jani, M. and J.C. Bailey (Krannert, IUSM). Introduction to Electrocardiography. Angel website, Medical Physiology, Resources, ECG Tutorial (https://daly.medicine.iu.edu/AngelUploads/Content/GROUP-050607-091123-SAM/_assoc/031C4908E6A5475AA794934E9D435E62/Intro_to_ECG.htm)
- Rhodes, R.A. and Bell, D.R. Medical Physiology: Principles for Clinical Medicine. Baltimore: Lippincott, 2009; Chapter 12.
[edit] Overall Learning Objective
- Understand the electrical signaling system in the heart, which is measured by the ECG and is essential for the coordinated function of pumping blood.
[edit] Specific Learning Objectives
- Know how two neighboring polarized and depolarized cardiac cells form an elementary dipole.
- Understand that the vectorial sum of all the elementary dipoles generates the deflections in an ECG.
- Know the various waves, complex, segments and intervals of an ECG.
- Know the different arrangements of the leads used to record a complete set of traces in an ECG.
- Understand how the electrical activities in different regions of the heart generate the different phases in an ECG.
- Understand the necessities of unipolar limb leads and unipolar chest leads in recording a complete ECG.
- Determine the mean electrical axis of the heart from any two coordinates in the Einthoven triangle.
- Draw a typical trace in a normal ECG with approximate scales in amplitude (mV) and duration (second).
- Know the physiological and pathophysiological information provided by an ECG.
- Understand how various dysfunctions in some regions of the heart can affect the rhythm and durations of intervals of an ECG.
[edit] Team-Based Learning (TBL) on ECG
- Assigned reading: 1) B&B, pp. 493-507; 2) notes, specific pages in Scheidt
[edit] Outline
- Introduction and overview
- Dipole representing the heart
- Phases and measurement of ECG
- Complete, 12 lead set of ECG recordings
- Arrhythmias & ischemia, infarct
- These notes contain all the information on the ECG that is needed for this course.
- Red flag indicates that you really must Know it!
[edit] Introduction and overview
- Matra: a mean electrical axis in healthy patient is at 60 degrees.
- Excitation from right atribum and SA down to ventricles will be at 60 degrees.
[edit] Dipole
- Dipole is the vectorial sum of all existing elementary dipoles.
- SA node depolarizes and AP travel down to AV node
- This vector will be defined by SA and AV which are neg and pos, respectively.
- This will generate the p wave on Lead 1 along the axis of zero degrees.
- The axis at 90 (avf = augmented; f for frontal) will also show the p wave.
- Excitation moves along septum
- Exciation makes a right hand turn (moves from left side of septum to right side).
- Lead 1 sees a negative deflection because it is going away from the main recording electrode.
- Lead AVF sees this as a positive deflection because exciation is going toward AVF.
- Q waves are not seen on aVF.
- Depolarizing the apex:
- Large positive R deflection.
- Larger beause of mor emass
- Epicardium still hasn't been depolarized.
- aVF more positive than lead 1
- Full depolarization of epicardium
- Gives largest R vector
- Depolarize posterior portion of left ventricle
- Gives S
- Negative because away from ?
RAT Questions 3: The greater duration of the ap of endocard cells gives you a positve T wave.
- Simulator via ecgsim.
- Uhm, awesome.
[edit] Phaseas and measurement of ECG
Who won the NP? Question 4: R wave in lead 2 of ECG Largest mean amplitude of any electrical axis because it is at about 60 degrees (the approximate mean electrical axis).
- Lead one:
- Right arm to left arm
- We assume the normal mean electrical axis
- stopped here on 01/14/11
- started here on 01/18/11
[edit] Lead 3
- Readiness question 5
- Assuming a normal electrical axis, we will have a smaller amplitude because the axis is at 120 degrees.
[edit] Phases of measurement
- The frontal plane is defined by the triangle.
- The augmented leads are the "a" leads.
- aVR is almost a flip of Lead II because it is almost the exact opposite degree.
- Lead II opposite would be -120
- aVR is -150
- aVL has a degree of -30
- should be zero because -30 is perpendicular to the 60 degrees
- so disregard the large signal seen in the aVL node
[edit] Back to slide 18
- Fan and glitter demonstration
[edit] Precordial leads
- precordials give you a closer view.
- they are largely used for determining where an MI occured.
- leads are directly on the chest.
- He won't ask which rib on which each goes or anything like that.
- V1 and V2 are considered septal leads.
- These leads are unipolar
- meaning you don't connect two leads on each, they are just the positive electrode.
- V5 and V5 are on either side of the normal electrical axis so they have similar amplitudes.
- Then the amplitude decreases from V5 to V1 because the vector becomes more and more perpendicular to the normal electrical axis.
[edit] Slide 23
[edit] Normal ECG
- Now leads are put all on the chest instead of the arms.
- The computer does lots of averaging and such for the readout.
- Question 4: what gives largest amplitude?
- Lead 2 because it has an axis along the normal electrical axis.
[edit] What can you get form 12 node ecg?
- Read them in a systematic way.
- Rhythm:
- 20-30 second strip form lead 2
- Gives relationship of P wave and QRS wave
- Look for normal QRS duration
- Look for BBB = bundle branch block in a wide QRS block
- RAte
- The R-R interval of 1 second means 60 beats per minute.
- Axis
- QRS geometric or inspection method
- Infarction
- ST segment isoelectric (normal), depression, or elevation; large Q waves.
- Damage can cause change in axis.
- Large Q waves will become huge and negative upon horrible infarction.
[edit] Calculating electrical axis
- We can estimate the electrical axis by calculating it from some numbers.
- Do the first two examnples on your own.
[edit] Example 3
- First we identify the amplitudes of the R wave from the leads.
- 9 in lead 2
- 8 in aVF
- You can also subtract the s wave from the R wave and get the same answer.
- Draw 2 perpendiculars
- Draw these at the appropriate unit taken from the amplitudes.
- The intersection of the two perpendiculars is the electrical axis.
[edit] The inspection method
- Use leads 1 and aVF extensively.
- Look at lead 1
- If positive, the mean electrical axis must be between -90 and 90.
- Look at lead aVF
- If positive, it must be from 180 to 0.
- If aVF and 1 are positive, it must be between 0 and 90
- And this is the normal range, so we know it is relatively normal just by these two being positive.
- If between 0 and -90 (upper left quadrant)
- Lead 1 is positive
- aVF is negative
- Some really strong athletes can lie in this quadrant.
- Lower right quadran
- Lead 1 is negative
- aVF is positive
- Use the geometric method to check yourself.
[edit] Find the most isoelectric lead
- In a normal electrical axis, aVL should be zero (flat lined).
[edit] MI
- Take home message is that
- ST segment should be isoelectric because that shows that you have normal depolarization and repolarization.
- ST depression is usually due to subendocardial microvascular artery constriction.
[edit] How does electrical axis change in MI?
- As cells die and release K, the AP will be a little stronger and will have a little faster repolarization.
- You can also get more T wave elevation.
- stopped here on 01/18/11 at 12PM.
- Ideal components (B&B, Fig. 20-6) – P, QRS, T, U (rare; papillary muscle repolarization) The entire, summed electrical activity of the heart is represented by the ECG and can be viewed in different planes by measuring the ECG from pairs of electrodes placed precisely on the patient. The frontal plane is viewed with standard and augmented limb leads and the transverse plane is viewed with precordial leads. The direction and magnitude of the electrical signal is a vector. Mean electrical axis is shown by the blue arrow.
I. Introduction and overview (continued)
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II. Dipole representing the heart
At any instant, the resultant dipole is a vectorial sum of all the existing elementary dipoles. Extracellular potentials; opposite intracell.
The “wavefront” of depolarization spreads from the SA node downward and leftward (green arrow). ECG does not show electrical activity of fine Bundle branches, Purkinje network.
-
-
+
+
-
+
Scheidt p 8A v1
Lead I (axis 0°)
Scheidt p 8A v1 Lead aVF (axis 90°)
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Scheidt p 8B v1
Scheidt p 8B v1
Lead I (axis 0°)
Lead aVF (axis 90°)
Depolarization through bundle branches and Purkinje network not detectable. Q wave from septal depolarization is small or absent.
-
+
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Scheidt p 9C v1
Scheidt p 9C v1
Lead I (axis 0°)
Lead aVF (axis 90°)
Massive depolarization spreads along Purkinje, conductile fibers, in ventricle from endocardium to epicardium. Largest muscle mass . largest vector.
-
-
-
-
-
+
+
+
+
+
S23283-020-f004 Massive depolarization spreads from endocardium to epicardium. Largest muscle mass . largest vector.
Scheidt p 9C v1 Scheidt p 9C v1 Lead I (axis 0°)
Lead aVF (axis 90°)
Lead aVF (axis 90°)
+
+
+
+
-
-
-
-
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Depolarization spreads upward, mainly rightward, completing depolarization of the ventricles.
Scheidt p 9D v1 Scheidt p 9D v1 Lead I (axis 0°)
Lead aVF (axis 90°)
S
+
+
-
-
S23283-020-f004 Scheidt p 10E v1 Scheidt p 10E v1 Lead I (axis 0°)
Lead aVF (axis 90°)
S
Completely depolarized ventricles are isopotential, giving flat ST segment normally.
-
-
-
-
S23283-020-f004 repolarizing.
Scheidt p 10E v1
Scheidt p 10E v1
Lead I (axis 0°)
Lead aVF (axis 90°)
S
S
... epicardium then endocardium. Resultant dipole points in the same direction as that during apical depolarization, but lower magnitude, thus T wave is positive normally.
+
+
-
-
II. Dipole representing the heart (continued)
Ventricular repolarization spreads from epicardium to endocardium. Epicardium normally repolarizes first (shorter action potential duration), before endocardium, thus the resultant dipole points in the same direction as that during apical depolarization.
ECGSIM – see dipoles, vector, views of heart
Current moving toward: positive electrode . upward deflection (Dipole (-).(+)) negative electrode . downward deflection
-
+
-
+
+
-
+
-
Normal
Abnormal
III. Phases and measurement of ECG
Standard limb leads define Einthoven’s triangle and enable different “views” of the electrical activity of the heart in the frontal plane. Start with Lead I with (-) electrode on right arm and (+) electrode on left arm, thus in the lead axis of 0°.
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frontal plane
-
+
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lead axis 0°
5.5
“Normal” mean electrical axis
small Q, S
-
+
Assume “normal” mean electrical axis (QRS axis; blue arrow) in the right to left and downward direction.
Lead I has (-) electrode on right arm and (+) electrode on left arm, thus in the lead axis of 0° (yellow arrow).
Resulting ECG for one cardiac cycle has small P wave, QRS amplitude of 5.5 mm in this example, flat ST segment, and positive T wave.
Q and S waves are small / absent.
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lead axis 60°
Analogy:
fan / wind blowing
Leads view electrical activity from unique positions
9
-
+
Again, assume “normal” mean electrical axis (QRS axis.
Lead II has (-) electrode on right arm and (+) electrode on left leg, thus in the lead axis of 60° (yellow arrow). Resulting ECG for one cardiac cycle has generally larger amplitude P, QRS, and T waves. The QRS amplitude (R wave) is 9 mm in this example, the ST segment remains flat, and positive T wave.
Use the analogy of the mean QRS axis being a fan / wind blowing in the direction of the blue arrow and you standing at the (+) electrode facing the wind. You will feel more wind (electrical activity) directly in your face in Lead II vs. standing in position of the (+) electrode in Lead I .
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lead axis 120°
5
Again, assume “normal” mean electrical axis (QRS axis).
Lead III has (-) electrode on left arm and (+) electrode on left leg, thus in the lead axis of 120° (yellow arrow).
Resulting ECG for one cardiac cycle has P wave, QRS amplitude (R wave) of 5 mm in this example, the ST segment remains flat, and positive T wave. The S wave is more negative than in Lead I.
Again, use the analogy of the mean QRS axis being a fan / wind blowing. You will feel about the same wind (electrical activity) in your face in Lead III vs. standing in position of the (+) electrode in Lead I and less than direct wind (electrical) in Lead II.
-
+
III. Phases and measurement of ECG (continued)
ECG is a vector with direction and magnitude. Augmented limb leads provide additional views in the frontal plane. Start with Lead aVR with (-) electrode defined with the electronics as centered in the chest and (+) electrode on right arm, thus in the lead axis of -150°.
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frontal plane
unipolar
-
+
S23283-020-f007a ~opposite Lead II
P
R
T
-7
6-16 Scheidt atlas 1 Scheidt, p. 89 “Normal”
lead axis -150°
-
+
Again, assume “normal” mean electrical axis (QRS axis). Lead aVR has (-) electrode centered in the chest/body and the (+) electrode on the right arm, thus in the lead axis of -150° (yellow arrow).
Resulting ECG for one cardiac cycle has nearly opposite polarity of Lead II ((-) P, R, and T waves, QRS amplitude (R wave) of -7 mm in this example, and the ST segment remains flat.
Use the analogy of the mean QRS axis being a fan / wind blowing. You will feel the wind (electrical activity) being pulled away from in your face in Lead aVR vs. standing in position of the (+) electrode in Lead II with direct wind (electrical) in your face. See Scheidt example of “normal”.
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P,Q, T
R
6-16 Scheidt atlas 1 Scheidt, p. 89 “Normal”
lead axis -30°
-
+
Again, assume “normal” mean electrical axis (QRS axis).
Lead aVL has (-) electrode centered in the chest/body and the (+) electrode on the left arm, thus in the lead axis of -30° (yellow arrow).
Resulting ECG for one cardiac cycle has P, Q, and T waves. The QRS amplitude (R wave) in this example is greater than predicted from the other Leads and our “normal” mean QRS. The ST segment remains flat.
Use the analogy of the mean QRS axis being a fan / wind blowing. If you are standing in Lead aVL in position of the (+) electrode perpendicular to the wind (electrical), then you should feel very little wind in your face. See Scheidt example of “normal”.
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lead axis 90°
-
+
Again, assume “normal” mean electrical axis (QRS axis).
Lead aVR has (-) electrode centered in the chest/body and the (+) electrode on the left leg, thus in the lead axis of 90° (yellow arrow).
Resulting ECG has clear P, small or no Q, and large T wave. The QRS amplitude (R wave) in this example is 8 mm, similar to the S wave (detects basal depolarization of ventricles well). The ST segment remains flat.
Analogy of mean QRS as fan / wind blowing – Standing in Lead aVR in position of (+) electrode you should feel wind in your face. See Scheidt example of “normal”.
Inferior Leads = II, III, aVF
8
6-16 Scheidt atlas 1
Scheidt, p. 89
“Normal”
III. Phases and measurement of ECG (continued)
Precordial leads are those placed directly on the chest in precise locations with landmarks provided by the sternum, intercostal spaces, midclavicular line, and axilla. Unipolar leads use (-) electrode defined electronically as centered in the heart and the (+) electrodes are on the chest, thus providing views in the transverse plane. Precordial leads provide a closer view and are often more sensitive. As typical with the frontal leads, the mean electrical axis is influenced by the mass of the heart.
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unipolar
(largest mass)
14
14
precordial – closer view, more sensitive
R
Tissue mass . recorded voltage amplitude
-
+
+
6-16 Scheidt atlas 1 Scheidt, p. 89, “Normal”
III. Phases and measurement of ECG (continued)
The similar amplitude QRS (R wave) of 14 mm in V5 and V6 of the ECG above indicate a mean QRS axis lying between V5 and V6 (blue arrow). The R wave gets progressively smaller through V4, V3, and V2. The R wave is negative in V1 and accompanied by a negative T wave, which are simply due to the lead axis being >90° from the mean QRS axis. This is similar to the Lead II vs. aVR examples previously. The “normal” example from Scheidt below shows the polarity of the QRS and T waves in V1. Precordial leads provide excellent information on location of myocardial electrical abnormalities because of their position on the chest. Specifically: Septal = V1, V2; anterior = V3, V4; lateral = V5, V6
P
R
T
IV. Complete, 12 lead set of ECG recordings
B&B Fig. 20-10 – Oriented in more conventional display format (e.g. Lead I upper left, Lead V4 upper right) that is shown in almost all subsequent slides; labeling not always provided.
“Normal”
B&B Fig20-10 v3
5.5
9
5
-8
8
IV. Complete, 12 lead set of ECG recordings (continued)
So what do I do with these ECGs? An enormous amount of information is provided for clinical diagnoses! Reading ECG The amount of information can be overwhelming (especially if ECG recordings are not high quality), so take a systematic approach in this condensed B&B Table 20-5 (and Dubin, 2000). 1. Rhythm (e.g. 20-30 s ECG record from lead 2) a. Determine relationship of P waves and QRS complexes. b. Identify pacemaker sinus = P waves regular interval, P before each QRS and QRS after each P c. PR intervals for AV blocks d. QRS duration narrow (normal) vs. wide for BBB 2. Rate Determine from waves, e.g. R-R interval 3. Axis QRS geometric or inspection method 4. Infarction ST segment isoelectric (normal), depression, or elevation; large Q waves
IV. Complete, 12 lead set of ECG recordings
Reading ECG (continued) 3. Axis Estimate mean QRS axis (and axes of other waves of interest) using the geometric method. – 3 examples
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Example 1
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Reading ECG (continued) 3. Axis – Estimate mean QRS axis using geometric method 1) Measure magnitude of QRS in leads I and II. 2) Mark on circle of axes +5.5 units on lead I +9 units on lead II. 3) Draw 2 perpendiculars. 4) Connect center of circle with intersection of 2 perpendiculars. 5) Estimate axis of arrow . ~50°
Example 2
5.5
9
~50°
B&B Fig20-10 v3
5.5
9
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Reading ECG (continued) 3. Axis – Estimate mean QRS axis using geometric method 1) Measure magnitude of QRS in leads II and aVF. 2) Mark on circle of axes +9 units on lead II +8 units on lead aVF. 3) Draw 2 perpendiculars. 4) Connect center of circle with intersection of 2 perpendiculars. 5) Estimate axis of arrow . ~50-55°
Example 3
B&B Fig20-10 v3
B&B Fig20-10 v3
9
8
9
8
50-55°
Reading ECG (continued) 3. Axis – Estimate mean QRS axis using inspection method 1) Locate axis quadrant with Leads I and aVF (next slide) Normal (~0 to 90°) Lead I – If QRS is positive then vector points to patient’s left side. Lead aVF – If QRS is positive then vector points downward to patient’s feet. “two thumbs-up” sign Left axis deviation (~0 to -90°; usually left ventricular hypertrophy) Lead I – QRS positive Lead aVF – QRS negative; vector points upward to patient’s head. Right axis deviation (~90 to 180°; usually right ventricular hypertrophy) Lead I – QRS negative; vector points to patient’s right side. Lead aVF – QRS positive 2) After locating axis quadrant locate limb lead where QRS is most isoelectric. The mean QRS will be perpendicular to the isoelectric lead. Two leads are perpendicular, but the correct lead will be located in the previously defined axis quandrant. See 2 slides ahead.
Reading ECG (continued) – locate axis quadrant
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Right axis deviation
I
aVF
Left axis deviation
I
aVF
Normal
I
aVF
Reading ECG (continued) – locate most isolectric lead
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for P wave,
~R wave
V. Arrhythmias and ischemia, infarct
A. Myocardial ischemia and injury leading to infarction (MI) – Regional decrease in blood flow (ischemia) caused by coronary artery occlusion; viewed by changes in different leads of the ECG. (B&B, Fig. 20-12A,B next slide) 1. Acute MI – ST segment elevation MI (STEMI); due to predominance of depolarized epicardial myocytes due to epicardial conduit artery occlusion See the next slide for the single cell basis for ST segment elevation of the ECG, which is similar to the “Translating single cell action potentials to the ECG” in the Cardiac Action Potential lecture. The decreased overshoot and duration of the action potential in the damaged myocyte results in difference between the potentials, therrby yielding ST segment elevation. epi = on top, ST elevation 2. Acute ischemia – ST segment depression; due to subendocardial microvascular artery constriction (or lack of dilation) subendo = below, ST depression See reading for TBL.
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Vm
~-80
~+20
~-50
1
2
3
4
1
2
3
4
“injury current”
1
2
3
4
5
1
2
4
5
endocard.
epicard.
5
5
endocard.
epicard.
3
REVIEW: CARDIAC ACTION POTENTIAL, ECG I & II
ELECTROCARDIOGRAM (EKG or ECG) TBL
Michael Sturek, Ph.D., Professor and Chair
Department of Cellular & Integrative Physiology, MS 385, 274-7772, Email msturek@iupui.edu
References Boron, W.F., and E.L. Boulpaep. (“B&B”) Medical Physiology. Philadelphia: Saunders, 2005
Lederer, Chapter 20, Cardiac Electrophysiology and the Electrocardiogram; focus on pp. 493-507
Scheidt, S. Basic Electrocardiography: ECG. West Caldwell, NJ: CIBA-GEIGY, 1986 (yes, 1986); select figures, pages here
Supplemental material to ECG I, II on slides 6-12.
Overall Learning Objective Apply basic principles of cellular cardiac electrophysiology and ECG to identify clinically significant ECG cases.
Specific Learning Objectives: KNOW CLINICALLY SIGNIFICANT ECGs 1. Normal
a. Identify wave components (P, Q, R, S, T), segments, sequence. b. Determine the mean electrical axis of the heart from any two coordinates in the Einthoven triangle.
ELECTROCARDIOGRAM (EKG or ECG) TBL Specific Learning Objectives: KNOW CLINICALLY SIGNIFICANT ECGs (continued) 2. Left axis deviation 3. Right axis deviation 4. Sinus bradycardia 5. Sinus tachycardia 6. Sinus arrhythmia 7. A-V block
a. 1st degree b. 2nd degree c. 3rd degree
8. Wolf-Parkinson-White (WPW) syndrome 9. left bundle branch block 10. right bundle branch block 11. ventricular tachycardia 12. ventricular fibrillation 13. long QT syndrome 14. myocardial ischemia (endocardial) 15. myocardial infarction
a. acute through chronic b. anterior, LV lateral c. anterior
16. Atrial flutter 17. Atrial fibrillation
