1. 12-Lead EKG
MEPN Level IV

2. OBJECTIVES
Discuss the changes in T wave and ST segment morphology with an MI
List the criteria for identification of right or left bundle branch blocks.
List the anatomically congruent leads associated with an inferior, lateral and anterior wall MI
Describe morphology of Q wave presence

3. Myocyte bundles are what make cardiac cells different from other cells
Myofibrils are individual units that slide over one another causing contraction
They pull the sarcomere together causing contraction
Ca+ is the primary stimulant for the effect of sarcomeres
Troponin is inside the sarcomere, this is the only place troponin comes from which is why it is cardiac specific

4. ECG Leads 6 limb leads (frontal plane) 3 bipolar leads
3 unipolar leads
6 precordial leads (horizontal plane)
V1 – V6
Mathematically Constructed
6 limb leads
6 precordial leads
Modified Chest Leads are roughly analogous to the precordial leads in a traditional 12-lead EKG. To obtain them with your three- or four-lead monitor, set the monitor to display Lead III, and move the left leg electrode to mimic the placement of the precordial leads: MCL1 in the fourth ICS, right sternal border; MCL2 in the fourth ICS, left sternal border; MCL4 in the fifth ICS, mid-clavicular line; MCL6 in the fifth ICS, midaxillary line; MCL3 midway between MCL2 and MCL4; and MCL5 midway between MCL4 and MCL6.

5. Einthoven’s Triangle Limb Leads BIPOLAR Lead I RA (-) to LA (+)
Lead II
RA (-) to LL (+)
Lead III
LA (-) to LL (+)
Lead III extends from the left arm to the left foot
Lead I extends from the right to the left arm
Lead II extends from the right arm to the left foot
Form an equilateral triangle known as Einthoven’s triangle
Bipolar (requires 2 limbs) and a ground lead (right leg)
Depolarization travels from NEGATIVE to POSITIVE
The EKG machine allows each limb electrode to be positive or negative
Pushing the leads to the center of the triangle creates three intersecting lines of reference

6. AUGMENTED (UNIPOLAR) LEADS
Augmented leads combine 2 leads together (the null point) from the center point of the triangle with one positive pole.
aVR (Augmented Voltage Right Arm positive) is a combination of bipolar Leads I and II
aVL (Augmented Voltage Left Arm Positive) is a combination of I and III
aVF (Augmented Voltage Left Foot positive) is a combination of Bipolar Leads II and III
Augmented Leads are unipolar leads
Single positive lead
aVR – least useful looks primarily at right atrium
Right arm (+)
aVL
Left arm (+)
aVF
Left leg (+)
The thought is the negative pole is in the center of the heart and positive pole is on any of the limb leads

7. WHAT ARE THE LEADS LOOKING AT? LIMB and AUGMENTED LEADS
II, III & AVF
WHAT ARE THE LEADS
LOOKING AT?
I & AVL
Where the positive electrode is positioned, determines what part of the heart is seen!
LIMB and AUGMENTED
LEADS

8. Precordial Lead Placement
V1 – 4th intercostal space right of sternum
V2 - 4th intercostal space left of sternum
V4 – 5th intercostal space midclavicular line
V3 – midway between V2 and V4
V6 – 5th intercostal space midaxillary line
V5 – same level as V4 at anterior axillary line between V4 and V6
R wave progression negative in V1 and V2
6 leads
Horizontal plane
V1 – V6
Each is a + lead
V3 isoelectric and/or biphasic
V5 and V6 are upright
Electrolyte and BBB defects cause changes in R wave progression

9. Same lead position as left side –
RIGHT SIDED EKG
V4R, the right-sided chest lead, can reveal ST segment changes that unmask a right ventricular myocardial infarction. RVI is present in percent of inferior wall myocardial infarctions. Many of these patients are highly dependent upon preload to maintain cardiac output, and administration of vasodilators like nitroglycerine may cause a precipitous drop in BP.
Right leads “look” directly at Right Ventricle and can show ST elevations in leads II. III. AVF, V4R , V5R and V6R
Be sure to label RIGHT SIDE EKG and the R’s after the lead numbers
The machine does not know left from right
The single most accurate tool used in measuring RVI.
90% sensitive and specific
Same lead position as left side –
looks directly at the
Right ventricle

10. Posterior View Posterior leads:
V7 – lateral to V6 at posterior axillary line
V8 – level of V7 at the mid-scapular line
V9 – level of V8 at the paravertebral line
(left posterior thorax midway from spine to V8)
Posterior View
Posterior Wall MI: Occlusion of the Right Coronary Artery (RCA) or the Posterior Descending Artery
No leads look at the posterior wall - unless a 15 lead EKG is done
Anterior Leads look at the infarct site from the opposite side (backwards)
ST depression in V1 & V2
Tall R waves in V1 and/or V2
Most often associated with Inferior MI
*Associated with dangerous conduction disturbances
V7-V9 electrodes extend in a horizontal line from V6
In V7-9 ST elevation of 0.5 mm and QRS amplitude is <10mm = posterior MI

12. PRECORDIAL LEADS
V1 & V2
V3 & V4
V5 & V6

13. Bottom line is continuous strip
calibration marker
LIMB LEADS
AUGUMENTED
LEADS
PRECORDIAL LEADS
Bottom line is continuous strip

14. R – Wave Progression
V3 is isoeletric or biphasic

15. R – Wave Progression
V3 is isoeletric or biphasic

16. Myocardial ischemia Myocardial injury
Various definitions are used. The term commonly refers to diffuse ST segment depression, usually with associated T wave inversion
Myocardial injury
Injury always points outward from the surface that is injured with ST segment elevation

17. Ischemia, Injury, Infarction Waveforms

18. ST segment should be electrically neutral
Myocardial ischemia
ST segment usually isoelectric or less than 1mm
T wave – Less than 6 mm high in limb leads, and 12 mm in precordial leads - upright in Leads I, II, V₃ to V₆, negative in aVR
Reflects ischemia or injury
Ischemia – ST depression and T wave opposite of normal
Injury – ST elevation with or without T wave changes
Various definitions are used. The term commonly refers to diffuse ST segment depression, usually with associated T wave inversion
Myocardial injury
Injury always points outward from the surface that is injured with ST segment elevation
ST segment should be electrically neutral

19. Visual aid in determining:
Ischemia or injury to myocardium
Normal should be at baseline
Depressed ST segment - >2 mm below baseline
ST segment depression is MOST specific for ischemia if the ST segment slopes down from the J point.
Horizontal or flat STs are also quite suspicious for ischemia.
Upsloping ST depression is only about 60% accurate for diagnosing ischemia.
ST segment depression
if transient - almost always due to acute myocardial ischemia
the ECG signs of ischemia may come and go fairly quickly — over a matter of minutes.

21. EKG 1

22. ST Segment Elevation
ST segment elevation is attributed to impending infarction
but can also be due to pericarditis or vasospastic (variant) angina.
The height of the ST segment is measured at a point 2 boxes after the end of the QRS complex
significant if it exceeds 1 mm in a limb lead or 2 mm in a precordial lead.
ST elevation is death of cells

23. EKG 2

24. T Waves T waves are normally positive in leads with a positive QRS
T waves are normally asymmetrical
T waves are normally not more than 5 mm high in limb leads or 10 mm high in precordial leads or 2/3 the height of the R wave
T waves are normally not more than 5 mm high in limb leads or 10 mm high in precordial leads or 2/3 the height of the R wave
Tall, symmetrical T waves
Hyperkalemia
Infarction or ischemia
Digitalis
Pericarditis
Broad, symmetrical, inverted T waves are classic for intracranial bleed or stroke
CVA
Increased intracranial pressure

25. T wave Ischemia Ischemia Hyperkalemia Ischemia
In some patients with partial thickness ischaemia the T waves show a biphasic pattern. This occurs particularly in the anterior chest leads and is an acute phenomenon. Biphasic T wave changes usually evolve and are often followed by symmetrical T wave inversion. These changes occur in patients with unstable or crescendo angina and strongly suggest myocardial ischaemia.
Hyperkalemia
Ischemia
Ischemia

26. Elevated T waves – symmetrical pointed > 2/3 of QRS = hyperkalemia (6.5-7.0)
Tall, symmetrical T waves
Hyperkalemia
Infarction or ischemia
Hyperkalemia
EKG 3

27. ST-T Wave Combination of infarction and often hyperkalemia
Called Tombstone ‘T’ because of the shape.
Usually a sign of impending cardiac death.
ST segment and T wave are combined

28. EKG 4

29. Pathology of an MI

30. Localization of ECG Pathology
Inferior: Abnormalities that appear in leads II, III, and aVF (called the inferior leads) indicate pathology on the inferior or diaphragmatic surface of the heart.
Lateral: Leads I, aVF, and V5-V6 are called lateral leads. Abnormality in these leads indicates pathology on the lateral, upper surface of the heart.
Anterior: Anterior pathology is seen in leads V1-V4, and often in lead I.
ST elevation in contiguous (congruent) leads most often represents acute infarction
There must be changes in more than 1 congruent lead for it to mean anything
ST depression in contiguous leads may represent acute ischemia
In acute infarction, ST elevation in contiguous leads coupled with reciprocal ST depression in non-infarcting leads is added evidence of an AMI

31. Overview of Infarcts Anterior Inferior Lateral Posterior Septal
Location of Infarct
Arterial Supply
Indicative Changes
Reciprocal Changes
Anterior
LAD
V1-V4
II, III, aVF
Inferior
RCA
I, aVL
Lateral
Circumflex
I, aVL, V5, V6 V1
Posterior
Posterior Descending (RCA)
None
V1, V2
Septal
Septal Perforating (LAD)
Posterior Descending (RCA
Loss of R wave in V1, V2, or V3
Not all MI’s have reciprocal changes, their presence may indicate a bigger infarct, more ischemic area. Sometimes reciprocal changes are more evident (stick out more) than ST elevation and help zero in on infarcted region.
Reciprocal changes
In addition to the primary changes that occur in the ECG leads facing the infarcted myocardium, "reciprocal changes" may occur in leads opposite to the site of infarction. The changes are just the inverse of the primary changes. Thus, "ST segment elevation and T wave inversion" will appear as "ST segment depression and tall pointed T waves", respectively. The inferior limb leads on the one hand and the precordial leads, together with leads I and aVL, on the other hand are "mutually opposite". Thus, primary changes in one of the above groups will usually be accompanied by reciprocal changes in the other group. It will be safe to assume that if on the ECG there is ST segment elevation in one group (as above) and ST segment depression in the other group, the elevation is the primary change and the ST segment depression is the secondary change.

32. T Wave Elevation T
ST Segment Elevation ST ST Q T
Pathological
Q Wave Q Q T
T Wave Inversion

33. EKG Changes from Infarction
First Detectable Change in EKG
Tall T-waves
increase in height
more symmetric
may occur in the first few minutes
hyperacute
Hyper-acute Phase

34. Acute Phase ST Segment Elevation Primary indication of injury
Occurs in first hour to hours
ST Segment Elevation in Leads
1mm or greater in limb leads
2 mm or greater in chest leads
Hallmark indication of AMI

35. Localization of myocardial injury
The different leads monitor different anatomic regions of the heart. Thus, the different leads are used to detect myocardial injury in their corresponding regions of the heart. In an ECG tracing, myocardial injury can be localized to the following anatomic regions of the heart:
Lateral wall: Left wall of the left ventricle. Leads I, aVL, V5, and V6 are used
Inferior wall: The part of the left ventricle resting on the diaphragm. Leads II, III, and aVF are used
Anterior wall: Ventral (front) wall of the left ventricle. Leads V2, V3, V4, and sometimes V1 and/or V5 are used
Posterior wall: The dorsal (back) part of the left ventricle. Leads V1, V2, V3, and V4 are used to monitor the reciprocal changes
Septal region: The intraventricular septum. Leads V1 and V2 are used
Right ventricle: Lead V4R is used. This lead is not part of the standard ECG leads and is placed in a similar manner as lead V4 but on the right side of the chest. Lead V4R is only placed if the patient is suspected of having a myocardial infarction involving the right ventricle.

36. View of Inferior Heart Wall
Leads II, III, aVF
Looks at inferior heart wall
Inferior Wall MI: Occlusion of Right Coronary Artery (RCA)
At least 1mm ST segment elevation in leads II, III, aVF
Reciprocal ST depression in leads I & aVL or precordial leads
Conduction defects:
Sinus bradycardia
Sinus arrest
1st degree block
Accelerated Idioventricular rhythm
The ECG changes associated with anterolateral myocardial infarction, including pathologic Q waves and repolarization abnormalities, are best seen in leads V2, V3, V4, V5. The anterior leads, leads I, aVL, V5, and/or V6, or the lateral leads may also be used to detect this type of infarction.
Inferior myocardial infarction
The blood supply of the posterior and inferior regions of the heart is provided by the Ramus Descendens Posterior (RDP), also known as the Posterior Descending Artery (PDA).
· • In 85% of cases, the RDP is a branch of the right coronary artery (RCA). When this is the case, the coronary circulation is described as a right-dominant system.
· • In 7% of cases, the RDP branches from the Ramus Circumflexus. When this is the case, the coronary circulation is described as a left-dominant system.
· • In the remaining 8% of cases, blood supply of the posterior and inferior regions of the heart is provided by both the right coronary artery and the RCx. When this is the case, the coronary circulation is described as a co-dominant system.
In most cases, an inferior myocardial infarction results from occlusion of the right coronary artery. In some cases, inferior myocardial infarction results from occlusion of the Ramus Circumflexus. The ECG changes associated with inferior myocardial infarction, including pathologic Q waves and repolarization abnormalities, are best seen in the inferior leads: II, III, and aVF.
Complications:
Brady arrhythmias – protective mechanism, 90% of blood supply for SA & AV nodes from the RCA
Hypotension – treated with fluids, consider right side involvement
Leads II, III and aVF
Predominately Right Coronary Artery
EKG changes
1st degree AV block
2nd or 3rd degree AV Blocks
N/V and/or bradycardia are common

37. Inferior
With Inferior Wall MI suspect Right Ventricular Wall Infarct
Signs of possible Right Ventricular Wall Infarct:
Hypotension
JVD
Clear lung sounds
EKG 5

38. Inferior
EKG 6

39. *Sometimes referred to as High Lateral or High Apical view*
View of Lateral Heart Wall
Leads I and aVL
Looks at lateral heart wall
Looks from the left arm toward heart
Lateral Wall MI: results from occlusion of the Left Circumflex Artery
At least 1 mm ST segment elevation in leads I, aVL, V5 & V6 and /or 2 mm ST segment elevation in V5 & V6
Reciprocal ST depression in V1
Sometimes an extension of an Anterior or Inferior MI
Conduction defects are rare
Leads I, aVL, V5 & V6
Left Circumflex
Usually in combo with other areas of infarct
EKG changes
Relative to other areas of involvement
*Sometimes referred to as High Lateral or High Apical view*

40. View of Lateral Heart Wall
Leads V5 & V6
Looks at lateral heart wall
Looks from the left lateral chest toward heart
*Sometimes referred to as Low Lateral or Low Apical view*

41. View of Entire Lateral Heart Wall
Leads I, aVL, V5, V6
- Looks at the lateral wall of the heart from two different perspectives
Lateral Wall

42. Lateral
EKG 7

43. Lateral
EKG 8

44. View of Anterior Heart Wall
Leads V3, V4
Looks at anterior heart wall
Looks from the left anterior chest
Anterior Wall infarct: Occlusion of the Left Anterior Descending Artery (LAD)
2mm ST segment elevation in two or more of leads V1-V4
Reciprocal changes in leads II, III, aVF
Lethal due to large myocardium involvement
Possible conduction defects:
Bundle Branch Block
2nd Degree Block Type II
CHB
Leads V1 – V4
Left Anterior Descending Artery
V1 and V2 indicative of septal involvement
EKG Changes
Left or Right Bundle Branch Blocks
2nd or 3rd Degree Heart block

45. Anterior
Anterior Wall infarct: Occlusion of the Left Anterior Descending Artery (LAD)
2mm ST segment elevation in two or more of leads V1-V4
Reciprocal changes in leads II, III, aVF
Lethal due to large myocardium involvement
Possible conduction defects:
Bundle Branch Block
2nd Degree Block Type II
CHB
EKG 9

46. Anterior
EKG 10

47. View of Septal Heart Wall
Leads V1, V2
Looks at septal heart wall
Looks along sternal borders
Septal Wall MI: caused by septal perforation involving the LAD or the Posterior Descending
Most often in the setting of an Anterior MI
Loss of R-wave in leads V1, V2 or V3
May have ST segment elevation in V1 & V2
No reciprocal changes

48. Putting it ALL together
ANTERIOR
LATERAL S E P T A L
LATERAL
LATERAL
INFERIOR

49. Q Waves Definition Septal depolarization
Normally present in I, aVL, V6

50. Two types of Q waves Non-pathologic Pathologic Narrow, shallow Q waves
Not visible in all leads
Pathologic
> 0.04 in duration; at least 1/4 to 1/3 height of R wave
Represent an infarcted area of myocardium
Q waves are significant if they are grater than 1 box in width or are larger than ¼ of the R wave, indicates MI or obstructive septal hypertrophy IHSS
causes: septal, infarction, IHSS
Septal, I, L, V5-6 occasionally inferior leads
Significant Q> ¼ R or Q > 1 box wide and not in lead III
HIS increased septal Qs, evidence of LVH

51. Part of inferior wall mi/pathological Q’s
PATHOLOGICAL Q WAVES

52. If the QRS duration is > .12
Bundle Branch Blocks
If the QRS duration is > .12
there is usually an abnormality of conduction of the ventricular impulse
The most common causes for prolonged QRS complexes is a bundle branch block
However, other conditions may also prolong the QRS duration.
The type of bundle branch block can usually be determined from the examination of three key leads: I, V1 and V6.

53. RBB Block
Interruption of impulse conduction through the right tract of the bundle
Lead V1 - rSR' & R' (seeing both ventricles depolarizing separately) are the result of the third wave of depolarization traveling back toward lead V1 to depolarize the right ventricle i.e. impulse goes down the LBB then around to the RBB
R’ is bigger because right side lead is closer to the impulse
If the complex is greater than 0.10 seconds, it represents an incomplete right bundle branch block. If the complex is greater than 0.12 seconds, it represents a complete right bundle branch block.
Most common ventricular conduction defect
Can be acute or chronic
Acute RBBB is associated with an acute anterior MI

54. EKG 11
RBBB

55. Always indicates a diseased heart More common in older adults
LBB Block
Always indicates a diseased heart
More common in older adults
Interruption in conduction of an impulse through the left branch of the bundle
Most commonly diagnosed using precordial leads
Bundle branch block can be diagnosed by pattern recognition of the QRS complexes in the V1 and V6 leads
these two leads look at the left ventricle
There is a wide QRS you don’t see the waves separately as in RBB you will see a notch
New LBBB can be diagnostic of myocardial infarction (MI).

56. EKG 12
LBBB