1. ““2 Minute 12 Leads”2 Minute 12 Leads”
John Bray, MA, NRP, CCEMTP
Indian River State College
2. Why all the fuss?
• Because a 12-Lead shows a 3 dimensional
view of the heart
• Because a simple 3-Lead shows a flat,
1 dimensional view (cartoon character)
• Infarcts can be hiding from a quick glance
• 12-Lead is a true DIAGNOSTIC ECG
32. “R” Wave Progression
• Used to confirm proper lead placement
– V1 is small and progressively increasing from right to left until
the QRS is fully upright in V5 and V6 The QRS size goes from
negative to positive
44. Lead-Specific ST Elevation
• Inferior MI
• Leads II, III, aVF, visualize the inferior
[ nearest the diaphragm ] surface of the heart
• Leads are adjacent and view adjoining
tissues located in inferior region of the left
54. Lead-Specific ST Elevation
• Lateral MI
• Leads V3, V4, V5, and V6 will illustrate an
• Leads II, III, aVF, v5, and v6 will illustrate an
• Leads v5, and v6 only will illustrate a low
• Leads v5, v6, Lead I and aVL will illustrate a
High Lateral MI
60. ST Segment Depression
• ST Segment
Depression occurs due
• Hypoxia results in
• Characterized by a dip
below isoelectric line
of 1 to 2 millimeters or
1 to 2 small boxes
61. ST Segment Depression
• Other Causes:
– Medication: Digitalis
– No irreversible injury
to the myocardium
– TIME IS MUSCLE !
65. ST Segment Elevation
• ST Segment
Elevation is a rise
above the isoelectric
line of 1 to 2
millimeters or one to
two small boxes
• Most common cause
is myocardial injury
66. ST Segment Elevation
• Other Causes:
– Coronary Artery
[ all leads ]
– Ventricular aneurysm
– Early repolarization
67. ST Segment Elevation
• Will occur within the first
1 to 2 hours after onset of
• TIME IS MUSCLE
68. Pathologic Q Waves
• Pathologic Q Waves
indicate irreversible tissue
damage or death of
• Defined as a width greater
then or equal to one small
box [ 1mm ] or depth
greater then one third of
the R wave in the same
71. Reciprocal Changes
• ST ↑ in II, III, AVF
• ST ↑ in V2, V3, V4
• ST ↓ in V1-V4
• Reciprocal ST ↓ in I, AVL
• Reciprocal ST ↓ in II, III,
• Reciprocal to Posterior
– 15 Lead ECG
72. 15 Lead ECG
• Posterior MI
• Leads V1, V2, V3, and V4 will illustrate a posterior MI with ST
• Utilize Leads.
– Take V4, V5, and V6 and place them posteriorly in V7, V8, and
V9. This is sometimes referred to as a 15-lead EKG.
• V4 is placed in the 5th
intercostal space, posterior axillary position
• V5 is placed in the 5th
intercostal space, midscapular line position =
• V6 is placed in the 5th
intercostal space, 2cm to the left of the spine
74. Bundle Branch Block
• Can be pre-existing
• Can be caused by ACS
• If AMI caused
– 60-70% associated with
– 40-60% mortality w/o
75. Bundle Branch Block
• May Produce
– ST elevation
– ST depression
– Tall T waves
– Inverted T waves
– Wide Q waves
• May Hide
– ST elevation
– ST depression
– Tall T waves
– Inverted T waves
– Wide Q waves
Can Mimic or Hide Evidence Needed to
76. BBB Problem
• BBB Problem
– ACS harder to identify on ECG when
– New or presumably new BBB is an
indication for thrombolytic therapy
80. Normal Ventricular Conduction
• Normal Conduction
– fibers of LBB begin conduction
– impulse travels across
interventricular septum from left
• towards + electrode creates small r
– travels across ventricles causing
depolarization of both
• LV contributes most to complex
– impulse travels away from +
electrode creates primarily
84. BBB Recognition
• Use V1
• Find Terminal force
• Identify direction of terminal
– Downward LBBB
– Upward RBBB
• Picture a Steering Wheel
– Right turn turn signal goes up
– Left turn turn signal goes down
88. Axis and Hemiblocks
• AXIS is defined as the general direction
that the electrical impulse travels down the
• Normal impulses should travel downward
from R to L. This is shown in Lead I and
VF as an upright QRS.
• Normal Range -30 to +90 DegreesNormal Range -30 to +90 Degrees
91. Left Axis Deviation
• Axis Range: 0 to –30 Degrees
– Physiologic Left Axis Deviation (LAD)
• Axis Range: -30 to –90 Degrees
– Pathological LAD
– Anterior Hemiblock
– Left BBB
– May develop into Complete Heart Block!
92. Right Axis Deviation
• Ranges 90-180 Degrees
• Downward QRS in Lead I
– Common in children and tall, thin adults
– HX of COPD?
• Over 180 Degrees? Think V-TACH!!
95. Assess Initial 12-Lead
Classify patients with acute ischemic chest pain into
1 of the 3 groups above.
• ST elevation or new or
presumably new LBBB:
strongly suspicious for
• ST-elevation AMI
• ST depression or dynamic
• High-risk unstable angina/
• Nondiagnostic ECG:
absence of changes
in ST segment or
96. OK, Great. So I see an infarct.
• You should be continuing your assessment
but allow yourself no more than 2 minutes
to analyze the 12 Lead ECG.
• After 2-3 mins, you may have to give repeat
doses or other meds.
• Look for “trending”: How is the patient
responding to treatment?
97. Medical ControlMedical Control
• Think about what you will say before
getting on the phone.
• Understand that you are not a doctor, but
that does not make you an idiot!
• Presentations should be given in plain
English, not “EMS-speech”
98. Talking on the phone
• Present the patient in this order:
– Identify yourself to the doctor
– Give your pt’s age, sex and chief complaint
– Describe how you found the patient
– If unconscious, what was told to you by others
– Patient’s medical Hx and Allergy status
– Initial V/S
– Pertinent Physical Exam findings
99. Still on the phone…
• Tell your interventions
– Start with BLS and then ALS
– Patient response to treatment
• Briefly discuss your 12 Lead findings
– NOT an interpretation, but where you see
• Give an ETA
• Request further orders
100. IV Therapy and the MI Patient
• IV placement is important, but not vital!
• Start with your PO and SL meds
• Obtain a 12 Lead ECG
• Start the IV
– Avoid more than 1 attempt
– Think Thrombolytic Therapy!
101. Arrival at the ED
• Present patient as “Mr. or Mrs.” not “the
chest pain” or “the heart attack”
• Have your 12 Lead out and ready for the
doctor to review
• Answer questions that are posed to you!
– Meds given
– IV attempts (be truthful!)
114. Practice Case 2
• 68 year old female
– Sudden onset of anxiety and restlessness,
– States she “can’t catch her breath”
– Denies chest pain or other discomfort
• History of IDDM and hypertension
• RR 22, P 110, BP 190/90, Sa02 88% on
NC at 4 lpm
The right coronary artery begins at the aorta, and after supplying some atrial tissue, supplies the right ventricle. It then travels around to the posterior side of the heart, and at the crux, turns sharply in a caudal direction becoming the posterior descending artery. The PDA supplies the inferior wall of the left ventricle.
At the crux, a small artery branches off supplying the AV node. This is why AV nodal blocks are common with RCA occlusions.
Note the septal, anterior and lateral walls of the left ventricle.
The LCA starts at the sinus of valsalva at the aortic base. It travels as the left main artery for several millimeters then bifurcates into the left anterior descending artery and the circumflex artery.
This slide illustrates the 3 4 format of the 12-lead ECG.
Each box represents 1 lead, and the viewpoint of that lead is indicated.
The positive electrode for leads II, III, and aVF is attached to the left leg. The ECG monitor uses this one electrode as the positive electrode for all three leads.
From that perspective, these leads “look up” and “see” the inferior wall of the left ventricle.
NOTE: A heart model is helpful at this juncture, particularly to remind students that the heart does not sit “straight up” in the chest.
NOTE: This is a posterior view of the heart.
The portion of the heart that rests on the diaphragm is called the “inferior wall”.
Leads II, III, and aVF, “look” up and see the inferior wall.
When ST segment elevation is noted in II, III and aVF, suspect an inferior infarction.
These leads are positioned one on each side of the sternum. From that placement they “look through” the right ventricle and “see” the septal wall.
NOTE: The septum is left ventricular tissue.
V1 and V2 “look through” the right ventricle to “see” the septum.
The positive electrode for these two leads is placed on the anterior wall of the left chest. This correlates to their designation as anterior leads.
Of course, ST segment elevation in V3 and V4 implies an anterior wall infarction.
V5 and V6 are positioned on the lateral wall of the left chest which is why these two leads also “see” the lateral wall of the left ventricle.
Leads I and aVL share the positive electrode on the left arm.
From the perspective of the left arm, these leads “see” the lateral wall of the left ventricle.
Portions of the lateral wall are shown here from both the anterior and posterior perspective.
Leads I, aVL, V5 and V6 “see” the lateral wall. When ST segment elevation is seen in these leads, consider a lateral wall infarction.
Each box represents one lead, and the viewpoint of that lead is indicated.
NOTE: Refer participants to their pocket card where this information is summarized as well.
This information will aid in understanding the ECG subsets in the next section.
Define ischemia, injury and infarct.
Note that the definitions are correlated with specific ECG criteria.
Note that “injury” is also ischemia and does not imply any permanent damage or death to tissue. The term injury simply means ischemia identified by ST segment elevation.
We have been looking for infarct based upon the presence of ST elevation.
As mentioned, not every lead is elevated when AMI is present, only the leads looking at the infarct site.
In fact, those leads which look at the infarct site from the opposite perspective tend to produce the opposite changes.
When a lead “sees” the AMI directly, the segment becomes elevated in that lead.
However, when a lead “sees” the infarct from the opposite perspective, the ST segment may be depressed in that lead.
Bundle Branch Block (BBB) has a number of potential causes.
BBB can be the result of a fibrosis or calcification of the ventricular conduction system. (Lev’s disease and Lenegre’s disease are examples.)
People can live well for many years with the BBB caused by these conditions. Unless there is evidence of worsening conduction (syncope, dropped beats, etc) these conditions are non-emergent.
BBB can also be caused by an ACS.
When BBB is caused by an ACS, it identifies a very high risk patient!
Literally, BBB can both mask and mimic all of the ECG changes associated with ACS!
The presence of a new BBB, or presumably new BBB, is an indication for thrombolytic therapy*.
At the physician’s discretion, thrombolytics may be administered to patients whose BBB obscures the diagnosis of AMI on the ECG.
*The 1996 ACC/AHA Guidelines for the Management of Patients with Acute Myocardial Infarction” lists BBB as a Class I indication for thrombolysis. (Definition of Class 1: Conditions for which there is evidence and/or general agreement that a given procedure or treatment is beneficial, useful, and effective)
A commonly held misconception is that any notch or distortion of the QRS indicates a BBB.
While BBB can cause a notch, a notch does not ensure the presence of a BBB.
Therefore, other criteria for BBB recognition are needed.
BBB widens the QRS (120ms or more).
This widening is due to the fact that the ventricles are forced to contract sequentially, thus requiring more time.
Other conditions widen the QRS; a common one would be ventricular rhythms either paced or spontaneous.
A differentiating factor between BBB and ventricular rhythms would be the presence of an underlying supraventricular rhythm.
Therefore, when a QRS of 120ms or more is produced by a supraventricular rhythm, think BBB.
This rule applies in all leads.
underlying rhythm sinus
QRS width 160ms
underlying rhythm sinus
QRS width 120ms
The “classic” pattern for RBBB in V1 is an RSR.
The “classic” pattern of LBBB in V1 is a QS complex.
There are many variations to these classic patterns, complicating the process of distinguishing RBBB from LBBB.
In addition, each form of BBB produces a different set of changes in V6.
Fortunately, a simplified approach does exist.
After BBB has been determined to exist, look at lead V1.
To identify the terminal force, first locate the J-point.
From the J-point, back up about 40 ms into the QRS.
Now determine if the terminal force (tail end) is pointing up or down.
Always remember, the following rules for differentiating RBBB from LBBB apply only to V1.
We will learn to identify the terminal force of the QRS in V1, and determine if it is positive or negative.
Simply stated, we will look at the tail end of the QRS complex and decide if it points up or down.
Have the participants review these four examples of V1 in the course guide and determine if the BBB is LBBB or RBBB.
The phrase “percutaneous coronary interventions” is now being used to refer to either “PTC-Angioplasty” or PTCA with stent placement. (See the next 2 slides.)
This slide just provides a different view of the PCI procedures.
Review the 12-lead ECG.
Go lead by lead, and pick one good complex in each lead.
Find the J point and ST segment.
Compare the ST to the TP segment, looking for 1 mm (1 small box) of elevation (ignore ST depression for now).
Place a check mark next to any lead with 1 mm of ST-segment elevation.
Localize the area of infarction.