12 Lead ECG Ch.8-14

Question 1

An ECG can never be used to ______ only to _____.

Answer 1

An ECG can never be used to rule out an MI only to rule one in. This is because it’s sensitivity rating only catches about 46-50% of acute changes, so a pt could be having an MI and the ECG won’t show it.

Question 2

What are the 3 categories of triage criteria?

Answer 2

• ST segment elevation or new onset of a LBBB
• T wave inversion or ST segment depression
• Nondiagnostic ECG

Question 3

What are the 4 indicators for ST Segment elevation and does does it mean for the heart?

Answer 3

Look for:
- Injury (damaged but salvageable)
- ST segment elevation > 1mm (2mm for septal leads)
- Present in 2 or more related or anatomically
contiguous leads
- Measure at J point (plus 40ms) to baseline

ST segment elevation means acute transmural injury - across the 3 layers of the heart- and is a significant finding

(as opposed to depression which may be caused by damage to only 1 layer of the heart)

Question 4

3 causes of ST segment depression?

Answer 4

• Reciprocal changes to ST segment elevation
• Ischemia or subendocardial injury
• Certain meds, such as digitalis

Question 5

Which is a more significant finding, ST segment elevation or depression?

Answer 5

Elevation because it indicates there is more damage to the heart (3 layers as opposed to 1 in dep.)

often there will be elevation also when there is depression found, and when both are present, the depression is considered to be reciprocal to the elevation

Question 6

What does it mean if there is ST segment depression when there is NOT Elevation found?

Answer 6

If elevation is not present when there is Depression, it is a sign that either the patient is experiencing myocardial ischemia or injury to a subendocardial wall, which involves only 1 layer of the heart muscle.

It is not triaged for reperfusion strategy (like ST elevation) but should still be treated with anticoagulant therapy and by MONA (morphine, oxygen, nitro, aspirin)

Question 7

What is the importance of an inverted T wave?

Answer 7

It is the result of the beginning of myocardial ischemia and an early warning sign to an AMI as it may show up just before ST segment elevation

After nitro is given and the ischemic area is re-perfused (if it worked) the ST segment elevation or depression might disappear but the T wave will still remain inverted indicating at a block in flow still exists

Question 8

What are 3 key points about inverted T waves?

Answer 8

• a sign of Ischemia (transient reduction in blood flow)
• Symmetrical inverted T waves in two or more related
  leads needed
• Inverted T waves normal in Leads V1 and III

Question 9

What is a Pathological Q wave?

Answer 9

a Q wave is considered pathological if it is more that 40ms wide (0.04sec) or 1/3 of the R wave height.

It is the sign that infarction or death of tissues has occurred

When seen with ST segment elevation, it indicates
ongoing acute myocardial infarction

Question 10

What are the 3 indicators of infarct (necrosis or death) shown by the Q wave?

Answer 10

• Pathological Q waves
• > 40ms, or 0.04sec wide, or 1/3 of R wave height
• When seen with ST segment elevation, it indicates
  ongoing acute myocardial infarction

Question 11

What is the ISAL chart and what is it used for?

Answer 11

It stands for I See All Leads and is an organized way of how to look at which leads for sign of an MI (ST elevation, depression, inverted T waves, Patho Q waves)

Inferior = II, III, aVF

Septal = V1, V2

Anterior = V3, V4

Lateral = V5 (low), V6 (low), I (high), aVL (high)

Question 12

Watch YouTube vid on how to do a 15 lead or its on pg 109!!

Answer 12

Watch YouTube vid on how to do a 15 lead or its on pg 109!!

Question 13

Why would you want to take a 15 lead ECG reading?

Answer 13

When there is evidence of an acute inferior or posterior infarction (post would be if there was ST dep in V1-V4)

Question 14

What lead is used to see a Right Ventricular Infarction?

What will it show when RVI is present?

Answer 14

V4R; you will see ST elevation if present

place a lead where V4 is on the left but do it on the right side; hints the V4+R

Question 15

What triad is a sign of Right Ventricular Infarction?

Answer 15

• JVD
• Hypotension either before or after Nitro is given (a
  RVI pt can be normotensive b/c of compensatory
  factors in vasoconstriction)
• Clear Lung sounds (ruling out pulmonary possibilities
  for JVD)

Question 16

Why is nitro not always ok to give a pt with chest pain?

Answer 16

First you must rule out possible Right Ventricular Infarction (RVI) b/c nitro can cause a severe drop in blood pressure.

It undoes the bodies compensatory mechanism of vasoconstriction to fight the RVI, so you could very quickly undo that compensation and since the RV is responsible for major preload of LV it will cause a quick drop in cardiac output that could tank your pt

Question 17

Before giving any nitrate or vasoactive drug what should you do?

Answer 17

Check lung sounds!

You should give large amounts of isotonic fluids to an MI pt, so make sure to regularly assess lung sounds to make sure fluids is not leaking into the pulmonary space

Question 18

How often is a posterior infarct present when there in an inferior present?

How do you see a posterior infarct?

Answer 18

50% of the time there is a posterior infarct when there is an inferior present

A Posterior MI is seen on a 15 lead (not a basic 12 lead) and is seen as ST elevation in Lead V8 & V9; with reciprocal ST depression in V1-V4

Question 19

How does a LBBB hide evidence of an AMI?

Answer 19

B/c the bundle branch block is slowing the repolarization of the left ventricle the ST segment elevation is normal for a LBBB and is not indicative of an MI, so basically the LBBB’s ST elevation is hiding what could be an AMI’s ST elevation that is resting just below the LBBB’s

Remember that when an LBBB is present, depolarization is switched from the normal Cardiac Conduction Cells to the myocardial cells which is much slow to depolarize, well they are also slow to REpolarize which is why the ST segment is elevated in a LBBB b/c the slow repol hinders the st segment from getting back to the isoelectric line

Question 20

What are the 2 sets of criteria that indicate an AMI exists with a LBBB on an ECG?

Answer 20

• New Onset of LBBB with associated symptoms of an
  AMI
• Changes in the QRS configuration that could be:
  a) Q waves seen in at least two lateral leads (I, aVL,
  V5, V6)
  b) R wave regression from leads V1 to V4
  c) Notching of the S wave in at least two of Leads V3-
  V5

Question 21

With a normal healthy heart, the P wave in lead II should be?

Answer 21

rounded, less than 3mm tall, and less than 120ms wide (0.012sec), and upright in leads II, II, avF, and upright/negative/biphasic in lead V1

Question 22

What will happen to a P wave if there is Right Atrial Enlargement (RAE)?

Answer 22

It will be tall (>2.5mm) and pointed in the inferior leads II, III, aVF

Since the right side of the heart is pulmonary a common memory aid is “3-P”:

• Prominent
• Pointed
• Pulmonary

Question 23

What are the clinical implications of RAE (right atrial enlargement)?

Answer 23

• generally not an acute problem
• frequently seen with right ventricular hypertrophy
• can be seen with other criteria pointing to another
  more severe problem such as a PE

Question 24

What will happen to a P wave if there is Left Atrial Enlargement (LAE)?

Answer 24

2 things:
- Lead II will have a wide (>0.12sec or 3mm) and a
notched (m-shape) P wave
- Lead V1 will have a broad, negative P wave >1mm

Question 25

What causes Right Ventricular Hypertrophy (RVH)? | What criterion show it is present?

Answer 25

It can be caused by increased pressure or volume in the right ventricle Criteria: - RAE (right atrial enlargement) - narrow QRS - right axis deviation - R wave height in V1 is greater or equal to 7mm - Asymmetrical downsloping ST segment (strain) in inferior leads

Question 26

Clinical implications of a LAE?

Answer 26

- same as the causes - no treatment of the specific problem - can give you clues as to overall pt hemodynamics

Question 27

Clinical implications of RVH?

Answer 27

- Not an acute problem - Can be confused with a Post hemiblock - Remember the hemodynamics that caused it

Question 28

What causes Left Ventricular Hypertrophy (LVH)? | What criterion show it is present?

Answer 28

It can be caused by increased pressure or volume in the left ventricle Criteria: - LAE, along with any other WRS voltage criteria - Generally narrow QRS or lightly widened with strain - Usually normal axis, although can be physiologic left as it progresses - May be the cause of an axis that is -15degrees or more

Question 29

What is the "Rule of 35" and what is it used for? | What is the other "Voltage Criterion"?

Answer 29

It is used to determine the presence of LVE If the Pt is older than 35, and the value of the deepest S wave in V1&V2 added to the value of the tallest R wave in lead V5&V6 is greater than 35; then you have LVE Other voltage criterion: - R wave in aVL is >11mm - R wave in any inferior leads (II, III, aVF) is >20mm - R wave in V6 is 20mm - R wave in V5 is >25mm - S wave inn V1&V2 is >25mm

Question 30

Must all voltage criterion be met to assume LVE?

Answer 30

NO! If the QRS complex is very large, assume hypertrophy. Strain is the biggest hallmark of LVH and will usually by identified and reported by the ECG machine with a message like "voltage criteria for LVH met" or "repolarization abnormality" which means "strain"

Question 31

How do you see "strain" on an ECG?

Answer 31

Lateral or inferior leads will show asymmetrical ST depression and T wave inversion that almost looks biphasic

Question 32

What are the 4 major functions of potassium in the heart and what are the normal ranges?

Answer 32

Normal Ranges of Potassium: 3.5-5 mEq/L - Prevents action potential from being too short (QT interval) - Allow for organized fast heart rates - Protects from excitability - Slows the heart rate in vagal conditions

Question 33

What are the rhythms that might be caused by Hypokalemia? What changes might you see on an ECG? (x5)

Answer 33

Hypokalemia = less than 3.5mEq/L (commonly caused by fluid loss) Atrial Flutter, Heart Blocks, or Bradycardia - ST segment depression - T-waves flattened or joined with U waves - U waves getting larger than the T waves as the potassium level falls - QT interval appearing to lengthen as T combines with U - PR interval increases

Question 34

What are the rhythms that might be caused by Hyperkalemia? | What changes might you see on an ECG? Mild, moderate, severe ranges

Answer 34

Hyperkalemia = more than 5mEq/L (commonly caused by renal failure) Vfib, asystole, at 10-12 mEq/L ``` MILD CASE = Less than 6.5mEq/L - Tall, tented, peaked T waves with narrow base - Best seen in II, III, V2, & V4 - Normal P waves MODERATE CASE = Less than 8mEq/L - QRS broadens - Broad S wave in V leads - Left axis deviation - ST segment is gone, contiguous w/ peaked T waves - P wave starts to flatten and diminish SEVERE CASE = More than 8mEq/L - P waves gone - Sine waves ```

Question 35

How do you see Hypo VS Hyper Calcemia on an ECG?

Answer 35

Hypocalcemia = Prolonged QT interval Hypercalcemia = Shortened QT interval (it controls contractibility)

Question 36

What is the QT interval and where does it start/end?

Answer 36

It is from the beginning of the QRS to the end of the T wave. It is the entire time of ventricular depolarization to repolarization and is essentially the entire Refractory Period.

Question 37

What is the difference between the QT and the QTc? How is QTc measured?

Answer 37

The QT is the measurement, the QTc represents the corrected QT interval for the current heart rate. QTc= QT interval / square root of R-R interval

Question 38

What are 2 ways to check if the QT interval is considered prolonged in a normal range heart rate (60-100)

Answer 38

- If more than half the R-R interval is prolonged - If the QTc number is over 0.47 sec or 470ms (again both only work if the heart rate is 60-100)

Question 39

What can cause a prolonged QT interval?

Answer 39

- Hypokalemia, hypocalcemia - Drugs - Liquid protein diets, myocarditis, AMI, LVH, & hypothermia

Question 40

What causes and what is the "Dig Effect"?

Answer 40

The "dig effect" can be caused by Digitalis in 60% of pts on it. It is a slight ST segment depression, with a scooped-out appearance to the ST segment. (best seen in lateral and inferior leads)

Question 41

What is Pericarditis and what are some signs and symptoms?

Answer 41

It is inflammation of the pericardium, the fibrous (not very stretchy) sac around the heart, which can cause: - chest pain, dyspnea, tachycardia, fever, weakness, chills - sharp, severe chest pain radiating to the back, neck, and jaw - symptoms made worse by lying flat; better by sitting up - often pleuritic pain, made worse by breathing - pain that lasts for hours and days - pericardial friction rub, heard along the lower left sternal border

Question 42

What sign will pericarditis show on an ECG?

Answer 42

In 90% of pts, pericarditis may show: - ST segment elevation - Concave in almost all leads except aVR and V1 - T wave elevation starting above the isoelectric line - ST segment depression, or T wave inversion - Almost all leads down (late stage sign)

Question 43

What are 4 ways to diagnose pericarditis?

Answer 43

- physical criteria: chest pain, pleuritic, relieving factors - No response to nitro - Pericardial rub - ECG changes that do not localize an artery (everything up!)

Question 44

How can an Acute PE be seen on an ECG?

Answer 44

An acute PE has no unique signs and symptoms, and must be looked for in clues in the history such as recent surgery or anticoagulants with chronic AFib. Only a large PE will have ECG findings: - sinus tachy - R atrial enlargement - R axis deviation - RBBB (possible)