Week 3-12- Lead Interpretation

Question 1

Limb Lead Placement

Answer 1

• Doesn’t matter if they are on the arms or the shoulders, as long as they are 10 cm from the heart

Question 2

12 Lead Electrodes Placement

Answer 2

V1 & V2- each side of the sternum at the 4th intercostal space
V4-5th- intercostal space, mid clavicular line (directly under the nipple)
V3- Between V2 & V4
V5- Anterior axillary line
V6- Mid-axillary line

Question 3

What does ST segment represent?

Answer 3

• ST segment represents section of complex in which ventricles are between electrical depolarization and repolarization

Question 4

Where is the ST segment measured?

Answer 4

• Measured from J point to beginning of T wave
• Measurement usually approximate because: J point is not sharp and beginning of T wave is not clearly visible

Question 5

What does the ST segment and T wave represent together?

Answer 5

• This is the area that reflects ischemia or injury to the myocardium
• ST depression and T waves in opposite direction from normal= ischemia
• ST elevation, with or without T wave change= myocardial injury

Question 6

What is the difference between an MI and Ischemia?

Answer 6

MI= complete block

Ischemia= partial block

Question 7

What are the key aspects to identify when examining an ST segment?

Answer 7

• ST elevation of at least 2 mm ST elevation in leads V1-V3 (2 contagious)
• At least 1 mm ST elevation in at least 2 other anatomically contagious leads
• ST depression is considered with any depression below baseline

Question 8

Tombstone Segment

Answer 8

• T waves that are flipped in leads I, aVL and V2 to V6= classic “tombstone” segment (indicates large myocardial infarction)

Question 9

What are the signs of ischemia?

Answer 9

• ST elevation or depression
• ST segment flat and/ or downward sloping

Question 10

What areas of the heart does the acute myocardial infarction (AMI)?

Answer 10

• Anterior wall
• Inferior wall
• Posterior wall
• Right ventricle
• Apex

Question 11

What combinations cover the AMI’s?

Answer 11

• Inferolateral
• Anterolateral
• Inferoposterior

Question 12

What happens when a myocardial cell is oxygen-deprived?

Answer 12

• It’s function begins to alter
• Initiates anaerobic metabolism (production of energy without O2)
• This creates acidosis, and is ineffective for the cell to function
• Cell begin to suffer injury, and will die if normal circulation and oxygenation are not restored

Question 13

Why do ischemia and injury develop?

Answer 13

• Ischemia and/ or injury develop because demands of the heart are not met by blood supply to that area
• Either an increase in demand or a decrease in supply can cause ischemia and/ or injury to develop

Question 14

Cardiac Circulation

Answer 14

• Arteries approach endocardium and divide into smaller branches until they form capillary beds of myocardium
• Single big branch supplies blood to wedge-shaped section of tissue, growing fatter as it moves from artery’s point of origin
• Cells die along the pattern of distribution of branch, perfusing that section of myocardium

Question 15

What are the three protective mechanisms of the heart?

Answer 15

1. Collateral circulation allows some areas of branch endocardium to be supplied by two different branch systems. (Overlap of areas of perfusion supplied by different arteries)
2. Oxygen from ventricles can diffuse into cells of nearby tissue
3. There may be some small vessels (thebesian veins), arising directly from the ventricles

• These mechanisms work to provide extra oxygen to the cells near the endocardium, making them less susceptible to ischemia and injury

Question 16

What does ischemia cause?

Answer 16

• Causes ST depression (remains more negative than surrounding tissues)
• T wave is flipped (causes repolarization to occur along abnormal pathway)

Question 17

Injury to the heart?

Answer 17

• Zone of injury does not repolarize completely
• Remains more positive than surrounding tissue, leading to ST elevation
• T remains flipped

Question 18

Infarction

Answer 18

• Dead tissue
• Does not generate any action potentials

Question 19

ECG progression in infarct

Answer 19

• ECG Pattern in AMI= extends from normal to full infarct
• First: T wave flattens then flips in early ischemia
• Then: ST elevation either flat or tombstoning
• Finally Q waves appear

Question 20

What is reciprocal changes?

Answer 20

• Refers to “mirror image” that occurs when two electrodes view the same AMI from opposite angles

Question 21

Anterior Wall AMI

Answer 21

• Rarely presents by itself. Commonly occurs with infarcts of septum, lateral wall, or both
• Leads that represents anterior wall= V3 and V4

Question 22

Lateral MI

Answer 22

• Can occur by themselves by showing changes in leads I, aVL, V5 and V6
• Can occur in combination with other areas as well

Question 23

Inferior Wall MI

Answer 23

• Produces changes in leads I, III, and aVF
• Commonly associated with additional involvement of lateral wall, posterior wall, and right ventricle
• Reciprocal changes will present as ST depression in leads I & aVL

Question 24

Right Ventricular AMI

Answer 24

• RV gets blood supply from the RCA
• Up to 50% of inferior MI will have RVI
• RV is preload dependent for Cardiac Output
• Nitrates cause preload reduction; thus use nitrates with extreme caution
• Hypotension in RVMI often responds well to IV fluid bolus (increase in preload)
• May require 1 L or more IV fluid bolus for hypotension

Question 25

What do additional ECG leads help with?

Answer 25

- Help to diagnose posterior and right ventricular infarcts - Direct changes occurring in the right ventricle are clearly seen in V4R - ANY time you see an inferior infarct, you should obtain right-sided leads

Question 26

V4R Lead Placement

Answer 26

- With any inferior STEMI on your 12 lead - Simplest way to rule out RVI is obtaining V4R - Take your V4 lead and place it in the exact same spot on the RIGHT side of the chest instead of the left (under the right nipple)

Question 27

15 Lead ECG Placement

Answer 27

To assess for Posterior Involvement - When: - Inferior STEMI - Anterior elevation/ depression (V1-V4) - You suspect MI and see no evidence on your 12 lead

Question 28

Where do you move the leads for 15 lead ECG?

Answer 28

- Move leads V4, V5 and V6 - They become V7, V8, and V9

Question 29

What are the PCP Interventions?

Answer 29

- Full assessment including detailed questioning re: hx prior to today and hx. of events today - Full set of vitals- including 12 lead - O2 if required - Rule in/out ASA - Rule in/out Nitro - If STEMI present- apply defib. Pads immediately - Transport is priority

Question 30

What is the provincial STEMI Bypass?

Answer 30

INCLUSION CRITERIA- Transport to HIU after calling - Adult (18 or over) and - Chest pain (or equivalent) consistent with cardiac ischemia and - Current episode of pain <12 hours and - 12 lead indicated an acute STEMI/ MI - At least 2mm ST elevation in at least 2 of the other anatomically contiguous lead OR - At least 1mm ST elevation in at least 2 of the other anatomically contiguous leads, OR - 12 lead ECG computer interpretation STEMI and paramedic agrees

Question 31

What are the contraindications going to the closest ED (STEMI bypass)?

Answer 31

- CTAS 1 and the paramedic is unable to secure the airway or ventilate - 12 leads consistent with LBBB, ventricular paced rhythm, or any STEMI micker - Transport to PCI Center is >60 mins from pt. contact (interventionist may still permit)

Question 32

Pt is experiencing a compilcation requiring PCP Diversion:

Answer 32

- Moderate to severe resp distress or the use of CPAP - Hemodynamic instability or SBP <90 mmHg at any point - VSA without ROSC

Question 33

Pt is experiencing a complication requiring ACP Diversion:

Answer 33

- Ventilation inadequate despite assistance - Hemodynamic instability unresponsive/ not amenable to ACP treatment/ management - VSA without ROSC

Question 34

What do we do right away once a STEMI has been found in the 12 lead?

Answer 34

Defib pads need to be applied right away

Question 35

When does Base hospital want a 12 lead, and how often do they acquire a 12 lead?

Answer 35

- If your first interpretation is non diagnostic- Three (3) 12 leads are required, (once on the scene, again prior to leaving, and once again upon arriving to hospital) - If your first interpretation is STEMI- only required to acquire one 12 lead if you diagnose a STEMI on scene