Week 3-12- Lead Interpretation Flashcards
Limb Lead Placement
- Doesn’t matter if they are on the arms or the shoulders, as long as they are 10 cm from the heart
12 Lead Electrodes Placement
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
What does ST segment represent?
- ST segment represents section of complex in which ventricles are between electrical depolarization and repolarization
Where is the ST segment measured?
- 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
What does the ST segment and T wave represent together?
- 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
What is the difference between an MI and Ischemia?
MI= complete block
Ischemia= partial block
What are the key aspects to identify when examining an ST segment?
- 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
Tombstone Segment
- T waves that are flipped in leads I, aVL and V2 to V6= classic “tombstone” segment (indicates large myocardial infarction)
What are the signs of ischemia?
- ST elevation or depression
- ST segment flat and/ or downward sloping
What areas of the heart does the acute myocardial infarction (AMI)?
- Anterior wall
- Inferior wall
- Posterior wall
- Right ventricle
- Apex
What combinations cover the AMI’s?
- Inferolateral
- Anterolateral
- Inferoposterior
What happens when a myocardial cell is oxygen-deprived?
- 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
Why do ischemia and injury develop?
- 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
Cardiac Circulation
- 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
What are the three protective mechanisms of the heart?
- 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)
- Oxygen from ventricles can diffuse into cells of nearby tissue
- 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