12 Lead Interpretation Flashcards
What are the 4 primary characteristics of cardiac cells?
1) Automaticity
2) Excitability
3) Conductivity
4) Contractility
Describe the Action Potential in Depolarization?
A five cycle phase in which the electrical charge changes in the intra/extracellular space through the cell membrane
Na and Ca move in (-)
K and Cl move out (+)
Describe Syncytium?
Cardiac muscle cells are grouped together and function as a unit and therefore will normally depolarize as a unit.
What is the Polarized state (resting potential) of the heart?
the resting state of the cardiac cell where the inside of the cell is electrically negative relative to the positive exterior of the cell.
Right before depolarization
What is the Depolarization (action potential) of the heart?
An electrical occurrence normally expected to result in myocardial contraction
Movement of ions back to a homeostasis point
What is the Repolarization (recovery state) of the heart?
The depolarized cell is polarized and positive changes are again on the outside and negative charges on the inside of the cell.
At homeostasis
When is the Absolute Refractory Period?
When the cardiac cell is unable to respond to any new electrical stimulus.
- When depolarization just happened (EARLY)
- Non - Conductive PAC’s
When is the Relative Refractory Period?
There period in which depolarization is almost complete and the cardiac cell can be stimulated to contract prematurely if the stimulus is stronger than normal
- Almost all of the ventricle has recovered from depolarization (LATE)
- BBB’s
Which leads are Bi-Polar leads?
I, II, III
- Also known as limb leads
Which leads are Uni-Polar leads?
AVR, AVF, AVL, V1- V6
- V1 - V6 also known as chest leads
How do you place a 15 - Lead EKG, and what does it show us?
V4 = V4R - 5th ICS to the right midclavicular line V5 = V8 - 5th ICS midscapular V6 = V9 - 5th ICS between V8 and the spine
Shows the Posterior Part of the Heart (V8 - V9)
Shows the Right side of the heart (V4R)
Which Ions are found inside the cell? and which are found outside?
Na and Ca are extracellular
K and Cl are intracellular
What is the “P” Wave? and what is a normal PR interval?
Atrial depolarization
0.12 - 0.2 seconds
What is the “QRS” Wave? and what is the normal QRS interval?
Depolarization of the Ventricles
less than 0.12
Describe “R” wave Progression?
As you go through V1 to V6 the R wave starts low then Peaks up and then back down
What is the “T” wave?
Repolarization of the Ventricles
Where is the “J” Point?
The junction between the ARS and the ST- segment
Where is the “QT” segment? and what does it represent?
- The beginning of the QRS to the end of the “T” wave
- Represents the duration of activation and recovery of the ventricular muscle
- Normal QT is 0.41 seconds
What is occurring during the “ST” segment and what does any change mean?
- It is the time between completion of depolarization and the onset of repolarization
- Elevation greater than 1 mm indicated infarction
- Depression greater than 0.5 mm indicate ischemia
Where is the “U” wave found?
After the “T” wave
What does it mean when there is a larger than normal Q wave?
Old MI
- Usually occurs 20 hours after a MI
Which leads look at the INFERIOR surface of the left ventricle?
II, III, AVF
- Predominantly supplied by the Right Coronary Artery (RCA)
Which leads look at the ANTERIOR surface of the left ventricle and septum?
V2, V3, V4
- Mostly perfused by the Left Anterior Descending branch of the left artery (LAD)
Which leads look at the LATERAL surface of the left side wall of the left ventricle?
I, AVL & V5, V6
- Mostly perfused by the Circumflex branch of the left artery (LCX)
Which leads look at the SEPTAL surface of the septum between the ventricles?
V1, V2
- Perfused partly by the RCA (posteriorly) and LAD (anteriorly)
Which leads look at the POSTERIOR surface?
All the V leads (chest leads)
- normally show ischemic changes (reciprocal changes)
- Perfused mainly by the Right Coronary Artery (RCA)
What are all the reciprocal changes that can be noted during ST-elevation?
Inferior ST elevation - Lateral ST depression
Lateral ST elevation - Inferior ST depression
Septal ST elevation - Posterior ST depression
Posterior ST elevation - Septal ST depression
What is the earliest sign of acute myocardial infarction in the affected area?
hyperacute T waves
What is the Pathophysiology of a BBB?
Loss of Syncytium
Delayed Conduction
What happens to the electrical impulse when there is a hemi-block?
Once it reaches the blocked portion the electrical impulse is sent through cell to cell transmission. (slower)
What occurs in a Left Anterior Fasicular Block (LAHB or LAFB)?
The blocked or delay in the anterior fascicle results in delayed activation of the anterior portion of the left ventricle
- Left Axis Deviation
What occurs in a Left Posterior Hemiblock (LPHB)?
Transmission of the electrical impulse proceeds normally along the main LBB and anterior fascicle but is blocked or delayed in the posterior fascicle.
-Right Axis Deviation
What occurs when there is a LBBB?
The right ventricle depolarizes and by means of cell-to-cell conduction the electrical impulse spreads from the right ventricle to the left ventricle
What occurs when there is a RBBB?
The Right Ventricle depolarizes by means of cell-to-cell conduction that spreads from the interventricular septum and Left Ventricle.
How wide does the QRS need to be in order to consider a BBB?
QRS needs to be wider than 0.12 seconds
What are some diseases and symptoms that could imitate a abnormal EKG?
- Pericarditis
- Early Repolarization
- Left Ventricular Hypertrophy
- Ventricular - Paced Rhythms
What does the “Q” wave represent and what is considered an abnormal Q wave?
The Q wave represents depolarization in the left ventricle occurring from the left to the right
- abnormal is greater than 0.04 seconds in width and greater than 2mm in depth
Which type of MI is referred to as the “Widowmaker”?
Anterior wall MI, with occlusion of the LAD
-LAD is the largest of the coronary arteries
If a Impulse is going toward an electrode will it be positive or negative?
If a Impulse is going away from an electrode with it be positive or negative?
Toward - Positive
Away - Negative
What is a Vector in terms of Axis Deviation?
Vector - a mark or symbol that can be used to describe any force having both magnitude and direction
What is Axis in terms of Axis Deviation?
Axis- The direction of the heart’s electrical current from positive to negative
What are Axis determinations used for?
- Diagnosing Ventricular Tachycardia
- Diagnosing Hemiblocks
- Identifying patients whose infarction is unstable
For a Normal Axis (0 to +90) LRQ what is the lead configuration?
Lead I Upright
Lead II Upright
Lead III Upright
For Physiologic Left Axis deviation (0 to -40) URQ what is the lead configuration?
Lead I Upright
Lead II Upright or Downward
Lead III Downward
For Pathological Left Axis deviation (-40 to -90) URQ what is the lead configuration?
Lead I Upright
Lead II Downward
Lead III Downward
For Right Axis Deviation (+90 - +180) LLQ what is the lead configuration?
Lead I Downward
Lead II Upright or Downward
Lead III Upright
- Normal for Pediatrics
For Extreme Right Axis Deviation (-90 - +180) LUQ what is the lead configuration?
Lead I Downward
Lead II Downward
Lead III Downward
What does a Peaked “P” wave usually mean?
Right Atrial Enlargment (RAE)
- Greater than 2.5 mm
What does it usually indicate when there is an increase in the duration of the “P” wave?
Left Atrial Enlargment (LAE)
- Widened “P” wave greater than 3 mm
What is SEX-PIN?
a mnemonic used to remember the origin of electrolytes
- Sodium External - Potassium Internal dominant electrolyte
What is the normal range of Potassium (K+)?
3.5 - 6.5 mEq/L
Less than 3.5 = hypokalemia
greater than 6.5 = hyperkalemia
less than 5.0 - Mild Hyperkalemia
6.0 -7.0 - Moderate Hyperkalemia
Greater than 7.0 - Severe Hyperkalemia (Sine Wave)
What is the normal range of Calcium (Ca)?
8.5 - 12 mg/dL
Less than 8.5 mg/dL - hypocalcemia
12-15 mg/dL - hypercalcemia
Hypokalemia and Hypomagnesemia will present with _________ T waves.
Flattened
Hyperkalemia and Hypermagnesemia will present with __________ T waves?
Peaked
What occurs during hypocalcemia and hypercalcemia?
Hypocalcemia will have prolonged QT intervals, and QRS / ST changes that mimic an MI
Hypercalcemia will have shortened QT intervals
To be significant an ST segment must exceed ____ in a limb lead or ____ in a precordial lead.
1mm, 2mm
ST segment depression is significant if it is at least one box below baseline or _____ beyond the QRS.
2mm
When determining a BBB which lead should be used?
V1
