Chapter 9 Flashcards
What are some indications a 12 lead ECG is needed?
- Abdominal or epigastric pain
- Assisting in dysrhythmia interpretation
- Chest pain or discomfort
- Diabetic ketoacidosis
- Dizziness
- Dyspnea
- Electrical injuries
- Known or suspected electrolyte imbalances
- Known or suspected medication overdoses
- Right or left ventricular failure
- Status before and after electrical therapy
- Stroke
- Syncope or near-syncope
- Unstable patient, unknown etiology
What leads view the lateral part of the heart?
V5, V6, aVL, DI
What leads view the inferior part of the heart?
aVF, DII, DIII
Which leads view the anterior part of the heart?
V3, V4
Which leads view the septum (part of heart)?
V1, V2
What happens when there is a lack of oxygen in the tissue due to low circulation?
- Ischemia
- Acute myocardial injury
- Myocardial infraction
Layout of the 12 lead ECG
Lateral - V5, V6, aVL, DI
Inferior - aVF, DII, DIII
Anterior - V3, V4
Septum - V1, V2
aVR - none
Vectors
Mean vector identifies the average of depolarization waves in one portion of the heart
Mean P vector — represents the average magnitude and direction of both right and left atrial depolarization
Mean QRS vector — represents the average magnitude and direction of both right and left ventricular depolarization
Axis
Mean axis — average direction of a mean vector — only identified on frontal plane
Axis of a lead — an imaginary line joining the positive and negative electrodes of a lead
Electrical axis — refers to determining the direction (or angle in degrees) in which the main vector of depolarization is pointed
Hexaxial reference system
The hexaxial reference system represents all of the frontal plane (limb) leads with the heart in the center
Forms a 360 degree circle around the heart
Normal axis of the heart is between -30 degrees and +90 degrees
Quadrant method = aVF +90 degrees
DI 0 degrees
Determine electrical axis
Look for the longest QRS in leads DI, DII, DIII, aVR, aVL, aVF
Look at longest S wave
- Calculate # of squares there are from isoelectric line up the R wave (in mmV)
- Calculate # of squares there are from isoelectric line down S wave (in mmV)
- Subtract
Estimate if they would look + or -
Determination of QRS quadrant deviation
DI (+) & aVF (+) = normal
DI (+) & aVF (-) = left axis deviation
DI (-) & aVF (+) = right axis deviation
DI (-) & aVF (-) = northwest extreme axis deviation or undetermined
Steps to analyze 12 lead ECG
- aVR - is it flipped? If it is, EKG was done correctly
- Move to most useful (most viewed lead) lead II (lateral) then continuous leads (DIII, aVF) — are they normal? Is there deviation?
- Followed in whatever order of sections (anterior, inferior, etc) you want to follow. Are they normal? Is there deviation
Acute coronary syndrome
Unstable angina (UA)
Non ST-segment elevation myocardial infarction (NSTEMI)
ST-segment elevation MI (STEMI) — sign of acute myocardial infarction
Indicative and reciprocal changes - what does each change mean (elevation, inverted waves, etc)
Inverted T waves - ischemia
ST elevation - acute myocardial infarction
Pathological Q wave (deep Q wave - more than 1/3 of QRS) - old scar of a myocardial infarction — abnormal
What do changes in 2 contiguous leads mean?
Indicative changes are significant when they are seen in at least two contiguous leads (two leads in the same heart area)
Two leads are contiguous if they look at the same or adjacent areas of the heart or if they are numerically consecutive chest leads
How do you assess the extent of infarction using leads?
Evaluate how many leads are showing indicative changes — changes in only a few leads suggests a smaller infarction
The more proximal the vessel blockage — the larger the infarction. The greater the number of leads showing indicative changes
Anterior infarction
Left main coronary artery supplies — left anterior descending artery (LAD) and circumflex artery (Cx)
Anterior myocardial infarction occurs when the blood supply to the LAD are teary is disrupted
Evidence of anterior myocardial infarction can be seen in leads V3 and V4.
Septal infarction
Changes in leads V1 and V2 will show septal infarction
If an infarction involve anterior wall AND septum, there will be changes in V1, V2, V3, V4
R wave progression
R wave becomes taller and S wave becomes smaller as the chest electrode is moved from right to left
V3 and V4 normally record an equiphasic RS complex — transitional zone
Transition zone is where the R wave amplitude begins to exceed the amplitude of the S wave
Early transition is when change is seen in V2
Late transition describes a delay in transition until leads V4 and V5
Poor R wave progression
Phrase used to describe R waves that decrease in size from V1 to V4
Lateral infarction
Seen in DI, aVL, V5 and V6
May be associated with an anterior, inferior, or posterior infarction
Inferior infarction
Seen in leads DII, DIII, aVF
Increased parasympathetic nervous system activity is common with inferior MIs, resulting in bradydysrhythmias
Conduction delays (first degree AV block, second degree AV block type 1) are common and are usually transient
Inferobasal infarction
Occur in conjunction with an inferior or lateral infarction
None of the 12 leads view posterior wall, additional leads (V7 to V9) may be used to view the posterior surface
Changes include STE in these leads
Mirror test may be helpful in recognizing the ECG changes suggesting an inferobasal MI
Right ventricular infarction
RVI is usually the result of a right coronary artery (RCA) occlusion.
Right side chest leads are used in this situation
Intraventricular conduction system — bundle of his
Normally the only electrical connection between atria and ventricles
Connects AV node with the bundle branches
Conducts impulse to right and left bundle branches
Intraventricular conduction system — right bundle branch
Travels down right side of inter ventricular septum
Conducts impulse to right ventricle
Long, thin, and more fragile than the left
Intraventricular conduction system — left bundle branch
Begins as a single structure that is short and thick (left common bundle branch or mainsterm)
Divides into subdivisions called fascicles
Bundle branch activation
Normally, left side of the interventricular septum is stimulated first
Electrical impulse then crosses the septum to stimulate the right side
Left and right ventricles are then depolarized at the same time
If the delay or block occurs in one of the bundle branches, the ventricles will not be depolarized at the same time — impulse travels first down the unblocked branch, stimulates that ventricle, impulse must then ravel from cell to cell through the myocardium to stimulate the other ventricle
Bundle branch block (BBB) - how to recognize it?
Measure the QRS complex duration
Select the widest QRS complex with a discernible beginning and end
Lead V1 is probably the single best lead to use when differentiating between forms of bundle branch block
How to recognize complete or incomplete BBB? Intraventricular conduction delay?
If a BBB pattern is discernible and the QRS measure 0.12 sec or more in an adult, it is called complete right or left bundle branch block
If a BBB pattern is discernible and the QRS duration is between 0.11 and 0.119 sec in adults, it is called an incomplete right or left BBB
If the QRS is wide but there is no BBB pattern, the term wide QRS or intraventricular conduction delay is used to describe the QRS
Easy way to figure out if its a right bundle branch block (RBBB) or a left bundle branch block (LBBB)
View lead V1
Move from the J point back into the QRS complex
Determine if the terminal portion (last 0.04sec) of the QRS complex is positive or negative
Positive — RBBB
Negative — LBBB
Causes of right BBB
Can occur in individuals with no underlying heart disease, but occurs more commonly in the presence of organic heart disease
May occur secondary to a right ventricular infarction
Causes of left BBB
May occur secondary to —
Anteroseptal (more common) or inferior MI
Conduction system degeneration
Acute heart failure
Acute pericarditis or myocarditis
Following cardiac procedures
Other causes of BBB
Aortic valve disease
Congenital, hypertensive, and rheumatic heart disease
Trauma (cardiac surgery)
Rate related BBB
Nonischemic diseases