CARDIOLOGY - Axis Deviation, BBB, Chamber Enlargement, STEMI Imitators (Week 12) Flashcards
Vector vs mean vector
Vector: an arrow that shows the direction of depolarization in the heart
Mean Vector: the general direction of depolarization (when interpreting ECGs)
The mean vector is ______ degrees
+59 (going down towards the hip)
Describe the vectors for the standard and augmented limb leads.
Standard leads:
- Lead I: 0
- Lead II: +60
- Lead III: +120
Agumented leads:
- Lead aVR: -150 (distance recording electrode)
- Lead aVL: -30 (in the upper hemisphere)
- Lead aVF: +90 “(in the lower hemisphere)
In normal electrical axis, where does the mean vector lie? Also describe the QRS characteristics.
Mean vector: lies between 0 and +90
- QRS is +ve in all standard limb leads
What is axis deviation?
refers to the movement of the axis to the right or left of its normal position
normal conditions and disease processes can cause axis deviation
Describe the current flow in left axis deviation and the characteristics of QRS in standard limb leads.
Mean vector: current flow is to the left of normal, lying between -1 and -90
In some cases, the axis may be rotated slightly more to the left, showing:
- Lead I: positive deflection of the QRS
- Lead II: positive or biphasic deflection of the QRS
- Lead III: negative deflection of QRS - because impulses are travelling away from lead III
Causes of left axis deviation
- normal variant, particularly in older and obese
- mechanical shifts associated with expiration and emphysema
- hyperkalemia
- dextrocardia - abnormal shift in apex of heart (more left than typical which is towards the hip)
- ascites or abdominal tumors - associated with liver disease
Describe the current flow in right axis deviation and the QRS characteristics.
Mean vector: current flow is to the right of normal, lying between +90 and +180
In some cases, the axis may be rotated slightly more to the right, showing:
- Lead I: negative defection in QRS
- Lead II: positive, negative or biphasic in QRS
- Lead III: positive deflection in QRS
Causes of right axis deviation
- normal variant, particularly young and thin
- mechanical shifts associated with inspiration and emphysema
- RVH
- COPD
- WPW syndrome
- pulmonary embolism
Describe the current flow in extreme right axis deviation and QRS characteristics. Also describe the causes of extreme right axis deviation.
- aka “no man’s land”
- axis is deviated towards right shoulder, meaning the direction of the vector is backwards
- Current flow lies between -91 and -179
- Lead I, II, III: negative deflection - since it’s moving away from direction of depolarization
- Causes: these would be the patients with impulses originating from the ventricles so causes of ventricular dysrhythmias can cause extreme right axis deviation
What is the easier method to determine axis deviation?
Two lead method of axis deviation
Where you’re using two leads that can be used to quickly estimate electrical axis (using Lead I and Lead aVF)
Using the two lead method of axis deviation, how would you recognize normal axis deviation?
Lead I: QRS complex is predominantly positive (upright)
Lead avF: QRS complex is predominantly postive (upright)
“TWO THUMBS UP” = GOOD
Using the two lead method of axis deviation, how would you recognize left axis deviation?
Lead I: QRS complex is predominantly positive (upright)
Lead aVF: QRS complex is predominantly negative (downwards)
“The thumbs have ‘left’ each other”
Using the two lead method of axis deviation, how would you deteremine there is right axis deviation?
Lead I: QRS complex is predominantly negative (downwards)
Lead aVF: QRS complex is predominanetly positive (upright)
“The thumbs are headed ‘right’ towards each other”
Using the two lead method of axis deviation, how would you deteremine there is extreme right axis deviation?
Lead I: QRS Complex is predominantly negative (downwards)
Lead aVF: QRS complex is predominantly negative (downwards)
“Two thumbs down = BAD”
What is equiphasic?
waveform is biphasic but equally upright and downright
Explain what an equiphasic QRS in Lead aVF means/represents?
If Lead aVF is equiphasic, impulse must be travelling PERPENDICULAR to this lead
AND
Lead I displays a -ve current, so a +ve current must exist on the opposite side of the hexaxial reference circle
so this would also be your right axis deviation (?) - double check this
What is both QRS are equiphasic?
indeterminate
Describe what Bundle Branch Block (BBB) is
An interruption in conduction between either bundle branches causing an unsynchronized depolarization
Describe the conduction pathway of BBB.
1) Atria depolarizes normally (depending upon underlying rhythm)
2) Impulse travels down unblocked branch and stimulates that ventricle
3) Because there’s a block in the other branch, the impulse must travel from cell-to -cell through the myocardium (rather than normal conduction pathway) slowly to stimulate the other ventricle ⇒ conduction is slower than normal (ECG shows widened QRS)
4) blocked ventricle thus depolarizes slightly later than normal ventricle (causing two separate depolarizations) ⇒ seen as single notched (rabbit ears) OR widened QRS
In order to determine the seriousness of the BBB and whether it’s a right or left BBB, what must we do?
obtain a 12 lead ECG
ECG criteria for identification of Right or left BBB
1) QRS duration ≥ 0.12 seconds (so 3 small squares or more)
2) QRS produced by supraventricular activity (i.e. from SA node, AV node, atria) - so there would be a p wave present (which you can confirm in Lead II)
* i.e. the QRS is not a paced beat and did not originate in the ventricles which typicall would have no p waves
When measuring a BBB on a 12-lea ECG, which lead and complex are you looking at?
- Confirm the presence of a p wave or atrial activity (such as a-fib) in Lead II
- Use Lead V1 as it’s probably the single best lead to use when differentiating between right and left BBB
- Select the widest QRS xomplex with a discernable beginning and end
After the two criteria for BBB has been met, what pattern in V1 should indicate a potential Right BBB?
rSR’ - sometimes called “M” or “rabbit ears”
After the two criteria for BBB has been met, what pattern in V1 should indicate a potential left BBB?
a QS pattern
note: STEMI imitator
True or False. All BBBs either present with rSR’ or QS pattern.
FALSE. They may also resemble a qR or rS pattern making the differentiation less clear
If you’res unable to differentiate between right or left BBB on a 12-lead, what should you do?
- focus on terminal force of the QRS complex (the final portion - last 0.04 secs) of the QRS
- the final portion reveals the ventricle that was last depolarized and therefore the bundle that is blocked
How do you identify which ventricle depolarized last using the terminal force?
Step 1: confirm QRS ≥ 0.12 seconds (in V1) and produced by supraventricular activity (p waves in Lead II)
Step 2: find J point in V1 and move J point backwards INTO the QRS complex by 1 small square (0.04 sec)
Step 3:
- if the last 0.04 seconds is deflected upright = right BBB
- if deflected downwards = left BBB
When can atrial and/or ventricular chamber enlargement occur?
May occur if there is a volume or pressure overload in the heart
Define the following terms in relation to the heart size.
1) Dilation
2) Hypertrophy
3) Enlargement
1) Dilation: an increase in the diameter of a chamber of the heart caused by volume overload; may be acute or chronic
2) Hypertrophy: an increase in the chamber thickness because of pressure overload; commonly accompanied by dilation
3) Enlargement: implies the presence of dilation, hypertrophy or both
Describe the normal parameters for a p wave and what the first half and second half of the p wave represent.
Normal parameters:
- Time: 0.10 secs or less (2.5mm or less)
- Voltage: No more than 0.25 mV (2.5mm)
1st half of p wave: represents the depolarization of the RA
2nd half of p wave: represents depoarlization of LA
Describe how you would identify Right Atrial Enlargement (RAE) and what can cause RAE.
- RAE produces abnormally tall and peaked P wave (>0.25mV in leads II, III, AVF) - always upright p waves
- can be caused by conditions that increase work of RA:
- COPD with or without hypertension
- Right ventricular failure
- Heart disease
Describe how you would identify Left Atrial Enlargement (LAE) and what could cause LAE.
- produces abnormally long latter part of the P wave (>0.10 seconds and often notched in Leads I, II, aVL, V4, V5, V6)
- may be biphasic in V1
- can be caused by conditions that increase the work of LA
- Hypertension
- LV failure
- mitral regurgitation (blood leaking back into LA)
Determine if there is any atrial enlargement, and if so, whethere there is RAE or LAE.
Determine if there is any atrial enlargement and if so, is it RAE or LAE?
Left atrial enlargement due to biphasic p wave in V1 and notched p waves in V4 and V5
note that biphasic (diphasic) p waves may indicate enlargement of both atria (tall AND long p waves = bi-atrial enlargement)
If you have tall and long p waves, what does this represent?
bi-atrial enlargment
What is ventricular enlargement and how does this present on a 12-lead?
When the ventricle muscle thickens (hypertrophies) when it sustains persistent pressure overload
Hypetrophy exaggerates the QRS complex in both height and depth in chest leads (?and limb leads), and often associated with ST segment depression and asymmetrical T wave inversion
What factors may affect QRS complex amplitude besides ventricular hypertrophy?
- age
- body weight
- presence of lung disease
- thin-chested individuals or young adults because chest electrodes are to close to their hearts
Describe how LVH would affect QRS complex height, depth, and direction.
- LVH produces QRS complexes that are exaggerated in amplitude (both height and depth in chest leads)
- More depolarization is noted going downwards towards patient’s left side (away from V1) ∴ V1 should have an inverted QS
- V5 views LV from the left side so increased depolarization going towards V5 would produce significantly taller R waves
How would you determine if LVH is present?
mm of S wave in V1 + mm of R in V5 - if it’s more than 35 mm then there is LVH
Determine if there is any ventricular hypertrophy, and if so, if it’s LVH or RVH.
Describe how RVH would affect QRS complex and what you would find on an 12-lead.
- RVH produces QRS complexes that are exaggerated in amplitude in chest leads
- with RVH, more depolarization is noted going AWAY from patient’s left side (towards the right i.e. towards V1)
- you’d see:
- a taller than normal R wave (≳7mm) and small S wave in V1 and V2
- deep S wave and short R wave in V5 and V6
- there should be a progressive decrease in height of R wave from right to left chest leads
Determine if there is any ventricular hypertrophy and if so, if it is RVH or LVH.
RVH
True or false. Reperfusion injury is time sensitive
True. TIME = MUSCLE
What is the golden hour?
the first hour after onset of a heart attack; a critical time period because you need to determine if the chest pain is STEMI in nature & get to the cath lab (otherwise go to the local hospital)
What is a STEMI imitator and why could improper STEMI diagnosis pose serious harm to the patient?
STEMI Imitator: ST elevation within 12 lead ECG, yet diagnosis other than an occluded coronary artery
Improper STEMI diagnosis may pose risks/harm including:
- inappropriate use of thrombolytics
- unnecessary coronary angiography
- delay in appropriate therapy
Paramedics’ goal is to provide accurate dx based on clinical history and ECG interpretation
What are some STEMI imitators? (9)
E - Electrolytes (Hyperkalemia)
L - Left BBB
E - Early repolarization (Benign)
V - Ventricular hypertrophy (Left)
A - Aneurysm (Ventricular)
T - Thailand (Brugada)
I - Inflammation (Percarditis)
O - Osborn waves (Hypothernia)
N - non-atherosclerotic vasospasm
Describe what hyperkalemia is and its role in cardiac function
Hyperkalemia: abnormally high level of potassium in the blood
K+ is essential for normal cardiac electrical activity; an increased amount in the ECF reduces myocardial excitability, affecting both conductive tissue and pacemaker function
Causes of hyperkalemia may include:
- excessive administration of potassium
- excessive use of salt substitutes
- wide spread cell damage (eg. crush injuries, burns)
- metabolic or respiratory acidosis
- acute or chronic renal failure - eg. missed dialysis treatments (they may be confused, weak, and SOB)
Signs and symptoms of hyperkalemia may include
- Head: confusion or altered LOC
- Chest: chest discomfort, SOB, conduction disturbances
- Abdomen: N/V
- Back/pelvis: decreased urinary output, diarrhea
- weakness (early sign) & paralysis (late sign)
Describe potential ECG changes in patients with hyperkalemia vs those who have normal potassium serum levels.
Normal K+ serum: 3.5 - 5.0 mEq/L
- Hyperkalemia patients may be asymptomatic but typical ECG changes may occur including
Mild cases: <6.5 mEq/L - normal p waves; tall, tented peaked T waves (Best seen in II, III, V2, and V4)
- looks similar to hyperacute phase of STEMI evolving (so STEMI imitator)
Moderate cases: <8 mEq/L - p wave starts to flatten; prolonged PR interval
- no ST segment with peaked T waves
- widened QRS Complex
- Broad S wave in V leads
- Left axis deviation
Severe cases: >8.5 mEq/L - absent P waves, sine wave (which can be mistaken for V-tach)
VF or asystole: 10-12 mEq/L
Examine the following 12-lead and determine what characteristics would indicate hyperkalemia?
tall, tented, peaked T waves (best seen in II, III, V2, V4)
Describe what a left BBB is and how it may be a STEMI imitator.
Left BBB: an interruption in the left bundle branch conduction causing an unsynchronized depolarization (the LV depolarizes slightly later than the RV causing two separate depolarizations seen as a wide QRS)
- A left BBB can look like a AMI so typically people do not even attempt to diagnose an AMI in the presence of a LBBB because you just can’t tell (therefore reperfusion therapy is commonly delayed or withheld)
- Reasons why:
- LBBB with or without AMI typicall presents with ST elevation
- As Q wave patterns are altered, it is difficult to diagnose a previous MI in the presence of a LBBB
Define concordance and discordance.
Concordance: QRS complex predominantly in the SAME direction of ST and/or T wave
Discordance: QRS complex predominantly in the OPPOSITE direction of the ST and/or T wave
Describe the “Sgarbossa” criteria for AMI with LBB
1) Concordant ST Elevation - ≥ 1mm in ANY lead(s) - SCORE 5
2) Concordant ST Depression - ≥ 1mm in V1-V3 - SCORE 3
3) Excessive Disconcordant ST Elevation - ≥ 1mm in ANY lead(s) (defined as ≳ than 25% of the depth of preceding S) - SCORE 2
This test has a 90% specificity for diagnosing an MI when a patient scores ≳3
What is Benign Early Repolarization (BER) and who does it typically occur in?
- aka “high take off J point elevation”
- Typically occurs in
- 1% of total population
- young healthy males (often resolves with age)
- chest pain patients who have used cocaine
Benign Early Repolarization is characterized by:
- Notched or “slurred” J point (best seen in V4, V5, and V6)
- Concave ST elevation (best seen in inferior and lateral leads)
- No reciprocal depression to suggest STEMI
What two conditions can often be difficult to differentiate between as they are both associated with concave ST elevation?
pericarditis and benign early repolarization
Examine the following 12-lead and describe which STEMI imitator is illustrated here. Provide your rationale.
Benign Early Repolarization
Describe LVH characteristics on a 12-lead and why it causes these ECG changes.
- Characterized by:
- ST elevation in leads with deep S waves (usually V1-V3)
- ST depression/T wave inversion in leads with tall R waves (lateral leads)
- An increase in muscle mass causes increase in the amount of depolarizing myocardial cells which results in tall R waves in V5 and deep S waves in V1
- most commonly associaed with HTN
*note: differentiating ST elevation due to LVH vs due to an AMI is difficulty due to little literature
Describe Left Ventricular Aneurysm and how it can be a STEMI imitator.
- myocardial wall thinning and/or bulging
- persistent ST elevation remaining in 1 in 4 patients following a STEMI (these patients may present with chest pain and be misdiagnosed with an AMI)
- Characterized by:
- ST elevation with varying morphologies (i.e. convex and concave)
- Pathological Q waves in affected ST elevation leads
- Inverted T wave of minimal magnitude
The absence of STEMI evolution may suggest a left ventricular aneurysm therefore serial ECGs are invaluable
Describe what Brugada Pattern is and what could cause it.
Brugada Pattern: aka thailand - a rare gene mutation (function loss of sodium channels) in patients with structurally normal hearts
Typically occurs in:
- 1 in 25 000 people (high incidence in southeast Asia)
- Males (70%)
- Can occur at any age, but typically 41 y.o.
May be exacerbated by:
- fever
- hypokalemia
- medications - antiarrhythmic medications are potent sodium channel blockers
How is Brugada Pattern characterized on a 12-lead/clinical presentation?
- coved or “saddle back” ST segment in V1 and V2
- Possible syncope
- No chest pain
Define pericarditis, identify potential causes, and describe the typical demographic in whic pericarditis affects.
- *Pericarditis:** inflammation of the pericardium
- *Acute pericarditis:** pericardium and myocardium just beneath it are inflamed, causing repolarization abnormalities
- Typically occurs in:
- young patients without cardiac risk factors but can occur in all ages
- Caused by:
- viral and autoimmune causes (most common)
- Bacterial diseases eg. TB
- Cancer
- Other sources of inflammation
Signs and Symptoms of pericarditis?
- Chest pain - sharp, severe radiating to back, neck and jaw; often pleuritic pain, made worse by breathing
- pain lasts hours to days
- Symptoms made worse by lying flat and better by sitting up
- Tachycardia
- Fever
- Weakness
- Fever/chills
Describe how pericarditis is characterized in a 12-lead.
- Concave ST elevation in almost all leads (except aVR and V1)
- T wave elevation above the isoelectric line
- 90% of pericarditis cases have the above ^ ECG evidence
- since periarditis DOES NOT involve coronary artery blockage, the ST elevation will NOT be limited to leads overlying area fed by certain coronary artery (i.e. it will be widespread through many leads
Examine this 12-lead and determine what STEMI imitator would produce such characteristics & rationale.
Pericarditis - widespread ST elevation (in almost all leads) & T wave elevation above isoeletric line
Describe hypothermia
- Core body temp (CBT) < 35 deg
- result of decreased heat production, an increase in heat loss, or a combo of both
- “Osborn waves” may be present in an ECG when CBT reaches 30 deg
- transient and will resolve when CBT returns to normal
ECG findings for hypothermia
- J point elevation (“Osborn wave”) - most prominent in precordial leads
- Prolonged PR, QRS, and QT interval
Examine the following 12-lead and determine what STEMI imitator produced such characteristics. Provide rationale.
Hypothermia - osborn waves present in V2, V3, and V4
What is Prinzmetal Angina? Describe the demographic is occurs in and when it occurs.
- an intense spasm in a segment of the coronary artery
- an atypical form of angina characterized by ST segment elevation in a 12-lead that disappears when pain subsides
- no clear demographic and occurs anywhere in the arteries; often associated with tobacco and cocaine use
- Typically occurs:
- at rest
- early morning or late night (may awake patient)
- in episodes lasting a few minutes (a duration long enough to cause dangerous dysrhythmias)
