Intraventricular Conduction Defects Flashcards
_______ occurs as a result of volume overload where chamber(s) stretches to accommodate increased blood volume
Dilation (Enlargement)
Condition in which muscular wall of the ventricle(s) becomes thicker than normal
Hypertrophy
_______ changes are used to identify Atrial Enlargement
P wave
______ changes are used to identify ventricular hypertrophy
QRS complex changes
Morphology of normal P waves
Upright and rounded in Lead II
Normal amplitude for P waves
0.5 - 2.5 mm (up to 2.5 small boxes)
Normal duration for P waves
0.06 - 0.10 s (60-100 ms, or up to 2.5 small boxes)
Initial portion of the p wave represents…
Right atrial depolarization
Terminal portion of the p wave represents…
Left atrial depolarization
When might you see right atrial dilation?
From greater filling pressures in chronic pulmonary disease (P pulmonale)
When might you see left atrial dilation?
Mitral valve pathology
Reduced ventricular compliance such as in LVH
(P mitrale)
The ideal leads for assessing atrial enlargement are…
Lead II and V1
Criteria for Right Atrial Enlargment
P wave > 2.5 mm tall
OR
The initial component of the P wave in V1 is larger than the terminal component if the P is biphasic (upward deflection > downward deflection)
Criteria for Left Atrial Enlargement
P wave > 0.10s (100ms)
OR
The terminal portion of the P wave in V1 is negative with a duration of ≥0.04s AND a depth of ≥1mm
Ventricular hypertrophy is commonly caused by …
Chronic, poorly treated hypertension
Most common characteristic of RVH in limb leads is…
Right axis deviation
In cases of RVH, what will you observe in the precordial leads?
R waves that are increased in amplitude over RV (leads V1-2) and decrease moving towards V6
What are the characteristic EKG changes in LVH?
In precordial leads, R waves are increased in amplitude over LV (leads V5 and V6)
S waves are deeper in leads V1 and V2
Criteria for LVH
Deepest S wave in V1/V2 + Tallest R wave in V5/V6 > 35mm
Or
R wave in Lead I + S wave in Lead III > 25mm
Or
R wave in aVL > 11mm
Criteria for RVH
Right axis deviation
Or
R wave > S wave in V1
Or
S wave > R wave in V6
What are the different divisions of the bundle branches?
Bundle of His divides into the Right and Left bundle branches
Left bundle branch further divides into septal, anterior, and posterior fascicles
Morphology of normal QRS complexes
Narrow
Duration ≤ 0.12s (120ms)
Electrical axis 0˚ to +90˚
One or both bundle branches failing to conduct impulses is referred to as…
A Bundle Branch Block (BBB)
Produces a delay in depolarization of the ventricles it supplies
Generalized criteria for a BBB
QRS > 0.12 s (120ms)
RR’ configuration with normal QRS interval
Incomplete BBB
What do we mean by “rabbit ear” QRS complex?
Double peaked or RR’
Due to bundle branch block (the delayed ventricle is represented by R’)
What are the possible sites of bundle branch blocks?
Right bundle branch block (RBBB)
Left bundle branch block (LBBB)
Fascicular blocks
• Left anterior fascicle (LAFB) or left anterior hemiblock (LAHB)
•Left posterior fascicle (LPFB) or left posterior hemiblock (LPHB)
Or any combo of the above
Criteria for a RBBB
QRS > 0.12s
M-shaped RR’ in V1***
Wide S wave in Lead I and V6***
(ST-T waves opposite of terminal portion of QRS)
Why do we see a RR’ (“rabbit ears”) QRS complex in V1 with RBBBs?
LV depolarizers normally but RV is delayed, represented by the R’ in the leads over the RV
When might you see a RBBB?
Coronary artery disease
Pulmonary embolism
What will you see on the EKG in RBBB with abnormal ST-T changes?
T wave oriented in SAME direction as terminal QRS forces in limb leads
(Normal ST-T are opposite terminal portion of QRS)
Criteria for LBBB
QRS > 0.12s
Wide R wave in Leads I and V6
QRS complexes shave tall R waves, with prolonged duration and either notched or flattened tops (not true “rabbit ears” like with RBBB)
Leads over RB show reciprocal, broad, deep S waves
Can you diagnose LVH in the setting of a complete LBBB?
Technically no, although some texts cite suggestive criteria
Can you diagnose RVH in the setting of RBBB?
Technically no, although some texts indicate the RVH is likely if the R’ in V1 is >15mm
How do you distinguish a hypertrophied ventricle from a BBB?
If a monophasic R wave is used to diagnose hypertrophy, it can mimic BBB but usually QRS < 0.12s (aka “incomplete BBB pattern”)
When a hypertrophied ventricle takes very long to depolarize, it can mimic a BBB - look for other criteria and clinical correlation
Add “cannot R/O” to your list (but with discretion)
Left or Right BBB:
QRS > 0.12s
Either
Left or Right BBB:
Tall, prolonged R waves that may be notched or flattened on top
LBBB
Left or Right BBB:
RR’ (M-shaped) in V1 or V2
RBBB
Left or Right BBB:
Wide R waves in Lead I and V6
LBBB
Left or Right BBB:
Wide S waves in Lead I and V6
RBBB
Left or Right BBB:
ST-T waves oriented opposite direction to terminal QRS forces
RBBB
What are hemiblocks?
Occur when one of the fascicles of the LBB is blocked
• Anterior fascicle
• Posterior fascicle
• (Septal fascicle)
Can you get a hemiblock off of the RBB?
No - RBB does not divide into separate fascicles
What is the key to detecting a hemiblock?
A change in the QRS axis, but the QRS duration is NOT prolonged (unless there is a concomitant RBBB)
A left anterior hemiblock (LAFB) will result in what axis?
LAD
A left posterior hemiblock (LPFB) will result in what axis?
RAD
Left anterior hemiblocks are characterized by…
Conduction blockage down the left anterior fascicle —> mean axis directed up and to the left
Result is a STRONG LAD (pathological: -45˚ to -90˚)
How do you recognize Left Anterior Hemiblock on EKG?
STRONG LAD
Tall R waves in Lead I
Deep S waves in Lead III
Usually normal QRS duration (< 0.12s)
Characteristics of a left posterior hemiblock
Blocked conduction down the posterior fascicle
Mean axis is directed down and to the right
How to recognize a left posterior hemiblock on EKG
STRONG RAD (≥ +120˚ to +180˚)
Tall R waves in Lead III
Deep S waves in Lead I
Usually normal QRS duration (<0.12s)
What do you need to r/o when considering a diagnosis of left posterior hemiblock?
Cor pulmonale
Pulmonary HTN
Which is more common - LAHB or LPHB?
LAHB
LPHB may be difficult to diagnose without …
Prior ECGs
Must r/o RVH or anterior infarction
What is a Bi-fascicular block?
RBBB plus either LAHB OR LPHB
Will see features of RBBB plus frontal plan features of the fascicular block (axis deviation)
• RBBB + LAHB —> LAD
•RBBB + LPHB —> RAD
When the QRS is prolonged without features of either RBBB or LBBB, this is called…
Nonspecific intraventricular conduction delay (or defect)
QRS > 0.12 s indicates slowed conduction but criteria for specific BBB or fascicular blocks not met
Causes of nonspecific IVCDs
Ventricular hypertrophy (esp LVH)
Myocardial infarction (peri-infarction blocks)
Certain antiarrhythmic drugs (ie quinidine, flecainide)
Hyperkalemia
Paced complexes
What is a Pre-excitation syndrome?
Accessory conduction pathways that sometimes exist between atria and ventricles
• WPW: Bundle of Kent
• LGL: James fibers
These bypass AV node and bundle of His and allow early depolarization of ventricles
Results in a SHORT PR interval
What is Wolff-Parkinson-White (WPW) Syndrome?
AV pathway - Bundle of Kent
Short PR interval (<0.12s) and wide QRS, with Delta wave seen in some leads
Patients with WPW syndrome are vulnerable to …
PSVT
Short PR interval
Wide QRS
Delta wave in some leads
Wolff-Parkinson-White (WPW) Syndrome
AV pathway = Bundle of Kent
What is Lown-Ganong-Levine (LGL) Syndrome?
Intranodal accessory pathway (James fibers)
PR interval short (<0.12s) and normal QRS complex
Absence of delta waves
Short PR interval
Normal QRS with no delta waves
Intranodal accessory pathway
Lown-Ganong-Levine (LGL) Syndrome
