AV Blocks, BBBs, Hemiblocks, & Hypertrophy Flashcards
A first degree heart block slows the _____ conduction, prolonging the _______ on ECG to more than ______ sec
AV node; PR interval 0.2 (more than one large square)
Note that PR remains consistently lengthened cycle to cycle
Second degree AV blocks allow some P waves to conduct to the ventricles (producing QRS response), while some are blocked —- leaving lone P waves without an associated QRS. What are the 2 types of second degree AV blocks?
Wenckebach (type I) = block occurs in AV node; produce series of cycles with progressive blocking of AV node conduction until final P wave is totally blocked, eliminating QRS response (progressive prolonging of PR interval). Each repeating Wenckebach series has a consistent P:QRS ratio like 3:2, 4:3, 5:4, etc. (one less QRS than P waves in the series)
Mobitz (type II) = block occurs below AV node (Purkinje fibers, His bundle, or bundle branches). Produce a series of cycles consisting of one normal cycle preceded by a series of paced P waves that fail to conduct through AV node (no QRS response). Each repeating Mobitz series has a consistent P:QRS ratio like 3:1, 4:1, 5:1, etc.
What is a 2:1 AV block?
Mobitz second degree AV block in which there is 2:1 ratio of 2 P waves to 1 QRS response
Both Wenckebach and Mobitz have missing QRSs so how can we differentiate between 2:1 Wenckebach and 2:1 Mobitz?
If the PR interval is lengthened, but the QRS is normal = most likely Wenckebach
If the PR interval is normal but the QRS is widened =most likely Mobitz
ECG findings with 3rd degree (complete) AV block
Atria are independently paced by SA node, while (depending on location of block) ventricles are independently paced
[P waves occur independently of the slower paced QRS complexes]
If a complete AV block occurs above the AV junction (i.e., in the upper AV node), then a junctional focus esccapes to pace the ventricles. On EKG, QRS’s appear ______ with a ventricular rate of ______/min
Normal (narrow); 40-60
When a complete AV block occurs below the AV junction, a ventricular focus escapes overdrive suppression to pace the ventricles at its slow inherent rate of only _____/min with _______ QRS’s; so slow that cerebral blood flow is compromised and _____ may ensue
20-40; widened; syncope
Intrinsic vs. extrinsic etiologies of SA node dysfunction
Intrinsic = degenerative, ischemic, inflammatory, infiltrative (e.g., amyloid), or rare mutations in Na+ channel or pacemaker current genes
Extrinsic = drugs like beta blockers, Ca channel blockers, digoxin; autonomic dysfunction, hypothyroidism
Symptoms of SA node dysfunction
Sx are d/t bradycardia (fatigue, weakness, lightheadedness, syncope) and/or episodes of associated tachycardia (e.g., rapid palpitations, angina) in pts with sick sinus syndrome
First degree AV blocks may be normal or secondary to increased _____ tone or drugs (e.g., beta blockers, diltiazem, verapamil, or digoxin)
Vagal (parasympathetic)
Causes of Wenckebach second degree AV block
Seen with drug intoxication (digitalis, beta blockers), increased vagal tone, inferior MI
Does Wenckebach require tx?
Only if symptomatic — can use atropine or temporary pacemaker
T/F: permanent pacemaker is indicated in Mobitz II second degree AV block
True
Autonomic causes of AV block
Carotid sinus hypersensitivity
Vasovagal
Metabolic/endocrine causes of AV block
Hyperkalemia
Hypermagnesemia
Hypothyroid
Adrenal insufficiency
Drug-related causes of AV block
Beta blockers Adenosine Ca chanel blockers Antiarrhythmics (classs I and III) Digitalis Lithium
Infectious causes of AV block
Endocarditis TB Lyme dz Chagas Syphilis Diphtheria Toxoplasmosis
Heritable/congenital causes of AV block
Congenital heart dz
Maternal SLE
Kearns-sayre syndrome
Myotonic dystrophy
Inflammatory causes of AV block
SLE
MCTD
RA
Sceroderma
Infiltrative causes of AV block
Amyloidosis
Sarcoid
Hemochromatosis
Neoplastic/traumatic causes of AV block
Lymphoma Mesothelioma Melanoma Radiation Catheter ablation
Comorbid conditions associated with 1st degree AV block
Atherosclerosis
HTN
Diabetes
What type of AV block is associated with inferior MI vs. anterior MI?
Inferior MI = Wenckebach
Anterior MI = Mobitz (II)
Underlying pathology in Wenckebach vs. Mobitz II AV blocks
Wenckebach: RCA disease, diaphragmatic infarct, edema around AV node
Mobitz II: LAD coronary artery disease, large anteroseptal infarct, chronic degeneration of conduction system
How do you treat 3rd degree AV block
Pacemaker
Characteristic EKG finding of a bundle branch block
Wide QRS with 2 peaks (representing non-simultaneous depolarization of the right and left ventricles)
ST segment — T waves slope off in opposite direction to QRS [if T waves are concordant it suggests ischemia or MI]
With bundle branch block, the QRS is widened to ____ seconds or more
0.12 (or 3 small squares)
If there is a bundle branch block, look at leads ___ and ____, and leads ____ and ____ for the R1R’
V1, V2 (right chest leads); V5, V6 (left chest leads)
If there is an R,R’ in chest leads V1 or V2, there is probably a _____ bundle branch block
Right
A quick trick to figure out what type of BBB there is is to look at V1. If V1 is positive, it is considered ____ BBB; if it is negative, it is ____ BBB
Right; left
In normal ventricular conduction, what is the origin of a small q wave in V5 and V6?
Right ventricular conduction
[v5/v6 is apex of heart; a small Q wave there means that some forces are travelling to RV to depolarize]
Which side of the septum is activated first in RBBB?
Left
In RBBB, why is there an S wave in V6?
V6 is the apex of the heart, S wave is small depolarization of left ventricle
Causes of prominent R wave in V1-V2
Normal Pectus or straight back RV diastolic volume overload WPW syndrome RVH Duchenne dystrophy
LBBB is more apt to occur with what 4 conditions?
HTN, ischemia, aortic stenosis, cardiomyopathy
LBBB with ____ axis deviation may be associated with more myocardial dysfunction, more dz in conduction system, and possibly higher mortality, while LBBB with ____ axis deviation is associated with congestive cardiomyopathy.
Left; right
What are hemiblocks?
The left bundle branch subdivides into anterior and posterior divisions; a hemiblock is a block of either of these divisions
The ______ usually renders blood supply to the SA node, AV node, bundle of His, and a variable twig to the posterior division of the left bundle branch; note that the _____ also sends a variable twig to the posterior division of the left bundle branch
RCA; LCA
A total occlusion of the anterior descending branch of the LCA may cause a subsequent _____ with _____ hemiblock, often associated with ____ axis deviation
RBBB; anterior; left
T/F: with anterior hemiblock, the QRS is widened only to .10 to .12 seconds, but association with other blocks of the bundle branch system will widen the QRS more
True
Anterior hemiblock is a block of the anterior division of the LBB. Finding a _____ in lead I and a wide and/or deep S wave in lead _____ helps to confirm the dx of anterior hemiblock
Q wave; III
[Q1S3]
With right bundle branch block, the mean QRS vector is within the normal range or shows minimal ____ axis deviation
However, when a pt develops a RBBB with _____ axis deviation, this is probably caused by anterior hemiblock, particularly if there is an acute anterior infarct
Right; left
Why are pure, isolated posterior hemiblocks rare?
Posterior division is short, thick, and often has dual blood supply
An inferior infarct may impair the blood supply to the ______ division of the left bundle branch
Posterior
Posterior hemiblocks cause ____ axis deviation due to late, unopposed depolarization forces toward that side.
When posterior hemiblock is suspected, look for deep or unusually wide ____ wave in lead I and ____ wave in lead III to help confirm diagnosis
Right
S; Q
[S1Q3]
A bundle branch block with a hemiblock is called a ______ block
Fascicular
What is a bifascicular block?
Generally refers to RBBB with block of either anterior or posterior division of the left bundle branch
A continuous normal EKG pattern with intermittent wide QRS pattern usually indicates intermittent ______
A continuous normal EKG pattern with intermittent change in QRS axis (e.g., upright QRS’s that transiently change to downward QRS’s) usually indicates intermittent _____
BBB; hemiblock
Lead ____ is directly over the atria, so the ___ wave in that lead is our best source of info about atrial enlargement
V1; P
The chest electrode that records V1 is considered _____ (+ or -)
positive
How do you tell if it is the right vs. the left atrium that is enlarged based on EKG?
If initial component of diphasic P wave in V1 is larger, then it is right atrial enlargement [also, if height of P wave in any limb lead exceeds 2.5 mm, even if not diphasic, it is likely right atrial enlargement]
If terminal portion of diphasic P wave in V1 is large and wide, there is left atrial enlargement
The QRS represents ventricular depolarization, so the QRS should be able to represent presence of ventricular hypertophy. In lead V1, the QRS is primarily ______ (positive or negative), and therefore the ___ wave is usually very short
negative; R
The QRS represents ventricular depolarization, so the QRS should be able to represent presence of ventricular hypertophy. In lead V1, the QRS is primarily negative, and therefore the R wave is usually very short. What changes occur with right ventricular hypertrophy?
QRS appears more positive with large R wave in V1
Also note that the R wave of V1 will get progressively smaller fom V2 to V3 to V4, etc.
[the S wave in lead V1 will be smaller than the R wave in RVH]
With RVH, there is often associated ____ axis deviation
right
What EKG changes occur with LVH?
QRS complexes have exaggerated amplitude (in height and depth), especially in the chest leads (V1-6)
S wave appears even deeper in V1 and there is a large R in V5
There is also left axis deviation
What T wave changes might be present with LVH?
Often T wave inversion and asymmetry
Usually best to check on V5 or V6 (since these are over left ventricle); asymmetry because inverted T wave has gradual downslope and very steep return to baseline
Ventricular strain is usually associated with ventricular hypertrophy, which displays on ECG as depression of the ____ segment
ST
EKG changes with RVH
R waves prominent in V1, V2, with R:S ratio > 1
Deep S waves in V5,V6
Others: RAD + 90degrees+, incomplete RBBB, ST-T strain pattern in II, III, aVF, P pulmonale, S1 S2 S3 pattern (kids)
