AV Block, BB Block, Hemi Block, Hypertrophy - Johnston Flashcards
Minor AV blocks lengthen the brief pause between atrial depolarization and ventricular 1 and most blocks completely block some (or all) supraventricular impulses from reaching the 2
- depolarizations
2. Ventricles
_ block retards AV Node conduction, prolonging PR interval more than one large sq (.2 sec) on EKG
1st degree block
Demarcate where PR interval starts and ends on an EKG
Starts at the beginning of the P wave and ends at the beginning of QRS complex
The PR interval normally should be less than one large square, which is less than _ seconds
0.2 seconds (2/10)
If you see PR interval elongation only one lead on one EKG, but all the other leads are normal, is AV block indicated?
Yes. Some kind of AV block is present if the PR interval is longer than one large square anywhere on an EKG.
What is a 2nd degree block?
An AV block that allows some degree of atrial depolarization (P wave present) to conduct to the ventricle (Q wave present), while some atrial depolarization are blocked, leaving lone P waves without an associated QRS. There are two general types of 2nd degree block.
What are the two types of 2nd degree blocks and where do they occur?
- Wenckebach (formerly called Type I) = block of AV Nodes
2. Mobitz (formerly Type II) = blocks of Purkinje fibers bindles (bundle of hiss)
Differentiate between Wenckebach and Mobitz blocks on an EKG
- Wenckebach = series of cycle with progressive blocking of AV Node conduction until the final P wave is totally blocked in the AV Node, eliminating the QRS response. Each repeating Wenchebach series has a consistent P:QRS ratio like 3:2, 4:3, 5:4, etc (one less QRS than P waves in series)
- Usually produce a series of cycles consisting of one normal P-QRS-T cycle preceded by a series of paced P waves that fail to conduct through AV Node (no QRS). each repeating Mobitz series has a consistent P:QRS ratio, like 3:1, 4:1, 5:1 , etc
On EKG, Wenchebach gradually prolongs the PR interval in each successive cycle, until the final P wave of the series fails to produce a _ response
QRS
Wenckebach is sometimes caused by _ excess (inhibits the AV Node) or drugs that mimic or induce _ effects.
Parasympathetic
True or false: With Mobitz, every cycle that is missing its QRS has a regular punctual P wave and never a premature P wave.
True
How would you differentiate Wenckebach vs Mobitz 2:1 AV block?
- If the PR interval is lengthened, but the QRS is normal = Wenckebach
- If PR interval is normal but the QRS is widened = Mobitz
To distinguish between Wenckebach vs Mobitz 2:1 block, what clinical maneuver is used?
Vagal Maneuver. Because Wenckebach starts at the AV Node, vagal maneuver will via parasympathetic stimulation, inhibit the AV node, increasing the number of series/cycle to produce 3:2 or 4:3 Wenchebach. But if the 2:1 is mobitz then vagal maneuver either eliminates the block, producing 1:1 AV conduction, or they have no effect.
_ Block is a total block of conduction to the ventricles, so atrial depolarization are not conducted to the ventricles. Therefore, an automaticity focus below the complete block escapes to pace the ventricles at its inherent rate.
3rd degree. Independent Atrial and ventricular rates (A-V dissociation).
what are the 2 types of 3rd degree block?
- Junctional rhythm (narrow QRS, normal/slow)
2. Ventricular rhythm (wide QRS, too slow rate)
What is meant by downward displacement of the pacemaker?
Absence of atrial activity with wide complex bradycardia indicates that neither the SA Node nor supraventricular foci are viable enough to pace the atria. This failure of all automaticity centers above the ventricles.
What are some causes of 1st degree heart block?
- Presence of atherosclerosis, HTN, DM enhances
- Degeneration of conduction system/fibrosis congential heart disease
- CAD-> ischemia
- Drugs - B.B, CCB, digitalis, antiarrhythmias,
- Endocrine: hypo and hyperthyroid, adrenal insufficiency
- inflammatory: RF, SLE, MCTD, myocarditis
- Infiltrative- amyloidosis, sarcoid, hemochromatosis
- Valvular calcification- mitral and aortic
Most common are atheroscelrotic, HTN and DM
How would a patient with 1st degree block present?
usually asymptomatic but on PE you’d see:
- decreased intensity of S1 on auscultation; short, soft, and blowing diastolic murmur at cardiac apex
What are some causes of 2nd degree Wenckebach (mobitz type I) blocks?
-All the causes of type 1 block but in addition and more pronounced: Digitalis toxicity, ischemic events (MI-infrior), and myocarditis.
How would a patient with 2nd degree Wenckebach block present?
- Asymptomatic in most cases
- presyncope
- recurrent syncope
- lightheadedness
- dizziness
- chest pain: only in setting of myocarditis
ON PE: regular, irregular pulse, bradycardia, hypotention, signs of hypoperfusion in severe cases.
If you suspect patient has 2nd degree heart block (wenckebach or mobitz), how would you work them up?
- electrolyte, Ca++ and Mg+
- Check cardiac enzymes (if ischemia is suspected
- myocarditis-related studies (if chest pain is present)
- digoxin levels
what are some causes of Mobitz type II block?
- Ischemic heart disease
- primary fibrotic disease (defect in His-Purkinje system distal to AV Node)
- scar formation from prior infarct (anterior MI(LAD))
- degeneration of conduction system
How would a patient with Mobitz type II block present?
Pts usually presents in an unpredictable manner. It's hard to predict if the block will progress or be transient. - lightheadedness - dizziness -syncope On PE: - regular irregular pulse -bradycardia -hypotension - signs of hypoperfusion
what are some causes of 3rd degree block?
- Congenital
- meds: antiarrhytmics, digoxin
- degenerative disease
- infections
- rheumatic disease
- infiltrative process
- neuromuscular diseas
- ischemia/infarct
- metabolic
- toxins
- Cardiac surgery: bypass, valve replacement, myocarditis, degenerative
How would a person with 3rd degree block present?
Profoundly symptomatic with dyspnea on exertion, syncope lightheadedness, fatigue, severe chest pain, sudden death
What are the physical findings of 3rd degree block?
- irregular, weak pulse
- wide pulse pressure
- cannon A waves
- signs of CHF
- signs of hypoperfusion
- agitations or unease
- tachy
- pale complexion
How is 3rd degree block treated?
- permanent ventricular pacemaker
AV block would most likely be associated with which type of infarction?
Cuz of the location of the conducting system you’d see it with infarction of Posterior/inferior wall (RCA) - Leads 2, 3, and AvF.
What causes the eventual dropped beat in Wenchebach?
SA nodal impulse reaches AV node closer and closer after the AV refractory period, until eventually the refractory period causes a dropped beat.
What is a bundle branch block?
block in right or in the left bundle branches. The blocked BB delays depolarization to the ventricle it supplies.
what is the characteristic look on a EKG for BBB?
widened QRS with two peaks.
(wide QRS >.12 sec or 3 small boxes)
T wave slopes off opposite to QRS
To diagnose a BBB which leads are examined?
Right chest leads (V1, V2)
Left chest leads (V5, V6)
Right BBB produces R,R’ in the _ chest leads,
right. V1 or V2.
If there is a R,R’ in the right chest leads V1 or V2, there is probably a _ BBB
Right
With a BBB, an R,R’ in the left chest leads V5 or V6 means that 1 block is present. The R’ represents 2.
- Left.
2. delayed depolarization of the left ventricle
Occasionally, the R,R’ in V5,V6 will appear only as _ peak with two tiny points in LBBB.
flattened
Occasionally there will be an R,R’ in a QRS of normal duration. This is called _
incomplete BBB
What is intermittent Mobitz?
Simultaneous RBBB and LBBB prevents depolarization from reaching the ventricles; this is a complete AV block. so block of one BB with intermittent block of the other produces intermittent complete AV block.
RBBB plus intermittent LBBB will record on EKG as _ . What about LBBB w/ intermittent RBBB?
continuous RBBB pattern QRS’s with intermittent episodes of complete AV block. (P waves w/o QRS). Same idea for LBBB with intermittent RBBB.
Punctual P wave (no QRS response) — >
2nd AV block; Moitz vs Wenckebach
Premature P’ wave no QRS response —>
non conducting PAB
Missed P-QRS-T cycle —>
SA Node transiently blocked (sinus block)
Generally, where are 1st degree blocks located in relation to the AV Node?
Within the proximity of the AV Node
P wave precedes each QRS complex but PR interval, though uniform is >.2 seconds. This is indicative of _
1st degree block
What is low voltage QRS complex and what is usually due to?
Low voltage QRS complex is when the QRS complexes in Leads I, II, III, avR, avL, and avF are all short (does not exceed 5mm). These are due to pulmonary disorders such as COPD, asthma, etc.
How would 1st degree block be treated?
Would not treat. Look for underlying cause.
In a 1st degree block, does the PR interval get progressively longer or remain consistantly lenghened cycle to cycle?
PR remains consistently lengthened cycle to cycle. It doesn’t progressively get longer.
How is axis deviation determined?
If leads 1 and AvF are both upright then it’s normal axis. If leads 1 is up and AvF is down then it’s Left axis deviation. If lead 1 is down and lead avF is up then it’s right axis deviation
With hypokalemia what kind of wave would you see?
Prominent U wave
With hyperkalemia what kind of wave would you see?
Peaked T waves
ST elevation in lead II, avF, reciprocal depression in leads I and avL indicates _
STEMI (inferior wall MI)
If a patient presents with epigastric pain, belching, diaphoresis and light headedness with significant ECG changes such as an ST elevation in leads II, III and AvF. what the most likely diagnosis? what is the significance of epigastric pain?
This patient most likely having a inferior wall MI (STEMI seen on EKG)
Epigastric pain can be a lot of things, but in this scenario it’s probably cuz of his MI– it’s frequently seen in inferior or diaphragmatic surface of heart attacks. They can come in with heightened vagal tone and so they’ll have waves of nausea, vomiting.
True or false: Mobitz type I is transient most of the type.
True
2nd degree AV block - Mobits type I is often seen with what kind of MI?
Inferior AMI
How does Mobitz type I look on a EKG?
progressive lengthening of PR interval with intermittent dropped beats (missing QRS). the ratio of P waves to QRS is usually: 4:3, 3:2, 2:1. and the cycle repeats.
Mobitz type II has a big association with what kind of MI?
Anterior myocardial infarction particularly involving the LAD
How is Mobitz type II recognized on a EKG?
- Sudden dropped QRS without prior PR lengthening.
- Usually PR interval will be normal length,.
How is a 3rd degree block recognized on an EKG?
- P waves never related to QRS complexes.
what are the two escaped rhythm seen with 3rd degree block?
- Above the AV node: junctional rhythm with narrow QRS (rate 4-55)
- Below the AV node: Ventricular pacemaker wide with wide QRS (rate 20-40)
How is a 3rd degree block recognized on a EKG?
- No relationship between P and QRS.
- Atria ventricle depolarize independently.
- you’ll see escaped rhythms either junctional or ventricular. If it’s juncitonal then QRS would be less frequent 40-55/min but normal-to narrow in shape. If it’s ventricular rhythm then QRS will be wide and even more less frequent 20-40/min
what is intrinsic deflection and where it commonly seen?
Time lapse from beginning of the QRS to the peak of the R wave. Seen in BBB and hypertrophy/dilated heart
On a EKG what are some common features of a BBB?
- wide QRS complex (.12 sec or greater 3sq or more)
- ST segment- T wave slope off in opposite direction to QRS
What are the criteria to recognize a BBB on an EKG?
- deep S wave (in V5 V6 for RBBB; in V1 and V2 for LBBB))
-
- Deep S wave in Lead I and avL, V5 and V6;
- Wide QRS in V1, V2
- ST depression
What is the KEG diagnosis?
RBBB
No septal Q wave (V5, V6)
Deep QRS in V1 V2 what is the EKG diagnosis?
LBBB
What are some causes of LBBB?
- HTN
- Ischemia
- Aortic stenosis
- cardiomyopathy
what is the implication of LBBB with LAD?
- more myocardial dysfunction
- more disease in conduction system
- Maybe higher mortality
LBBB with RAD is associated with _
Congestive cardiomyopathy
In LBBB, leads I and avL usually have features of which other lead?
V6
T wave changes is common with BBB, usually polarity is opposite of QRS direction. If T wave polarity is in the same direction of the QRS, it is called 1 and is due to 2
- Primary T wave change
2. Ischemia
Absence of Q wave in Led I, and deep QRS in lead V1 is indicative of what EKG diagnosis?
LBBB
No Q wave in V5, V6; wide QRS in Leaves I and AvL; and deep QRS in leads V1-3. These findings are diagnostic of _
LBBB
LBBB is often associated with what valvular disease?
aortic stenosis
A 60 year old man presents with mild dyspnea on exertion (DOE) and has hx of valvular heart disease with HTN. EKG shows Deep QRS in V1-3; absence of Q wave in V5 and V6. What is the EKG diagnosis and what valvular disease is it associated with?
LBBB. Aortic stenosis.
Which fasciular block is more common?
Left anterior hemiblock (LAH)
Explain oreintation of the QRS complex would look in Leads I and AVF for Left anterior hemiblock and left posterior hemiblock
LAH = in I QRS is up, in AvF QRS is down
LPH = in I QRS is down, in avF QRS is up
Explain the EKG criteria for LAH
- Left axis deviation
- small Q in leads I and avL, small R in II, III and avF
- usually normal QRS duration
- Late intrinsicoid deflection in avL
- increased QRS voltage in limb leads
- Deep S waves on II, III and avF can also be seen
Exlain the EKG criteria for LPH
- Right axis deviation
- small R in leads I and avL
- Usually normal QRS duration
- Late intrinsicoid deflection in avF
- Increased QRS voltage in limb leads
- No evidence for right ventricular hypertrophy
what are some causes of LAH?
- disease in conduction system
LAH is often associated with which type of MI?
left anterior descending occlusion –> Anterior MI
What leads should you look at to identify atrial enlargement either hypertrophy or dilation?
Leads I, II, III, and V1
In an right atrial hypertrophy, what are the characteristic EKG findings?
tall, pointed P waves in leads II, III and AVF and greater than .1 mv in leads V1 and V2. Taller in III than in I.
What are the characteristic finding for Left atrial enlargement?
Wide, notched; taller in lead I than in III. (P wave looks like an M)
- 2nd half of P wave is negative in V1 or III
what are some causes of RAE?
_ associated with tricuspid disease or pulmonary HTN
- COPD, PE, MS or MR are causes of pulmonary HTN
What are some causes of LAE?
Mitral stenosis, mitral regurg
Can EKG pattern distinguish between distinguish between concentric hypertrophy and dilated chambers?
No. EKG only sees that the total muscle mass of the ventricles have increased and produces a stronger QRS.
What are the criteria for diagnosing VLH on a EKG?
- R wave in I + S in III > 25mm
- R in AVL > 11mm
- R in V6 > 26mm
what are some causes of RVH?
- chronic lung disease - COPD, RVOT obstruction, VSD
- Congenital: TOF, pulm stenosis, transposition of great vessels
What are characteristic findings of RVH on EKG?
- RAD +90 or more
- R in V1 >7mm
- R in V1 + in V6 > 10mm
- R/S ratio in V1 > 1mm
- S/R ratio in V6 > 1mm
- Late intrinsicoid deflection in V1
- Incomplete RBBB
- ST-T strain pattern in II, III, AVF
What are some causes of dominant R waves in V1?
- RVH
- Posterior or lateral MI
- WPW
- Hypertrophic cardiomyopathy
- Muscular dystrophy
- Normal variant
A 68-year-old man with hypertension, coronary artery disease, and hyperlipidemia presents to his primary care physician for an annual check-up. He reports that he has recently been having repeated episodes of dizziness and light-headedness on a daily basis. As a result, he has significantly reduced his physical activities. Currently, he feels well. His vital signs are HR 52 bpm, BP 130/80 mmHg, RR 11 rpm, T 98.2F. Cardiac exam reveals a bradycardic, regular rhythm with no extra sounds or murmurs. His medications include atorvastatin, aspirin, hydrochlorothiazide, lisinopril, and metoprolol. An ECG showed sinus tachycardia. What is the most appropriate next step in the management of this patient?
- Stop patient’s lisinopril
- Stop patient’s metoprolol
- Prescribe patient atropine
- Ask patient to call if symptoms return
- Initiate transcutaneous pacing
- Stop patient’s metoprolol
This patient’s history and ECG are concerning for sick sinus syndrome, specifically persistent severe sinus bradycardia. All medications that may worsen bradycardia should be avoided.
A 68-year-old male presents to the emergency department with complaints of “a fluttering sensation in the chest”, dizziness, and a syncopal episode earlier today. Vital signs are as follows: T 37.7, HR 40 (irregular), BP 90/56, RR 28, O2 Sat 95% RA. Physical exam is significant for a weak pulse, widened pulse pressure, crackles auscultated at the bilateral lung bases, and cannon a-waves noted at the internal jugular veins. An electrocardiogram is obtained and showed signs of complete heart block. Which of the following is the best next step in the management of this patient?
- No intervention required; discharge and follow-up as outpatient
- Initiate digoxin therapy
- Start IV verapamil
- Temporary pacemaker placement and work-up for potential underlying etiology
- Permanent dual-chamber pacemaker placement
- Temporary pacemaker placement and work up for potential underlying etiology
