AV Block, BB Block, Hemi Block, Hypertrophy - Johnston Flashcards
(92 cards)
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
