AV blocks (Johnston) Flashcards
AV block
-A block in the cardiac conduction system that causes disruption of atrial-to-ventricular electrical conduction
PR interval is
-from the ONSET of the P wave to end of P wave (just prior to upstroke of QRS complex)
Normal PR interval is
0.12-0.20 seconds
Characteristics of First degree AV block
- P wave precedes QRS complex!!! but PR interval, although uniform is >0.2 sec
- PR interval is fixed but prolonged (>0.2 sec)
- Minor A-V conduction defect with delay at or below A-V node
- PARTIAL block only
*(each small square is 0.04 seconds; each big square is 0.2 seconds so 1st degree AV block if PR >5 small boxes)
Etiology of 1st degree AV block
- Atherosclerosis, HTN, Diabetes
- Degeneration of conduction system/FIBROSIS congenital heart disease (CHD)
- CAD–ischemia
- Drugs
- Endocrine
- Infiltrative
- Valvular calcification (mitral, aortic)
Drugs associated with 1st degree AV block
- B-blocker
- CCB
- Digitalis
- Antiarrhythmias (class I & III)
Endocrine disorders associated with 1st degree AV block
- Hypothyroid
- Hyperthyroid
- Adrenal insufficiency
Inflammatory conditions associated with 1st degree AV block
- RF
- SLE
- MCTD
- Myocarditis
Infiltrative conditions associated with 1st degree AV block
- Amyloidosis
- Sarcoidosis
- Hemochromatosis
Intermittent claudication means
-symptomatic discomfort/pain usually due to an atherosclerotic occlusive disease of vessels in lower extremityu
Low amplitude of QRS complex less than 5mm (low voltage QRS) indicates
- Lung disease!
- Obstructive lung disease-COPD, asthma, Pulmonary HTN
- Hyperinflation of lungs, increased A-P diameter
Hypokalemia in EKG is seen as
-Prominent U waves, flattening of T wave
Hyperkalemia in EKG is seen as
-Peaked T waves, widened QRS complex, absence of P wave (with higher potassium levels)
Epigastric burning, belching diaphoresis can frequently be seen in
- inferior or diaphragmatic surface of heart attacks
- affects inferior wall of heart
- characterized by heightened vagal tone–nausea, vomiting
Lightheadedness can be caused by
-Bradycardia
Symptomatic vs asymptomatic bradycardia treatment
- Asymptomatic–leave alone
- Symtomatic = ATROPINE!!
ST-T changes suggesting early ventricular depolarization symptoms
-usually asymptomatic!
Inferior wall MI associated with what symptoms
- HIEGHTENED VAGAL TONE–epigastric burning, GI manifestations
- Bradycardia–highetened vagal tone slows down the heart
- Diaphoresis
- Levine’s sign–patient puts hand over sternum due to chest pain
2 types of Second Degree AV block
- Mobitz I (Wenckebach)
- Mobitz II
Mobitz I (Weckebach) is characterized by
- Progressive PR-interval prolongation Prior to Dropped QRS
- “Grouped beats”
- Progressing lengthening results from earlier arrival in relative refractory period of A-V conduction
- Implies impairment of A-V conduction (A-V node)
- Transient
- Level of block is at level of AV node
- Narrow QRS complex
Etiology of Mobitz I
- All things that cause 1st degree AV block
- Digitalis toxicity
- Ischemic events–INFERIOR MI!!!
- Myocarditis
Sequence of events seen in Mobitz I 2nd degree AV block
- Progressive lengthening of PR interval with intermittent dropped beats:
1) Good rapid cond. across AV node, normal PR interval
2) Conduction less good, PR longer
3) Conduction even worse; even longer PR interval
4) Conduction fails so QRS is dropped
5) AV node recovers so PR is normal again
Acute inferior MI is associated with ST elevation in what leads??
-II, III and AVF
Etiology of 2nd degree AV Block Mobitz Type II
- Ischemic Heart disease
- Maybe seen with acute ANTERIOR MI because block is DISTAL (below) TO AV NODE
- Degeneration of conduction system
Characteristics of 2nd degree Av Block Mobitz Type II
- PR interval uniform
- Dropped beat (QRS) bc P wave fails to conduct
- Occurs at the level of: Bundle of His, Both Bundle branches, Fascicular branches (aka BELOW/DISTAL to AV node)
- Progressive/Irreversible
- WORSE prognosis than Mobitz Type I
Name the disorder based on the following EKG findings:
- AV block at the level of bundle of His or at bilateral bundle branches or trifascicular
- PR intervals do NOT lengthen
- Sudden dropped QRS without prior changes/lengthening
-Mobitz Type II Second Degree AV block (Non-Wenckebach)
“High” vs “Low” AV block: site of block
- High= Crest of AV node
- Low: Bundle of His, Bilateral bundle branch or trifascicular
“High” vs “Low” AV block: Type of escape rhythm
- High: Junctional escape rhythm, Narrow QRS, Adequate rate (40-55)
- Low: Ventricular escape rhythm, Wide QRS, Inadequate rate (20-40); danger of systole or ventricular tachycardia
“High” vs “Low” AV block: underlying pathology
High (assoc with mobitz I): Right CAD, diaphragmatic infarction, edema around AV node
Low (assoc with Mobitz II): LAD CAD, large anteroseptal infarction or chronic degeneration of conduction system
“High” vs “Low” AV block: rhythm before complete block
- High: preceded by Mobitz I (Wenckebach) 2nd degree AV block
- Low: Preceded by Mobitz II 2nd degree AV block
What do you see in a Left Bundle Branch block?
-Leads I, II, V5 and V6 look similar
Third Degree Heart Block (complete heart block) characteristics
- P waves NEVER related to QRS complexes
- Two independent rhythms: (AV Dissociation)–no P waves conduct to ventricle
- Can occur above OR blow AV node:
- Above: Junctional rhythm (narrow QRS rate 40-55)
- Below: Ventricular pacemaker, wide QRS (rate 20-40)
Etiology of 3rd degree Heart Block
- Ischemic
- Infiltrative diseases
- Cardiac surgery: by-pass, valve replacement, myocarditis, degenerative
In a complete 3rd degree AV block, when the conduction of supra ventricular depolarizations to the ventricles is completely blocked, what happens?
- An automaticity focus escapes to pace the ventricles at its inherent rate
- Junctional focus: normal (narrow) QRS, ventricular rate 40-60
- Ventricular focus: PVC like QRS, ventricular rate 20-40
How do you treat a 3rd degree AV block
-Pacemaker!
On every ECG, check
- PR interval: increased consistently in 1st degree AV block, Progressively increases with Wenckebach, Totally variable in 3rd degree block, decreased in WPW and LGL syndromes
- P without QRS response: Wenckebach and Mobitz II AV blocks; 3rd degree blocks=independent
