AV Blocks - EKGs Flashcards
An AV blocks causes what on the EKG?
Missing or delayed QRS following a normal P wave
1º AV Block - EKG
- Sinus rhythm
- Uniform PR delay each time
- PR interval > 0.2 sec (1 big box)
How to measure PR interval?
Start of P to start of QRS
Most common cause of 1º AV block
Atherosclerosis (ischemia) –> conduction degeneration/fibrosis
List the first 9 big boxes for calculating HR
300, 150, 100, 75, 60, 50, 43, 38, 33
Diagnosing low QRS voltage
Average total height of QRS in 1,2,3
Causes of low QRS voltage
Hypothyroid, chronic COPD, pericardial effusion, obesity, amyloid deposit
Leads to look for infarctions (ST depressions/elevations)
2, 3, F = inferior wall (RCA)
1, L = lateral wall (LCX)
V1-V6 = septum/apex (LAD)
AV block would most likely be associated with which type of infarction? Why?
Posterior/inferior wall (RCA) - 2, 3, AVF
- LOCATION OF CONDUCTION SYSTEM
Primary AV block (via MI) is classically associated with what cardiac change?
Heightened vagal tones –> sinus bradycardia (slow HR)
2 types of Secondary AV block
Mobitz 1 (Wenckebach) Mobitz 2
Mobitz 1 (Wenckebach)
- Progressively longer PR-intervals
- Eventually a dropped QRS
- “Grouped beats”
How to remember causes of Mobitz 1?
Same causes as 1º AV block
A Mobitz 1 (Wenckebach) signifies a problem where?
AV node
3 MAIN causes of Wenckebach
- Digitalis toxicity
- Inferior MI
- Myocarditis
What causes the eventual dropped beat in Wenckebach?
SA nodal impulse reaches AV node closer and closer after the AV refractory period, until eventually the refractory period causes a dropped beat
4:3 Wenckebach
Every 4 P waves = 3 QRS’s (4th one dropped)
Causes of Mobitz type 2
- Ischemic heart disease
- ANTERIOR MI (LAD)
Mobitz type 2 - EKG
- Uniform PR intervals throughout
- Eventual dropped QRS
A Mobitz 2 signifies a problem where?
BELOW the AV node (bundle, BBs, fascicular branches)
Progression/prognosis of Mobitz 1 vs. Mobitz 2
1 = transient, ok prognosis 2 = progressive, irreversible, BAD prognosis
See dropped QRST beats + ST elevation (precordial leads)
Anterior MI –> Mobitz type 2 2º AV block
“Escape rhythm”, QRS, rate in Mobitz 1 vs. Mobitz 2
Mobitz 1 – Junctional, narrow QRS, adequate rate
Mobitz 2 – Ventricular, wide QRS, inadequate rate
3º AV block - EKG
- Independent atrial and ventricular rates (A-V dissociation)
- Count p wave rate vs. QRS wave rate
2 types of 3º AV block
Junctional rhythm (narrow QRS, normal/slow rate) Ventricular rhythm (wide QRS, too slow rate)
Junctional vs. Ventricular rhythms
J = external pacemaker ABOVE the AV node V = external pacemaker BELOW the AV node
Main cause of 3º Heart Block
Ischemia (MI, etc.)
How to treat 3º Heart Block?
Pacemaker
On EVERY ECG, check what 2 things?
- PR interval (multiple)
- P to QRS relationship
