Heart Block Flashcards
Define 1st degree heart block
PR interval >200ms (5 small squares)
marked 1st degree heart block is PR interval >300ms (7.5 small squares)
List causes of 1st degree heart block
1) Inferior MI (RCA or LCX)
2) AV nodal blocking drugs
1. digoxin
2. amiodarone
3. beta-blockers
4. calcium channel blockers
3) Hyperkalemia
4) Hypokalemia
5) Myocarditis
6) Increased vagal tone e.g. atheletes
7) Normal variant
What is the clinical significance of 1st degree heart block?
1) No hemodynamic disturbance
2) Therefore no treatment required
Define 2nd degree heart block
1) Intermittent non-conducted p waves
2) Divided into Mobitz type 1 and 2
1. Type 1 –> progressive prolong PR interval
2. Type 2 –> fixed prolong PR interval
Outline the features of 2nd degree heart block Mobitz Type 1 (aka Wenckebach Phenomenon)
1) Progressive prolong PR interval culminating in non-conducted P wave (therefore rmb 2 components!!!)
1. Progressive prolong PR interval
2. non-conducted P wave (not needed for diagnoses
but helps support!!!)
2) PR interval longest just before dropped beat
3) PR interval shortest just after dropped beat
4) PP interval remains constant
5) RR interval progressively shortens w/each beat
6) QRS complexes cluster into groups separated by short pauses
http://lifeinthefastlane.com/ecg-exigency-016-2/
What is the mechanism of 2nd degree heart block Mobitz Type 1?
1) Reversible conduction block at AV node
- malfunctioning AV nodes progressively fatigue until they fail to conduct an impulse
- differs from His-Purkinje system where failure is sudden and unexpected producing Mobitz Type 2 block
List causes of 2nd degree heart block Mobitz Type 1
1) Inferior MI (RCA or LCX)
2) AV nodal blocking drugs
1. digoxin
2. amiodarone
3. beta-blockers
4. calcium channel blockers
3) Myocarditis
4) Post cardiac surgery e.g. mitral valve repair
5) Increased vagal tone e.g. athletes
What is the clinical significance of 2nd degree heart block Mobitz Type 1 ?
1) Benign rhythm causing minimal hemodynamic disturbance
2) Low risk of progression to 3rd degree heart block
3) Asymptomatic patients require no treatment
4) Symptomatic patients respond to atropine
5) Permanent pacing usually not required
Outline the features of 2nd degree heart block Mobitz Type 2
1) Absent progressive prolong PR interval i.e. PR interval constant
2) P waves march through at constant rate
3) Some P waves are not conducted
4) PP interval remain constant
What is the mechanism of 2nd degree heart block Mobitz Type 2?
1) Conduction failure at level of His-Purkinje system below level of AV node –> sudden unexpected conduction failure
2) More likely due to structural damage to conducting system as opposed to functional suppression of AV conduction seen in Mobitz type 1
3) Associated w/LBBB or bifascicular block
4) Location of conduction block varies
1. 75% below bundle of His –> broad QRS
2. 25% in bundle of His –> narrow QRS
5) May or may not have pattern to conduction blockade
1. Not all has 2:1 or 3:1 pattern
List the causes of 2nd degree heart block Mobitz Type 2
1) Inferior MI (RCA or LCX)
2) AV nodal blocking drugs
1. digoxin
2. amiodarone
3. beta-blockers
4. calcium channel blockers
3) Hyperkalemia
4) Myocarditis
5) Post cardiac surgery e.g. mitral valve repair
6) Infiltrative/fibrosis of conduction system
1. Amyloidosis
2. Sarcoidosis
3. Hemochromatosis
4. Lenegre’s disease
5. Lev’s disease
What is the clinical significance of 2nd degree heart block Mobitz Type 2
1) More likely than Mobitz Type 1 to be associated w/hemodynamic compromise
2) Risk of severe bradycardia
3) Risk of progression to 3rd degree heart block
4) Risk of sudden onset hemodynamic instability causes sudden and unexpected syncope (Stokes-Adams attack)
5) 35% risk of asystole per year –> risk of sudden cardiac death
6) Requires immediate admission for
1. cardiac monitoring
2. temporary pacing
3. permanent pacemaker
