6 Bradycardia/conduction disturbances Flashcards
What are some clinical patterns of SA dysfunction?
- sinus bradycardia
- sinus pauses
- bradycardia-tachycardia syndrome
Define sinus bradycardia. What symptoms would a patient experience?
- Rate <60 bpm
- P waves separated by > 5 big boxes (1 sec)
- Nonspecific symptoms; fatigue, listlessness, dyspnea, worsening CHF
Define a sinus pause. When are they symptomatic?
- An abrupt pause in SN activity and associate atrial activity
- Pauses >3 seconds (not occuring during sleep) may result in symptoms
- patient often complains of headache/syncopy
What is brady/tachy syndrome? What are some common causes?
- Concomitant intermittent atrial arrhythmias (such as AF) and sinus pauses or bradycardia when in SR
- Causes:
- AF/SN dysfunction in the elderly (from atrial fibrosis associated with advancing age)
- Drugs used to treat AF may produce SN dysfunction and associated bradycardia
How do you often treat brady/tachy syndrome?
Drugs (such as Ca blockers) to treat tachy
PLUS pacemaker implantation to prevent worse brady
When will you not see a P wave?
When the signal originates below the AV node (e.g. junctional escape rhythm)
What are the 3 forms of complete (3rd degree) AV block?
- Complete block in the upper AV node, leaving junctional foci to escape and pace the ventricles
**stable junctional escape (40-60 bpm) - Complete block of the entire AV node or in the His bundle leaves only a ventricular focus to pace
**unstable ventricular escape (>20-40bpm) - Below the His bundle, all paths are completely blocked so a ventricular focus escapes
**unstable ventricular escape (>20-40bpm)
Define 1st degree AV block
- AV conduction delay only
- Usually mild/no symptoms
- Observe:
- PR prolongation > 0.2 sec (1 big box)
- 1:1 AV relationship (regular rate)
- No dropped beats, no brady
Define 2nd degree AV block
- Intermittent failure of AV conduction
- Some P waves conduct, others are blocked
- Irregular ventricular rate (when beats drop out)
Define 3rd degree AV block
- Also called complete block (no AV conduction)
- Ventricular rate usually regular and unrelated to atrial activity (atria and ventricles beat independently= AV dissociation)
Describe the locations of block commonly seen in 2nd degree block
- AV node (e.g. Wenckebach)
- gradually progressive (PR prolongation -> dropped beats -> complete block)
- usually narrow QRS (not affecting His system)
- accompanied by stable well tolerated junctional escape rhythms (rates 40-60)
- clinically benign
- His-Purkinje (e.g. Mobitz II)
- rapidly and abruptly progressive (occasional dropped beats -> long period of dropped beats -> complete block)
- usually wide QRS >120 ms
- accompanied by unstable and slow ventricular escape rhythms (rate 30-40 or none/asystole)
- clinically malignant
Describe Mobitz type I AV block
- type of 2nd degree AV block
- commonly called Wenckebach block
- progressive PR interval prolongation followed by blocked beat
- the most common form of 2nd degree block
- usually caused by block within the AV node (therefore narrow/normal QRS)
Describe Mobitz type II AV block
- type of 2nd degree AV block
- sudden intermittent loss of AV conduction without preceding PR prolongation
- usually due to infranodal block (within His bundle or BOTH branches…. wide QRS)
- may progress abruptly and unexpectedly to complete heart block
Describe high grade AV block
- type of 2nd degree AV block
- 2 or more consecutive P waves are not conducted (majority of P waves not conducted with occasional conduction)
Contrast junctional and ventricular escape for 3rd degree AV block
- BOTH= AV dissociation
- junctional escape (AV nodal block)
- originates in distal AV node or proximal His
- usually narrow QRS
- well tolerated rate (40-60 bpm)
- ventricular escape (Infranodal block)
- originates in distal conduction system or ventricular myocardium
- QRS is always wide (>120 ms)
- slow rate (20-40 bpm) may be very poorly tolerated
Where does bundle branch block occur?
BEYOND the Bundle of His
In a normal heart beat, how does conduction flow through the bundle branches?
The left bundle usually is activated first (with the right following slightly after)
In left BBB, how does conduction flow through the bundle branches?
The right bundle branch is activated normally… The left ventricle is still activated but not until it receives conduction from the right ventricle (later… left bundle branch not working)
How does left BBB look on EKG?
- wide QRS >0.12 seconds
- broad deep S in V1
- broad R in V6
What are some rules of thumb when determing L/R BBB?
- Left= usually with “divet” at the top of R… NOT “rabbit ears”
- Right= “rabbit ears” or “M pattern” aka RSR’ pattern in V1
In right BBB, how does conduction flow through the bundle branches?
Unilateral conduction through left ventricle (that system works fine… QRS looks normal at the beginning) followed by “round about” slow depolarization of the right ventricle
How does right BBB look on EKG?
- Wide QRS > 0.12 seconds
- RSR’ in V1 (rabbit ears)
- Deep S in V6
Describe left fascicular blocks
- also called “hemiblocks”
- partial block of either anterior or posterior division of the left bundle branch
- characterized by an unexplained left or right axis deviation
Describe a left anterior fascicular block (LAFB)
- late “crawl” of signal to the left shifts the observed heart axis to the left
- can look at other EKG findings but assume LAFB if there’s an unexplained left axis deviation
- Left Anterior think Left Axis
Describe a left posterior fascicular block (LPFB)
- late “crawl” of signal to the right shifts the observed heart axis to the right
- can look at other EKG findings but assume LPFB if there’s an unexplained right axis deviation
- very RARE
