Johnston Conduction Disturbances & Hypertrophy of Atria and Ventricle Flashcards
What is an AV block?
- block in cardiac conduction system that causes a disruption of atrial to ventricular electrical conductioni
What is the criteria for a first degree AV block?
- PR interval more than 0.20 sec
- P wave precedes QRS
- Minor AV defect with delay at or below AV node
What causes a 1st degree AV block?
- Atherosclerosis
- Htn
- Diabetes
- FIbrosis
What is happening, what is rate and rhythm?
Sinus Bradycardia
PR interval= 7x .04= 0.8 so first degree AV block
What is Mobitz I (Wenchkenbach) 2nd degree AV block?
- Progressive lengthening of PR interval, prolongation prior to a dropped QRS
- Grouped beats
- Progressive lengthening of the PR interval results from earlier arrival in relative refractory period of the AV conduction
Etiology of Mobitz I?
- All things that cause 1 AV block
- Digitalis toxicity
- Ischemic events particularly Inferior MI
- Myocarditis
What will a QRS complex look like on a second degree AV block Mobitz type 1?
Narrow
What is this
- Inferior wall MI-ST elevations
- Lead 2 rhythm strip on the bottom has 4 beats followed by dropped QRS
- Each PR interval before the dropped beat is longer and longer
- Mobitz I 4:3 (4 atrial beats to 3 ventricular beats)
What is Mobitz type II 2nd degree AV block is seen with what? What is the prognosis and why?
- Seen in anterior wall infarctions
- Worse prognosis than Mobitz I
- Because the block is distal to AV node
- occurs at bundle HIS
- both bundle branches
- Fascicular branches
What happens with the PR interval on Mobitz II?
- It is normal, there is no prolongation before dropping a QRS, it occurs randomly
What is third degree heart block? What is the solution if it is sustained? Where does it occur?
- aka complete heart block
- P waves don’t relate to QRS, two independent rhythms are present
- pacemaker is solution
- Can occur above or below AV node
Where does 3rd degree heart block occur and what is the rate of each? What do QRS complexes look like?
- Above has a junctional rhythm with narrow QRS rate of 40-55
- Below AV has ventricular pacemaker with a wide QRS and rate of 20-40
what is happening?
- complete heart block
- Independent atrial activity
- junctional escape rhythm bc QRS is narrow and rate is in 50’s
- P waves are at rate of 125
what is this?
1 AVB
What are the characteristics of bungle branch blocks?
- Wide QRS complex greater than three small squares 0.12 seconds
- ST segment has T waves sloping off in opposite direction to the QRS
What leads do you look at for a right bundle branch block?
V1
AVL
V6
V2
Morphology of leads for a RBBB?
R, S, Rprime
Complete right bungle branch block
Wide QRS
What is happening
- lead 1 deep S wave and similar on AVL and V6
- RSR’ on V1 and widening on V2
- Complete RBBB
What is LBBB?
- Q wave is missisng
- Should be seen in V5 and V6 but not there
- monophasic R, wide RS
What leads do you look at for LBBB
Leads I
and AVL
V1 and V6
What is a Hemiblock?
- Blockage of one of two main divisions of the left bundle branch
What type of hemiblock is more common?
Left anterior hemiblock (LAH)
Criteria for left anterior hemiblock (fascicular) block?
- Left axis deviation, usually >-60
- Small Q in leads I and AVL
- Small R in II, III and AVF
- Increased QRS voltage in limb leads