ECG Conduction Disturbances And Hypertrophy

Question 1

What is an AV block?

Answer 1

A block in the cardiac conduction system that causes a disruption of atrial to ventricular electrical conduction

Question 2

What are the classifications of AV block?

Answer 2

First, second, and third degree

Question 3

What is a first degree AV block?

Answer 3

P wave precedes QRS complex
PR interval > 0.20 seconds
Minor AV conduction defect with delay at or below AV node

Question 4

What are etiologies for first degree AV block?

Answer 4

Can be a normal variant
Atherosclerosis, HTN, DM
Degeneration of conduction system/fibrosis congenital heart disease
CAD, ischemia
Drugs (BB, digitalis, anti-arrhythmias)
Hypothyroid, hyperthyroidism, adrenal insufficiency
Inflammatory (RF, SLE, MCTD, myocarditis)
Infiltration (amyloidosis, sarcoidosis, hemochromatosis)
Valvular calcification (mitral or aortic)

Question 5

What are the two types of second degree AV block?

Answer 5

Mobitz (Wencke Bach)

Mobitz II

Question 6

What is wenkebach AV block?

Answer 6

Progressive PR interval 
Prolongation prior to dropped QRS 
Grouped beats, narrow QRS complex 
Etiology includes all the things that cause first degree block, digitalis toxicity, ischemic events, myocarditis 
May be seen with inferior AMI
Level of block is at level of AV node

Question 7

What are the etiologies for mobitz type II?

Answer 7

Ischemic heart disease
May be seen with acute anterior MI
Degeneration of conduction system

Question 8

Describe mobitz type II block

Answer 8

PR interval uniform
Dropped beat (QRS), P wave fails to conduct
This block occurs at the level of bundle of His, both bundle branches, fascicular branches
Progressive/irreversible
May be seen with anterior AMI because block is distal to AV node
Worse prognosis

Question 9

What is a third degree heart block?

Answer 9

P waves never related to QRS complexes s
Two independent rhythms (AV dissociation); no P waves conduct to the ventricle
Can occur above or below AV node

Question 10

What is it called when a third degree block occurs above the AV node?

Answer 10

Junctional rhythm (narrow QRS) 
Rate 40-55

Question 11

What is it called when the third degree block occurs below the AV node?

Answer 11

Ventricular pacemaker
Wide QRS
Rate 20-40

Question 12

What it the etiology for a third degree block?

Answer 12

Ischemic
Infiltrative diseases
Cardiac surgery (bypass, valve replacement, myocarditis, degenerative)

Question 13

What are common features of a bundle branch block?

Answer 13

Wide QRS complex (.12 sec or greater)
ST segment (T wave slope off in opposite direction to QRS)

Question 14

Left bundle branch block tends to occur with which conditions?

Answer 14

HTN, ischemia, aortic stenosis, cardiomyopathy

Question 15

Describe LBBB with LAD

Answer 15

More myocardial dysfunction
More disease in conduction system
Maybe higher mortality

Question 16

Describe LBBB with RAD

Answer 16

Think congestive cardiomyopathy

Question 17

What is a hemiblock?

Answer 17

Term for blockage of one of two main divisions of left bundle branch
Can be left anterior or posterior hemiblock

Question 18

Which hemiblock is more common?

Answer 18

Left anterior hemiblock

Question 19

What is the etiology for LAH?

Answer 19

Disease in conduction system

Often associated with MI (left anterior descending occlusion)

Question 20

What is the criteria for a LAH?

Answer 20

Left axis deviation (usually > -60 degrees)
Small Q in leads I and AVL
Small R in leads II, III and AVF
Usually normal QRS duration

Question 21

What is the etiology for LPH?

Answer 21

Disease in conduction system

Question 22

What is the criteria for a LPH?

Answer 22

Right axis deviation usually > +120 degrees 
Small R in leads I and AVL
Small Q in leads II, III and AVF
S1Q3 (s in I and Q in III) 
No evidence of RVH

Question 23

What are causes of atrial enlargement?

Answer 23

Increase in volume of blood in the chamber
Increase in resistance to blood flow out of the chamber
Volume overload or diastolic overload (dilation)
Pressure overload or systolic overload (causes hypertrophy)
Good leads I, II, III and V1
RA activated first, LA activated later

Question 24

What is right atrial enlargement associated with?

Answer 24

TV disease or pulmonary HTN

COPD, PE, MS or MR are causes of pulmonary HTN

Question 25

Describe left atrial enlargement

Answer 25

P-mitrale “M” signs to P wave, broad notched P wave duration .11 s and amplitude of terminal negatively directed portion in V1 to greater than .1mV or 1mm deep and 0.04s with sight axis of P wave
Cause include MS or MR

Question 26

Describe left ventricular hypertrophy

Answer 26

MCC is HTN
Other causes include AS, AI, hypertrophic cardiomyopathy and coarction of aorta
Wall of the LV is thicker so impulse will take longer to traverse it and arrive at epicardial surface
Voltage and interval of QRS complex will increase, producing deeper S waves over RV and taller R waves over LV

Question 27

Describe right ventricular hypertrophy

Answer 27

Causes include chronic lunch disease such as COPD, RVOT obstruction, VSD
Congenital causes include tetralogy of fallot, pulmonic stenosis, transposition of great vessels
Mitral stenosis, tricuspid regurgitation
R:S ratio greater than 1

Question 28

What are some clues to RVH?

Answer 28

RAD +90 or more 
R in V1 7mm or more 
R in V1 + S in V6 10mm or more 
R/S ratio in V1 >1 or more 
S/R ratio in V6 >1 or more 
Late intrinsicoid deflection in V1 (.03 or more) 
Incomplete RBBB 
ST-T strain pattern in II, III, AVF