ECG Conduction Disturbances And Hypertrophy Flashcards
What is an AV block?
A block in the cardiac conduction system that causes a disruption of atrial to ventricular electrical conduction
What are the classifications of AV block?
First, second, and third degree
What is a first degree AV block?
P wave precedes QRS complex
PR interval > 0.20 seconds
Minor AV conduction defect with delay at or below AV node
What are etiologies for first degree AV block?
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)
What are the two types of second degree AV block?
Mobitz (Wencke Bach)
Mobitz II
What is wenkebach AV block?
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
What are the etiologies for mobitz type II?
Ischemic heart disease
May be seen with acute anterior MI
Degeneration of conduction system
Describe mobitz type II block
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
What is a third degree heart block?
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
What is it called when a third degree block occurs above the AV node?
Junctional rhythm (narrow QRS) Rate 40-55
What is it called when the third degree block occurs below the AV node?
Ventricular pacemaker
Wide QRS
Rate 20-40
What it the etiology for a third degree block?
Ischemic
Infiltrative diseases
Cardiac surgery (bypass, valve replacement, myocarditis, degenerative)
What are common features of a bundle branch block?
Wide QRS complex (.12 sec or greater) ST segment (T wave slope off in opposite direction to QRS)
Left bundle branch block tends to occur with which conditions?
HTN, ischemia, aortic stenosis, cardiomyopathy
Describe LBBB with LAD
More myocardial dysfunction
More disease in conduction system
Maybe higher mortality
Describe LBBB with RAD
Think congestive cardiomyopathy
What is a hemiblock?
Term for blockage of one of two main divisions of left bundle branch
Can be left anterior or posterior hemiblock
Which hemiblock is more common?
Left anterior hemiblock
What is the etiology for LAH?
Disease in conduction system
Often associated with MI (left anterior descending occlusion)
What is the criteria for a LAH?
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
What is the etiology for LPH?
Disease in conduction system
What is the criteria for a LPH?
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
What are causes of atrial enlargement?
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
What is right atrial enlargement associated with?
TV disease or pulmonary HTN
COPD, PE, MS or MR are causes of pulmonary HTN
Describe left atrial enlargement
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
Describe left ventricular hypertrophy
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
Describe right ventricular hypertrophy
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
What are some clues to RVH?
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
