Lecture 6 (Intraventricular Conduction Defects) Flashcards
Right atrial enlargement cause
chronic pulmonary diseases may cause it in the response to the need for greater filling pressures in the right ventricles
Left atrial enlargement cause
mitral regurgitation due to blood being forced backwards into the left atria
leads to asses atrial enlargement
II and V1
RAE finding on EKG
increased amplitude of the first part of the p wave
LAE finding on EKG
increased NEGATIVE amplitude in the terminal portion of the p wave in V1 Increased duration or width of the P wave
Ventricular Hypertrophy Causes
caused by chronic poOrly treated HTN-bc there is more muscle to depolarize there is more electrical activity occuring in the hypertrophied muscle
-reflected by changes in amplitude of portions of the QRS complex
Ventricular Hypertrophy general EKG findings
V1 electrode normally positive-wave of depolarization moving through LV mmoving away from electrode
-mainly produces negative QRS complexes (short R with larger S waves)
RVH EKG findings
- most common characteristic in limb leads is RAD
- in precordial leads R waves are more positiv which lie closer to lead V1
LVH EKG findings
- increased R wave amplitude in precordial leads over LV (V5-V6)
- S waves are smaller in leads over LV (V5-V6) but larger in leads over RV (leads V1-0V2)
Bundle Branches
Bundle of His divides into right and left bundle branches
-left bundle branch divides into SEPTAL, ANTERIOR, and POSTERIOR fascicles
Normal QRS complex
narrow
Bundle Branch Block definition
- results in one or both bundle branches failing to conduct impulses
- produces delay in depolarization of the ventricle it supplies
Bundle Branch Block EKG findings
QRS MUST BE >/=0.12s
FOR BBB-RR’ configuration with normal QRS interval is called an “INCOMPLETE BBB”-widened QRS complex-RR’ configuration in chest leads
RR’ configuration in chest leads
- 2 peaks or rabbit ears
- the delayed ventricle is represented by R’
Possible sites of BBB
- RBBB (right bundle branch block)
- LBBB (left BBB)
- LAHB/LAFB (left anterior hemiblock or fascicular block)
- LPHB/LPFB(left posterior hemiblock or fascicular block
- any combination of the above
RBBB Criteria
Main ones: -Prolonged QRS (complete has QRS >0.12s) -M-shaped RR' in lead V1 -Wide S wave in Lead 1 and V6 Others:-LV depolarizes normally but RV is delayed, represented by R'
RBBB seen in
CAD, Pulmonary embolism
Frontal plane QRS axis in RBBB
should be in normal range (0-+90)
ST-T waves in RBBB
normal ST-T waves in RBBB should be oriented opposite to the direction of the terminal QRS forced
LBBB
Main criteria:
-Prolonged QRS
-Wide R wave in leads 1 and V6
Other criteria:
-QRS waves have tall R waves with prolonged duration and either nothced or flattened tops of the complexes
-true rabbit ears are less likely than in RBBB
-Leads over RV show reciprocal, broad, deep S waves
BBB plus LVH or RVH
- NOT POSSIBLE TO DIAGNOSE LVH OR RVH IN THE SETTING OF LBBB(for LVH) or RBBB(for RVH)
- some texts indicate that RVH is likely if the R’ in V1 is >15mm
Hemiblock definition
when one of the fascicles of the LBB is blocked
3 LBB fascicles
anterior, posterior, septal
-septal not involved in hemiblocks
Key to detecting a hemiblock
- CHANGE IN THE QRS AXIS but the QRS DURATION IS NOT PROLONGED, unless there is concomitant RBBB
- the right bundle does not divide into separate fascicles
Left Anterior Hemiblock definition
blocked conduction down the left anterior fascicle
-mean axis is directed up and to the left
Left Anterior Hemiblock EKG findings
- LAD (minus 45-minus 90)*
- tall R waves in leads 1
- Deep S waves in aVf
- Usually normal QRS duration
Left Posterior Hemiblock definition
posterior fascicle is blocks
-depolarization moves downward and to the right
Left Posterior Hemiblock EKG findings
- RAD (>/=+120 TO +180)*
- normal QRS +120)
- no evidence of RVH or anterior infarction
What do you want to do for left posterior hemiblock before diagnosing?
- exclude other causes of RAD: cor pulmonale, pulm HTN etc
- no evidence of RVH or anterior infarction
- LPHB may be difficult to dx w/o prior EKGs
Bifascicular Block definition
- RBBB plus with LAHB or LPHB (LPHB is uncommon)
- features of RBBB plus frontal plane features of the fascicular block-axis deviation
Bifascicular Block EKG findings
- RBBB + LAHB (LAD of -45 to -90)
- RBBB + LPHB (RAD of >+120)
Nonspecific IVCD
-when either QRS IS PROLONGED w/o features of RBBB or LBBB this is called nonspecific intraventricular delay (or defect)
Nonspecific IVCD EKG findings
- QRS duration >0.11s indication slowed conduction of the ventricles
- criteria for specific bundle branch or fascicular blocks not met
Causes of nonspecific IVCD
- Ventricular hypertrophy (esp LVH)
- MI (so called PERIINFARCTION BLOCKS)
- Certain antiarrhythmic drugs (quinidine, flecainide)
- Hyperkalemia
Preexcitation Syndrome
- accessory conduction pathways sometimes exist between atria and ventricles
- Bypass AV node and bundle of His and allow early depolarization of ventricles
- RESULTS IN SHORT PR INTERVAL
Preexcitation Syndrome examples
- WPW:bundle of kent
- LGL: James fibers
Wolff-Parkinson-White Syndrome EKG findings
- PR interval
WPW patients at risk for:
PSVT
Delta Wave
-seen in WPW-sloping upward of PR segment…cannot calculate PR segment
Lown-Ganong -Levine Syndrome
-Intranodal accessory pathway (JAMES FIBERS) bypasses the normal delay in AV node-PR interval
