ADVANCED ECG INTERPRETATION

Posted by e-Medical PPT Monday, August 6, 2012
Quick and Easy AXIS DETERMINATION
Left axis deviation - negative QRS in lead AVF
Right axis deviation - negative QRS in lead I
Severe Right axis deviation negative QRS in BOTH lead I and AVF

Why do we care about axis determination in the ER?  
Left axis deviation(LAD) :  LBBB, LAFB, Mechanical shift due to ascites or elevated diaphragm, left atrial hypertrophy
Right axis deviation(RAD) : RBBB, LPFB, right ventricular hypertrophy, dextrocardia, Pulmonary Embolism
Both RAD and LAD can be caused by COPD, Hyperkalemia, MI, WPW

Right Bundle Branch Block
QRS more than 0.12 sec
Predominantly positive rSR’ in V 1-2
Wide slurred S in lead I
Left bundle branch block (Both fascicles are blocked)
QRS more than 0.12 sec
Deep S in V 1-3
Tall R and RsR’  in lateral leads: I, AVL, &  V 5-6 

AV-BLOCKS
1st degree - PR > 0.2 sec
2nd degree
Mobitz I (Wenckebach) PR increases until a QRS is blocked
Mobitz II - blocked QRS (2:1, 3:1, 4:1)
PR interval is fixed and usually normal, then p-waves with dropped beats
3rd degree - disassociation of PP and RR, the PP intervals and RR intervals are constant

TYPES OF DYSRHYTHMIAS
Re-entry (SVT, WPW)
Two parallel pathways with different rates and refractory periods
Something alters the refractory period and the alternative pathway becomes dominant
This causes a unidirectional conduction block, and a circuitous conduction pathway forms.

Enhanced or Triggered  (PACs, PVCs, Afib, MFAT)
Conduction cells act as Pacemaker cells 
Conduction cells can be enhanced and become dominant in the setting of ischemia, sepsis, electrolyte imbalance or toxins.
Some dysrhythmias start with enhanced or triggered activity, but follow a circuitous pathway seen in re-entry.  (Atrial flutter, Vtach)
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