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Nur 463 SKM dysrhthmias and critical situations Notes
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Adv. Medsurg Notes– PowerPoint and SK&MChapters 7 & 10 – Cardiac Dysrhythmias and Rapid Response teams/Code Blue
OVERVIEW OF CARDIAC PHYSIOLOGY AND ELECTROPHYSIOLOGY
Physiology
o Specialized cells called pacemaker cells have property of automaticity
Automaticity cells can generate a stimulus or an action potential without outside stimulation
Signal conducted through fibers generates contraction
o Coordinated electrical activity = cardiac cycle
1. Impulse generated from pacemaker cells in RA called SA node
2. Passes through the interndoal tracts and reaches the AV node
Located in the AV junction area between atria and ventricles
o AV node has backup system where they can fire an impulse if they do not
receive an impulse from the SA node
During this time, impulse is slowed for ventricular filling during ventricular diastole (VD)
o Passive ventricular filling – pressure in atria overcomes the pressure of the
valves and the ventricles begin to fill
o Active ventricular filling – atria contract to squeeze blood into ventricles
3. Impulse is conducted through the bundle of His to ventricles through bundle branches
Bundle branches = L + R Bundle branch = made up of purkinji fibers
4. Electrical signal causes atrial systole (contraction) blood ejects into ventricles
Atrial kick – extra push of blood into the ventricles to increase CO
5. Muscle fibers becomes stimulated and cause ventricular systole
During this time atria are relaxed and begin filling with blood
o Break down of mechanical contraction
1. Atrial diastole atrial filling
All valves closed
2. Early atrial systole increase in atrial pressure opens AV valves
Ventricles fill
3. Atrial systole + atrial kick atrial contraction and emptying
Ventricles become filled
4. Early ventricular systole ventricles begin to contract
Pressure closes AV valves
Atria are relaxed
5. Ventricular systoles ventricular contraction
Increased pressure in ventricles
Aortic and pulmonic valves are open
Blood ejected into aorta (LV) and pulmonary artery (RV)
6. Early atrial diastole ventricles are empty and relax
Aortic and pulmonary valves are closed
Cycle repeats from step 1.
THE 12 LEAD EKG
Leads looking at the heart from 12 different angles
o 3 standard limb leads (I, II, III) bipolar leads (positive and negative lead)
Placed on the arms and legs
Lead I
Records magnitude and direction of current flow b/n negative lead on the right arm to
the positive lead on the left arm
o Records flow from right arm to left arm
Lead II
Records activity b/n negative lead on right arm and the positive lead on the left leg
, o Records flow from right arm to left leg
Normal ECG wave forms are upright in these leads, lead II produces most upright
waveform
Goes through the largest part of the heart better picture d/t more electrical activity
Lead III
Records activity from the negative lead on the left arm to the positive lead on the left leg
o Records flow from left arm to left leg
Not the same degree of amplitude as you would in lead II, but still get a good picture
o You would prefer this lead dependent on the damage to the heart (EX:
cardiomyopathy)
The LV might shift left so a better picture would be to the left side
o Also dependent on the shape of the heart and where it is in the chest wall
o 3 augmented limb leads (aVR, aVL, aVF) unipolar (record electrical flow in only one direction)
From heart out to the body
aVR from heart to right arm
aVL form heart to left foot
aVF from heart to left arm
o A stands for augmented d/t small ECG complexes (they must be augmented or
enlarged)
o V stands for voltage
o Subscripts R, L, and F stand for location (right arm, left arm, left foot)
Where the electrode is located
They are like a mirror image of the other types of leads
Provide confirmation of standard leads
o 6 precordial leads (V1, V2, V3, V4, V5, V6) chest leads that are unipolar
Placed over the heart (do not need to know locations, just for own reference)
V1 4th intercostal space (ICS), right sternal boarder (RSB)
o Major lead for dysrhythmia monitoring
Will be used in tandem with lead III
V2 4th ISC LSB
V3 halfway between V2 and V4
o Best to recognize ischemic changes in the heart
Used in tandem with lead III for myocardial ischemia for at risk pt
Acute coronary syndrome, risk for silent ischemia, recent cardiac
interventions
th
V4 5 ICS, LMCL (midclavicular line)
th
V5 5 ICS, LAAL (anterior axillary line)
V6 5th ICS, LMAL (midaxillary line)
Offer a good picture of ventricular activity
Unipolar positive electrode and the AV node as central reference
Impulses direction
o Toward electrode = positive QRS complex
o Away from electrode = negative QRS complex
CARDIAC MONITORING
Telemetry
o Most ICUs use a 5-lead system
Limb leads are placed (I, II, III)
One precordial lead is placed can be moved for different views
o Most ERs use a three lead system
Limb leads I, II, III
RA and LA leads are placed just above the clavicles
LL lead is placed on the left abdominal area below umbilicus
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