Date post: | 22-Dec-2015 |
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Uses of ECG Tracing
• Ischemia/infarct
• Arrhythmias
• Ventricular and atrial enlargements
• Conduction defects
• Pericarditis
• Effects of some drugs and electrolytes
How to Conduct an ECG
1. Patient lies flat on back2. Electrodes are placed on
the body3. Sites may need to be
shaved or cleaned to ensure the leads will stick properly.
4. Patient will lie as still as possible, hold breath, or put hands under bottom to keep from moving.
5. The results are then printed out on paper for MD to review.
Lead Placements
• V1 - Junction of the 4th ICS, Right sternal border• V2 - Junction of the 4th ICS, Left sternal border• V3 - Midway between V2 and V4• V4 - Junction of 5th ICS, Mid clavicle• V5 - Anterior aspect of axilla, same line as V4• V6 - Mid axilla, same line a V4• 4 limb leads (for grounding etc)
Understanding the Waves
• One small box = 0.04 seconds
• One large box = 0.2 seconds
• 5 large boxes = 1 second
Understanding the Waves
• Baseline (what is it?)
• P wave – Length of time it takes the impulse to pass from
the SA node to the AV node– Should precede every QRS wave
• PR interval– Should be no longer than 0.12 – 0.2
Understanding the Waves
• QRS– Should be no longer than 0.12
– If energy is going towards a positive electrode (camera), the picture will show a positive QRS complex
– If energy is going away from positive electrode, the picture will show a negative QRS complex
– If energy is toward the positive electrode and then passes by it, the QRS will be biphasic
– Ventricle contracting
Step 1 = Rate• Different ways to calculate a rate:
– a) ECG usually tells you– b) Locate a QRS that is close to a big line and count to
next big line: 300, 150, 100, 75, 60, 50
– c) take a 6 second strip, count QRS and multiply by 10 (hint: the middle of V3 on the lead II strip is 6 seconds)
Step 2 = Intervals• We assess intervals to see where the
impulse is coming from (pacemaker beat)
• Remember:– PR interval: normal is 0.12 - 0.2– QRS interval: normal is less than or equal to
0.12
Atrial Arrhythmias
• Atrial fibrillation (A-fib)– irregular rate– no discernable P waves– increased risk of strokes due to clots that might
form due to fibrillation (patients are usually on anticoagulation therapy)
Blocks Cont’• 2nd degree AV block (Mobitz)
– a) type I (Wenckebach)• longer and longer PR intervals until a QRS is dropped
Blocks Cont’• 3rd degree AV block
– HR <40 bpm– a complete block of electrical activity from
atria to ventricle– P’s are regular
Ventricular Rhythms
• Ventricular fibrillation– complete breakdown of all rhythm– a) course– b) fine
Ventricular Rhythms Cont’
• Ventricular tachycardia (V-tach)– impulse originates in the ventricle– always has a wide QRS complex
MI’s
• How can you tell on an ECG that your patient is having a heart attack?
• T waves
• Different views of heart will show different injured areas of heart
MI’s
• How else can you tell that your patient has had an MI?
• Cardiac Markers– CK will show in 4-6 hours (starts to come back
down after 1 day)– Troponin will show in 4-6 hours (may stay
elevated for weeks)– Others are: LDH, CK-MB, myoglobin, AST
Locating an MI
Area Leads Artery Complications
Inferior II, III, aVF Rightcoronary
Bradycardia
Anterior V1, V2, V3,V4
Left anteriordescending
Pulm edema,hypotensive
Lateral I, aVL, V5,V6
Circumflex
I Lateral (circumflex) aVR V1 Anterior (Lt ant desc) V4 Anterior
II Inferior (Rt coronary) aVL Lateral V2 Anterior V5 Lateral
III Inferior aVF Inferior V3 Anterior V6 Lateral