ECG lecture of PTMD

ELECTROCARDIOGRAM



Normal Sinus Rhythm
• Each P wave is followed by a QRS
• P wave rate is 60 bpm
Rate < 60 = sinus bradycardia
Rate > 60 = sinus tachycardia

P wave – atrial depolarization

PR segment – conduction delay through AV node
- normally <200 msec / 0.12 – 0.20 sec

QRS complex – ventricular depolarization
- normally <120 msec / .08 - .12 sec

QT interval – mechanical contraction of the ventricles

T wave – ventricular repolarization

Atrial repolarization is masked by QRS complex

ST segment – isoelectric, ventricles depolarized

U wave – caused by hypokalemia


ANALYZING THE ECG

1. RATE

The first step is to determine the RATE, which can be eyeballed by the following technique. Locate the QRS (the big spike) complex that is closest to a dark vertical line. Then count either forward or backwards to the next QRS complex. For each dark vertical line you pass, select the next number off the mnemonic "300-150-100-75-60-50" to estimate the rate in beats per minute (BPM).
In other words if you pass 2 lines before the next QRS, the heart rate (HR) would be less than 150. Remember that this is merely an estimate

2. RHYTHM
- determine if its sinus or an ectopic rhythm
- If there is a P wave before each QRS and the P is in the same direction as the QRS, the rhythm can be said to be sinus.

3. AXIS
normal axis- I (+) and AVF (+)
- I (+) and left axis deviationAVF (-)
right axis deviation- I (-) and AVF (+)
- extreme right axis deviationI (-) and AVF (-)
*LEADS (important for MI)
• V1 V2 -- anterior note: sometimes V1 V2 V3 V4 (anterior)
• V3 V4 --septal
• V5-V6, I, aVL -- lateral
• II, III, aVF – inferior

4. HYPERTROPHY

Right Atrial Hypertrophy
o P wave in lead II taller than 2.5mm (2.5 small squares)



Left Atrial Hypertrophy
-P wave duration > 0.12s in frontal plane (usually lead II)
-Notched P wave in limb leads with the inter-peak duration > 0.04s

Right Ventricular Hypertrophy
-Reversal of precordial pattern
-Tall R in V1 and V2
-Deep S in V5 and V6
-Normal QRS duration



Left Ventricular Hypertrophy
-S in V1 or V2) + (R in V5 or V6) >35 mm (over age 35)



CONDUCTION ABNORMALITIES
ATRIO-VENTRICULAR (AV) BLOCKS





RHYTHM ABNORMALITIES


SUPRAVENTRICULAR TACHYARRHYTHMIAS


1. Sinus Tachycardia
- Ventricular rate >100 bpm
-Normal P waves before every QRS

2. Paroxysmal Atrial Tachycardia (PAT)
-Rapid ectopic pacemaker in atrium (not sinus node)
-Rate > 100 bpm
-P wave with unusual axis before each normal QRS




3. Atrial Flutter
-A characteristic 'sawtooth' or 'picket-fence' waveform of an intra-atrial re-entry circuit usually at about 300 bpm.

4. Atrial Fibrillation
- Wavy baseline without discernible P waves
- Variable and irregular QRS response
- The rhythm is irregularly irregular

5. Premature Ventricular Contraction

o Ectopic beats arise from ventricular foci
o Common and often benign
o It is usually asymptomatic, but may cause palpitations
o Causese include hypoxia, electrolyte abnormalities, hyperthyroidism
o ECG tracings revealed early, wide QRS complexes that are not preceded by a P wave.
o PVCs are followed by a compensatory pause
o No treatment if asymptomatic. If symptomatic, give B-Blockers or other antiarrhythmics. Treat the underlying causes





6. Ventricular Tachycardia
o Associated with CAD and MI
o Three or more consecutive PVCs
o Wide QRS complexes in a regular and rapid rhythm
o AV dissociation

7. Ventricular Fibrillation
o A completely erratic rhythm with no identifiable waves.
o Treat with immediate electrical cardioversion and ACLS protocol