The ECG in clinical practice: making the diagnosis at a glance

Prepared and presented by Dr LukojiSpecialist Physician

DEFINITION:

• Graphic recording of the electrical activity (potential) of the heart on a standard paper grid.

CONDUCTION SYSTEM (FLIP CHART)• Sinus node (initiate the electrical impulse): 60-

80/minutes: fires the impulse to the atria• AV node (CS in RA): only electrical connection

between atria and ventricles: transmit the impulse from the atria to the ventricle: slows down the impulse (filter and regulator)

• Bundle of His: made out of 2 branches: LBB and RBB

• Purkinje network: within the ventricle

CONDUCTION SYSTEM

How ECG is generated:

• Impulse depolarizes successively the atria then the ventricles follow by repolarization for each .

• Depolarization and repolarization are then recorder graphically as an ECG in form of a curve by means of electrodes attached to the patient’s body surface at conventional spots.

• Depolarization and repolarization generate waves on the tracing.

ECG curve

Deconstructing the ECG curve:

• P wave: atrial depolarization• QRS complex: ventricular depolarization (varies)• T wave: ventricular repolarization• Isoelectric line• Calibration signal (rectang=10mm=1mv)• ECG generally prints at a speed of 25mm/sec• Leads: standards (I,II,III), augmented (aVF, aVL, aVR)

&precordial (V1 to V6) • Leads#electrodes

Electrodes placement

• Proper placement is key to accurate tracing hence accurate diagnosis.

• Ensure proper skin preparation• Ensure patient is calm (explain)• Connect electrodes at appropriate spots

(chest electrodes!)

The precordial leads: correct placement

ECG stepwise analysis• Check calibration• Check paper speed• Check patient identity• If needed have a caliper and lens• I take a minimum of 5 minutes to analyze each

ECG (you do not need to hurry, details are key for accurate diagnosis)

• Get senior colleague opinion if doubt (overdiagnosis or underdiagnosis)

• Automated interpretation from ECG machine is often misleading: beware!!!

What to look for: general impression and rhythm analysis

• What is the rhythm: NSR or not?• What is the heart rate?• P wave duration• Intervals measurement: P, PR, QRS, QT• QRS axis• QRS duration• QRS amplitude: low voltage, sokolow, RSS• QRS infarction signs• Rotation and transition zone• ST and T segment• T-U wave

Sinus rythm1• P positive in lead I and II• Every P wave is followed by QRS complex• PR interval is constant• QRS interval is constant• 2. Heart rate: 300/large square between R-R interval

P wave duration

Prolong P wave: P mitrale

Right atrial hypertrophy: P pulmonale

PR interval

Prolonged PR

Short PR duration (pre-excitation syndrome)

Short PR duration

Prolong QRS duration

how prolonged QRS occurs

Bundle branch block

Bundle branch block

Clockwise rotation

Counterclockwise rotation

Illustration of LVH

ST depression and T inversion

T wave inversion

ST SEGMENT AND ACS