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ECG, THE BASICS

UNIVERSITY OF DEBRECEN

FACULTY OF MEDICINE

DIVISION OF CLINICAL PHYSIOLOGY

Ventricular action potential

slow Ca2+ influx and K+ outflux

fast K+ outflux

fast Na+ influx

Development of ECG waves

VECTOR SUM

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Standard bipolar leads

Augmented leads

Precordial and dorsal leads

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ECG waves

P wave development

Polarity of P wave

RIGHT ATRIUMAV NODE

SA NODELEFT ATRIUM

aVR

V1

negative P wave

Biphasic P wave

Left atrial activation

Right atrialactivation

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His bundle electrogram

Phases of ventricular activation

1.

4.

2.

3.

Different kinds of QRScomplexes

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Orientation of ECG leads

Precordial leads, R wave progression

Early transition(Clockwise rotation, e.g. deep inspiration)

R=SV4-5 V1-2

Late transition(Counterclockwise rot.,

e.g. deep expiration)

Ventricular activation time (VAT)

ENDO EPI(long AP) (short AP)

DEPOL.

REPOL.

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ST segment, T and U waves

ST segment

J-point

60-80 ms

Degree of ST segment deviation

Isoelectric line (TP)

Steps of ECG evaluation

1. Rhythm generator2. Heart rate3. R-axis4. P-, PQ-, QRS-, ST-, QT-times5. Wave morphology6. Interpretation

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Heart rate

The hexaaxial system- The tallest positive QRS is found in the ECG lead that points directly

toward the QRS axis.

- The most negative QRS is seen in the ECG lead that points directlyaway from the QRS axis.

- An equiphasic QRS is in the ECG lead that is at right angles to theQRS axis.

aVR aVL

aVFIII II

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QRS axis determination and QRS axis deviations

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QRS axis determination and QRS axis deviations

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