The Standard 12 lead ECG ECG Waves Orientation

The Standard 12 -lead ECG 新光醫院急診科醫師 張志華

ECG Waves

Orientation

Standard Limb Leads

Einthoven's Triangle

Limb Leads * * *

Precordial Leads

Rate • 300 / 中格數 Irregular rate • No of R in 6 -s strip x 10

Rate and Rhythm ?

Axis: Normal I a. VF

Left Axis Deviation (LAD) a. VR I a. VF

Right Axis Deviation (RAD) a. VR I a. VF

Axis ?

Einthoven's Triangle

Measurements • Heart Rate: – 60 - 100 bpm • PR Interval: – 0. 12 - 0. 20 sec • QRS Duration: – 0. 06 - 0. 10 sec • QT Interval (QTc < 0. 40 sec; abnormal if > 0. 425 sec) – Bazett's Formula: • QTc = QT/ RR (in seconds) – Poor Man's Guide to upper limits of QT: • • • For HR = 70 bpm, QT < 0. 40 sec HR ↑ 10 bpm above 70 - 0. 02 sec HR ↓ 10 bpm below 70 + 0. 02 sec If HR = 80 bpm QT < 0. 38 sec If HR = 60 bpm QT < 0. 42 sec

Test

Precordial Leads

Precordial Leads • Small r-waves begin in V 1 or V 2 and progress in size to V 5 • The R-V 6 is usually smaller than R-V 5 • In reverse, the s-waves begin in V 6 or V 5 and progress in size to V 2 • S-V 1 is usually smaller than S-V 2 • The usual transition from S>R in the right precordial leads to R>S in the left precordial leads is V 3 or V 4 • Small "septal" q-waves may be seen in leads V 5 and V 6

Precordial (chest) electrodes V 5 & V 6 located over left ventricle V 1 & V 2 located over right ventricle V 3 & V 4 located over interventricular septum

Counter-clockwise Rotation

Clockwise Rotation

Measurements • Heart Rate: – 60 - 100 bpm • PR Interval: – 0. 12 - 0. 20 sec • QRS Duration: – 0. 06 - 0. 10 sec • QT Interval (QTc < 0. 40 sec) – Bazett's Formula: • QTc = QT/ RR (in seconds) – Poor Man's Guide to upper limits of QT: • • • For HR = 70 bpm, QT < 0. 40 sec HR ↑ 10 bpm above 70 - 0. 02 sec HR ↓ 10 bpm below 70 + 0. 02 sec If HR = 80 bpm QT < 0. 38 sec If HR = 60 bpm QT < 0. 42 sec

ECG Waves

Intervals QRS (3) (3 -5) RR PR (1) QT (2)

Test

QT Interval • Ccorrected QT – QTc = measured QT / sq-root RR in seconds – Upper limit for QTc = 0. 44 sec • Long QT Syndrome - "LQTS" – QTc > 0. 47 sec for males – > 0. 48 sec in females – Increased vulnerability to malignant ventricular arrhythmias, syncope, and sudden death – Prototype: Torsade-de-pointes, a polymorphic ventricular tachycardia characterized by varying QRS morphology and amplitude around the isoelectric baseline.

LQTS Causes : – Drugs • Many antiarrhythmics • Tricyclics • Phenothiazines – Electrolyte abnormalities ( ↓K+, ↓ Ca++, ↓ Mg++) – CNS disease (SAH, stroke, trauma) – Hereditary LQTS (e. g. , Romano-Ward Syndrome) – Coronary Heart Disease (some post-MI patients)