RhythmicalExcitation

of the Heart

RhythmicalExcitation

of the Heart

Chapter 10Chapter 10Chapter 11

The Normal Electrocardiogram

Action potentials of specialized fibersSection II-plate 11, Netter

“Normal electrocardiogram”.

Guyton, Figure 11-1. Copyright 2000, WB Saunders Company, All Rights Reserved

1 inch = 1 sec

0.2 sec

Note the “time calibration”

P-Q Interval (or P-R if Q is missing) ~ 0.16 sec

QT Interval ~ 0.35 sec

5 big blocks = 1sec

(P-Q)

Recording depolarization and repolarization waves from a cardiac

muscle fiber.

Guyton Figure 11-2. Copyright 2000, WB Saunders Company, All Rights Reserved

See Guyton –Figure 11-3

Instantaneous potentialsdeveloped

the surface of a cardiac muscle mass.

Guyton Figure 11-4. Copyright 2000, WB Saunders Company, All Rights Reserved

Flow of current in the chest around partially depolarized ventricles.

Guyton Figure 11-5. Copyright 2000, WB Saunders Company, All Rights Reserved

Guyton Figure 11-6.Copyright 2000, WB Saunders Company, All Rights Reserved

Einthoven’s Triangle

Three Biopolar Limb Leads:conventional arrangement of electrodes for recording standard ECG leads.

0.5 mV

1.2 mV

0.7 mV

Normal ECGs recorded from the three standard limb leads.

Einthoven’s law: if the electrical potentials of any two limb leads are known, the third one can be determined. The sum of the voltages in leads I and III equals Lead II.

Figure 11-7. Copyright 2000, WB Saunders Company, All Rights Reserved

5000 ohms

Connections of the body with the ECG for recording chest leads (precordial leads).

Guyton Figure 11-8. Copyright 2000, WB Saunders Company, All Rights Reserved

Normal ECGs recorded from the six standard chest leads

Guyton Figure 11-9. Copyright 2000, WB Saunders Company, All Rights Reserved

Connections of the body with the ECG for recording unipolar augmented leads.

aVR aVL

aVF

Recordings between one limb and the other two limbs.

Normal ECGs recorded from the three augmented unipolar limb leads.

Recordings between one limb and the other two limbs.

Guyton Figure 11-10. Copyright 2000, WB Saunders Company, All Rights Reserved