Electrocardiography

Electrocardiography Bernardo D. Morantte Jr.M.D. Department of Medicine College of Medicine Pamantasan Ng Lungsod Ng Maynila

Electrocardiography (EKG)  The electrical activation of the muscle cells and the conduction system of the heart is the basis for electrocardiography.

 The EKG is the recording of the electrical activation of the heart.

Action potential Electrical stimulus



Phases of repolarization

Na, Ca

extracellular

1

40

2

0

3

- 40

0

K

- 80 -100

Cell Membrane

4

Intracellular

threshold mV 1 msec ARP Resting membrane potential

RRP

ARP = absolute refractory period RRP = relative refractory period

Electrical activation of the heart SA node

LA RA

AV node

EKG

LV RV

P

RBB

LBB

RS

Q T

EKG R R on T pattern

R

Hyper-repolarized T

p

(vulnerable period ) U

0

PR

ST

Q S ARR

RRP

T

QRS

Electrode placement -90 0

-600

- 120

0

Posterior aVR

I

aVL

-300 aVL

aVR - 150

0

P 4th v1 RICS V2 V3 V6 V4 V5 III II

QRS

+1800

+150 Frontal plane Hexaxial reference aVF

P QRS

00 I V6 V5 +300 V4

+1200 III

Anterior0 + 90 V1 aVF

+600 II V3 V2

Horizontal plane hexaxial reference

R/S progression

P and QRS vector frontal plane SA node

LA RA

AV node

EKG

LV Left axis deviation -90 -60

P

RV

-30

Q RS

+180

T

+150 Right axis deviation +120 +90

0 +30 +60

QRS axis determination -90 0

- 1200

-600

Frontal Plane R

aVR - 1500

*

P

-300 aVL

T

1800

00 I

1500

300

EKG

*Tallest R wave

600 II

120

0

III

900 aVF

EKG Time Measurements at 25 mm / second paper speed Time intervals R

T p

PR

10 mm = 1mV

QT QRS

40 msec.

200 msec. 1 second

calibration signal

Voltage Measurements Time intervals R

T P

10 mm = 1mV

S 40 msec.

= 0.1 mV

200 msec. 1 second

calibration signal

EKG V1 RAH= P > 2.5 mm RVH= R/S > 1 : RAD or R V1 >7.5

V5

LVH= S V1 +R V5 > 35 mm + LAD or R V5 > 26 mm LAH = broad notched P inV5 or biphasic P in V1 with deep negative component

RVH and RAH LVH and LAH

Atrial (AR) and ventricular rates (VR) at paper speed of 25 mm per second for regular rhythm

Time intervals

Ex: 300/5 = 60 R

R

T

P

P

Formula: 40 msec.

1. VR =

200 msec. 1 second

2 VR =

300 No. of large squares 1500 No. of small squares

Caution before reading the EKG Make sure that the paper speed is at 25 mm per second Make sure that the calibration is 10 mm = 1mV Make sure that the electrodes have been placed properly

Non-standard EKG recordings Be aware ! R P

T

5 mm =1mV

Calibration signal

12.5 mm / sec. paper speed

PR interval

QRS

50 mm / sec paper speed.

QT interval

Inversion of right and left limb leads -900

-600

- 120

0

aVR

I

aVL

-300 aVL

aVR - 150

0

v1 V2 V3 V6 V4 V5 III II

P

+1800

QRS

QRS

V5 +300

+150 P

Frontal plane

00 I V6

V4 aVF

+1200 + 900

III V1

aVF

+600 II V3 V2

Horizontal plane hexaxial reference

Dextrocardia

-900

-600

- 120

0

Posterior aVR

I

aVL aVR - 1500

v1 V2 V3 V6 V4 V5 III II

-300 aVL P

+1800

P

V6

QRS +150

V5 +300

QRS

Frontal plane

V4 aVF

+1200 V2R III

Anterior + 900 V1 aVF

+600 II V3 V2

Horizontal plane hexaxial reference

Inversion of right arm and left foot -90 leads- 120 -60 0

0

0

aVR

I

aVL

-300 aVL

aVR - 1500

v1 V2 V3 V6 V4 V5 III II

P

+1800

QRS

QRS

V5 +300

+150 P

Frontal plane

00 I V6

V4 aVF

+1200 + 900

III V1

aVF

+600 II V3 V2

Horizontal plane hexaxial reference

Inversion of left arm and left foot -90 leads -60 - 120 0

0

0

aVR

I

aVL

-300 aVL

aVR - 1500

QRS

+1800 90

v1 V2 V3 V6 V4 V5 III II

P

V6 QRS

+150 P

Frontal plane

00 I V6 V5 +300 V4

aVF

+1200 + 900

III V1

aVF

+600 II V3 V2

Horizontal plane hexaxial reference

EKG

EKG