What is an ECG?

• The electrocardiogram (ECG) is a graphic

recording of the electrical potentials

produced in association with the heart

beat.

Uses

• Chamber hypertrophy

• MI

• Arrhythmias

• Pericarditis

• Systemic diseases

• Effect of drugs

• Electrolyte imbalance

ECG Graph Paper

X- Axis time in seconds

Y- A

xis Am

plitu de in mill volts

+

+ +

- - -

ECG Bipolar Limb Leads

R L

F

R

F

L

• Standard ECG is recorded in 12 leads

• Six Limb leads – I, II, III, aVR, aVL, aVF• Six Chest Leads – V1 V2 V3 V4 V5 & V6• I, II and III are called bipolar leads• I between LA and RA

• II between LF and RA

• III between LF and LA

ECG Bipolar Limb Leads

ECG Unipolar Limb Leads

++

+

Lead aVR Lead aVL Lead aVF

R L

F

• aVR, aVL, aVF are called unipolar leads

• aVR – from Right Arm Positive

• aVL – from Left Arm Positive

• aVF – from Left Foot Positive

ECG Unipolar Limb Leads

ECG Chest Leads

The Six Chest Leads

TRANSVERSE PLANE

Precordial (chest) Lead Position • V1 Fourth ICS, right sternal border • V2 Fourth ICS, left sternal border • V3 Equidistant between V2 and V4 • V4 Fifth ICS, left Mid clavicular Line• V5 Fifth ICS Left anterior axillary line• V6 Fifth ICS Left mid axillary line

ECG Chest Leads

Precordial Leads

Anatomic Groups(Summary)

ILateral

aVRNone

V1

Septal

V4

Anterior

IIInferior

aVLLateral

V2

Septal

V5

Lateral

IIIInferior

aVFInferior

V3

Anterior

V6

Lateral

Other Leads

• V7: Posterior Axillary Line

• V8: Posterior Scapular Line

• V9: Left border of the spine

• V3R-9R: Right Sided Leads (V2R = V1)

• VE: Ensiform cartilage

• E: Esophageal lead

Pitfalls

• Patient Identity

• Proper relaxation

• Good contact between skin & electrode

• Proper Standardization

• Properly grounded

• Electrical Equipment

Pacemakers of the Heart

• SA Node - Dominant pacemaker with an intrinsic rate of 60 - 100 beats/minute.

• AV Node - Back-up pacemaker with an intrinsic rate of 40 - 60 beats/minute.

• Ventricular cells - Back-up pacemaker with an intrinsic rate of 20 - 45 bpm.

Phases of Cardiac Action Potential

i) Phase 0: Upstroke or rapid depolarization.

(a) Atrial and ventricular muscles and HIS and Purkinje fibres- rapid upstroke and

largeVmax.

Due to opening of fast Na+ channels.

(b) Normal SA & AV node - slow upstroke and reduced Vmax.

Due to opening of Ca++ channels.

ii) Phase 1 : Early rapid repolarization.

iii) Phase 2 : Plateau phase.

iv) Phase 3 : Final rapid repolarization.

v) Phase 4 : Resting membrane potential or diastolic depolarization (-90mv)

LARA

LL

ECG Recordings (QRS Vector pointing leftward, inferiorly & posteriorly)

3 Bipolar Limb Leads:

I = RA vs. LA (+)

LARA

LL

ECG Recordings (QRS Vector pointing leftward, inferiorly & posteriorly)

3 Bipolar Limb Leads:

I = RA vs. LA (+)

II = RA vs. LL (+)

LARA

LL

ECG Recordings (QRS Vector pointing leftward, inferiorly & posteriorly)

3 Bipolar Limb Leads:

I = RA vs. LA (+)

II = RA vs. LL (+)

III = LA vs. LL (+)

LARA

LL

ECG Recordings (QRS Vector pointing leftward, inferiorly & posteriorly)

3 Bipolar Limb Leads:

I = RA vs. LA (+)

II = RA vs. LL (+)

III = LA vs. LL (+)

3 Augmented Limb Leads:

aVR = (LA-LL) vs. RA(+)

LARA

LL

ECG Recordings (QRS Vector pointing leftward, inferiorly & posteriorly)

3 Bipolar Limb Leads:

I = RA vs. LA (+)

II = RA vs. LL (+)

III = LA vs. LL (+)

3 Augmented Limb Leads:

aVR = (LA-LL) vs. RA(+)

aVL = (RA-LL) vs. LA(+)

LARA

LL

ECG Recordings (QRS Vector pointing leftward, inferiorly & posteriorly)

3 Bipolar Limb Leads:

I = RA vs. LA (+)

II = RA vs. LL (+)

III = LA vs. LL (+)

3 Augmented Limb Leads:

aVR = (LA-LL) vs. RA(+)

aVL = (RA-LL) vs. LA(+)

aVF = (RA-LA) vs. LL(+)

V1 V2V3

V4

V5

V6

6 PRECORDIAL (CHEST) LEADS

Spine

Sternum

ECG Recordings: (QRS vector---leftward, inferiorly and posteriorly

3 Bipolar Limb Leads I = RA vs. LA(+) II = RA vs. LL(+) III = LA vs. LL(+)3 Augmented Limb Leads aVR = (LA-LL) vs. RA(+) aVL = (RA-LL) vs. LA(+) aVF = (RA-LA) vs. LL(+)

6 Precordial (Chest) Leads: Indifferent electrode (RA-LA-LL) vs.chest lead moved from position V1 through position V6.

Normal Impulse Conduction

Sinoatrial node

AV node

Bundle of His

Bundle Branches

Purkinje fibers

Impulse Conduction & the ECG

Sinoatrial node

AV node

Bundle of His

Bundle Branches

Purkinje fibers

The “PQRST”

• P wave - Atrial depolarization

• T wave - Ventricular repolarization

• QRS - Ventricular depolarization

The PR Interval

Atrial depolarization

+

delay in AV junction

(AV node/Bundle of His)

(delay allows time for the atria to contract before the ventricles contract)

ECG Complex

• P Wave is Atrial contraction – Normal 0.12 sec

• PR interval is from the beginning of P wave to the beginning of QRS – Normal up to 0.2 sec

• QRS is Ventricular contraction –Normal 0.08 sec

• ST segment – Normal Isoelectic (electric silence)

• QT Interval – From the beginning of QRS to the end of T wave – Normal – 0.40 sec

• RR Interval – One Cardiac cycle 0.80 sec

Reporting of ECG

1. Standardization2. Rhythm3. Heart rate4. PR interval5. QRS interval6. QT/QTc interval7. Axis8. P wave

9. Precordial R wave progression

10. Abnormal Q wave

11. ST Segment

12. T wave

13. U wave