Download - Ecg 1
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