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ECG MONITORING
Introduction to the E.C.G.
• 1924 - Noble prize – Einthoven
for discovery of EKG
• It can provide evidence to
support a diagnosis, but
remember…..LOOK AT THE
PATIENT NOT JUST THE PAPER
or Monitor
• Is essential in the diagnosis of
chest pain and abnormal heart
rhythms
• Is helpful in diagnosing
breathlessness
Principles of Electrocardiograph
• Electrocardiograph – is
the instrument that
records the electrical
activity of the heart
• Electrocardiogram
(ECG) is the record of
that activity
• It works on the
principle of
Galvanometer
3
• In the perioperative setting, electrocardiography serves
two main functions: diagnosis and monitoring.
• In the preoperative period, the standard 12-lead ECG is
performed mainly for risk assessment. It is used to
provide information on the patient's baseline (chronic)
cardiac status with regard to myocardial ischemia and
conduction or rhythm abnormalities as part of the
whole preoperative clinical assessment.
• During and after surgery the ECG is used mainly for
monitoring to detect changes in rate and rhythm or
myocardial ischemia
Waveforms & Intervals
Segments and Intervals
• Segment – Straight line b/w waves
• Interval – wave + segment
• ST segment – end of ventricular depolarization to
start of vent. repolarization
• QT interval – QRS complex + ST segment + T wave
ventricular cycle, 40% of each cardiac cycle
ECG Graph Paper
 Runs at a paper speed of 25 mm/sec
 Each small block of ECG paper is 1 mm2
 At speed of 25 mm/s, 1 small block = 0.04 s
 5 small blocks make up 1 large block = 0.20 s
 Hence, there are 5 large blocks/sec
 Voltage: 1 mm = 0.1 mV between each individual block
vertically
ECG MONITORING SYSTEMS
1. Three electrode monitoring system
2. Five electrode monitoring system
3. Ten electrode,twelve lead monitoring system.
• The three-electrode system :simplest and most common
•
•
•
•
mode .
Monitoring of three bipolar leads by recording the potential
difference between each of three pairs of electrodes: lead I , lead
II, lead III, or other modified chest leads.
ADVANTAGE: -good enough to track the heart rate,
- detect R waves for synchronized direct-current (DC)
shock in cardioversion
-and detect ventricular fibrillation.
DISADVANTAGE: Inadequate for diagnosing more complex
arrhythmias, such as distinguishing between RBBB and left bundlebranch block (LBBB) or between ventricular tachycardia (VT) and
supraventricular tachycardia (SVT).
Inadequate for ST-segment monitoring thus NOT sensitive for
detecting ischemia.
• Five-electrode monitoring system, the four limb electrodes,
LA, RA, LL, and RL placed at their corresponding monitoring
locations, allow any of the six limb leads to be obtained (leads I, II,
III, aVR, aVL, and aVF), and a fifth chest electrode can be placed in
any of the standard V1 through V6 locations .
• V1 is the preferred lead for special arrhythmia monitoring,
• The other precordial leads, especially V3 to V5, are the preferred
leads for ischemia monitoring. The five-electrode monitoring
system is currently the standard for monitoring patients with
suspected perioperative myocardial ischemia.
• TWELVE LEAD ECG MONITORING:
The RA and LA electrodes were attached to the right and left
infraclavicular fossae, and the LL electrode was attached to the left
iliac fossa. The RL electrode usually placed on the right iliac fossa
along with 6 precordial leads.
• ADVANTAGE:
ST-segment monitoring software has been developed to analyze all
12 leads and to sound an alarm for ST-segment changes. Therefore,
if lead II is being displayed but the patient has a transient ischemic
event involving lead V5, an ST alarm would be triggered.
ECG interpretation :step-by-step
• Rate
• Rhythm
• Cardiac Axis
• P – wave
• PR - interval
• QRS Complex
• ST Segment
• QT interval (T & U wave)
• Other ECG signs
RATE
CALCULATING RATE
lead II - rhythm strip. Look at # (squares) b/w
one R-R interval.
Rate
=
300
number of BIG SQUARE b/w R-R
OR
Rate
=
1500
number of SMALL SQUARE b/w R-R
CALCULATING RATE
Eg
Rate = 300
3
or
Rate = 100 beats/minute
Rate =
1500
15
RHYTHM
RHYTHM
P -QRS relationships- Lead II is commonly used
Regular or irregular?
Ventricular rhythm –measured by R-R interval &
Atrial rhythm - measured P-P interval.
RHYTHM
Normal Sinus Rhythm
ECG rhythm -usual rate b/w 60-100 bpm, every
P wave must be followed by a QRS & every
QRS is preceded by P wave.
P wave is upright in leads I and II
AXIS
AXIS
• Axis refers to general direction of heart's
depolarization wave front (or mean electrical
vector) in the frontal plane.
• In healthy conducting system - axis is related to
where the major muscle bulk of heart lies.
AXIS
• Leads were based on Einthoven triangle and
associated with limb leads.
• Leads put heart in middle of this triangle.
• Lead I, II and III are bipolar leads. Lead aVR, aVL
and aVF are augmented leads, V1-V6 are chest
leads
Einthoven triangle
AXIS
Basics of 12 Lead ECG's
Determining AXIS
Technique : Two Lead Method
Uses just 2 leads of the 6 limb leads
Look at Lead I & aVF
AXIS
1. Lead I & aVF divide
thorax into quadrants,
(Lt, N , Rt, No Man's)
2. If Lead I & aVF are both
upright- Axis is normal.
3. If lead I is upright & lead
aVF is downward - Axis is
Left.
AXIS
4. If lead aVF is upright &
lead I is downward Axis is Rt
5. If both leads are
downward - Axis is
extreme Right Shoulder
& most often is Vent.
Tachy
CARDIAC AXIS
CARDIAC AXIS
Positive
Positive
N Axis
CARDIAC AXIS
CARDIAC AXIS
Positive
Negative
LAD
CARDIAC AXIS
CARDIAC AXIS
Negative
Positive
RAD
P Wave
P Wave
Depolarization of both atria
• Relationship b/w P & QRS - distinguish various
arrhythmias
• Shape
&
enlargement
duration
of
P
-
indicate
atrial
P Wave
• Always +ve in lead I & II
• Always -ve in lead aVR
• <3 small sqs - duration
• <2.5 small sqs - amplitude
• Best seen in lead II
P Pulmonale
P MITRALE
PR Interval
PR INTERVAL
Onset of P wave to onset of QRS
• Normal = 0.12 - 2.0 sec
• Represents A to V conduction time (via bundle
of hiss)
Prolonged PR interval indicate AV block
QRS Complex
QRS COMPLEX
Ventricular depolarization
• Is d/t contraction of Ventricular mass
• Normal duration = 0.08 - 0.12 secs
Q wave >25% the height of R wave or >0.04 sec
is abnormal; may represent MI
QRS complex
Poor R Wave Progression in V1 to V6: suggests prior anterior MI
Pathologic Q wave: previous MI. Q wave amplitude 25% or more of
the subsequent R wave, OR > 0.04 s in width + > 2 mm in amplitude
in more than one lead
ST Segment
ST Segment
• Connects QRS complex & T wave
• Duration = 0.08 - 0.12 sec
T Wave
– “small to moderate” size +ve deflection wave
after QRS complex,(0.12-0.16s)
– It is 1/3rd - 2/3rd that of corresponding R wave
U Wave
– Septal repolarization (not always seen on ECG)
QT Interval
•Beginning of QRS to end of T wave
• Normal QT is usually about 0.40 sec
• QT variations are based on HR- faster HR
,shorter QT .
•Hence QTc.
QTC = QT / √ RR interval
Hypertrophy
LVH: S in V1 or V2 + R in V5 or V6 ≥
35 mm.
RVH: V1 R/S ratio >1 or V6
S/R ratio >1.
The electrocardiographic
manifestation of RBBB consists of
prominent and notched R waves
with rsr′, rsR′, or rSR′ on the rightsided leads and wide S waves on the
left-sided leads, along with QRS
prolongation (≥120 msec).
LBBB prolonged QRS
duration(>120ms), abnormal QRS
complex, and ST-T wave
abnormalities. There is also a broad,
sometimes notched R wave in the leftsided leads (I, aVL, V5, V6) with deep S
waves in the right precordial leads and
absent septal Q waves.
ACUTE ST SEGMENT DEPRESSION
Acute ST Elevation Inferior MI
Atrial Flutter
Atrial Fibrillation
HEART BLOCKS
VENTRICULAR FIBRILLATION
Ventricular fibrillation - irregular rhythm due to rapid discharge of
impulses from one or more ventricular foci or from multiple wandering
reentrant circuits in the ventricles. The ventricular contractions are erratic
and are represented on the ECG by bizarre patterns of various size and
configuration. P waves are not seen.
VENTRICULAR PREMATURE BEATS
• VPBs result from ectopic pacemaker activity arising below the AV
junction resulting in a wide (>0.12-second), bizarre QRS complex.
• There is no P wave associated with a VPB.
• VPBs are common during anesthesia- 15% of observed arrhythmias.
• Results in a fully compensatory pause consisting of the interval
from the VPB to the expected normal QRS, which is blocked at the
AV node, plus a normal sinus interval.
VENTRICULAR TACHYCARDIA
• The presence of three or
more sequential VPBs defines
VT. Diagnostic criteria include
the presence of fusion beats,
capture beats, and AV
dissociation.
• By duration, non sustained VT
lasts three beats and up to 30
seconds, and sustained VT
lasts 30 seconds or longer
• Heart rate: 100 to 200 /min.
• Rhythm: Generally regular, but
may be irregular if the VT is
paroxysmal.
• P/QRS: Usually no fixed
relationship because VT is a
form of AV dissociation in which
the P waves can be seen
marching through the QRS
complex.
• QRS complex: Wide, more than
0.12 second.
• Significance: Acute onset is life
threatening and requires
immediate treatment.
HYPERKALEMIA
HYPOKALEMIA
• ST segment depression,
• Decreased t wave
amplitude f/b T wave
inversion
• Increased U wave
height.
• Increased PR interval
and features of heart
block
Thank you