2025 ECG Quiz 2 Flashcards
ECG Basics
Discovering Electrocardiography
Giovani Aldini (1762-1834): Italian physicist, and professor. Famous for performing public spectacles in London using electricity to “reanimate” an executed human being.
Rudolph von Köelliker (1817-1905): Swiss anatomist, physiologist and histologist. Proved the electrical currents of the heart by attaching a galvanometer to the base and apex of a frog heart and linking it directly to the sciatic nerve of the amputated leg to cause contraction.
Alexander Muirhead (1848-1920): Attached wires to a sick patient’s wrists to obtain an electronic record of their heartbeat.
Willem Einthoven (1860-1927): Dutch doctor and inventor.
1895. Credited for the invention of ECG and distinguishes five deflections which he names P, Q, R, S, and T.
1901. Invents the first practical “string galvanometer” which produced an ECG tracing by placing leads on a patient’s skin.
1924. Wins the Nobel Prize in Medicine for his work on the ECG.
Dr. Frank Norman Wilson (1890-1952): American Cardiologist.
1934. Joined multiple leads to define ‘Wilson’s Central Terminal’, to create a central ground point from which the Unipolar leads were developed
Dr. Emanuel Goldberger (1913-1994): American Cardiologist.
1942. Increased Wilson’s Unipolar lead voltage by 50% and created augmented leads aVR, aVL, and aVF.
Defining ECG
A graphical representation of voltage, over time, of the heart’s electrical activity
Signal is captured and externally recorded by skin electrodes.
The device used to produce this record is called an electrocardiograph.
The word is derived from electro (greek for electricity), cardio (greek for heart), graph (greek root meaning “to write”).
Translated to German as “Elektrokardiogramm,” which is where we get the abbreviation EKG from
ECG Clinical Applications
Diagnosis of arrhythmias and cardiac abnormalities
Indication of myocardial damage
Detection of electrolyte disturbances
Screening tool for diagnosis of ischemic disease
Can indicate anatomic and physiologic state of the heart (i.e. hypertrophy, stenosis, etc.)
Can diagnose some non-cardiac pathology (i.e. PE, hypothermia, etc.)
Gold standard for noninvasive diagnosis of cardiac diseases.
Role of Anesthesia Provider
Proper application
Recognition of normal vs abnormal readings
Interpretation of these readings
Correlation of this data with clinical scenario, i.e. normal vs abnormal or benign vs malignant
ECG Theory
There is an innate electrical conduction system of the heart
Depolarization & repolarization are active electrical events
Using electrodes and specialized equipment, this electrical activity can be recorded onto an ECG
Normal conduction should be predictable
Any deviation may be a normal or pathological
ECG electrodes record the average direction and voltage of all the electrical flow within the heart
The magnitude and polarity of the signal depends on position of electrodes, average direction of current, and average magnitude of current
More myocardial mass generates more magnitude/voltage
ECG Paper
“Continuous roll of graph paper” consisting of light and dark perpendicular lines.
Light/small squares = 1×1mm
Dark/large squares = 5×5mm
X-axis = time
Y-axis = voltage
Standard calibration:
10mm = 1mv
Speed of 25mm/sec
ECG Reading on Red Tape
Vectors
Vector = size & direction of movement b/t two points
Mean vector = The average direction & size of all vectors
Leads translate electrical forces into a single vector on ECG
Each electrode records only average current flow at any given moment.
Angle of orientation = average direction of current flow
Length = voltage (amplitude)
Leads and Electrodes
A negative (-) electrode and a positive (+) electrode produce a single lead.
Electrodes are the conductive pads that are attached to the body
A Lead measures the electrical potential difference between the two locations.
The (-) electrode is called the reference electrode.
The (+) electrode is called the exploring electrode.
Think of the (+) electrode as an eye, looking at the heart.
Depolarization Creates Deflections
Waves recorded on one side of body look different from those recorded on other side.
A wave of depolarization moving towards a (+) electrode causes a positive deflection on EKG.
A wave of depolarization moving away from a (+) electrode causes a negative deflection on EKG.
Electrode in Middle of Cell and Deflections
(+) Electrode located in middle of cell results in following:
Initial positive deflection, then negative deflection, then return to baseline.
Depolarization recedes, causing negative deflection.
EKG returns to baseline when entire muscle is depolarized.
This produces a biphasic wave.
Repolarization Creates Deflections
Repolarization wave results in deflections opposite of those associated with a depolarization wave.
A wave of repolarization moving towards a (➕) electrode causes a negative deflection.
A wave of repolarization moving away from a (➕) electrode causes a positive deflection on EKG.
Biphasic wave has a negative deflection first and then positive deflection second
Depolarization and Repolarization Deflection on Heart
Depolarization towards a (+)electrode = positive deflection
Depolarization away from a (+)electrode = negative deflection
Repolarization towards a (+)electrode = negative deflection
Repolarization away from a (+)electrode = positive deflection
Depolarization 90° to the (+)electrode = Biphasic deflection
These concepts apply to the entire heart
Waveform Morphology
Waves
Deflections (positive or negative)
P Wave, QRS Complex, T Wave, U Wave
Segments
Straight line connecting two waves
PR Segment, ST Segment
Intervals
At least one wave plus a segment
PR Interval, QT Interval
Lead II
P Wave
Atrial Depolarization
Rate: 60-100 bpm
<10% variation
Height: <2.5mm
Duration: 0.08-0.1s
Results in right and left atrial contraction
Right atrium depolarizes before left, and finishes earlier
First half represents right atrial depolarization
Second half represents left atrial depolarization
Mean electrical vector travels towards the (➕) electrode = Positive deflection
P Wave in Limb Leads
Atrial depolarization begins in sinus node in upper right atrium and moves to left atrium
Vector of current flow is right to left and slightly inferiorly
Atria generate small voltage: less than 0.25 mV per lead
Amplitude is most positive in lead II and most negative in lead aVR
Leads I and aVL and II and aVF record positive deflection
Lead III records biphasic P wave
Lead aVR records negative deflection
P Wave in Precordial Leads
Leads V5 and V6 record positive deflection
Lead V1 records biphasic wave
Leads V2 through V4 are variable
PR Segment
AV Node Pause
Duration: ~0.1 sec
No electrical energy movement = Isoelectric line
Delay allows atria to finish ejecting blood before ventricular contraction begins.
PR Interval
Beginning of Atrial depolarization to beginning of Ventricular Depolarization
Duration: 0.12-0.2 sec
Electrical Conducting Cells (Interventricular Septum)
Triggers Q Wave
Q Wave
Depolarization of of the interventricular septum
Septal fascicle depolarizes first
Wave travels from left to right to depolarize the upper septum
Mean electrical vector travels away from (+) electrode, leading to a (-) negative deflection.
R Wave
Depolarization of the remaining portion of septum
Depolarization flows inside, out
Endocardium to epicardium
Left ventricle is thick, therefore large amounts of electrical activity traveling directly towards (➕) electrode
Large positive deflection results
S Wave
Upper and posterior left ventricular depolarization
Last region to depolarize is the annulus fibrosis
Most of heart is already depolarized
Mean Vector traveling away from (➕) electrode, therefore negative deflection
S wave always follows a positive deflection
Terminal event (end of depolarization)
The end of the S wave is called the “J Point”
QRS Complex
Ventricular Depolarization
Duration: 0.06-0.1 sec
Narrow/normal = <100ms
Intermediate = 100-120ms
Wide/abnormal = >120ms
… when looking at ECG Paper
After delay in AV node, depolarizing wave enters ventricles via ventricular conducting system.
Ventricular conducting system consists of three parts:
Bundle of His emerges from AV node and divides into right and left bundle branches.
Right Bundle Branch carries current down right side of interventricular septum to apex of right ventricle.
Left Bundle Branch divides into three major fascicles:
Septal fascicle
Anterior fascicle
Posterior fascicle
The end of the QRS complex is called as the “J Point.”
QRS Complex Variations
1st negative deflection = Q wave
1st positive deflection = R wave
2nd positive deflection = R’ (prime) wave
1st negative deflection after a positive deflection = S wave
Complex with no positive deflection = QS wave
QRS Complex Morphology due to Septum Depolarization
Interventricular septum depolarizes left to right
Septal depolarization (when visible) produces a small negative deflection or Q wave
Visible in leads I, aVL, V5, and V6
Normal septal Q waves usually have amplitude no greater than 0.1 mV
QRS Complex in Limb Leads
Left ventricle dominates QRS complex
Mean vector moves caudal and left
Large positive deflection, or R wave, in left lateral and inferior leads
Deep negative deflection, or S wave, in lead aVR
QRS Complex in Precordial Leads
Deep S wave visible in VI
Tall R waves in V5 and V6
Lead V2, V3, V4 may be biphasic
ST Segment
Complete Ventricular Depolarization
Duration: 5-150ms
Ventricles are completely depolarized
During ARP
Prior to repolarization
Connects terminus of QRS complex (J Point) and the T wave.
Represents the initial “plateau” phase of repolarization
Is usually isoelectric
May be depressed or elevated with myocardial infarction or ischemia
T Wave Lead II
T Wave
Ventricular Repolarization
Height: 1/3 – 2/3 of R wave
Duration: 0.160 sec
Phase 3 of myocardial cell action potential, rapid repolarization
Corresponds to the relative refractory period
T Wave in Limb and Precordial Leads
Ventricular repolarization
Frequently variable in appearance.
Repolarization wave travels in opposite direction of depolarization.
Same leads that record positive deflection in depolarization record positive deflection in repolarization
Tall positive R waves seen with tall positive waves
QT Interval
Beginning of Ventricular Depolarization to End of Ventricular Repolarization
<0.44 sec
Approximately 40% of conduction cycle
Duration is inversely proportionate to HR
Tachycardia = shorter QTI
Bradycardia = longer QTI
QT Interval – Beginning of QRS Complex to end of T wave – Absolute
Refractory Period is the beginning of QRS to PEAK of T wave
The last half of T-wave is known as relative refractory period
U Wave
Thought to be cause by repolarization of Purkinje fibers
Exact source is unclear.
Small Amplitude: 0.1-33mV
Not easily detected on ECG because of small size
Enlarged and prominent U waves associated with hypokalemia
Inverted U wave may represent myocardial ischemia
High incidence of LAD involvement
May indicate LV volume overload
Cardiac Cycle as ECG
Normal heart rate (60-100 bpm)
Regular rhythm
The sinus node should pace the heart
P waves must be round, all the same shape, and present before every QRS complex in a ratio of 1:1
Normal P wave axis (0 to +75 degrees)
Normal PR Interval (120-200ms), QRS complex (60-100ms) and QT interval (<440ms)
QRS complex positive in leads I, II, aVF and V3–V6, and negative in lead aVR
Where the 12 Leads/”Views” Come From
10 skin electrodes produce 12 leads
Leads “view” the heart from a different angles
4 electrodes on arms & legs create the 6 limb leads (3 Standard and 3 Augmented)
Six electrodes on chest create 6 Unipolar
Precordial leads (Chest leads)
Standard positioning of electrodes allows comparison between EKGs.
Standard Limb Leads (Leads I, II, III)
View heart from frontal plane at 3 angles of orientation.
Limb leads are bipolar (physical NEG & POS electrodes)
Form Einthoven’s Triangle = RA, LA, & LL
Augmented Limb Leads
Unipolar Augmented lead = 1 physical electrode + 1 virtual electrode
Input combined from physical electrodes to create a virtual lead as the negative pole = Unipolar
Unipolar = single dedicated physical electrode
Goldberger’s Central Terminal uses 2 limb electrodes to mathematically create a virtual central negative pole.
This gave rise to our Unipolar Augmented Leads = aVR, aVL, aVF
Six Limb Lead Chart
Six Limb Lead Heart Wheel
Precordial Leads
View heart in the horizontal plane
Record impulses traveling anteriorly and posteriorly
Unipolar with only one physical electrode
Wilson’s central terminal is the negative pole
Six chest electrodes are positive poles
Precordial Electrode Placement
12 Lead View
12 Lead View on ECG Paper
Perioperative 12, 5, 3 Lead ECG
12-lead ECG
Utilized preoperatively as a screening test performed by ECG technician
Usually only ordered for certain patients based on AHA risk assessment guidelines and hospital specific protocols
5-lead ECG
White (RA), green (RL), black (LA), red (LL), and brown (V1-V6 depending)
3-lead ECG
White (RA), black (LA), and red (LL)
Routine OR use
Lead II view is most common
Non-Remarkable 12-Lead ECG
