Lab 1 - ECG Flashcards
What is electrocardiography?
Technique for recording changes in electrical potential associated w/depolarization + repolarization of myocardium
What are the 3 potential applications of ECG?*
- To determine HR more accurately than by pulse counting (+ provide record of HR which can be rechecked after measurement made)
- To watch for abnormal heart rhythms e.g. minimize risk to patient/subject during exercise stress test
- Aid in diagnosis (by cardiologist) of heart conditions e.g. myocardial ischemia, myocardial infarction
When does the wave of depolarization begin? How does the spread
Begins in SA node (“pacemaker”), then spreads across atria, then through specialized conducting system to ventricles, eventually spreads across ventricles
Wave of depolariztion + repolarization of myocardium spread from heart thruout body
Why does human tissue conduct electric current well?
Cause of water + electrolyte content of body
Is it possible to sense the electric potentials at the surface of skin? If so, how?
Yes but the electric signal at surface of skin has small amplitude (~1mV) so special equipment required to detect signals aka ELECTROCARDIOGRAPH which detects, amplifies, and displays signals; ELECTROCARDIOGRAM is the tracing
What is the fxn of transducer?
Sense physical phenomena and produce electrical signal
Whats an electrode*
Type of transducer which changes IONIC into ELECTRIC current
How do electrodes fxn?
- behave like miniature electrochemical batteries
- generate own DC voltage on which cardiac electric signals are superimposed + transmitted to ECG
- ECG electrode must be designed so provides relatively low + stable impedance when placed on skin
Pros of electrodes
Inexpensive to make, conveniently manipulated by practitioner
What is the fxn of the gel component of the electrode pair
Hydrate skin, lowering electrode-skin impedance
Ways to lower electrode-skin impedance?
Inc skin contract area of conductive surface
What can happen is the electrode doesn’t provide stable interface btwn gel and skin
Wandering baseline, or excessive electrical interference, and/or unusually large muscle artifact during recording
Where do flat plate electrodes go
Secured to wrists and ankles w/straps
Where do suction cups go
Applied to chest
How do disposable floating electrodes differ
- Have adhesive surface protected by a peel-off backing (better at holding in place)
Describe the steps of good skin prep
- Skin at sites where electrodes r to b applied rubbed w/lipid solvent e.g. ethanol, to remove skin oil
- If hairy, site should be shaved
- Analogous to stripping plastic insulation from electric wire to inc electrical conductivity
What is electrode paste/jelly and its fxn
Aqueous suspension of electrolytes, ensures good electrical continuity between electrode + skin
Fxn of reference electrode aka ground electrode?
- Improves quality of tracing
- allows ECG (machine) to identify + eliminate electrical “noise” found over large region of body
- also used in EMG (electromyography)
Two fxns of grounding
- PREVENTS ELECTRIC SHOCK to subject or operator. Provides LOW RESISTANCE PATHWAY TO EARTH (“ground”) for current which can reach outer case of ECG machine due to a fault
- If nerves/muscles electrically stimulated from surface, current from stimulus travels not only to tissues but ACROSS SKIN. “STIMULUS ARTIFACT” can distort/obliterate the smaller signal being recorded from nerve/muscle unless diverted to resistance pathway to earth. E.g. Ulnar nerve stimulated @ elbow + EMG from finger muscles recorded, ground electrode on wrist would catch stimulus artifact before reaches fingers
What is a patient cable in ECG?
Bundle of wires that the electrodes are attached to
What is fxn of patient cable
Wires transmit electric signal from electrode to ECG
List the five features/controls that most ECGs have in common
- Calibration button
- Sensitivity selection
- Lead selector button
- Chart speed selector switch
- Auxiliary output terminal
Fxn of calibration button?
- Depressing button generates 1 mV calibration signal
- Tracing of calibration signal needs to be recorded at beginning and end of each series of ECG recordings
- Essential for calculation of AMPLITUDES e.g. QRS amplitude
Fxn of sensitivity selection aka gain selector
- Allows magnify or suppress amplitude of recording
- Sensitivity should be set that tracing occupies as much of paper as possible
- Settings of 0.5, 1.0, 2.0 cm/mV; 1.0 cm/mV is STANDARD
What is a lead selector button
Lead is specific configuration, or combo, of electrodes e.g. 12-lead ECG obtained w/only 10 electrodes
What is chart speed selector switch fxn
- Machines allow choice btwn 25-50 mmxs^-1
- Chart speed is recorded on ECG tracing so that intervals e.g. HR, PR interval, QRS duration, QT interval) can be calculated.
- Usually choose 25 mmxs^-1 cause sufficient precision on horizontal (time) scale. Also creates compact recording + conserve chart paper
- Faster chart speed = able to look more carefully at changes in interval durations
What is the auxiliary output terminal
This socket can receive a cable, which will carry ECG signal to another output device like oscilloscope or computer
What happens when current flows towards the positive electrode?
Needle on ECG deflect upwards
What happens when current flows away from the positive electrode?
Needle on ECG deflect downwards
What is needed to eliminate 60 Hz interference
- Good skin prep
- Presence of differential amplifier
- Reference electrode
- Adequate grounding
What is the ideal configuration for patient, ECG etc
Recording device btwn patient and power source
How is technical problem: skeletal muscle tremor caused? How does it look on ECG? How to prevent
Talking laughing shivering or skeletal muscle contractions
- irregular in height n frequency
- tell them to hold still
How is technical problem: motion artifact
- slipping of electrodes over surface of skin
- sudden large upward/downward deflection on ECG
How is technical problem: wandering baseline
- whole tracing moves up or down
- excessively deep respiration, by electrode paste drying up, electrode pulling away from skin, excessive tension on patient cable
What does PAR Q stand for
Physical Activity Readiness Questionnaire
What is PAR Q recommended as
Min standard of entry for low-mod intensity exercise programs
What was PAR Q designed for
Identify small # of adults for whom PA is inappropriate for
What result on PAR Q would mean the individual should consult his or her physician?
- 7 yes/no Q’s (7 of 19 that were shown to be the best predictors of those individuals at risk to exercise)
- A yes response to one or more means individual should consult physician
Of the 7 item q in PAR Q, how many should consult physican on average. Are all these truths
- 26% would need to consult physician
- 1/3 of these false pos aka no basis for advising against
- 5% false neg aka 5 of 100 cautioned against exercise would answer “no” to all 7 q’s
Ischemic heart disease fuxn of?
Genetics, aging, lifestyle factors
3 reasons for exercise stress testing?
- To diagnose abnormal response to exercise denoting CVD
- To assess PA of patients w/known CVD
- TO assess PA of individuals without known CVD
How are exercise stress tests designed
- Single stage where work rate is constant
2. Multistage bike or treadmill w/several work periods, each performed at higher work rate
Purpose of small increments in WR
Determine threshold for myocardial ischemia
What is ramp protocol
Inc at constant continuous rate
Ideal total test time
8-12 mins
How do tests end
- Reach certain objective criteria e.g. onset of angina
2. Fatigue (reached individuals max physical working capacity)
What should precede stress test
ECG and BP measurement (baseline to which exercise ECG can b compared to)
What is stress test limited in
Inability to show extent n specific location of disease
Criterion measure of CAD?
Abnormal coronary angiogram
Angiogram % of false negs
30
What is sensitivity
% of patients w/disease who have an abnormal test
- % of patients w/disease correctly identified on exercise testing
What is specificity
% of patients w/out disease who have normal test
- % of patients w/out disease correctly identified on exercise testing
What is fxnal capacity
Highest WR completed in exercise test before exhaustion
What is fxnal capacity depended on
Gender and age
What is angina
Pain or discomfort in upper chest region caused by hypoxia caused by ischemia
What med can be prescribed to angina patients
Nitroglycerine tablets which dilate coronary arteries
How is insufficient oxygen supply to myocardium detected or coronary insufficiency
ST segment depression of one mm or more below ECG isoelectric line
Magnitude of myocardial ischemia proportional to ___
amt of ST depression, number of ECG leads involved, duration of ST segment depression in recovery
What is PVC? Caused by? Looks like?
Premature ventricular contractions, when ventricles demonstrate disorganized electrical activity
- Portions of ventricle become spontaneously depolarized
- Abnormal, high, long duration QRS
Should exercise be stopped if see PVC
No, only if more than 30% beats are PVC, if they appear at diff phases of cycle, or R portion of PVC superimposed on normal T wave
How does ventricular fibrillation look like
Irregular appearance
- ventricles don’t contract in coordinated manner
- CO falls
How does abnormal HR response during exercise n recovery look compared 2 normal
Normal: progressive inc in HR w/WR. Rapid return of HR 10-20 beats/min above pre-exercise lvls w/in min or two of cessation of exercise
Abnormal: rapid, large inc in HR early in exercise or continued elevation of HR after exercise terminated
Fxn of beta blockers
Suppress HR response to exercise
Fxn of beta blockers
Suppress HR response to exercise
What is normal BP response to graded dynamic exercise is a progressive inc in systolic BP from __ to ___
120 to 190 mm Hg
How much does diastolic BP change w/exercise
Less than 10mm
When should exercise be discontinued
Systolic BP of >250 of diastolic BP >115
Max exercise systolic BP of ____ suggests poor prognosis
<140
What are some signs n symptoms of exercise stress test indicating CVD
- Clammy skin
- Persistent fatigue
- Blueness of lips or nails
How to terminate exercse
Thats enough for today
How to calculate heart rate thru arthmitic:
5 cardiac cycles span 80 mm, chart speed is 25 mm/s
5 beats/100mm x 25mm/s x 60s/min = 94beats/min
Method 2 of HR
HR (b/min) = 1500/R to R distance
Method 3 of HR
- Count .5 squares btwn two adjacent QRS
- 1 square is 300 beats/min, 2 is 150 beats/min
What is the mean electrical axis
Avg of all instantaneous vectors that are generated as ventricles depolarize
What is a normal mean electrical axis
-30 to +105 degrees
When is there a left axis deviation
Les than -30
When is there a right axis deviation
More than +105
How does the heart hang during inspiration vs. expiration
Inspiration: more vertically, inc mean electrical axis e.g. 59 to 90
Expiration: more horizontal, dec mean electrical axis
How can pathology alter mean electrical axis of heart
- Hypertrophy of one side of ventricle displaces vector to that side cause more electrical activity there e.g. left ventricular hypertrophy dec MEA
What is exercise 1 (20 mins)
Deliberately Producing Technical Problems in an ECG
What is aim of exercise 1
Understand causes of 4 technical problems encountered in ECG
What are the 4 technical problems
- 60 Hz interference
- Skeletal muscle tremor
- Motion artifact
- Wandering baseline
What are the steps in 60 Hz interference (4)
- Prep skin (ethanol wipe and shaving if necessary) + use electrode paste or disposable electrodes. Put limb electrodes on subject n record Lead I trace
- Remove lead wire from right leg electrode and record lead I trace
- Replace lead wire from RL electrode n put power cord near subject or have subject grasp power cord. Record Lead I trace.
- Disable filter fxn on ECG machine and repeat #3
What are the steps in Skeletal Muscle Tremor (1)
Perform one of the following: Valsalva maneuvar, talking, isometric contraction of forearms. RECORD LEAD I TRACE
What are the steps in Motion Artifact (1)
Gently tug on lead wires in patient cable. Record Lead I trace
What are the steps in Wandering baseline (1)
Perform deep breathing. Record Lead I trace.
What is exercise 2 (45 mins)
Resting 12-lead ECG from one individual
Aim of resting 12 lead ECG from one individual?
Obtain 12 lead ECG from one subject at rest
Procedure for exercise 2
- Locate positions of 6 chest electrodes
- Mark each positions w/inedible marking pen
- Prep skin at each site
- Prep skin at anterior aspect of both wrists n at meial aspects at both ankles just superior to medial malleolus
- Position subject supine
- Apply pre galled dispoable electrodes to wrists n ankles
- apply pre galled and disposable electrodes to chest sites
- Attach each wire to appropriate electrfoe.
- Record subjects name, gender, n age on beginning of tracing
- Write chart speed at beginning
- Record calibration signal
- Record short strip (20-25cm) from lead I and label “I” on this tracing
- Record short strip from each of the other 11 leads. Label each strip w/lead from which it was recorded
- Mount a short (3-4 QRS complexes) piece of training
What is exercise 3
Effect of Respiration on MEA of heart
What is aim of exercise 3
Observe effects of respiration on MEA of heart
Procedure for exercise 3
- Same subject. Wrist n ankle electrodes needed
- Sitting up on table NOT SUPINE
- Breathe normally
- Record short (3-4 QRS complexes) strip of each of Leads I and III
- Inspire 3 quarters of max inspiration, and hold inspiration
- Record another short strip 3-4 QRS complexes
- Perform 3/4 max expiration and hold. Record short strips from Lead I and III
- Calculate MEA of heart for normal breahting, inspiration, expritation
- Power off ECG, remove wires from electrodes, remove electrodes from subject, clean electrode paste off subject w/water n kleenex
What is exercise 4
Changes in ECG during dynamic exercise
Aim?
Observe changes in ECH during dynamic exercise
Time for ex 4
20 mins
Procedure for exercise 4 changes in ECG during dynamic exercise
- Prep subject
- Place electrodes:
Typically LA (pos) wrist, RA (neg) wrist, RL (reference) ankle. But movement causes wandering baseline and movement artifacts. So, LA is positioned at V6, RA is at right side of chest (bilaterally symmetrical to V6), reference at FLAT PORTION of RIGHT SCAPULA or 7th cervical vertebra - Subject seated on bicycle ergometer
- Record calibration signal
- Record short (20-25cm) strip from Lead I at chart speed of 50 mm. Label as PRE EXERCISE
- Moderately heavy work rate (80% max HR). Tension is 1.5 kp and frequency is 60 rpm. Bike for 4 mins
- Record ECG for Lead 1 at 3:40
- After 1 min of recovery, record final ECG and label Recovery.
Placement for V1?
Right border of sternum in 4th intercoastal space
Placement for V2?
Left border of sternum in 4th intercoastal space
Placement for V3?
Halfway btwn sites for V2 and V4
Placement for V4?
along a vertical line drawn downward from middle of clavicle at lvl of 5th intercostal space
Placement for V5?
anterior axillary line at same lvl of V4 (5th intercostal space)
Placement for V6?
mid axillary line at same lvl of V4 (5th intercostal space)
