The Electrocardiogram

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My notes from Chapter 2: Basic Electrophysiology Section: The Electrocardiogram ECGs Made Easy 4th Ed., 2011 Barbara Aehlert, RN, BSPA

electrocardiogram

records the electrical activity of a large mass of atrial and ventricular cells as specific waveforms and complexes [p41]

think of ECG as voltmeter...

records the electrical voltage (potentials) generated by depolarization of the heart's cells [p41]

basic function of the ECG

detect current flow as measured on the patient's skin [p41]

purposes of ECG monitoring

~monitor a patient's HR
~evaluate the effects of disease or injury on heart function
evaluate pacemaker function
~evaluate the response to meds
obtain a baseline recording before, during, and after a medical procedure
[p41]

ECG can provide info about...

~orientation of the heart in the chest
~conduction disturbances
~electrical effects of meds and electrolytes
~the mass of cardiac muscle
~presence of ischemic damage
[p41]

ECG does not provide info about...

mechanical (contractile) condition of the myocardium [p42]

to evaluate the effectiveness of the heart's mechanical activity, assess...

the patient's pulse and blood pressure [p42]

ECG does not directly record the activity of the heart's electrical system since these structures are too small, instead is shows...

ECG shows the activation and recovery of the working cells of the heart's electrical system [p42]

electrode

the paper, plastic, or metal device that contains conductive media and is applied to the patient's skin [p42]

3 types of electrodes

metal disks
metal suction cup
disposable disk
[p42]

disposable disk electrodes

adhesive ring with a conductive substance in the center [p42]

lead

a record (tracing) of electrical activity between 2 electrodes [p42]

leads measure

the average current flow at a specific time in a portion of thee heart [p42]

leads allow viewing of the heart's electrical activity in 2 different planes______ and _____.

frontal (coronal)
horizontal (transverse)
[p43]

12-lead ECG provides views of...

in both frontal and horizontal planes and views the surfaces of the left ventricle from 12 different angles [p43]

12-lead ECG can identify...

ischemia, injury, and infarction affecting any area of the heart [p43]

step 1 of ECG monitoring

explain the procedure to the patient while checking the equipment; no loose pins and no frayed or broken cable or lead wires; adequate paper supply; connect ECG cable to machine; connect lead wires to ECG cable; turn power on to monitor; adjust screen contrast if necessary [p42]

step 2 of ECG monitoring

open a package of ECG electrodes; make sure gel is moist; attach electrode to each lead wire [p42]

step 3 of ECG monitoring

prep patient's skin; rub skin with dry gauze pad; shave if needed [p43]

step 4 of ECG monitoring

one at a time, remove the backing from each electrode and apply them to the patient; place limb leads anywhere on appropriate limb; do not place over bony areas, broken skin, joints, skin ceases, scar tissue, burns, or rashes; connect the lead wires to the electrodes [p43]

step 5 of ECG monitoring

coach the patient to relax; select the desired lead on the cardiac monitor; adjust ECG size if necessary; feel patient's pulse and compare to HR on monitor; set HR alarm on monitor according to agency's policy [p43]

step 6 of ECG monitoring

select print/record button to obtain a copy of patient's ECG; interpret rhythm; assess patient to find out how he is tolerating the rate and rhythm; attach rhythm strip to the patient's record/report; continue patient care [p43]

frontal plane leads

view heart from the front of the body as if it were flat; directions are superior, inferior, right and left; 6 leads view frontal plane; 3 bipolar leads and 3 unipolar leads [p44]

bipolar leads
standard limb leads

Leads I, II, III
ECG lead that has a positive and negative electrode; records the difference in electrical potential between 2 selected electrodes [p44]

unipolar lead
unipolar limb leads
augmented limb leads

aVR, aVL, VF
single positive electrode and a reference point [p44]

axis of the lead

imaginary line joining the positive and negative electrodes of a lead [p44]

Einthoven's triangle

the axes of the tree limbs leads forming an equilateral triangle with the heart at the center [p44]

lead I

records the difference in electrical potential between the left arm (+) and the right arm (-) electrodes; 3rd electrode is ground that minimizes electrical activity from other sources; LATERAL surface of the Left ventricle [p44]

lead II

records the difference in electrical potential between the left leg (+) and right arm (-) electrodes; INFERIOR surface of the Left ventricle [p44/45]

lead III

records the difference in electrical potential between the left leg (+) and left arm (-) electrodes; INFERIOR surface of the Left ventricle [p45]

augmented limb leads

"a" augmented
"V" voltage
aVR - augmented Voltage Right arm
aVL - augmented Voltage Left arm
aVF - augmented Voltage left Foot (leg)
[p45]

aVR, aVL, aVF

distinct positive pole; unipolar leads; in place of a single negative pole these leads have multiple negative poles, creating a negative field (central terminal) - heart at the center [p46]

aVR

Right arm - views the heart from the right shoulder (+) and views the base of the heart (the atria and great vessels) - doesn't view any wall of the heart [p46]

aVL

Left arm - combines views from right arm and left leg with the view being from the Left arm and orientated to the lateral wall of the left ventricle [p46]

aVF

Left foot/leg - combines views front he right arm and left arm toward the left leg, viewing the inferior surface of the left ventricle from the left leg [p46]

Augmented Leads

LEAD/+ electrode/heart surface viewed
aVR - right arm - none
aVL - left arm - lateral
aVF - left leg - inferior
[p46]

horizontal plane leads

view the heart as if the body were sliced in half horizontally; directions are anterior, posterior, right, and left; 6 chest (precordial or "V") leads view the heart in the horizontal plane; view front and left side of the heart [p46]

chest leads

V1, V2, V3,V4,V5,V6; each electrode place in "V" position is positive; negative electrode is found at the electrical center of the heart; chest leads are unipolar leads [p46]

lead V1

4th intercostal space, just to the right of the sternum; views Septum [p46]

lead V2

4th intercostal space, just to the left of the sternum; views Septum [p46]

lead V3

a line midway between V2 and V4; views Anterior [p46]

lead V4

left midclavicular line in the 5th intercostal space; views Anterior [p46/47]

lead V4R

if a right myocardial infarction is suspected, lead V4 may be moved to the same anatomic location as V4, but on the right side of the chest; viewed for ECG changes consistent with acute MI [p47]

lead V5

left anterior axillary line at the same level as V4; views Lateral [p47]

lead V6

left midaxillary line at the same level as V4; views Lateral [p47]

right chest leads

used to view specific surfaces of the heart; used when right ventricular myocardial infarction is suspected; placement identical to standard chest leads except on right side of chest; if time doesn't permit, use only V4R [p47]

posterior chest leads

used to view posterior surface of heart; placed further left and toward the back; placed on same horizontal line as V4 to V6; lead V7 is placed on the posterior axillary line, V8-angle of the scapula (posterior scapular line); lead V9-over the left border of spine [p47]

modified chest leads (MCL)

bipolar chest leads that are variations of the unipolar chest leads; each MCL consists of a + and - electrode applied to a specific location on the chest; accuracy is important [p47]

uses for MCL

detecting bundle branch blocks, differentiating right and left premature beats, and differentiating supraventricular tachycardia from ventricular tachycardia [p47]

lead MCL1

variation of lead V1 and views the ventricular septum; neg placed below the left clavicle toward left shoulder; positive placed to the right of the sternum in the 4th intercostal space; QRS complex usually appears negative [p47]

lead MCL6

variation of lead V6and views low lateral wall of the left ventricle; neg placed below the left clavicle toward left shoulder and positive is placed at the 5th intercostal space, left midaxillary line [p47]

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