Intro to EKGs Flashcards by Kyra Porter

electrical conduction pathway through the heart

SA (sinus) node → atria → AV node → bundle of His → right and left bundle branches → Purkinje fibers → ventricles

note - left bundle branch divides into left anterior fascicle and left posterior fascicle

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SA node (sinus node) - general

*located in upper part of crista terminalis near SVC opening
*“pacemaker” inherent dominance with slow phase of upstroke
*has the fastest automaticity of all the electrically active regions of the heart

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AV node - general

*located in interatrial septum near coronary sinus opening
*blood supply usually from the RCA
*100msec delay allows time for ventricular filling
*has slower automaticity compared to the sinus node

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pacemaker rates in the heart (general)

SA > AV > bundle of His/Purkinje/ventricles

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speed of conduction in the heart (general)

bundle of His/Purkinje > atria > ventricles > AV node

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P wave

atrial depolarization

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PR interval

*time from start of atrial depolarization to start of ventricular depolarization
*normal: 120-200 msec

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PR segment

*isoelectric
*time from END of atrial depolarization, BEFORE start of ventricular depolarization
*represents the signal as it travels through the AV node

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QRS complex

*ventricular depolarization
*normal: ~ 100 msec

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QT interval

*time from the beginning of the QRS (ventricular depolarization) to the end of the T wave (end of ventricular repolarization)
*ventricular depolarization, mechanical contraction of the ventricles, and ventricular repolarization

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T wave

*ventricular repolarization

note - T-wave inversion may indicate ischemia or recent MI

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J point

*junction between end of QRS complex and start of ST segment

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ST segment

*isoelectric
*measured from the end of the QRS complex to the beginning of the T wave
*represents the period between ventricular depolarization and repolarization

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appearance of the QRS complex

*even though it is always labeled as the “QRS”, not every QRS has to have a q wave, r wave, or s wave
*R wave is ALWAYS A POSITIVE DEFLECTION (UP)
*Q wave is a negative deflection in front of the R wave
*S wave is a negative deflection after an R wave

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standard EKG speed is

25 mm/sec

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standard EKG records how long?

10 seconds

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vertical axis of EKG readout

*vertical axis: voltage (measured in mV)
*1 big box (composed of 5 small boxes) = 0.5 mV
*2 big boxes = 1 mV

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horizontal axis of EKG readout

*horizontal axis: time (measured in msec or sec)
*1 big box = 200 ms (0.2 seconds)
*5 big boxes = 1 SECOND (1000 msec)

EKG electrodes & leads

*electrodes (stickers) detect electrical activity
*an ECG “lead” connects the electrodes to the ECG machine
*leads are specific to location; electrodes are not
*by placing them at specific, fixed locations, they enable us to understand how electricity flows through the heart
*integrating the information obtained from different leads can help up to piece together a diagnosis

direction of EKG deflections, based on direction of electrical signal (relative to the leads)

*if electrical signal is coming TOWARDS the electrode/lead, it will cause an upward or “positive” deflection
*if electrical signal is going AWAY FROM the electrode/lead, it will cause an downward or “negative” deflection
*if electrical signal is parallel (not coming toward or going away from) the lead, it will cause positive and negative deflections to be equal, or it may even be flat; this is termed “isoelectric”

mnemonics for placement of ECG leads

*WHITE to the RIGHT → white limb lead goes to the right shoulder/arm
*red to left ribs
*SMOKE OVER FIRE → black over red on the left side
*snow over grass → white over green on the right side

EKG UNIPOLAR limb leads

*unipolar leads mean these leads use only a positive electrode, and measure the flow of electricity relative to that fixed point
1. lead aVR: right shoulder
2. lead aVL: left shoulder
3. lead aVF: left leg
4. note - there is a lead to the right leg, but this is just an “electrical ground”; we don’t look at it

EKG lead: aVR

*unipolar limb lead
*placement: right shoulder
*lead color: WHITE (white to the right)

EKG lead: aVL

*unipolar limb lead
*placement: left shoulder
*lead color: BLACK (SMOKE > fire)

EKG lead: aVF

*unipolar limb lead *placement: left leg *lead color: RED (smoke > FIRE)

EKG BIPOLAR limb leads

*bipolar: information from 2 leads is used to create a waveform *one electrode can be taken to be positive and the other is negative *creates Einthoven's Triangle *leads I, II, and III

EKG lead: lead I

*right shoulder = negative *left shoulder = positive

EKG lead: lead II

*right shoulder = negative *left leg = positive

EKG lead: lead III

*left shoulder = negative *right shoulder = positive

EKG map

*NORMAL: highest QRS between -30 degrees and +90 degrees (aVL, aVF, lead I, or lead II) *if QRS is highest from -30 to -90, then there is LEFT AXIS DEVIATION *if QRS if highest from +90 to +180, then there is RIGHT AXIS DEVIATION

EKG map: left axis deviation

*lead I positive; lead II negative *if QRS is highest from -30 to -90 on EKG map *causes may include: inferior wall MI, left anterior fascicular block, left ventricular hypertrophy

EKG map: right axis deviation

*lead I negative; aVF positive *if QRS is highest from +90 to +180 on EKG *causes may include: right ventricular hypertrophy, acute right heart strain, left posterior fascicular block

EKG map: severe right axis deviation

*lead I negative; aVF negative *if QRS is highest between -90 and 180 *should never happen; leads are likely placed incorrectly

EKG precordial leads

V1: lower right sternal border V2: lower left sternal border V3 - V5: spaced roughly equidistant from each other between V2 and V6 V6: left midaxillary line

QRS axis based on EKG: stepwise approach

*start at lead 1: positive or negative? -if POSITIVE: look at lead 2 -if NEGATIVE: look at lead aVF

QRS axis based on EKG: if lead 1 is positive...

*look at lead 2: -if POSITIVE: normal -if NEGATIVE: LEFT axis deviation

QRS axis based on EKG: if lead 1 is negative...

*look at lead aVF: -if POSITIVE: RIGHT axis deviation -if NEGATIVE: EXTREME right axis deviation (check your leads)

QRS axis based on EKG: lead 1 POSITIVE, lead 2 POSITIVE

NORMAL QRS axis

QRS axis based on EKG: lead 1 POSITIVE, lead 2 NEGATIVE

LEFT QRS axis deviation

QRS axis based on EKG: lead 1 NEGATIVE, lead aVF POSITIVE

RIGHT QRS axis deviation

QRS axis based on EKG: lead 1 NEGATIVE, lead aVF NEGATIVE

EXTREME RIGHT axis deviation (check your leads)

bradycardia

heart rate < 60 bpm

tachycardia

heart rate > 100 bpm

how can you calculate HR based on EKG?

1. count # of QRS complexes, and multiply by 6 (b/c an EKG measures for 10 seconds) 2. the 300 rule: HR = 300 divided by the number of big boxes between the QRS complexes (see image)