ekg/ecg

ekg/ecg

electrokardiogram/electrocardiogram

interchangeable

typical conduction pathway

SA node: 60-100bpm (intrinsic closer to 100, parasympathetic brings number down)

AV node: 40-60 bpm (can also pace the heart at a slower rate if SA node is compromised)

Bundle of His

Bundle branches: 25-40bpm

Purkinje fibers: 25-40bpm

each segment can take over pacing if normal conduction is interrupted higher in the pathway

EKG represents ?

electrical activity (y axis) against time (x axis)

cardiac action potential triggers flows of what ions across the cell membrane?

potassium, calcium, sodium

myocardial depolarization

wave spreads quickly and should cause synchronized contraction of heart muscle

refractory period

each cell has a period where additional electrical stimulation will not cause another depolarization

vector of electrical activity toward an EKG lead

positive deflection (above the line)

vector of electrical activity away from EKG lead

negative deflection (below the line)

12 lead EKG

leads represent different views of heart

limb leads: bipolar (I, II, III); unipolar (aVR, aVL, aVF)

chest leads: V1-V6

10 electrodes give 12 views

telemetry

5 electrodes

provides bipolar leads (I, II, III) and 1 unipolar lead

typically used in hospital setting for quick identification of HR and rhythm

does not diagnose ischemia

EKG paper

x-axis is time

each small box = 0.04 seconds

5 small boxes=1 big box

1 big box=0.20 seconds

5 big box=1 second

phases of cardiac cycle on EKG

P wave

PR interval

QRS complex

ST segment

T wave

R-R interval=1 complete cardiac cycle

P wave

SA node impulse starts atrial depolarization

impulse→AV node→ventricles

heart events: atrial depolarization and contraction (atrial kick)

PR interval

time between atrial depolarization and ventricular depolarization

normal=0.12-0.20 seconds

QRS complex

impulse spreads from AV node→bundle of His→bundle branches→purkinje fibers

heart events: ventricular depolarization and contraction (systole)

should happen quickly

normal=0.06-0.10 se

T wave

pause in electrical activity followed by ventricular repolarization

ST segment and T wave are both sensitive to mismatch btwn myocardial oxygen supply and demand

heart events: ventricular repolarization and relaxation (diastole)

QT interval

represents time btwn start & end of ventricular repolarization

should be <½ of RR interval when rhythm is regular

decr w/ higher HR

short interval is insignificant

long interval=long refractory period=more risk for dysrhythmias

possible causes of long QT interval

ischemia, electrolyte imbalances, medications, hypothermia, heredity

estimating heart rate on EKG for regular rhythms only

find an R that is close to a heavy line

count how many large boxes until the next R

more accurate estimate of HR on EKG

mark a 6-second strip: 30 large boxes

count how many R’s present

multiply by 10 to get beats/min

works for regular and irregular heart rhythms

systematic interpretation of EKGs

is the R-R interval the same for each beat?: indicates whether rhythm is regular/irregular

estimate/calculate HR

is there a P wave for every QRS complex?

QRS complex fore very P wave?

what is the PR interval?

are the QRS complexes narrow, do they all look the same?

does anything else look abnormal?

normal sinus rhythm

R-R interval is the same for each beat

HR btwn 60-100 bpm

every P wave has a QRS complex, PR interval between 0.12-0.20 seconds (<1 large box)

every QRS complex has a P wave

every QRS complex is narrow and looks consistent (duration <0.12 seconds or <3 small boxes)

sinus tachycardia

sinus rhythm >100bpm

occurs in response to excs, stress, anxiety, pain, dehydration, stimulants

less common causes: hyperthyroidism, anemia, blood loss

incr myocardial O2 demand (workload on the heart)

sinus bradycardia

sinus rhythm <60 bpm

may occur in highly conditioned athletes

other potential causes: infection, hypothyroidism, sleep apnea, beta blockers, rheumatoid conditions, TBI

may decr CO

sinus dysrhythmia/sinus arrhythmia

all features of normal sinus rhythm except irregular R-R intervals

normal variant of sinus rhythm that occurs w/ respiratory pattern

may be due to fluctuating stimulation of vagus nerve during breathing cycle

sinus arrest/sinus block

SA node fails to initiate an impulse—missing P wave

P waves are normal, identical, occur before every QRS

PR interval normal

QRS complex is narrow, normal

R-R interval is regular except for when pause occurs

caused by sudden incr in para activity, diseased SA node, infection, digoxin toxicity

implications: long pauses can reduce CO and cause syncope

supraventricular arrhythmias/dysrhythmias

abnormal conduction occurs above the ventricles

QRS complexes remain narrow and normal

ventricular arrhythmias/dysrhythmias

ectopic pacemaker occurs w/in ventricle

QRS complexes are wide and abnormal shape

conduction blocks

normal conduction is interrupted

types of supraventricular arrhythmias

premature atrial complexes (PACs)

atrial tachycardia

supraventricular tachycardia

atrial fibrillation

atrial flutter

premature atrial complex

early beat initiated w/in atria but not SA node

“ectopic”

rhythm: skipped/early beat may be felt by pt or on palpation

P wave present for every QRS complex, but different size/shape or buried in T wave from previous beat

PR interval normal

QRS narrow and normal

implications: usually benign; incr freq may lead to atrial fibrillation or SVT; may be caused by stress, nicotine, caffeine, alcohol, hypoxemia

multiple PACs

atrial bigeminy

atrial tachycardia

atrial bigeminy

alternating regular beats and PACs

atrial tachycardia

3 or more PACs consecutively

may be paroxysmal—comes on spontaneously and self-resolves

may be sustained w/ HR 140-250 bpm

supraventricular tachycardia

ectopic pacemaker in atria

rhythm: very regular

rate >100bpm, often higher

P waves: hidden in preceding T waves

PR interval: unable to measure

QRS complex narrow and normal

implications: high HR→reduced ventricular filling time; impaired CO; syncope

atrial fibrillation

inconsistent, irregular R-R intervals w/o clear P waves

multiple simultaneous impulses from different locations in atria

rhythm: very irregular w/o clear pattern

rate: may be normal (rate controlled) or tachycardia (rapid ventricular response)

P waves not present, may see fibrillation wave

PR interval NA

QRS narrow and normal

implications: incr risk of embroils stroke, loss of atrial kick→impair ventricular filling, esp. at higher HR

atrial flutter

P waves replaced by F waves with sawtooth appearance

ectopic focus in atria depolarizes repetitively at a rate of 250-350 bpm

rhythm: regular

rate: normal or elevated, determined only by ventricular depolarization, conduction ratio can be 2:1 up to 8:1

P waves replaced by rapid F waves

no PR interval

normal narrow QRS

implications: hemodynamically stability depends on ventricular rate

junctional rhythm

no impulse from SA node

AV node takes over pacing

rhythm: regular

rate: 40-60 bpm (intrinsic AV node rate)

P waves not present, may be inverted or hidden in QRS

PR interval unmeasurable

QRS normal and narrow

implications: loss of atrial kick, lower HR can impact CO

ventricular arrhythmias

premature ventricular complexes (PVCs)—unifocal, multifocal, ventricular bigeminy/trigeminy/quadrigeminy, couplets

premature ventricular complexes

ectopic focus in the ventricle causes early QRS

QRS wide and abnormal shape bc impulse doesn’t follow normal conduction pathway

ventricular contraction slower, less synchronized

PVCs may be followed by a pause before normal rhythm resumes

implications: impaired ventricular filling and contraction, decr SV→decr CO

more=potential to deteriorate to VT or V fib

unifocal PVC

all look the same

multifocal PVC

PVCs look different

couplets PVC

2 consecutive PVCs

bigeminy PVC

alternating normal beats and PVCs

trigeminy PVCs

2 normal beats followed by PVC

quadrigeminy PVC

3 normal beats followed by PVC

ventricular tachycardia

3+ consecutive PVCs

may be sustained or non-sustained, w or w/o pulse

rhyth: regular

rate: 100-250 bpm

no P wave

no PR interval

QRS wide and abnormal

potential causes: electrolyte abnormality, ischemic heart disease, meds, hypoxemia

implications: significant impairment in CO, potential to degenerate to V fib

ventricular fibrillation

irregular quivering of ventricle/myocardium

result: no CO

rhythm: irregular w/o discernible P wave, QRS complex, T wave

pt has no pulse

medical emergency, requires immediate CPR and defibrillation

conduction blocks

first degree AV block

second degree AV block, type 1 and 2

third degree/complete heart block

bundle branch blocks

first degree AV block

PR interval abnormally long

rhythm: regular

rate; usually normal

P wave normal

PR interval >0.20 seconds

QRS occurs after each P wave, narrow and normal

potential causes; ischemia, electrolyte abnormalities, incr vaal tone, rheumatoid conditions

implications: slowed transmission of impulses from atria to ventricles

typically asymptomatic