Cardiac Electrophysiology Flashcards by Alex Stein

Wave of depolarization ____ contraction

Preceeds

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Pacemaker

SA node

Where the impulse is initiated = rate of about 70 impulses/min

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1 cardiac cycle: SA Node –>

AV node –> Delay –> AV bundle –> L/R bundle branches –> Purkinje fibers

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Resting Cardiac Ventricular Cell

Na Ca and K

Na and Ca higher outside
K higher inside
So at rest, inside is negative and outside is positive

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Action Potentials differ depending on

Location in heart

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What sets the pace

SA node

No nerves needed, everything starts here

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Automaticity

SA node is leaky to Na –> Threshold

AP is similar in AV node, but slower so SA node is what is setting the pace

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What causes the upstroke

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What is happening during repolarization

K is leaving the cell

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Influence of ANS on Heart Rate - NE

B1 –> cAMP –> (+) Ltype Ca channel

Inc if –> inc slope of phase 4 –> reach threshold faster –> inc heart rate

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Influence of ANS on Heart Rate - Ach

Muscarinic receptors –> dec cAMP –> (-) L type Ca channel
Dec if –> dec slop of phase 4 –> reach threshold slower –> dec heart rate
Ach hyperpolarizes the membrane and shifts the threshold upward

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Effective Refractory Period

No new AP can form

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Relative Refractory Period

Is possible for a new AP to form but is very difficult

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What is purpose of refractory period

Helps control AP direction, prevents tetany, and allows chambers time to fill

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Phase 0

Influx of Na

Upstroke

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Phase 1

Kto = transient outward

Lets K squeak out

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Phase 2

Calcium channels (influx)
Maintain depolarization

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Phase 3

Repolarize

K leaves the cell

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How is electrical activity measured in the heart

3 major waves

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3 major waves

P wave = atrial depolarization
QRS complex = ventricular depolarization
T wave = ventricular repolarization
- Tau wave = atrial repolarization masked by QRS complex

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Clinical Uses of measuring heart activity

Arrhythmias
Ischemia and infarction
Heart orientation
Abnormal electrolytes and drugs

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Inflections occur due to

Electrical activity (potential) traveling toward the positive electrode

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Fibrous Skeleton

Plate of fibrous dense CT btw atria and ventricles
Electrical insulation
Site for muscle attachment

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ECG provides signal info on

Direction that signal is moving
Speed at which signal is moving (r-r interval; basis for heart rate)
Mass of tissue through which it is moving (thicker mass, higher peak will be)

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P Wave

Atrial Depolarization +

QRS Complex

Ventricular Depolarization | - + -

T Wave

Ventricular Repolarization +

How many electrodes does a 12 lead ECG use

10 electrodes | RU, LU, RL, LL, V1-V6 (precordial/chest)

Bipolar, Limb, Standard Leads

I, II, III - frontal plane

Augmented Leads

aVL, aVR, aVF - frontal plane

Chest or Precordial Leads

V1 - V6 - Transverse plane

Biggest QRS complex from which lead

Lead II

V1 and V2 give more info on what

Right side of the heart | Located on either side of sternum

V3 - V6 give more info on what

Left side of the heart | V3/V4 - septal area

Purpose of an augmented lead

Designed to start in the center of the heart To where it is exploring to aVR - starts at center and goes to right

How does augmented start in middle of heart?

Vector of two different sites. aVR for Ex Vector of LU and LL to start in center of heart

aVR pos or neg deflection

Negative deflection | Starts in center and goes to right towards negative electrode

aVL pos or neg deflection

Positive deflection | Starts in Center and goes to left side

aVF goes towards

Starts in center and goes towards feet

Why is there positive deflection

heart signal going toward positive electrode

Bipolar Leads

``` Ex: Right arm to Left arm One end is - and one is + Hash mark = 0 point in center of the two Current flowing to the left of hashmark would be neg deflection and to right would be positive deflection R(-) 0 L(+) ```

Augmented Unipolar Lead

Inc size of signal by tying 2 electrodes together and have them brought to ground Current flowing toward exploring electrode causes positive deflection

Chest Unipolar Lead

Bipolar and augmented leads all look at heart in coronal plane Chest does it in transverse place - allows us to collect info about anterior/posterior heart

12 leads provide how many views of heart

12 | more views = more diagnostic info

Mean Electrical Axis

Tells us net direction the depolarization or repolarization is headng

Normal value for mean electrical axis

between -30 and +90 toward the apex of the heart

1 box =

300 beats per mnute

If number of boxes is 3?

300/3 = 100 beats per minute

If number of boxes is 2?

300/2 = 150 beats per minute | Sinus Tachycardia

If number of boxes is 4?

Normal Sinus Rhythm | 300/4 = 70 beats per minute

1st step when look at ECG

Make sure P wave preceeds QRS and T follows

2nd step when look at ECG

Check rate - number of boxes between

3rd step when look at ECG

Check for inconsistencies or potential pathologies

If number of boxes is 6?

Sinus Bradycardia 300/6 = 35 beats per minute Can be pathological or athlete

Bradycardia in athletes?

Hypertrophy More filling time Parasympathetic inc.

Extopic Beat

Beat that riginates outside of the SA node

Multiform PVCs

Premature ventricular contraction Ectopic foci in the ventricle Could happen to anyone - coffee, exam Pathological if happens like every 4 beats or something but generally is fine

PACs

Early triggering of beat Premature atrial contraction - ectopic foci in the atria Wouldn't really feel this - is more common

Atrial Fibrillation

Most common cardiac arrhythmia May be asymptomatic but often results in palpation, chest pain, and fainting Primary worry = can lead to stroke No P before QRS

Ventricular Fibrillation

Medical emergency Leads to cardiac arrest Early AED use improves diagnosis No performance from the heart at all - need to get AD out

Heart Block

Signal is partially or completely blocked from reaching the ventricles

First Degree Heart Block

Slowed from A to V - common in athletes

Third Degree Heart Block

More dissociation between atria and ventricle No P wave Atria and ventricles acting at their own tune

ST Segment Issues

ST segment depression - ischemia T wave inversion - ischemia ST segment elevation - ischemia

What percent of individuals with angina show normal ECGs

30%

Stress Test

detects silent ischemia - changes in heart that can occur in absence of anginal pain