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CardioPulm > Cardiac AP + ECG Interpretation > Flashcards

Cardiac AP + ECG Interpretation Flashcards

1
Q

What four ions determine the electro-chemical gradient in cardiac cells?

A

K+
Na+
Ca2+
Cl-

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2
Q

What is the resting membrane potential in cardiac cells?

A

-90mV

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3
Q

What ions are primarily responsible for the resting membrane potential of cardiac muscle?

A

K+ equilibrium potential

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4
Q

At rest only these channels are open and the RMP is -90mV

A

K+ channels

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5
Q

What causes voltage gated Na+ ion channels to open?

A

Wave of depolarization from one end of the membrane causes the adjacent sodium channels to open.

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6
Q

What does cardiac AP depend on?

A

Similar to skeletal muscle it depends on time varying membrane conductance.

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7
Q

What are the 5 phases of the cardiac action potential?

A

Phase 0 - Upstroke
Phase 1 -Early Repolarization
Phase 2 - Plataeu
Phase 3 - Actual Repolarization
Phase 4 - RMP

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8
Q

What happens in Phase 0 of Cardiac AP

A

Heart muscle reaches threshold to generate AP.
Fast upstroke = fast AP = fast conduction
Membrane permeability = Na+

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9
Q

What happens in phase 1 of cardiac AP

A

Early repolarization. VG K+ channels open just a little and K+ eflux causes small repolarization to happen. Little drop in MP

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10
Q

What happens in phase 2 of cardiac AP?

A

Plateau. There is abalance between Ca2+ influx and K+ eflux so slight balance between depolarization and repolarization. This is the main difference from skeletal muscle APs

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11
Q

What happens in phase 3 of cardiac AP?

A

Actual Repolarization = VG K+ channels open for real and no more Ca2+ influx. Moving back to K+ equilibrium.

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12
Q

What happens in phase 4 of cardiac AP?

A

Background K+ channels are open again so cells reach RMP again. Back at around -90mv

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13
Q

What phases of cardiac AP correspond with EKG reading?

A

Phase 0 = QRS complex
Phase 1 = end of QRS complex
Phase 2 = ST segment
Phase 3 = T wave

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14
Q

The QRS is primarily caused by movement of what ion?

A

Myocardial Na+ ion.

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15
Q

The T wave is a result of movement of what ion?

A

K+ ion movement

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16
Q

What part of the Cardiac AP is the refractory period?

A

During the plateau phase and during first part of the actual repolarization phase — this part the myocardium cannot be stimulated again.

Phase 2 - Phase 3 of AP graph

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17
Q

During abnormal conditions the myocardium CAN be stimulated here?

A

Later part of actual repolarization phase (phase 3) and hyperpolarization
Abnormal conditions like: ischemia, re-entrant currents, and altered electrolytes

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18
Q

A patient with Hypokalemia might affect what phases of cardiac AP?

A

Slower time course of phase 2 and 3 due to not enough K+ so repolarization takes longer.

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19
Q

What direction is the deflection when depolarization current moves toward the electrode?

A

Positive deflection above isoelectric line

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20
Q

What direction is the deflection when depolarization current moves away from the electrode?

A

Negative deflection below isoelectric line

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21
Q

AT REST, what channels are open and what is equilibrium potential?

A

K+ channels open
Na+ channels close
Eq Potential = -90mV

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22
Q

During DEPOLARIZATION what channels are open and what is membrane potential?

A

K+ stay open
Na+ open
Membrane potential = +30mV

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23
Q

When an ECG is calibrated how much does the little block measure? And the big block?

A

Little block measures 0.1mV vertical and measures 0.04 seconds horizontally
Big block measures 0.5mV vertically and measures 0.2 seconds horizontally

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24
Q

What are the 12 leads for a 12 lead EKG?

A
  • 6 Limb leads = bipolar leads 1, 2, 3 and unipolar leads AVr, AVl, AVf
  • 6 chest leads = V1-V6
25
Q

What is the sequence for the conduction of the heart?

A

SA node -> AV node -> slight pause in AV node -> Bundle of His -> L/R bundle branches -> purkinje fibers -> spread depolarization to myocytes.

26
Q

How does depolarization spread to R and L atrias?

A

Via inter- and intra- atrial tracts called Bachman’s bundle

27
Q

Damage to the inter and intra atrial bundles can lead to?

A

Disruption of the P wave
Atrial Fibrillation

28
Q

What are the components to a normal wave form on an EKG?

A

P wave - atrial depolarization
QRS - ventricular depolarization
T wave - Ventricular repolarization

29
Q

What are the intervals of an EKG?

A

PR interval and QT interval

30
Q

What does the PR interval show?

A

Time for the SA node to fire, get to AV node, AV node to pause for a sec, and start signal to ventricles .
Duration of the PR interval depends on conduction velocity at the AV node

31
Q

What does the QT interval show?

A

Full time it takes for the ventricles to fully contract and fully relax.

32
Q

What does the QRS reflect?

A

Conduction through the myocardium. Due to extensive branching of the purkinje fibers.

33
Q

What does the ST segment represent?

A

Delay between depolarization and repolarization of the ventricles. Normally at the isoelectric line

34
Q

How can you determine HR from an EKG?

A
  • If you get a 6 second strip - count number of QRS and multiply by 10 — just an estimate
  • Can count down from the a QRS on a darker line and count each big box down 300-150-100-75-60.
  • Can count number of small boxes from one QRS to the next and divide into 1500
35
Q

What is a good sequence to interpret an ECG?

A
  1. Is it regular?
  2. Is the HR normal - between 60-100
  3. Look at P and QRS - are there p waves, and is it a 1:1 ratio
  4. Look at QRS complex - is it too long?
  5. Look at PR interval - is it too long?
36
Q

What can sinus bradycardia be caused by?

A

Normal in athletes due to increased stroke volume
- can be caused by beta blockers, calcium channel blockers, antiarrhythmic drugs, or vagal stimulation

37
Q

What is sinus arrhythmia?

A

Irregularity caused by SA node often due to altered vagal stimulation.

38
Q

What does a left axis deviation suggest?

A

LV Hypertrophy

39
Q

What does a R axis shift suggest?

A

RV Hypertrophy or MI

40
Q

What is the first thing checked when MI is suspected?

A

If T wave is inverted or ST segment depression is present.

41
Q

What are the 3 important determinants of CO?

A
  • Preload
  • Afterload
  • Contractility
42
Q

What is preload

A

Volume with which ventricle is loaded
- determined by venous return and atrial kick
- starling law = greater stretch= greater force

43
Q

What is afterload

A

Resistance to blood flow
- Diastolic BP is primary determinant

44
Q

What is contractility?

A

State of the cardiac muscle with regard to ability to generate force
- In heart failure contractility goes down
- in Acute and chronic exercise contractility goes up

45
Q

How is contractility typically measured?

A

Ejection Fraction

46
Q

What does the contractile state of the heart depend on?

A
  1. Intrinsic factors = training, disease, structure
  2. Autonomic Nervous System - ACh for vagus N, NE for cardiac nns
  3. Hormonal factors = epi, angiotensin, other hormones
47
Q

How is contractility regulated?

A

Through Ca2+
- amount of calcium influx determines the level of activation of cardiac muscle
- drugs like calcium channel blockers, beta blockers, digitalis affect contractility by altering Ca2+ delivery

48
Q

What is the baroreceptor cardiac reflex?

A
  • Carotid body senses increases in BP and alters vasodilation, HR, and contractility to normalize BP
49
Q

What is the bainbridge Reflex?

A

R Atrium senses increases in blood volume and modulates HR
* responsible for respiratory ECG rhythm

50
Q

What is the chemoreceptor cardiac reflex?

A

Brain stem sense CO2, H+, and O2 levels and alters HR, BP, contractility, and respiration

51
Q

Where is the primary site of resistance in the body’s circulatory system?

A

Arterioles
Smaller radius

52
Q

What is most of the body’s resistance set up?

A

In parallel. Loss of a part of the body like amputation increases the total peripheral resistance

53
Q

What is the radius of a blood vessel determined by?

A
  • Local metabolic needs
  • Vasoactive substances - adenosine, K+, H+
  • CNS - sympathetic NS
  • Hormones - Epi, angiotensin, antidiuretic H
54
Q

Where does nutrient and waste exchange occur in circulatory system?

A

Capillaries and venules by 2 different mechanisms - diffusion and filtration

55
Q

What is diffusion vs. Filtration really important for?

A

Diffusion = most important for nutrient/waste exchange
Filtration = most important for fluid balance

56
Q

What are the effects of exercise on contractility and HR?

A

Contractility and heart rate increase at the same time that resistance decreases causing a net effect of SBP increase

57
Q

What happens to DBP when large mm groups are exercised vs when small mm groups are exercised?

A
  • large mm groups = DBP either remains constant or may decrease
  • small mm groups = DBP may increase slightly
58
Q

Resistance exercise produces an increase in both SBP and DBP

A

True

59
Q

What are some abnormal responses to exercise on HR?

A
  • HR rises very rapidly — deconditioning or CV problem limiting the Stroke Volume
  • HR rises just a little — often due to cardiac meds or heart disease
  • Decrease in HR — indicative of severe disease and/or arrhythmias

CardioPulm (4 decks)

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