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A Physiology > 2.2. Electrocardiography, the human electrocardiogram. > Flashcards

2.2. Electrocardiography, the human electrocardiogram. Flashcards

1
Q

I. Electrocardiogram (ECG)
1. What is the role of Electrocardiogram (ECG)?

A
  1. The electrocardiogram (ECG) uses surface electrodes to measure changes in potential that result from heart activity.
  2. It measures the signals of pacemaker cells (SA + AV node), but since they are not powerful enough to be detect, the inflections on the ECG result from the depolarization and repolarization of the cardiac myocytes.
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2
Q

I. Electrocardiogram (ECG)
2. From the surface of the human body, electrical signals can only be recorded if…..

A
  1. A large number of cells in the organ perform electrical activity
  2. Perform the electrical activity in a synchronized matter
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3
Q

II. Basic principles of EC recording
1. What are the basic principles of ECG recording

A
  1. When ions are flowing into or out of the extracellular space, the surface electrodes can detect a change in potential during that time period
  2. When depolarization travels in the direction of a positive electrode, this is read by the ECG as a positive inflection, or when depolarization travels towards a negative electrode, it registers as a negative inflection
  3. When repolarization travels in the direction of a positive electrode, the ECG registers a negative inflection, and vice versa
  4. When there is no large net change in ion flow, then the electrodes do not detect any change in voltage and a baseline (0 mV) is detected
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4
Q

II. Basic principles of EC recording
2. What are the directions of De- and repolarization in ventricular wall?

A

De- and repolarization are propagated in the opposite direction in the ventricular wall:
- Depolarization begins at subendocardial -> subepicardial region
- Repolarization from subepicardial region -> subendocardial

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5
Q

III. Dipole vector / heart vector
1. Definition of heart vector

A
  • Heart vector: vectorial sum of elementary dipole vector
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6
Q

III. Dipole vector / heart vector
2. What are the characteristics of heart vector?

A
  • The electrical activity of the heart can be approximated at each moment with the heart vector
  • The heart vector changes during the cyclic activity of the heart
  • The magnitude and direction of the heart vector depends on:
    1. The number of fibers, de- or repolarizing in a unit time
    2. The direction of spread of de/repolarization
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7
Q

III. Dipole vector / heart vector
3. What do the magnitude and direction of the heart vector depend on?

A
  1. The number of fibers, de- or repolarizing in a unit time
  2. The direction of spread of de/repolarization
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8
Q

III. Dipole vector / heart vector
4. What determines the sequence of depolarization in the atrial and ventricular muscle?

A

It is determined by the excitatory and conductive system of the heart
(SA node (depol. atrial muscle)
-> AV node
-> bundle of His (repol.)
-> bundle branches
-> Purkinje fibers
-> depolarization spreads to the ventricular walls)

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9
Q

III. Dipole vector / heart vector
5. What is the sequence of depolarization in the atrial and ventricular muscle is determined by the excitatory and conductive system of the heart?

A

It is determined by the excitatory and SA node (depol. atrial muscle)
-> AV node
-> bundle of His (repol.)
-> bundle branches
-> Purkinje fibers
-> depolarization spreads to the ventricular walls

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10
Q

IV. Direction of depolarization in the frontal plane
1. What are the 5 basic directions of depolarization in the frontal plane?

A
  1. Atrial depolarization, SA-AV (excitation)
  2. Ventricular septum, left -> right (ventricular depol.)
  3. Septum, to the apex (depol.)
  4. Most part of the ventricular wall, endo -> epicardial
  5. Posterobasal part of the left ventriclewalls)
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11
Q

IV. Direction of depolarization in the frontal plane
2A. What are the Movements of the tip of the heart vector in the frontal plane

A
  1. Atrial depolarization
  2. Ventricular depolarization
  3. Ventricular repolarization
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12
Q

IV. Direction of depolarization in the frontal plane - Movement of the tip of the heart vector in the frontal plane
2B. How does the tip of the heart vector in the frontal plane move in case of Atrial depolarization (1)

A
  • Early part of diastole (regions hyperpolarized + all dipole vectors = 0)
  • Atria depolarizes by excitation
    -> excitation delayed in AV node
    -> Ventricles not depolarized
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13
Q

IV. Direction of depolarization in the frontal plane - Movement of the tip of the heart vector in the frontal plane
2C. How does the tip of the heart vector in the frontal plane move in case of Ventricular depolarization (2)?

A
  • Heart vector goes to the opposite direction of the atrial depolarization
  • When septum depolarizes
    -> large heart vector
  • Whole ventricles depolarized
    -> heart vector = 0
    => Atrial repolarization occurs in time with ventricular depolarization
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14
Q

IV. Direction of depolarization in the frontal plane - Movement of the tip of the heart vector in the frontal plane
2D. How does the tip of the heart vector in the frontal plane move in case of Ventricular repolarization (3)?

A
  • Will have opposite direction than ventricular depolarization
  • Will go the same direction as atrial depolarization
  • Not so rapid or synchronized
    => Loop of ventricular repolarization is smaller than the loop of ventricular depolarization
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15
Q

IV. Direction of depolarization in the frontal plane - Movement of the tip of the heart vector in the frontal plane
2E. How do Movements of the tip of the heart vector in the frontal plane correspond to the Segment and intervals of the ECG?

A
  1. Atrial depolarization
    = P wave
  2. Ventricular depolarization
    = QRS
  3. Ventricular repolarization
    = T
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16
Q

V. Segment and intervals of the ECG
1. List 5 important Segment and intervals of the ECG

A
  1. ST segment (isoelectric)
  2. P wave
  3. QRS complex
  4. PR interval (isoelectric)
  5. QT interval
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17
Q

V. Segment and intervals of the ECG
2. What are the representation and duration of ST segment (isoelectric)?

A

Representation: Interval between ventr. depol. and repol
Duration: Maximal change : 0.1 - 0.2mV

18
Q

V. Segment and intervals of the ECG
3. What are the representation and duration of P wave?

A

Representation: Atrial depolarization
Duration: < 0.1 s (0,08 – 0,10s)

19
Q

V. Segment and intervals of the ECG
2. What are the representation and duration of ST segment (isoelectric)?

A

Representation:
Duration:

20
Q

V. Segment and intervals of the ECG
4. What are the representation and duration of QRS complex?

A

Representation: Ventricular depolarization
Duration: < 0.12 s
(0,06 – 0,10s (0,5 -2mV))

21
Q

V. Segment and intervals of the ECG
5. What are the representation and duration of PR interval (isoelectric)?

A

Representation: Conduction from atria to ventricle (delay AV-n)
Duration: 0,12 – 0,20s

22
Q

V. Segment and intervals of the ECG
6. What are the representation and duration of QT interval?

A

Representation: Duration of ventr. depol + repol.
Duration: 0,36 – 0,40s

23
Q

V. Segment and intervals of the ECG
2. What are the representation and duration of ST segment (isoelectric)?

A

Representation:
Duration:

24
Q

VI. What are the 2 types of Leads in ECG

A

Can be either unipolar or bipolar

25
Q

VI. Leads in ECG
2. What are the characteristics of Unipolar leads?

A

Measure the electric impulses of a point in regard to a reference point

26
Q

VI. Leads in ECG
3. What are the characteristics of Bipolar leads?

A

register the voltage between 2 electrodes (one positive, one negative)
-> only the perpendicular projections of the vector on the line connecting the electrodes gives the measurable potential difference
-> if vector is parallel, it does not give any voltage

27
Q

VII. Einthoven’s triangle
1. What are the characteristics of Einthoven’s triangle?

A
  • equilateral triangle whose apices are located in both shoulder and the pubic bone (hip)
  • cardiac vectors lie in the center of the triangle
  • oriented in the frontal plane of the body -> only projection of vector on the frontal plane is detected
  • this triangle has 3 standard limb leads (bipolar)
    1. Lead I:RA(-)+LA(+)
    2. Lead II: RA (-) + LL (+)
    3. Lead III: LL (+) + LA (-)
28
Q

VII. Einthoven’s triangle
2. What are the 3 standard limb leads (bipolar)?

A
  1. Lead I:RA(-)+LA(+)
  2. Lead II: RA (-) + LL (+)
  3. Lead III: LL (+) + LA (-)
29
Q

VII. Einthoven’s triangle
3. What is the mechanism of Einthoven’s triangle?

A
  1. Einthoven has chosen the polarity of the leads in a manner that the wave of the highest amplitude (R-wave) is positive in all 3 leads
  2. Potential difference in lead II is the sum of the potential differences in I and III
30
Q

VII. Einthoven’s triangle - Augmented limb leads (Goldberger leads)
4A. What are the characteristics of Augmented limb leads (Goldberger leads)?

A
  • Unipolar leads: the potential of the active (exploring) electrodes compared to the indifferent (reference) electrode of zero potential
  • There are also 3 augmented unipolar limb leads (Goldberger’s) in the triangle of Einthoven
    1. aVR (augm. Unipolar right) = R arm, axis = -150 degrees
    2. aVL (augm. Unipolar left) = L arm, axis = - 30 degrees
    3. aVF (augm. Unipolar foot) = L leg, axis = + 90 degrees
31
Q

VII. Einthoven’s triangle - Augmented limb leads (Goldberger leads)
4B. How do Augmented limb leads (Goldberger leads) work?

A
  • There are also 3 augmented unipolar limb leads (Goldberger’s) in the triangle of Einthoven
    -> The reference point in the middle of the heart is defined by 3 bipolar limb leads
    1. aVR (augm. Unipolar right) = R arm, axis = -150 degrees
    2. aVL (augm. Unipolar left) = L arm, axis = - 30 degrees
    3. aVF (augm. Unipolar foot) = L leg, axis = + 90 degrees
  • The angle between the lines of aVR and lead II is only 30 degrees, the projections are somewhat similar. But the polarity is opposite!
    -> Therefore, the aVR signal is ‘’almost’’ the mirror image of the signal of the lead II
32
Q

VIII. Unipolar precordial (Wilson) leads
1. What are the characteristics of Unipolar precordial (Wilson) leads

A
  • Reference electrode is the same as in the case of unipolar leads
  • Active electrodes to defined points on the chest projection to (an almost) horizontal plane
  • The most important difference compared to the hexa-axial system is that the active electrodes are close to the heart
  • The electrode ‘’senses’’ the nearby heart muscle better
  • ‘’local’’ information from the different areas of the myocardium
33
Q

VIII. Unipolar precordial (Wilson) leads
2. How do ECG in V1 – V6 leads work?

A
  • V1 in general: ‘’negative R-wave’’, P-wave may be biphasic
    -> R-wave gradual change from (-) to (+)
  • V5, V6: in general positive R-wave, positive P-wave
34
Q

IX. RR distance and heart frequency
1. What is the definition and role of RR distance?

A
  • The distance between 2 R-peaks of the adjacent QRS-complexes
  • Time it takes to cover a RR-distance (0,6 – 1,0s) can be used to calculate the HR
35
Q

IX. RR distance and heart frequency
2. Examples of RR distances and their interpretations?

A
  • 0,6 s -> frequency = 100/min
  • 0,8 s -> frequency = 75/ min
  • 1,0 s -> frequency = 60/ min
36
Q

IX. RR distance and heart frequency
3. What happen if frequency is larger than 100/min?

A

It cause tachycardia

(Tachycardia (tak-ih-KAHR-dee-uh) is the medical term for a heart rate over 100 beats a minute. Many types of irregular heart rhythms (arrhythmias) can cause tachycardia. A fast heart rate isn’t always a concern. For instance, the heart rate typically rises during exercise or as a response to stress.)

37
Q

IX. RR distance and heart frequency
4. What happen if frequency is LESS than 60/min?

A

Frequency < 60/min = bradycardia

(Bradycardia (brad-e-KAHR-dee-uh) is a slow heart rate. The hearts of adults at rest usually beat between 60 and 100 times a minute. If you have bradycardia, your heart beats fewer than 60 times a minute)

38
Q

IX. RR distance and heart frequency
5. What are characteristics of Respiratory sinus arrhythmia?

A
  1. Explains the inconsistency in successive RR distances in a healthy individual.
  2. HR changes according to the respiratory phases
    - Inspiration:
    -> ↓P intrathoracic +P arterial
    -> stimulates baroreceptors
    -> ↓vagal tone
    -> HR↑
  • Expiration:
    -> ↑ P intrathoracic +P arterial
    -> baroreceptors less stimulated
    -> vagal tone unsuppressed
    -> HR↓
39
Q

X. What is the Criteria of the normal sinus rhythm

A
40
Q

XI. How is the electrical axis of the heart constructed?

A
  • Electrical axis of the heart ≈ mean QRS vector
  • Calculated by the values of QRS- complexes from different leads
  • EX: (lead I = R-Q-S = +7 units) and (lead II = R-Q-S = +10 units)

A Physiology (88 decks)

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