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Cardiopulmonary Renal > ECG 1 > Flashcards

ECG 1 Flashcards

1
Q

Summarize the cardiac cycle

A

Action potential is generated in the sinus node (SA node) and spread to the atria producing atrial contraction —>

  1. Atrial systole

S1-mitral and tricuspid valve

  1. Isovolumetric contraction
  2. Rapid ventricular ejection
  3. Reduced ventricular ejection

S2- aortic & pulmonary valve closure

  1. Isovolumetric ventricular Relaxation
  2. Rapid ventricular filling
  3. Reduced ventricular filling
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2
Q

Explain the sequence of depolarization of the cardiac muscle

A

AP generation in the SA node

Right/left atrium depolarization —> atrial contraction

AV node depolarization (delay)

Bundle of His

Septum depolarization

Apex depolarization

Ventricle walls depolarization —> ventricular contraction

Atria repolarization (atria relaxation) occurs during ventricular depolarization

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3
Q

What is an electrocardiogram?

A

Is an amplified, timed recording of the electrical activity of the heart, as detected on the surface of the body.

The recording gives a plot of voltage as a function of time

Body serves as a volume conductor

The heart generates a collection of changing dipoles (vectors) during DEPOLARIZATION & REPOLARIZATION

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4
Q

What is the recording speed of calibratated paper ?

A

Recording speed:

25mm/s
1mm= 0.04s

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5
Q

Describe the horizontal axis of calibratated paper

A

Horizontal axis- time

1 small square= 0.04 seconds

1 big square = 5 small squares

1 big squares= 0.2 secs

300 big squares= 1 min

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6
Q

Describe the vertical axis kf the calibratated paper

A

1 big square 0.5 mV

1 small square= 0.1 mV

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7
Q

What does calibratated paper record?

A

Depolarization or repolarization—> voltage change(mV)—> recorded on moving calibrated paper against time

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8
Q

What are the components of ECG ?

A
  • Waves are deflections above or below baseline
    • P, QRS, T, U waves

Segments baseline between two waves

  • PR segment
  • ST segment
  • TP segment

Intervals include wave(s) & segments
PR interval
QT interval
RR interval

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9
Q

What are the waves of the ECG?

A
  • p wave
  • QRS segment
  • T wave
  • U wave
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10
Q

What are the segments of the ECG?

A

PR segment

ST Segment

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11
Q

What is the point of ECG?

A

J point

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12
Q

What are the intervals of the ECG?

A

PR interval

ST interval

QT interval

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13
Q

What is a dipole?

A

The difference of polarity between two neighboring locations is called dipole

When a portion of myocardium becomes depolarized from an Action potential , it’s polarity is temporarily reversed, becoming positive on the inside and negative on the outside relative to the neighboring of opposite charge, or polarity, within the myocardium

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14
Q

When do you have a dipole?

A

When the myocardium it’s partially depolarized.
-Dipoles are present only when a portion of the myocardium is in the process of depolarization or repolarization while other portions are not.

They are not formed when the entire myocardium is depolarized or repolarized

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15
Q

What is a vector?

A

A vector is an object that has both magnitude and direction

Examples: force, velocity, dipoles generated in the heart during depolarization and repolarization

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16
Q

How to record the electrical activity of the heart?

A

Lead- electrode connection that records the potential difference between 2 electrodes and one of those electrodes is designated as the positive input

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17
Q

How to record the electrical activity of the HEEART?

A

All the cells are in phase 4 (resting membrane potential) isoelectric line IN ALL THE LEADS (ECG: TP segment)

All the cells are in phase 2 (plateau phase) isoelectric line IN ALL LEADS (ECG: ST segment)

Depolarization vector pointing towards the positive electrode
Positive deflection wave

Repolarization vector traveling away from a positive electrode produces positive deflection

Depolarization vector perpendicular to an ELECTRODE AXIS
Produces no net deflection

18
Q

What are leads?

A

Refers to an imaginary line between two ECG electrodes

19
Q

What is Einthoven’s triangle ?

A

3 leads

20
Q

What are the 5 ECG Interpretation rules?

A
  1. A wave of depolarization traveling toward a a positive electrode results in a positive deflection in the ECG tracing
    Corollary: a wave of depolarization traveling away from a positive electrode results in a negative deflection
  2. A wave of repolarization traveling towards a positive electrode results in a negative deflection.
    Corollary: a wave of repolarization traveling away from a positive electrode results in a positive deflection
  3. A wave of depolarization or repolarization oriented perpendicular to an electrode axis has no net deflection
  4. The instantaneous amplitude if the measured potentials depends upon the orientation of the positive electrode relative to the mean electrical vector
  5. Voltage amplitude (positive or negative) is directly related to the mass of tissue undergoing depolarization or repolarization
21
Q

Explain the origin of ECG wave forms

A

Moment to moment orientation and magnitude of net dipoles in the heart determine the formation of ECG wave forms

  • Atrial depolarization: p wave
  • AV node and bundle of His delay: PR segment

-Ventricular depolarization: QRS complex
Atrial repolarization is masked by the ventricular depolarization

  • Ventricles are totally depolarized: ST segment
  • Ventricles repolarization: T wave
  • Arrium and ventricles at resting membrane potential (phase 4): TP segment
22
Q

What is the origin of the P wave?

A

Wave of depolarization that spreads from SA node throughout the atria

Duration 0.08 seconds - 0.1 seconds (2-2.5mm)

Atrial repolarization is not visible in the ECG because it occurs during ventricular depolarization

23
Q

What is the origin of the PR segment?

A

Brief isoelectric (zero voltage ) period after P wave

Represents the time in which the atrial cells are depolarized, and the impulse is traveling within the AV node (decreased conduction velocity)

24
Q

What is the origin of the PR interval?

A

Period from the onset of P wave to the beginning of QRS complex

Duration: 0.12-0.20(3 mm- 5 mm)

Represents the time between the onset of atrial depolarization and the onset of ventricular depolarization

PR interval > 0.2s (5 mm): AV block

25
Q

What is the QRS complex?

A

Represents ventricular depolarization

Duration: 0.06s - 0.1s (1.5 mm- 2.5 mm)

QRS complex duration> 0.12s: intraventricular block

26
Q

Summarize ventricular depolarization sequence

A
  1. Septum depolarization
  2. Free wall depolarization
  3. Base of the LV depolarization
27
Q

What is the function of ST segment?

A

Isoelectric period following QRS complex

Entire ventricle is depolarized

Roughly corresponds with the plateau phase of the ventricular myocyte action potential

ST depression/elevation: diagnosis of ischemia

28
Q

Where is the J point?

A

Junction between end of QRS complex and start of ST segment

29
Q

Whaat is the function of T wave?

A

Represents ventricular repolarization (phase 3 of the action potential)

Last longer than depolarization

T-wave inversion may indicate ischemia or recent myocardial infarction

30
Q

Describe the ventricular repolarization

A

Depolarization of the ventricles occurs first in the subEndocardial region and then in the subepicardial region.

Duration of ventricular action potentials in the subEndocardial myocardium is longer than in the subepicardial myocardium, therefore, subendocardial myocardium is the first to depolarize and the last to repolarize

31
Q

Describe atrial repolarization appearance

A

Atrial repolarization do not appear as a separate deflection of the ECG because it generates a low voltage and it is masked by much larger QRS complex which is present at the same time

First myocardial cells to to repolarize, therefore, it produces a negative deflection

32
Q

What does the QT interval represent?

A

Represents ventricular depolarization-ventricular contraction-ventricular repolarization

Roughly estimates duration of ventrivular action potential

Duration: 0.2-0.4s (depending on heart rate)

In practice, QT interval is expressed as a corrected QT (Q-Tc) interval:

Q-Tc= QT interval/ (square root of RR interval). Normal Q-Tc interval < 0.44

> 0.44: prolonged QT interval, high risk of arrythmias

33
Q

What is the function of TP segment?

A

End of T wave to beginning of the P wave

Phase 4 of ventricular action potential

Represents the electrical resting state

It is traditionally used as the baseline reference from which to assess PR and ST deviations

34
Q

Explain RR (QRS-QRS interval) interval:

A

This equals 1 heart beat

It is measured from one point on a given QRS complex to the corresponding point on the next (usually the peak of R-wave, or nadir of an S or QS wave)

The instantaneous heart rate (beats per min) = 60/RR interval when the RR is measured in seconds (sec)

35
Q

Describe regular HR

A

The “count off” method requires memorizing the sequence:

300- 150- 100- 75- 60-50

Then use this sequence to count the number of large boxes between two consecutive beats:

The second QRS falls between 75 and 60 bpm; therefore, the heart rate is approximately midway between them about 67 bpm. Knowing that the heart rate is approximately 60-70 bpm is certainly close enough

36
Q

Describe irregular heart rate

A

ECG recording paper often indicates 3 sec time makers at the top of bottom of the tracing

To calculate the heart rate, count the number of QRS complexes between the 3 sec markers (= 6 beats in this example) and multiply by 20. Thus, the heart rate here is approximately 120 bpm

It’s even easier (and more accurate) to count the number of complexes between the first and third markers on the strip (representing 6 sec of the recordin) and then multiply by 10 to determine the heart rate.

Method 3 is particularly helpful for measuring irregular heart rates

37
Q

What are the ECG manifestations during acute ischemia?

A

Within hours: peaked T-waves and ST-segment changes (either ST segment depression of elevation )

Within 24 hours: T-wave inversion and ST-segment resolution

Within a few days: pathologic Q waves
-Q wave duration 40 msec

  • Q-wave more than one third(1/3) of the QRS amplitude
  • Scar tissue, electrically dead
38
Q

Contrast subEndocardial infarcts and transmural infarcts

A

Subendocardial infarcts- ST segment depression

Transmural infarction-ST segment elevation

39
Q

Describe current of injury

A

Abnormal current flow caused by acute ischemia

Current of injury underlies the pathophysiology of both ST elevations and ST depressions caused by acute ischemia

  • diastolic current theory
  • systolic current theory
40
Q

Contrast systolic current theory and diastolic current theory of current injury

A

Diastolic current theory- partial depolarization of injured myocardium in diastole before stimulation phase 4

Shifts ECG baseline downward/upward

Systolic current theory- reduced resting membrane potential and repolarize more rapidly phases 0- 3

Current of injury from normally depolarized cells to the ischemic cells

41
Q

What is the origin of current of injury?

A

Cell ischemia—> less ATP —> decreased Na+/K+ ATPase pump—> ischemic cell action potential:

Reduction of the resting membrane potential (phase 4)

Slower and shorter action potential (decreased slope of and less amplitude of phase 0)
repolarization more rapidly

Cardiopulmonary Renal (35 decks)

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