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CPR 1 > Lecture 13 > Flashcards

Lecture 13 Flashcards

1
Q

What is an ELECTROCARDIOGRAM

(ECG)?

A

An ELECTROCARDIOGRAM (ECG) is an amplified, timed recording of the electrical activity of the heart, as detected on the surface of the body.

-Plot of voltage as a function of time.

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2
Q

Describe the lines of an ECG

A

-3 lines (Leads) w 4 parts

Parts:

1) Standard bipolar leads
2) Augmented limb leads
3) Chest/precordial leads

Parts 1 and 2:
-Record electrical activity of the heart in frontal (Coronal) plane

Parts 3 and 4:
-Record electrical activity of the heart in the horizontal plane (Chest)

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3
Q

Whats the recording speed of the Calibrated paper?

A

-Measures the horizontal axis-time (milliseconds)

1 Small square:
25 mm/s = 0.04 seconds

1 Big square= 5 small squares
0.20 seconds

300 big squares
1 min

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4
Q

Whats the recording voltage of the Calibrated paper?

A

-Measures the vertical amplitude axis-millivolts

1 big square = 0.5 mV

1 small square = 0.1 mV

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5
Q

What are the components of ECG tracing?

A

1) Waves –> deflections/baseline
- P, QRS complex, T, U wave

2) Segments –> baseline between 2 waves
- PR, ST, TP segments

3) Intervals –> Includes waves and segments
- PR, QT, RR interval

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6
Q

What’s the significance of lead (line 2)?

A

-Reference point for many factors (Ex: HR) bc has main vector of heart

Cycle:
-P wave =

  • QRS = reference –> ventricular depolarizaion
  • T wave =
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7
Q

Origin of ECG waveforms

Dipoles

A

Depolarization/Repolarization –> Dipole vectors –> Leads record ECG

Dipoles:
-Difference of polarity between two neighboring locations (One pos, one neg)

-Occur When the myocardium is partially depolarized

  • = repolarization
    += depolarization
    (Follows charge direction)
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8
Q

What’s a Vector

A

-an object that has both magnitude and direction
(Ex: Force, velocity, dipole, depolarization, repolarization)

-Can combine vectors that go into the same direction (Ex: SA Node vectors)

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9
Q

How do we record electrical activity of the heart?

A

1) Lead –> Electrode connection
- Records the potential difference between 2 electrodes
- (One positive one negative electrode)

2) Electroaxis –> Connects positive and negative electrode (Imaginary)

3) Isoelectric line
- All cells are in phase 2 (plateau phase) or Phase 4 (resting)
- In all leads (Flat line)

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10
Q

Origins of the ECG Waveforms

P wave

Pr Segment

QRS Complex

ST Segment

T Wave

TP Segment

A

P wave
-Atrial depolarization

PR Segment
-A-v node and bundle of HIS delay

QRS Complex
-Ventricular depolarization

ST Segment
-Ventricles totally depolarized

T Wave
-Ventricular repolarization

TP Segment
-Atrium and ventricules at resting membrane portential (phase 4)

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11
Q

ECG INTERPRETATION

Rules

A

1) A wave of depolarization traveling toward a
positive electrode results in a positive deflection
in the ECG tracing

2) A wave of repolarization traveling towards a positive electrode results in a negative deflection
3) A wave of depolarization or repolarization oriented perpendicular to an electrode axis has no net deflection.

4) The instantaneous amplitude of 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

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12
Q

P Waves:

A
  • Wave of depolarization that spreads from SA node throughout the atria
  • Duration 0.08 – 0.10 seconds (2 – 2,5 mm)
  • Atrial repolarization is not visible in the ECG because it occurs during ventricular depolarization
  • Positive deflections
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13
Q

P Waves:

A
  • Wave of depolarization that spreads from SA node throughout the atria
  • Duration 0.08 – 0.10 seconds (2 – 2,5 mm)
  • Atrial repolarization is not visible in the ECG because it occurs during ventricular depolarization
  • Positive deflections in triangle
  • Highest voltage P wave leads will be the one that goes in the same direction (Parallel) as the projection vector
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14
Q

PR Interval:

A

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

Duration: 0.12 – 0.20 (3mm – 5mm)

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

PR interval > 0.20 s (5mm): AV block

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15
Q

QRS Complex:

A

Represents ventricular depolarization

Duration: 0.06 s – 0.10 s (1.5mm – 2.5 mm)

QRS complex duration > 0.12 s: Intraventricular block

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16
Q

ST Segment

A

Isoelectric period following QRS complex

Entire ventricle is depolarized

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

ST depression/elevation: diagnosis of ischemia

17
Q

J Point

A

Junction between end of QRS complex and start of ST segment

18
Q

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

19
Q

Ventricular Depolarization sequence

A

1) Septum depolarization
2) Free wall depolarization
3) Base of the LV depolarization

-These make up QRS Complex

20
Q

Ventricular Repolarization

A

-Depolarization of the ventricles occurs first in the subendocardial region and then in the subepicardial region

21
Q

Atrial repolarization

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.

22
Q

Qt Interval

A

Represents ventricular depolarization-ventricular contraction- ventricular repolarization

Measures the avg of the Duration of the ventricular action potential

Roughly estimates duration of ventricular action potential

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

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

Q-Tc =
𝑸𝑻 𝒊𝒏𝒕𝒆𝒓𝒗𝒂𝒍/√𝑹𝑹 𝒊𝒏𝒕𝒆𝒓𝒗𝒂𝒍
Normal Q-Tc interval < 0.44
> 0.44: prolonged QT interval, high risk of arrythmias

23
Q

TP Segments

A

End of the 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

24
Q

The RR (QRS–QRS) interval: = 1 Heart Beat

A

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).

25
Q

Normal HR

Fast HR

Irregular HR

A

Normal HR
-Second QRS falls between 75 and 60bpm = HR halfway between them
(Must memorize sequence: 300, 150, 100, 75, 60, 50) = big squares

Fast HR
>100bpm

Irregular HR
-Use 3 second markers and count QRS complexes between them, then multiple them by 20 = HR

26
Q

Ventricular Action Potential and ECG

A

Phases:
0 = Depolarization
-QRS

1 =
-ST segment

2 =
-ST Segment –> all cells depolarized

3 = Repolarization
-T

4 = Resting

-QT represented by phases 1-3

27
Q

Myocardial Ischemia/Infarction

ECG manifestations during ACUTE ISCHEMIA

A

Within Hours:
-Peaked T-waves
-ST-segment changes (either
ST-segment depression or elevation)

Withing 24hrs:

  • T-wave inversion
  • ST-Segment resolution

Within a few days:

  • Pathologic Q wave
  • Q-wave duration 40msec
  • Q-wave more than one third (1/3) of the QRS amplitude
  • Scar tissue, electrically dead
28
Q

Subendocardial Infarcts

Transmural Infarcts

A

1) Subendocardial Infarcts
- ST segment depression

2) Transmural Infarcts (Whole wall of ventricule)
- ST segment elevation

29
Q

Origin of ST segment
deviation

Diastolic Current Theory

Systolic Current Theory

A

Current of injury = Abnormal current flow caused by acute ischemia
-Pathologies caused by ST elevation/ depression

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
30
Q

What happens in result of cell ischemia?

A

-Less ATP produced –> Decrease Na+/K+ ATPase PUMP –> Resting membrane potential decreases

Systolic Current Theory
phase 2 increases (Shifting ST directly)

Diastolic Current Theory
-phase 4 decreases (Shifting resting baseline)

31
Q

St Segment Elevation Myocardial Infarction Localization

A

Infarct Location, Artery, Leads with ST elevation or Q waves:

1)Anteroseptal
-Left Anterior, Descending Artery (LAD)
V1-V2

2) Anteroapical
- distal LAD
- V3-V4

3) Anterolateral
LAD or Left Circumflex, Artery (LCX)
-V5-V6

4) Lateral
- LCX I, aVL

5) Inferior
- Right Coronary Artery
- II, III, aVF

6) Posterior
-Posterior Descending Artery
-V7-V9, ST depression in V1-V3 with
tall R waves

CPR 1 (32 decks)

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