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Evaluation of the Cardiac System > Electrocardiographic Waveform Acute Ischemia and Infarction > Flashcards

Electrocardiographic Waveform Acute Ischemia and Infarction Flashcards

1
Q

What is Acute myocardial ischemia and infarction?

A

Series of metabolic, ionic, and pathological changes in the region supplied by the occluded coronary artery that cause characteristic changes in the ST segment QRS complex and T wave

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2
Q

What is the sequence of ECG changes associated with acute ischemia and infarction?

A

1: Peaking of T wave
2: ST segment elevation or depression
3: development of abnormal Q waves
4: T wave inversion

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3
Q

What is the earliest ECG manifestation of acute transmural ischemia?

A

Peaking of the T wave

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4
Q

What is the most frequently observed early ECG in the hospital

A

ST elevation and depression

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5
Q

What causes the ST changes?

A

Voltage gradients across the border between the ischemic and non ischemic regions that result in a electrical current flowing across the ischemic border.

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6
Q

What are the factors that cause ST Elevation or Depression

A

Extent
Location of the Ischemic Zone
Relationship of the ECG electrodes to the ischemic zone

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7
Q

Electrodes that directly overlie the region of ischemia will record what and the other electrodes will record what?

A

-ST elevation
ST depression or no change

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8
Q

What is Subendocardial Ischemia?

A

Damage to the subendocardial layer of the left ventricle

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9
Q

What causes subendocardial ischemia?

A

Often brought on by exercise in patients with flow limiting coronary artery obstruction.

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10
Q

What will show in all leads during a sub endocardial ischemia?

A

ST depression

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11
Q

What does development of Q waves indicate?

A

Absent conduction through the infarcted region and may last indefinently

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12
Q

What mimic abnormal Q waves that is associated with infarction?

A

Hypertrophy of the interventricular septum and interventricular conduction disturbances. Such as ventricular preexcitation.

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13
Q

Various ECG changes in an acute transmural ischemic event help with what?

A

Localization
Estimation of the extent of the ischemic or infarcted region
Identification of the occluded vessel

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14
Q

What does the ECG waveform consist of?

A

P wave
PR interval
QRS complex
ST segment
T wave
U wave

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15
Q

What does the P wave reflect?

A

Depolarization of the Atria

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16
Q

QRS reflects?

A

Depolarization of the Ventricles

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17
Q

What does the ST segment and T wave reflect?

A

Repolarization of the ventricles

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18
Q

What does the U wave reflect?

A

After the T wave and is believed to be a electromechanical event coupled to ventricular relaxation

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19
Q

When does the depolarization of the sinus node occur?

A

Before the P wave, but it is too small to be recorded on the ECG machine

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20
Q

When does the electrical activity of the AV node and His-Purkinje system occur?

A

During PR interval, electrically silent

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21
Q

What causes the P wave?

A

Voltage gradients created as the atrial cells sequentially depolarize

22
Q

Where is the sinus node located?

A

Junction of the superior vena cava and right atrium

23
Q

What direction does atrial depolarization occur during sinus rhythm?

A

Right to left,
Superior to inferior, Anterior to Posterior.

24
Q

Where is the P wave recorded in the leads?

A

Upright in 1 2 and aVL which leads V3 and V6.
Inverted or negative in aVR
In lead v1 P wave may be upright, biphasic, or inverted

25
Q

What can cause affects in the P wave?

A

Atrial hypertrophy
Atrial Dilation
Slowing of inter atrial and intra atrial conduction

26
Q

If the abnormal focus is close to the sinus node what does the P wave resemble?

A

A normal sinus P wave

27
Q

If the abnormal focus is further away to the sinus node what does the P wave resemble?

A

The further away, the more abnormal the sequence will be.

28
Q

When does the PR interval extend from?

A

Onset of the P wave to the onset of the QRS complex.

29
Q

What does the PR interval consist of?

A

Atrial repolarization
Depolarization of the AV junction (AV node, common His bundle, two bundle branches, Purkinjie fiber network)

30
Q

What factors may block or prolong the PR interval?

A

Decreased sympathetic tone
Increase of vagal tone
drugs
electrolyte abnormalities
Ischemia
Infectious diseases

31
Q

When AV conduction is completely blocked what happens?

A

P waves will be dissociated from the QRS complex

32
Q

What happens when the PR interval is shortened and what is it diagnosed as?

A

PR interval is shortened when impulses bypass the AV node and reach the ventricles via AV nodal bypass tract to cause ventricular pre excitation

Wolff Parkinson White pattern

33
Q

What is the first portion of the ventricle to be depolarized in the QRS complex?

A

Interventricular Septum

34
Q

How is the QRS complex activated?

A

Fibers from the left bundle branch

35
Q

What direction does the QRS complex depolarize?

A

Left side to right

36
Q

Where does the QRS complex impulse spread through?

A

His-Purkinje system
From the endocardium to the epicardium
Apex to the base

37
Q

When is the QRS complex upright or positive in the ECG?

A

Leads 1, V5, V6. posterior leads

38
Q

When is the QRS complex negative or inverted?

A

Leads aVR and V1, anterior leads

39
Q

What causes QRS complex abnormalities seen on the ECG?

A

Bundle branch blocks
Fascicular blocks
Ventricular pre excitation
interventricular conduction disturbances
ventricular ectopic beats

40
Q

What does fascicular blocks reflect?

A

Reflect conduction slowing in one fascicle of the left bundle
Shift of electrical axis and subtle changes in initial portion of QRS complex

41
Q

What does bundle branch blocks on the ECG reflect?

A

Conduction slowing or interruption in the right or left bundle branch.

42
Q

What is bundle branch blocks caused by?

A

Fibrosis
Calcification
Congenital abnormalities involving conducting system

43
Q

Slowing of the QRS configuration without change of sequence can be caused by?

A

-Cardioactive drugs
-Increase in potassium concentration
-Diffuse fibrosis or scaring
-Patients with severe cardiomyopathies

44
Q

What does the fascicular block alter in ECG?

A

Initial portion of the QRS complex and electrical axis

45
Q

Abnormalities in the sequence of depolarization are always associated with?

A

Abnormalities in the sequence of repolarization

46
Q

What factors affect the amplitude of the QRS complex?

A

Thickness of the ventricular walls
Presence of pleural or pericardial fluid
increase in body mass
Age
Sex
Race

47
Q

What is the ST segment isoelectric with?

A

TP and PR segments

48
Q

How does the T wave reflect in ECG leads?

A

Upright or positive in leads I V5 and V6
Inverted in leads aVR and V1

49
Q

What are the guidelines so approach interpreting T wave abnornmalities

A

T wave amplitude should be >10% of QRS amplitude
Inverted T waves in lead I are abnormal

50
Q

What is the U wave most easily seen in?

A

V2 and V4

51
Q

What is an increase in U wave amplitude associated with?

A

Hypokalemia
Direct acting cardiac drugs
Congenital long QT syndrome

Evaluation of the Cardiac System (4 decks)

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