Electrocardiographic Waveform Acute Ischemia and Infarction

Question 1

What is Acute myocardial ischemia and infarction?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

What is the earliest ECG manifestation of acute transmural ischemia?

Answer 3

Peaking of the T wave

Question 4

What is the most frequently observed early ECG in the hospital

Answer 4

ST elevation and depression

Question 5

What causes the ST changes?

Answer 5

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

Question 6

What are the factors that cause ST Elevation or Depression

Answer 6

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

Question 7

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

Answer 7

-ST elevation
ST depression or no change

Question 8

What is Subendocardial Ischemia?

Answer 8

Damage to the subendocardial layer of the left ventricle

Question 9

What causes subendocardial ischemia?

Answer 9

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

Question 10

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

Answer 10

ST depression

Question 11

What does development of Q waves indicate?

Answer 11

Absent conduction through the infarcted region and may last indefinently

Question 12

What mimic abnormal Q waves that is associated with infarction?

Answer 12

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

Question 13

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

Answer 13

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

Question 14

What does the ECG waveform consist of?

Answer 14

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

Question 15

What does the P wave reflect?

Answer 15

Depolarization of the Atria

Question 16

QRS reflects?

Answer 16

Depolarization of the Ventricles

Question 17

What does the ST segment and T wave reflect?

Answer 17

Repolarization of the ventricles

Question 18

What does the U wave reflect?

Answer 18

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

Question 19

When does the depolarization of the sinus node occur?

Answer 19

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

Question 20

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

Answer 20

During PR interval, electrically silent

Question 21

What causes the P wave?

Answer 21

Voltage gradients created as the atrial cells sequentially depolarize

Question 22

Where is the sinus node located?

Answer 22

Junction of the superior vena cava and right atrium

Question 23

What direction does atrial depolarization occur during sinus rhythm?

Answer 23

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

Question 24

Where is the P wave recorded in the leads?

Answer 24

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

Question 25

What can cause affects in the P wave?

Answer 25

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

Question 26

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

Answer 26

A normal sinus P wave

Question 27

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

Answer 27

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

Question 28

When does the PR interval extend from?

Answer 28

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

Question 29

What does the PR interval consist of?

Answer 29

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

Question 30

What factors may block or prolong the PR interval?

Answer 30

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

Question 31

When AV conduction is completely blocked what happens?

Answer 31

P waves will be dissociated from the QRS complex

Question 32

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

Answer 32

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

Question 33

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

Answer 33

Interventricular Septum

Question 34

How is the QRS complex activated?

Answer 34

Fibers from the left bundle branch

Question 35

What direction does the QRS complex depolarize?

Answer 35

Left side to right

Question 36

Where does the QRS complex impulse spread through?

Answer 36

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

Question 37

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

Answer 37

Leads 1, V5, V6. posterior leads

Question 38

When is the QRS complex negative or inverted?

Answer 38

Leads aVR and V1, anterior leads

Question 39

What causes QRS complex abnormalities seen on the ECG?

Answer 39

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

Question 40

What does fascicular blocks reflect?

Answer 40

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

Question 41

What does bundle branch blocks on the ECG reflect?

Answer 41

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

Question 42

What is bundle branch blocks caused by?

Answer 42

Fibrosis Calcification Congenital abnormalities involving conducting system

Question 43

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

Answer 43

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

Question 44

What does the fascicular block alter in ECG?

Answer 44

Initial portion of the QRS complex and electrical axis

Question 45

Abnormalities in the sequence of depolarization are always associated with?

Answer 45

Abnormalities in the sequence of repolarization

Question 46

What factors affect the amplitude of the QRS complex?

Answer 46

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

Question 47

What is the ST segment isoelectric with?

Answer 47

TP and PR segments

Question 48

How does the T wave reflect in ECG leads?

Answer 48

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

Question 49

What are the guidelines so approach interpreting T wave abnornmalities

Answer 49

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

Question 50

What is the U wave most easily seen in?

Answer 50

V2 and V4

Question 51

What is an increase in U wave amplitude associated with?

Answer 51

Hypokalemia Direct acting cardiac drugs Congenital long QT syndrome