Vectorial Analysis Of ECG abnormalities Of Coronary Blood Flow And Cardiac Muscle

Question 1

What is a cardiac electrical vector?

Answer 1

It is an arrow that points towards the direction of the cardiac electrical impulses. The length of the arrow is proportional to the voltage of the cardiac impulse at any given instant.

Question 2

What is the average direction of the mean QRS vector in a normal heart?

Answer 2

59 degree.

Question 3

What is known as the axis of the lead ?

Answer 3

It is the direction of the electrical vector from the negative electrode to the positive electrode.

Question 4

What is the axis of lead 1 ?

Answer 4

0 degree

Question 5

What is the axis of lead 2 ?

Answer 5

+ 60 degree. The negative pole of the lead two is at -120 degree.

Question 6

Axis of lead 3 ?

Answer 6

+ 120 degree and the negative pole is -60 degree.

Question 7

Axis of lead aVR ?

Answer 7

210 degree

Question 8

Axis of lead aVL ?

Answer 8

-30 degree

Question 9

Axis of lead aVF?

Answer 9

90 degree

Question 10

How to calculate the instantaneous recorded voltage in a given lead ?

Answer 10

Length of the projected vector/ length of the mean cardiac vector*2 mV.

Question 11

When the cardiac vector is in perpendicular direction to the axis of a given lead, the voltage recorded by the given lead will be?

Answer 11

Low

Question 12

When the mean cardiac vector is exactly at the axis of a given lead___?

Answer 12

The entire voltage will be recorded

Question 13

What is the ventricular repolarization vector physiology?

Answer 13

The ventricular repolarization vector moves from apical epicardial surface to the endocardial and septal area. It is postulated to occur because of the fact that the high Blood pressure inside the ventricles during contraction reduces coronary blood flow to the endocardium as compared to the epicardium.

Question 14

Why is the T wave in all three limb leads positive?

Answer 14

Overall ventricular repolarization vector is towards the apex of the heart as a result the normal T waves in all three bipolar limb leads are positive.

Question 15

The onset and duration of the T wave?

Answer 15

It begins 0.15 seconds after depolarization and reaches its full form by 0.35 seconds which is when the repolarization finishes.

Question 16

What is the cause of delayed endocardial repolarization, even though the septum and the endocardium are depolarized first ?

Answer 16

The causes are two:
The endocardium and the septum have longer duration of contraction than the other parts of the ventricles.
The increased blood pressure within the ventricles greatly reduces endocardial coronary perfusion as compared to the epicardium. Therefore, the epicardial surface undergoes repolarization first

Question 17

Why is atrial T waves negative?

Answer 17

The atrial repolarization vector originates at the SA nodal area of atrial myocadrium. Which is the area of the origin of atrial depolarization as well. Therefore, the repolarization vector is negative in bipolar limb leads. However, in normal ECGs the atrial T waves are not seen as it co-occurs with the QRS Complex

Question 18

What is the mean electrical axis of the ventricular depolarization vector?

Answer 18

59 degree with normal variation range of 20 to 100 degrees.

Question 19

What are the causes of normal variability in the mean ventricular depolarization vector axis in normal hearts?

Answer 19

1) the difference in the purkinje system distribution
2) the difference between the properties of the heart muscles.

Question 20

What are the consequences of change in position of the heart within the thorax on ECG axis?

Answer 20

• At the end of the deep expiration the heart angulate to the left which may incur left axis deviation. While at the end of deep inspiration the opposite happens causing right axis deviation.
• when a person lies down, especially obese people the abdominal content and viceral fat can push the heart to the left and cause left axis deviation.
• In obesity the diaphragm pushes the heart upward and to the left causing left axis deviation.
• The right axis deviation can be seen when people stand up during deep inspiration, and in tall lanky people in whom the heart hangs downward.

Question 21

What are the pathological causes of left axis deviation?

Answer 21

The left ventricular hypertrophy occurs in arterial hypertension, aortic regurgitation, aortic valvular stenosis,in anaerobic athletes and in congenital heart conditions.

Question 22

Pathological causes of right ventricular hypertrophy?

Answer 22

Congenital pulmonary valve stenosis, tetralogy of Fallot, and interventricular septal defects can incur RVH and right axis deviation

Question 23

Mechanism of left axis deviation due to left bundle branch block?

Answer 23

As opposed to the normal simultaneous depolarization of ventricular mass by the bilateral purkinje system. In left bundle branch block. The depolarization vector first speeds through the RBB and depolarizes the right ventricle and then the depolarization spreads to the left through the ventricular syncsytium. Consequently, even when the right ventricle becomes electronegative the left ventricle remains electropositive, which shifts the cardiac depolarization vector to the left. The Left axis deviation in this condition can be as high as -50 degree.

Question 24

ECG characteristic of left axis deviation due to LBBB?

Answer 24

Wider QRS Complex+ predominantly negative lead two and three+ positive lead 1 and aVL

Question 25

Mechanism of right axis deviation due to RBBB?

Answer 25

RBBB causes delayed depolarization of the right ventricle. The left ventricle becomes electronegative approximately 0.1 seconds before the right as a result the mean cardiac vector will be deviated to the right

Question 26

ECG characteristic of RBBB induced right axis deviation?

Answer 26

Negative QRS Complex in lead 1 and largest positive QRS in lead 3 followed by lead 2. The duration of the QRS Complex will be widened.

Question 27

What is the definition of high voltage ECG ?

Answer 27

If the sum of the voltages of lead 1, 2,and 3 is greater than 4 mV the patient is considered to have a high voltage ECG.

Question 28

How to calculate the voltage of the QRS Complex in bipolar limb leads?

Answer 28

The number of small boxes from the peak of the R wave to the bottom of the S wave* 0.1

Question 29

What causes high voltage ECG?

Answer 29

It is caused by increased muscle mass of the ventricles. In left ventricular hypertrophy a narrow complex high voltage QRS Complex occurs in conjunction with left axis deviation. In right ventricular hypertrophy the converse happens.

Question 30

What are the intrensic cardiac causes of low voltage ECG?

Answer 30

The low voltage wide QRS Complex ECGs are seen in people with old MI and resultant diminished muscle mass. The widening of the QRS Complex occurs due to the depolarization wave moves through the myocardium very slowly.
Infiltrative myocardial diseases such as cardiac amyloidosis in which abnormal proteins infiltrate myocardium leading to reduced voltage.

Question 31

The extra cardiac causes of low voltage ECG ?

Answer 31

Pericardial effusion, pulmonary effusion and pulmonary emphysema: in which the cardiac electrical current conduction through the lungs is significantly reduced due to excessive air in the lungs + excessive enveloping of the heart by the lungs which make the lung an insulator for cardiac current conduction.

Question 32

The normal duration of the QRS Complex?

Answer 32

0.06 to 0.08 seconds

Question 33

The duration of the QRS Complex in cardiac hypertrophy or dilation?

Answer 33

0.09 to 0.12 seconds

Question 34

QRS duration in Partial and complete BBB?

Answer 34

In partial BBB = 0.12 and 0.14 seconds.
In complete BBB= 0.14 seconds or more

Question 35

What are the causes of bizarre patterns of QRS Complex with multiple peaks and rapid axis shifts?

Answer 35

1) Destruction of the cardiac myosyncsytium in various locations with replacement of scar tissue.
2) multiple small blocks in the conductive system.

Question 36

What is the definition of the current of injury in ECG ?

Answer 36

The direct or indirect injury to the heart muscles causes such parts to remain depolarized partially or fully. When these conditions occur the current flows between the injured depolarized areas and normal areas even during the heart beats. The ECG abnormalities observed in this context are called current of injury.

Question 37

What are the causes of current of injury to the heart?

Answer 37

1) mechanical trauma 2) infections that damage the muscle membrane 3) cardiac ischemia due to coronary artery blood flow abnormalities

Question 38

What is the J point in ECG?

Answer 38

It is the point at which the entire ventricular syncsytium is depolarized. Regardless of whether the cardiac syncsytium has permanently depolarized injured areas or not at the time point of the emergence of J point the voltage of ECG will be Zero.

Question 39

What is the diastolic correlate of the ECG ?

Answer 39

The TP segment

Question 40

What is the most important diagnostic feature of ECG in acute coronary thrombosis?

Answer 40

The current of injury. It is the strong current flows from the permanently depolarized or partially repolarized focus of injury on the cardiac muscle.

Question 41

How to calculate injury potential in each ECG lead?

Answer 41

The voltage difference between the Osbourne’s wave or J point line and the onset point of ECG immediately before the P wave.

Question 42

In what polarity of the direction of the injury potential the focus of injury localized?

Answer 42

Negative pole

Question 43

Prominent Q wave in lead 1 indicates?

Answer 43

Old anterior wall MI

Question 44

Prominent Q wave in lead 3 indicates?

Answer 44

Posterior wall MI

Question 45

The T wave morphology and vector deviation in LBBB?

Answer 45

The T wave will be inverted as opposed to the upright T wave because the right ventricle start to repolarize well ahead of the left ventricle, which will shift the axis of T wave towards the right ventricle.

Question 46

What is the mechanism of T wave inversion and other T wave abnormalities?

Answer 46

If there is an abnormally short period of depolarization at the base of the ventricles. The repolarization will also begin at the base instead of the apex. In that case the mean repolarization vector will be directed towards the base and therefore the T wave will be negative.

Question 47

What is the most common cause of shortening of depolarization of cardiac muscles ?

Answer 47

Mild ischemia

Question 48

What is the mechanism of mild ischemia induced T abnormalities?

Answer 48

Increased current flow through the potassium channels as a result the depolarization period of this area decreases out of proportion to other parts. This will cause the T waves to be inverted or biphasic.

Question 49

What are the causes of myocardial ischemia?

Answer 49

Chronic progressive coronary stenosis, acute coronary occlusion, coronary artery spasm, relative coronary insufficiency that occurs during exercise or severe anemia.

Question 50

What is the effect of digitalis on the T wave morphology?

Answer 50

Digitalis is an ionotropic drug which increases the contractile function of the heart in heart failure by increasing calcium availability. When it is overdosed, it may cause disproportionate depolarization and repolarization of the ventricle which is manifested as inverted or biphasic T waves.