EKG Basics

Question 1

How can you determine heart rate on an EKG

Answer 1

300 divided by the number of big boxes between two QRS complexes

The space between two QRS complexes represent a heartbeat

Question 2

What are some conditions that could shift the QRS axis to the left

Answer 2

LBBB
Ventricular rhythm

Question 3

What are some conditions that could cause a right axis deviation (QRS axis between +90 and +180)

Answer 3

RBBB
RVH

Question 4

What is the normal QRS axis

Answer 4

-30 to +90

Question 5

How do you do the axis quick method

Answer 5

Look at aVr: Make sure it’s negative
Look at I, II: If both positive, axis is normal
If II is negative: Left axis deviation
If I is negative: Right axis deviation

Question 6

What is the normal PR interval

Answer 6

120-200 ms
Should not be bigger than one big box

Question 7

You can develop a prolonged PR interval when you have

Answer 7

A first degree AV block

Question 8

In what condition could you develop a short PR interval

Answer 8

WPW

Question 9

What is a normal QRS interval

Answer 9

<120ms (less than 3 small boxes)

One small box is 40ms

Question 10

What condition could cause prolonged QRS complex

Answer 10

Bundle branch blocks

Question 11

Ideally in an ECG when should a T wave end

Answer 11

Before the halfway point between two QRS complexes

Question 12

What condition is common to cause a short Qt interval

Answer 12

Hypercalcemia

Question 13

What conditions are common to cause a long Qt interval

Answer 13

Hypocalcemia
Drugs (anti-rhythmics)
Long QT syndrome

Question 14

How does hypocalcemia cause a prolonged QT interval

Answer 14

During the plateau phase of myocyte action potential, calcium moves into myocytes. In the setting of hypocalcemia, there is less driving force to move calcium into myocytes. So it takes longer for calcium to fill the cell for muscles to depolarize and repolarize increasing the plateau phase, increasing the Qt interval

Qt interval: Phase which represents the time required for myocytes in the ventricles to depolarize and repolarize

Question 15

What is a notable feared outcome of Qt prolongation

Answer 15

Torsade de Pointes

Question 16

What is Torsade de Pointes

Answer 16

A special form of ventricular tachycardia where QRS complexes alternate between small and large
Occurs in Qt prolongation
Results in cardiac arrest

Question 17

What could be the causes of a Torsade de Pointes

Answer 17

Antiarrhythmic drugs
Hypokalemia and hypomagnesemia
Rarely from hypocalcemia

Question 18

What is the physiological cause of a congenital long Qt syndrome

Answer 18

Abnormal Na/K channels in the heart

Question 19

What are some variants of congenital long Qt syndrome

Answer 19

Jervell and Lange-Nielsen syndrome

Question 20

What are some drugs that could cause an acquired long Qt syndrome

Answer 20

Antiarrhythmic drugs
Levofloxacin (antibiotic)
Haldol (antipsychotic)
Many other drugs
Congenital LQTS: need to avoid these drugs

Question 21

What are the causes of peaked T waves

Answer 21

Hyperkalemia
Early ischemia (hyperacute t waves - often precedes ST segment elevation in acute ischemia)

Question 22

What is a U wave

Answer 22

Upward deflection that comes after the T wave
Origin unclear
May represent repolarization of Purkinje fibres (there are other theories)
Can be normal but also seen in hypokalemia