EKG Basics Flashcards
How can you determine heart rate on an EKG
300 divided by the number of big boxes between two QRS complexes
The space between two QRS complexes represent a heartbeat
What are some conditions that could shift the QRS axis to the left
LBBB
Ventricular rhythm
What are some conditions that could cause a right axis deviation (QRS axis between +90 and +180)
RBBB
RVH
What is the normal QRS axis
-30 to +90
How do you do the axis quick method
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
What is the normal PR interval
120-200 ms
Should not be bigger than one big box
You can develop a prolonged PR interval when you have
A first degree AV block
In what condition could you develop a short PR interval
WPW
What is a normal QRS interval
<120ms (less than 3 small boxes)
One small box is 40ms
What condition could cause prolonged QRS complex
Bundle branch blocks
Ideally in an ECG when should a T wave end
Before the halfway point between two QRS complexes
What condition is common to cause a short Qt interval
Hypercalcemia
What conditions are common to cause a long Qt interval
Hypocalcemia
Drugs (anti-rhythmics)
Long QT syndrome
How does hypocalcemia cause a prolonged QT interval
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
What is a notable feared outcome of Qt prolongation
Torsade de Pointes
What is Torsade de Pointes
A special form of ventricular tachycardia where QRS complexes alternate between small and large
Occurs in Qt prolongation
Results in cardiac arrest
What could be the causes of a Torsade de Pointes
Antiarrhythmic drugs
Hypokalemia and hypomagnesemia
Rarely from hypocalcemia
What is the physiological cause of a congenital long Qt syndrome
Abnormal Na/K channels in the heart
What are some variants of congenital long Qt syndrome
Jervell and Lange-Nielsen syndrome
What are some drugs that could cause an acquired long Qt syndrome
Antiarrhythmic drugs
Levofloxacin (antibiotic)
Haldol (antipsychotic)
Many other drugs
Congenital LQTS: need to avoid these drugs
What are the causes of peaked T waves
Hyperkalemia
Early ischemia (hyperacute t waves - often precedes ST segment elevation in acute ischemia)
What is a U wave
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
