EKG Flashcards
What can an EKG tell?
1) anatomical orientation of the heart;
2) size of the chambers;
3) rhythm and conduction disturbances;
4) cardiac injury;
5) effects of drug or electrolyte disturbances
What are the conventions of the x and y axes of an EKG?
x-axis = TIME each large box (5 mm) = 0.2 sec; each small box (1 mm) = 0.04 sec y-axis = VOLTAGE each large box (5 mm) = 0.5 mvolt; each small box (1 mm) = 0.1 mvolt
What is the P wave?
atrial depolarization
What is the QRS complex?
ventricular depolarization
What is the T wave?
ventricular repolarization
What is the RR interval determine?
Heart rate
What does the PR interval determine?
The delay of an electrical impulse by the AV node that allows atrial emptying
What does the QRS duration determine?
The health of the His/Purkinje system
What does the QT interval determine?
The measure of an action potential width of ventricular myocytes
What does the ST interval determine?
The plateau phase of an action potential in ventricular myocytes
How can a heart rate be calculated?
60 sec/min // R-R rate (sec/beat)
What is the electrical basis of EKG?
Electrodes detect direction in which a depolarization is happening (+ if towards the electrode or - if away from the electrode) and the intensity of the depolarization as a result of tissue mass–large tissues tend to have larger depolarizations
Why is the T wave positive on an EKG?
Repolarization starts in the epicardium and works deep to the endocardium so the direction of the vector is opposite of the anticipated; with a negative vector and a negative electrical change, the overall magnitude of the vector is positive and points towards the electrode
What are the three standard limb leads?
1) Right arm (-) to Left foot (+)
2) Right arm (-) to Left foot (+)
3) Left arm (-) to Left foot (+)
What are the three augmented limb leads?
1) Right arm (+) and the sum of left arm and left foot (-)
2) Left arm (+) and the sum of left foot and right arm (-)
3) Left leg (+) and the sum of the right arm and left arm (-)
What are the points of the Einthoven triangle?
The shoulders and umbilicus/groin
What is the normal mean QRS axis and what are the two conditions necessary to fulfill it?
between -30 degrees and +90 degrees
QRS must be positive in Lead 1 and Lead 2
How can the axis be determined?
1) Find the isoelectric lead. The vector is perpendicular to this lead.
2) Determine if the perpendicularity is positive or negative depending on nearby leads
Factors that can cause an abnormal axis
1) Physical–posture, height, weight
2) Pathological–ventricular hypertrophy, myocardial damage, or bundle branch block
What are precordial leads?
Leads placed transversely across the chest (V1-V6) to determine the vector within the chest; V4 is usually the isoelectric vector
What is the most common cause of a long QT interval?
Genetic mutation of many ion channels (collectively termed congenital long QT syndromes), drugs, as well as metabolic and electrolyte disturbances
What are clinical concerns for a long QT interval?
syncope and potentially fatal arrhythmias
Which channel can have genetic mutations that affect the ability of a cell to repolarize?
KCNH2 (hERG)
What is the consequence of a genetic mutation in hERG channels?
Ca++ channels can recover from inactivation before the tissue is repolarized and premature action potentials can fire
