Lecture 10 EKG / Lab 10 EKG Flashcards
flow of AP / conduction through the heart and matching heart contraction
SA node generates AP –> spreads through myocardial cells through gap junctions and both atria contract –> conduction of electrical activity through AV bundles, RBB, LBB and Purkinje fibers –> ventricles contract as atria repolarize –> ventricles repolarize
why SA node is the dominant node
rate is faster than that of other pacemaker cells in AV node or Purkinje fibers
ecotopic beat
when heart rate is not by SA node by other pacemaker cells possibly in AV node or Purkinje
3 waves of EKG and their cause
- P wave = atria contract
- QRS complex = ventricles contract (and to a lesser degree atria repolarize)
- T wave = ventricles repolarize
causes of positive and negative deflection in EKG reading
- positive = AP in heart goes in direction of positive pole and summates
- negative = AP towards negative pole (summation leads to subtraction in this case)
explain stone thrown in pond analogy to how EKG works
- throwing rock in pond creates concentric circles of waves that can be disrupted by a rock in the middle of the pond
- electrical current generated by leads are disrupted by electrical activity of the heart
bipolar limb leads and list all 3 and direction
- both poles are on the body
- lead 1 = right arm –> left arm
- lead 2 = right arm –> left leg
- lead 3 = left arm –> left leg
unipolar limb leads, where is the ground, list all 3
- AVR, AVL, and AVF standing for right, left, and foot
- the machine is the ground
unipolar chest leads, how many electrodes on body, how many total
- 6 total, only 1 pole on body, machine serves as the ground
leads and which planes they are on
- coronal plane has bipolar limb leads and unipolar limb leads
- transverse plane (parallel to ground) has
why longer recording of lead 2
- lead 2 is parallel to heart axis / midline and usually has best recording
standard conversion of paper number of squares to time
- 5 large squares = 1 second
- 1 large square = 200 ms
PR interval, normal length, and what heart activities
- PR interval = start of P wave to beginning of QRS
- normal = < 200 ms = 1 large square
- SA node fires, atria contract, all of atria and AV node are depolarized
ST segment
between QRS and T wave, flat
QRS complex, average length
- < 120 ms otherwise it is considered broad or elongated and abnormal
- elongation indicates ectopic beat
how to calculate heart rate
- atria = 300 / number of squares between P waves
- ventricular = 300 / number of squares between QRS complex
first degree AV block - cause, EKG reading
- long PR interval > 200ms
- caused by delay in conduction of electricity down AV bundle
second degree AV block,ventricular vs atria heart rate, 2 types
- Mobitz 1 = progressive elongation of PR Interval
- Mobitz 2 = QRS complex after every 2-3 P wave making atrial rate much faster than ventricle rate
3rd degree aka complete AV block - EKG
- atria and ventricle beat separately and ventricle is controlled by ectopic pacemaker
- QRS complex is elongated due to ectopic origin, lots of PVC
- ventricle rate is slow and atria rate is faster than usualy as sympathetic system tries to compensate for decreased cardiac output
NSR and 2 questions
- normal sinus rhythm
- is there a P wave and is it immediately followed by QRS?
rhythm vs rate
- rhythm = is P wave present and quickly followed by QRS
- rate = frequency of QRS and P waves
sinus bradycardia - why sinus, why bradycardia, causes
- sinus = normal rhythm, P wave followed by QRS
- bradycardia = slow rate, <40
- can be athletes or pathological
sinus tachycardia - why sinus, why tachycardia, causes
- sinus = normal rhythm, P wave followed by QRS
- tachycardia because fast rate > 100 bpm
- caused by exercise or sympathetic system
ventricular tachycardia - why each name, characteristic EKG signs
- name because ventricle beats very quickly
- elongated QRS due to PVC and ectopic pacemakers in the ventricles
ventricular fibrillation - treatment, cause
- irregular activity in the heart
- caused by many areas of ischemia and many circus rhythms in the ventricles which cause ventricles to shake/spasm
- electrical defibrillation depolarizes all cells at the same time in attempts to restore sinus rhythm but doesn’t solve underlying problem of ischemia,
flutter vs fibrillation
- flutter = fast heart rate
- fibrilation = irregular heart activity
cardiac output formula
- cardiac output = heart rate * stroke volume = volume pumped / minute
why is it only safe to exercise at 80-90% of maximum heart rate
- if heart rate is too high, diastole is too short for ventricles to fill up with blood and cardiac output decreases
calculate maximum heart rate based on age
220 - age
- exercise to 80-90% of max heart rate only
2 examples of conditions wiht ectopic beats
- 3rd degree AV node block
- VTach
ST segment depression and cause
- dip in ST segment
- caused by ischemia of heart cells (not enough oxygen)
ST segment elevation cause
- caused by myocardial infarction
T wave inversion and cause
sign of ischemia
PVC and cause (in term of pacemaker location)
- PVC = premature ventricular contraction
- caused by ectopic pace maker
PVC, ischemia, and circus rhythm
- ischemia causes circus rhythms in the heart which acts as ectopic pace maker and cause PVC and elongated QRS
VTach, VFib, and number of circus rhythms
- VTach = a few or many PVC due to a few circus rhythms
- VFib = many circus rhythms and irregular, random heart electrical activity
biphasic QRS in chest lead cause
- chest leads are not along the axis/midline of the heart
