EKG lecture 1 (4.3.25) Flashcards
Describe a 12 lead EKG
Recording of the electrical activity of the heart from 12 different “points” of observation
All the waves we see on an EKG are manifestations of depolarization and repolarization of cardiac cells
Describe cardiac cells
1) Resting state is polarized - insides (-) charged relative to outside (+)
2) Polarity maintained/restored by membrane ion pumps (Na+, K+, CA++, Cl-) which require constant source of energy
1) Explain depolarization
2) What do pacemaker cells do?
1) Depolarization is propagated from cell to cell as a wave of depolarization or flow of electricity, that is transmitted across the entire heart and can be detected/recorded by surface electrodes = EKG
2) Depolarize spontaneously and initiate the wave of depolarization
Describe repolarization
1) Occurs after depolarization is complete
2) Restores resting cellular polarity via repolarization
3) Uses membrane ion pumps to reverse and restore the relative (+) outside vs. (-) inside the cell – energy dependent process
4) Detected/recorded by surface electrodes of EKG
5) All the waves we see on EKG are manifestations of these 2 processes – depolarization and repolarization
1) What are pacemaker cells?
2) What are electrical conducting cells?
3) What are myocardial cells responsible for?
1) Under normal circumstances, the electrical ‘generator’ for the heart.
SA node **
2) “Hard wiring” of the heart.
His Perkinji system
3) Responsible for heart contractions (the ‘Pump’)
Pacemaker cells:
1) Able to depolarize _____________ over and over.
2) What 2 things determine rate?
1) spontaneously
2) Innate electrical characteristics of the cell
+ external neurohormonal input.
SA node:
1) Where is it and what is it?
2) What rate does it fire at? What alters it? Explain
3) What does each firing result in?
1) Right atrium; dominant pacer of the heart
2) ~ 60-100/min rate, varied by ANS – sympathetic vs parasympathetic responding to activity and stress
-If devoid of normal vagal input – fires about 100/min
3) Each firing of SA node results in a wave of depolarization and thus the contraction of the cardiac cycle
Electrical conducting cells:
1) What are they?
2) Name a part of the atrial conduction system
3) What are the parts of the ventricular conduction system?
1) Hard wiring “interstate” of the heart
2) Bachman’s bundle – rapid right to left atrial conduction
3) Bundle of His, branches
Purkinje fibers
1) What makes up the majority of the cardiac tissue?
2) What are these?
3) What does depolarization result in? How is this different from other tissue?
1) Myocardial cells
2) Contractile unit of the heart
3) Depolarization results in Ca++ release and contraction of actin and myosin
-Wave of depolarization occurs but more slowly than with pacemaker or conduction tissue……allows time for filling of the pump prior to contraction
Automaticity of cardiac tissue:
1) What cardiac cells can act as pacemakers?
2) Is automaticity normally occurring? Explain
1) All cardiac cells
2) Automaticity normally suppressed unless SA node fails or externally stimulated by ANS, drugs, or cardiac disease
1) Tracing on EKG represent electrical activity of ____________ cells
2) What has insufficient voltage to be recorded by surface electrodes?
1) myocardial
2) Pacemaker and conduction electrical activity
1) What are 2 parts of EKG tracings?
2) What does duration represent?
3) What does amplitude represent?
4) What is another factor of EKG findings?
1) waves and straight lines
2) Duration – fractions of seconds = TIME
Amplitude – millivolts (mV) = HEIGHT
3) Shape
What are the parts of a basic 12 lead EKG? (ex: P wave)
P-Waves, QRS Complexes, T-Waves, and Some Straight Lines
Explain what the P wave represents
1) Atrial depolarization
2) Wave of depolarization in atria = P wave = atrial contraction
3) SA node (electrically silent on EKG) located in right atrium, therefore RA depolarizes 1st
4) Once right and left atrial depolarization complete, EKG is electrically silent (flat)
Explain the AV pause
1) AV node – “electrical gate” @ junction of atria and ventricles = PR segment on EKG
2) Wave of depolarization from atria pauses; allows atria time to finish contraction prior to ventricular contraction (finish filling with atrial kick, pre-load the ventricles)
3) ANS innervation for rate control (chronotropic): B blockers and CCBs can affect this
What 2 meds can affect the AV pause? Explain
1) B-blocker (Metoprolol) slows rate down
2) CCB (verapamil) slows rate down, also affects contractility (inotropy)
Ventricular depolarization:
1) What initiates this?
2) What is it represented as?
3) What does parts of the conduction system does it include?
1) SA node
2) Ventricular depolarization down electrical conducting cells = ventricular systole = QRS on EKG:
3) Bundle of His; Bundle branches; Terminal Purkinje fibers
1) _______________ atrial contraction = P wave
2) AV node pause = ______ segment
3) Ventricular depolarization down electrical conducting cells = ventricular systole = _________ on EKG
1) Atrial depolarization
2) PR
3) QRS
List the parts of the bundle of His
Right and left bundle branches
1) Right bundle branch – down right IV septum to apex of right ventricle
2) Left bundle branch:
a) Septal fascicle – depolarizes the septum left to rightdirection (Q wave)
b) Anterior fascicle – runs along anterior wall of left ventricle
c) Posterior fascicle – runs along the posterior wall
What delivers electrical current to the ventricular myocardium?
Purkinje fibers
QRS complex:
1) What occurs early on?
2) What depolarize at the same time? Which do we see on EKG?
1) Depolarization of IV septum by septal fasicle of LBB
2) Right and left ventricles depolarize at nearly the same time but most of what we see on EKG = left ventricle
1) What does depolarization result in?
2) What are the parts of depolarization on an EKG?
1) Depolarization = contraction
2) Atrial = P wave, AV node pause = PR segment, Ventricular = QRS wave
1) What does the (brief) refractory period on an EKG represent?
2) What are the 2 parts?
1) Resistant to further stimulation
2) Atrial = PR segment, Ventricle = ST segment
1) What does repolarization do?
2) Where does atrial repolarization occur on an EKG?
2) What represents ventricular repolarization?
1) Restore electronegativity of interior (resting potential)
2) Buried in QRS depolarization
3) T wave
Ventricular repolarization:
1) Is it fast?
2) How does this show up on an EKG?
1) Slower process than depolarization
2) T wave broader than QRS (= longer duration)
True or false: Not all flat lines are bad
True
1) Define segment
2) Define interval
1) Flat lines connecting 2 waves
2) A flat line + at least one wave
(Aka, interval is longer and contains a wave, segment is just the time between waves)
List what each of the following show as on EKG and define each:
1) PR interval
2) PR segment
1) PR interval = P wave + flat line connecting to the QRS complex
-Start of atrial depole to start of ventricle depole
2) PR segment = Flat line from end of P wave to start of QRS complex
-Measures time from end of atrial depol. to start of ventricular depole
1) What does the ST segment measure?
2) What abt the QT interval?
1) Measures time from end of ventricular depole to beginning of ventricular repole
2) Measures time from be beginning of ventricular depole to end of ventricular repole
