EKG Basics Flashcards
Cardiac cells
(myocytes)
Polarized at rest
membrane pumps used to keep inside of cells electronegative
Sodium/Potassium Pump
3 Na outside for every 2 K inside
requires ATP to pump
Pacemaker Cells
Electrical power source of heart
depolarize spontaneously with innate characteristics and neurohormonal input
serving as the source of depolarization wave
Sinus Node (SA node)
Pacemaker
located in the RA, dominant pacemaker at 60 - 100 bpm
can be altered by autonomic NS input
Automaticity
All heart cells can behave as pacemaker but remain suppressed unless SA node fails
SA Node Intrinsic Pacing
60 - 100 bpm
Atrial Foci Intrinsic Pacing
60 - 75 bpm
Junctional Foci (AV Node) Intrinsic Pacing
40 - 60 bpm
Ventricular Foci Intrinsic Pacing
25 - 40 bpm
Electrical Conducting Cells
Hard wiring of the heart
carry the current quickly and efficiently to distant portions of the heart
(Purkinje fibers of the ventricles, Bachman’s bundle of the atria)
Myocardial Cells
Contractile machinery of the heart
constituting the largest part of heart tissue
Responsible for repeated excitation-contraction coupling
Light Lines/Small Boxes of EKG Paper
1X1 mm squares
Dark Lines/Big Boxes of EKG Paper
5X5 mm squares
Horizontal Axis of EKG Paper
Time
Small square = 0.04 sec
Large square = 0.2 sec
Vertical Axis of EKG Paper
Voltage
Small square = 0.1 mV
Large square = 0.5 mV
P Wave
Records depolarization through atrial myocardium
First part of P wave = RA depolarization (SA node in RA)
Second part of P wave = LA depolarization
AV Nodal Delay
There is a “gate” at the AV node to delay conduction from atria to ventricles
Allows the atria to finish contracting and empty their volume of blood before ventricles can contract
Ventricular Depolarization
AV nodal delay (1/10 sec) –>
AV Bundle, Bundle of His –>
R & L Bundle Branches –>
Terminal Purkinje Fibers
QRS Complex
Marks the beginning of ventricular depolarization and contraction
(amplitude is greater than P wave b/c ventricles are so much larger)
T Wave
Represents wave of ventricular repolarization
(restoration of electronegative state)
wave of atrial repolarization is obscured by QRS complex
Segment
Connects 2 waves
Interval
Encompasses at least 1 wave and a segment
Depolarization Deflections
wave moves twd + electrode = + deflection
waves moves away from + electrode = - deflection
waves moves perpendicular to + electrode = biphasic
Repolarization Deflections
Opposite/Reverse of depolarizing wave deflections
Perpendicular = biphasic w/ - deflection preceding
V1
4th intercostal right of sternum
V2
4th intercostal left of sternum
V3
between V2 and V4
V4
5th intercostal at midclavicular line
V5
5th intercostal at anterior axillary line
V6
5th intercostal at midaxillary line
Precordial Leads
Horizontal (coronal) Plane
record electric activity moving anteriorly and posteriorly
Limb Leads
Vertical (frontal) Plane
record electric activity moving up, down, left, right
Anterior View of Heart
V2, V3, V4
Left Lateral View of Heart
I, aVL, V5, V6
Inferior View of Heart
II, III, aVF
Right Ventricular View of Heart
aVR, V1
R Wave Progression
V1 to V5 increasing amplitude of R wave
12-Lead EKG
P wave: + II (inferior & left lateral leads), - aVR, biphasic III & V1
QRS: R-R progression in V1 - V5
T wave: usually positive in leads with + T waves
