2025 ECG Quiz 1 Flashcards
Cardiovascular A+P
Phases of Heart Beat
Systole = Contraction
Diastole = Relaxation
Layers of the Heart
Endocardium: Inner lining of myocardium (valves)
Myocardium: Contractile muscle tissue
Epicardium: outermost layer made of visceral (inner) serous layer of pericardium
Pericardial cavity: potential space, some serous fluid
Pericardium: 2 layers = 1 fibrous (protective) outer + 1 serous (epicardium)
Flow of Blood Through Heart
Super Vena Cava and Inferior Vena Cava -> Vena Cava -> Right Atrium -> Pass Through Tricuspid Valve -> Right Ventricle -> Pulmonary Trunk Semilunar Valve -> Pulmonary Arteries -> Lungs -> Pulmonary Veins -> Left Atrium -> Pass Through the Bicuspid Valve (Mitral) -> Left Ventricle -> Aortic Semilunar Valve -> Aorta -> Brachiocephalic Artery/Left Common Carotid/Left Subclavian/Abdominal Aorta
Isovolumetric Contraction/Relaxation
Where - Ventricles
When - point of closure of inlet valves (when ventricular pressure surpasses atrial) to time of outlet valves open
… for relaxation after the contraction of the ventricles and the atria building pressure
Important - allows ventricle to build up enough pressure to open semilunar valve
… for atria to build up pressure to open cuspid valves
Pressure Gradient
Blood flow from an area of high pressure to low pressure
Coronary Arteries and Veins
Sinuses of Valsalva drain to coronary arteries
Myocardium perfused during diastole
Left coronary bifurcates quickly into Circumflex and LAD
Coronary Veins - oxygen poor blood to RA
Coronary Artery Blockage
MI - myocardial infarction, “heart attack”
NSTEMI - does not show significant ST-Segment elevation, partial blockage of coronary artery
STEMI - ST Elevation, complete blockage of a coronary artery
STEMI vs NSTEMI
Myocardial Cells Actions Terminology:
Automaticity
Excitability
Conductivity
Contractility
automaticity - spontaneous electrical impulses
excitability - reaction to stimuli
conductivity - transmission of impulses
contractility - physical shortening of cell
3 Variation of Myocardial Cells
Pacemaker cells
exhibit spontaneity:
- Native pacemakers cells are concentrated in the SA node
- Latent pacemakers cells can be found in other parts of right atrium and conduction pathways
Electrical Conducting Cells
conduits for rapid transmission and modulation of electrical impulses
Myocardial Cells
responsible for mechanical performance, pumping action
Pacemaker Cells
Small cells, 5-10 micrometers long, normally concentrated in the SA node
Unique action potential resulting in spontaneous and repeated depolarization
Contain leaky ion channels
Typical SA nodal, or native, cell impulses rate is between 60-100 bpm (normal sinus rhythm)
Latent cell impulses can originate from atrial, AV nodal, ventricular and conduction pathway tissues.
Respond to Stimuli
- sympathetic vs parasympathetic tone
- increases/decreases in demand
BPM: SA Node, AV Node (How Connected?), Atrial Pacemaker, Ventricular Pacemaker
SA: 60-100 (normal sinus rhythm)
AV: 40-60
Atrial Pacemaker: 60-75
Ventricular: 30-45
SA Node and AV Node connected by internodal tracts
Pacemaker Cells Action Potential
3 Phases:
Upstroke/Depolarization: Rapid Influx of Ca2+
Repolarization: Outflux of K+
Prepotential/Diastolic Depolarization: Slow Influx of Na+
No absolute (effective) refractory period
No true resting state due to slow influx of Na+, Ca+
Respond to autonomic nervous system regulation
Electrical Conducting Cells
Conduits for electrical impulses, hard-wiring
Rapid transmission to distal portions of the heart
Modulation of impulses, as seen in the slowing of conduction in the AV node followed by rapid transmission through the ventricular conducting system
Bachman’s bundle
Left Bundle Branches (Septal, anterior, posterior) and Right Bundle Branch
Purkinje system
Myocardial Cells
Responsible for mechanical performance, contracting muscle action
Larger in size at 50-100 micrometers long
Contain the contractile proteins actin and myosin
Release intracellular Ca2+ in response to wave of depolarization
Excitation-contraction coupling
May develop “acquired automaticity” due to leaky ion channels (Ex as a result of hypoxia)
Myocardial Cell Action Potential Propagation =
Rapid and forceful due to the Intercalated Disk features
Cycles of depolarization and repolarization
Results in contraction of the depolarized cell
Initiates depolarization of adjacent cells through gap junctions, resulting in a wave of contraction
ECG is the composite representation of these action potentials at a given point in time
Myocardial Cells Action Potential
Phase 0 (upstroke/depolarization): activation (opening) of voltage-gated Na+ channels. Na+ entry and decreased K+ permeability… in addition around -40mV slow Ca+ channels open
Phase 1 (early rapid repolarization): inactivation (closure) of Na+ channel and transient increase in K+ permeability
Phase 2 (plateau): RESULTS FROM CONTINUED ACTIVATION OF SLOW CALCIUM CHANNELS… paired with the release of the calcium stored intracellularly in the sarcoplasmic reticulum
Phase 3 (final repolarization): inactivation of slow calcium channels and increased permeability to K+
Phase 4 (resting potential, diastolic depolarization): normal permeability restored in atrial and ventricular cells
Pacemaker Action Potential through Muscle Contraction Overview
