cardiac notes

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Transcript of cardiac notes

Cardiac Nursing Applied Anatomy And Physiology:

hollow muscular behind the sternum and between the lungs has heart wall has 3 layers:

Endocardium thin lining, covers valves Myocardium muscular layer Epicardium thin covering(mesothelium) Pericardium invaginated sac Visceral attached to the exterior of myocardium Parietal attached to the great vessels and diaphragm

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separated into 2 pumps: right heart pumps blood through the lungs left heart pumps blood through the peripheral organs chambers of the heart atrium weak pump and blood reservoir ventricle main force that propels blood to pulmonary and peripheral circulation Blood Supply

Arteries Coronary artery 1st branch of aorta Right Coronary o SA nodal Branch supplies SA node o Right marginal Branch supplies the right border of the heart o AV nodal branch supplies the AV node o Posterior interventricular artery supplies both ventricles Left Coronary o Circumflex branch supplies SA node in 40 % of people o Left marginal supplies the left ventricle o Anterior interventricular branch aka Left anterior descending(LAD)supplies both ventricles and interventricular septum2

o Lateral branch terminates in ant surface of the heart Veins Coronary sinus main vein of the heart Ant interventricular vein or Great Cardiac vein main tributary of the coronary sinus Post interventricular vein or Middle cardiac vein Small Cardiac vein Left Posterior ventricular vein Left Marginal Vein Oblique vein remnant of SVC, small unsignificant Smallest cardiac veins- valveless Action Potential Resting Membrane Potentials -85 to -95 mV cardiac muscle -90 to -100 mV Purkinje fibers Circulation

Blood from head and UE; Trunk and LE Superior Vena Cava: Inferior Vena Cava Right Atrium Tricuspid Valve Right Ventricle Pulmonary Valve Pulmonary Artery Lungs Pulmonary Vein Left Atrium

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Mitral Valve Left Ventricle Aortic valve Aorta

Myocardial cell Intercalated disks Cell membranes that separates individual cells from each other Two Groups of Myocardial Cells Cells specialized for impulse generation and conduction Automatic cells Found in SA, AV nodes and Purkinje system(transitional cells) Cells specialized for contraction Non Automatic Cells Specialized Cardiac Cells

Nodal tissues SA Node( Sino-atrial, Keith and Flack) Primary Pacemaker Between SVC and RA Vagal and symphatetic innervation Sinus Rhythms AV Node( Atrioventricular , Kent and Tawara) At the right atrium4

3 zones o AN Zone(atrionodal) o N Zone (nodal) o NH zone (nodal HIS) Internodal and Interatrial Pathways Connects SA and AV Node Ant. Internodal(bachman) tract Middle Internodal(wenkebach) tract Posterior internodal(Thorel) tract Bundle of His/ Purkinje Fibers Provides for ventricular conduction system Fastest conduction among cardiac tissues Right bundle Left Bundle Septal branches and 2 fascicles Mechanism of Contraction of Contractile Cardiac Muscle Fibers 1. Na+ influx from extracellular space, causes positive feedback opening of voltage-gated Na+ channels; membrane potential quickly depolarizes (-90 to +30 mV); Na+ channels close within 3 ms of opening. Depolarization causes release of Ca++ from sarcoplasmic reticulum (as in skeletal muscle), allowing sliding actin and myosin to proceed. Depolarization ALSO causes opening of slow Ca++ channels on the membrane (special to cardiac muscle), further increasing Ca++ influx and activation of filaments. This causes more prolonged depolarization than in skeletal muscle, resulting in a plateau action potential, rather than a "spiked" action potential (as in skeletal muscle cells).

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Differences Between Skeletal & Cardiac MUSCLE Contraction

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1.

All-or-None Law - Gap junctions allow all cardiac muscle cells to be linked electrochemically, so that activation of a small group of cells spreads like a wave throughout the entire heart. This is essential for "synchronistic" contraction of the heart as opposed to skeletal muscle. Automicity (Autorhythmicity) - some cardiac muscle cells are "self-excitable" allowing for rhythmic waves of contraction to adjacent cells throughout the heart. Skeletal muscle cells must be stimulated by independent motor neurons as part of a motor unit. Length of Absolute Refractory Period - The absolute refractory period of cardiac muscle cells is much longer than skeletal muscle cells (250 ms vs. 2-3 ms), preventing wave summation and tetanic contractions which would cause the heart to stop pumping rhythmically. Internal Conduction (Stimulation) System of the Heart A. General Properties of Conduction 1. 2. heart can beat rhythmically without nervous input nodal system (cardiac conduction system) - special autorhythmic cells of heart that initiate impulses for wave-like contraction of entire heart (no nervous stimulation needed for these) gap junctions - electrically couple all cardiac muscle cells so that depolarization sweeps across heart in sequential fashion from atria to ventricles

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B.

"Pacemaker" Features of Autorhythmic Cells 1. pacemaker potentials - "autorhythmic cells" of heart muscle create action potentials in rhythmic fashion; this is due to unstable resting potentials which slowly drift back toward threshold voltage after repolarization from a previous cycle.

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Theoretical Mechanism of Pacemaker Potential: a. b. c. K+ leak channels allow K+ OUT of the cell more slowly than in skeletal muscle Na+ slowly leaks into cell, causing membrane potential to slowly drift up to the threshold to trigger Ca++ influx from outside (-40 mV) when threshold for voltage-gated Ca++ channels is reached (-40 mV), fast calcium channels open, permitting explosive entry of Ca++ from of the cell, causing sharp rise in level of depolarization when peak depolarization is achieved, voltage-gated K+ channels open, causing repolarization to the "unstable resting potential" cycle begins again at step a. C. Anatomical Sequence of Excitation of the Heart 1. Autorhythmic Cell Location & Order of Impulses (right atrium) sinoatrial node (SA) (right AV valve) atrioventricular node (AV) atrioventricular bundle (bundle of His) right & left bundle of His branches Purkinje fibers of ventricular walls (from SA through complete heart contraction = 220 ms = 0.22 s) a. sinoatrial node (SA node) "the pacemaker" - has the fastest autorhythmic rate (70-80 per minute), and sets the pace for the entire heart; this rhythm is called the sinus rhythm; located in right atrial wall, just inferior to the superior vena cava7

d. e.

b.

atrioventricular node (AV node) - impulses pass from SA via gap junctions in about 40 ms.; impulses are delayed about 100 ms to allow completion of the contraction of both atria; located just above tricuspid valve (between right atrium & ventricle) atrioventricular bundle (bundle of His) - in the interATRIAL septum (connects L and R atria) L and R bundle of His branches - within the interVENTRICULAR septum (between L and R ventricles) Purkinje fibers - within the lateral walls of both the L and R ventricles; since left ventricle much larger, Purkinjes more elaborate here; Purkinje fibers innervate papillary muscles before ventricle walls so AV can valves prevent backflow External Innervation Regulating Heart Function 1. 2. heart can beat without external innervation external innervation is from AUTONOMIC SYSTEM

c. d. e.

Parasympathetic (acetylcholine) DECREASES rate of contractions cardioinhibitory center (medulla) vagus nerve (cranial X) heart Sympathetic (norepinephrine) INCREASES rate of contractions cardioacceleratory center (medulla) lateral horn of spinal cord to preganglionics Tl-T5 postganlionics cervical/thoracic ganglia heart The Normal Cardiac Cycle

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A.

General Concepts 1. 2. 3. systole - period of chamber contraction diastole - period of chamber relaxation cardiac cycle - all events of systole and diastole during one heart flow cycle Events of Cardiac Cycle 1. mid-to-late ventricular diastole: ventricles filled the AV valves are open pressure: LOW in chambers; HIGH in aorta/pulmonary trunk aortic/pulmonary semilunar valves CLOSED blood flows from vena cavas/pulmonary vein INTO atria blood flows through AV valves INTO ventricles (70%) atrial systole propels more blood > ventricles (30%) atrial diastole returns through end of cycle 2. ventricular systole: blood ejected from heart filled ventricles begin to contract, AV valves CLOSE isovolumetric contraction phase - ventricles CLOSED contraction of closed ventricles increases pressure ventricular ejection phase - blood forced out semilunar valves open, blood -> aorta & pulmonary trunk 3. isovolumetric relaxation: early ventricular diastole

B.

ventricles relax, ventricular pressure becomes LOW semilunar valves close, aorta & pulmonary trunk backflow dicrotic notch - brief increase in aortic pressure TOTAL CARDIAC CYCLE TIME (normal 70 beats/minute) atrial systole (contraction) ventricular systole (contraction) quiescent period (relaxation) Heart Sounds: Stethoscope Listening9

= = =

0.8 second 0.1 second 0.3 second = 0.4 second

A.

Overview of Heart Sounds 1. lub-dub, - , lub, dub, 2. lub - closure of AV valves, onset of ventricular systole 3. dub - closure of semilunar valves, onset of diastole 4. Pause - quiescent period of cardiac cycle 5. Tricuspid valve (lub) - RT 5th intercostal, medial 6. Mitral valve (lub) - LT 5th intercostal, lateral 7. Aortic semilunar valve (dub) - RT 2nd intercostal 8. Pulmonary semilunar valve (dub) - LT 2nd intercostals

1. S1- due to closure of the AV valves 2. S2- due to the closure of the semi-lunar valves 3. S3- du