Chapter 9: Cardiac class set

Conduction System (order and coordination of contraction)

- Atrial excitation and contraction are complete before ventricular contraction begins - Excitation of cardiac muscle fibers is coordinated so each chamber contracts as a unit - The pair of atria and pair of ventricles should be coordinated so that each pair contract simultaneously

Heart Valves

- Blood flows through the heart in one direction—from veins, to atria, to ventricles, to arteries - Heart valves ensure that blood flows in the right direction through the heart - Valves are positioned so that they open and close passively due to pressure differences

Right vs. Left

- Both sides of the heart pump simultaneously - Each side pumps same volume of blood - Right side pumps with lower pressure than the left side - Heart muscle on the left side is (2x) thicker than the muscle on the right side

Electrical Conduction

- Cardiac impulse originates at SA node - Action potential spreads throughout right and left atria - Impulse passes from atria into ventricles through AV node - Action potential briefly delayed at AV node to allow complete ventricular filling before ventricular contraction - Impulse travels rapidly down interventricular septum through bundle of His - Impulse rapidly moves throughout myocardium through Purkinje fibers - Remainder of ventricular cells activated by impulses moving through gap junctions

Cardiac muscle anatomy

- Cardiac muscle fibers are interconnected by intercalated discs and form functional syncytia - Intercalated discs contain desmosomes and gap junctions - Desmesomes holds cells together - Gap junctions allow action potentials to spread from cardiac cell to cell

Heart Volumes

- End-diastolic volume (EDV) is the volume of blood in the ventricle when filling is complete (130 mL) - End-systolic volume (ESV) is the volume of blood remaining in the ventricle when ejection is complete (60 mL) - Stroke volume (SV) is the volume of blood pumped out by each ventricle per beat (EDV-ESV) (70 mL)

Nourishing the Heart

- Heart gets its own blood supply through the coronary circulation during diastole - Coronary blood flow normally varies to keep pace with cardiac oxygen needs - Coronary artery disease (CAD) refers to pathological changes within the coronary artery walls that diminish blood flow - Atherosclerotic coronary artery disease can deprive the heart of O2

Semilunar Valves

- Lie at the juncture where the major artery leaves the ventricle - Prevent blood from flowing from arteries back into ventricles when the ventricle relaxes - Left valve is the aortic valve - Right valve is the pulmonary valve

Atrioventricular Valves

- Positioned between the atrium and the ventricle - Prevent backflow of blood from ventricles into atria during ventricular contraction - Right AV valve, also called tricuspid valve - Left AV valve, also called bicuspid valve or mitral valve

ECG Abnormalities in rate

- Tachycardia is heart rate of more than 100 beats per minute - Bradycarida is heart rate of less than 60 beats per minute

ECG

- The ECG is a record of the overall spread of electrical activity through the heart - P wave represents atrial depolarization - QRS complex represents ventricular depolarization - T wave represents ventricular repolarization

Cardiac Action Potential

- The action potential of cardiac contractile cells shows a plateau phase - Ensures adequate ejection time - Long refractory period occurs in conjunction with plateau phase and prevents cardiac muscle cell summation and tetanus

Electrical Activity

- The heart is self-excitable, initiating its own rhythmic contractions - Contractile cells, 99% of the cardiac muscle cells, do the mechanical work of pumping - Autorhythmic cells initiate and conduct the action potentials that promote muscle contraction

Mechanical Events of the Cardiac Cycle

- The mechanical events of the cardiac cycle contraction are brought about by the rhythmic changes in electrical activity - The heart alternately contracts to empty and relaxes to fill - Systole refers to cardiac muscle contraction - Diastole refers to cardiac muscle relaxation

Heart Sounds

- Valve closing produces two normal heart sounds - First heart sound (S1) or "lub" is caused by closing of the AV valves during ventricular systole - Second heart sound (S2) or "dub" is caused by closing of the aortic and pulmonary valves during ventricular diastole - Defective valve function produces turbulent blood flow - This can be heard as a heart murmur - Abnormal valves may be either stenotic and not open completely or insufficient and not close completely

Major Events of Cardiac Cycle

- Ventricular diastole: ventricles fill with blood - Isovolumetric ventricular contraction: ventricles contract, all 4 valves are closed, pressure rises - Ventricular ejection: pressure forces blood past the semilunar valves - Ventricular repolarization: pressure falls, return to ventricular diastole

ECG Abnormalities in rhythm

-Atrial Flutter- depolarizations between 200 and 380 -Atrial fibrillation is rapid, irregular, uncoordinated depolarizations of the atria with no definite P waves - Ventricular fibrillation is uncoordinated, chaotic ventricular contractions with no detectable pattern or rhythm - Heart block comes from defects in the cardiac conducting system

complete heart block

-There is damage between the atria and ventricles preventing communication between the SA and AV nodes. -The heart is beating at 30bmp (AV nodal pace). -Patient usually become comatose

Parasympathetic effects

1. Enhanced K+ permiabilty hyperpolarizes the SA node cell membrane moving it further away from threshold 2. decreases AV node excitability 3. Weakens contraction by reducing the plateau phase.

Sympathetic effects

1. Main effect: speed up depolarization of SA node 2. Reduce AV node delay 3. hastes conduction through PF and HIS 4. Strengthens contractions by increasing Plateau phase

Left-ventricular pressure-volume loop for a single cardiac cycle.

1. The AV valve opens. 2. Passive ventricular filling occurs. Volume increases considerably and pressure increases slightly as blood enters. 3. Atrial contraction completes ventricular filling. End-diastolic volume is reached at the end of this phase. 4. The AV valve closes. 5. Isovolumetric ventricular contraction occurs. Volume remains constant; pressure increases markedly. 6. The aortic valve opens 7. A stroke volume of blood is ejected. Volume decreases considerably as pressure peaks, then falls slightly as blood leaves. End-systolic volume is reached at the end of this phase. 8. The aortic valve closes. 9. Isovolumetric ventricular relaxation occurs. Volume remains constant; pressure falls sharply. 10. Back to step 1.

Cardiac output is normally __ L/minute

5

SV is normally ___ mL

70mL

Parasympathetic neurotransmission

ACh released from vagus nerve binds to muscarinic cholinergic receptors coupled to an ihibitory Gprotein decreasing cAMP activity.

First heart sound (S1) or "lub" is caused by closing of the _____ valves

AV

Endocrine control of HR

Adrenal Medulla releases epinephrine to enhance sympathetic stimulation

Premature ventricular contraction

An ectopic focus among the purkinje fibers starts initiating action potentials faster than the SA node. Leads to variable periods of rapid heart rate usually due to stress, caffeine, lack of sleep, possibly heart disease

Second heart sound (S2) or "dub" is caused by closing of the _____ valves

Aortic and pulmonary

Any variation from the normal rhythm and sequence of excitation

Arrhythmia

after load

Arterial blood pressure the ventricle must overcome to pump blood out of the heart

Ca+ induced Ca+ release

As Ca+ slowly enters the cell during the plateau phase, it causes the Sarcoplasmic Reticulum to release large amounts of stored Ca+ to maintain the Ca+ levels needed for extended contraction of cardiac muscle.

________ coronary artery disease can deprive the heart of O2

Atherosclerotic

________ cells initiate and conduct the action potentials that promote muscle contraction

Autorhythmic

Cells originate at AV node and enters interventricular septum

Bundle of His (atrioventricular bundle)

ventricle fibrillation

Chaotic ventricular contractions due to erratic impulses death imminent in 4 min if rate not restored no distinguishable QRS

internodal pathway

Connection between SA and AV, only way signal gets from atria to ventricles. Causes pause (nodal delay) to allow for complete filling of V before contraction.

_______ cells, 99% of the cardiac muscle cells, do the mechanical work of pumping

Contractile

Refers to pathological changes within the coronary artery walls that diminish blood flow

Coronary artery disease (CAD)

Cardiac myopathies

Damage to the heart muscle - Myocardial ischemia- low O2 delivery to cardiac tissue - necrosis- complete tissue death -myocardial infarction blocked cardiac vessel

Systolic Heart failure

Decreased cardiac contractility causes 1) damaged heart muscle 2) chronically high afterload from high BP

Increased sympathetic stimulation results in increased strength of contraction and increased stroke volume, which is ______ (extrinsic/intrinsic) control

Extrinsic

T/F the parasympathetic and sympathetic nervous systems equally innervate the atria and ventricles

F, the Para mainly innervates the atria, sympathetic does both atria and ventricles

T/F: Cardiac output is the volume of blood ejected by each ventricle each contraction

F: Cardiac output is the volume of blood ejected by each ventricle each MINUTE

decompensated systolic HF

Forward failure- heart can no longer pump enough volume to the tissues Backward failure- heart cant pump out enough blood (Stroke Volume < End Diastolic Volume) causing back up of blood. This leads to congestive heart failure

What happens during the slow depolarization phase in autorhythmic cells

Funny channels open allowing Na+ in and slow closing of K+ channels preventing their efflux. (slowly making it more positive) Halfway through depolarization transient Ca+ channels open and the funny channels close bringing the membrane to threshold.

Pressure-volume loop

Graphic representation showing the volume and pressure changes in the ventricle When valves open and close allowing blood to enter and leave the ventricle

Comes from defects in the cardiac conducting system

Heart block 2:1 or 3:1 block means ventricle only responds to every 2nd or 3rd signal from SA Complete block means there is no communication between the A and V

Defective valve function produces turbulent blood flow, can be heard as a...

Heart murmur

Diastolic HF

Heart muscle stiffens Ejection Fraction is consistent but less volume overall is pumped symptoms are the same as Systolic Heart Failure

Heart Wall

Heart walls are composed primarily of spirally arranged cardiac muscle fibers Three layers: - inner layer, endocardium, lines the heart - middle layer, myocardium, cardiac muscle - external layer, epicardium, covers the heart

Falling phase (repolarization) of CCC action potential

Inactivation of Ca+ channels stopping their influx Opening of K+ allowing it to move out of the cell Returns membrane to negative potential.

Increased venous return ______ (increases/decreases) ventricular filling (increased EDV)

Increases

Abnormal valves may be _____ and not close completely

Insufficient, swish or gurgle

two things that control stroke volume

Intrinsic (EDV, frank-starling law) and extrinsic (sympathetic)

Event when ventricles contract, all 4 valves are closed, and pressure rises

Isovolumetric ventricular contraction

Plateau phase of CCC action potential

L type Ca+ channels open resulting in a slow influx of Ca+ prolonging the positivity of the cell. (creates plateau) Closes transient and leaky K+ channels preventing it from leaving cell

Increased EDV results in a ____ (larger/smaller) stroke volume

Larger

Channels responsible for maintained resting potential in contractile cardiac cells (CCC)

Leaky K+ channels

_______ occurs in conjunction with plateau phase and prevents cardiac muscle cell summation and tetanus

Long refractory period

Sympathetic neurotransmission

Norepinepherine binds to B1 andrenergic receptors coupled to a stimulatory G protein that accelerates cAPM

funny channels

Open when the membrane is hyperpolarized at the end of the previous action potential. Allows Na+ to enter the cell maintaining the pacemaker rhythm.

_____ represents atrial depolarization

P wave

_____ represents the AV node delay

PR segment

What three moments are represented by baseline, zero conduction on the ECG

PR segment, ST segment, TP segment

Cardiac autorhythmic cells display ______ activity - their membrane potential slowly depolarizes between action potentials, drifting to threshold

Pacemaker

ST segment

Plateau phase when ventricles are completely depolarized

Terminal fibers that extend from bundle of His and spread throughout ventricular myocardium

Purkinje fibers

_____ represents ventricular depolarization

QRS complex

Fibrillation

Random, uncoordinated excitation and contraction of cardiac cells

Thromboembolism

Ruptured plaque can cause the formation of a Thrombus due to the exposed collogen at the site of vessel damage. Blockage of a vessel by a freely floating clot (embolus) cuts off blood supply to tissue

The __ node is the pacemaker of the heart

SA

Cardiac Conduction System

Sinoatrial node (SA node) - in right atria near opening of superior vena cava - pacemaker of the heart Atrioventricular node (AV node) - small bundle of cells located at base of right atrium near septum Bundle of His (atrioventricular bundle) - cells originate at AV node and enters interventricular septum Purkinje fibers - terminal fibers that extend from bundle of His and spread throughout ventricular myocardium

Cardiac muscle fibers are _____ arranged

Spirally

Abnormal valves may be _____ and not open completely

Stenotic, causes whistling sound

Cardiac output = heart rate x _____ volume

Stroke

Volume of blood pumped out by each ventricle per beat (EDV-ESV)

Stroke volume (SV)

T/F: Heart rate is decreased by parasympathetic stimulation and increased by sympathetic stimulation

T

T/F: Atrial excitation and contraction are complete before ventricular contraction begins

T

_____ represents ventricular repolarization

T wave

80% of ventricle is filled prior to atrial contraction (T/F)

T, AV valves are open during Vdiastole allowing blood to fill during relaxation

Compensations for Heart failure

Temporary increased sympathetic activity kidneys retain salt and fluid to raise EDV

Phenomena described by the length-_____ relationship Frank-Starling law (intrinsic control)

Tension

What happens to the channels in the repolarization phase of autorhythmic cells

The LCa+ channels close and K+channels open, stopping the influx of Ca+ and allowing the rapid eflux of K+ (returns the inside of the cell back to negative)

Circulatory System

The circulatory system is the transport system of the body Three basic components: - heart (the pump) - the blood vessels (the passageways) - the blood (the transport medium)

What channels open and close at threshold in autorhythmic cells

Transient Ca+ channels close and long lasting Ca+ channels open.

The heart is a dual pump

Two blood flow circuits: - pulmonary circulation-between the heart and lungs - systemic circulation-between the heart and other body systems

Which is more dangerous Afib or Vfib

Vfib

CCC action potential depolarization

Voltage gated Na+ channels open when the membrane reaches threshold (-70)

TP segment

When the heart muscle is completely repolarized (ventricle filling)

Changes in stroke volume with a) extrinsic (sympathetic stimulation) b) both extrinsic and intrinsic (sympathetic stimulation and increased EDV)

a)100 ml stroke volume vs 70mL in normal pumping, b) 140mL stroke volume vs 70mL in normal pumping

Common control by autonomic nervous system

alters cAMP activity in innervated cardiac cells

What happens at peak membrane potential of CCC

at peak potential (+30) transient K+ channels open allowing a temporary efflux of K+ into the cell causing a mild repolarization

wiggers diagram

concurrent graph if ECG, pressure changes, volume changes, valve activity, and heart sounds of the left side of the heart

How does the frank-starling curve change with heart failure

down and to the right

interatrial pathway

extends from SA node throughout right atrium to left atrium gap junctions ensure both atria are depolarized simultaneously

Atrial fibrillation

is rapid, irregular, uncoordinated depolarizations of the atria with no definite P waves Causes a pulse deficit where the heart rate on the ECG is higher than the pulse rate at wrist because the ventricle doesn't have time to fill with the rapid irregular beats making peripheral pulse weak.

Which two mechanisms maintain the cyclic pacemaker depoalrization in autorhythmic cells

membrane clock mechanism and Ca+ clock mechanism

Atrial Flutter

rapid regular sequence of atrial depolarizations between 200 and 380bpm 2:1, 3:1 rhythm means not all SA impulses cause a fire in the AV node, keeping V contraction below 200

Common cause of valvular stenosis or insufficiency

rheumatic fever triggered by strep bacteria

lub-dup-whistle, lub-dup-swish

stenoic AV valve, insufficient AV valve

lub-whistle-dup, lub-swish-dup

stenoic aortic or pulmonary valve , insufficient aortic or pulmonary valve

Stroke volume is determined by venous return and by _______ activity

sympathetic