Year 1; Phase 2; Pbl 7

Front 1

Describe the membrane which surrounds the heart

Back 1

- the pericardium

- pericardium has two main parts: (1) fibrous pericardium and (2)serous pericardium

-the fibrous pericardium is superficial. It holds the heart in placein the mediastimum and prevents the heart from overstretching.

-the serous pericardium is deeper and more delicate. Perichardialcells in the serous pericardium secrete pericardial fluid, whichreduces friction between the layers as the heart contracts.

Front 2

Describe the 3 layers of the heart wall

Back 2

- heart wall has threelayers: epicardium (external), myocardium (middle) and endocardium(internal)

- epicardum has twolayers (pericarduim) and supplies the myocardium

- myocardium is composedof cardiac muscle and is responsible for initiating contraction –95% of heart wall

- endothelium is a thinlayer of connective tissue. It lines the chambers of the heart andcovers the valves. Reduces friction during blood flow.

Front 3

What is the function of auricles and sulci?

Back 3

- found in the chambers of the heart

- on the anterior of eachatria is a pouch-like structure called the auricle. They increase theamount of blood the atria can hold

- the chambers also havevarious sulci containing vessels and fat. They mark the externalboundaries between the chambers of the heart.

Front 4

Describe the right atrium

Back 4

- receives blood from thesuperior vena cava, inferior vena cava and coronary sinus. Theposterior wall is smooth while the anterior muscle is rough due tothe presence of pectineal muscles.

- left and right atriaare separated by interatrial septum. It contains the fossa ovalis,which is the remnant of the foramen ovale – an opening found in thefoetal heart.

- blood then passes intothe ventricles via the tricuspid valve (right atrioventricular valve)

Front 5

Describe the right ventricle

Back 5

-contains several ridges composed of raised cardiac muscle (trabeculaecarneae)

-the cusps of the tricuspid valve are attached to chodae tendinae,which are in turn connected to papillary muscles

-the left and right ventricles are separated by the intraventriclarseptum

-blood passes from the right ventricle through the right/pulmonarysemilunar valve into the pulmonary trunk, which then divides into theright and left pulmonary arteries

Front 6

Describe the left atrium

Back 6

- receives blood from thelungs through four pulmonary veins

- posterior is smooth;anterior is also smooth as the pectineal muscle are confined to theauricle

- blood passes from thelet atrium into the left ventricle via the bicuspid valve

Front 7

Describe the left ventricle

Back 7

- thickest chamber

- forms the apex of theheart

- like the rightventricle, contains trabeculae carnae and has chordae tendinae thatanchor the cusps

- blood passes from theleft ventricle into the ascending aorta via the aortic/left semilunarvalve

Front 8

Describe the structure and function of the heart valves

Back 8

- atrioventricular(tricuspid/bicuspid) valves: opening and closing is largely mediatedby pressure changes, though also supported by pappilary muscles,which prevent the cusps of the valve moving into the atria (whichwould cause backflow)

- semilunar valves: 3moon-shaped cusps, each of which is attached to the arterial wall.Shape prevents back flow and opens and closes in response to pressurechanges

Front 9

Describe the coronary circulation

Back 9

- myocardium has its ownvessels - coronary or cardiac circulation

- coronary arteriesdescend from the aorta and encircle the heart. When the heartcontracts they are squeezed closed, but when the heart relaxes, highpressure in the aorta propels the blood through the coronaryarteries.

- two main arteries -the right and left coronary arteries – extend from the ascendingaorta and supply the myocardium

- circulflex branch liesin the coronary sulcus and provides oxygenated blood to the walls ofthe left ventricle and left atrium

- regions of heart areusually provided blood from more than one artery, and they usuallyconnect. When this happens it is called a anastomoses

- anastosmoses providealternate routes for blood flow – called collateral circulation.The heart has many anastomoses, proving detours fro blood if arterieshave been blocked

Front 10

Describe the passage of blood through the heart and body

Back 10

Front 11

Describe the 3 stages of an action potential

Back 11

Front 12

Describe the two types of conductive fibres in the heart

Back 12

-the rhythmic and continuous contraction of the heart is due toself-exciteable, autorhythmic fibres

-they repeatedly produce action potentials and can functionindependently of innervation

- autorhythmic fibres have two main functions: (1) act as a pacemaker,and (2) form the cardiac conduction system – specialised cardiacmuscle fibres which provide a path for cardiac excitation.

Front 13

Describe the passage of an action potential through the fibres of the heart

Back 13

(1)Begins in the sinoatrial node. Their resting potential is unstable –they repeatedly depolarise. When the pacemaker potential reaches itsthreshold, an action potential is triggered. This propagates throughthe atria via gap junctions in the intercalated disks, causing theatria to contract.

(2)The action potential reaches the atrioventricular node. The actionpotential slows due to differences in structure, allowing the atriato empty blood into the ventricles.

(3)Action potential arrives at the Bundle of His (atrioventricularbundle). This is the site where action potential can be transferredform the atria to the ventricles (in other regions, the heart isinsulated by the fibrous skeleton)

(4)action potential reaches the right and left bundle fibres towards theapex

(5)Purkinje fibres conduct the action potential upwards through theventricles, causing them to contract and the blood to pushed upwardsto the semilunar valves

Front 14

Describe S1 heart sounds

Back 14

- first heart sounds

-caused by closure of the bicuspid and tricuspid valves in earlysystole

-loudest at the apex of the heart

-high frequency

– best heard with diaphragm of the stethescope

-mitral valve closes slightly quicker, but so quick that human earshear it as one sound. An exception to this would be a bundle branchblock, can cause spitting due to delayed closure of the tricuspid

-intensity of the S1 sound is determined by three factors: (1)distance between the valve leaflets (P-R interval), (2) mobility ofleaflets (e.g. healthy vs stenosed), and (3) the rate of rise inventricular pressure.

-

Front 15

Describe S2 heart sounds

Back 15

- second heart sounds

-closure of the aortic (A2) and pulmonic (P2) valves – semilunarvalves.

-they are normally heard as one sound during expiration, but areaudibly split duringinspiration. This is due to pressure changes during inspirationcausing A2 to occur early, and P2 to be delayed.

Front 16

Describe S3 sounds

Back 16

- third heart sound

- when present, occurs inearly diastole

- occurs followingopening of the AV valves during rapid filling of the ventricles

- a dull, low pitchedsound heard best with the bell of the stethescope

- thought to be due totensing of the chordae tendineae during rapid filling and expansionof the ventricle

- S3 is normal inchildren and young adults as it implies supple ventricles capable ofnormal rapid expansion. In older adults, it is often pathological ,suggesting volume overload due to congestive heart failure, orincreased transvalvular flow with regurgitation. Pathological S3 issometimes referred to as a ventricular gallop.

Front 17

Describe S4 sounds

Back 17

- fourth heart sound

- when present, occurs inlate diastole and coincides with contraction of the atria

- produced when the left(or right) atria contracts vigorously against a stiffened ventricle.As such, it is usually pathological, signifying reduced ventricularcompliance from hypertrophy or ischaemia

- a dull, low pitchedsound heard best with the bell of the stethescope

- best heard at the apex

- sometimes referred toas atrial gallop

Front 18

Define a heart murmur

Back 18

an abnormal, extra sound during the heartbeat cycle made by blood moving through the heart and its valves

Front 19

List 5 causes of heart murmurs

Back 19

- flow across a partialobstruction

- increased flow throughnormal structures

- ejection into a dilatedchamber

- regurgitant flow acrossan incompetent valve

- abnormal shunting ofblood from vascular chamber to a lower pressure chamber

Front 20

List 7 ways which a murmur may be described

Back 20

- timing: whether itoccurs in systole, diastole or is continuous

- intensity: quantifiedby grading systems

-pitch: high to low frequency caused by pressure gradients

-shape: how the murmur changes in intensity from onset to oompletione.g. diamond shape which rises and then falls in intensity-location: location of the murmurs maximum intensity

-radiation: murmurs can be heard to move to other regions of he chestbased on the direction of turbulent blood flow

-manuevers: murmurs can be differentiated by asking patients to move indifferent ways e.g. standing, valsalva (forceful expiration againstclosed airway), clenching fists)

Front 21

Back 21

Front 22

Describe the uses of x-ray for assessing the heart

Back 22

- generally of limited use due to it being similar density to blood

-exception is when there is calcification

-borders are clearer as the lungs have different density

- can be used to assess size of the heart: cardiothoracicratio – maximum width of the heart divided maximum internaldiamater of the thoracic cage

Front 23

Describe how echocardiography is used to assess the heart

Back 23

-High-frequency (ultrasonic) waves generated by a piezoelectricelement travel through the body and are reflected at interfaces wherethere are differences in the acoustic impedance of adjacent tissues.

-The reflected waves return to the transducer and are recorded. Themachine measures the time elapsed between the initiation andreception of the sound waves, allowing it to calculate the distancebetween the transducer and each anatomic reflecting surface.

-Images are then constructed from these calculations.

Front 24

Describe how ECG is used to assess the heart

Back 24

-used to assess the electrical and muscular functions of the heart.While it is a relatively simple test to perform, the interpretationof the ECG tracing requires significant amounts of training. Numeroustextbooks are devoted to the subject.

- The heart is a twostage electrical pump and the heart's electrical activity can bemeasured by electrodes placed on the skin. The electrocardiogram canmeasure the rate and rhythm of the heartbeat, as well as provideindirect evidence of blood flow to the heart

- A standardizedsystem has been developed for the electrode placement for a routineECG. Ten electrodes are needed to produce 12 electrical views of theheart. An electrode lead, or patch, is placed on each arm and leg andsix are placed across the chest wall. The signals received from eachelectrode are recorded. The printed view of these recordings is theelectrocardiogram.

Front 25

Describe how CT is used to assess the heart

Back 25

-Spiral (helical) CT may be used to evaluate pericarditis, congenitalcardiac disorders (especially abnormal arteriovenous connections),disorders of the great vessels (eg, aortic aneurysm, aorticdissection), cardiac tumors, acute pulmonary embolism, chronicpulmonary thromboembolic disease, and arrhythmogenic rightventricular dysplasia. However, CT requires a radiopaque dye, whichmay limit its use in patients with renal impairment.

-Electron beam CT , formerly called ultrafast CT or cine CT, unlikeconventional CT, does not use a moving x-ray source and target.Instead, the direction of the x-ray beam is guided by a magneticfield and detected by an array of stationary detectors. Becausemechanical motion is not required, images can be acquired in afraction of a second (and recorded at a specific point in the cardiaccycle). Electron beam CT is used primarily to detect and quantifycoronary artery calcification, an early sign of atherosclerosis.However, spatial resolution is poor and the equipment cannot be usedfor noncardiac disorders, so newer standard CT techniques arebecoming preferred for cardiac use.

-Multidetector CT (MDCT), with ≥ 64 detectors, has a very rapid scantime; some advanced machines may generate an image from a singleheartbeat, although typical acquisition times are 30 sec. Dual-sourceCT uses 2 x-ray sources and 2 multidetector arrays on a singlegantry, which cuts scan time in half. Both of these modalities appearable to identify coronary calcifications and flow-limiting (ie, >50% stenosis) coronary artery obstruction. Typically, an IV contrastagent is used, although nonenhanced scans can detect coronary arterycalcification.

Front 26

Describe how MRI is used to assess the heart

Back 26

-Standard MRI is useful for evaluating areas around the heart,particularly the mediastinum and great vessels (eg, for studyinganeurysms, dissections, and stenoses).

-With ECG-gated data acquisition, image resolution can approach thatof CT or echocardiography, clearly delineating myocardial wallthickness and motion, chamber volumes, intraluminal masses or clot,and valve planes.