cardiology teaching package

7/25/2019 Cardiology Teaching Package

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Cardiology Teaching Package

A Beginners Guide to Normal Heart Function, Sinus Rhythm & Common Cardiac

Arrhythmias

The Heart

The heart itself is made up of cham!ers, " atria and " #entricles$ %eo'ygenated !lood

returns to the right side of the heart #ia the #enous circulation$ (t is pumped into the right

#entricle and then to the lungs )here car!on dio'ide is released and o'ygen is a!sor!ed$ The

o'ygenated !lood then tra#els !ac* to the left side of the heart into the left atria, then into the

left #entricle from )here it is pumped into the aorta and arterial circulation$

(mage+ The passage of !lood through the heart

The pressure created in the arteries !y the contraction of the left #entricle is the systolic !lood

pressure$ nce the left #entricle has fully contracted it !egins to rela' and refill )ith !lood

from the left atria$ The pressure in the arteries falls )hilst the #entricle refills$ This is the

diastolic blood pressure.

The atrio#entricular septum completely separates the " sides of the heart$ -nless there is aseptal defect, the " sides of the heart ne#er directly communicate$ Blood tra#els from right

side to left side #ia the lungs only$ Ho)e#er the chambers themselves work together$ The

" atria contract simultaneously, and the " #entricles contract simultaneously$

So )hat )e need to *no) ne't is .)hat causes these cham!ers to contract/.$

Cardiac Conduction System

Going !ac* to the analogy of the central heating system, the pump, pipes and radiators are of

no use unless connected to a po)er supply$ The pump needs electricity to )or*$ The human

heart has a similar need for a po)er source and also uses electricity$ Than*fully )e don0t need


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to plug oursel#es in to the mains, the heart is a!le to create it0s o)n electrical impulses and

control the route the impulses ta*e #ia a specialised conduction path)ay$

This path)ay is made up of 1 elements+

2$ The sinoatrial 3SA4 node

"$ The atrio#entricular 3A54 node

6$ The !undle of His

$ The left and right !undle !ranches

1$ The 7ur*in8e fi!res

(mage+ The cardiac conduction system

The SA node is the natural pacema*er of the heart$ 9ou may ha#e heard of permanent

pacema*ers 377:s4 and temporary pacing )ires 3T7;s4 )hich are used )hen the SA node

has ceased to function properly$

The SA node releases electrical stimuli at a regular rate, the rate is dictated !y the needs of

the !ody$


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myocardial cells contract in less than one third of a second$ So fast that it appears

instantaneous$

The electrical stimulus from the SA node e#entually reaches the A5 node and is delayed

!riefly so that the contracting atria ha#e enough time to pump all the !lood into the

#entricles$ nce the atria are empty of !lood the #al#es !et)een the atria and #entricles close$At this point the atria !egin to refill and the electrical stimulus passes through the A5 node

and Bundle of His into the Bundle !ranches and 7ur*in8e fi!res$

(magine the !undle !ranches as motor)ays, if you li*e, )ith the 7ur*in8e fi!res as A and B

roads that spread )idely across the #entricles $ (n this )ay all the cells in the #entricles

recei#e an electrical stimulus causing them to contract$

-sing the same domino analogy, around == million myocardial cells that ma*e up the

#entricles contract in less than one third of a second$ As the #entricles contract, the right

#entricle pumps !lood to the lungs )here car!on dio'ide is released and o'ygen is a!sor!ed,

)hilst the left #entricle pumps !lood into the aorta from )here it passes into the coronary andarterial circulation$

At this point the #entricles are empty, the atria are full and the #al#es !et)een them are

closed$ The SA node is a!out to release another electrical stimulus and the process is a!out to

repeat itself$ Ho)e#er, there is a 6rd section to this process$ The SA node and A5 node

contain only one stimulus$ Therefore e#ery time the nodes release a stimulus they must

recharge !efore they can do it again$

Imagine you are washing your car and have a bucket of water to rinse off the soap. You

throw the bucket of water over the car but find you need another one. The bucket does not

magically refill. You have to pause to fill it.

(n the case of the heart, the SA node recharges )hilst the atria are refilling, and the A5 node

recharges )hen the #entricles are refilling$ (n this )ay there is no need for a pause in heart

function$ Again, this process ta*es less than one third of a second$

The times gi#en for the 6 different stages are !ased on a heart rate of >= !pm , or 2 !eat per

second$

The term used for the release 3discharge4 of an electrical stimulus is .depolarisation., and the

term for recharging is .repolarisation.$

So, the 6 stages of a single heart !eat are+

2$ Atrial depolarisation

"$ 5entricular depolarisation

6$ Atrial and #entricular repolarisation$

As the atria repolarise during ventricular contraction, there is no wave representing

atrial repolarisation as it is buried in the QS.


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Cardiology Teaching Package


Arrhythmias

ole o! the "C# $achine

The


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Similarly, lead 5> 3midleft a'illa, 1th intercostal space4, )ill al)ays see the electrical

stimulus coming to)ards it and therefore the )a#es e'pressed in 5> for sinus rhythm, p?rst,

)ill al)ays !e point up)ards$

(mage+ Rhythm strip of sinus rhythm recorded from


Arrhythmias

"C# %ead Placement

The system of positioning of leads for performing a 2"lead


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Chest %eads

There are 2= )ires on an chest leads are positioned as !elo)+

(mage+ 7ositioning of the > chest leads

The > leads are la!elled as .5. leads and num!ered 52 to 5>$ They are positioned in specific

positions on the ri! cage$ To position then accurately it is important to !e a!le to identify the

.angle of @ouis., or .sternal angle.$


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To find it on yourself, place your fingers gently at the !ase of your throat in a central position

and mo#e your fingers do)n)ard until you can feel the top of the sternum, or ri! cage$ From

this position, continue to mo#e your fingers do)n)ard until you feel a !oney lump$ This is

the .angle of @ouis.$

The angle of @ouis is most easily found )hen the patient is lying do)n as the surroundingtissue is tighter against the ri! cage$

From the angle of @ouis, mo#e your fingers to the right and you )ill feel a gap !et)een the

ri!s$ This gap is the "nd (ntercostal space$ From this position, run your fingers do)n)ard

across the ne't ri!, and the ne't one$ The space you are in is the th intercostal space$ ;here

this space meets the sternum is the position for 52$

Go !ac* to the .angle of @ouis. and mo#e into the "nd intercostal space on the left$ :o#e

do)n o#er the ne't " ri!s and you ha#e found the th intercostal space$ ;here this space

meets the sternum is the position for 5"$

From this position, slide your fingers do)n)ard o#er the ne't ri! and you are in the 1th

intercostal space $ No) loo* at the chest and identify the left cla#icle, a !one that runs from

the left shoulder to the top of the sternum$ The position for 5 is in the 1th intercostal space ,

in line )ith the middle of the cla#icle 3midcla#icular4$ 56 sits mid)ay !et)een 5" and 5$

Follo) the 1th intercostal space to the left until your fingers are immediately !elo) the

!eginning of the a'illa, or underarm area$ This is the position for 51$

Follo) this line of the 1th intercostal space a little further until you are immediately !elo)

the centre point of the a'illa, 3mida'illa4$ This is the position for 5>$

No) loo* at the picture !elo) sho)ing the position of the heart in relation to the ri!cage and

you get an idea as to )hich areas are !eing loo*ed at !y these leads$

(mage+ Heart position in relation to the ri! cage


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%imb %eads

@im! leads are made up of leads placed on the e'tremities+ left and right )rist left and

right an*le$

The lead connected to the right an*le is a neutral lead, li*e you )ould find in an electric plug$

(t is there to complete an electrical circuit and plays no role in the


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;ell, so far )e ha#e nine )ires$ They all loo* directly at the heart )ith tunnel #ision$ They

only gi#e information !ased on )hat is immediately in front of them$ These nine )ires are

*no)n as .unipolar leads.$

The three acti#e peripheral leads are A5r, A5@, and A5f$

The .A5. stands for .Augmented 5ector.$ The last letter refers to position, )hich are as

follo)s+

%abel $eaning o! label Position o! lead on body

A5r Augmented #ector right Right )rist

A5@ Augmented #ector left @eft )rist

A5f Augmented #ector foot @eft foot

These 6 leads create a triangle )ith the heart in the middle, as !elo)$ The lines into the centre

indicate the line of sight of these leads$

(mage+ @ine of site of the unipolar leads

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