Electrical properties of the heart Flashcards

1
Q

excitation-contraction coupling.

A

actin myosin fillaments overlap - cross bridges oull closer together. sarcolemma is membrane surrounding whole muscle.

t - tubule deviations rul down tubule (transferse)

sarcoplasmic reticulum acts as calcium store.

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2
Q

Why does cardiac muscle have a longer depolarisation time than skeletal muscle?

A

To allow for regulation of the amount of calcium getting into the cell, the calcium released inside the cell and so the strength of contraction

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3
Q

What does cardiac muscle form to allow it to function as a unit?

A

A functional syncytium

*A syncytium is a mass of cells that have merged together. The muscle cells in the cardiac syncytium are derived from the mesoderm. *

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4
Q

What allows the functional syncytium to work?

A

Gap junctions - electrical connections
Desmosomes - physical connections

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5
Q

What is the cardiac output of the heart?

A

5l / minute
CO = SV x HR

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6
Q

sarcoplasmic reticulum acts as__

A

calcium store

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7
Q

in skeletal muscle how would the sarcoplasmic reticulum get activated

A

sat at -90mv; activated by motor neuron releasing acetylcholine and binds to nicotinic receptors at end plate;

depolarises cell = evoke an action potential in muscle membrane

action potential will travel along being self-propagated by voltage-gated sodium channels

all along membrane then down t tubules and through interaction with sarcoplasmic reticulum which release calcium inside cells = calcium binds to troponin

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8
Q

Why does cardiac muscle have a longer action potential period than skeletal muscle regarding a long refractory period?

A

Stops the cardiac muscle from exhibiting tetanus

(twitch contraction which creates sustained contraction tetanus if you wish to keep a muscle contracted) skeletal good for holding things and avoiding dropping

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9
Q

QRS in chest leads v1 and v2 are usually

A

negative.

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10
Q

When venous return decreases there is a corresponding decrease in .

A

cardiac output

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11
Q

is the type of penicillin used for prophylaxis against rheumatic fever and rheumatic heart disease.

A

Benzathine penicillin G

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12
Q

Infants with (dextro-transposition of the great vessels/levo-transposition of the great vessels) might not show symptoms at birth, but will eventually develop heart failure later in life.

A

(dextro-transposition of the great vessels/levo-transposition of the great vessels) levo-transposition of the great vessels

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13
Q

Infantile coarctation of the aorta is associated with both patent ductus arteriosus and (chromosomal anomaly) syndrome.

A

Turner syndrome.

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14
Q

There is a ____ to ____ shunt between the atria in hypoplastic left heart syndrome.

A

left to right shunt

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15
Q

The normal axis of the heart points downward and to the patient’s

A

left

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16
Q

__is the imaging test of choice to diagnose deep venous thrombosis.

A

Compression ultrasound with doppler

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17
Q

What are capillaries made up like

A

Exchange vessels
Very narrow lumen and thin wall
BP very low

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18
Q

What are veins made up like

A

Low resistance so blood can get back to the heart
Wide lumen
2/3 of blood stored in veins = capacitance vessels

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19
Q

What is MAP determined by

A

Cardiac output and total peripheral resistance

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20
Q

end-diastolic volume -

A

the left ventricle is filled with the maximum volume of blood,

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21
Q

Preload -

A

amount blood left in left ventricle before contraction (determined by end diastolic pressure) = volume work of heart

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22
Q

Stroke volume -

A

blood vol(l) pumped by heart per contraction - determined by blood filling ventricle, compliance of ventricular myocardium.

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23
Q

Cardiac output-

A

blood pumped by heart per minute (co=svxhr)

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24
Q

MAP -

A

is the average arterial pressure throughout one cardiac cycle, systole, and diastole. influenced by co and systemic vascular resistance

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25
can be used for reversing witnessed ventricular fibrillation in the absence of defibrillators.
Precordial thump
26
What is a functional syncytium?
A group of cells that are synchronised electrically in an action potential
27
How is arteriolar resistance controlled
Extrinsic neural control Extrinsic hormonal control Intrinsic control - individual tissue
28
how long is the action potential of cardiac muscle how long action potential for skeletal muscle
cardiac 250msec skeletal 2 msec
29
what involvement does calcium have with contraction strength?
More calcium from ECF = more forceful contraction calcium release does not saturate troponin, so regulation of calcium release can be used to vary the strength of contraction
30
What cells have unstable resting membrane potentials?
pace maker cells - spontaneously depolarise to threshold firing action potential
31
basic electrophysiology cell heart non-pacemaker
K+ higher in cell - leaky potassium channels Ca+ and cl higher outside. - cannot get in without pumps -90mv reached resting state.
32
basic electrophysiology cell heart non-pacemaker what makes it depolarise?
the neighbouring cells depolarising (syncytium) 0 - rapid depolarisation - rapid sodium influx 1 - early repolarisation - efflux potassium 2 - plateau - the slow influx of calcium 3 - final repolarisation - efflux of potassium 4 restoration of ionic concentration ions - resting potential restored by na+/k+atpase. slow entry of na+ into the cell until a threshold for new action potential
33
What else affects contractility
Inotropes - epinephrine, Hypercalcaemia Thyroid hormones Glucagon
34
action potential pacemaker cells
**Action potential** Increase in Permeability to calcium (L type) channels (voltage-gated) open slower but stay open longer **Pre potential** (pacemaker potential) - gradual decrease permeability to potassium (k+) (leaky channel shutting) **(early phase)** Sodium (Na+) moved into the cell through "funny channels" (open in response to hyperpolarisation/repolarisation of previous action potential). = slowly depolarises until threshold met (responsible for instable resting membrane potential) **(later)** increase permeability to Calcium (T-type) (voltage gated) transient small amount ca+ open more hyperpolarised potentials. Strong inward calcium current responsible for rapid polarisation,
35
AV node conduction
0.05 m/sec
36
What separates atria from ventricles and what is significant about its conduction
annulus fibrosus - non conducting depolatisation evoked in atria here cant get straight across to ventricles
37
Hyaline arteriolosclerosis of the ______ the glomerulus in diabetes mellitus leads to a high glomerular filtration pressure and resultant microalbuminuria
efferent arteriole
38
what wave caused the p wave?
the depolarization of the atria
39
what wave causes the QRS complex
depolarisation of the ventricles
40
what wave causes the T wave?
repolarisation of the ventricles
41
What decreases contractility
Ach by vagus nerve on m2 Hypocalcaemia Ischaemia - hypoxia Hyperkalaemia Barbituarates
42
What does hyperkalemia do to the heart?
Fibrillation and heart block
43
ECG explain 1st-degree block
delayed p - q interval the atrioventricular node is a delay box slowing the conduction of action potential to ventricles this can slow/ stop so no depolarisation from the atrium to the ventricle. delay **normal interval p wave to start QRS complex should be less than 0.18 seconds. one large square is 0.2s**
44
2nd degree block ECG
some depolarisations don't get through at all. the increasing delay between Q to QRS interval and sometimes no QRS
45
3rd-degree heart block ECG
no transmission between atria and ventricles depolarising from another place (not coordinating with atrium) hence inverted t wave
46
atrial flutter (conduction disorder) ECG
normal P QRS t sequence but each depolarising occurring quicker than should so superventricular tachycardia.
47
atrial flutter
atria and pacemaker isn't depolarising spread of a wave of depolarisation across the atria. individual cells depolarising causing AF
48
ventricular fibrillation ECG
Lethan uncoordinated depolarisation in ventricles. defibrillator - to depolarise all cells same time = enters a refractory period pacemaker cells able to try to start rhythm again
49
standard ecg box
augmented limb leads aVR aVL aVF are derived from the same three electrodes as leads I, II, and III, but they use Goldberger's central terminal as their negative pole.
50
precordial/ chest leads
labelled v1-v6
51
standard ECG limb leads
SLL 1 - left arm wrt right arm SLL 2 = left leg wrt right arm SLL 3 - left leg wrt left arm
52
pr interval
time from atrial depolarisation to ventricle depolarisation (normally 0.12-0.2 seconds)
53
duration of QRS complex
time for whole ventricle to depolarise 0.08
54
time for wt interval
time spend while ventricle depolarised/repolarises (0.42) varies
55
what rhythm should the paper run at/be callibrated for?
25mm/sec
56
calibrating pulse should be \_\_
0.2 sec = 1 large square
57
how to measure heart rate on the ECG
measure r-r interval and work out how many in 60 seconds. - count 30 squares (6 seconds) and multiply by 10
58
what are the ranges in ecg: normal bradycardia tachycardia
normal 60-100 bradycardia \< 60 bpm tackycardia \>100 bpm
59
what is more severe? st elevation or non st elevation
stemi is more severe
60
what direction does the x axir relate to
area of repolarisation
61
which of these is not a coronary artery left marginal artery diagonal artery infra-cardiac artery left anterior descenting artery
infra-cardiac artery
62
how long does 5 large squares relate to if the machine is callibrated correctly?
1 second. each square = 0.2 seconds
63
what anatomical plane do ecg measure in?
frontal
64
chest leads are unipolar what point do they measure voltage charge from? mcburnys point wilsons central terminal sternum midclavicular point
wilsons central terminal
65
what speed should ecg machine run as standard in mm/s
25mm/s
66
the qt interval encompasses which electrical events? ventricular depolarisation ventricular repolarisation+ atrial repolarisation atrial depolarisation+atrial repolarisation + ventricular depolarisation ventricular depolarisation + atrial repolarisation + ventricular repolarisation
ventricular depolarisation + atrial repolarisation + ventricular repolarisation
67
what is standard paper setting for ecg machine
1mv oer 10mm 25mm/s
68
how many seconds does 5 small squared on ECG printout correspond to if the machine is running standard speed? 2. 5s 0. 2s 1s 10s
0.2s
69
which lead is not considered a limb lead? v1 green yellow avf
v1
70
what is a normal pr interval length 150ms 0. 9s 2. 4s 0. 5ms
150ms
71
which of these gives greatest detail of the size of the heart? ap chest xray 12 lead ecg cardiac MRI cardiac ECHO
cardial MRI
72