CVR: Cardiology Flashcards
1
Q
When do the coronary arteries fill with blood?
A
During diastole.
2
Q
Where on the ECG does ventricular repolarisation occur?
A
In the T wave.
3
Q
What is a normal PR interval?
A
120-300 ms (3-5 small squares on an ECG).
4
Q
What is a normal QRS complex width?
A
less than 120ms (3 small squares on an ECG).
5
Q
What is the QT interval a measurement of?
A
Measure of time from ventricular depolarisation to repolarisation.
6
Q
What is the difference between normal QT intervals for men and women?
A
Women can be 20ms longer (350-460ms) than men (350-440ms).
7
Q
What does a bipolar lead on a 12 lead ECG measure?
A
Measures potential difference (voltage) between two electrodes; one electrode designated positive, other negative.
8
Q
Name the three bipolar leads on a 12 lead ECG.
A
Leads I, II, and III are all bipolar leads.
9
Q
What does a unipolar lead measure on a 12 lead ECG?
A
Measures potential difference (voltage) between an electrode (positive) and a combined reference electrode (negative) using data from other electrodes. Reference point on a 12 lead ECG is the middle of the heart.
10
Q
Name the nine unipolar leads on a 12 lead ECG.
A
aVR, aVL, and aVF are all unipolar.
V1-V6 are also unipolar.
11
Q
On a normal 12 lead ECG, lead I and II both have positive QRS complexes. What is left axis deviation?
A
When lead I is positive QRS, lead II is negative.
They are Leaving each other. Left axis deviation.
12
Q
On a normal 12 lead ECG, lead I and II both have positive QRS complexes. What is right axis deviation?
A
Lead I has negative QRS, lead II positive.
They are Reaching toward each other. Right axis deviation.
13
Q
Which coronary artery is represented by the inferior leads?
A
RCA (right coronary artery).
14
Q
On a 12 lead ECG, the inferior leads represent the right coronary artery. Name the three inferior leads.
A
Lead II, III, aVF.
15
Q
Which coronary artery is represented by the lateral leads?
A
Left circumflex.
16
Q
On a 12 lead ECG, the lateral leads represent the left circumflex artery. Name the four lateral leads.
A
Lead I, aVL, V5 & V6
17
Q
Which plane of the heart do the limb leads represent?
A
Coronal plane.
18
Q
Which plane of the heart do the chest leads represent?
A
Transverse plane.
19
Q
Which chest leads represent the septal part of the heart and which coronary artery does this relate to?
A
V1 & V2
LAD (Left Anterior Descending).
20
Q
Which chest leads represent the anterior part of the heart and which coronary artery does this relate to?
A
V3 & V4
LAD (Left Anterior Descending).
21
Q
ECG as a graph, what is the X axis and what is the Y axis?
A
X = time
Y = voltage
22
Q
What are capacitance vessels?
A
Veins and venules; they hold the majority of blood in the body and can accommodate changes in blood volume.
23
Q
What holds a larger percentage of blood volume, large systemic veins or systemic arteries?
A
Systemic veins; 20%
(systemic arteries = 10%)
24
Q
What would happen to MAP if the aortic valve failed?
A
Diastolic pressure would be lost, therefore MAP would decrease.
25
Which vessels provide the principal site of resistance to vascular flow?
The arterioles.
26
What is the relationship between radius and flow in Total Arteriolar Resistance (TPR)?
When vascular smooth muscle contracts (vasoconstriction), radius decreases, which increases resistance, therefore decreasing flow.
27
What does the nernst equation calculate?
Resting membrane potential.
28
Name a channel/pump that is active in myocyte membrane during resting potential.
Na/K ATPase pump.
29
Why are Na/K ATPase pumps active during resting potential?
Using active transport, K+ is pumped into cell and Na+ is pumped out of cell, against their concentration gradient, creating a voltage.
30
When do voltage gated sodium channels open in myocyte cell membranes, and what happens?
Depolarisation, once certain action potential reached.
Large number of Na+ ions enter cell down their concentration gradient, causing charge inside the cell to increase rapidly.
31
What happens in the small dip at the end of depolarisation in the cardiac action potential graph?
Transient outward potassium channel triggered to open by depolarisation, small number of K+ ions allowed to leave cell causing a small repolarisation (the dip).
32
Why does the cardiac action potential graph plateau after depolarisation, instead of rapid repolarisation?
Slow calcium channels maintain the depolarisation by allowing slow influx of Ca+ ions into the cell.
33
When do delayed rectifier channels (voltage gated K channels) open during the cardiac action potential cycle?
During repolarisation to make charge inside the cell more negative again, cause large quantity of potassium to leave the cell by passive diffusion.
34
How does the action potential spread along a muscle fibre and through the myocardium syncytium (in three steps)?
1. Local depolarisation activates nearby Na+ channels, Na+ ions rush into cell.
2. This causes adjacent Na+ channels to open.
3. At gap junctions, Na+ ions allowed to travel directly across from one cell cytoplasm to next.
35
During phase 2 of cardiac action potential, slow calcium channels allow calcium to diffuse into the cell. How does intracellular calcium concentration become further amplified during this phase?
When intracellular calcium levels reach a certain threshold, RyR calcium receptors trigger SR (sarcoplasmic reticulum) to release its stored calcium.
36
How does calcium cause contraction in the troponin-tropomyosin-actin complex (4 steps)?
1. Calcium binds to troponin.
2. Troponin moves tropomyosin to reveal myosin binding sites.
3. Myosin head can then cross-link with actin.
4. Myosin head pivots causing muscle contraction.
37
How does Sino-Atrial Node (SAN) myocytes differ in action potential from normal myocytes?
SAN myocyte has gradual increase towards depolarisation constantly, once reaches certain threshold triggers full depolarisation.
While normal myocytes do this too, SAN myocytes trend towards depolarisation more rapidly.
38
What is the funny current?
Mixed sodium/potassium inward channel in SAN myocytes that is always open, causes the more rapid trend towards depolarisation.
39
How is heart rate increased/decreased in relation to calcium channels in the SAN?
Through actions on either number or permeability of calcium ion channels.
40
Why does ageing affect heart rate?
Number of calcium channels decreases with age, causing slower depolarisation in SAN.
41
Why is the QRS complex higher voltage than P wave?
The ventricles have more muscle mass than the atria.
42
What is a chronotrope?
Something which increases the heart rate.
43
What is an inotrope?
Something which increases the force of contraction.
44
Does parasympathetic stimulation increase or decrease HR, force of contraction, and CO?
Decreases all three.
45
Which hormones control the sympathetic stimulation of the heart?
Adrenaline and noradrenaline.
46
What hormone controls parasympathetic stimulation of the heart?
Acetylcholine.
47
How does the His-Purkinje system allow rapid conduction of electrical impulse?
High permeability at gap junctions and very large fibres.
48
How does the Atrioventricular Node (AVN) delay the electrical impulse?
AVN has fewer gap junctions.
49
What happens to fast (voltage-gated) Na+ channels during the absolute refractory period (during plateau phase) in the cardiac cycle?
Closed and inactivatable, so depolarisation cannot occur too early, allowing heart time to refill.
50
The relative refractory period occurs during repolarisation, when K+ channels are still open. What state are the Na+ channels in during the relative refractory period?
Some Na+ channels are still inactivated, others have returned to a closed resting state.
51
What affect does sympathetic stimulation have on the heart?
Increases HR and contractility (positive inotropic and chronotropic effect)
52
ECG paper is made of small 1mm squares and big 5mm squares. How many small squares is 1 second on an ECG?
25 x small squares (or 5 x big squares!)
(speed = 25mm/sec)
53
How many squares represent 1mV on an ECG?
2 big squares (10x small 1mm squares).
54
How would you calculate the rate on an ECG?
Number of QRS segments x6
(1 ECG = 10 seconds)
55
What does a positive deflection mean on an ECG?
Net current flow is towards the lead.
56
What part of the ECG represents the SAN firing and atria depolarising?
P wave.
57
What is happening during the PR interval?
Delay of signal passing through AV node.
58
How does the respiratory pump aid venous return during inspiration?
Diaphragm increases intra-abominal pressure, increasing pressure in abdominal veins. Decreases pressure in thorax, decreasing pressure in right atrium and intrathoracic veins.
This pressure difference increases venous return to the heart.
59
What is the equation for cardiac output?
CO = HR x SV
(cardiac output = heart rate x stroke volume)
60
What is cardiac output?
How many litres of blood the heart pumps in one minute.
61
What is stroke volume?
The volume of blood pumped from the left ventricle per contraction.
62
What is the equation for mean arterial pressure (MAP)?
MAP = diastolic + 1/3 pulse pressure.
63
How is pulse pressure calculated?
Pulse pressure = systolic - diastolic.
64
In physics, Ohm's law states voltage = current/flow x resistance (V=IR).
How does this relate to the equation for blood pressure?
BP = CO x TPR
V = I x R
65
Poiseuille's Law states flow = difference in pressure upstream-downstream / resistance to flow (Q=P1-P2/R).
What is important to remember about the calculation of resistance to flow in this equation, in relation to the radius of blood vessels?
Radius is to the power of 4, so is very influential.
Resistance to flow is inversely proportional to the radius; as radius is larger (vessels dilate), resistance decreases, which increases flow.
66
In the Frank-Starling Mechanism, stroke volume increases as end-diastolic volume (EDV) increases, due to the length-tension relationship of muscle.
But what happens to stroke volume if EDV is too low or too high?
Stroke volume decreases.
EDV too low (e.g. hypovolaemia): sarcomeres aren't stretched enough to contract forcefully.
EDV too high (e.g. heart failure): sarcomeres are overstretched and can't contract efficiently.
67
Arteries and arterioles maintain constant pressure by myogenic autoregulation. Explain how this occurs.
When vascular smooth muscle is under increased pressure it is stretched (vasodilation).
When pressure is lower, it responds by constricting (vasoconstriction).
68
Nitric Oxide (NO) is produced in vascular endothelium; it is a type of Endothelium Derived Relaxing Factor (EDRF).
What effect does NO have on vascular endothelium?
Vasodilation.
69
Endothelin is a peptide produced in vascular endothelium.
What effect does endothelin have on vascular smooth muscle?
Vasoconstriction.
70
Name three inhibitors of endothelin production.
NO (Nitric Oxide).
Prostacyclin.
ANP (Atrial Natriuretic Peptide).
71
Prostacyclin is produced in vascular endothelium.
What affect does prostacyclin have on blood vessels?
Vasodilation.
72
Does adrenaline cause vasoconstriction or vasodilation?
Vasoconstriction in the skin, but causes vasodilation in vital organs to increase flow to these important areas.
73
Where are the primary (high-pressure arterial) baroreceptors?
In the carotid sinus and aortic arch.
74
Where are the secondary (low-pressure cardiovascular) baroreceptors?
Veins, atria, and pulmonary vessels.
75
What nerve sends afferent signals from the carotid baroreceptors?
Glossopharyngeal (cranial nerve IX).
76
What nerve sends afferent signals from the aortic baroreceptors?
Vagus (cranial nerve X).
77
What happens to baroreceptors when there is long-term change e.g. in hypertension?
They adapt/reset to a new baseline.
78
Which part of the brain receives information from baroreceptors, chemoreceptors to monitor and control blood pressure?
The medulla oblongata.
79
What are the short-term and long-term controls of BP?
Short-term: baroreceptors.
Long-term: blood volume (controlled by kidneys, RASS)
80
How are myocytes linked together?
The cells physically slot together at intercalated discs, and are linked by desmosomes and gap junctions.
81
How do desmosomes provide mechanical strength and strong adhesion between cells?
By intercellular links joining the intermediate filaments of cells together.
82
What organ receives the largest proportion of cardiac output?
The liver.
83
What visceral sensory information do the chemoreceptors of the aortic bodies detect?
Arterial O2 and CO2 levels.
84
Renin is a proteolytic enzyme.
What is the principal site of renin production?
Juxtaglomerular cells in the kidneys.
85
Anti-diuretic hormone (ADH) acts on the kidneys to promote water retention.
What is the site of synthesis of ADH (antidiuretic hormone)?
Synthesised in the hypothalamus.
However, it is then stored in the posterior pituitary gland!
86
Renin is a proteolytic enzyme. What is the key action of renin in the renin-angiotensin-aldosterone system (RAAS)?
Renin converts angiotensinogen into angiotensin I.
87
Aldosterone is a steroid hormone in the renin-angiotensin-aldosterone system (RAAS).
Where is aldosterone synthesised?
The adrenal cortex.
88
In the renin-angiotensin-aldosterone system (RAAS), release of aldosterone is stimulation by angiotensin II. What affect does aldosterone have in the kidneys?
Increases water retention by increasing sodium reabsorption and potassium secretion.
89
Sensible fluid loss is that which is easily measured e.g. urine output, vomit, fluid in surgical drains.
Give an example of insensible fluid loss.
Sweating, water lost from respiration, evaporation during abdominal surgery.
(Insensible fluid loss is loss that is not easily measured)
90
What are Starling forces?
The hydrostatic and oncotic forces involved in the movement of fluid between plasma in capillaries and interstitial fluid.
91
The left ventricle forms the apex of the heart. Where is the apex beat palpable?
Left 5th intercostal space, midclavicular line.
92
How do inotropes increase contractility?
Increase Ca+ ingress and release from sarcoplasmic reticulum, therefore more Ca+ binds to TnC, increasing contractility of myofibrils.
93
What is excitation-contraction coupling?
Process of converting an electrical stimulus (excitation) to a mechanical response (contraction).
94
"When the heart is relaxing it isn't resting!"
What does this mean?
When the heart is relaxed, it is still working hard, using ATP to pump Ca ions back into sarcoplasmic reticulum or out of the myocytes.
95
Why is the T-tubule important in myocytes?
To allow calcium into the cell closer to the SR and myofibrils.
96
The myocyte uses the sodium/calcium exchanger to remove calcium from the cytoplasm during relaxation. How does this work?
Uses electrochemical potential to allow 3x sodium ions into the cell in exchange for 1x calcium ion to leave.
(Sodium gradient is then maintained by Na+/K+ ATPase)
97
The protein titin acts like a molecular spring in the myofibrils, providing elasticity. What different parts of the myofibril does it attach to?
Attaches myosin to actin at the Z discs.
98
What is the function of Troponin I (TnI) in the troponin complex?
TnI inhibits any interaction between actin and myosin.
99
What is the function of Troponin C (TnC) in the troponin complex?
TnC binds to calcium, moves TnI and TnT (hence tropomyosin) away from actin, exposes actin binding site to myosin heads.
100
What is the function of Troponin T (TnT) in the troponin complex?
TnT binds to tropomyosin to anchor the troponin complex and helps position the tropomyosin on actin, to also prevent myosin binding to actin.
101
What is a sarcomere?
The functional unit of myofibril, the region between two Z-lines.
102
What is isovolumic contraction?
Part of the cardiac cycle where the ventricle contracts without causing any change in the volume of blood in the ventricle.
103
What pressure does the left ventricle need to reach to open the aortic valve?
Diastolic pressure.
104
The ejection fraction is the percentage of blood ejected with each beat. What is the ejection fraction in females vs males?
Females = 65%
Males = 55%
105
What do the 1st and 2nd heart sounds ("Lub dub") correspond to?
1st = closing of mitral valve "lub" This is just after the start of isovolumic contraction.
2nd = closing of aortic valve "dub" This is also the start of isovolumic relaxation.
106
What is the early phase of filling?
When pressure in the left atrium increases above pressure in the left ventricle, blood rushes into ventricle passively prior to any atrial contraction.
107
In a young healthy adult, what percentage of blood from the left atrium moves into the ventricle during early phase of filling?
85%
108
In young healthy adults/athletes/pregnancy, the early phase of filling can create a 3rd heart sound (gallop). When is the 3rd heart sound pathological and what does it suggest?
In adults over middle age, suggestive of congestive heart failure.
109
When does diastasis occur in the cardiac cycle?
When pressure in left atrium and left ventricle becomes equalised due to early phase of filling equalising the pressure.
110
When might you hear the 4th heart sound?
Galloping sound of blood being forced into stiff or hypertrophic left ventricle during atrial contraction.
111
A patient with AF has developed a hypertrophic left ventricle. Would you hear a 4th heart sound?
No! Because they don't have any atrial augmentation/contraction.
112
Preload is also called end-diastolic pressure. What does this refer to?
The volume of blood present before left ventricular contraction has started.
113
What is afterload?
The amount of pressure the heart needs to exert against systemic vascular resistance to pump blood out of the ventricle.
114
How does titin relate to Starling's law?
Titin in myofibril keeps the unit tight. If the heart is overfilled and go beyond the capacity and stretch/elasticity of the titin, the heart is unable to contract efficiently.
115
What is elasticity of the heart?
The ability of the myocardium to recover its normal resting shape.
116
How is ejection fraction calculated?
Stroke volume/end-diastolic volume.
117
What do pressure-volume loop graphs demonstrate?
Changing relationship between pressure and volume in left ventricle during cardiac cycle.
118
What are three stages of atherogenesis that can lead to thrombosis by plaque rupture/fissure?
1. Fatty streak
2. Fibrous plaque
3. Athero-sclerotic plaque
119
What two arteries does the left coronary artery divide into?
Left anterior descending (LAD) and circumflex.
120
Why is the oxygen saturation in coronary venous blood very low compared to other veins?
Oxygen extraction by the heart muscle is very high.
121
Which part of the ECG has a normal duration of 120-200ms (0.12-0.2 sec)?
PR interval.
122
Which lead in a 12-lead ECG yields complexes that are normally inverted compared to the anterior and inferior leads?
Lead aVR
123
The end diastolic volume (EDV) in the average healthy person’s left ventricle is 120mls.
If we assume normal ventricular function, what is a normal end systolic volume (ESV)?
50ml
124
The AVN is supplied by the atrioventricular nodal branch. Does this artery originate from the left or right coronary artery in most people?
The right coronary artery.
