Cardio Flashcards
What is an ECG?
A representation of the electrical events of the cardiac cycle.
What can ECG’s can identify?
- Arrhythmia’s
- Myocardial ischaemia and infarction
- Pericarditis
- Chamber hypertrophy
- Electrolyte disturbances
- Drug toxicity
What is the SA node?
It is the dominant pacemaker with an intrinsic rate of 60-100 bpm.
The fastest depolarising tissue.
What is the AV node?
The back-up pacemaker with an intrinsic rate of 40 - 60 bpm.
What are ventricular cells?
The back-up pacemaker with an intrinsic 20-45 bpm.
What is the impulse conduction pathway?
Sinoatrial node –> AV node –> Bundle of His –> Bundle branches –> Purkinje fibres
What are the normal time durations for depolarisations/ repolarisations/ node delays?
AV node delays: 0.12-0.2s
Atrial depolarisation: 0.08-0.1s
Ventricular depolarisations: 0.06-0.1s
Describe the PQRST wave…
P wave: atrial depolarisation (every lead apart from aVR)
PR interval: time taken for atria to depolarise and electrical activation to get through AV node
QRS complex: ventricular depolarisation
ST segment: interval between depolarisation and repolarisation
T wave: ventricular repolarisation
What is tachycardia?
increased heart rate
What is bradychardia?
decreased heart rate
What is dextrocardia?
heart is on the right side of the chest instead of the left
What is seen on an ECG for an acute anterolateral myocardial infarction?
ST segments are raised in anterior (V3 -V4) and lateral (V5 - V6) leads
What is seen on an ECG for an acute inferior MI?
ST segments are raised in inferior (II, III, aVF) leads
Why is atrial repolarisation not seen on an ECG?
Atrial repolarisation is usually not evident on an ECG since it occurs at the same time as the QTS complex so is hidden.
What are the box representations on the ECG paper?
Horizontally: - One small box = 0.04s - One large box = 0.20s Vertically: - One large box = 0.5mV
What is the cardiac definition of the left ventricle?
Palpated in the 5th intercostal space and mid-clavicular line, responsible for the apex beat.
What is the definition of stroke volume?
The volume of blood ejected from each ventricle during systole.
What is the definition of cardiac output?
The volume of blood each ventricle pumps as a function of time (litres per min).
CO (L/min) = SV (L) x HR (BPM)
What is the total peripheral resistance?
The total resistance to flow in systemic blood vessels from beginning of aorta to vena cava.
Arterioles - provide most resistance.
What is the definition of preload?
The volume of blood in the left ventricle which stretches the cardiac myocytes before left ventricular contraction. Vol. of blood in ventricles before it pumps.
Decreased by vein dilation.
What is the definition of afterload?
The pressure the left ventricle must overcome to eject blood during contraction.
Dilated arteries decrease afterload.
What is the definition of contractility?
Force of contraction and the change in fibre length - how hard the heart pumps.
What is the definition of elasticity?
Myocardial ability to recover recover normal shape after systolic stress.
What is the definition of diastolic dispensibility?
The pressure required to fill the ventricle to the same diastolic volume.
What is the definition of compliance?
How easily the heart chamber expands when filled with blood volume.
What is Starlings law?
Force of contraction is proportional to the end diastolic length of cardiac muscle fibre.
The more the ventricle fills, the harder it contracts.
Explain the relationship of end diastolic volume, preload, sarcomere stretch, stroke volume and force of contractions…
↑ venous return = ↑ end diastolic volume = ↑ preload = ↑ sarcomere
stretch = ↑ force of contraction = ↑ stroke volume and force of
contractions
What is the effect of standing on the cardiac output and what other effects does this have?
Standing decreases venous return due to gravity, so cardiac output decreases, causing a drop in blood pressure, stimulating baroreceptors to increase blood pressure.
Explain the heart sounds…
S1 - mitral cand tricuspid valve closure
S2 - aortic and pulmonary valve closure
S3 - in early diastole during rapid ventricular filling, associated with mitral regurgitation and heart failure, normal in children and pregnant women
S4 - “Gallop”, in late diastole, blood being forced into still hypertrophic ventricle - associated with left ventricular hypertrophy
In ischaemic heart disease, what coronary arteries commonly develop atheroscerosis?
Circumflex, Left anterior descending (LAD), Right coronary arteries
What are the risk factors for atherosclerosis?
- Age; increasing age = increased risk
- Tobacco smoking; leads to endothelium erosion
- High serum cholesterol
- Obesity; more pericardial fat = increase in inflammation
- Diabetes; hyperglycaemia damages the endothelium
- Hypertension
- Family history
Where is atherosclerosis plaque distributed?
- Found within peripheral and coronary arteries
- Focal distribution along the artery length
Describe the structure of an atherosclerotic plaque…
A complex lesion of:
- lipid
- necrotic core
- connective tissue
- fibrous “cap”
What can be the effects of atherosclerotic plaque?
Plaque will either occlude the vessel lumen resulting in a restriction of blood flow (ANGINA), or it may rupture (thrombus formation and subsequent death)
Describe the process of atherosclerosis formation…
- Initiated by an injury to the endothelial cells, resulting in endothelial dysfunction.
- Chemoattractants are released from endothelium to attract leukocytes, which then accumulate and migrate into the vessel wall.
- Chemoattractants are released from site of injury and concentration gradient is produced.
What inflammatory cytokines are found in plaques?
IL-1 (most important)
Il-6
IFN-gamma