Cardiothoracics Flashcards
What causes a valve to open?
Pressure in greater in the given chamber in comparison to the next chamber or artery.
What are septal defects?
A whole in the heart, reducing the efficiency of the heart.
Can cause long-term structural changes due to pressure changes and resulting hypertrophy (to make up for changes in pressure)
Can be atrial or ventricular
What are calcification of valves and what do they cause?
Calcium build up on the valves of the heart.
Common, especially in elderly
Valve may not close properly, which will allow backflow of blood during diastole.
Can cause hypertrophy as heart has to work harder
What are the heart sounds you listen to within the heart?
1st is AV valves closing, ventricular pressure would then increase. Should just hear one sound as the two valves should close at the same time.
2nd sound is the pulmonary and aortic valves closing. Should be one sound as they close at the same time.
What are Korotkoff sounds?
Sound of turbulent blood flow, related to taking blood pressure
What controls blood flow?
Valves opening and shutting
What way do ventricles contract?
From the apex of the heart so they can push blood in the correct direction
What is the stroke volume of the heart?
Amount ejected per beat
How can you increase the stroke volume of the heart?
Strenuous activity increases contractility which will increase amount being ejected as well as increasing heart rate
How do you calculate cardiac output?
Stroke volume x Heart rate per minute
Stroke volume normally ~5L/min
Each side pumps about 5L
What is Starling’s law?
The more you stretch the heart, the harder it contracts
What determines the heart rate?
SA Node
Wants to work at 100bpm, but it is kept under control
What does the AV node do?
It slows conduction and can act as secondary pacemaker
What causes fibrillation?
SA node??
Lack of equal conduction to either side of heart, no coordination
Ventricular fibrillation will kill you
What does an ECG do?
Detects phasic changes in potential difference between two electrodes
Allows you to track heart rhythm and electrical activity
What does a P wave measure
Atrial depolarization
What does the QRS complex measure?
Ventricular depolarization
this is when they should start to contract
What does the T wave measure?
Ventricular repolarization
What does an ECG NOT tell you?
Does not tell you how well the heart is contracting
Why dont we see atrial repolarization?
It is hidden by the QRS complex
What is the PR interval indicating?
A delay in electrical transmission through the AV node
What does the ST segment represent, and how can it be used in diagnosis?
The time between depolarization and repolarization of the ventricles.
Important in diagnosing myocardial ischemia
What does the R-R interval on an ECG measure?
Time between heart beats
Can indicatin brady/tachycardia
What phase (0-4) of cellular action potential is represented by the ST segment?
Phase 2- inward movement of calcium leading to the plateau phase (balance of Ca and K movement), seen as the ST segment (i.e. may change in patients with an MI)
Refractory period stops us from continually activating the heart, and is the plateau phase
Important in diagnosing myocardial ischemia (it is changed, and can be depressed or elevated on an ECG in comparison to the PR segment)
What does the R-R interval measure?
Time between heart beats
Can indicating brady/tachycardia
Describe the phases of action potential in a cardiac myocyte.
Phase 0- Rapid Na influx causing depolarization
Phase 1- minor repolarization (initial K efflux while Ca channels slowly open)
Phase 2- influx of calcium leading to the plateau phase (balance of Ca and K movement), seen as the ST segment
Phase 3- efflux of K causing repolarization (Ca channels closing)
Phase 4- Ca/Na gradually leaks into cell reducing permeability of potassium so less moves out, more Ca moves in, resulting in small creep up to the threshold
How does input from the Vagus nerve change heart rate? Include ions in your answer
Acetylcholine release from Vagus nerve binds to M2 and keeps heart rate lower by increasing permeability to potassium so it is able to leak out, taking longer time to reach threshold
How does the SNS increase heart rate?
Noradrenaline release from SNS binds which increases calcium influx into the SA node, reaching threshold sooner
What causes muscles in the heart to contract?
Calcium influx through T-tubules
Can cause calcium-induced calcium release, which will cause the myocyte to contract
What is digoxin?
A drug that increases intracellular calcium causing the heart to contract more strongly.
Explain the movement of ions during the membrane potential plateau in the action potential of cardiac cells.
Sodium moves in causing depolarization which switches on potassium currents causing K to move out, causing repolarization.
This opens Calcium channels, which moves Ca in, causing a balance (outflux K vs Ca influx) out giving plateau.
Ca will eventually shut, and K will continue to exit, causing repolarization
What is inotropy
Strength of contraction
What is the dromotropy?
Speed of electrical impulses within heart
What cells line the vessels and inside of heart chamber?
Endothelial cells
Why are endothelial cells important in the vessels?
Prevent platelet aggregation (nitric oxide and prostacyclin)
Local blood pressure
Angiogenesis
Permeability barrier for nutrients/fluid
,
.
How does calcification of vessels impact blood pressure?
High calcification score will increase chance of coronary event.
It reduces elasticity, increasing blood pressure within the vessel.
How do you measure the mean arterial blood pressure?
Diastolic BP + 1/3 Pulse Pressure (systolic - diastolic)
This is the average pressure throughout the system
OR MAP= cardiac output x total peripheral resistance
OR MAP =( (2xDBP) + SBP ) / 3
How much of total blood volume in found in capillaries?
5%
~25000 mLs
What is colloid and hydrostatic pressure?
Osmotic (colloid) pressure drawing fluid back into capillaries (same on arteriole and venule side, overall pressure changes)
Hydrostatic is the pressure of blood being pushed through small area, pushing fluid out of capillaries, higher at arteriole end
What is an exception to the starling pressure forces in circulation?
Pulmonary hydrostatic pressure is much lower (colloid is the same), resulting in net transfer
How can heart failure cause oedema?
Backup of blood in pulmonary circulation, pulmonary hydrostatic pressure goes up pushing fluid into the lungs.
In combination with gravity when lying down, fluid will accumulate, resulting in pulmonary oedema (especially at night).
Can give nitrates, ACE inhibitors to treat.