Cardiology Flashcards
What are the classes of antiarrhythmic drugs:
Class 1: Inhibiting the fast sodium channel decreasing the slope of phase 0
Class 2: Beta adrenergic antagonists (blockers)
Class 3: Potassium channel blocker Ik
Class 4: Calcium channel blockers
What is the MOA of Class 1a antiarrhythmic drugs and give two examples?
Procainamide, quinidine, dispyramide
Fast sodium channel blocking effects, modreate blockade of the the delayed rectifier potassium current Ikr
What is the MOA of Class 1b antiarrhythmic drugs and give two examples
Lidocaine, Mexiletine
Inhibit fast Na channel primarily in the open state with rapid onset/offset kinetics
Enhanced ability with acidosis, hyperkalemia and partially depolarized cells
What is the MOA of Class 1c antiarrhythmic drugs and give two examples
Flecainide, propafenone; potent blockade of fast sodium channels with greater effects as the depolarization rate increases
What is the MOA of Class 2 antiarrhythmic drugs and give two examples
Esmolol, atenolol, propranolol
Inhibit the current If , important pacemaker current- also promotes proarrhythmic depolarization in damaged myocytes
Inhibit the inward calcium current Ica-L indirectly by decreasing cAMP
What is the MOA of Class 3 antiarrhythmic drugs and give two examples
Sotalol, Amiodarone
Block repolarizing of Ik results in prolongation of action ptoeintal during and effective refractory period
What is the MOA of Class 4 antiarrhythmic drugs and give two examples
Diltizam and verapimil
Slow AV nodal conduction, Prolong refractory period of nodal tissue
Inhibits the inflow of Ca via voltage sensitive Ca channels during depolarization
How are lidocaine and mexiletine excreted
Hepatic clearance determines serum concentration
Mexiletine: Highly protien bound with renal clearance
When are beta blockers contraindicated
sinus nodal dysfunction, AV nodal conduction disturbances, pulmonary disease or overt CHF
What is the difference between atenolol metroprol and propanolol
B1 selectivity: Atenolol, Esmolol, metroprol
Kidney excreted atenolol
Proparanolol- non specific beta blocker
What are the additional benefits of Amiodarone
Has properties of all 4 classes of antiarrhythmic
Negative sided effects hepatopathies, and thrombocytopenia
What is the MOA of digioxin
autonomic nervous system by enhancing central and peripheral vagal tone
When is magnesium sulfate administered
Torsades de pointes
When suspected is low secondary to furosemide administration
What are additional benifits of Sotalol
Non selective beta blocked with Ikr inhibition at lower doses…. Higher doses see Class 3 efffects.
Excreted soley by the kidneys
Describe the events in a cardiac cycle starting with diastolic
: Diastolic- Mitral valve opens (right side would be pulmonic) once the left ventricular pressure is lower then left atrial pressure. There is rapid filling initially, then filling of both the atria and ventricle simultaneously. Finally after a p-wave there is contraction of the atria
Systole: Action potential passes through AV node- Contraction of the ventricles allows ventricular pressure to rise above atrium and the mitral valve closes due to increased pressure. Period called isovolumetric contraction. As contraction continues the LV pressure continues to increase when exceeds that of aorta it opens.
Initial rapid entry of blood into the aorta causing a rise in pressure then drops off. Then when the ventricular pressure drops below that of the aortic pressure. Dicrotic notch in pressure wave is due to back flow of blood through the valve leaflets as the pressure drops. Closure of aortic valve. Isovolumetric relaxation phase as the mitral valve is closed, when the pressure falls below that of the atria it opens again
Describe the pressure and volume changes in the atria, ventricles, and aorta during each phase of the cardiac cycle
Diastole: AP High to low, AVol High then decrease to small; VP Low to high, VVol Low to high; Aortic Pressure Low, AVol Low
Systole: AP Low to high, Avol Small then fills; V Pres High to low, VVol High to low; Aortic Press High then drops
A Volu High to low
Compare and contrast the mechanical events in the left and right heart pump
The events are the same, with equal volume; the difference right side is low pressure as there is less resistance in the lungs compared to the high pressure side of the left.
How do the cardiac sounds correlate to the electrical and mechanical events of the cardiac cycle?
S1: Corresponds with closure of the mitral/tricuspid valves
S2: corresponds with closing of the aortic/pulmonic valves
S3 Ventricle, S4 atrial gallop
The pressure in the ventricles is directly linked to the volume and the stretch of the heart muscle. Describe these relationships and discuss how changes in one variable alters the other variables.
Pressure and volume are linked to the tension and length of the cardiac muscle cells in the ventricular wall.
Diastolic filling increase in pressure causes a corresponding increase in muscle tension which passively stretches the resting cardiac muscle to greater lengths. End diastolic pressure = ventricular preload it sets the end diastolic volume and resting length of the cardiac muscle fibers at end diastole.
Systemic atrial pressure= ventricular afterload because it determines the tension that must be developed by cardiac muscle fibers before they can shorten
What is the Frank Starling Law of the heart
Stroke volume increases as cardiac filling increases.
All factors have to remain the same…. More your stretch the more you snap
- How do changes in ventricular preload affect the stroke volume? What about the ventricular pressure-volume relationship?
The relationship is curvilinear, (at very high filling pressures) it is nearly linear over the normal operation range of the heart.
- What is the effect of altered ventricular after load on stroke volume and the ventricular pressure-volume relationship?
An increased afterload, at a constant preload, has a negative effect on cardiac muscle cell shortening.
Ventricular function is adversely influenced by abnormally high ventricular afterload… less stroke volume is decreased because end-systolic volume is increased
The effect of changes on end-systolic volume (stroke volume) is quite small- normal function hear
What is ejection fraction
(end diastolic volume-end systolic volume)/end diastolic volume
Cardiac function curves plot cardiac output against cardiac filling pressure. Describe and diagram how cardiac sympathetic nerve activity affects these curves.
CO increases at a constant filling pressure with an increase in cardiac sympathetic acitivity: 1) increased activity increases heart rate 2) increases stroke volume by increasing cardiac contractility.
What are the effects of the sympathetic nervous system on the heart
Inotropy- contractility – ventricles Harder
Chronotropy- Rate- SA Node faster
Dromotropy- conduction velocity in the AV node faster
Lusitropy – Relaxation ventricles faster
What are the determinants of myocardial oxygen demand and consumption? Which of these things are fixed/determined, and which things can we alter when managing critically ill patients?
Myocardial oxygen consumption is directly related to energy use as an aerobic process. The highest energy expenditure is during isovolumetric contraction (50%). The work is determined by cardiac afterload.
More efficient- less oxygen with lower heart rate and higher stroke volume to maintain cardiac output.
How will an increase in contractility change the slope of the line on the pressure volume loop of the heart
Increased contractility will increase the slope of the ling and shift it to the left.
What is the Fick Principle and how do we use this to determine cardiac output?
The amount of substance consumed by an organ/tissue is equal to what goes in minus what goes out. This is rearranged algebreically to solve for blood flow through an organ.
CO is then generally with oxygen content with a arterial- venous (at the level of the right heart)
CO= L blood/min
- What is the cardiac index? How is it different from cardiac output?
Cardiac index is equal to cardiac output corrected for the individuals size Generally in m^2
Dog 150-200 ml/kg/min
Cat 200 ml/kg/min
What is Ohm’s law of hydrodynamics and what are the implications of this in relation to tissue perfusion
The pressure difference (driving pressure) between two sites is the flow between the sites X the resistance between theses sites.
ABP= CO X SVR
What are the determinants of central venous pressure
Effecitve blood volume at site of measurement, pleural pressure (which influeneces transmural pressure across the great veins and heart), venous vascular resistance, and right heart ‘function’
What are the determinants of the pulmonary artery pressure? Why would we want to measure the pulmonary arterial pressure?
Analogous to ABP, but is of the pulmonary circulation.
CO X PVR
Pulmonary vascular resistance affected by pleural pressure variation (disease vs. respiratory cycle) and pulmonary venous pressures
What is a water manometer, how is it used, and which measurements (ABP, CVP, PAOP, etc) can we obtain with it
Fluid filled system of tubing and manometer- water is continuous from catheter to the manometer; pressure is reported as the height of the fluid within the column direct measurement at the catheter tip. Used for CVP only (ABP is too high). Measured in cmH2O.
Report a single value considered the mean intravascular pressure in the cavity.
- What are the components of a fluid-filled hemodynamic monitoring system?
Manometer: tubing, three way stopcock, water monometer and fluid reservoir
Electronic system: tubing, at least one stopcock, pressure transducer, pressurized fluid reservoir, a flush device a cable connecting the transducer to a processor and the processor-display
Describe how to set up a direct arterial blood pressure system
Arterial catheter is in place. The transducer is flushed with hepranized saline ( using 1 liter bag 0.9% NaCl with 1 unit per ml of heparin). There is a semi rigid line that goes from the transducer to the patient and from the transducer to the bag. The bag is maintained pressured at 300 mmHg The entire line should be primed with heparin saline above. The monitor is turned on and the connection from the transducer to the monitor plugged in. The transducer should be at the level of the heart and flushed once connected. Once connected (transducer to arterial line) and flushed A waveform should appear on the screen. The line should be flushed to ensure an adequate waveform appears. A square test may be preformed.
Describe how to zero a direct arterial blood pressure system
Zeroied- opening the tranducer’s stopcock port to the atmosphere and depressing the zero button on the electronic monitoring; done at initial set up and anytime systme components are removed or replaced or if any problems occur with reading.
Describe how to calibrate a direct arterial blood pressure system
after it is zeroied, must be calibrated prior to use. Per monitor’s manufacture guidelines.
Describe how level a direct arterial blood pressure system
eliminate the influence of gravity- the reference point is the right atrium (zero reference point). The tranducer placed at the level of the RA and zeroed at that point by opening the three-way valve to air. Should be performed prior to every measurement. Sternum is good landmark.
What is the natural frequency in a direct arterial blood pressure system
very structure when stimulated naturally vibrates at a characteristic frequency which is cycles per second or hertz (Hz). Adding components together alters a systems natural frequency.
What is damping in a direct arterial blood pressure system
is measures as coefficeitn. Higher is more significant damping— overdamped has slurred upstrokes/downstrokes, loss of detail and generally flatened appearance (falsely narrowed low systolic high diastolic. Underdamped contain non physiologic points/spikes, extra waves and exaggerated falsely high systolic and low diastolic
What is a square test in a direct arterial blood pressure system
fast flush will allow you to evaluate
How is MAP calculated from a direct arterial pressure waveform
DAP + (SAP-DAP)/3
Underestimated with tachycardia as have decreased filling time
What are the determinants of systolic arterial pressure
stroke volume, velocity of left ventricular ejection, SVR, arterial distensibility, and left ventricular preload.
Define pulse pressure
The difference between SAP and DAP. This is what is palpated
How do you calculate systolic pressure variation
SP max-SP Min
Humans SPV > 10 mmHg has been show to correlate with hypovolemia
How do you calculate Delta up and delta down
Up= SP Max- SP Ref Down= SP Ref-SP Min
SP ref= Meausring SP During an end expiratory pause
No better correlation than systolic pressure variation in human patients with sepsis for hypovolemia
How do you calculate the pulse pressure variation
% = (PPmax-PPmin)/ [(PPmax+PPmin)/2]
This is over a single breath. Higher PPV (>15%) are most likely to correlate with hypovolemia and volume responsiveness
What is the distal pulse amplification
changes that occur to the pressure wave moves from central arterial circulation out to the periphery.
Name three indirect blood pressure measurements
Doppler flow
Oscillometric
Plethysmograph
Describe doppler flow indirect blood pressure measurements and list two advantages/disadvantages
A cuff is placed above the piezo crystal. The crystal is placed over the artery with ultrasound gel. Generally, need to shave to have good contact. The cuff attached to a syphgometer and inflated until pulse is no longer heard. Slowly release the cuff until the pulse is heard.
Advantage: Good for patients that are small (<10 kg)
Patients in low flow states
Disadvantage: In cats likely represents mean, wears in dogs more likely to be systolic
Difficult to obtain if patient hairy- requires clipping of fur
Requires patient handling which may be difficult
Describe Oscillometric
indirect blood pressure measurements and list two advantages/disadvantages
Cuff is placed on the antebrachium, over the tibia, metatarsus or the tail. Cuff should measure 40% of the circumference as with above. The cuff is fully inflated to a pressure where there is no blood flow through artery. As it decreases blood flow returns causing dectable vibrations in the arterial wall. Dependent on pulses pressures and artery stiffness
Advantage- Minimal training/expertise needed
Don’t need to restrain patient once cuff is placed.
Disadvantage- While generally gives you systolic/diastolic mean it is all calculated based on mean and therefore only one value is a true measured value.
Requires appropriate cuff size. If too big may get falsely low reading or too high falsely high readings.
Describe plethysmograph indirect blood pressure measurements and list two advantages/disadvantages
Technique where use a cuff as with doppler above. Monitor for when the waveform returns use a pulse oximetry. The pulse ox monitor is placed distal to the cuff. Once the duff is inflated the waveform will not be present. Once waveform is first detected this is systolic pressure.
Advantages: requires less restraint than with doppler
Good for patients with low flow states
Disadvantages: May be difficult to obtain waveform on hairy or pigmented skin.
Dependent on accurate cuff size for accurate measurement
Describe how to place an pulmonary artery catheter
The patient is appropriately sedated. The right jugular vein is clipped and sterile prepped while patient is in left lateral or dorsal recumbency. ECG monitor should be in place. An 18 ga catheter is placed into the jugular vien. An guide wire is placed to the level of the thoracic inlet. The catheter is removed. A dilator is introduced then removed. Prior to placement integrity of balloon is tested. The pulmonary artery catheter (Swan-Ganz) is placed. The distal hole should lie within the pulmonary artery and the proximal hole in the atrium to take measurements. The ECG should be monitored as the tip of the catheter passes through the right atrium, right ventricle and into the right atrium. Besides taking measurements, fluoroscopy may be used to visualize placement
List 2 advantages and disadvantages of placing a pulmonary artery catheter
Advantage: Able to measure pulmonary artery pressures and central venous pressures.
Using thermodilution may measure cardiac output
Disadvantages: placement requires sedation; Complications such as damage to cardiac structures