Cardiovascular Flashcards
What does pulse pressure refer to?
Pulse pressure equals the difference between the systolic and diastolic arterial pressures.
Which of the following does NOT contribute to the delivery of oxygen to the tissue?
Blood pressure, cardiac output, hemoglobin, or PaO2?
Blood pressure
Define arterial blood pressure
The product of cardiac output (CO) and total peripheral resistance (TPR) also known as systemic vascular resistance (SVR).
Define hypotension
A systolic ABP of <100 mmHg or MAP of <60 mmHg.
If the dicrotic notch on an arterial wave form is high and approaches the systolic pressure, what can this indicate?
Vasoconstriction
Describe the top of an arterial wave form
The peak systolic blood pressure where maximum pressure is generated during ventricular ejection of blood into the systemic arterial system.
What does the start of an arterial waveform represent and what is the name of the limb?
The systolic upstroke or anacrotic limb
Describe the rapid decline on an arterial waveform and what is the name of the limb?
There is a rapid decline in arterial pressure as ventricular contraction comes to an end shown on the dicrotic limb. The dicrotic indicates aortic valve closure.
What does the lowest point indicate in an arterial waveform?
Diastolic blood pressure.
What does the area under the arterial waveform represent?
Mean arterial pressure.
What is the difference between the systolic and diastolic blood pressure?
The pulse pressure.
If the dicrotic notch on an arterial wave form is low and approaches the diastolic pressure, what can this indicate?
Vasodilation
What can cause an arterial waveform to become overdamped or dull/rounded in appearance.
Air bubbles in the connection tubing, a blood clot in the arterial catheter, and if the connection tubing is too compliant or not stiff enough.
What will an underdamped arterial waveform appear like?
Tall and sharp
Define coronary perfusion pressure
The pressure gradient that drives coronary blood pressure and is a surrogate for coronary blood flow. It is the difference between diastolic aortic pressure (DAP) and right atrial diastolic pressure (RADP).
What is DAP - RADP = and what do they mean?
DAP - RADP = CPP
Diastolic aortic pressure - right atrial diastolic pressure = coronary perfusion pressure
What measurement of CPP is thought to be needed for ROSC to occur?
15 mmHg
Define vasodilation
The INCREASE (opening/dilation) in the internal diameter of blood vessels that is caused by the relaxation of smooth muscles within the wall of the vessels can an INCREASE in blood flow due to a DECREASE in SVR.
Key characteristics of a normal sinus rhythm (NSR)
Often a narrow QRS complex and upright P wave in lead II
Key characteristics of sinus bradycardia
A narrow QRS with upright P wave and a HR below 50.
*Can be produced with vagal stimulation or due to Sick Sinus Syndrome, drug induced or shock.
Key characteristics of sinus tachycardia
Narrow QRS and HR above 150 but below 180.
*Results from increased sympathetic stimulation (pain, fever, increased oxygen demand, hypovolemia).
Key characteristics of a sinus arrhythmia
Narrow QRS with upright P wave, but irregular pattern that fluctuates with inspiration (HR increases) and expiration (HR decreases).
What are the three most common arrest rhythms seen in veterinary CPA?
- Asystole
- Pulseless electrical activity
- Ventricular fibrillation
Define asystole
The absence of cardiac electrical activity and appears as a “flat line” on ECG.
Without electrical activity there is no mechanical function which means no blood is being pumped out of the heart and into circulation.
Define pulseless electrical activity or PEA.
AKA electromechanical dissociation, often appears as a normal ECG tracing but may also appear wide and bizzare. There may be P waves, QRS complexes, and T waves but with no cardiac muscular activity and therefore no cardiac output or perfusion.
Define ventricular fibrillation
ECG tracing will appear erratic and chaotic with no discernible rhythmic or normal waveforms.
This means the mechanical activity of the heart is also chaotic, rapid and disorganized and caused by numerous myocardiocytes firing erratically.
AKA “bag of worms”
Can be course and fine
Not a perfusing rhythm and REQUIRES defibrillation immediately.
Where is the heart’s normal or natural pacemaker located?
At the sinoatrial node (SA node)
What is the initial defibrillator dose for a biphasic defibrillator?
2-4 J/kg
What is the initial defibrillator dose for a monophasic defibrillator?
4-6 J/kg
At what percentage do you increase your defibrillation dose each time upon unsuccessful defibrillation?
50%
If ventricular fibrillation rhythm recognition is delayed for more than four minutes, why must you perform two minutes of chest compressions BEFORE defibrillating?
To allow the myocardium to replenish the energy stores lost during fibrillation.
Cardiomyocytes will be unable to respond to the shock without available intracellular energy.
In circumstances of refractory fibrillation despite defibrillation, or if one is not available, what drugs can be given for chemical defibrillation?
Amiodarone or lidocaine.
This form of defibrillation is rarely successful.
Name 4 things that determine blood pressure
- Heart rate
- Volume of blood ejected by the heart on each beat
- Diameter and elasticity of the vessels
- Blood volume
What is blood pressure?
A measurement that estimates blood flow to end organs. It is a function of the tone in the arteries and the volume of blood ejected from the heart.
Or:
The pressure exerted by circulating blood on the walls of blood vessels. It’s made up of a systolic and diastolic component.
The systolic component is created at the end of a cardiac cycle when the ventricles are contracting and represents a peak pressure in the arteries. The diastolic pressure is the minimum pressure in the arteries at the beginning each cardiac cycle when the ventricles are filled with blood.
BP = SVT x CO
What does a pulse oximeter measure?
SpO2 or hemoglobin saturation as an indirect measurement of arterial oxygen content. Expressed as a percentage.
Name 4 limitations of a pulse oximeter
- Low pulse pressure (hypotension/tachycardia
- Vasoconstriction of the patient is hypothermic
- Issues with other light absorbing hemoglobin forms such as smoke inhalation
- Proper contact and positioning with the mucous membranes
Define cardiac action potential
Rapid change in membrane potential, or voltage, across the cardiac cell membrane.
Define resting membrane potential and its approximate millivolts.
The heart is at a state of rest with a resting membrane potential of approximately -90mV.
What are the two main ions found outside the cardiac cell at rest?
Sodium and chloride.
What is the main ion found inside the cardiac cell at rest?
Potassium.
Define cardiac threshold potential.
The critical level to which a membrane potential must reach to initiate an action potential.
When does the action potential begin?
When the voltage suddenly becomes more positive which is known as depolarization or phase 0.
What does the P wave represent on ECG?
Atrial contraction
What does the flat segment between the P wave and the QRS complex represent?
A period of rest where the AV electrical impulse depolarizing the heart is intently delayed allowing the atria to finish their contracting.
What does the QRS complex represent?
Ventricular depolarization.
What is not visible on an ECG?
Atrial depolarization as it is masked by the QRS complex.
What does the T wave represent on ECG?
Ventricular repolarization.
What is atrial contraction also known as?
Systole.
What is ventricular systole also known as?
Isovolumic or isometric contraction.
What is ventricular rest also known as?
Diastole.
What are three things that contribute to stroke volume?
- Cardiac preload
- Cardiac contractility
- Cardiac afterload
Define cardiac preload.
The force acting to stretch the ventricular fibers at the end of diastole, or end diastolic volume. Can also be thought of as blood volume returning to the heart.
Define cardiac afterload.
The tension created within the left ventricle immediately prior to aortic valve opening that the heart muscle must overcome for blood to leave the heart.
Define cardiac contractility.
The strength or ability of the heart to contract.
List the “tree of life’s” individual blood pressure components.
Blood pressure = SVR x CO
Cardiac output = SV x HR
Stroke volume includes: preload, contractility and afterload
Describe the vicious cycle of heart failure.
What is MVO2?
Myocardial oxygen consumption.
