Cardiovascular Flashcards
Chronotropy:
HR
Inotropy
strength of contractility
dromotropy
conduction velocity (how fast an action potential travels per time)
lusitropy
Rate of myocardial relaxation (during diastole)
What is the function of the sodium-potassium pump?
Maintains the cardiac cell’s resting potential. It separates charge across the cell membrane keeping the inside of the cell relatively negative and the outside relatively positive
How does the sodium-potassium pump work?
see photo in cardiac AandP
It removes Na+ that enters the cell during depolarization.
It returns K+ that has left the cell during repolarization.
For every 3 Na+ ions it removes, it brings 2 K+ ions into cell
What are the 5 phases of the ventricular action potential?
see photo in cardiac A&P module
Phase 0: Depolarization Phase 1: Initial repolarization Phase 2: Plateau Phase 3: Repolarization Phase 4: restoration of resting membrane potential
What is the ionic movement during Phase 0 of the ventricular action potential?
Na+ influx (depolarization)
What is the ionic movement during Phase 1 of the ventricular action potential?
K+ efflux and Cl- influx (initial repolarization)
What is the ionic movement during Phase 2 of the ventricular action potential?
Ca++ influx (plateau)
K+ efflux also
What is the ionic movement during Phase 3 of the ventricular action potential?
K+ efflux (repolarization)
K+ exits faster than Ca++ enters
What is the ionic movement during Phase 4 of the ventricular action potential?
Na+/K+ pump restores resting membrane potential
List the 3 phases of the SA node action potential.
see photo in cardiac A&P module
Phase 4: Spontaneous depolarization
Phase 0: Depolarization
Phase 3: Repolarization
What is the ionic movement during Phase 4 of the SA node action potential?
Leaky to Na+ (Ca++ influx at very end) (spontaneous depolarization)
What is the ionic movement during Phase 0 of the SA node action potential?
Ca++ influx (depolarization)
What is the ionic movement during Phase 3 of the SA node action potential?
K+ efflux (repolarization)
What determines the intrinsic heart rate?
rate of spontaneous phase 4 depolarization in the SA node
What physiologic factors can increase the intrinsic heart rate?
- Increasing rate of spontaneous phase 4 depolarization (reaches TP faster)
- TP becomes more negative (shorter distance between RMP and TP)
- RMP becomes less negative (shorter distance between RMP and TP)
When the resting membrane potential and the threshold potential of the SA node are close it is __________ for the cell to depolarize.
easier
When the resting membrane potential and the threshold potential of the SA node are far it is __________ for the cell to depolarize.
harder
What is the calculation for MAP?
MAP= (SBP + 2DBP)/3
-or-
MAP= [(CO x SVR)/80] + CVP
What is normal MAP?
70-105 mmHg
What is the formula for SVR?
SVR= [(MAP-CVP)/CO] x 80
What is normal SVR?
800-1500 dynes/sec/cm^5
What is the formula for PVR?
PVR= [(MPAP-PAOP)/CO]x80
What is normal PVR?
150-250 dynes/sec/cm^5
What is the Frank-Starling relationship?
Describes the relationship between ventricular volume (preload) and ventricular output (CO).
Increase preload–> increase myocyte stretch–> increase ventricular output, to a point.
What happens with overfilling and the frank-starling relationship?
(see photo in CV A&P module)
Additional volume overstretches ventricular sarcomeres, decreasing number of cross bridges that can be formed & ultimately CO is reduced. Contributes to pulmonary congestion and increased PAOP
What values can be used to represent ventricular volume (x-axis) in the Frank-Starling curve?
CVP PAD PAOP LAP LVEDP LVEDV RVEDV
What values can be used to represent ventricular output (y-axis) in the Frank-Starling curve?
CO
SV
LVSW
RVSW
What things increase cardiac contractility?
- SNS stimulation
- Catecholamines
- Ca++
- Digitalis
- Phosphodiesterase inhibitors
What things decrease cardiac contractility?
- Myocardial ischemia
- Severe hypoxia
- Acidosis
- Hypercapnia
- Hyperkalemia
- Hypocalcemia
- VA
- Propofol
- Beta-blockers
- CCBs
Discuss excitation-contraction coupling in the cardiac myocyte:
(see photo in CV A and P)
- myocardial cell membrane depolarizes.
- Plateau of ventricular action potential (phase 2), Ca++ enters the cardiac myocyte through L-type Ca++ channels in the T-tubules.
- Ca++ influx turns on the ryanodine-2 receptor –> releases Ca++ from sarcoplasmic reticulum (aka cal induced cal release)
- Ca++ binds to troponin C (myocardial contraction)
- Ca++ unbinds troponin C (Myocardial relaxation)
- Most Ca++ is returned to sarcoplasmic reticulum via SERCA2 pump.
- In SR, Ca++ binds to storage proteins called calsequestrin.
- Repeat
What is afterload?
How do we measure it?
The force the ventricle must overcome to eject it stroke volume.
*In the clinical setting we use the systemic vascular resistance as a surrogate for LV afterload.
What law can be used to describe ventricular afterload?
Law of Laplace
wall stress = (intraventricular pressure x radius)/ ventricular thickness
intraventricular pressure pushes heart apart.
wall stress holds heart together.
Cardiac wall stress is reduced by:
Decreased intraventricular pressure
Decreased radius
increased wall thickness
3 conditions that set afterload proximal to the systemic circulation:
Aortic stenosis
Hypertrophic cardiomyopathy
Coarctation of the aorta
Relate the 6 stages of the cardiac cycle to the LV pressure-volume loop:
(see photo CV A and P)
- Rapid filling: diastole
- Reduced filling: diastole
- Atrial kick: diastole
- Isovolumetric contraction: systole
- Ejection: systole
- Isovolumetric relaxation: diastole
How do you calculate ejection fraction?
Stroke volume/ end-diastolic volume) x 100
How do you calculate stroke volume?
EDV - ESV = SV
Normal EF:
LV dysfunction EF:
Normal: 60-70%
Dysfunction: < 40%
Best TEE view for diagnosing myocardial ischemia:
see photo in CV A&p
Midpapillary muscle level in short axis
Calculate coronary perfusion pressure:
CPP = Aortic DBP - LVEDP
How can CPP be improved?
by increasing Aortic DBP or decreasing LVEDP (PAOP)
Which region of the heart is most susceptible to myocardial ischemia?
Why?
LV subendocardium.
It is best perfused during diastole. As aortic pressure increases, LV tissue compresses its own blood supply. High compressive pressure coupled with decreased coronary blood flow during systole increases coronary vascular resistance.
What factors decrease myocardial oxygen DELIVERY?
Decreased coronary flow:
- tachycardia
- decreased aortic pressure
- decreased vessel diameter (spasm or hypocapnia)
- increased end diastolic pressure
Decreased CaO2:
- hypoxemia
- anemia
Decreased O2 extraction:
- left shift (decreased P50)
- decreased capillary density
What factors increase myocardial oxygen DEMAND?
Tachycardia HTN SNS stimulation Increased wall tension Increased EDV Increased afterload Increased contractility
Nitric Oxide pathway:
see photo in CV A&P
- Nitric oxide synthase catalyzes the conversion of L-arginine to NO.
- NO diffuses from the endothelium to the smooth muscle.
- NO activates guanylate cyclase
- GC converts guanosine triphosphate (GTP) to cyclic guanosine monophosphate (cGMP).
- Increased cGMP reduces intracellular calcium, leading to smooth muscle relaxation.
- Phosphodiesterase deactivates cGMP to guanosine monophosphate (GMP) (this step turns off the NO mechanism)
Where do heart sounds match up on the LV pressure-volume loop?
(see photo CV valvular disease)
S1: closure of the mitral and tricuspid valves (marks onset of systole) (bottom right corner)
S2: Closure of Aortic and pulmonic vlaves (marks onset of diastole) (top left corner)
S3: may suggest systolic dysfunction (normal in kids and athletes) (bottom left corner)
S4: may suggest diastolic dysfunction (bottom right corner between S1 and S3
what are the 2 primary ways a heart valve can fail?
Stenosis:
- fixed obstruction to forward flow during chamber systole.
- Chamber must generate a higher than normal pressure to eject.
Regurgitation:
- Vavle is incompetent
- Some blood flows forwards and some blood flows backwards during chamber systole.
How does the heart compensate for pressure overload? Volume overload?
(see photo in CV valve disease)
Stenosis: pressure overload Concentric hypertrophy (walls thicken) Sarcomeres added in parallel
Regurgitation: Volume overload Eccentric hypertrophy (chamber dilated) Sarcomeres added in series
Hemodynamic goals for Aortic Stenosis:
HR: slow normal preload: increased SVR: 0 to increased contractility: 0 PVR: 0
Hemodynamic goals for Mitral Stenosis:
HR: Slow normal Preload: 0 SVR: 0 Contractility: 0 PVR: avoid increases
Hemodynamic goals for Aortic Insufficiency:
HR: increased Preload: 0 to increased SVR: decreased contractility: 0 PVR: 0
Hemodynamic goals for Mitral Insufficiency:
HR: increased Preload: 0 to increased SVR: decreased contractility: 0 PVR: avoid increase