Cardiac Flashcards
Detail the conduction pathway starting with the SA node (normal pacemaker).
- SA node
- Internodal tracts - AV node + Bachmann’s bundle (to LA)
- AV node
- Bundle of His
- Bundle branches
- Purkinje fibers
- Ventricular muscle
Action potentials with plateau phases are found where?
Atrial and ventricular muscle cells
Action potentials that are biphasic (depolarization + repolarization withOUT plateau phase) are found where?
SA and AV node
Atrial + Ventricular Muscle Cell Action Potential
4: Resting -90 mV (leak K channels, K OUT)
0: Rapid depolarization + 30 mV (Na IN)
1: Brief repolarization (Cl IN, K OUT)
2: Plateau (Ca IN) - Na channel in the inactivated state
3: Repolarization (K OUT) - Na channel becomes activated
4: Diastole (Na/K pump)
SA + AV Node Action Potential
4: Resting -70 mV
0: Slow depolarization (Ca + Na IN)
3: Repolarization (K OUT)
4: Diastole — spontaneous depolarization to threshold = K OUT decreases progressively, Na IN increases progressively, last 1/3rd Ca IN
What is the resting potential of the ventricular cell?
- 90 mV
How does the action potential of the AV node differ from the SA node?
The action potential of the AV node has a slower phase 4 depolarization
Changing the ______ of _______ depolarization causes heart rate to change.
Slope of phase 4
On what phase of the nodal action potential does digitalis /CCB work to slow heart rate?
Phase 4
On what phase of the nodal action potential does lidocaine/phenytoin work to control ventricular dysrhythmias?
Phase 4
On what phase of the cardiac ventricular action potential do CCB work?
Phase 2
What happens to the duration of the plateau with hypocalcemia?
Ca diffuses IN at a slower rate - plateau is prolonged
What happens to the duration of the plateau with hypercalcemia?
Ca diffuses IN at a faster rate - plateau is shortened
Ventricular depolarization proceeds from the ______ wall of the septum to the ____ wall.
Left or right?
Left to right
*Overall spread of depolarization is to the LEFT b/c the LV is normally electrically predominant
Right Bundle Branch Block
How do you make the diagnosis?
Look at V1 and V6
V1: rSR’ complex, broad R’ wave - “rabbit ears”
V6: qRs complex, broad S wave
Left Bundle Branch Block
How do you make the diagnosis?
Look at V1 and V6
V1: loss of normal septal r wave
V6: loss of normal septal q wave, wide + entirely positive R wave with a notch
Abnormally wide QRS complex
First Degree Heart Block
PR interval is > 0.2 sec
greater than one big box
Second Degree Heart Block
Mobitz Type I
Wenckebach
Progressive increase in the PR interval…until a DROP (missed QRS)
Second Degree Heart Block
Mobitz Type II
SUDDEN missed QRS
P waves are normal
Third Degree Heart Block
Complete Heart Block
Dissociated P waves and QRS
Sinus Arrhythmia
Inspiration - increase or decrease in HR? Why?
What is this reflex called?
Inspiration - INCREASE in HR
Intrathoracic press falls - IVC widens - VR increases - RA stretches - HR increases reflexively
*This is the Bainbridge reflex
Transmural ischemia is characterized by symmetrically inverted ____ waves.
T
Transmural injury demonstrates ST segment _______ greater than ____ mm.
Elevation
1
Calcium Disturbances and ECG
What happens with hypercalcemia?
What happens with hypocalcemia?
Hypercalcemia - shortened QT segment
Hypocalcemia - prolonged QT segment
*The QT interval reflects the duration of the plateau phase (phase 2)
Potassium Disturbances and ECG
What happens with hyperkalemia?
What happens with hypokalemia?
Hyperkalemia - peaked T waves
Hypokalemia - prominent U waves
What 2 drugs should be avoided with Wolff-Parkinson-White Syndrome?
- Digoxin
- CCB - Verapamil
* B/c they increase conduction through the accessory bypass tract - bundle of Kent
What is the best overall lead for detecting an MI?
V5
Inferior MI
Leads?
Coronary artery supply?
II, III, aVF
RCA
Anterior MI
Leads?
Coronary artery supply?
V1-V4
LAD
Lateral MI
Leads?
Coronary artery supply?
I, aVL, V5, V6
Circumflex
MAP is determined by what 2 factors?
- CO
2. SVR
CO is determined by what 2 factors?
- HR
- SV
CO = HR x SV
SV is determined by what 3 factors?
- Preload
- Afterload
- Contractility
Preload is determined by what 2 factors?
- Intravascular volume
2. Venous tone
What is the major determinant of intravascular volume?
Amount of sodium
What hormone is the most important for controlling vascular volume?
Aldosterone
Frank-Starling Law of the Heart
Increased ventricular filling - Increased preload
Increased preload - Increased SV
Contractility is determined by the _______ environment of the cardiac cell.
Chemical
Pressure Overload Hypertrophy
LV concentric hypertrophy
Chamber size remains unchanged
Causes - coarctation of aorta, aortic stenosis, untreated HTN
*IHSS does NOT apply to this situation (size of LV chamber decreases)
Volume Overload Hypertrophy
LV eccentric hypertrophy
Chamber size dilates
Causes - mitral regurgitation, aortic regurgitation, morbid obesity
Ventricular hypertrophy in response to pressure or volume overload is an application of the ________.
Law of Laplace
LV Pressure-Volume Loops
Y-axis: LV pressure X-axis: LV volume A: ESV, mitral valve opens A-B: diastolic filling B: EDV, preload, mitral valve closes B-C: isovolumic contraction C: afterload, aortic valve opens C-D: ejection D: aortic valve closes D-A: isovolumic relaxation *SV is the width of the loop
When does systole begin and end on the P-V loop?
Begin - B
End - D
When does diastole begin and end on the P-V loop?
Begin - D
End - B
What happens with an increase in preload (fluid bolus)? EDV ESV SV BP HR/SVR
EDV: increases ESV: stays the same SV: increases BP: increases HR/SVR: decreases, reflex *Pressure-volume loop widens withOUT a change in ESV
What happens with an increase in afterload (neo)? EDV ESV SV BP/SVR HR
EDV: increases ESV: increases SV: decreases BP/SVR: increases HR: decreases, reflex *Pressure-volume loop shifts UP and to the RIGHT (greater pressures and volumes)
What happens with an increase in contractility (calcium)? EDV ESV SV BP HR/SVR
EDV: decreases ESV: decreases SV: increases BP: increases HR/SVR: decreases, reflex *Pressure-volume loop shifts UP and to the LEFT (greater pressures, smaller volumes)
P-V loop shift to the RIGHT means…
Greater volumes
P-V loop shift UP means…
Greater pressures
P-V loop shift to the LEFT means…
Smaller volumes
P-V loop shift DOWN means…
Smaller pressures
When stroke volume falls either as a result of an increase in ______ or a decrease in _______, the volume of blood in the LV chamber increases - chamber dilates.
Increase in afterload
Decrease in contractility
When stroke volume increases either as a result of an increase in _______ or a decrease in _______, the volume of the blood in the LV chamber decreases - chamber shrinks.
Increase in contractility
Decrease in afterload
When preload increases, the P-V loop shifts…
P-V loop widens
EDV increases
When preload decreases, the P-V loop shifts…
P-V loop narrows
EDV decreases
When afterload increases, the P-V loop shifts…
UP and to the RIGHT
Greater pressures, greater volumes
When afterload decreases, the P-V loop shifts…
DOWN and to the LEFT
Lower pressures, smaller volumes
When contractility increases, the P-V loop shifts…
UP and to the LEFT
Greater pressures, smaller volumes
When contractility decreases, the P-V loops shifts…
DOWN and to the RIGHT
Lower pressures, greater volumes
The P-V loop in IHSS is unique. Describe the shift.
UP and to the LEFT
Greater pressures, smaller volumes
Narrow and very high!
Describe the P-V loop of aortic stenosis.
Increased afterload
UP
Greater pressures, volumes stay about the same
Concentric hypertrophy
Describe the P-V loop of mitral stenosis.
Decreased preload
Decreased EDV
Lower pressures, smaller volumes
Describe the P-V loop of aortic regurgitation.
Acute vs. chronic
No isovolemic relaxation phase
Acute - P-V loop is small
Chronic - P-V loop is large (eccentric hypertrophy)
Describe the P-V loop of mitral regurgitation.
Acute vs. chronic
No isovolemic contraction phase
Acute - P-V loop is small
Chronic - P-V loop is large (eccentric hypertrophy)
Ventricular Function Curves
Explain the shift with an increased preload.
Decreased preload?
Increased preload - point shifts to the RIGHT on the same curve
Decreased preload - point shifts to the LEFT on the same curve
Ventricular Function Curves
Y-axis?
X-Axis?
Y-axis: stroke volume
X-axis: PCWP (EDV)
Ventricular Function Curves
Explain the shift with an increased afterload.
Decreased afterload?
Increased afterload - curve shifts DOWN and to the RIGHT
Decreased afterload - curve shifts UP and to the LEFT
Ventricular Function Curves
Explain the shift with an increased contractility.
Decreased contractility?
Increased contractility - curve shifts UP and to the LEFT
Decreased contractility - curve shifts DOWN and to the RIGHT
Formula for SV
Normal SV
SV = CO/HR
(CO = HR x SV)
Normal SV = 60 mL
Formula for SI
Normal SI
SI = SV/BSA
Normal SI = 40 mL
Formula for SVR
SVR = (MAP - CVP)/CO x 80
Formula for PVR
PVR = (PAP - PCWP)/CO x 80
Baroreceptor Reflex
- Increase in BP
- Increase stretch of baroreceptors
- Increase in action potentials in afferents (sensory) of:
Vagus nerve (aortic arch)
Hering’s nerve (carotid sinus)
to CV centers in medulla - Increase in action potentials in Vagus nerve (efferent) + Decrease in action potentials to sympathetic nerves
- Decrease in BP
Where are the baroreceptors found?
- Carotid sinus
2. Aortic arch
Afferent action potentials from the baroreceptors of the aortic arch are carried to the brainstem centers via what nerve?
Vagus
Afferent action potentials from the baroreceptors of the carotid sinus are carried to the brainstem centers via what nerve?
Hering’s — a branch of the Glossopharyngeal
Which are physiologically more important: the carotid or aortic arch baroreceptors?
Carotid baroreceptors
Nitric Oxide
Pathway?
Produced by?
Regulated by?
L -arginine - nitric oxide synthase - nitric oxide - activates guanyl cyclase - triggers the production of cGMP - smooth muscle relaxes
Produced by endothelial cells of the vascular wall
Regulated by calcium, bradykinin, Ach
How do sodium nitroprusside, nitroglycerine, and dinitrate work?
They “donate” NO molecules at the vascular wall to promote vasodilation
Sodium nitroprusside has NO in its configuration
Nitroglycerine metabolism leads to the generation of a NO molecule
How does hydralazine work?
It is a membrane hyperpolarizing agent via activation of K channels
*Arterial dilator
Nitroprusside and nitroglycerine have __________ as well as vasodilatory actions.
Bronchodilator
What explains the following statement:
Nitroglycerine works on venous capacitance vessels and nitroprusside works on arterial and venous capacitance vessels.
The nitric oxide generating system for nitroglycerin is found primarily in the VENOUS vasculature.
*Nitroglycerin = venodilator
The nitric oxide generating system for sodium nitroprusside is found in BOTH the arterial and venous vascular circuits.
*Nitroprusside = arterial and venous dilator
If 2 thermodilution curves are shown…how do you determine which curve has the highest CO?
The smaller curve has the highest CO
CO is inversely proportional to the area under the thermodilution curve
Increased area under the thermodilution curve - Decreased CO
Bainbridge Reflex
- SVC dilates
- Venous pressure falls
- Pressure gradient increases
- Venous return increases
- HR increases d/t increased CVP
List determinants of myocardial oxygen supply.
- O2 content (Hct, %sat)
- DBP
- CVR
- HR
List determinants of myocardial oxygen demand.
- HR
- Afterload
- Prelaod
- Contractility
What hemodynamic change is most important to avoid in the patient with CAD?
Tachycardia
*Double jeopardy - increases O2 consumption + decreases O2 supply
The pulse pressure _______ as the arterial pressure waveform passes into more peripheral arterial vessels.
Increases
*Pulse pressure is greatest in the dorsalis pedis
What is the increase in pulse pressure as the pressure wave moves peripherally attributable to?
An increase in SBP + a decrease in DBP
*Superimposition principle
MAP = the area under the arterial pressure curve divided by what?
Time
Are CCB venous or arterial dilators?
Arterial dilators
Cause a decrease in HR
Which CCB causes a reflex increase in HR?
Nifedipine
Are ACE-I venous or arterial dilators?
Arterial dilators
How do Inamrinone and Milrinone increase myocardial contractility and decrease SVR/relax vascular smooth muscle?
By blocking the breakdown of cAMP
Name 3 indications for Adenosine.
- Slow conduction through the AV node
- Interrupt reentry pathways through the AV node
- Restore NSR in SVT patients (WPW syndrome too!)
* 6-12 mg IV RAPID, no hemodynamic effects, elimination half-time < 10 sec
Hypertrophic Cardiomyopathy w/ or w/o Ventricular Outflow Obstruction
IHSS
HOCM
Diastolic dysfunction - concentric hypertrophy
Represents a dynamic stenosis of the aortic outflow tract
Venturi effect draws leaflet out as blood rushes by (Bernoulli’s Law)
Conditions normally impairing LV function will actually improve function in this disease
SLOW (keep sinus), FULL, TIGHT, DECREASE contractility
Volume is the 1st line of defense for hypotension
Tx - BB, CCB
NO spinal or epidural
Arterial waveform may be bifid (bisferiens pulse) in what condition?
IHSS
Aortic + Mitral Regurgitation
Systolic dysfunction - eccentric hypertrophy
Fast, Full, Forward
Regurgitant volume depends on ______ and the _____ across the aortic valve.
HR
Diastolic pressure gradient
Symptoms of regurgitation are minimal when volume remains under ___% of stroke volume, but is severe if it exceeds ___% of stroke volume.
40%
60%
What 4 factors determine degree of regurgitation?
- Size of valve orifice
- Pressure gradient
- Systole time (time for regurge)
- Aortic outflow impedance (SVR)
Symptomatic Progression of Regurgitant Factors
< 30% mild symptoms
30-60% mod symptoms
> 60% severe symptoms
The height of V-waves is _____ related to atrial and pulmonary vascular compliance.
The height of V-waves is _____ proportional to pulmonary blood flow and regurgitant volume.
Inversely
Directly
Aortic Stenosis
Diastolic dysfunction - concentric hypertrophy
Most common valvular disorder in the US
Triad - angina, syncope, DOE
SLOW, FULL, TIGHT
Critical aortic stenosis occurs with an aortic orifice of ___ cm2 and a transvalvular pressure gradient of ____ mmHg.
0.8
50
Mitral Stenosis
Diastolic dysfunction - RV concentric hypertrophy
90% will present with CHF + Afib
SLOW, FULL, TIGHT
In mitral stenosis, the enlarged left atrium may apply pressure to what structure and cause hoarseness?
Left recurrent laryngeal nerve
Mitral stenosis is usually due to…
The most common cause of aortic stenosis is…
Rheumatic fever
Symptoms of mitral stenosis occur when the mitral valve orifice is < than how many cm2?
< 2
Acute aortic regurgitation presents with a sudden onset of ________ and _________.
Pulmonary edema
Hypotension
The patient has WPW syndrome. Afib develops. How should the Afib be treated?
RVR then cardioversion
Procainamide
AVOID verapamil or digitalis
Concentric hypertrophy may be one of the best ways to decrease _________.
Wall tension
Law of LaPlace: T = Pr/2h (h=wall thickness)
What is the best indicator of diastolic dysfunction?
Decrease in LV compliance
What valve problem is associated with both a systolic and diastolic murmur?
Aortic stenosis
Or a combo of mitral and aortic regurge
A very low diastolic pressure and wide pulse pressure suggest…
Aortic regurgitation
Why is it important to maintain afterload in the patient with aortic stenosis?
To maintain coronary perfusion pressure
What reflects the severity of the outflow tract obstruction in IHSS?
LV-aortic systolic pressure gradient
What is the normal ACT? What ACT indicates adequate heparinization for cardiopulmonary bypass?
70-110 seconds
ACT > 400
Give 2 possible reasons for decreased effectiveness of heparin.
- Nitroglycerine
2. AT III deficiency - 2 units of FFP
To what temp can you cool a patient before V.Fib?
V.Fib begins b/t 25-30 deg C
Blood draining from what cardiac vessels explains why the LV will fill during cardiopulmonary bypass for aortocoronary bypass graft surgery?
Thebesian and bronchial veins
What is the normal CVP during cardiopulmonary bypass? What does an increased CVP indicate?
Normally CVP = 0
An increased CVP indicates there is an obstruction to venous drainage
How should you treat elevated blood pressure during the rewarming phase of cardiopulmonary bypass? The pump flow is 50-70 mL/kg/min, which is normal.
Increased volatile agent
Unless, poor ventricular function (myocardial depression) - vasodilator
What % of coronary bypass patient return to surgery? When?
4-10% in the 1st 24 hrs
What is the characteristic EKG change with digitalis?
Down sloping of the ST segment
Which is the best standard limb lead for detecting arrhythmias?
Lead II
The patient is hypokalemic. What change in HR may be seen?
Increased
What are 3 characteristic changes seen on the ECG with hypercalcemia?
- Short QT
- Prolongation of QRS complex
- Widening of T wave
Flat T-waves are seen with what 2 electrolyte imbalances?
- Hypokalemia
- Hypocalcemia
* Both of these also have prolongation of QT interval
Prolongation of PR interval is seen with what 2 electrolyte imbalances
- Hypokalemia
2. Hyperkalemia
What are 2 causes of ST segment depression?
- Subendocardial ischemia
2. Subendocardial infarction
What are 2 causes of ST segment elevation?
- Transmural ischemia (Prinzmetal’s angina)
2. Transmural infarction
Where are the leads placed for Lead I? Lead II? Lead III?
Lead I: L.arm = pos, R.arm = neg
Lead II: R.arm = neg, L.leg = pos
Lead III: L.arm = neg, L.leg = pos
The upstroke of the arterial pressure waveform is determined by what 2 factors?
- Contractility
- SVR
*Steep upstroke with increased contractility or decreased SVR
What determines the position of the dicrotic notch in relation to the peak of the arterial blood pressure waveform?
CO
- Dicrotic notch will be high on the descending limb if SV is high
- The position of the dicrotic notch is probably most determined by preload
Which diagnostic test is best for determining CAD: resting ECG, Holter monitor ECG, stress ECG, stress thallium testing?
Stress ECG has a high specificity of 90%
What are the 2 most significant risk factors identified by the Goldman Cardiac Risk Index for non-cardiac surgery?
- Myocardial infarction
2. S3 gallop
Elective surgery is best not performed until how much time has elapsed after a MI?
Six months
Which types of surgery cause the biggest risk of perioperative reinfarction?
Intrathoracic
Intraabdominal
Lasting longer than 3 hours
What is the likelihood that a patient will experience an infarction in the perioperative period?
< 10%
How is LV compliance assessed?
Doppler electrocardiography
*LV compliance is the best indicator of diastolic function
What Swan-Ganz catheter data suggest LV failure?
Decreased CO/CI
Increased preload/PCWP
What is the hallmark of decreased cardiac reserve and low CO?
Fatigue at rest with minimal reserve
4 METs: flight of stairs without fatigue, walking at 4 mph, run a short distance, recreational sports
Is the hypotension that accompanies cardiac tamponade due to a change in preload, afterload, or contractility?
Preload
*The principle hemodynamic feature is a decrease in CO
What is Beck’s triad?
- Hypotension
- JVD
- Muffled heart sounds
Explain pulsus paradoxus in cardiac tamponade.
Normally, SBP decreases 6 mmHg or less during inspiration
Tamponade, SBP decreases > 10 mmHg during inspiration = pulsus paradoxus
What should be the goals for the patient with pericardial tamponade?
Avoid vasodilation
Avoid cardiac depression
Fast and Full!
Induction agent of choice - Ketamine
Takayasu’s Arteritis
Pulseless disease
Absence of palpable peripheral pulses
Chronic inflammation of the aorta and its major branches
Primarily affects young Asian females
S/S reflect decreased perfusion
Tx - corticosteroids
Anesthesia goal - maintain perfusion pressure
What does an S3 heart sound during mid-diastole indicate?
CHF
List the VRG. What % of CO goes to each of these organs?
Lungs 100% Liver 25% Kidney 20% Brain 15% Heart 5%
75% of CO, 10% of total body mass
What causes a change in BP when changing the patient’s position?
Altered preload
The resistance to BF is greatest in the…
Arterioles
*Greatest decrease in pressure in the arterial tree occurs in the arterioles
What are the 2 determinants of pulse pressure ?
- SV
- Arterial compliance
*PP increase when either CO increases or arterial compliance decreases
The arterial system contains what % of the total blood volume?
Venous - 64%
Arterial - 13%
Capillaries - 7%
Albumin is responsible for ___% of the total colloid osmotic pressure in the plasma.
80%
How does hypercapnia/acidosis affect systemic vasculature? Pulmonary vasculature?
Systemic - decrease SVR
Pulmonary - increase PVR
*Both HTN and hypotension may occur with hypercapnia
What is unusual about the flow pattern in the left and right coronary arteries during systole and diastole?
Flow through the R ventricle is sustained during both systole and diastole
What is the venous saturation of coronary blood?
30% (PO2 = 18-20 mmHg)
- O2 extraction level of coronary blood is 70%
- O2 consumption rate 8-10 mL O2/100g/min
Is coronary BF autoregulated?
What is the formula for coronary perfusion pressure?
YES, b/t 60-160 mmHg
CPP = aortic DBP - LVEDP(PCWP)
What most determines coronary BF?
Myocardial metabolism
Coronary dilation in response to increased metabolic demand
What is the most potent local vasodilator substance released by cardiac cells?
Adenosine
Arrange the following in order that shows greatest to least effect on myocardial O2 consumption: afterload, preload, and HR
HR > afterload > preload
Where is the density of capillaries the greatest in the LV?
Subendocardium
Higher blood flow, greater O2 requirements
Most vulnerable to ischemia
What anesthetic agents can trigger or modulate the myocardial preconditioning response? What anesthetic agents can antagonize the effect?
Good - volatile agents, adenosine, opioids
Bad - Ketamine
In what segment of the cardiac conduction system is the action potential conducted slowest? Fastest?
Slowest - AV node
Fastest - Purkinje fibers
*Phase 4 depolarization is fastest in the SA node and slowest in the Purkinje fibers (SA node - 60-100, AV node - 40-60, Purkinje - 15-40)
Is the heart equally innervated by the SNS and PNS?
NO!
SNS - both atria and ventricle + both nodes
PNS - atria + both nodes
What cardiac electrical event is represented by the PR interval?
Action potentials passing through the AV node
What cardiac electrical event is represented by the QT segment?
Ventricular action potential is in phase 2, the plateau phase
Ventricular contraction
What 2 electrolytes are membrane potential stabilizers (decrease the excitability of the cell)?
- HYPERcalcium
2. HYPERmag
