Determinants of MVO2 demand (3)
1. Wall stress = P*r/2h (preload and afterload)
2. Heart Rate
Determinants of MVO2 supply (4)
CBF: AoDP - LVEDP / Coronary Vasc Resistance
-- also diastolic time, collaterals, cap density
O2 content: Hb * SaO2
Hb/O2 dissociation curve
Goals for CAD: Preload
keep heart small to reduce wall tension and LVEDP, increase perfusion pressure
Goals for CAD: Afterload
Maintain: hypertension better than hypotension
Goals for CAD: Contractility
Depression (if LV fxn normal)
Goals for CAD: Rate & Rhythm
Aortic Stenosis: What kind of Overload?
Aortic Stenosis symptoms linked with Death
angina: 5 years, syncope 3 years, dyspnea 2 years (Barash)
Aortic Stenosis symptoms appear at what AVA?
Aortic Valve Area <= 0.8 cm2
Aortic Stenosis: atrial kick is what % of LVEDV?
Goals for AS: Preload
Goals for AS: Afterload
Goals for AS: Contractility
may need inotropes if hypotension persists
Goals for AS: Rate & Rhythm
Avoid bradycardia (low CO) or tachycardia (ischemia); sinus (needs atrial kick)
Treatment for LV dysfunction in AS patient
arterial dilator (SNP or Nicardipine) to lower afterload without lowering preload
What subset of hypertrophic cardiomyopathy patients have HoCM?
20-30% have hypertropic obstructive cardiomyopathy from subvalvular obstruction
Explain the heart anatomy of a HoCM patient in systole
Systolic septal bulging into LVOT
What to avoid in HoCM patient?
Increased contractility or HR, Decreased preload or afterload: these all facilitate septal-leaflet contact
By what mechanism do HoCM patients have mitral regurgitation, if not from valve pathology?
Anterior MV leaflet is pulled toward septum, which is systolic anterior motion (SAM), resulting in a MR jet directed posteriorly
Why do HoCM patients have angina despite clean coronaries?
High systolic LV pressure prevents the coronary microcirculation from supplying the hypertrophied myocardium
How do you treat HoCM with a pacemaker?
DDD with a short AV delay will pre-excite the LV apex, resulting in paradoxical septal motion: the result is decreased ejection velocity, no SAM, and reduced LVOT gradient
HCM goals: Preload
Full; treat hypotension with volume
HCM goals: Afterload
Increased; use a-agonists for hypotension
HCM goals: Contractility
HCM goals: Rate & Rhythm
normal range, sinus
Aortic Insufficiency: what kind of overload?
Volume first, then pressure
Aortic Insufficiency: LV hypertrophy is concentric or eccentric?
Aortic Insufficiency goals: Preload
Normal to slightly increased
Aortic Insufficiency goals: Afterload
Decrease with anesthetics or vasodilators; otherwise regurgitant fraction of SV will increase, increasing overload
Aortic Insufficiency goals: Contractility
Aortic Insufficiency goals: Rate & Rhythm
Increase to reduce ventricular volume (less filling time) and raise diastolic aortic pressure (better CPP); rhythm not a problem
Aortic Insufficiency goals: CPB
Beware ventricular distension going onto bypass; either insert LV vent or immediate Aortic crossclamp if this occurs
Aortic Insufficiency goals: Cardioplegia
Give retrograde, as with bad AI antegrade cardioplegia will not reach coronary ostia
Mitral Stenosis causes (2)
1. Rheumatic Fever (rare in US)
2. atherosclerosis induced mitral annular calcification
Mitral Stenosis physiologic results
Poor LV filling results in decreased preload and increased afterload from reflex vasoconstriction
Why do pregnant women with mitral stenosis develop pulmonary edema?
Increased cardiac output and tachycardia increase left atrial pressure by the square of the original effect; this is pronounced in MS because the valve area is small
Mitral stenosis leads to what other valvular abnormality?
Tricuspid regurgitation (due to RV volume overload)
What arrhythmia is often the first manifestation of mitral stenosis and why?
Atrial fibrillation due to LA dilation
Mitral Stenosis goals: Preload
maintain and avoid hypovolemia
Mitral Stenosis goals: Afterload
Prevent pulmonary vasoconstriction (hypoxia, hypercarbia)
May need inotropes for systemic hypotension
Mitral Stenosis goals: Contractility
Intact; RV dysfunction if longstanding pulmonary hypertension
Mitral Stenosis goals: Rate
Avoid tachycardia! Maintain at low end of normal.
Mitral Stenosis goals: Rhythm
Maintain ventricular response in AFib
Mitral Stenosis goals: CPB after MVR
LV preload and filling pressures may be elevated, as function does not improve immediately
In mitral stenosis how high is the PCWP related to the LVDP?
PCWP is higher by at least the transvalvular pressure gradient
In mitral stenosis, why does volume replacement fail as a treatment for hypovolemia?
Hypotension is usually not due to hypovolemia, but poor contractility; use an inotrope or a mild peripheral vasoconstriction (beware RV failure with excess vasoconstriction!)
Mitral Regurgitation structural causes (6)
MVP, Rheumatic disease, Congenital cleft MV, Drug-related, Endocarditis, and post-MI papillary muscle rupture
Mitral Regurgitation functional causes (2)
Annular dilation from DCM, or LV ischemia from ischemic heart disease
Mitral Regurgitation: what kind of overload?
Why do patients with severe MR have a normal EF?
Stroke volume increases as it includes blood ejected back to the LA as well as forward to the aorta
Mitral Regurgitation Goals: Preload
Slightly increased, but preload reduction can reduce regurgitant flow
Mitral Regurgitation Goals: Afterload
DECREASE with anesthetics and vasodilators
Mitral Regurgitation Goals: Contractility
May be depressed, take care with myocardial depressants
Mitral Regurgitation Goals: Rate & Rhythm
slightly increased; if AFib, control ventricular response
Mitral Regurgitation Goals: CPB after MVR
New valve increases afterload, reveals myocardial failure, use inotropes
After a mitral valve repair, a patient deteriorates despite increased vasodilators and inotropes - why?
Patient likely has HoCM picture with SAM; give volume expanders and vasoconstrictors
Mortality of Acute Aortic Dissection Ascending
Type A: mortality 1-2%/hr after symptom onset; without surgery mortality is 50% in one month
Mortality of Acute Aortic Dissection Descending
Type B: 30-day mortality of 10%
Symptom of Type A aortic dissection
Symptom of Type B aortic dissection
back or abdominal pain
Acute Aortic Dissection Goals: Preload
Increase if acute AI, increase if tamponade
Acute Aortic Dissection Goals: Afterload
Acute Aortic Dissection Goals: Contractility
May be depressed
Acute Aortic Dissection Goals: Rate
Decrease! HR <60; use beta-blocker or CCB if COPD
Acute Aortic Dissection Goals: Rhythm
If AFib, control ventricular response
Acute Aortic Dissection Goals: CPB
Need alternate site for arterial (inflow) cannula, may use DHCA
CPB Circuit: List location of tubing going AWAY from patient
1) RA or SVC/IVC Venous Return (by gravity) to oxygenator, 2) Coronary suction to reservoir, 3) LV Vent to reservoir; reservoir then goes to oxygenator via filter
CPB Circuit: List location of tubing going TO patient
Arterial return (from pump via filter); goes to femoral artery or aorta
List two common LV vent sites
1) left superior pulmonary vein, 2) aortic root via antegrade cardioplegia cannula
Reasons for elevated CPB arterial line pressure
1) aortic dissection (cannula shoved into vasa media), 2) arteria cannula obstructed against wall
What are the two tasks a CPB oxygenator does?
on venous blood 1) oxygenate, 2) remove carbon dioxide
Arterial inflow line pressure gauge should read what?
200-300 mmHg (Jensen)
Bubble oxygenator pros and cons
Pro: cheap, Con: destruction of blood elements if >90 minutes
Membrane oxygenator pros and cons
Pro: Micropore membranes eliminate destructive gas-blood interface; Con: expensive
Difference between roller and centrifugal CPB pumps
Centrifugal pump flow is dependent on pump preload and afterload
Where is the flowmeter on the CPB machine with centrifugal pumps?
On arterial side
Why use albumin prime in CPB?
Reduce postoperative edema
Why use extra calcium in CPB prime?
Reduce hypocalcemia after transfusion
What is the average CPB prime volume?
Lowest safe Hct on CPB?
17-20% (17=Barash, 20=Jensen)
During isovolemic hemodilution, does SvO2 remain normal due to increased cardiac contractility or decreased blood viscosity?
Decreased blood viscosity
Name an advantage of hemodilution while on CPB
Lower blood viscosity from hemodilution offsets higher blood viscosity from hypothermia
What is the half-life of heparin in a normothermic patient?
What is the half-life of heparin in a hypothermic patient?
Up to 3 hours
After heparin bolus, the ACT is <380; DDx?
1) forgot to flush in heparin, 2) AT-III deficiency: treat with FFP or recombinant AT-III
What is pre-CPB dose of heparin? What is expected ACT?
400 U/kg; >380
What is acceptable ACT for starting CPB?
In a patient on aprotinin, what is acceptable ACT for starting CPB and why?
>700 with celite; aprotinin delays activation of intrinsic pathway via XIIa, prolongs celite ACT. With kaolin ACT, kaolin activates intrinsic pathway and makes ACT more reliable.
How are heparin levels measured intraoperatively?
Hepcon - add known doses of protamine sequentially to find optimum dose
What is heparin/protamine neutralization ratio?
1mg protamine to 100U heparin
List direct thrombin inhibitors
Hirudin (from salivary gland of leech) and bivalirudin
Retrograde autologous priming: crystalloid prime is drained, and retrograde blood via arterial cannula fills reservoir