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test 5 Flashcards

1
Q

myocardial protection pre-1955

A

Systemic hypothermia

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2
Q

1955 myocardial protection

A

-Melrose advocated the use of high potassium solutions to induce cardiac quiescence. Caused permanent myocardial injury.

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3
Q

1956 myocardial protection

A

-Lillehei introduced retrograde cardioplegia

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4
Q

1973 myocardial protection

A

-Gay & Ebert reintroduced hyperkalemic arrest with lower potassium concentrations (<20 mmol), preventing permanent myocardial injury.

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5
Q

1979 myocardial protection

A

-Buckberg & Follette introduced blood cardioplegia

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6
Q

europe myocardial protection

A

š-Bretschneider HTK (histadine, tryptophan, alpha ketoglutarate)
š -Low Calcium, low sodium, procaine with histadine buffers
š -Non-depolarizing arrest
š NOW – Custodial HTK
-St. Thomas Solution (London)
š -Intracellular ionic concentration
š -Normocalcemia, hyperkalemia (16mmol/L)
š -NOW – Plegiol in US

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7
Q

Coronary Blood flow is determined by hemodynamic factors

A

-š Perfusion pressure
š- Coronary Vascular Resistance
š -Q = P/R

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8
Q

Delivery of Oxygen (DO2) to myocardium (oxygen supply) is determined by two factors:

A
  • Coronary blood flow (ml/min)
    š- Oxygen content of the blood (ml O2 /mL blood)
    š -O2 Delivery = CBF x CaO2
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9
Q

Consumption and Demand often used interchangeably

A

-š Not equal
š -Demand = Need
š -Consumption = Actual amount of oxygen consumed per minute

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10
Q

how is oxygen used

A

-š Regenerate ATP
š *Na/K-ATPase pump
-š Myocyte contraction and relaxation

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11
Q

Oxygen consumption (mL O2/min per 100g):
arrested heart\
resting heart rate
heavy exercise

A

2
8
70

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12
Q

using hypothermia and fibrillation

A

-reduces workload of the heart

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13
Q

Lowest level of Cardiac Oxygen Consumption

A

-When heart is arrested

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14
Q

Highest level of Cardiac Oxygen Consumption

A
  • Shortly after weaning from bypass

š *Heart is repaying oxygen debt

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15
Q

Ischemia results when oxygen delivery does not meet

A

-Oxygen demand
-šSupply/Demand
š *Normally – Supply is greater than demand – Ratio >1
š *With Ischemia – Supply is less than demand – Ratio <1
-ANAEROBIC metabolism
š -Production of lactic acid

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16
Q

result of the lactic acid buildup

A

š- Decreased intracellular pH
š -decreases the stability of the cellular membranes
š -Decreases the stability of the mitochondrial membranes.
š -Impairs Na-K ATPase
*šLeads to calcium influx
*šCalcium overload

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17
Q

ATP generated from aerobic metabolism is used preferentially for 1_________, whereas anaerobically produced ATP is used for 2___________

A
  1. myocardial contraction (work)

2. Cell survival and repair (work to survive)

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18
Q

increase in heart demand for oxygen, what needs to be done

A
  • increase in coronary blood flow

- can’t extract more

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19
Q

Coronary blood flow is dependent on the and normal flow pressure

A
  • transmural gradient
  • Coronary Perfusion Pressure = DBP - LVEDP
  • normal 60-80 mmHg
  • Pressure gradient of at least 15mmHg may be necessary for survival
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20
Q

coronary blood flow during isovolumetric contraction and ejection compared to diastole

A
  • flow is lower than during diastole
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21
Q

Myocardial Protection: Pre-Ischemic Intervention

A 
-š Minimize on-going ischemia
š *Pharmacology (ie. Nitroglycerin)
-š Prevent ventricular distension
š *Vent!!!
-š Myocardial preconditioning
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22
Q

Myocardial Protection: Preconditioning

A
  • Myocardium that has undergone one or more brief periods of ischemia may be better able to tolerate subsequent prolonged ischemia.
  • getting the heart used to ischemia
  • for beating heart it might help
  • also used when myocardial protection not optimal
23
Q

Myocardial preconditioning can be achieved by

A
  • ischemia
  • drugs
  • Cardiopulmonary bypass itself may override these other methods and be the “best” preconditioning tool
24
Q

Why give Cardioplegia?

A
  • Cardiac quiescence
    š- Bloodless field
    š- Preservation of myocardial function
    š- Induces myocardial hypothermia
25
Goals of Hypothermic Cardioplegia
- š Immediate / sustained electromechanical arrest - š Rapid / sustained homogenous myocardial cooling - š Maintenance of therapeutic additives in effective concentrations - š Periodic washout of metabolic inhibitors
26
Without cardioplegic arrest
- šIrreversible ischemic injury šwithin 20 minutes
27
With myocardial protection strategies
- Can prolong ischemia to more than 4-5 hours without irreversible damage
28
Normal Cardiac Action Potential
``` PHASES: •0 – Na+ influx •1 – Transient K+ efflux •2 – Ca++ influx •3 – K+ efflux •4 – Na/K ATPase ```
29
Mechanism of Potassium Arrest
- šWith a blood potassium of 8-10 mEq/L, depolarization of the cell occurs and sodium rushes into the cell. - šBecause the extracellular potassium is so high the cell cannot repolarize and the sodium remains inside the cell. *sodium gates do not reset: fast-gates remain open; slow gates remain closed š- After AoXC, potassium washes out of the extracellular space (Repolarization) - stops phase 3
30
Mechanism of Custodial-HTK (“Low Sodium”)
- stops phase 0 | - nonpolarizing phase
31
Mechanism of Del Nido (“Low Calcium”)
- stops phase 2 - stop contraction phase - still depolarized but arresting in this phase
32
Components of Myocardial Protection
- š Route of delivery * antegrade / retrograde / both / directly into opstia / conduits - š Composition of solution * Crystalloid / Blood / Microplegia - š Temperature - Delivery interval * Intermittent / Continuous - š Additives - š Monitoring - š Preparation for reperfusion (hotshot)
33
Antegrade pros
* Simple | * Mimics normal coronary flow
34
Antegrade cons
* Requires competent Aortic Valve * Can interrupt surgery * Advanced CAD
35
Retrograde pros
* Avoids limitations from AI and CAD * Doesn’t interrupt surgery * Augments de-airing
36
Retrograde cons
• Catheter placement difficult • Closely monitor pressure
37
Integrated (both) pros
• Uniform distribution of cardioplegia
38
Integrated (both) cons
* Complex | * Closely monitor pressures
39
Antegrade Delivery
- šInitial dose = ~10-15 mL/kg - šUp to 30 mL/kg in pediatric patients. - 4:1 CPG = 4 parts blood = 800mL AND š1 part CPG = 200mL - šSubsequent doses are * šLess Volume * šLower potassium concentration
40
Antegrade Delivery pressures and flow
- šLine pressure: *š125-150 mmHg š *Goal : Maintain a ROOT pressure of 50- 100mmHg - šFlow is generally 250-400 mL/min *š150 ml/minute/m2
41
Antegrade Delivery Benefits
``` -š Easy š- Physiological flow pattern š- Quick arrest š- Appropriate distribution to the right and left heart. š- Root is tolerant of higher pressures ```
42
Antegrade Delivery disadvantages
-š Requires competent aortic valve -š Poor distal perfusion in diseased arteries -š Poor subendocardial perfusion (especially in LVH)
43
Retrograde Delivery
- šDelivered into Coronary Sinus *šMust be vented š- A balloon is inflated on the cannula that provides two functions: *šPrevents backflow *šHolds cannula in place *šFlow is ~200 mL/min *šFlow should be titrated to maintain a coronary sinus pressure of 30-40 mmHg.
44
Retrograde Delivery benefits
-š Ideal for aortic valve regurgitation -š Good distal perfusion of obstructed arteries -š Retrograde flushing of emboli – augments de-airing -š Does not impede conduct of case - can run continuously š *Warm continuous
45
Retrograde Delivery disadvantages
š- Catheter placement can be difficult -š Impaired right heart protection š* Right coronary veins drain into the right atrium -š Surgical skill required for placement of cannula -š Distracting to perfusionist -š Possible coronary sinus rupture
46
Direct Ostial Delivery
-š Not as common as traditional antegrade or retrograde. š *Position dependent -š Hand-held cannula used to directly perfuse ostia š *AVR š *Aneurysm / Dissection -š 250-300 mmHg required (circuit pressure) š *High pressures due to small cannula orifice. -š 150-250 mL/min š *Normal perfusion is 5-8% of cardiac output
47
Delivery Through Grafts
- šAfter the initial dose for CABG, may infuse cardioplegia directly into the vein grafts. š *Infusion pressure of 50 mmHg š *Flow rate of 50-100 mL/min. - Surgeon may use hand-held syringe
48
Delivery Through Grafts Allows surgeon to check
- šAnastamosis - šAdequacy of flow - šFlow to previously under-perfused areas
49
Delivery Through Grafts benefits
- Allows antegrade protection of areas of coronary artery disease - š Obviates limitations from aortic insufficiency and coronary artery disease - š Allows delivery without need to pressurize aortic root or interrupt surgery
50
Delivery Through Grafts disadvantage
-š Requires graft placement š- Complexity š- Distribution only to those areas perfused by graft
51
Integrated Delivery
- šIt is common to give a large arresting dose of antegrade cardioplegia, followed by a smaller dose of retrograde cardioplegia. - šMore likely to perfuse all areas of the heart.
52
Integrated Delivery benefits
- šBenefits of all methods utilized
53
Integrated Delivery disadvantages
- šComplexity

Perf tech II (16 decks)

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