1. Myocardial Preservation
- Cooper University Hospital: School of Perfusion 2014
- Michael F. Hancock, CCP

2. Myocardial Protection
Surgical Goal- Preserve and Protect the heart during any cardiac procedure
Surgical preference in many cases is to operate on a bloodless, motionless heart
Several different ways to achieve this
Careful attention must be paid to preserve it’s function and protect it from injury during this time

3. Bloodless, Motionless Heart
Achieved by:
Elective Asystole
Induced ischemic periods
Elective Ventricular Fibrillation
Continuous coronary perfusion
Intermittent Aortic Occlusion
Intermittent ischemic periods
Each method will come with it’s own degree of ischemia and negative sequelae

4. Myocardial Muscle Contraction
Basic structural unit of muscle tissue is the Sarcomere
2 main components involved in contraction are the thick myosin filaments and thin actin filaments
An action potential is spread via the transverse tubule
Stored intracellular Ca++ is released and the actin filament slides onto the myosin head, know as the Power Stroke
ATP then powers the release of Ca++ from the Actin which causes muscle relaxation

5. Ischemia
“Inadequate tissue perfusion to sustain steady-state oxidative metabolism at a given level of cardiac performance”- Gravlee
Lack of blood flow to tissues
Decreased O2 delivery
Decreased Waste removal (Metabolites accumulate)
Anaerobic Metabolism takes place during ischemic periods
Only 2 moles of ATP produced
Compared to 36 moles of ATP during Aerobic Metabolism
Makes it very difficult to keep up with the demands of cardiac muscle
We must take action to lower O2 requirements during this time

6. Cardiac Muscle Requirements
The cardiac muscle uses ~70% of O2 delivered to it (O2 Extraction)
Most organs use only ~30%
O2 Consumption-
Normal- 8.0cc O2/100g/min at 37°
Empty Beating Heart- 5.6cc O2/100g/min
Arrested- 1.1cc O2/100g/min
Arrested and Cooled- 0.3cc O2/100g/min

7. Ischemic Injury
Injury can occur when oxygen supply does not meet demand
Inadequate O2 delivery
Inadequate Waste removal
Metablites need to be washed out
CO2, Lactate, H+ ions
Buildup can cause injury, injury can be spread to other areas following reperfusion
Warm Unprotected Ischemia
Ischemia < 30 minutes = Myocardial Stunning
Reversible
Ischemia > 30 minutes = Necrosis
Irreversible

8. Ischemic Injury
Lack of O2 prevents energy production necessary for membrane stabilization of blood vessels
Increased vascular permeability
Myocardial edema
Intracellular calcium buildup
Calcium is the most important ion in reperfusion injury
Leads to hypercontracture and death of myocytes and cardiac dysrhythmias
Generation of oxgyen free radicals
Release of proteolytic enzymes and leukocyte activation that destroy endothelium

9. Myocardial Protection
Goal of myocardial protection is to reduce ischemic injury and reperfusion injury
Both surgical technique and pharmacologic interventions are employed to achieve this goal
Allow the surgeon to operate on a motionless heart while still protecting and preserving it’s function

10. Myocardial Protection Strategies
Elective Asystole
Produced by cardioplegia solution delivery
Elective Ventricular Fibrillation
Allows continuous coronary perfusion with minimal heart motion
Intermittent Aortic Cross-Clamping
Intermittent clamping of the aorta during each anastamosis
Off-Pump Surgery

11. Elective Asystole
Delivering a cardioplegic solution to provide electromechanical arrest to the heart
Cardiac metabolic demands are reduced by 80-90%
Places heart in a state of flaccid depolarization
Aorta is cross-clamped to isolate the coronary arteries from the systemic circulation
Maintenance doses of cardioplegic solution are given throughout the case to keep the heart arrested and protected

12. Elective Ventricular Fibrillation
Ventricular fibrillation is induced to provide a virtually motionless heart
Hypothermia induces fibrillation and patient is kept under that temperature
Fibrillation can be induced electrically
No cross-clamp is applied
Continuous coronary artery perfusion is maintained
Need local tourniquets on vessels being worked on to allow visualization of grafts
Tourniquet sites are potential sites for future injury
Used for calcified aorta cases where cross-clamping isn’t possible or dangerous
“Porcelain Aorta”- rock hard aorta

13. Intermittent Aortic Occlusion
Aorta is cross-clamped only when surgeon is doing a distal anastamosis
Partial sidebiter clamp is applied on the aorta during proximal anastamosis
No cardioplegia delivery
Forces surgeons to work fast
Multiple clamping sites on aorta can be sites for future blockages, thrombus formation or injury

14. Off-Pump Surgery
Beating heart surgery allows the normal physiologic flow of blood to be maintained throughout the case, under ideal conditions
Thorough attention must be paid to blood pressure, ECG, and blood gas analysis to ensure adequate perfusion of the heart is taking place
Must be able to tolerate manipulation of the heart during distal anastomis

15. Cardioplegic Arrest
Cardioplegic solution is delivered immediately following cross-clamp application to provide rapid electromechanical arrest
Prevents depletion of energy rich phosphates that would be caused by ischemia
Left ventricular venting must be employed before the cross-clamp application to prevent blood traveling through the heart and being ejected against the clamp
Also prevents blood that is in the heart from reaching the coronary arteries during the cross-clamp period
Can lead to electrical activity due to coronary perfusion
Reduces myocardial O2 demands by 80-90%

16. Cardioplegic Solution
Hyperkalemic (↑ Potassium) Solution-
Potassium depolarizes the myocyte membrane by flooding the extracellular matrix of the cell
Increased extracellular K+ will prevent myocyte exciteability causing electromechanical arrest
Prevents K+ from moving out of the cell, which prevents contraction
Heart in a state of flaccid depolarization, or prolonged diastole
Cardioplegic solution is washed out by non-coronary collaterals which requires maintenance doses of cardioplegia every minutes
Concentration of Potassium is usually mEq/L under hypothermic conditions
Concentrations don’t usually exceed mEq/L due to vascular endothelial damage to coronary arteries
Higher concentrations may be required for normothermic delivery

17. Cardioplegia Additives
Calcium-
Important ion needed for contraction
Extracellular hypocalcemia is dangerous because it sets the table for calcium loading during reperfusion
Normal levels of Ca++ should be maintained to prevent Ca++ loading during reperfusion
Ca++ Loading-
Rapid influx of Ca++ ions into the cell which causes hypercontracture, leading to depletion of ATP sources and eventually cell stunning or death

18. Calcium
Low extracellular Ca++ can produce arrest by not having Ca++ available for muscle contraction
Excessive Ca++ levels cause “Stone Heart” due to Calcium Loading Paradox causing hypercontracture and cell stunning or death
Heart uses all the available ATP to contract rapidly then runs out of energy

19. Cardioplegia Additives
Magnesium-
Competitive inhibitor of Ca++
Prevents Ca++ loading in cells
Provides membrane stabilization
Decreases potential for cardiac arrhythmias
Increases myocardial contractility
We give 2g of Magnesium in the prime and 2g when the cross-clamp is removed
Time of reperfusion is the most critical point for the potential for Ca++ loading

20. Cardioplegia Additives
Sodium-
Ion responsible for membrane stability and regulation of fluid shifting
Want to keep normal concentrations of Na+
Chloride-
Ion responsible for electrical neutrality inside the cell
Want to keep normal concentrations of Cl-
Bicarbonate/THAM-
Buffers used to maintain an alkalotic solution to counteract the acidosis produced by ischemia
THAM is a better buffer than bicarbonate in plegic solutions

21. Cardioplegia Additives
Osmotic Regulators
A hypertonic solution is ideal to prevent myocardial edema
Hypertonic solutions will pull in fluid from myocardial tissue preventing fluid passage into tissue
Albumin- plasma protein that provides hypertonicity
Mannitol- sugar that provides hypertonicity
Oxygen-free radical scavenger
Glucose- sugar that provides hypertonicity

22. Cardioplegia Additives
Lidocaine-
Ventricular antiarrhythmic
Membrane stabilizer
Glutamate/Aspartate-
Increases myocardial O2 uptake
Best given in induction dose and a “hot shot” before x-clamp removal
Prevents generation of Oxygen-free Radicals
Adenosine-
Cardioprotective autocoid produced by the endothelium
Acts as a vasodilator during autoregulation of coronary bloodflow
KATP Channel opener
Prevents Ca++ influx
Prevents dysrhythmias

23. Hypothermic Cardioplegia
Hypothermia reduces metabolic oxygen demand 7% for every 1° decrease in temperature
Cardioplegia delivered at a profound hypothermic temperature (~4° in our case) will reduce myocardial O2 demand by ~97%
Provides great myocardial protection by limiting O2 requirements during the ischemic period
Combination of both hyperkalemia and hypothermia will both provide electromechanical arrest and reduce myocardial O2 demands

24. Warm Cardioplegia Warm continuous cardioplegia
Used to prevent myocardial injury due to extreme hypothermia of tissue
Advocates claim electromechanical arrest provides enough protection due to hyperkalemia
Say hypothermia is an added benefit, but not needed or desired in their case
Provides constant washout of metabolites
Must delivery plegia at a lower K+ concentration due to it being delivered constantly
Also an option for cold agglutinins patients where cold cardioplegia is contraindicated

25. Cardioplegia Types Straight Crystalloid Solution
Pre-made solution with electrolytes and buffers
St. Thomas Solution or Plegisol
Additional Potassium can be added if desired
Can be delivered as straight crystalloid, no blood
Blood Cardioplegia (Most common)-
Use crystalloid solution mixed in a ratio with blood from the pump
We use it mixed 4 parts blood: 1 part crystalloid
Some places like Lourdes, use an all blood model, no crystalloid solution in the spike bags
“Plegia bag” is whole blood with potassium and other additives injected in
Can give in a mixed ratio with pump blood

26. Straight Crystalloid Plegia
No blood buffering, oxygenation, or waste removal
More hemodilution due to excessive crystalloid delivery

27. Blood Cardioplegia
Most places use blood cardioplegia mixed in a 4:1 ratio
Takes advantage of the buffering capabilities of blood and also it’s delivery of oxgyen, nutrients, and waste removal
Can mix blood with a pre-made solution or inject your own drugs into the blood
Cold Blood Cardioplegia offers O2 delivery but due to severe hypothermia of blood, the O2 released to the tissues is low due to the oxygen-hemoglobin dissociation curve
Do we need a lot ?

28. Induction Dose and Maintenance Doses
Induction doses are typically given at a volume of mL/kg (usually ~1L)
Higher concentration of K+ is ideal for the induction dose
Maintenance doses are given at a lower concentration and lower volume amounts

29. Cardioplegia Delivery Types
Antegrade- follows the normal pathway of the blood
Delivered via the aortic root
Retrograde- travels backwards into a vein and out of an artery
Delivered via the Coronary Sinus
Ostial- directly into the coronary ostia
Delivered via handheld cannulas
Vein Graft- directly into the proximal end of a vein graft providing flow distal to the blockage
Delivered via a small vein cannula hooked up to plegia Y line at the field

30. Antegrade Cardioplegia
Root cannula placed between the X-clamp and the aortic valve
Often a Vent is Y’d into this line to vent the heart when plegia isn’t running
Plegia is delivered at a rate to close the aortic valve and flow into coronary ostia
May have to flow hard to close the valve then back down to perfuse with acceptable pressure
Antegrade Flows- ~300cc/min
Antegrade Pressure mm Hg
Read as plegia line pressure at pump

31. Antegrade Cardioplegia
Antegrade with Aortic Root Vent Y’d in

32. Antegrade Delivery Issues
Patient’s with Aortic Insufficiency
Plegia will flow into the LV because the valve is incompetant and will not fully close
May have to flow higher to pressurize in the root
May have to abandon antegrade and go retrograde
If a Aortic Root Vent is in place, it must be OFF, or your delivered plegia will be sucked back into your pump before reaching the coronaries
Can be detected by not being able to pressurize in the root or extra root vent return

33. Retrograde Cardioplegia
Retrograde given into the Coronary Sinus
A balloon cathetar is wedged into the sinus and will auto inflate upon delivery of cardioplegia
Balloon is deflated when plegia is off
Coronary Sinus pressure is read at the cathetar tip

34. Retrograde Cardioplegia
Retrograde plegia will offer protection distal to coronary blockages that are unable to be perfused by antegrade plegia
Coronary sinus is the main venous drainage system of the Left Heart so the Right Heart is slightly under-protected during retrograde delivery

35. Retrograde Delivery
Blood travels into coronary sinus and comes out of the coronary ostia in aortic root
Collected by aortic root vent
Used for valve surgery when aorta is opened and antegrade isn’t possible
Used for CABG patients with critical stenosis
Retrograde Flows cc/min
Retrograde Pressures mm Hg
Read from coronary sinus cathetar tip, transduced to anesthesia or back to us at pump using 3rd pressure line
Retrograde Line Pressure- maintain line pressure of plegia delivery system at ~ mm Hg

36. Retrograde Delivery Issues
Surgeon can have difficulty inserting it
Noticed by unable to pressurize the coronary sinus
Balloon rupture, balloon will be unable to inflate, so delivery will go into the coronary sinus and directly into the right atrium, not allowing adequate protection
Coronary Sinus cathetar in too far, seen by high sinus pressure and high line pressures
Persistent Left Superior Vena Cava- SVC drains into the Coronary Sinus, which prevents us from using retrograde plegia
Seen by TEE
Coronary Sinus Ostia is huge

37. Coronary Ostial Plegia
Plegia delivered directly into the coronary ostia using small handheld cannulas
Used when antegrade delivery is impossible due to AI
Used when delivery of retrograde plegia is ineffective
Separate cannulas used for Left Coronary Ostia and Right Coronary Ostia
Left Main Coronary Ostial Flow- ~ cc/min
Pressure read on line pressure- ~ mm Hg
Right Main Coronary Ostial Flow- ~100 cc/min
Smaller vessel
Pressure read on line pressure- ~ cc/min

38. Vein Graft Cardioplegia
Plegia is given directly into a vein graft via a small vessel cannula
Used when retrograde is exclusively used, vein graft plegia is often run down the RCA graft to provide protection to the right heart
Used to flow down all coronary grafts to both offer protection distal to a blockage, and to check the patency of their graft and to see the flows they will get down it
Vein Graft Flow- ~ cc/min depending on vein size
Vein Graft Pressure- read on line pressure mm Hg

39. Issues Arresting the Heart
Plegia System?
Patient?
Solution?
Give some examples…

40. Issues Arresting the Heart
Plegia System-
Temperature of solution (hypothermia=fast arrest)
Inadequate flows/pressures (come up on flow)
Occlusions set correctly
Solution-
K+ levels not high enough
K+ bags are clamped out

41. Issues Arresting the Heart
Patient-
Delivery impeded
Coronary Sinus Cathetar issue
Not in correctly
Balloon deflated
Delivery cannula dislodged
Plegia being vented back to us
Anatomy
Patient has AI (inadequate antegrade delivery)
Prior CABG operation, LIMA graft washing out cardioplegia
Must clamp the LIMA graft before giving plegia
PLSVC- no retrograde delivery

42. Parameters Monitored ECG- Time Intervals-
Look for asystole during cardioplegia induction
Monitor ECG activity in between plegia doses
If activity presents, alert surgeon and prepare to give a dose of plegia
Time Intervals-
Time between doses is ischemic time
Alert surgeon every minutes
Potassium Levels- hyperkalemia will ensue due to plegia administration
Excessive K+ levels can be treated by us

43. Hyperkalemia Can produce arrhythmias
Can produce a prolonged state of diastole
Seen by tall peaked T Waves on ECG
↑ K+ causes Ca++ loading in the cells

44. Hyperkalemia Interventions- Insulin and Dextrose Administration-
Most effective way to combat hyperkalemia on CPB
10 units regular insulin and 25g dextrose for K+ ~6-7
Adjust dose depending on K+ level
Insulin acts as a transport mechanism to bring K+ and sugar into the cells
Must replace glucose levels to avoid hypoglycemia
ZBUF- Zero Balance Ultrafiltration
Using hemoconcentrator to pull of K+ and replacing the fluid with normal saline to restore Na and Cl
Bicarbonate Administration-
Drives K+ into the cells
Minimal effect seen

45. Venting the Heart
Constant venting of the heart during cross-clamp period is essential for maintaning arrest
Blood returning from the bronchial circulation or blood not drained by the venous cannula can travel through the aortic valve into the coronary ostia and perfuse the coronaries
This can lead to premature beats and ECG activity when the surgeon is working
Monitor the ECG for P waves or other activity and alert the surgeon