Antonio Maria CALAFIORE

1. Choices and possibilities to optimise myocardial protection during ischemic periods Antonio Maria CALAFIORE

2. Technical success and avoidance of intraoperative damage are both the main targets of any cardiac operation. The early and late success of a cardiac procedure is related to how well the surgeon corrected the mechanical problem, and how carefully myocardial protection avoided secondary dysfunctional effects of aortic clamping for technical repair.

3. Myocardial ischemia is characterized by rapid accumulation of protons, cessation of electron transport and initiation of the inefficient process of anaerobic metabolism. Reperfusion injury is a major complication characterized by restoration of flow to a previously ischemic heart.

4. Ischemia/reperfusion injury Significant evidence now exists that the primary mediators of reversible and irreversible myocardial ischemia/reperfusion injury include intracellular Ca++ overload during ischemia/reperfusion and oxidative stress induced by reactive oxygen species generated at the onset of reperfusion.

5. Ischemia/reperfusion injury Intracellular Ca++ overloadat the onset of reperfusion is due to restoration of intracellular pH via Na+/H+ exchange with consequent reversed Na+/Ca++ exchange. Reduction of free energy for ATP hydrolysis causes reduced efficiency of pumps to maintain intracellular Ca++ homeostasis.

6. Ischemia/reperfusion injury Reactive oxygen species (ROS), including superoxyde anion (O2¯), hydrogen peroxide (H2O2) and the hydroxil radical (OH), are derivatives of many biological systems and in high concentration are associated with oxidative stress and consequent cardiovascular tissue injury.

7. Ischemia/reperfusion injury Neutrophils activation and nitroxide (NO) are involved in ROS production. Neutrophils, activated by inflammatory mediators, respond by rolling, adhering and transmigrating across the endothelial layer to reach the extravascular interstitium.

8. Ischemia/reperfusion injury Neutrophils contain a potent arsenal of proteolitic and cytotoxic substances. Activated neutrophils release hystotoxic enzymes such as elastase, myeloperoxidase, collagenase and others. They also release cytokines and oxygen free radicals.

9. Ischemia/reperfusion injury NO can also interact with ROS to generate various reactive nitrogen species and appears capable of both contributing and reducing injury. In the absence of normal levels of its cofactors, nitric oxide sinthase itself can generate superoxide anion.

10. Ischemia/reperfusion injury Regardless of which stage is being addressed, current cardioprotection strategies are designed to reduce cellular and subcelluar ROS formation and oxidative stress, and to prevent intracellular Ca++ overload.

11. Cardioplegia Cardiac arrest during cardiac surgery in a flaccid diastolic state (with reduction in myocardial oxygen consumption as important consequence) can be achieved by targeting various points in the excitation-contraction coupling pathway.

12. Cardioplegia The agents used for this purpose induce either a depolarized arrest (the membrane potential is higher than –80mV) or a polarized or hyperpolarized arrest (the membrane potential is maintained at –80mV or at lower levels).

13. Cardioplegia

14. Depolarized cardiac arrest The most commonly used method for inducing rapid diastolic arrest is moderate elevation of the extracellular [K+] (15 to 40 mmol/L). As [K+] increases, the resting Em becomes progressively more depolarized.

15. Depolarized cardiac arrest As Em depolarizes to around –65 mV ([K+] around 10 mmol/L), the voltage-dependent fast Na+ channel is inactivated, preventing the rapid Na+-induced spike of the action potential and arresting the heart in diastole.

16. Depolarized cardiac arrest With further increase of [K+] (around 30 mmol/L), resting Em becomes –40 mV with consequent activation of the slow Ca++ channel and Ca++ overload. The beneficial effects of increasing [K+] is then limited to a narrow window.

17. Depolarized cardiac arrest The increase of intracellular [Ca++] will causecontracture even in the arrested conditions and will contribute to Ca++ overload and reperfusion injury. Energy-dependent transmembrane pumps remain active in an attempt to correct this abnormal ionic gradient, further depleting critical energy supplies.

18. Depolarized cardiac arrest High concentration of extracellular Mg++ can arrest alone the heart, possibly by displacing Ca++ from the rapid exchangeable sarcolemmal binding sites involved in the excitation-contraction coupling. As concentrations required are too high, it is used normally as an effective additive protective agent.

19. Polarized cardiac arrest An alternative to depolarization is to maintain polarization of the Em close to the resting Em.

20. Polarized cardiac arrest It can be obtainedthrough different mechanisms. @ blockage of Na+ channels (procaine, lidocaine), preventing the rapid, Na+ induced depolarization of the action potential @ opening of ATP-sensitive K+ channels, causing Em to be shifted towards the K+ equilibrium potential (nicorandil, pinacidil, diazoxide)

21. Even if adverse side effects can be anticipated, K+ CPL is today the only reliable tool we have to arrest the heart. Different agents can be used as additive, but we are far from clinical utilization of polarizing or hyperpolarizing solutions.

22. Cardioplegic solutions There are two types of crystalloid cardioplegic solutions: the intracellular (absent or low concentration of Na+ and Ca++) and the extracellular (high concentration of Na+, Ca++ and Mg++) one. [K+] is between 10 and 40 mEq/L, and both contains bicarbonate for buffering. Hypothermia is a fundamental component of the cardioplegic strategy.

23. Cardioplegic solutions Blood cardioplegia can be used with a variety of different dilutions, temperature, components and delivered, as the crystalloid one, with different routes. In the last decade, with the introduction of warm blood cardioplegia, many publications suggested the following trends.

24. Cardioplegic solutions The assumption that continuous oxygenated perfusion of the normothermically arrested heart enables the perfect matching of energy demand and supply so that ischemia is eliminated is probably an oversemplification. Some metabolic damage can occur, probably due to loss of contraction and consequent interruption of lymphatic flow and edema.

25. Cardioplegic solutions The assumption that hyopothermia gives superior protection is discussed. Randomized trial showed lower TnI release(lower myocardial damage) in intermittent lukewarm or warm blood cardioplegia (CPL) if compared with cold blood CPL.

26. Myocardial oxygen uptake mL/ 100 mg/ min

27. Cardioplegic solutions The initially attractive concept of aerobic arrest inherent in continuous oxygenated perfusion has been somewhat diverted in an intermittent pattern of CPL delivery.

28. A 31P-nuclear magnetic resonance study of intermittent warm blood Cardioplegia.Tian e coll. J Thorac Cardiovasc Surg 1995;109:1155-63.

29. Cardioplegic solutions This is not an homogeneous entity, as ischemic intervals are still not clearly stated. It is very likely that 13-15 min of ischemia in such conditions are well tolerated, but temperature of the perfusate, duration of the reperfusion phases are part of the equation.

30. Route of administration Retrograde CPL administration is very popular among the cardiac surgeons. However, there are evidences that retroperfusion of the heart is less effective than the antegrade. The particular anatomy of the coronary veins is the main reason, as its unpredictibility avoids an uniform CPL distribution. This was demonstrated in the animals and in the humans.

31. Route of administration Tian et al. Retrograde cardioplegia. J Thorac Cardiovasc Surg 2003;125:872-880

32. Route of administration Nevertheless, clinical results are globally satisfying, but retrograde CPL delivery has to be used in conjunction with the antegrade route to obtain an effective cardioprotection.

33. Cardioplegic strategy • From what previously described, the best way to avoid ischemia/reperfusion injury is to avoid ischemia. This is unrealistic, as: • it is not possible to reproduce the same conditions of working heart while operating on the heart, except in some sporadic cases • 2) a compromise is needed between the necessity of protecting the heart and the quality of the surgical treatment.

34. Cardioplegic strategy Since 1991 we heve been using a protocol for intermittent antegrade warm blood cardioplegia in all the patients we are operated on.

35. Cardioplegic strategy The cardioplegia temperature is the same of the perfusate (isothermic cardioplegia). Today there is no conceptual evidence against the use of a temperature between 32° and 37°C. But, according to the surgeon’s preference, the perfusate temperature can be lowered as much as necessary, as in case of DHCA.

36. Intermittent Antegrade Warm Blood Cardioplegia Blood is taken directly from the oxygenator and, by means of a 1/4 inch tubing and a roller pump, is injected into the aortic root or coronary ostia. The tubing is connected to a syringe pump that delivers K+ (1 ml=2mEq). A bubble trap is positioned before the aortic root.

37. Intermittent Antegrade Warm Blood Cardioplegia Infusion protocol Flow rate DoseDuration Roller pump Syringe pump [K+] (min) (ml/min) (ml/h) (mEq/l) 1st 2 300 push 2 ml than 150 18-20 2nd 2 200 60 10 3th 2 200 60 10 4th 2 200 60 10 5th2 200 40 6.7 6th 2 200 40 6.7

38. Intermittent Antegrade Warm Blood Cardioplegia Doses following the first one are administered after each anastomoses during coronary surgery and after 15 minutes during non coronary surgery.

39. Intermittent Antegrade Warm Blood Cardioplegia To prevent the opening of the Ca++ channels, we added to the previous protocol the injection of 1 g of Mg++ sulphate at the end of the 1st dose. If necessary, Mg++ sulphate can be further administered at lower dose (200 mg).

40. Intermittent Antegrade Warm Blood Cardioplegia In presence of waveform contraction K+ administration has not to be increased, but reduced, and Mg++ injected (Em is higher than –40 mV with subsequent opening of the slow Ca++-channels). In presence of well organized contractions a dose of CPL with higher [K+] has to be repeated.

41. Intermittent Antegrade Warm Blood Cardioplegia This protocol is used everytime the ascending aorta is not opened: coronary artery bypass grafting, mitral valve surgery, surgery for LV scars, and so on. According to the surgeon’s preference, ischemic interval can be shortened and/or reperfusion time can be lengthened. This because of the flexibility of the technique.

42. Cardioplegic strategy In particular conditions, as when the ascending aorta is opened, when there is a mild aortic regurgitation or in selected patients with low ejection fraction and/or dilated cardiomyopathy, the retrograde route can be added.

43. Cardioplegic strategy Cardioplegia is always blood and K+, supplemented, when necessary, with Mg++. CPL is administered antegrade and retrograde, antegrade (following the usual protocol) at least every 30 minutes, retrograde as long as possible at a fixed rate (150 ml/min), in relationship with the surgical necessities.

44. Cardioplegic strategy In the last part of the procedure, retrograde administration can deliver only blood without K+ to facilitate intracellular K+ washout and to re-establish energy stores.

45. Cardioplegic strategy Purpose of any strategy we use is to minimize TnI release, even if with long cross clamping times.

46. Cardioplegic strategy We must be aware that also minor damages to the heart can produce, in the midterm, unsatisfying results, compromising what was done in the surgical theatre.

47. January 1982 – December 2001 CABG n = 2901 IAWBC 2171 (74.8%) cold blood CPL 266 (9.2%) cold cristalloid CPL 464 (16.0%)

48. 91.41.3 90.11.5 88.01.1 84.81.6 CKMB  19 UI/L CKMB 20- 38 UI/L CKMB 39- 57 UI/L CKMB  58 UI/L p 0.0012

49. 88.71.5 86.41.6 85.91.1 CKMB  19 UI/L CKMB 20- 38 UI/L CKMB 39- 57 UI/L CKMB  58 UI/L 79.61.9 p < 0.0001

50. % MB  19 MB 20-38 MB  58 MB 39-57