CPB & Myocardial Protection Seoul National University Hospital Department of Thoracic & Cardiovascular Surgery

Reperfusion-induced Injury 1. Definition A paradox extension of ischemic damage, which occurs during reperfusion after myocardial ischemia 1) Reperfusion arrhythmia 2) Myocardial stunning 2. Mechanisms 1) Impaired calcium homeostasis 2) Oxygen free radical during early reperfusion

Optimal Organ Preservation 1. Prevention of ischemia-reperfusion injury 2. Minimization of cell swelling and edema 3. Prevention of intracellular acidosis 4. Provision of substrate for regeneration of high-energy phosphate on reperfusion

Adverse Effects of Cooling in Myocardial Protection 1. Impairs the Na-K adenosine triphosphate (ATPase) 2. Impairs the mitochondrial adenosine triphosphate (ATP) translocase 3. Impairs sarcoplasmic reticular Ca ATPase 4. Impairs oxygen–hemoglobin dissociation Thus hindering cell volume control, energy metabolism, Ca sequestration, and oxygen delivery

Disadvantages of Hypothermia on Myocardial Protection 1. Effects on membrane stability 2. Effects on enzyme function 3. Effects on tissue calcium accumulation 4. Effects on cellular volume regulation

Edema after CBP in Neonate 1. Capillary permeability is naturally higher in younger people 2. Greater exposure to bypass prosthetic surface area relative to neonate’s endothelial surface area 3. Larger ratio of prime volume to blood volume than in older 4. Exposure to greater extremes of temperature as well as low-flow or circulatory arrest, thereby increasing the risk of ischemia-reperfusion injury

Coronary Vasomotor Dysfunction Endothelial dependant cyclic guanosine monophosphate – mediated vasorelaxation (response to acetylcholine) Endothelial independant cyclic GMP-mediated vasorelaxation (response to Na-nitroprusside, nitroglycerin) Beta-adrenergic cyclic adenosine monophosphate – mediated vasorelaxation (response to isuprel)

Myocardium before Reperfusion Energy depletion state High energy phosphate to cellular repair Washout adenosine, inosine, hypoxanthine & xanthine Breakdown of purine base derived from AMP ~~ Reperfusion (O2 supply) produce superoxide, hydrogen peroxide ion  O2 radical combine to Fe  production of hydroxyl ion  myocardial damage

Re-oxygenation Injury in Pediatric CPB Re-oxygenation injury is a real source of postoperative cardiac and pulmonary dysfunction White blood cells play an integral role in the production of oxygen-free radicals that are responsible for the damage This injury can be modified and possibly ameliorated by changes in the intra-operative management of cardiopulmonary bypass

Limiting Re-oxygenation Injury in Pediatric CPB  Bypass Protocol 1. Wash & leucodepleted blood prime 2. In-line arterial filter 3. Initiate bypass using normoxic management(PaO nnHg) & FiO2 is increased slowly over 20 minutes to maintain a PaO2 of mmHg

Pathogenesis of Reperfusion Injury 1. Activated neutrophils Oxygen free radicals, namely, superoxide anions, hydroxyl radicals, hypochlorous acid 2. Platelet-activating factor is also involved in the activation of platelets and neutrophils in the inflammatory process & is synthesized during tissue reperfusion.

Injury after Ischemia & Reperfusion 1st component of myocardial injury induced by biochemical changes mediated by ischemia. ATP depletion, ATP catabolite, acidosis, influx of Na, Ca, activation of phospholipase, proteolytic enzyme & complements 2nd component of myocardial injury is reperfusion phenomena by production of oxygen free radicals. 1. ATP catabolism providing xanthine oxidase substrates 2. Neutrophil-complement activation 3. Phospholipase-arachidonic acid pathway intermediates 4. Electron transport in mitochondria 5. Autooxidation of catecholamine 6. Others not yet identified

Characteristics of Reperfusion Injury Extracellular calcium movement to the intracellular, especially in the mitochondria Explosive cell swelling with reduction of postischemic blood flow & reduced ventricular compliance Inability to use delivered oxygen

Role of Neutrophils after Ischemic Reperfusion Under condition of hypoxemia or ischemia, coronary vascular endothelium expresses sites that bind neutrophils on reperfusion. Once bound, the neutrophil may be activated by several pathways. 1) Superoxide production by xanthine oxidase 2) Complement activation 3) Leukotriene production

Deleterious Effects of Activated Neutrophil 1. Direct myocardial injury NADPH oxidase on the surface of neutrophil produces superoxide anions, hydroxyl radicals, and hypochlorous acid. 2. Mechanical obstruction of capillaries It prevents reperfusion to the distal area of myocardium. 3. Depress calcium transport and calcium stimulated magnesium dependent ATP activity. 4. Lipid peroxidation of cellular membrane It disrupts cellular homeostasis, resulting edema. 5. Oxidation of arachidonic acid Liberation of leucotrienes, prostaglandins, and thromboxanes

Endothelial Damage Process Oxygen free radicals through formation of xanthine oxidase in the endothelium Complement activation -- PMNL -- O2 free radical Release of adenosine diphosphate or formation of thromboxanthine Platelet induced endothelial injury

Roles of NO in Myocardial Ischemia- Reperfusion Injury 1. Beneficial effects 1) Decreased leukocyte accumulation 2) Inhibition of platelet aggregation 3) Neutralization of superoxide radicals 2. Deleterious effects : Production of peroxynitrite, free radicals both direct & indirect cytotoxic properties

Oxygen Derived Free Radicals Inhibitor of free radical generation Allopurinol Free radical scavenging enzymes Reduce the release of lipid peroxidation Superoxide dismutase & catalase Iron chelating agent Slowing the rate of reaction by decreasing the availability of metacatalyst Deferoxamine

Oxygen Free Radical Production Oxygen free radicals directly alter tissue structure and cell membrane through lipid peroxidation & inactivation of membrane band enzyme. 1.Sources of oxygen free radicals Xanthine metabolism, arachidonic acid metabolism, catecholamine oxidation, & electron transport in mitochodria, neutrophil activation in ECF 2. Cell types Myocytes, endothelial cell, monocyte, polymorphonuclear leucocyte are responsible for O2 free radical production during reperfusion.

Mechanisms of Preconditioning - induced Protection 1.Reduced glycogen content prior to sustained ischemic period 2. Adenosine receptor stimulation 3. Slower metabolism because of ischemia 4. Protein kinase C stimulation 5. Calcitonin gene-related peptide from cardiac sensory nerves

Potential Mechanisms of Ischemic Preconditioning 1. Activation of A 1 adenosine receptors 2. Activation or opening of ATP-sensitive K- channels & subsequent cardioplegic effect 3. Induction of heat-shock proteins 4. Preservation of cellular ATP levels by slowing the rate of ATP depletion

Chemical Principles Inducing Cardiac Arrest Myocardial depletion of calcium Myocardial depletion of sodium Elevation of extracellular sodium Elevation of extracellular magnesium Infusion of local anesthetic agents Infusion of calcium & antagonistics

Function of Cardioplegic Protection 1. Electromechanical arrest 2. Function of temperature effect 3. Function of oxygen content 4. Substrate enhancement 5. Buffering capacity

Cardioplegic Solution ; Additives (I) Potassium Depolarize the myocardial cell, producing sustained diastole Magnesium Depress the inherent rhythmicity of pacemaker cell and myocardial contractility (magnesium block the inward flow of sodium into the cells and compete with calcium at activation site of ATP) Calcium Actively associated with excitation contraction (uptake of calcium is ATP dependant) Following excitataion, calcium in ECF with sodium moved into the cell and released calcium in the sarcoplasmic reticulum cause sarcomere shorting by complex of calcium and tropin-tropomyosin - after then decrease of cytosolic calcium level, begin to diastole - active calcium pumping to ECF

Cardioplegic Solution ; Additives (II) Local anesthetic agents Act upon cell membrane by blocking sodium, slow calcium channel, and calcium channels of sarcoplasmic reticulum Hypothermia Substrate enhancement Membrane stabilizer - controversial Calcium channel blockers Beta-blockers Secondary additives Glucose, pH, osmolarity Cardioplegic distribution Asanguineous versus sanguineous

Advantages of Blood in Cardioplegia Particulate rheologic action which promote perfusion of coronary artery and distribution Buffering capacity of Hb Increased onconicity prevent edema Ability of blood to provide a physiologic calcium concentration Ability of RBC to provide enzyme active in the removal of O 2 – free radical

Advantages of Blood Cardioplegia Excellent buffering capacity Increase tissue perfusion Lower coronary perfusion pressure & less edema Oxygen carrying capacity Less leftward shift of oxyhemoglobin dissociation with decreasing tempertature

Terminal Warm Blood Cardioplegia 1. Lower the oxygen demands by keeping the heart in an arrested state, when utilization capacity is impaired. 2. Allow the heart to channel energy resources toward the ionic & cellular homeostasis, while optimizing the metabolic rate.

Adverse Effects of Cold Blood Cardioplegia 1. Elevated levels of ADP & impairment of mitrochondrial respiration & oxidative phosphorylation 2. Inhibits citrate synthetase, a key rate-limiting enzyme in Krebs cycle vital to maintenance of aerobic metabolism 3. Myocardial depression of glucose, lactate, and fatty acid oxidation 4. Increased coronary vascular resistance, which could negatively influence myocyte perfusion 5. Potentiate ventricular fibrillation after removal of x-clamp