Studies of controlled reperfusion after ischemia. XXI. Reperfusate composition: superiority of blood cardioplegia over crystalloid cardioplegia in limiting reperfusion damage--importance of endogenous oxygen free radical scavengers in red blood cells

Postischemic damage is caused partially by oxygen free radical-mediated injury. This study will show that (1) crystalloid cardioplegia with room air oxygen is deleterious because it is devoid of free radical scavengers and (2) blood cardioplegia limits damage because it contains endogenous free radical scavengers in red blood cells. METHODS: Thirty-two dogs underwent 2 hours of ligation of the left anterior descending coronary artery followed by 20 minutes of regional blood cardioplegic reperfusion on bypass. Ten dogs received only the blood cardioplegic solution (containing its endogenous free radical scavengers); five received initial blood cardioplegia (5 minutes) with endogenous free radical scavengers (catalase and glutathione peroxidase) blocked by aminotriazole and N-ethylmaleimide, respectively; 12 received initial crystalloid cardioplegic solution oxygenated by room air (oxygen tension = 150 mm Hg); seven without and five with exogenous free radical scavengers (superoxide dismutase, catalase, coenzyme Q10); five received initial deoxygenated crystalloid cardioplegic solution (oxygen tension = 6 mm Hg); and five received deoxygenated crystalloid cardioplegic solution. RESULTS: Blood cardioplegia with endogenous free radical scavengers produced the best recovery of systolic shortening (69% systolic shortening) and resulted in the least histochemical damage (11% triphenyltetrazolium chloride nonstaining). The worst recovery and most damage occurred if blood cardioplegia was preceded by oxygenated crystalloid cardioplegia (3% systolic shortening, 48% triphenyltetrazolium chloride nonstaining; p less than 0.05 versus blood cardioplegia) or if free radical scavengers were blocked in the initial period of blood cardioplegia (3% systolic shortening, 41% triphenyltetrazolium chloride nonstaining; p less than 0.05 versus blood cardioplegia). Conversely, deoxygenation or supplementation of oxygenated crystalloid cardioplegic solution with exogenous free radical scavengers restored 60% systolic shortening (p less than 0.05 versus oxygenated crystalloid cardioplegia) and 54% systolic shortening (p less than 0.05 versus oxygenated crystalloid cardioplegia) and reduced damage to 34% and 21% (both p less than 0.05 versus oxygenated crystalloid cardioplegia). CONCLUSION: Blood cardioplegic solutions containing their own endogenous free radical scavengers are superior to crystalloid cardioplegic solutions, because they limit oxygen-mediated perfusion damage and restore contractile function. Initial crystalloid cardioplegic washout negates the salutary effect of blood cardioplegia. Exogenous free radical scavenger supplementation or deoxygenation of the cardioplegic reperfusate is necessary only if crystalloid cardioplegia is used.     

Studies of controlled reperfusion after ischemia. XVIII. Reperfusion conditions: attenuation of the regional ischemic effect by temporary total vented bypass before controlled reperfusion

This study tests the hypothesis that total vented bypass can attenuate the regional ischemic effect during a defined time interval before controlled blood cardioplegic reperfusion. Thirty-three dogs underwent 2 or 4 hours of occlusion of the left anterior descending coronary artery and then received a regional blood cardioplegic reperfusate on total vented bypass. Cardiopulmonary bypass and reperfusion were started after 2 hours of ischemia in eight dogs, and after 4 hours of ischemia in 25 others. Among the 25 dogs, seven had total vented bypass started after the first 2 hours of the 4 hours of regional ischemia. Segmental shortening (ultrasonic crystals), tissue water content (wet/dry weight), and histochemical damage (triphenyltetrazolium chloride stain) were assessed 2 hours after reperfusion. Dogs reperfused after 2 hours of ischemia recovered 73% +/- 8% of control systolic shortening and sustained only 11% triphenyltetrazolium chloride nonstaining. Dogs undergoing 4 hours of regional ischemia, but with total vented bypass 2 hours before reperfusion had improved recovery of systolic shortening (49% versus 31%, p less than 0.05), limited epicardial edema (79.6% versus 81.1% water content, p less than 0.05), and reduced histochemical damage (24% versus 39% triphenyltetrazolium chloride nonstaining, p less than 0.05). These findings imply that institution of total vented bypass during ischemia attenuates the infarct process, increases regional recovery of contractility, limits edema and restricts histochemical damage, and may be a useful adjunct to myocardial salvage when controlled reperfusion can be provided.     

Studies of controlled reperfusion after ischemia. XX. Reperfusate composition: detrimental effects of initial asanguineous cardioplegic washout after acute coronary occlusion

This study tests whether initial asanguineous washout of potentially toxic substances that accumulate during ischemia improves recovery produced by blood cardioplegic reperfusion and evaluates the role of plasma versus whole blood cardioplegia. METHODS: Twenty-four dogs underwent 2 hours of occlusion of the left anterior descending coronary artery and 20 minutes of blood cardioplegic reperfusion on total vented bypass. In 13 dogs, a 5-minute infusion of either a crystalloid (n = 7) or plasma (n = 6) cardioplegic solution (containing the same pH, calcium potassium, and osmolarity as blood cardioplegia) was given immediately before reoxygenation with blood cardioplegia. Regional oxygen uptake and coronary vascular resistance were measured during controlled reperfusion, and segmental shortening (ultrasonic crystals), tissue water content, and histochemical damage (triphenyltetrazolium chloride stain) were assessed 1 hour after bypass was discontinued. RESULTS: Asanguineous cardioplegic washout before reoxygenation with blood cardioplegic solution resulted in a progressive (+42%) increase in coronary vascular resistances (from 123 to 176 units, p less than 0.05) and low oxygen utilization during 20 minutes of blood cardioplegic reperfusion (29 ml/100 gm, p less than 0.05); coronary vascular resistance remained low throughout blood cardioplegic reperfusion without washout (from 109 to 98 units), and oxygen utilization was 54 ml/100 gm (p less than 0.05). Neither plasma nor crystalloid washout restored substantial regional systolic shortening (3% systolic shortening versus 73% systolic shortening with blood cardioplegia), and asanguineous washout caused more myocardial edema (81.1% +/- 80.9% versus 79.5% water content, p less than 0.05) and produced extensive transmural triphenyltetrazolium chloride damage (48% +/- 41% versus 8% nonstaining in area at risk, p less than 0.05) than initial blood cardioplegic reperfusion. CONCLUSION: Asanguineous cardioplegic washout before blood cardioplegic reperfusion limits oxygen utilization during subsequent controlled reperfusion, restricts early recovery of systolic shortening, allows more myocardial edema, and produces extensive histochemical damage, which may be avoided by initial reoxygenation with blood cardioplegia. The red blood cells appear more important than the plasma components of blood cardioplegia.     

Studies of controlled reperfusion after ischemia. XVII. Reperfusion conditions: controlled reperfusion through an internal mammary artery graft--a new technique emphasizing fixed pressure versus fixed flow

This study tests the usefulness of delivering a controlled reperfusate through an internal mammary graft after acute ischemia by applying a percutaneous technique of mammary artery cannulation and compares reperfusion at fixed pressure versus fixed flow. Methods: Twenty-one dogs underwent 2 hours of ligation of the left anterior descending coronary artery followed by regional controlled revascularization on total vented bypass. A reperfusion catheter was introduced percutaneously from the brachial artery into the internal mammary artery. Five dogs received normal blood reperfusion at 50 mm Hg pressure, and eight dogs received a regional blood cardioplegic reperfusate at 50 mm Hg before reperfusion with normal blood. Eight additional dogs received regional cardioplegia at 30 ml/min for 20 minutes. Coronary vascular resistance, segmental shortening (ultrasonic crystals), tissue water content, and histochemical damage (triphenyltetrazolium chloride stain) were assessed. Results: Reperfusion with normal blood increased coronary vascular resistance progressively to 62% above initial values (p less than 0.05) and failed to restore regional contractility (9% +/- 6% systolic shortening, p less than 0.05). In contrast, coronary resistance remained low throughout blood cardioplegic reperfusion at fixed pressure and the reperfused muscle recovered immediate contractility (73% systolic shortening, p less than 0.05). Controlled reperfusion at a fixed flow rate resulted in pressure that ranged from 30 to 80 mm Hg, slightly less recovery of systolic shortening (57%), and less return of contractile reserve (81% versus 114%, p less than 0.05). Regional blood cardioplegic reperfusion limited edema formation (79.5 versus 82% water content, p less than 0.05) and histochemical damage (11% versus 50% area of necrosis/area at risk, p less than 0.05). Conclusion: An internal mammary artery graft can be used effectively in the setting of acute ischemia if a controlled blood cardioplegic reperfusate is delivered through it to ensure limitation of histochemical damage, low reflow phenomenon, and restoration of immediate segmental contractility. Controlled-pressure reperfusion seems superior to fixed-flow reperfusion. A technique is described that may allow preoperative insertion of the reperfusion catheter in the internal mammary artery in the catheterization laboratory.     

Studies of controlled reperfusion after ischemia. XXII. Reperfusate composition: effects of leukocyte depletion of blood and blood cardioplegic reperfusates after acute coronary occlusion

OBJECTIVES: This study evaluates the role of leukocyte depletion during initial reoxygenation with normal blood and blood cardioplegic reperfusates in limiting reperfusion damage. METHODS: Twenty-eight dogs underwent 2 hours of ligation of the left anterior descending coronary artery. The initial reperfusate (37 degrees C) was delivered on total vented bypass to the left anterior descending artery by a calibrated pump via an internal mammary artery graft at 50 mm Hg for 20 minutes. Eight dogs received normal (normokalemic, nonenriched) blood reperfusion (leukocyte count 8000/mm3) and six were reperfused with leukocyte-depleted normal blood (leukocyte count less than 100/mm3). Of 14 dogs reperfused with substrate-enriched (hyperkalemic) blood cardioplegic solution, six received a cardioplegic solution with a leukocyte count less than 100/mm3. RESULTS: Leukocyte depletion of normal blood reduced reperfusion-induced arrhythmias from 63% to 17% (p less than 0.05). Coronary vascular resistance at initial reperfusion was low and remained low during substrate-enriched blood cardioplegic reperfusion with both normal and reduced leukocyte counts. In contrast, coronary vascular resistance rose 63% with normal blood reperfusion, and this increase was avoided by leukocyte depletion (2.6 versus 4.0 mm Hg x ml/min, p less than 0.05). Coronary vascular resistance after 20 minutes was, however, higher than that with blood cardioplegia with normal or decreased leukocyte counts. Negligible functional recovery followed reperfusion with normal blood and leukocyte-depleted blood (12% and 6% of control systolic shortening). In contrast, substantial segmental recovery followed blood cardioplegic reperfusion (73% systolic shortening, p less than 0.05) but was not improved by leukopheresis (81% systolic shortening). Leukocyte depletion of normal blood reperfusate reduced histochemical damage from 53% to 38% (p less than 0.05), but the least histochemical damage followed blood cardioplegic reperfusion with a normal or reduced leukocyte count (8% or 11%, p less than 0.05). CONCLUSIONS: These findings suggest an important role for leukocytes in reperfusion damage, but reperfusate leukocyte filtration alone is inferior to blood cardioplegic reperfusion. Leukocyte depletion of blood cardioplegic solutions seems unnecessary after only 2 hours of ischemia.     

Studies on prolonged acute regional ischemia. II. Implications of progression from dyskinesia to akinesia in the ischemic segment

This study analyzed the pattern of regional wall motion in 58 dogs undergoing 4 to 6 hours of left anterior descending coronary artery occlusion. Regional wall motion was measured by ultrasonic crystals and ischemic muscle either remained dyskinetic (-40% of control systolic shortening, n = 26) or progressed toward akinesia (less than 20% of control systolic shortening or greater than 50% reduction in passive lengthening, n = 32). Ten dogs underwent unmodified blood reperfusion. Regional blood flow (radioactive microspheres), histochemical damage (triphenyltetrazolium chloride staining), and mitochondrial function were determined. Hearts showing persistent dyskinesia had more collateral flow (12 versus 2 ml/100 gm/min, p less than 0.05), less histochemical damage (26% versus 63% area at risk/area of nonstaining, p less than 0.05), and better retention of mitochondrial oxidative phosphorylation capacity (adenosine triphosphate, 622 versus 444 nmol/mg protein/min, p less than 0.05), and tended toward mitochondrial calcium accumulation (48 versus 64 nmol/mg protein). Unmodified blood reperfusion after 4 hours of ischemia produced prompt akinesia (-2% +/- 3% systolic shortening) and was associated with increased edema (82% water content), caused the low-reflow phenomenon (19% control subendocardial flow, 13 ml/100 gm/min), and increased histochemical damage (69% triphenyltetrazolium chloride nonstaining, p less than 0.05). These findings suggest that persistent dyskinesia during early ischemia (first 6 hours) may reflect a relatively optimistic sign, as regression to akinesia occurs in muscle with less collateral flow, more impaired mitochondrial function, worsened calcium homeostasis, and more severe histochemical and ultrastructural damage. These observations imply that careful evaluation of ischemic wall motion may provide a valuable insight into potential muscle salvage.     

Reversal of ischemic damage with secondary blood cardioplegia.

After severe ischemic injury, it is usually necessary to prolong bypass to enhance recovery. This study tests the hypothesis that the best reversal of ischemic damage is achieved by briefly rearresting the postischemic heart with a continuous infusion of an oxygenated cardioplegic solution (secondary blood cardioplegia) during the period when bypass must be prolonged. Twenty dogs underwent 45 minutes of normothermic ischemic arrest. Fifteen minutes after unclamping, no heart could support the systemic circulation. In all dogs, oxygen demands were lowered by extending bypass for 30 minutes. In 10 of these dogs, demands were further lowered by rearresting the heart for 5 minutes with a continuous infusion of a 37 degrees C blood cardioplegic solution (K+28 mEq/L; pH 7.6; Ca++ 1 mEq/L) at a pressure of 50 mm Hg. Hearts treated with secondary blood cardioplegia showed greater recovery in the rate of contraction (-dP/dt 75% versus 62%, p less than 0.05) and relaxation (-dP/dt 76% versus 58%, p less than 0.05), better recovery of compliance (85% versus 51%, p less than 0.05), a higher stroke work index (0.72 versus 0.50 gm-m/Kg, p less than 0.05), and more ability to augment oxygen uptake (85% versus 45%, p less than 0.05) to meet the demands of the working heart than hearts treated by prolonging bypass alone. We conclude that rearresting the heart with a brief, continuous infusion of a blood cardioplegic solution results in more complete reversal of ischemic damage than possible by prolongation of a bypass alone. We believe that the increased recovery with secondary cardioplegia results from diversion of delivered oxygen toward reparative processes rather than its being expended needlessly on electromechanical work during the time when bypass must be prolonged.     

Myocardial protection during prolonged aortic cross-clamping. Comparison of blood and crystalloid cardioplegia

We compared the ability of blood and crystalloid cardioplegia to protect the myocardium during prolonged arrest. Twelve dogs underwent 180 minutes of continuous arrest. Group I (six dogs) received 750 ml of blood cardioplegic solution (potassium chloride 30 mEq/L) initially and every 30 minutes. Group II (six dogs) received an identical amount of crystalloid cardioplegic solution (potassium chloride 30 mEq, methylprednisolone 1 gm, and 50% dextrose in water 16 ml/L of electrolyte solution). Temperature was 10 degrees C and pH 8.0 in both groups. Studies of myocardial biochemistry, physiology, and ultrastructure were completed before arrest and 30 minutes after normothermic reperfusion. Biopsy specimens for determination of adenosine triphosphate were obtained before, during, and after the arrest interval. Regional myocardial blood flow, total coronary blood flow, and myocardial oxygen consumption were statistically unchanged in Group I (p greater than 0.05). Total coronary blood flow rose 196% +/- 49% in Group II (p less than 0.005), and left ventricular endocardial/epicardial flow ratio fell significantly in this group from 1.51 +/- 0.18 to 0.8 +/- 0.09, p less than 0.01 (mean +/- standard error of the mean. The rise in myocardial oxygen consumption was not significant in this group (34% +/- 36%, p greater than 0.05). Ventricular function and compliance were statistically unchanged in both groups. In Group II, adenosine triphosphate fell 18% +/- 3.4% (p less than 0.005) after 30 minutes of reperfusion; it was unchanged in Group I. Ultrastructural appearance in both groups correlated with these changes. We conclude that blood cardioplegia offers several distinct advantages over crystalloid cardioplegia during prolonged arrest.     

Studies of controlled reperfusion after ischemia. XXIII. Deleterious effects of simulated thrombolysis preceding simulated coronary artery bypass grafting with controlled blood cardioplegic reperfusion

This study tests whether simulated thrombolysis before controlled reperfusion (i.e., simulated coronary artery bypass) causes reperfusion injury that obviates the benefits of subsequent controlled reperfusion and results in unnecessary ventricular arrhythmias. Fifteen dogs underwent acute occlusion of the left anterior descending coronary artery. In 10 dogs we simulated thrombolysis after 1 hour of ischemia (delivering 10% to 15% of control flow at 5 ml/min), followed 1 hour later by either normal blood reperfusion at systemic pressure (to simulate percutaneous transluminal coronary angioplasty) in five dogs or regionally controlled blood cardioplegic reperfusion on bypass in five others to simulate coronary bypass. In five dogs ischemia was prolonged to 2 hours, and the initial reperfusate was blood cardioplegic solution on total vented bypass (to simulate primary coronary bypass). All hearts receiving simulated thrombolysis (100%) after 1 hour of ischemia had reperfusion-induced ventricular fibrillation. All hearts treated by simulated angioplasty recovered regional contractility (56% of control systolic shortening), whereas there was no (0%) recovery of spontaneous contractility after subsequent blood cardioplegic reperfusion, and only two (40%) dogs had contractile reserve capacity (6% +/- 49%). Conversely, surgically controlled blood cardioplegic reperfusion without preceding low-flow normal blood reperfusion after 2 hours of ischemia resulted in no ventricular arrhythmias (0%; p less than 0.05 versus simulated coronary artery bypass after simulated thrombolysis), 72% +/- 7% (p less than 0.05 versus simulated coronary artery bypass after simulated thrombolysis) recovery of regional contractility (ultrasonic crystals), and 114% +/- 11% (p less than 0.05 versus simulated coronary artery bypass after simulated thrombolysis) recovery of contractile reserve with calcium chloride stimulation. We conclude that controlled reperfusion (simulating coronary artery bypass) with blood cardioplegic solution produces immediate functional recovery and avoids the ventricular fibrillation that follows simulated thrombolysis despite the need for prolonged ischemic time. Preceding controlled reperfusion by normal blood reperfusion (simulated thrombolysis) shortens the ischemic time but nullifies immediate functional recovery possible by simulated coronary bypass and produces unnecessary arrhythmias.     

Overdose reperfusion of blood cardioplegic solution. A preventable cause of postischemic myocardial depression

Reperfusion of warm blood cardioplegic solution is useful in minimizing reperfusion damage after ischemia. This study tests the hypothesis that overzealous administration of blood cardioplegic solution at reperfusion counteracts these benefits and can lead to a prevalence of depressed ventricular performance and mortality similar to that seen after normal blood reperfusion. Thirty-one dogs underwent 45 minutes of 37 degrees C global ischemia on vented bypass. Six received normal blood reperfusion and 25 were reperfused with a warm aspartate/glutamate-enriched blood cardioplegic solution; of these, eight received high-dose (3600 +/- 600 ml) and 17 received limited-dose (1180 +/- 120 ml) blood cardioplegic reperfusion over 10 to 20 minutes. High-dose blood cardioplegic perfusion (5100 +/- 200 ml) without prior ischemia was tested in an additional five dogs. High-dose blood cardioplegia without preceding ischemia did not alter ventricular function (peak stroke work index 96% of control). After ischemia, normal blood reperfusion (no cardioplegia) resulted in marked left ventricular dysfunction (peak stroke work index 36% of control, p less than 0.05 versus control) and a 33% mortality rate (2/6 died). High-dose cardioplegic reperfusion yielded marginal recovery of stroke work index (40% of control, p less than 0.05 versus control) and a 25% mortality rate (2/8 died). In contrast, limited-dose reperfusion of blood cardioplegic solution allowed 100% survival (17/17) and restored stroke work index to 90% of control (1.3 versus 1.45 gm.m/kg). We conclude that reperfusion damage can be avoided by initial reoxygenation with limited doses of substrate-enriched blood cardioplegic solution. Conversely, high-dose reperfusion of blood cardioplegic solution offsets this benefit, reduces recovery substantially, and may be lethal.     

Safety of prolonged aortic clamping with blood cardioplegia. III. Aspartate enrichment of glutamate-blood cardioplegia in energy-depleted hearts after ischemic and reperfusion injury

This study tests the hypothesis that aspartate enrichment of glutamate-blood cardioplegia improves metabolic and functional recovery after ischemic and reperfusion damage. Ischemic and reperfusion damage were produced in 15 dogs by 45 minutes of aortic clamping at 37 degrees C and 5 minutes of blood reperfusion, before 2 more hours of aortic clamping (simulated operation). Six received multidose blood cardioplegia at 4 degrees C. In nine others, the cardioplegic solution was infused at 37 degrees C for the first 5 minutes, followed by multidose infusions at 4 degrees C. Four received 26 mmol glutamate-enriched cardioplegic solution. In five, the glutamate (13 mmol) cardioplegic solution was enriched with aspartate (13 mmol). Oxygen uptake and ventricular function (stroke work index, left atrial pressure) were measured. These data suggest aspartate enrichment produced the highest oxygen uptake (32 +/- 4 versus 17 +/- 2 ml/100 gm for glutamate and 7 +/- 1 ml/100 gm for 4 degrees C blood cardioplegia). Complete functional recovery occurred in aspartate/glutamate-treated hearts (stroke work index 90% +/- 4%, left atrial pressure 12 +/- 2 mm Hg), whereas recovery was incomplete with both glutamate alone (stroke work index 66% +/- 14%, left atrial pressure 20 +/- 3 mm Hg) and 4 degrees C blood cardioplegia at low cardiac outputs. Eight of 10 hearts not receiving aspartate failed at high cardiac outputs. Aspartate enrichment of glutamate-blood cardioplegia improves recovery after severe ischemic/reperfusion damage by improving oxidative metabolism during cardioplegic infusion and during postischemic work.     

Effects of reperfusion after acute coronary occlusion on the beating, working heart compared to the arrested heart treated locally and globally with cardioplegia

To determine whether acutely ischemic myocardium could be more effectively salvaged by reperfusion on cardiopulmonary bypass (CPB) in the cardioplegia-treated heart than with reperfusion in the beating, working heart, 52 greyhound dogs underwent 3 hours of left anterior descending (LAD) occlusion and were randomly assigned to one of four groups. In Group I (19 dogs) the LAD occlusion was released at 3 hours and reperfusion continued in the beating, working heart for an additional 3 hours. Group II (six dogs), Group III (14 dogs), and Group IV (13 dogs) were placed on CPB and underwent 45 minutes of hypothermic ischemic arrest protected by aortic root potassium cardioplegia. In Group II, only aortic root potassium cardioplegia was given; in Group III, the ischemic area was perfused with potassium cardioplegic solution via a graft from the internal mammary artery (IMA) to the LAD. In Group IV, blood cardioplegic solution via the IMA-LAD graft was used. After the cross-clamp and local occlusion were removed, CPB was discontinued after an additional 45 minutes and reperfusion was continued off CPB for an additional 1 1/2 hours (total 6 hours). The ischemic area at risk was determined by injecting monastryl blue dye via the left atrium while the LAD was briefly reoccluded. After the animal had been sacrificed and the left ventricle had been sectioned, the area of myocardial necrosis was determined by nonstaining with triphenyltetrazolium chloride (TTC). For each group, the ratios of area of necrosis/area at risk (AN/AR) were calculated and postreperfusion arrhythmias were documented. Postreperfusion arrhythmias were noted in 11 of 12 animals in the beating, working heart group and only two of 24 in the combined CPB groups. The mean AN/AR was 66% +/- 2% in the beating, working heart (Group I), 59% +/- 6% after infusion of potassium cardioplegic solution into the aortic root (Group II), 57% +/- 6% with blood cardioplegia (Group IV), and 38% +/- 6.5% after global and local application of the potassium cardioplegic solution into the ischemic area (Group III). This study suggests that the reperfused ischemic myocardium will sustain less necrosis and less postreperfusion arrhythmias when the heart is protected by global and local cold potassium cardioplegia on CPB.     

Studies of retrograde cardioplegia. II. Advantages of antegrade/retrograde cardioplegia to optimize distribution in jeopardized myocardium

This study tests the hypothesis that retrograde/antegrade cardioplegic delivery can overcome the limitations of poor cardioplegic distribution resulting from either technique alone and, potentially, may expand the safety of using internal mammary artery grafts in cardiac muscle in jeopardy of inadequate cardioplegic protection. Jeopardized myocardium was produced in 20 dogs by ligating the left anterior descending coronary artery for 15 minutes before starting cardiopulmonary bypass and by 1 hour of aortic clamping with multidose 6 degrees C cold blood cardioplegia. Five dogs received antegrade cardioplegia via the aortic root. Ten dogs received retrograde cardioplegia via the coronary sinus. Five additional dogs received retrograde/antegrade cardioplegia via both routes. The ligature on the left anterior descending coronary artery was removed after aortic unclamping, and regional myocardial temperature (thermistor probe), segmental shortening (ultrasonic crystals), and global left ventricular and right ventricular myocardial function were evaluated. Antegrade cardioplegia produced excellent right ventricular cooling (14 degrees C) and allowed complete right ventricular functional recovery. However, it failed to cool muscle supplied by the left anterior descending coronary artery (only 31 degrees versus 12 degrees C, p less than 0.05), postischemic global left ventricular function recovered only 38% (p less than 0.05), and segmental shortening in the region supplied by the left anterior descending coronary artery recovered only 22% (p less than 0.05). Retrograde cardioplegia produced homogeneous cooling (17 degrees C) and allowed near normal recovery of global and regional left ventricular function (99% and 86%), but right ventricular cooling was variable (19 degrees to 30 degrees C) and right ventricular function recovered inconstantly (range 64% to 100%, average 82%). The best myocardial protection occurred after retrograde/antegrade cardioplegia; myocardial cooling was homogeneous, left ventricular and right ventricular global function recovered completely (95% and 90%), and regional contractility in muscle supplied by the left anterior descending coronary artery returned to 84% of control. We conclude that retrograde/antegrade cardioplegia provides better myocardial protection than either technique alone, ensures good cardioplegic distribution to the left and right ventricles, and allows regional delivery of cardioplegic flow to segments supplied by occluded arteries.(ABSTRACT TRUNCATED AT 400 WORDS)     

Studies of retrograde cardioplegia. I. Capillary blood flow distribution to myocardium supplied by open and occluded arteries

This study defines the nutritive (i.e., capillary) distribution of blood cardioplegic solutions delivered via retrograde and antegrade techniques to muscle supplied by open and occluded coronary arteries where myocardial segments are in jeopardy of inadequate cardioplegic protection. Open-chest anesthetized dogs were studied by mixing radioactive microspheres (15 +/- 5 microns) with a blood cardioplegic solution and administering cardioplegia either into the coronary sinus or into the proximal aorta with the left anterior descending coronary artery open or occluded (30% +/- 2% area at risk). Nutritive flow (i.e., percentage of delivered 15 microns microspheres trapped in myocardial capillaries) during retrograde infusions averaged 65% versus 87% with antegrade cardioplegia (p less than 0.05). Retrograde and antegrade cardioplegic nutritive flow to all left ventricular regions was comparable with the left anterior descending coronary artery open (65 versus 82 ml/100 gm/min, p greater than 0.05), and both methods provided preferential hyperperfusion of subendocardial muscle (endocardial/epicardial ratios 1.6 and 1.5, respectively). Nutritive flow to muscle supplied by the occluded left anterior descending coronary artery was preserved better by retrograde than antegrade cardioplegia (35 versus 5 ml/100 gm/min, p less than 0.05). Preferential subendocardial hyperperfusion was maintained during retrograde cardioplegia (52 ml/100 gm/min, endocardial/epicardial ratio 1.6), but flow was redistributed away from subendocardial muscle with antegrade cardioplegia (less than 2 ml/100 gm/min, endocardial/epicardial, 0.29, p less than 0.05). Left ventricular flow was reduced markedly during retrograde infusion with the left anterior descending coronary artery open or occluded (23 and 12 ml/100 gm/min), but septal cooling was superior to antegrade cardioplegia (15 degrees +/- 1 degree C versus 20% +/- 3%, p less than 0.05) despite near-normal antegrade septal flow (the left anterior descending coronary artery was ligated beyond the first septal branch). Right ventricular nutritive flow was only 7 ml/100 gm/min during retrograde coronary sinus perfusion and was maintained normally with antegrade cardioplegia.(ABSTRACT TRUNCATED AT 400 WORDS)     

Donor hearts with impaired hemodynamics. Benefit of warm substrate-enriched blood cardioplegic solution for induction of cardioplegia during cardiac harvesting.

Brain-dead donors frequently show circulatory deterioration and often require so much inotropic support that the donor heart is of questionable value. This experimental study quantifies the cardiac metabolic consequences of brain death and the role of warm blood cardioplegic solution for induction of cardioplegia to improve the quality of potential donor hearts with impaired hemodynamics. Twelve dogs were subjected to brain death by interrupting cerebral blood flow (ligation of innominate artery, carotid arteries, and superior vena cava) and were followed up for as long as 6 hours. Each showed progressive hemodynamic deterioration, necessitating inotropic support (dopamine, calcium, and epinephrine) and large amounts of volume replacement (hetastarch; Hespan) to support the circulation (maintain mean arterial blood pressure greater than 60 mm Hg). Biopsy specimens were taken after 6 hours, or when irreversible ventricular fibrillation occurred, and were analyzed for adenosine triphosphate, creatine phosphate, glycogen, glutamate, and lactate. In six dogs the aorta was then clamped, and a 10-minute infusion of warm (37 degrees C) substrate-enriched aspartate/glutamate blood cardioplegic solution (with the dog's own blood) was given by roller pump to simulate warm induction during the harvesting process. Biopsies were then repeated. Myocardial metabolism, expressed as percent of control values, during brain death was characterized by the following: (1) moderate energy depletion (adenosine triphosphate fell 25% +/- 8%, creatine phosphate fell 55% +/- 15%; p less than 0.05 versus control: mean +/- standard error of the mean); (2) substrate depletion (tissue glutamate fell 48% +/- 9.5%, glycogen fell 66% +/- 7.5%; p less than 0.05 versus control: mean +/- standard error of the mean); and (3) evidence of anaerobic metabolism (lactate increased 374% +/- 95%; p less than 0.05 versus control: mean +/- standard error of the mean). Warm induction of blood cardioplegia in these energy- and substrate-depleted ischemic hearts showed (1) return of creatine phosphate levels to normal (113% +/- 16.8%), (2) replenishment of glutamate (201% +/- 24% of control; p less than 0.05 versus control: mean +/- standard error of the mean), and (3) 43% +/- 14% reduction in myocardial lactate content; (p less than 0.05 versus brain-dead animals). These data suggest that brain-dead donors requiring inotropic support sustain energy and substrate depletion and ischemic damage that can be reversed by a brief period of induction of cardioplegia with a warm substrate-enriched blood cardioplegic solution before harvesting.(ABSTRACT TRUNCATED AT 400 WORDS)     

Studies of myocardial protection in the immature heart. V. Safety of prolonged aortic clamping with hypocalcemic glutamate/aspartate blood cardioplegia

This study tests the hypothesis that multidose, hypocalcemic aspartate/glutamate-enriched blood cardioplegia provides safe and effective protection during prolonged aortic clamping of immature hearts. Of 17 puppies (6 to 8 weeks of age, 3 to 5 kg) placed on vented cardiopulmonary bypass, five were subjected to 60 minutes of 37 degrees C global ischemia without cardioplegic protection and seven underwent 120 minutes of aortic clamping with 4 degrees C multidose aspartate/glutamate-enriched blood cardioplegia ([Ca++] = 0.2 mmol/L), preceded and followed by 37 degrees C blood cardioplegic induction and reperfusion. Five puppies underwent blood cardioplegic perfusion for 10 minutes without intervening ischemia to assess the effect of the cardioplegic solution and the delivery techniques. Left ventricular performance was assessed 30 minutes after bypass was discontinued (Starling function curves). Hearts were studied for high-energy phosphates and tissue amino acids. One hour of normothermic ischemia resulted in profound functional depression, with peak stroke work index only 43% of control (0.7 +/- 0.1 versus 1.7 +/- 0.2 gm x m/kg, p less than 0.05). There was 70% depletion of adenosine triphosphate (7.6 +/- 1 versus control 20.3 +/- 1 mumol/gm dry weight, p less than 0.05) and 75% glutamate loss (6.6 +/- 1 versus control 26.4 +/- 3 mumol/gm, p less than 0.05). In contrast, after 2 hours of aortic clamping with multidose blood cardioplegia preceded and followed by 37 degrees C blood cardioplegia, there was complete recovery of left ventricular function (peak stroke work index 1.6 +/- 0.2 gm x m/kg) and maintenance of adenosine triphosphates, glutamate, and aspartate levels at or above control levels adenosine triphosphate 18 +/- 2 mumol/gm, aspartate 21 +/- 1 versus control 2 mumol/gm, and glutamate 25.4 +/- 2 mumol/gm). Puppy hearts receiving blood cardioplegic perfusion without ischemia had complete recovery of control stroke work index. We conclude that methods of myocardial protection used in adults, with amino acid-enriched, reduced-calcium blood cardioplegia, can be applied safely to the neonatal heart and allow for complete functional and metabolic recovery after prolonged aortic clamping.     

Reducing postischemic reperfusion damage in neonates using a terminal warm substrate-enriched blood cardioplegic reperfusate

BACKGROUND: In adult cardiac operations, a warm cardioplegic reperfusate ("hot shot") before removing the aortic cross-clamp improves postbypass myocardial function and metabolic recovery. This modality, however, is rarely used in infants, despite the fact that postbypass cardiac dysfunction remains problematic, especially in cyanotic ("stressed") patients. METHODS: To produce stress, 15 neonatal piglets underwent 60 minutes of ventilator hypoxia (fraction of inspired oxygen, 8% to 10%). All piglets then received similar protection with multidose cold blood cardioplegic solution during 70 minutes of arrest and were separated into three groups to examine the role of a warm reperfusate as well as possible augmentation by aspartate and glutamate enrichment. In 5 piglets (group 1), the cross-clamp was simply removed; in 5 (group 2), an unsupplemented warm blood cardioplegic reperfusate was given; and in 5 (group 3), the warm reperfusate was enriched with aspartate and glutamate. Myocardial function was assessed using pressure-volume loops and expressed as a percentage of control. RESULTS: Compared with hearts receiving reperfusion with unmodified blood (group 1), a warm unsupplemented cardioplegic reperfusate (group 2) slightly improved systolic contractility (end-systolic elastance, 41% versus 50%; p < 0.05 versus group 1) and preload recruitable stroke work (41% versus 52%; p < 0.05 versus group 1), reduced diastolic stiffness (263% versus 245%; p < 0.05 versus group 1), and increased adenosine triphosphate (10.7 versus 11.9 microg/g tissue, p < 0.05 versus group 1). However, if aspartate and glutamate was included in the warm reperfusate (group 3), there was complete recovery of systolic function (end-systolic elastance, 105%+/-3%; p < 0.001 versus all groups) and preload recruitable stroke work (103%+/-2%; p < 0.001 versus all groups), a minimal rise in diastolic stiffness (154%+/-7%; p < 0.001 versus all groups), and preservation of adenosine triphosphate (15.5+/-0.5 microg/g; p < 0.001 versus all groups). CONCLUSIONS: A warm cardioplegic reperfusate helps reduce the reperfusion injury, resulting in improved myocardial function and metabolic recovery in hypoxic (stressed) neonatal hearts, and this effect is maximized if the reperfusate is enriched with aspartate and glutamate, which completely preserves myocardial function.     

Optimal myocardial protection with fluosol cardioplegia

An oxygenated perfluorocarbon cardioplegic solution was examined, utilizing a blood-perfused canine model. Twenty-one animals were divided into three equal groups, and each animal received Fluosol cardioplegia at one of three infusion temperatures: 20 degrees C, or 4 degrees C. All hearts underwent 90 minutes of ischemia, during which time 150 ml of the cardioplegic solution was infused every 30 minutes. Myocardial oxygen and carbon dioxide tensions (PmO2 and PmCO2) were monitored continually using mass spectrometry, and myocardial oxygen consumption was calculated with each cardioplegic injection. The mean increase in PmO2 was 7.1 +/- 0.9 mm Hg with 20 degrees C Fluosol infusions, 31.1 +/- 4.7 mm Hg with 10 degrees C Fluosol injections, and 22.2 +/- 4.7 mm Hg with infusions of 4 degrees C Fluosol. Average myocardial oxygen consumptioN, expressed as cubic centimeters of oxygen per 100 gm of left ventricle (wet weight), was 21.2 +/- 0.5 with 20 degrees C Fluosol, 22.8 +/- 1.3 for 10 degrees C Fluosol, and 19.6 +/- 1.0 for 4 degrees C Fluosol. Mean myocardial temperatures with infusions of 20 degrees C, 10 degrees C, and 4 degrees C solutions were 21.4 +/- 0.1 degree C, 16.9 +/- 0.4 degree C, and 15.9 +/- 0.5 degree C, respectively. After 45 minutes of reperfusion, maximum rate of rise of left ventricular pressure, expressed as percentage of preischemic control, was 70.9 +/- 3.9% for 20 degrees C Fluosol, 90.9 +/- 3.2% for 10 degrees C Fluosol, and 90.4 +/- 2.3% for 4 degrees C Fluosol (p less than 0.005, 20 degrees C versus 10 degrees C, 4 degrees C Fluosol). In addition, the 10 degrees C and 4 degrees C Fluosol hearts had essentially normal structure by light and electron microscopy. These data demonstrate tht Fluosol cardioplegia results in near optimal myocardial protection when infused at cold temperatures (4 degrees C to 10 degree C). The increases intramyocardial oxygen and myocardial oxygen consumption with each injection demonstrate that there is enhanced oxygen delivery and utilization, which may account for the improved functional recovery observed in these hearts.     

Effects of diltiazem cardioplegia on global function, segmental contractility, and the area of necrosis after acute coronary artery occlusion and surgical reperfusion

We investigated the effects of diltiazem cardioplegia on myocardial function and infarct size in the region of the left anterior descending artery after acute occlusion and reperfusion during cardiopulmonary bypass. Sheep (30 kg) were subjected to 1 hour of regional myocardial ischemia by occlusion of the left anterior descending artery and assigned to a control (n = 8) or experimental group (n = 5). Control animals were placed on cardiopulmonary bypass and the heart arrested with potassium cardioplegia. The left anterior descending artery was released and two additional doses of 100 ml of cardioplegic solution were infused during the total cross-clamp time of 30 minutes. The animals were then weaned from bypass after 1 hour and beating, working reperfusion maintained for an additional 4 hours. The experimental group followed the same protocol except that the cardioplegic solution contained diltiazem (1.4 mg/L). Segmental myocardial function was determined by pairs of ultrasonic crystals in the area at risk, control segment, and minor axis. Global contractility was determined from maximum derivative of left ventricular pressure and cardiac output. The area at risk was determined by injecting monastral blue dye into the left atrium with the left anterior descending artery briefly reoccluded, and the area of necrosis was determined by measuring with a planimeter non-triphenyltetrazolium chloride stained areas in the sectioned left ventricle. After 5 hours of reperfusion, not only did the diltiazem group demonstrate better global contractility as defined by the derivative of left ventricular pressure (1853 +/- 292 versus 979 +/- 191, p = 0.05) but, in addition, the systolic shortening in the ischemic area improved significantly when compared with the control group (9.4 +/- 4 versus 2.13 +/- 0.77, p = 0.05). The group receiving diltiazem cardioplegia had an area of necrosis to area at risk ratio of 31.4% +/- 3%, which was significantly better than this ratio in the control group of 60.75% +/- 7% (p = 0.01). Diltiazem cardioplegia results in improved global and segmental contractility and limits the infarct size after occlusion of the left anterior descending artery and surgical reperfusion.     

Surgical revascularization of acute (1 hour) coronary occlusion: blood versus crystalloid cardioplegia

This study compares blood versus crystalloid cardioplegia in restoring contractile function, and high-energy phosphate and tissue water content in a myocardial segment after 1 hour of coronary artery occlusion. Anesthetized dogs underwent instrumentation with the chest open to measure left ventricular and aortic pressures, and systolic shortening in the myocardium perfused by the left anterior descending coronary artery (LAD) was measured with ultrasonic crystals. In 21 dogs, the LAD was occluded for an hour, thereby replacing systolic shortening with passive lengthening averaging -28.7 +/- 6.2% of control shortening in both groups. The dogs were then placed on total bypass, and arrest was achieved with multidose crystalloid (N = 10) or blood cardioplegia (N = 11). The ligatures were released just prior to the second infusion of cardioplegic solution. Postischemic subendocardial levels of adenosine triphosphate were comparably depleted with crystalloid and blood cardioplegia (55.2% and 44.0%, respectively, of control). Subendocardial increases in water content were similar for crystalloid (3.62%) and blood (3.16%) cardioplegia. Recovery of segmental shortening was significantly greater with blood than crystalloid cardioplegia (31.5 +/- 8.2% versus 4.9 +/- 6.6% of control, respectively). We conclude that the composition and the delivery of blood cardioplegia used in this study restore greater postischemic function than crystalloid cardioplegia in acute evolving myocardial infarction.