Hours Of Aortic Cross-clamping Research Articles

The Effect of Nitecapone, a New Antioxidant, on Myocardial Function After Aortic Cross-clamping in Experimental Heart Ischemia.

During aortic cross-clamping, the myocardium suffers from global ischemia, which is followed by reperfusion after declamping. The generation of free oxygen radicals increases during reperfusion, resulting in arrhythmias and impaired cardiac function. This study was conducted to evaluate the effect of a novel antioxidant nitecapone (NC) on cardiac reperfusion injury in vivo. Twelve pigs were anesthetized and after sternotomy the aorta and the right atrium were cannulated for cardiopulmonary bypass. The heart was arrested with either +4 degreesC crystalloid cardioplegia alone in the control group (n = 6) or cardioplegia with NC (50 µM) added in the NC group (n = 6). Cardioplegia was added every 20 minutes. After 1 hour of aortic cross-clamping, blood samples for oxidative stress analysis were taken, and hemodynamic profile surveillance continued for 90 minutes. Heart rate (p = 0.04) and left ventricular end diastolic pressure (LVEDP) (p = 0.04) were significantly lower in the NC group than in the C group after aortic declamping. Cardiac output and myocardial contractility (dP/dtmax) were also enhanced in the group receiving NC, but the difference was not statistically significant. At 30 minutes after reperfusion, the coronary production (coronary sinus-aorta) of thiobarbituric acid reactive substances correlated inversely with cardiac output (r = -0.90, p = 0.001) and stroke volume (r = -0.82, p = 0.007). The effect of NC on lipid peroxidation seems to be modest and therefore the target of NC is unclear. NC would appear, however, to be a beneficial additive in the crystalloid cardioplegia in terms of functional recovery.

Is Warm Retrograde Blood Cardioplegia Better Than Cold for Myocardial Protection?

Background. This study tests the hypothesis that continuous normothermic retrograde blood cardioplegia is superior to cold intermittent blood cardioplegia in protecting the left and right side of the heart transmurally during an extended cross-clamping period. Methods. Twelve anesthetized, open chest dogs were placed on cardiopulmonary bypass and randomized to receive continuous warm (n = 6) or intermittent cold cardioprotection (n = 6) during a 3-hour aortic cross-clamp period. Transmural left ventricular muscle biopsy specimens were taken before the initiation of cardiopulmonary bypass and 90 and 180 minutes after cross-clamping. Right ventricular (RV) biopsy specimens were taken 180 minutes after aortic cross-clamping. Biopsy specimens were analyzed for adenosine triphosphate, creatine phosphate, and lactate levels and for morphologic changes via electron microscopy. Results. At the end of 180 minutes of cardiopulmonary bypass, the adenosine triphosphate contents of endocardial and epicardial halves of the left ventricular myocardium were only slightly degraded in both cardioplegia groups; a significantly greater reduction in adenosine triphosphate levels occurred in the RV of the warm compared with the cold group ( p < 0.02). The difference in creatine phosphate values in the left ventricle between the cold group (35.2 ± 23.4 nmol/mg cardiac protein) and the warm animals (64.4 ± 24.9 nmol/mg cardiac protein) was not statistically significant, but the RV creatine phosphate stores were significantly better preserved in the warm compared with the cold cardioplegia group ( p < 0.02). Lactate levels increased to a similar extent in both groups, but both values rose significantly over baseline ( p < 0.03). Importantly the electron microscopic score of the left ventricle and RV indicated that cells were reversibly and not irreversibly damaged with both cardioplegic protections. Conclusions. These results suggest the following: (1) Chemical arrest is a major contributor of myocardial preservation during diastolic arrest as used in clinical cardiac surgery. (2) Both methods preserve the ultrastructure of the myocytes transmurally during 3 hours of aortic cross-clamping. (3) Both techniques protect the RV and left ventricle; however, to provide optimal protection of the RV, alternated retrograde and antegrade perfusion might be beneficial over retrograde cardioplegia flow alone, in particular with warm cardioplegia. (Ann Thorac Surg 1997;63:98–104)

Comparison of blood-based and asanguineous cardioplegic solutions administered at 4° C: An ultrastructural morphometric study in the dog

Although several studies have shown better myocardial preservation with blood-based than asanguineous cardioplegic solutions at myocardial temperatures above 15 degrees C, one might suspect that blood would become unsafe at lower temperatures because of increased oxygen-hemoglobin affinity and viscosity. We compared myocardial preservation in dogs subjected to 6 hours of aortic crossclamping and treated with modified Roe's asanguineous cardioplegic solution at 4 degrees C (group CA), blood cardioplegic solution at 4 degrees C (CB), or blood cardioplegic solution at 27 degrees C (WB, four dogs per group). Myocardial preservation was assessed by triphenyltetrazolium staining of whole hearts, and by analysis of ultrastructure and morphometric analysis of mitochondria in myocardial biopsies from three sites in each heart (left ventricle subepicardium and subendocardium and right ventricle). Tetrazolium staining showed no difference in preservation among the three treatment groups (no necrosis in any heart). For two of the three biopsy sites (left ventricular subepicardium and right ventricle), ultrastructural and morphometric analyses demonstrated signs of more severe subcellular injury in group CA than in CB (p = 0.013 to 0.004), whereas equivalent preservation with all treatments was observed in the left ventricular endocardial site. Functional recovery also appeared to be equivalent between treatments, to the extent that all dogs were successfully weaned from bypass after 20 minutes of reperfusion. We conclude that the safety and effectiveness of blood cardioplegia is not compromised by infusion at 4 degrees C compared with 27 degrees C and that myocardial preservation is not improved by using asanguineous cardioplegia instead of blood cardioplegia at 4 degrees C.

Regional Changes in Myocardial Acid Production during Ischemic Arrest: A Comparison of Sanguineous and Asanguineous Cardioplegia

Regional differences in myocardial acid production have not been characterized during administration of either asanguineous or sanguineous cardioplegia. To investigate this, miniature glass pH electrodes were placed in the right ventricular (RV) myocardium, the left ventricular subendocardial (LV endo) region, and the subepicardial (LV epi) region in a canine model. Multiple doses of either blood cardioplegia (Group 1; N = 11) or crystalloid cardioplegia (Group 2; N = 11) were administered during 4 hours of aortic cross-clamping. The accumulation of hydrogen ions during the cross-clamp period was greater in Group 2 than Group 1 in the LV endo region (629 ± 79 nm/L versus 66 ± 31 nm/L; p < 0.001), the LV epi region (623 ± 66 nm/L versus 72 ± 32 nm/L; p < 0.001), and the RV myocardium (814 ± 296 nm/L versus 150 ± 54 nm/L; p < 0.05). Within each group, the time course of myocardial pH and the accumulation of hydrogen ions did not differ among the LV endo region, LV epi region, and the RV myocardium ( p = not significant). These data indicate that transmural and interventricular differences in myocardial pH and hydrogen ion accumulation are not produced in the vented, arrested canine heart. In addition, when compared with asanguineous cardioplegia, blood cardioplegia globally and transmurally reduces acid accumulation during ischemic arrest.

Constant-pressure aortic root perfusion versus cardioplegia and hypothermia: Comparison of methods of myocardial protection

Both coronary perfusion and hypothermic cardioplegia are widely used methods of myocardial protection during aortic valve replacement. A theoretical objection to coronary perfusion is that it is not synchronized with cardiac contractions. Accordingly, a special pump was designed to provide perfusion at a constant range of pressure. Twenty dogs were studied during 4 hours of bypass. In six dogs no manipulations were carried out and hearts were allowed to beat in a nonworking state. Seven dogs underwent 2 hours of aortic cross-clamping and constant-pressure aortic root perfusion. Seven dogs underwent 2 hours of uninterrupted aortic occlusion with myocardial protection being maintained by cold potassium-induced arrest, Contractility did not change significantly in any of the three groups. All animals demonstrated significant hyperemia after bypass but normal endocardial/epicardial flow ratios. Although compliance deteriorated in all groups, the most striking changes were seen following 4 hours of bypass alone or constant-pressure aortic root perfusion. Hypothermic potassium arrest, in contrast, provided a slightly greater degree of myocardial protection, perhaps both by limiting the degree of ischemic injury directly and by excluding the heart from the circulating blood and the pump oxygenator system.

Effect of temperature of cardioplegic solution

This study tests the hypothesis that the efficacy of cardioplegic solution depends upon its chemical constituents rather than on its temperature alone. A standard preparation of right heart bypass in the dog was utilized. Left ventricular function curves were inscribed before and after 1 hour of aortic cross-clamping. No deterioration in function was observed in nonischemic control hearts or in hearts protected with cardioplegic solution consisting of potassium chloride (25 mEq. per liter) and mannitol (12.5 Gm. per liter in 5 percent dextrose and 0.2 percent saline at either 4 degrees C or 28 degrees C. Severe myocardial depression was observed in hearts rendered ischemic for 1 hour at 28 degrees C. without protection and also in hearts perfused with 5 percent dextrose and 0.2 percent saline at 28 degrees C. without the potassium chloride and mannitol. The evidence from this study indicates that cardioplegic solution exerts a protective effect beyond that which is afforded by hypothermia.

Myocardial protection by intermittent perfusion with cardioplegic solution versus intermittent coronary perfusion with cold blood

The myocardial protection provided by cardioplegic solution using buffered, isosmotic potassium (30 mEq. per liter) was compared with intermittent cold coronary perfusion for 2 hours of aortic cross-clamping in dogs. The cardioplegic solution (Group CS) or cold blood (Group CB) was infused every 15 minutes through a cooling coil to reduce the perfusate temperature to 5 degrees C. Myocardial function after 30 minutes of reperfusion and rewarming was reduced in Group CB with a significant reduction in peak systolic pressure at a left ventricular (LV) balloon volume of 20 ml. and a significant reduction of dp/dt. In contrast, in Group CS, LV function was unchanged from the base-line period. LV compliance also was significantly reduced in Group CB while being unchanged in Group CS. Myocardial extravascular water content, obtained by dessication, was significantly higher in Group CB than in Group CS, which may explain the reduction in compliance. Electron microscopy showed normal ultrastructure in Group CS but extracellular edema in Group CB. Total coronary blood flow showed a sustained increase during reperfusion in both groups. Oxygen consumption rose with rewarming to base-line levels in both groups, whereas lactate and pyruvate consumption was reduced in both groups, particularly Group CB. Cardioplegic solution thus appears to be superior to the intermittent perfusion of cold blood for myocardial protection. The addition of potassium arrest, by markedly reducing myocardial metabolism, improves the protection afforded by cold blood perfusion alone.

Drip retrograde coronary sinus perfusion for myocardial protection during aortic cross-clamping

Moderate hypothermia is one of the methods utilized for myocardial protection when the aortic root is cross-clamped but not opened. A combination of low-pressure, low-flow retrograde coronary sinus perfusion (RCSP) with oxygenated blood at moderate hypothermia (29 degrees C.) was demonstrated to yield significantly better protection to left ventricular function in dogs than does moderate hypothermia alone. Ventricular function was recorded before and after 1 hour of aortic cross-clamping at identical preloads and heart rates. Aortic pressure was returned to a level as close to base line as possible by constriction of the descending aorta. The average mean aortic pressure of the animals perfused retrograde at 29 degrees C. was returned to within 4 per cent of base line. By contrast, in the animals protected with moderate hypothermia alone, the pressure could be returned only to a level which was 37 per cent lower than base line. In animals protected with moderate hypothermia alone, cardiac output dropped 62 per cent, left ventricular stroke work (LVSW) 75 per cent, and peak dp/dt 44 per cent. In the animals protected with RCSP and moderate hypothermia, the cardiac output dropped 6 per cent, LVSW 9 per cent, and peak dp/dt 5 per cent. The differences in the changes noted between these two groups were significant for LVSW and dp/dt at a level of p less than 0.01 and for cardiac output and aortic pressure at a level of p less than 0.05. These results suggest that RCSP may be indicated when moderate hypothermia is otherwise chosen to be the sole source of myocardial protection.

Platelet response to regional and systemic shock.

Hemorrhage in dogs to 30 mm. Hg did not produce platelet aggregation. Significant platelet aggregation was shown in stored blood delivered through the standard blood administration set, in the splanchnic circulation in endotoxic shock, and in the inferior vena cava following three hours of aortic cross-clamping. Pulmonary trapping of platelet aggregates could not be shown by serial screen filtration pressure measurements.