Normothermic blood cardioplegia

Cardioplegia in Open Heart Surgery: Age Matters

INTRODUCTION

Cardioplegia is a pharmacological approach essential for the protection of the heart from ischemia-reperfusion (I-R) injury. Over the years, numerous cardioplegic solutions have been developed, with each cardioplegic approach having its advantages and disadvantages. Cardioplegic solutions can be divided into crystalloid and blood cardioplegic solutions, and an experienced surgeon chooses the type of solution based on the individual needs of patients in order to provide optimal heart protection. Importantly, the pediatric immature myocardium is structurally, physiologically, and metabolically different from the adult heart, and consequently its needs to achieve cardioplegic arrest strongly differ. Therefore, the present review aimed to provide a summary of the cardioplegic solutions available to pediatric patients with a special focus on emphasizing differences in heart injury after various cardioplegic solutions, the dosing strategies, and regimens.

MATERIAL AND METHODS

The PubMed database was searched using the terms cardioplegia, I-R, and pediatric population, and studies that investigated the influence of cardioplegic strategies on markers of cardiac muscle damage were further analyzed in this review.

CONCLUSIONS

A large body of evidence suggested more prominent benefits achieved with blood compared to those with crystalloid cardioplegia in pediatric myocardium preservation. However, standardized and uniform protocols have not been established so far, and an experienced surgeon chooses the type of cardioplegia solution based on the individual needs of patients, while the severity of myocardial damage strongly depends on the type and duration of the surgical procedure, overall patient condition, and presence of comorbidities, etc.

Involvement of microtubules in the tolerance of cardiomyocytes to cold ischemia-reperfusion

Before transplantation, the heart graft is preserved by the use of cold storage in order to limit ischemia-reperfusion stress. However, sustained exposure to low temperature may induce myocardial ultrastructural damage, particularly microtubules (MT) disruption. Previous data suggested that tubulin-binding agents are able to attenuate cold-induced cytoskeleton alterations. Thus, the aim of the present work was to study the influence of docetaxel (DX, a tubulin-binding taxane) on the effects of deep hypothermia (4 degrees C) and of simulated cold ischemia-reperfusion on the MT network and oxidative stress of cardiomyocyte (CM) in monolayer cultures prepared from newborn rat ventricles. The MT network was explored by immunocytochemistry and Western-blotting, the cell stress by tetrazolium dye assay (MTT) and lactate dehydrogenase (LDH) release, and the superoxide production by the dihydroethidium probe (DHE). The MT assembly remained stable after 4 and 8 h of hypothermia. Tubulin acetylation was promoted in CM subjected to 4-h hypothermia. Low temperature reduced the mitochondrial function and increased the basal LDH release. The cold ischemia during 4 and 8 h preserved MT network. Docetaxel promoted MT polymerization and tubulin acetylation in basal and in cold conditions. This drug decreased the release of LDH induced by cold ischemia. Moreover, hypothermia (4 h) significantly raised the anion superoxide production. Docetaxel decreased this oxidative stress in the control CM and in CM submitted to 4 h of hypothermia. These data demonstrated that stabilizing MT with DX exerted a protective effect on CM subjected to hypothermia and to cold ischemia-reperfusion. Tubulin-ligands should be thus considered to improve the tolerance of the heart graft toward stressing conservative conditions.

Does veno-arterial bypass without an artificial lung improve the outcome in dogs undergoing cardiac arrest?

We hypothesized that maintaining circulation and blood pressure by veno-arterial bypass (V-A bypass) without oxygenation would improve cardiopulmonary resuscitation (CPR) and survival rates. A total of 32 dogs, divided into four groups, were subjected to normothermic ventricular fibrillation (VF) for 15 min. The method of CPR was the same in the four groups, except for the method and timing of V-A bypass. We attempted to resuscitate the dogs without V-A bypass (control), with V-A bypass not including an artificial lung during VF, with V-A bypass not including an artificial lung during CPR, and with V-A bypass including an artificial lung during CPR. CPR was continued until restoration of spontaneous circulation (ROSC) or for 30 min. Although blood pressure was well maintained, severe hypoxemia was observed during V-A bypass without an artificial lung. The resultant hypoxemia was very detrimental. ROSC was achieved more easily in all dogs in the bypass group with an artificial lung. No significant difference in survival rates was demonstrated among the four groups (P = 0.11). We concluded that V-A bypass without oxygenation does not improve the chances for CPR and outcome after cardiac arrest in dogs. Our results suggest that oxygenation is indispensable in CPR.

Coronary flow response after myocardial ischemia may predict level of functional recovery

Is there a quantity, potentially measurable in the operating theater, which predicts rapid recovery of heart power output after surgical intervention with ischemia? We have enhanced our blood-perfused, ejecting, isolated rat heart model for use inside the magnet of an NMR spectrometer, in order to conduct fundamental research into cardioprotective techniques. To provide a baseline, we investigated the effect of normothermic ischemic insults of varying duration. Hemodynamic and metabolic data were collected, and analyzed to seek measures predictive of rapid recovery of aortic power output, which was selected as the most important measure of function. The presence of erythrocytes in the perfusate ensures that oxygen supply is sufficient to support a physiological workload, and that there is reserve coronary flow. On reperfusion, reactive hyperemia occurs: coronary flow increases to a peak, then declines to a steady value. This response was mathematically modeled, and the data for each of fifteen experiments were fitted to the model. Correlating power output recovery against time to reach peak coronary flow yielded the following equation: R = -0.45 log10tp + 1.74 where R is the ratio of power output ten minutes after reperfusion to that before the ischemic insult, and tp is the time taken to reach peak coronary flow, in seconds. The correlation is very significant (p = 0.005). In the clinic, coronary flow response on reperfusion could be used to predict the patient's need for post-operative support.

Myocardial substrate oxidation during warm continuous blood cardioplegia

BACKGROUND

Although long-chain fatty acids are a major energy substrate utilized by the myocardium, changes in the substrate balance toward a predominating fatty acid utilization could jeopardize the myocardium during cardiac operative procedures.

METHODS

In the present study myocardial substrate utilization was examined during warm continuous blood cardioplegia (4 hours, 37 degrees C), using pigs undergoing cardiopulmonary bypass. Hearts were perfused antegradely in a closed extracorporeal circuit in which cardioplegic donor blood (hematocrit, 22%) containing 14C-glucose and 3H-oleate was delivered to the heart. Arterial and coronary sinus blood samples were taken at intervals for determination of plasma concentrations of energy substrates, as well as glucose and oleate oxidation rates (14CO2 and 3HOH production).

RESULTS

The concentration of fatty acids in the cardioplegic perfusate did not change significantly during the cardiac arrest period. The mean concentration of glucose showed a 30% decline (not significant), whereas the lactate concentration increased from a starting value of 3.12 +/- 0.27 to 6.31 +/- 0.72 mmol/L at the end (mean +/- standard error of the mean; n = 8; p < 0.05). Only fatty acid levels showed a significant (positive) arterial-coronary sinus difference. Myocardial oxidation of oleate varied between 302 +/- 71 and 650 +/- 66 nmol.min-1.heart-1, whereas the range of variation for glucose oxidation was 144 +/- 64 to 355 +/- 107 nmol.min-1.heart-1. However, the changes in fatty acid levels and glucose oxidation rates during the cardiac arrest period were not statistically significant. We calculated that overall glucose oxidation accounted for less than 5% of the total aerobic energy production.

CONCLUSIONS

The present results demonstrate overreliance on fatty acids as a source of energy during warm continuous blood cardioplegia, consistent with a condition of myocardial insulin resistance.

Cardiac surgical conditions induced by beta-blockade: effect on myocardial fluid balance

BACKGROUND

Both crystalloid and blood cardioplegia result in cardiac dysfunction associated with myocardial edema. This edema is partially due to the lack of myocardial contraction during cardioplegia, which stops myocardial lymph flow. As an alternative, acceptable surgical conditions have been created in patients undergoing coronary artery bypass operations with esmolol-induced minimal myocardial contraction. We hypothesized that minimal myocardial contraction during circulatory support using either standard cardiopulmonary bypass (CPB) or a biventricular assist device would prevent myocardial edema by maintaining cardiac lymphatic function and thus prevent cardiac dysfunction.

METHODS

We placed 6 dogs on CPB and 6 dogs on a biventricular assist device and serially measured myocardial lymph flow rate and myocardial water content in both groups and preload recruitable stroke work only in the CPB dogs. In all dogs we minimized heart rate with esmolol for 1 hour during total circulatory support.

RESULTS

Although myocardial lymph flow remained at baseline level during CPB and increased during biventricular assistance, myocardial water accumulation still occurred during circulatory support. However, as edema resolved rapidly after separation from circulatory support, myocardial water content was only slightly increased after CPB and biventricular assistance, and preload recruitable stroke work was normal.

CONCLUSIONS

Our data suggest that minimal myocardial contraction during both CPB and biventricular assistance supports myocardial lymphatic function, resulting in minimal myocardial edema formation associated with normal left ventricular performance after circulatory support. The concept of minimal myocardial contraction may be a useful alternative for myocardial protection, especially in high-risk patients with compromised left ventricular function.

Normothermic Cardiopulmonary Bypass

Normothermic cardiopuhnonary bypass avoids the detrimental systemic effects of hypothermia. It is a safe and effective technique of systemic perfusion during cardiopulmonaiy bypass. Myocardial preservation is not compromised when electromechanical quiescence is maintained. Cerebral protection is comparable to that of systemic hypothermia. Low vascular resistance is common and easily treated with higher perfusion flows or vasopressors during bypass and facilitates weaning from bypass. Duration of cardiopulmonary bypass is significantly shortened by the absence of systemic cooling and rewarming phases. Clinical outcomes of patients undergoing cardiac, surgery with normothermic bypass compare favorably with those receiving moderate hypothermia.

Intermittent warm blood cardioplegia. Warm Heart Investigators

BACKGROUND

Warm heart surgery implies continuous perfusion with normothermic blood cardioplegia. Interruption of cardioplegia, however, facilitates construction of distal coronary anastomoses and is the method practiced by many surgeons. To determine whether intermittency is harmful, we present results from 720 coronary bypass patients, protected with intermittent antegrade warm blood cardioplegia, that were derived from a previous study of normothermic versus hypothermic cardioplegia.

METHODS AND RESULTS

Mean +/- SD age was 60.8 +/- 9.0 years; 27% of cases were urgent; 16% of patients had > 50% left main stenosis, and 19% had grade III or IV ventricles. A mean of 3.2 +/- 0.9 grafts was constructed. The average aortic cross-clamp time was 61.8 +/- 22.2 minutes. The longest single time off cardioplegia (LTOC) averaged 11.4 +/- 4.0 minutes per patient. The cumulative time off cardioplegia as a percentage of the cross-clamp time (PTOC) was 48.2 +/- 18.6% per patient. LTOC and PTOC were divided into quartiles (LTOC, < 10, 10 to 11, 12 to 13, and > 13 minutes; PTOC, < 36%, 36% to 49%, 50% to 62%, and > 62%) and related to the prespecified composite outcome of mortality, myocardial infarction according to serial CK-MB sampling, and low-output syndrome (LOS). Longer LTOC was harmful (event rates per quartile, 13.5%, 10.3%, 10.9%, and 19.0%; P = .046), whereas longer PTOC was protective (16.1%, 17.2%, 9.4%, and 10.6%; P = .07). Stepwise logistic regression was performed, controlling for demographic and angiographic predictors. In the multivariate models, LTOC remained detrimental (P = .07) and PTOC remained beneficial (P = .053). Additional modeling after entering surgeon identity (P < .001) into the risk equation eliminated the PTOC effect, whereas LTOC remained predictive of adverse outcomes (P = .053; odds ratio, 1.06; 95% CI, 1.00, 1.13).

CONCLUSIONS

The data indicate that a reasonable margin of safety exists with intermittent, antegrade warm blood cardioplegia. Repeated interruptions of warm blood cardioplegia are unlikely to lead to adverse clinical results if single interruptions are < or = 13 minutes.

Normothermic continuous antegrade blood cardioplegia does not prevent myocardial edema and cardiac dysfunction

BACKGROUND

Normothermic continuous blood cardioplegia (BC) has been proposed to completely protect the myocardium during cardiac surgery. However, previous work from our laboratory suggests that BC could cause myocardial edema that produces cardiac dysfunction. The purpose of this present study was to evaluate the impact of BC on myocardial fluid balance and left ventricular function.

METHODS AND RESULTS

In 11 dogs, myocardial water content (MWC) was determined by microgravimetry. Myocardial lymph flow rate was measured after cannulation of the major prenodal cardiac lymphatic. Preload recruitable stroke work (PRSW) was calculated by sonomicrometry and micromanometry. The dogs were placed on normothermic cardiopulmonary bypass (CPB), and BC was delivered at either 80 to 90 mm Hg (BChigh; n = 6) or 40 to 50 mm Hg (BClow; n = 5) for 1 hour. Coronary sinus lactate and oxygen saturation monitoring demonstrated ischemia avoidance. BC was associated with substantial myocardial lymph flow rate decrease (P < .05) and myocardial edema development in both groups. MWC increased from 76.0 +/- 1.9% to 79.2 +/- 1.7% (P < .05) after 10 minutes of BChigh and from 75.9 +/- 0.6% to 78.9 +/- 1.4% (P < .05) after 30 minutes of BClow. PRSW decreased to 63 +/- 19% (BChigh) and 69 +/- 15% of control (BClow) at 30 minutes after CPB (P < .05). Myocardial lymph flow rate increases of threefold to fourfold that of control (P < .05) resulted in significant myocardial edema reduction associated with PRSW improvement to 71 +/- 17% (BChigh) and to 78 +/- 11% (BClow) at 2 hours after CPB.

CONCLUSIONS

We conclude that BC is associated with compromised cardiac function despite ischemia avoidance. This cardiac dysfunction is due to myocardial edema caused by the combination of increased myocardial microvascular fluid filtration and decreased myocardial lymph flow rate during BC.

Timing of tracheal extubation in adult cardiac surgery patients

In this article, we examine 14 studies conducted from 1974 to 1994 on "early" endotracheal extubation (0 to 12 hours postoperatively) in adult cardiac surgery patients. Aspects reviewed include: criteria for patient selection; criteria for extubation; analyses of feasibility and safety; effects of anesthetic technique; and patient morbidity. Advantages and disadvantages of early or "fast-track" extubation are discussed as are directions for future research. Selection criteria varied among studies; patients were most commonly excluded because of severe, preexisting pulmonary disease or ventricular dysfunction. Based on the studies examined, however, at least 70% to 80% of adult patients would meet selection criteria. Three universal criteria were applied in all studies: (1) patient is awake and responsive; (2) adequate gas exchange while breathing spontaneously; and (3) cardiovascular stability. To facilitate early extubation in appropriately selected patients, the choice of anesthetic technique and postoperative sedation technique appears to be important. Anesthetic techniques based on inhalational anesthetic agents, supplemented by moderate doses of narcotics, are more appropriate than high-dose narcotic anesthesia for early extubation protocols. Postoperative sedation with propofol, which has a rapid offset of action, may be particularly advantageous. Every published investigation has concluded that early extubation is safe, feasible, and desirable. Morbidity and mortality have not been shown to be affected by early extubation. Anesthetic technique and the patient's medical condition are the two major factors to consider in accomplishing early extubation.

Warm heart surgery: a prospective comparison between normothermic and tepid temperature

Due to concerns about complications from normothermic core temperature during cardiopulmonary bypass, we initiated a prospective randomized study of 200 consecutive patients. In one group (group A), both the heart and the body temperature were kept at 37 degree C. In the second group (group B), both the body and myocardial temperature were allowed to drift down to 34 degree C. There were no differences between these two groups in age, sex, preoperative numbers of elective, urgent, emergent, redo patients, or coronary artery bypass (CAB), valve, CAB/valve procedures. Their preoperative neurological, pulmonary, renal, and vascular disease status were similar. Preoperative EF was 53% in group A (100 patients) and 52.5% in group B (100 patients). Group A required more volume (p = 0.001) and had less urine output (p = 0.03) during and post bypass. Group A required more phenylephrine hydrochloride (p = 0.05) and had more difficulty managing blood pressure. Strokes and renal failure necessitating dialysis occurred more often in group A but without statistical significance. More difficulties occurred in the normothermic (37 degrees C) group and cardioprotective effects of warm heart surgery may remain intact at 34 degrees C. Mild "drifted/tepid" hypothermic heart surgery could be a better and safer procedure.