Comparison of two strategies for myocardial management during coronary artery operations

Custodiol-N versus Custodiol: a prospective randomized double-blind multicenter phase III trial in patients undergoing elective coronary bypass surgery

OBJECTIVE

HTK-Solution (Custodiol) is a well-established cardioplegic and organ preservation solution. We currently developed a novel HTK-based solution, Custodiol-N, which includes iron chelators to reduce oxidative injury, as well as L-arginine, to improve endothelial function. In this first in-human study, Custodiol-N compared to Custodiol in patients undergoing elective coronary artery bypass surgery. The aim of this comparison was to evaluate the safety and ability of Custodiol-N to protect cardiac tissue.

METHODS

The study was designed as a prospective randomized double-blind non-inferiority trial. Primary end-point was area under the curve (AUC) of creatine kinase MB (CK-MB) within the first 24 h after surgery. Secondary end-points included peak CK-MB and troponin-T and AUC of troponin-T release, cardiac index, cumulative catecholamine dose, ICU-stay and mortality. All values in the abstract are given as mean ± SD, p < 0.05 was considered statistically significant.

RESULTS

Early termination of the trial was performed per protocol as the primary non-inferiority end-point was reached after inclusion of 101 patients. CK-MB AUC (878 ± 549 vs 779 ± 439 h* U/l, non-inferiority p < 0.001, Custodiol vs Custodiol-N) and troponin-T AUC (12990 ± 8347 vs 13498 ± 6513 h*pg/ml, noninferiority p < 0.001, Custodiol vs Custodiol-N) were similar in both groups. Although the trial was designed for non-inferiority, peak CK-MB (52 ± 40 vs. 42 ± 28 U/l, superiority p < 0.03, Custodiol vs Custodiol-N) was significantly lower in the Custodiol-N group.

CONCLUSION

This study shows that Custodiol-N is safe and provides similar cardiac protection as the established HTK-Custodiol solution. Significantly reduced peak CK-MB levels in the Custodiol-N group in the full analysis set may implicate a beneficial effect on ischaemia/reperfusion injury in the setting of coronary bypass surgery.

Metabolic derangement and cardiac injury early after reperfusion following intermittent cross-clamp fibrillation in patients undergoing coronary artery bypass graft surgery using conventional or miniaturized cardiopulmonary bypass

Myocardial ischemic stress and early reperfusion injury in patients undergoing coronary artery bypass grafting (CABG) operated on using intermittent cross-clamp fibrillation (ICCF) are not presently known. The role of mini-cardiopulmonary bypass (mCPB) versus conventional CPB (cCPB) during ICCF has not been investigated. These issues have been addressed as secondary objective of randomised controlled trial (ISRCTN30610605) comparing cCPB and mCPB. Twenty-six patients undergoing primary elective CABG using ICCF were randomised to either cCPB or mCPB. Paired left ventricular biopsies collected from 21 patients at the beginning and at the end of CPB were used to measure intracellular substrates (ATP and related compounds). Cardiac troponin T (cTnT) and CK-MB levels were measured in plasma collected from all patients preoperatively and after 1, 30, 60, 120, and 300 min after institution of CPB. ICCF was associated with significant ischemic stress as seen by fall in energy-rich phosphates early after reperfusion. There was also a fall in nicotinamide adenine dinucleotide (NAD(+)) indicating cardiomyocyte death which was confirmed by early release of cTnT and CK-MB during CPB. Ischemic stress and early myocardial injury were similar for cCPB and mCPB. However, the overall cardiac injury was significantly lower in the mCPB group as measured by cTnT (mean ± SEM: 96 ± 14 vs. 59 ± 8 µg/l, p = 0.02), but not with CK-MB. ICCF is associated with significant metabolic derangement and early myocardial injury. This early outcome was not affected by the CPB technique. However, the overall cardiac injury was lower for mCPB only when measured using cTnT.

Effect on the brain of two techniques of myocardial protection

This study compared the occurrence of intraoperative microemboli and postoperative changes in neuropsychological performance in 195 patients undergoing coronary artery bypass grafting who were randomized to intermittent crossclamp fibrillation or cardioplegic arrest. Cerebral microemboli were recorded from cannulation to 15 min after decannulation, using transcranial Doppler in 166 patients. Microemboli in relation to 9 surgical events were also noted. Neuropsychological change scores were obtained by comparing cognitive performance preoperatively with that at 6-8 weeks after surgery. The median number of microemboli detected was 105 (range, 9-1,757) in the fibrillation group, and 110 (range, 1-1,306) in the cardioplegia group, with no significant difference between groups. There was also no significant difference between groups in the generation of microemboli during any of the surgical events. Neuropsychological tests were completed postoperatively by 177 participants, with no significant differences in performance found between the 2 groups. Given the equivalence of the effect of intermittent crossclamp fibrillation and cardioplegic arrest on microemboli and neuropsychology, consideration of which form of myocardial protection to employ should perhaps focus more on which method affords most protection to the heart.

'Conditioning' the heart during surgery

Coronary heart disease (CHD) is the leading cause of death worldwide. Coronary artery bypass graft (CABG) surgery remains the procedure of choice for coronary artery revascularisation in a large number of patients with severe CHD. However, the profile of patients undergoing CABG surgery is changing with increasingly higher-risk patients being operated upon, resulting in significant morbidity and mortality in this patient group. Myocardial injury sustained during cardiac surgery, most of which can be attributed to acute myocardial ischaemia-reperfusion injury, is associated with worse short-term and long-term clinical outcomes. Clearly, new treatment strategies are required to protect the heart during cardiac surgery in terms of reducing myocardial injury and preserving left ventricular systolic function, such that clinical outcomes can be improved. 'Conditioning' the heart to harness its endogenous cardioprotective capabilities using either brief ischaemia or pharmacological agents, provides a potentially novel approach to myocardial protection during cardiac surgery, and is the subject of this review article.

Does Intermittent Aortic Cross Clamping Decrease the Incidence of Atrial Fibrillation after Coronary Bypass Surgery?

Atrial fibrillation (AF) is the most common arrhythmia after coronary artery bypass grafting (CABG). AF is a vexing problem that causes morbidity, prolongs hospital stay, and increases costs. Numerous factors have been suggested to play a role in the development of AF. The aim of this study was to evaluate the effect of intermittent aortic cross clamping (IACC) compared with hypothermic cardioplegic solution (HCS) in the development of postoperative AF. We evaluated data obtained from 345 patients undergoing CABG with HCS (HCS group, n = 212) and IACC (IACC group, n = 173) between April 2004 and August 2005. Diabetes mellitus was observed more often in the HCS group (P < .05), otherwise both groups had similar preoperative characteristics including sex, age, the number of distal anastomoses, left ventricle ejection fraction, history of myocardial infarction, and use of beta-blocker medication. The only statistically significant difference between the groups was higher postoperative Ca-antagonist use in the HCS group. Rates of postoperative AF, however, were significantly lower in the IACC group (21.52%) than that in the HCS group (11.05%; P < .01). Postoperative Ca-antagonist use in the HCS group and smoking in the IACC group were independent predictors of AF after CABG. The incidence of postoperative AF after CABG with IACC was reduced compared with HCS. IACC with ventricular fibrillation may exert a counteractive effect against AF.

Coronary bypass grafting using crossclamp fibrillation does not result in reliable reperfusion of the myocardium when the crossclamp is intermittently released: a prospective cohort study

Background

Cross-clamp fibrillation is a well established method of performing coronary grafting, but its clinical effect on the myocardium is unknown. We sought to measure these effects clinically using the Khuri Intramyocardial pH monitor.

Methods

50 episodes of cross-clamping were recorded in 16 patients who underwent CABG with crossclamp-fibrillation. An Intramyocardial pH probe measured the level of acidosis in the anterior and posterior myocardium in real-time. The pH at the start and end of each period of cross-clamping was recorded.

Results

It became very apparent that the pH of some patients recovered quickly while others entirely failed to recover. Thus the patients were split into 2 groups according to whether the pH recovered to above 6.8 after the first crossclamp-release (N = 8 in each group). Initial pH was 7.133 (range 6.974–7.239). After the first period of crossclamping the pH dropped to 6.381 (range 6.034–6.684). The pH in recoverers prior to the second XC application was 6.990(range 6.808–7.222) compared to only 6.455 (range 6.200–6.737) in patient's whose myocardium did not recover (P < 0.0005). This finding was repeated after the second XC release (mean pH 7.005 vs 6.537) and the third (mean pH 6.736 vs 6.376). However prior to separation from bypass the pH was close to the initial pH in both groups (7.062 vs 7.038).

Conclusion

Crossclamp fibrillation does not result in reliable reperfusion of the myocardium between periods of crossclamping.

Experimental studies on myocardial protection with intermittent cross-clamp fibrillation: additive effect of the sodium-hydrogen exchanger inhibitor, cariporide

BACKGROUND

We previously showed that intermittent cross clamping with fibrillation affords myocardial protection equivalent to cardioplegic arrest. In this study, we examined whether cariporide (Aventis Pharma, Frankfurt, Germany), a specific sodium-hydrogen exchanger inhibitor, enhanced the protective effect of intermittent cross-clamp fibrillation (ICCF).

METHODS

Isolated rat hearts were Langendorff-perfused (20 mins) with bicarbonate buffer and function (left ventricular developed pressure) measured. In each of three separate protocols that incorporated progressively longer ischemic durations, hearts were randomly allocated to one of three groups: group 1 was the control group with 40, 60, or 80 minutes of continuous global ischemia. Group 2 was the ICCF group with 4, 6, or 8 cycles of 10 minutes ICCF and 10 minutes of reperfusion in sinus rhythm. Group 3 was the ICCF plus cariporide group, which was the same as group 2, but also with 3 micromoles/L cariporide present in perfusate from 10 minutes before the ICCF cycles. Hearts were reperfused for 60 minutes with drug-free buffer and recovery (percentage of initial function) was measured. Hearts were maintained at 37 degrees C throughout the protocols. In protocol 3 (80 minutes ischemia per 8 cycles of ICCF), creatine kinase leakage (myocardial injury) and triphenyl tetrazolium chloride staining (myocardial viability) were also measured. Protocols 1, 2, and 3 had n = 8 hearts, n = 6 hearts, and n = 6 hearts in each group, respectively.

RESULTS

In the three protocols, the recoveries of left ventricular developed pressure in the control group, the ICCF group, and the ICCF plus cariporide group, respectively, for protocol 1 were: 26% +/- 3%, 70% +/- 2% (p < 0.05 vs the control group) and 74% +/- 2% (p < 0.05 vs the control group), respectively. For protocol 2 these were: 16% +/- 2%, 55% +/- 1% (p < 0.05 vs the control group), and 70% +/- 3% (p < 0.05 vs the control and ICCF groups), respectively. For protocol 3 these were: 8% +/- 2%, 41% +/- 3% (p < 0.05 vs the control group), and 63% +/- 2% (p < 0.05 vs the control and ICCF groups), respectively. Recovery of left ventricular end-diastolic pressure mirrored that of left ventricular developed pressure in all protocols. In protocol 3, total creatine kinase leakage (international units per gram wet weight) was 88 +/- 12, 47 +/- 4 (p < 0.05 vs the control group), and 17 +/- 1 (p < 0.05 vs the control and ICCF groups), respectively, and triphenyl tetrazolium chloride staining (arbitrary units per gram wet weight) was 0.17 +/- 0.04 in the control group, 0.39 +/- 0.04 (p < 0.05 vs the control group) in the ICCF group, and 0.47 +/- 0.08 (p < 0.05 vs the control group) in the ICCF plus cariporide group, respectively.

CONCLUSIONS

Sodium-hydrogen exchanger inhibition with cariporide enhances the myocardial protection afforded by ICCF, with the additive benefit becoming more apparent with increasing severity of the ischemic insult. Sodium-hydrogen exchanger inhibition may provide a significant protective reserve during ICCF, particularly when longer procedures are required.

Surgical nurse assistants in cardiac surgery: a UK trainee's perspective

OBJECTIVE

To assess the impact of surgical nurse assistants on surgical training based on a comparative audit of case-mix and outcome of coronary revascularizations assisted by surgical nurse assistants vs. surgical trainees.

METHODS

Relevant recent articles on Calman reform of specialist training and European working time directive (EWTD) on junior doctor working hours were reviewed for the discussion. For the audit prospectively entered data of elective and expedite first time coronary artery bypass grafting cases from 2000 to 2003 were analysed. Group A (n=233, Consultant+Surgical nurse assistant), group B (n=1067, Consultant+Junior surgical trainee). Chi-square test, t-test and Fisher's test were used as appropriate for statistical analysis.

RESULTS

Comparative preoperative variables were gender (P=0.8), body mass index (P=0.9), smoking (P=0.3), diabetes mellitus (P=0.2), hypertension (P=1), peripheral vascular disease (P=0.5), previous cerebrovascular accident (CVA)/transient ischemic attack (TIA) (P=0.3), renal dysfunction (P=0.4), preoperative rhythm disturbances (P=0.3), previous Q-wave myocardial infarction (MI) (P=0.4), Canadian Cardiovascular Society angina class (P=0.4), New York Heart Association heart failure class (P=0.4) and left ventricular function (P=0.4). Patients in group B were of higher risk due to age (P=0.01), coronary disease severity (P=0.05), left main stem disease (P=0.001), Parsonnet score (P=0.0001) and Euroscore (P=0.005. Regarding the myocardial protection technique, intermittent cross-clamp fibrillation was used more frequently in group A while antegrade-retrograde cold blood cardioplegia and off-pump coronary artery bypass were used more in group B (P=0.0001). The cross-clamp (P=0.0001) and operation time (P=0.0001) were significantly lower in group A despite a comparable mean number of grafts (P=0.2). There was no significant difference in the immediate postoperative outcome ventilation time (P=0.2), intensive care unit stay, postoperative stay (P=0.2), re-exploration for bleeding (P=0.5), inotrope+intra-aortic balloon pump (P=0.2), postoperative MI (P=0.9), postoperative rhythm disturbances (P=0.9), CVA/TIA (P=0.8), renal dysfunction (P=0.6), wound infection (P=0.7), sternal re-wiring (P=0.2), multi-organ failure (P=0.4) or mortality (P=0.1).

CONCLUSIONS

Surgical nurse assistants can be used effectively in low-risk cases without compromising postoperative results. However, initiatives to tackle the EWTD should be focused on areas that do not compromise the training needs of junior surgical trainees. An intermediate grade between the present senior house officer and registrar grades could be a way forward.

Coronary surgery with non-cardioplegic methods in patients with advanced left ventricular dysfunction: immediate and long term results

OBJECTIVE

To evaluate perioperative results and long term survival in patients with severe left ventricular (LV) dysfunction undergoing coronary artery bypass grafting (CABG) using non-cardioplegic methods.

METHODS

From April 1990 through December 1999, 4100 consecutive patients underwent isolated CABG using hypothermic ventricular fibrillation. Of these, 141 (3.4%) had severe LV dysfunction (ejection fraction < 30%). Mean age was 58.3 (9.6) years. 64 patients (45.4%) were in Canadian Cardiovascular Society class III or IV and 16 (11.3%) were subjected to urgent or emergent surgery. A previous myocardial infarction was recorded in 127 (90.1%). The majority (89.4%) had triple vessel and 26 (18.4%) had left main disease. The mean number of grafts per patient was 3.1. At least one internal thoracic artery was used in all patients and 21 (14.8%) had bilateral internal thoracic artery grafts (1.2 arterial grafts per patient).

RESULTS

Perioperative mortality was 2.8% (4 patients) and the incidence of acute myocardial infarction 2.8%. 50 (35.5%) patients required inotropes but only 16 (11.3%) required it for longer than 24 hours; 5 patients (3.5%) needed mechanical support. The incidence of renal failure was 3.5%. Mean duration of hospital stay was 9.6 (8.3) days. Follow up was 95% complete and extended for a mean of 57 (30) months. Late mortality was 11.5%. Actuarial survival rates at 1, 3, and 5 years were 96%, 91%, and 86%, respectively.

CONCLUSIONS

Non-cardioplegic techniques are safe and effective in preserving the myocardium during CABG in patients with coronary artery disease and poor LV function, with low operative mortality and morbidity, and encouraging medium to long term survival rates.

Myocardial protection with oxygenated esmolol cardioplegia during prolonged normothermic ischemia in the rat

OBJECTIVE

We previously showed that arrest with multidose infusions of high-dose (1 mmol/L) esmolol (an ultra-short-acting beta-blocker) in oxygenated Krebs-Henseleit buffer (esmolol cardioplegia) provided complete myocardial protection after 40 minutes of normothermic (37 degrees C) global ischemia in isolated rat hearts. In this study we investigated the importance of oxygenation for protection with esmolol cardioplegia, compared it with that of St Thomas' Hospital cardioplegia, and determined the protective efficacy of multidose esmolol cardioplegia for extended ischemic durations.

METHODS

Isolated rat hearts (n = 6/group) were perfused in the Langendorff mode at constant pressure (75 mm Hg) with oxygenated Krebs-Henseleit bicarbonate buffer at 37 degrees C. The first part of the first study had four groups: (i) multidose (every 15 minutes) oxygenated (95% oxygen/5% carbon dioxide) Krebs-Henseleit buffer during 60 minutes of global ischemia, (ii) multidose deoxygenated (95% nitrogen/5% carbon dioxide) Krebs-Henseleit buffer during 60 minutes of global ischemia, (iii) multidose oxygenated esmolol cardioplegia during 60 minutes of global ischemia, and (iv) multidose deoxygenated esmolol cardioplegia during 60 minutes of global ischemia. The second part of the first study had three groups: (v) multidose St Thomas' Hospital solution during 60 minutes of global ischemia, (vi) multidose oxygenated St Thomas' Hospital solution during 60 minutes of global ischemia, and (vii) multidose oxygenated esmolol cardioplegia during 60 minutes of global ischemia. In the second study, hearts were randomly assigned to 60, 75, 90, or 120 minutes of global ischemia and at each ischemic duration were subjected to multidose oxygenated constant flow or constant pressure infusion of (i) Krebs-Henseleit buffer (constant flow), (ii) Krebs-Henseleit buffer (constant pressure), (iii) esmolol cardioplegia (constant flow), or (iv) esmolol cardioplegia (constant pressure). All hearts were reperfused for 60 minutes, and recovery of function was measured.

RESULTS

Multidose infusion of oxygenated esmolol cardioplegia completely protected the hearts (97% +/- 5%) after 60 minutes of 37 degrees C global ischemia. Deoxygenated esmolol cardioplegia was significantly less protective (45% +/- 8%). Oxygenation of St Thomas' Hospital solution did not alter its protective efficacy in this study (70% +/- 4% vs 69% +/- 7%). Infusion of esmolol cardioplegia at constant pressure provided complete protection for 60, 75, and 90 minutes (104% +/- 5%, 95% +/- 5%, and 95% +/- 3%, respectively), whereas protection with constant-flow esmolol cardioplegic infusion was significantly decreased at ischemic durations longer than 60 minutes. This decrease in efficacy of constant-flow esmolol cardioplegia was associated with increasing coronary perfusion pressure leading to myocardial injury.

CONCLUSIONS

Oxygenation of esmolol cardioplegia (Krebs-Henseleit buffer plus 1.0 mmol/L esmolol) was essential for optimal myocardial protection. Multidose infusion of oxygenated esmolol cardioplegia provided good myocardial protection during extended periods of normothermic ischemia. Esmolol cardioplegia may provide an efficacious alternative to hyperkalemia.

Isolated myocardial revascularization with intermittent aortic cross-clamping: experience with 800 cases

BACKGROUND

We investigated the clinical outcome of elective and nonelective myocardial revascularization performed with intermittent aortic cross-clamping.

METHODS

Prospective data on 800 consecutive patients (from May 1996 to July 2000), who underwent isolated myocardial revascularization with intermittent aortic cross-clamping, were analyzed. A subgroup analysis was performed on the elective (n = 520), urgent (n = 226), and emergency (n = 54) procedures.

RESULTS

The elective group of patients had a mean age of 61.5 +/- 9.46 years, mean Parsonnet score of 5.23 +/- 5.1, and mean number of distal anastomoses of 3.22 +/- 1.04. The hospital mortality was 0.57%. The urgent group of patients had a mean age of 63.06 +/- 10.43 years, mean Parsonnet score of 6.73 +/- 6.22, and mean number of distal anastomoses of 3.21 +/- 1.04. The hospital mortality was 3.09%. The emergency group of patients had a mean age of 63.75 +/- 9.63 years, mean Parsonnet score of 11.24 +/- 11, and mean number of distal anastomoses of 2.87 +/- 0.86. Hospital mortality was 5.55%. Postoperative hospital stay was 7.11 +/- 5.47 days for the elective group, 7.59 +/- 5.07 days for the urgent group, and 7.40 +/- 4.01 days for the emergency group.

CONCLUSIONS

Intermittent aortic cross-clamping is a safe technique both in elective and nonelective patients. The mortality and morbidity in the three subgroups analyzed reflects patients' distribution against Parsonnet score.

Biochemical assessment of myocardial injury after cardiac surgery: effects of a platelet activating factor antagonist, bilateral internal thoracic artery grafts, and coronary endarterectomy

OBJECTIVE

Platelet activating factor antagonists reduce ischemia-reperfusion injury in experiments, but there is no supportive clinical evidence.

METHODS

A single-center, double-blind, minimized, placebo-controlled, randomized trial of low-dose (10 mg) or high-dose (100 mg) platelet activating factor antagonist was conducted in 150 patients undergoing coronary artery bypass grafting. Myocardial injury was determined by serial measurements of the MB isoenzyme of creatine kinase and cardiac troponin T. The effects of single or bilateral internal thoracic artery grafting and coronary endarterectomy on myocardial injury were also assessed.

RESULTS

The placebo and platelet activating factor antagonist groups were similar with respect to preoperative, intraoperative, and postoperative factors. Four patients (2.7%) died before discharge, 3 from cardiac events. Thirteen patients (9%) had biochemical evidence of myocardial infarction, of whom 3 died. Stepwise multiple regression analysis demonstrated that duration of cardiopulmonary bypass was the most important determinant of elevations in creatine kinase MB isoenzyme and cardiac troponin T up to 6 hours after the operation and that the use of a platelet activating factor antagonist and the number of internal thoracic artery grafts did not influence myocardial injury at any time. Endarterectomy was performed in 11 patients (7%), of whom 6 (55%) had biochemically defined myocardial infarction and of whom 1 died (9%). Endarterectomy was the most important determinant of elevated levels of creatine kinase MB isoenzyme and cardiac troponin T 24 and 48 hours after the operation.

CONCLUSION

Platelet activating factor antagonists do not reduce perioperative myocardial injury. Bilateral and single internal thoracic artery grafting results in similar levels of myocardial injury, whereas endarterectomy is frequently associated with biochemical evidence of myocardial injury.

Aortocoronary bypass grafting: a comparison of HTK cardioplegia vs. intermittent aortic cross-clamping

OBJECTIVE

Intermittend, hypothermic aortic cross-clamping (IAC) with myocardial fibrillation and cardioplegic arrest (CA) have been established both as effective methods for coronary artery bypass surgery (CABG). Nevertheless, there exists controversy about the more beneficial cardioprotective effect of one of these procedures in CABG-patients.

METHODS

In this prospective study we compared the clinical outcome, ischemic serum-markers (CK, CK-MB, Troponin I), electrocardiogram (ECG)-changes, and hemodynamic data of 103 patients. Randomization in group I (IAC; n=52) or group II (CA; n=51) was done consecutively, all data were compared by Student's t-test or chi(2)-test and P<0.05 was regarded as significant. The Bretschneider-HTK solution was used for cardioplegic arrest. Data were collected before operation, before ischemic arrest, after 5 and 60 min of reperfusion, 1 and 6 h after operation, 1, 2 and 10 days postoperatively.

RESULTS

There were no significant differences between both groups regarding general patient data: age (IAC: 64. 8+/-9.2 vs. CA: 63.8+/-9.0 years), left ventricular function (ejection fraction: IAC: 62+/-14 vs. CA: 64+/-13%), the amount of bypassed vessels (IAC: 3.4+/-0.5 vs. CA: 3.6+/-0.5), total bypass time (IAC: 113+/-31 vs. CA 108+/-20 min). The total time of ischemia was significantly less in the IAC group with 37+/-10 vs. 48+/-10 min in the CA group. In the IAC-group, a higher mortality was noticed (7. 7 vs. 3.9%; N.S.). This was combined with a significantly higher amount of patients with peak serum-values of CK-MB (>40 U/l) and troponin I (>50 ng/ml), 17 in the IAC-group (33%) vs. eight in CA-group (16%). Cerebral strokes were seen in two IAC-patients and none in CA-patients (NS). ECG-changes occurred in 22 IAC patients (42%) vs. 16 CA patients (31%); persistent ischemia related ECG-changes in six IAC (11.5%) vs. five CA-patients (9.8%).

CONCLUSIONS

Both cardioprotective methods, IAC and HTK-cardioplegia, seem to offer sufficient myocardial protection in normal CABG-procedures. Although neurologic disorders and mortality rates were higher in patients with intermittent aortic cross-clamping, the differences to the cardioplegia group were not significant. According to the analysis of increased ECG-changes, higher CK-MB and troponin I values, which occurred especially in patients with myocardial ischemia time longer than 40 min, we conclude that cardioplegic arrest with HTK seems to offer more beneficial effects in procedures with prolonged ischemia.

Experimental study of intermittent crossclamping with fibrillation and myocardial protection: reduced injury from shorter cumulative ischemia or intrinsic protective effect?

OBJECTIVE

During coronary artery revascularization, some surgeons favor intermittent crossclamping with ventricular fibrillation in preference to cardioplegic ischemic arrest for myocardial protection. It is unclear, however, whether intermittent crossclamping with fibrillation is equally protective or whether ischemic injury is reduced as a consequence of shorter cumulative ischemia.

METHODS

We used isolated, Langendorff-perfused rat hearts, measured preischemic function (left ventricular developed pressure) with an intraventricular balloon, and then subjected the hearts to either (1) 40 minutes of global ischemia, (2) a 2-minute infusion of cardioplegic solution and 40 minutes of ischemia, (3) multidose (every 10 minutes) infusions of cardioplegic solution during 40 minutes of ischemia, (4) continuous ventricular fibrillation during 40 minutes of ischemia, (5) intermittent (4 x 10 minutes) ischemia with 10 minutes of reperfusion, (6) intermittent (4 x 10 minutes) ischemia preceded by intermittent cardioplegia, (7) intermittent (4 x 10 minutes) ischemia with ventricular fibrillation, (8) continuous (40 minutes) ventricular fibrillation during coronary perfusion, or (9) intermittent (4 x 10 minutes) ventricular fibrillation (with perfusion). All protocols were followed by 60 minutes of reperfusion.

RESULTS

After 60 minutes of reperfusion, the percentage recovery of left ventricular developed pressure for groups 1 through 9 was as follows: 32% +/- 2%, 57% +/- 6%, 82% +/- 3%, 19% +/- 3%, 73% +/- 3%, 70% +/- 3%, 78% +/- 4%, 55% +/- 2%, and 57% +/- 3%, respectively. No significant differences were identified among groups 3, 5, and 7, but the percentage recovery of developed pressure in group 3 was significantly higher than that in group 6; the degree of recovery in groups 3 and 5 to 7 was significantly (P <.05) higher than in groups 1, 2, 4, 8, and 9. Early recovery was significantly (P <.05) more rapid in groups 3 and 5 to 9, reaching a plateau (of 55%-80%) by 10 minutes of reperfusion; in groups 1, 2, and 4, the recovery plateau occurred after 50 minutes. Left ventricular end-diastolic pressure was elevated in groups 1, 2, and 4 but was almost unchanged from baseline in the other groups.

CONCLUSIONS

A similar level of myocardial protection was achieved with multidose (intermittent) cardioplegia or intermittent crossclamping (with or without fibrillation), indicating that intrinsic preservation by intermittent crossclamping with fibrillation does not exacerbate ischemic injury.

Coronary Artery Bypass Surgery without Cardioplegia: Early Results

From November 1996 to April 1999, 348 patients underwent isolated non-cardioplegic coronary artery bypass grafting at a new center. There were 123 (35%) patients aged over 60 years, 48 (14%) were female, 70 (20%) had a left ventricular ejection fraction below 0.3. Coronary artery bypass graft surgery was performed using hypothermic intermittent ischemic fibrillatory arrest of the heart. The left internal mammary artery was used in 97% of cases. Mean grafts per patient was 3.5. Sixty-three patients (18%) underwent 65 coronary endarterectomies. The overall operative mortality rate was 2.3% (8/348). Follow-up was 97% complete. Mean follow-up was 14.9 ± 8 months (range, 1 to 30 months). Freedom from angina was 98.3% at 6 months, 97% at 12 months, and 97% at 24 months. The overall survival was 96.7% at 6 months, 95.8% at 12 months, and 94.4% at 24 months. It was concluded that this method of myocardial protection for isolated coronary artery bypass graft surgery provided excellent operating conditions in this group of patients.

A controlled trial of substrate-enhanced, warm reperfusion ("hot shot") versus simple reperfusion

BACKGROUND

Modified reperfusion after aortic cross-clamping is claimed to reduce myocardial injury, thus improving postoperative myocardial performance.

METHODS

We measured perioperative release of creatine kinase-MB and troponin-T in 40 patients undergoing valve replacement (combined with coronary grafts in 12 cases) to determine whether infusion of a modified reperfusate before cross-clamp removal reduced myocardial injury. Patients were randomly allocated to one of two groups with minimization for age, surgeon, operation, and ventricular function. The control group received unmodified reperfusion, while the study group received a normothermic reperfusate, enhanced with glutamate and aspartate, for 5 minutes before removal of the cross-clamp. Serial determinations of troponin-T, creatine kinase-MB isoforms, and total creatine kinase-MB activity were made up to 5 days postoperatively. Requirements for inotropic support and evidence of myocardial infarction were documented.

RESULTS

Creatine kinase-MB activity, creatine kinase-MB isoforms, and troponin-T were not significantly different between the two groups. There were no differences in the incidence of postoperative myocardial infarction or in inotrope requirement.

CONCLUSIONS

Our study did not demonstrate any advantage in using modified reperfusion in this group of patients.

Intraoperative cardiac troponin T release and lactate metabolism during coronary artery surgery: comparison of beating heart with conventional coronary artery surgery with cardiopulmonary bypass

OBJECTIVE

To compare cardiac troponin T release and lactate metabolism in coronary sinus and arterial blood during uncomplicated coronary grafting on the beating heart with conventional coronary grafting using cardiopulmonary bypass.

DESIGN

A prospective observational study with simultaneous sampling of coronary sinus and arterial blood: before and 1, 4, 10, and 20 minutes after reperfusion for analysis of cardiac troponin T and lactate. Cardiac troponin T was also analysed in venous samples taken 3, 6, 24, 48, and 72 hours after surgery.

SETTING

Cardiac surgical unit in a tertiary referral centre.

PATIENTS

18 patients undergoing coronary grafting on the beating heart (10 single vessel and eight two-vessel grafting) and eight undergoing two-vessel grafting with cardiopulmonary bypass.

RESULTS

Cardiac troponin T was detected in coronary sinus blood in all patients by 20 minutes after beating heart coronary artery surgery before arterial concentrations were consistently increased. Peak arterial and coronary sinus cardiac troponin T values on the beating heart during single (0.03 (0 to 0. 05) and 0.09 (0.07 to 0.16 microg/l, respectively) and two-vessel grafting (0.1 (0.07 to 0.11) and 0.19 (0.14 to 0.25) microg/l) were lower than the values obtained during cardiopulmonary bypass (0.64 (0.52 to 0.72) and 1.4 (0.9 to 2.0) microg/l) (p < 0.05). The area under the curve of venous cardiac troponin T over 72 hours for two-vessel grafting on the beating heart was less than with cardiopulmonary bypass (13 (10 to 16) v 68 (26 to 102) microg.h/l) (p < 0.001). Lactate extraction began within one minute of snare release during beating heart coronary surgery while lactate was still being produced 20 minutes after cross clamp release following cardiopulmonary bypass.

CONCLUSIONS

Lower intraoperative and serial venous cardiac troponin T concentrations suggest a lesser degree of myocyte injury during beating heart coronary artery surgery than during cardiopulmonary bypass. Oxidative metabolism also recovers more rapidly with beating heart coronary artery surgery than with conventional coronary grafting. Coronary sinus cardiac troponin T concentrations increased earlier and were greater than arterial concentrations during beating heart surgery, suggesting that this may be a more sensitive method of intraoperative assessment of myocardial injury.

Influence of normothermic systemic perfusion temperature on cold myocardial protection during coronary artery bypass surgery

OBJECTIVE

To determine the effect of normothermic systemic perfusion on myocardial injury when using cold cardioplegic techniques in patients undergoing coronary artery bypass surgery.

METHOD

Sixty six patients with stable angina pectoris were prospectively randomized into three groups according to cardiopulmonary bypass temperature: hypothermia (28 degrees C, n = 22), moderate hypothermia (32 degrees C, n = 22) and normothermia (37 degrees C, n = 22). All patients received cold antegrade crystalloid cardioplegia and topical cooling with saline at 4 degrees C. Serum samples were collected for troponin T and I estimation preoperatively, 4 hours after removal of the aortic cross clamp, and 12, 24, 36 and 48 hours postoperatively. In addition, serial electrocardiographic studies were undertaken on days 1, 3 and 5.

RESULTS

Patients were similar with regard to preoperative and intraoperative characteristics Four patients showed ECG changes typical of perioperative myocardial infarction but remained clinically well (28 degrees C, one; 32 degrees C, one; 37 degrees C, two). In the remaining 62 patients, serum troponin T increased significantly from a mean baseline value of 0.02 ng/ml to 1.5+/-0.9 ng/ml 4 hours after removal of the aortic cross-clamp (P<0.0001). Similarly, troponin I increased from 0.06 ng/ml to 0.63+/-0.47 ng/ml 12 hours after reperfusion (P<0.0001). Serum concentrations of both markers subsequently declined with time but remained higher than preoperative values at 48 hours. There were no differences between the three groups with respect to peak and cumulative serum troponin release. Normothermic cardiopulmonary bypass did not compromise the efficacy of cold myocardial protection when assessed by serum troponin concentrations in low risk patients undergoing coronary revascularization.

Intraoperative release of troponin T in coronary venous and arterial blood and its relation to recovery of left ventricular function and oxidative metabolism following coronary artery surgery

OBJECTIVE

To investigate the intraoperative release of troponin T during uncomplicated coronary artery surgery and to determine its relation to ischaemic time and to recovery of left ventricular function and oxidative metabolism.

DESIGN

A prospective observational study.

SETTING

Cardiac surgical unit in a tertiary referral centre.

METHODS

Troponin T, creatine kinase, and lactate were analysed from arterial and coronary sinus samples taken before operation, and 1, 4, 6, 10, 20, 35, and 45 minutes after cross clamp release. Net myocardial troponin T release and lactate extraction were derived from their respective arteriovenous differences. Haemodynamic measurements were made using a thermodilution pulmonary artery catheter.

PATIENTS

45 patients, mean (SD) age 62 (9) years, with two or three vessel coronary artery disease and chronic stable angina undergoing routine coronary artery surgery.

RESULTS

Before operation, troponin T concentrations were not raised, but within one minute of cross clamp release they increased progressively in both coronary sinus and arterial blood for the entire 45 minutes of reperfusion studied. Coronary sinus troponin T concentrations were consistently higher than arterial concentrations at all time points (p < 0.001), indicating net troponin T release by the myocardium. Peak net troponin T release and area under the curve of net troponin T release correlated closely with ischaemic time (r = 0.58 and r = 0.61, p < 0.0001 for both). Area under the curve of arterial troponin T concentration was also significantly correlated with ischaemic time (r = 0.44, p < 0.01). Patients with cross clamp times longer than 72 minutes (upper quartile for ischaemic time) had greater troponin T release, delayed reversion to lactate extraction, and lower left ventricular stroke work index three hours after surgery, compared with patients who had short (< 50 minutes, lower quartile) and intermediate (51-71 minutes, interquartile) cross clamp times. Peak net troponin T release and area under the curve of arterial troponin T concentration were inversely correlated with left ventricular stroke work index three hours after surgery (r = -0.57, r = -0.38, p < 0.01).

CONCLUSIONS

Troponin T concentrations increased in every patient after cross clamp release, and were consistently higher in coronary sinus blood than in arterial blood, indicating net myocardial release of troponin T during the period of reperfusion. Intraoperative net troponin T release has functional significance, as it is closely related to ischaemic time and reflects delayed recovery of left ventricular function and oxidative metabolism; therefore, its measurement may contribute to the perioperative assessment of myocardial injury sustained during coronary artery surgery.

Cold blood cardioplegia or intermittent cross-clamping in coronary artery bypass grafting?

BACKGROUND

We determined that cold blood cardioplegia and intermittent ventricular fibrillation with ischemia were associated with similar enzyme and myocardial protein leakage in a randomized, prospective study of 40 patients. We have continued to use both methods in our unit, according to surgeons' preference.

METHODS

In our database we have reviewed 1,923 patients who have undergone first-time elective or urgent coronary artery bypass grafting from January 1992 to May 1997.

RESULTS

Five hundred seventy-eight patients underwent coronary artery bypass grafting with cold blood cardioplegia and 1,345 had ventricular fibrillation and aortic cross-clamping. The preoperative factors were virtually identical. Intraoperative differences were only those inherent to the two techniques: temperature and cross-clamp time. Mortality was 2.5% for ventricular fibrillation and aortic cross-clamping arrest and 2.1% for cardioplegia (p=0.55 by chi2 test). There was a higher use of the intraaortic balloon pump in the ventricular fibrillation and aortic cross-clamping group (2.4% versus 1.0%; p=0.04), but no other differences in outcome were detected.

CONCLUSIONS

A truly randomized trial to demonstrate which technique is superior is impractical at this level of difference because it would require 37,000 patients to avoid a beta error. We have to base our practice on the retrospective data available. Each technique has its merits in practice, which are discussed.

Prospective randomized trial of single clamp technique versus intermittent ischaemic arrest: myocardial and neurological outcome

OBJECTIVE

To explore the hypothesis that intermittent ischaemic arrest (IIA) provides better myocardial preservation but generates a larger number of cerebral microemboli (ME) and consequently a higher incidence of post-operative cerebral dysfunction compared with the single clamp technique (SCT).

METHODS

Ninety-one patients with stable angina undergoing elective CABG with no clinical evidence of aortic or cerebro-vascular or neurological disease were prospectively randomized to: IIA (n = 43) or SCT with intermittent anterograde cold blood cardioplegia (n = 48). Myocardial preservation was assessed by measuring serum CK-MB, Troponin-T (TnT) and Troponin-I (TnI) and from pre- and post-operative ECGs and left ventricular (LV) function by echocardiography. Intra-operative cerebral ME were counted by transcranial Doppler of the right middle cerebral artery. All patients completed the Luria Nebraska Neuropsychological Battery (LNNB) tests for motor, visual, reading, memory and intellectual processes the day before surgery and at 1 week and 6 months post-operatively. Serum levels of the neuro-specific protein S-100 were measured.

RESULTS

The two groups were comparable for age, sex, extent of coronary disease, previous myocardial infarction, diabetes, hypertension and number of arterial and venous grafts. The median number of ME detected per patient was 34 (range 4-208) and was similar in both groups. Protein S-100 levels remained normal and similar in both groups at all times except in one patient with SCT who had an operative stroke. LNNB scores were similarly depressed at 1 week and recovered in all cases at 6 months. There was no correlation between the number of ME and LNNB scores. Median peak TnI levels were 0.64 microg/l with IIA vs. 0.87 microg/l with SCT (P = NS) and TnT 0.8 microg/l vs. 1.08 microg/l (P < 0.03). SCT was however associated with longer mean ischaemic (67.6 +/- 16.1 vs. 34.5 +/- 16.5 min, P < 0.001) and mean bypass time (88.5 +/- 18.2 vs. 74.6 +/- 26.3 min, P < 0.004) than IIA. Four patients with SCT and none with IIA had ECG changes suggestive of MI (P = 0.04).

CONCLUSION

During elective CABG in patients with no clinical evidence of aortic or cerebro-vascular disease the incidence of peri-operative ME and post-operative neuropsychological disturbances are comparable with both techniques of myocardial preservation. Biochemical analysis suggests that IIA provides more effective myocardial preservation.

Ischemic preconditioning prior to myocardial protection with cold blood cardioplegia in coronary surgery

OBJECTIVE

Encouraging results on myocardial preconditioning in experimental models of infarction, stunning or prolonged ischemia raise the question whether preconditioning techniques may enhance conventional cardioplegic protection used for routine coronary surgery.

METHODS

A prospective clinical trial was conducted to investigate the effect of additional ischemic normothermic preconditioning prior to cardioplegic arrest applying cold blood cardioplegia in patients scheduled for routine coronary surgery (3 vessel disease, left ventricular ejection fraction > 50%). Two cross clamp periods of 5 min with the hearts beating in sinus rhythm were applied followed by 10 min of reperfusion, each (n = 7, group I). Inducing moderate hypothermia cold blood cardioplegia was delivered antegradely. In control groups, cold intermittent blood cardioplegia (n = 7, group II) was used alone. Coronary sinus effluents were analyzed for release of creatine kinase (CK), CK-MB, lactate, and troponin T at 1, 3, 6, 9, and 12 h. In addition, postoperative catecholamine requirements were monitored.

RESULTS

The procedure was tolerated well, and no perioperative myocardial infarction in any of the groups studied occurred. Concentrations of lactate tended to be higher in group I, but this difference was not significant. In addition, no significant differences for concentrations of CK, CK-MB, and troponin T were found. Following ischemic preconditioning an increased dosage of dopamine was required within the first 12 h postoperatively (group I: 2.63 +/- 1.44 microg/kg/min, group II: 0.89 +/- 1.06 microg/kg/min).

CONCLUSIONS

Combining ischemic preconditioning and cardioplegic protection with cold blood cardioplegia does not appear to ameliorate myocardial protection when compared to cardioplegic protection applying cold blood cardioplegia alone. Inversely, contractile function seemed to be impaired when applying this protocol of ischemic preconditioning.

Ischaemic preconditioning reduces troponin T release in patients undergoing coronary artery bypass surgery

OBJECTIVE

To investigate whether ischaemic preconditioning could reduce myocardial injury, as manifest by troponin T release, in patients undergoing elective coronary artery bypass surgery.

DESIGN

Randomised controlled trial.

SETTING

Cardiothoracic unit of a tertiary care centre.

PATIENTS

Patients with three vessel coronary artery disease and stable angina admitted for first time elective coronary artery bypass surgery were invited to take part in the study; 33 patients were randomised into control or preconditioning groups.

INTERVENTION

Patients in the preconditioning group were exposed to two additional three minute periods of myocardial ischaemia at the beginning of the revascularisation operation, before the ischaemic period used for the first coronary artery bypass graft distal anastomosis.

MAIN OUTCOME MEASURE

Serum troponin T concentration at 72 hours after cardiopulmonary bypass.

RESULTS

The troponin T assays were performed by blinded observers at a different hospital. All patients had undetectable serum troponin T (< 0.1 microgram/l) before cardiopulmonary bypass, and troponin T was raised postoperatively in all patients. At 72 hours, serum troponin T was lower (P = 0.05) in the preconditioned group (median 0.3 microgram/l) than in the control group (median 1.4 micrograms/l).

CONCLUSIONS

The direct application of a preconditioning stimulus in clinical practice has been shown, for the first time, to protect patients against irreversible myocyte injury.

Biochemical markers of myocardial injury during cardiac operations

The evaluation of myocardial damage in relation to cardiac operation from a clinical and a research perspective is of great importance, particularly for the evaluation of different cardioprotective strategies. Although measurements of serum biochemical markers have often been used, their value has been limited by their lack of sensitivity and specificity in the presence of skeletal muscle damage. A newer range of markers are now available that may reliably indicate both perioperative myocardial infarction, as well as more subtle degrees of subclinical myocyte injury. In this review, the application of biochemical markers for clinical and research purposes during cardiac operation is considered.

Intermittent aortic cross-clamping and cold crystalloid cardioplegia for low-risk coronary patients

BACKGROUND

Blood cardioplegic strategies have been shown to increase myocardial oxygen uptake, replenish depleted energy stores, and improve myocardial function and survival in the high-risk subset of patients. However, the superiority of these techniques over intermittent aortic cross-clamping and crystalloid cardioplegia in low-risk patients is still controversial.

METHODS

This study consisted of two parts. In the first part, we assessed the results of a recent cohort of 399 consecutive low-risk patients undergoing their first coronary artery bypass grafting between 1993 and 1995 using cold crystalloid cardioplegia (n = 128) and intermittent aortic cross-clamping (n = 271). In the second part of the study, 40 consecutive low-risk patients undergoing elective first time coronary artery bypass grafting were randomly divided into two equal groups. One group received cold crystalloid cardioplegia and the other group had myocardial management with intermittent aortic cross-clamping. The two groups were compared with respect to hemodynamic, biochemical and ultrastructural changes.

RESULTS

The overall mortality rate, the perioperative myocardial in the need for intraaortic balloon pumps, and the need for inotropic agents were 0.25%, 1.5%, 1%, and 5.8%, respectively. No significant differences were observed between the groups with respect to these clinically defined end points.

CONCLUSIONS

Both intermittent aortic cross-clamping and cold crystalloid cardioplegia techniques may be used safely in low-risk patients undergoing first-time coronary artery bypass grafting.

Can ischemic preconditioning ensure optimal myocardial protection when delivery of cardioplegia is impaired?

BACKGROUND

Ischemic preconditioning is a potent protective intervention that is effective in all species studied. We have previously shown it to be as effective as cardioplegia; however, we have also shown that their combined use does not afford greater protection than the use of either alone. In the present study we investigated whether coincident ischemic preconditioning could compensate for inadequate cardioplegic protection when the delivery of cardioplegia was impaired, such as occurs in the presence of severe coronary stenosis or occlusion.

METHODS AND RESULTS

Isolated rat hearts were subjected to 30 minutes of global ischemia followed by 40 minutes of reperfusion. Four groups of hearts (n = 12 per group) were studied: group 1, controls (no intervention); group 2, cardioplegia administered to hearts with a proximally occluded coronary artery; group 3, ischemic preconditioning applied before ischemia; and group 4, ischemic preconditioning and cardioplegia given in combination to hearts with a proximally occluded coronary artery. The postischemic recovery of left ventricular (LV) developed pressure (LVDP), expressed as a percentage of preischemic values, was significantly greater (P < .05) in preconditioned hearts (64 +/- 3%) than in control hearts (24 +/- 4%) or hearts treated with suboptimal cardioplegia (43 +/- 5%). Hearts with preconditioning plus cardioplegia recovered to an extent similar to that seen with preconditioning alone (59 +/- 2%). LV end-diastolic pressure was greater in control hearts (58 +/- 4 mm Hg) than in hearts with cardioplegia (41 +/- 4 mm Hg; P < .05 versus group 1) despite the incomplete delivery of the cardioplegia; the best protection was observed in preconditioned hearts and hearts with preconditioning plus cardioplegia (24 +/- 1 and 26 +/- 2 mm Hg, respectively; P < .05 versus groups 1 and 2).

CONCLUSIONS

When the delivery of cardioplegia was impaired, myocardial protection (postischemic LVDP) was better served by ischemic preconditioning. Under the same conditions, the combination of cardioplegia plus preconditioning afforded superior protection compared with cardioplegia alone. These results may be of clinical interest since most patients who undergo surgery for ischemic heart disease suffer from severe coronary artery lesions that can prevent the adequate delivery of cardioplegia.