Adverse 30-Day Outcomes After Cardiac Surgery: Predictive Role of Intraoperative Myocardial Acidosis

Myocardial tissue CO2 tension detects coronary blood flow reduction after coronary artery bypass in real-time†

BACKGROUND

Coronary stenosis after coronary artery bypass grafting (CABG) may lead to myocardial ischaemia and is clinically difficult to diagnose. In a CABG model, we aimed at defining variables that detect hypoperfusion in real-time and correlate with impaired regional ventricular function by monitoring myocardial tissue metabolism.

METHODS

Off-pump CABG was performed in 10 pigs. Graft blood flow was reduced in 18 min intervals to 75, 50, and 25% of baseline flow with reperfusion between each flow reduction. Myocardial tissue Pco2 (Pt(CO2)), Po2, pH, glucose, lactate, and glycerol from the graft supplied region and a control region were obtained. Regional cardiac function was assessed as radial strain.

RESULTS

In comparison with baseline, myocardial pH decreased during 75, 50, and 25% flow reduction (-0.15; -0.22; -0.37, respectively, all P<0.05) whereas Pt(CO2) increased (+4.6 kPa; +7.8 kPa; +12.9 kPa, respectively, all P<0.05). pH and Pt(CO2) returned to baseline upon reperfusion. Lactate and glycerol increased flow-dependently, while glucose decreased. Regional ventricular contractile function declined significantly. All measured variables remained normal in the control region. Pt(CO2) correlated strongly with tissue lactate, pH, and contractile function (R=0.86, R=-0.91, R=-0.70, respectively, all P<0.001). New conductometric Pt(CO2) sensors were in agreement with established fibre-optic probes. Cardiac output was not altered.

CONCLUSIONS

Myocardial pH and Pt(CO2) monitoring can quantify the degree of regional tissue hypoperfusion in real-time and correlated well with cellular metabolism and contractile function, whereas cardiac output did not. New robust conductometric Pt(CO2) sensors have the potential to serve as a clinical cardiac monitoring tool during surgery and postoperatively.

Cold intermittent cardioplegia reduces the acidosis during prolonged cardiac surgery with cardiopulmonary bypass

The effect on acid-base balance efficacy of intermittent warm and cold blood cardioplegia (IWBC, ICBC) was assessed in 44 patients who underwent cardiac surgery with prolonged aortic cross clamping. With this purpose a customized multi sensor probe was inserted in the coronary sinus, and pH, PO(2), PCO(2) and temperature were continuously measured at 1 Hz sampling rate. The mean cross-clamping time was of 76 ± 26 min on 19 IWBC cases and of 80 ± 24 min on 14 ICBC cases. With IWBC perfusion, at the end of every ischemic period, the lowest pH and PO(2) progressively decreased and the maximal PCO(2) increased. During ICBC the minimum of pH and PO(2) and maximum of PCO2 at the end of different ischemic period during time were constant, also during long cross-clamping time. With IWBC, myocardial ischemia seemed not completely reversed by standardized reperfusions, as reflected by steady deterioration of PCO(2) and pH after each reperfusion.

Intraoperative myocardial acidosis as a risk for hospital readmission after cardiac surgery

BACKGROUND

This study elucidates the relationship between intraoperative myocardial acidosis/ischemia and the risk of unplanned hospital readmissions within 30 days and 6 months after cardiac surgery.

METHODS

Myocardial tissue pH (corrected to 37 degrees C: pH(37C)) was monitored in 221 patients during cardiac surgery. Regional myocardial acidosis was defined in terms of specific pH thresholds.

RESULTS

Fourteen percent and 27% of the patients were readmitted within 30 days and 6 months postoperatively, respectively. The mean number of readmissions was 1.67 +/- 1.24; pH(37C) <6.85 at the end of cardiopulmonary bypass (CPB) was identified as the threshold most significantly associated with readmission. This threshold was associated with a 6-fold increased risk of readmission within 30 days and a 5-fold increased risk within 6 months.

CONCLUSIONS

Persistent regional myocardial acidosis after weaning from CPB independently determines unplanned readmission rates up to 6 months postoperatively. This study underscores the importance of avoiding myocardial tissue acidosis during cardiac surgery.

Myocardial protection of insulin and potassium in a porcine ischemia-reperfusion model

BACKGROUND

We previously evaluated cardioprotective effects of glucose-insulin-potassium (GIK) in a porcine ischemia-reperfusion model; our results showed less myocardial pH decrease during ischemia and reperfusion and faster normalization of ATP and glucose during reperfusion. The proposed protective mechanism was facilitation of glucose transport for myocardial metabolism. The objective of this study was to assess the impact of insulin-potassium (IK) alone on myocardial metabolism.

METHODS

Male swine received continuous infusion of IK (IK group, n = 10), GIK (GIK group, n = 10), or standard lactated Ringer's (LR) solution (controls, n = 10). Induction of 20 minutes of ischemia in the left anterior descending (LAD) artery distribution was followed by 20 minutes of reperfusion. Real-time biosensors recorded pH and glucose levels in ischemic and nonischemic beds. Myocardial biopsies in the distribution of the LAD assessed ATP levels. Groups were compared using the Kruskal-Wallis and Mann-Whitney tests.

RESULTS

Real-time data are presented as percent change from baseline. At less than 10 minutes of ischemia, the average pH change was less for the IK group than the LR group (0.03% +/- 0.21% vs -2.06% +/- 1.23%; P = .001), and the pH change in the IK group was similar to the GIK group. After 10 minutes of ischemia and during the first 10 minutes of reperfusion, the IK group experienced pH changes that were similar to the LR group. Biopsies after 20 minutes of ischemia and 20 minutes of reperfusion showed less of a decline in ATP levels for the IK group compared to the LR group. Glucose at all time points demonstrated no statistically significant differences.

CONCLUSION

IK infusion alone demonstrates cardioprotective effects during early ischemia; however, compared to GIK infusion after 20 minutes of ischemia and reperfusion, myocardial pH and glucose levels were not sustained. Although insulin may facilitate glucose transport during ischemia, additional glucose in combination with IK enhances myocardial protection during reperfusion. This finding suggests that GIK enhancement during acute ischemia-reperfusion may improve myocardial protection.

Bypass surgery with psychological and spiritual support (the By.pass study): study design and research methods

Effects of psychological as well as spiritual interventions on outcome in cardiac surgery have mostly been studied with a focus on presurgical interventions. Systematically controlled analyses of the effects of psychological and spiritual interventions depending on the patients' preference have not been performed so far, although these studies would help to assign patients to an adequate support. The By.pass study is a bi-center, controlled trial of patients undergoing coronary bypass surgery and coronary bypass surgery combined with valve replacement surgery in 2 different German hospitals. Patients are assigned to 1 of 5 conditions, mainly according to their personal therapeutic preference: preference for psychological interventions (group 1), preference for spiritual interventions (group 2), or preference for no intervention (group 5). Patients who are open for any kind of intervention are randomly assigned either to psychological (group 3) or spiritual interventions (group 4). Six months before the start and 6 months after the end of the treatment phase, patients were assigned to the control groups. These were asked about their subjective preference (psychological, spiritual, no intervention, or no specific preference) as well but received no interventions. Patients will be enrolled from October 2006 to December 2009. The 6-month follow-up will be completed in July 2010.

Troponin I after cardiac surgery and its implications on myocardial protection, outcomes, and cost

BACKGROUND

Myocardial acidosis during cardiac surgery and postoperative troponin I are markers of myocardial damage that have been shown to predict adverse outcomes. We investigated the relationship between troponin I and myocardial tissue pH, patient outcomes, and cost.

METHODS

Data were prospectively collected on 205 cardiac surgery patients. Troponin I was sampled upon arrival to the intensive care unit (ICU) and every 6 hours thereafter for 24 hours. The lowest pH encountered during aortic cross clamp (LpH) was related to postoperative troponin I on the multivariate level. Multivariate models were constructed to predict adverse events (AE) and cost.

RESULTS

LpH was an independent inverse determinant of postoperative troponin I (P = .0067). Troponin I and its interaction with LpH were multivariate predictors of AE (P = .0012; .0001;odds ratio = 6.9, 10.2, respectively). Troponin I independently predicts surgical ICU (SICU) cost (P = .0256).

CONCLUSION

Postoperative troponin I elevation reflects intraoperative myocardial acidosis and damage. The strong relationship between troponin I, AE, and cost indicates the damage incurred is clinically and economically relevant. Strategies to ameliorate intraoperative myocardial tissue acidosis will decrease troponin I release, subsequent AE, and associated costs.

Intermittent antegrade cardioplegia: isolated heart preservation with the Asporto heart preservation device

BACKGROUND

A major problem in procurement of donor hearts is the limited time a donor heart remains viable. After cardiectomy, ischemic hypoxia is the main cause of donor heart degradation. The global myocardial ischemia causes a cascade of oxygen radical formation that cumulates in an elevation in hydrogen ions (decrease in pH), irreversible cellular injury, and potential microvascular changes in perfusion.

OBJECTIVE

To determine the changes of prolonged storage times on donor heart microvasculature and the effects of intermittent antegrade perfusion.

MATERIALS AND METHODS

Using porcine hearts flushed with a Ribosol-based cardioplegic solution, we examined how storage time affects microvascular myocardial perfusion by using contrast-enhanced magnetic resonance imaging at a mean (SD) of 6.1 (0.6) hours (n = 13) or 15.6 (0.6) hours (n = 11) after cardiectomy. Finally, to determine if administration of cardioplegic solution affects pH and microvascular perfusion, isolated hearts (group 1, n = 9) given a single antegrade dose, were compared with hearts (group 2, n = 8) given intermittent antegrade cardioplegia (150 mL, every 30 min, 150 mL/min) by a heart preservation device. Khuri pH probes in left and right ventricular tissue continuously measured hydrogen ion levels, and perfusion intensity on magnetic resonance images was plotted against time.

RESULTS

Myocardial perfusion measured via magnetic resonance imaging at 6.1 hours was significantly greater than at 15.6 hours (67% vs 30%, P = .00008). In group 1 hearts, the mean (SD) for pH at the end of 6 hours decreased to 6.2 (0.2). In group 2, hearts that received intermittent antegrade cardioplegia, pH at the end of 6 hours was higher at 6.7 (0.3) (P = .0005). Magnetic resonance imaging showed no significant differences between the 2 groups in contrast enhancement (group 1, 62%; group 2, 40%) or in the wet/dry weight ratio.

CONCLUSION

Intermittent perfusion maintains a significantly higher myocardial pH than does a conventional single antegrade dose. This difference may translate into an improved quality of donor hearts procured for transplantation, allowing longer distance procurement, tissue matching, improved outcomes for transplant recipients, and ideally a decrease in transplant-related costs.

Intermittent Antegrade Cardioplegia: Isolated Heart Preservation with the Asporto Heart Preservation Device

Background

A major problem in procurement of donor hearts is the limited time a donor heart remains viable. After cardiectomy, ischemic hypoxia is the main cause of donor heart degradation. The global myocardial ischemia causes a cascade of oxygen radical formation that cumulates in an elevation in hydrogen ions (decrease in pH), irreversible cellular injury, and potential microvascular changes in perfusion.

Objective

To determine the changes of prolonged storage times on donor heart microvasculature and the effects of intermittent antegrade perfusion.

Materials and Methods

Using porcine hearts flushed with a Ribosol-based cardioplegic solution, we examined how storage time affects microvascular myocardial perfusion by using contrast-enhanced magnetic resonance imaging at a mean (SD) of 6.1 (0.6) hours (n=13) or 15.6 (0.6) hours (n=11) after cardiectomy. Finally, to determine if administration of cardioplegic solution affects pH and microvascular perfusion, isolated hearts (group 1, n=9) given a single antegrade dose, were compared with hearts (group 2, n=8) given intermittent antegrade cardioplegia (150 mL, every 30 min, 150 mL/min) by a heart preservation device. Khuri pH probes in left and right ventricular tissue continuously measured hydrogen ion levels, and perfusion intensity on magnetic resonance images was plotted against time.

Results

Myocardial perfusion measured via magnetic resonance imaging at 6.1 hours was significantly greater than at 15.6 hours (67% vs 30%, P=.00008). In group 1 hearts, the mean (SD) for pH at the end of 6 hours decreased to 6.2 (0.2). In group 2, hearts that received intermittent antegrade cardioplegia, pH at the end of 6 hours was higher at 6.7 (0.3) ( P=.0005). Magnetic resonance imaging showed no significant differences between the 2 groups in contrast enhancement (group 1, 62%; group 2, 40%) or in the wet/dry weight ratio.

Conclusion

Intermittent perfusion maintains a significantly higher myocardial pH than does a conventional single antegrade dose. This difference may translate into an improved quality of donor hearts procured for transplantation, allowing longer distance procurement, tissue matching, improved outcomes for transplant recipients, and ideally a decrease in transplant-related costs.

Patients with diabetes mellitus undergoing cardiac surgery are at greater risk for developing intraoperative myocardial acidosis

OBJECTIVE

In patients undergoing cardiac surgery, intraoperative myocardial acidosis, which quantifies regional myocardial ischemia, has been shown to increase the risk of adverse postoperative outcomes. In this study, we sought to determine the course of intraoperative myocardial acidosis and its impact on postoperative survival in patients with diabetes mellitus undergoing cardiac surgery.

METHODS

Intraoperative myocardial tissue pH(37C) was continuously measured in the anterior and posterior left ventricular walls in 264 patients undergoing cardiac surgery; 74 (28.0%) of the patients had diabetes (insulin-dependent diabetes: 54%; non-insulin dependent diabetes: 46%). The shortest time required to reach intraoperative myocardial tissue pH < 6.34 during aortic occlusion and > 6.73 during reperfusion were compared in 3 patient groups: insulin-dependent, non-insulin dependent, and nondiabetic. These pH thresholds have been demonstrated to be associated with adverse postoperative long-term survival.

RESULTS

The median times to reach intraoperative myocardial tissue pH(37C) < 6.34 during aortic occlusion were 14, 23, and 36 minutes in the insulin-dependent, non-insulin dependent, and non-diabetic groups, respectively (P = .003). The time taken to reach intraoperative myocardial tissue pH(37C) > 6.73 during reperfusion was similar between the 3 groups. After adjusting for relevant pre- and intraoperative parameters, the risk of developing intraoperative myocardial tissue pH < 6.34 during aortic occlusion was 73% higher in patients with insulin-dependent diabetes mellitus (P = .022) but the same in with patients with non-insulin dependent diabetes mellitus (P = .98) when compared with patients without diabetes. Patients with insulin-dependent diabetes mellitus also had nearly threefold decrease in long-term survival compared with that of patients without diabetes (P = .0007).

CONCLUSIONS

Patients with insulin-dependent diabetes mellitus undergoing cardiac surgery are at a greater risk of developing intraoperative myocardial acidosis/ischemia and of decreased survival postoperatively compared with patients without diabetes.