Methods for the metabolic quantification of regional myocardial ischemia

Changes in myocardial lactate, pyruvate and lactate-pyruvate ratio during cardiopulmonary bypass for elective adult cardiac surgery: Early indicator of morbidity

BACKGROUND

Myocardial lactate assays have been established as a standard method to compare various myocardial protection strategies. This study was designed to test whether coronary sinus (CS) lactates, pyruvate and lactate-pyruvate (LP) ratio correlates with myocardial dysfunction and predict postoperative outcomes.

MATERIALS AND METHODS

This prospective observational study was conducted on 40 adult patients undergoing elective cardiac surgery with the aid of cardiopulmonary bypass (CPB). CS blood sampling was done for estimation of myocardial lactate (ML), pyruvate (MP) and lactate-pyruvate ratio (MLPR) namely: pre-CPB (T(1)), after removal of aortic cross clamp (T(2)) and 30 minutes post-CPB (T(3)).

RESULTS

Baseline myocardial LPR strongly correlated with Troponin-I at T1 (σ: 0.6). Patients were sub grouped according to the median value of myocardial lactate (2.9) at baseline T1 into low myocardial lactate (LML) group, mean (2.39±0.4 mmol/l), n=19 and a high myocardial lactate (HML) group, mean (3.65±0.9 mmol/l), n = 21. A significant increase in PL, ML, MLPR and TropI occurred in both groups as compared to baseline. Patients in HML group had significant longer period of ICU stay. Patients with higher inotrope score had significantly higher ML (T2, T3). ML with a baseline value of 2.9 mmol/l had 70.83% sensitivity and 62.5% specificity (ROC area: 0.7109 Std error: 0.09) while myocardial pyruvate with a baseline value of 0.07 mmol/l has 79.17% sensitivity and 68.75% specificity (ROC area: 0.7852, Std error: 0.0765) for predicting inotrope requirement after CPB.

CONCLUSION

CS lactate, pyruvate and LP ratio correlate with myocardial function and can predict postoperative outcome.

Troponin I and Lactate From Coronary Sinus Predict Cardiac Complications After Myocardial Revascularization

BACKGROUND

Postoperative troponin I and lactate elevation are related to cardiac complications after myocardial revascularization. We sought to evaluate earlier predictive value for acute myocardial infarction (AMI) and myocardial damage of troponin I and lactate after myocardial revascularization.

METHODS

In all, 183 consecutive isolated myocardial revascularizations were prospectively enrolled in the study. Troponin I and lactate were sampled preoperatively and intraoperatively from the coronary sinus, and at 12, 24, 48, and 72 hours. Hospital outcome was recorded. Receiver operating curves for coronary sinus troponin I and lactate were constructed to differentiate patients with or without AMI and myocardial damage.

RESULTS

Acute myocardial infarction developed in 6 patients (3.2%), with higher troponin I and lactate at all time points (p < 0.05), longer intubation time (p = 0.003), intensive care unit stay (p = 0.001), hospital stay (p = 0.001), higher atrial fibrillation (p = 0.001), and worse ventricular function (p = 0.001). Myocardial damage developed in 6 patients (3.2%), showing higher troponin I at all time points (p < 0.001), higher intraoperative lactate (p = 0.04), longer intubation time (p = 0.005), and intensive care unit stay (p = 0.03). Receiver operating characteristic curves demonstrated coronary sinus troponin I greater than 0.94 microg/L (area under the curve [AUC] 0.820 +/- 0.075; sensitivity 90.0%, specificity 68.9%) as a better discriminator between patients with or without AMI than lactate level greater than 2.85 mmol/L (AUC 0.686 +/- 0.090; sensitivity 80.0%; specificity 72.9%); troponin I greater than 0.65 microg/L was a better discriminator between patients with or without myocardial damage (AUC 0.834 +/- 0.061; sensitivity 93.8%, specificity 71.5%), than lactate greater than 2.05 mmol/L (AUC 0.627 +/- 0.067; sensitivity 87.5%; specificity 70.7%).

CONCLUSIONS

Coronary sinus troponin I and lactate are predictive for cardiac complications after myocardial revascularization. Intraoperative biochemical assays should be routinely performed to establish preventative strategies to reduce further myocardial damage.

Intraoperative metabolic monitoring of the heart: II. Online measurement of myocardial tissue pH

Under conditions of ischemia, the hydrogen ion [H+] accumulates in the myocardial tissue in proportion to the magnitude of the ischemic insult. The accumulation of [H+] is the result of both increased anaerobic production of [H+] secondary to decreased substrate and decreased washout of [H+] secondary to decreased coronary perfusion. The Khuri tissue pH electrode/monitoring system has been developed and validated over the past two decades. Its scientific basis and correlates have been established, and it is the only system that has been approved for use in humans. Myocardial tissue pH has been monitored in the anterior and posterior walls of the left ventricle in more than 700 patients undergoing major cardiac surgery. An understanding of the relationship between pH and temperature and between the pH and [H+] in tissues is important for the proper interpretation of the myocardial pH data generated in the course of an operation. Intraoperative monitoring of myocardial pH is the only modality available to the cardiac surgeon for online assessment and improvement of the adequacy of myocardial protection. By defining myocardial protection in terms of protection from myocardial tissue acidosis, this technology provides a new tool with which the comparative efficacy of the various myocardial protection techniques can be assessed. It also provides an online tool for assessing the adequacy of coronary revascularization, and has the potential of improving procedures and outcomes for off-pump coronary artery bypass grafting.

Intraoperative metabolic monitoring of the heart: I. Clinical assessment of coronary sinus metabolites

Numerous clinical studies have corroborated the ability of intraoperative sampling of coronary sinus blood to measure changes in myocardial metabolism induced by ischemia and reperfusion. Among other changes, cardiac arrest induces a period of obligate myocardial lactate production that persists for an indeterminate amount of time after reperfusion. Coronary sinus lactate assays have been established as a standard method to compare various myocardial protection strategies. Current methodology requires detailed sample processing, precluding real-time feedback in the operating room. Newer devices hold promise in allowing the online assessment of myocardial metabolism; however, these methods await precise validation.

Cardiovascular effects of periodic occlusions of the upper airways in dogs

Hypoxemia and decreased intrathoracic pressure have been postulated as contributing causes of cardiovascular morbidity in obstructive sleep apnea syndrome (OSAS). Because of the difficulty of manipulating experimental conditions in humans, we developed an anesthetized closed-chest dog model, simulating the periodic airway occlusions of OSAS by periodic occlusions of the endotracheal tube (PUO). Using a periodicity of 60 s occluded, followed by 60 s ventilation for five to seven cycles, we measured heart rate (HR), cardiac output (CO), arterial pressure (Pa); left ventricular (LV) end-diastolic and end-systolic transmural pressure; dp/dt of LV pressure; left anterior descending (LAD) coronary blood flow (CBF), and regional myocardial contractility and intramyocardial pH. Four experimental conditions were studied: room air (RA) breathing (PO2 = 40); 100% O2 breathing (O2), and RA and O2 breathing with critical LAD stenosis (CS). Under all conditions PUO produced decreases in CO (10 to 30%) and proportional decreases in Pa. HR decreased, and in all but RA conditions stroke volume was unchanged. During the obstructed phase, indices of LV preload decreased. Indices of LV afterload also decreased except for LAD-perfused myocardium under RACS conditions. This latter was shown to be associated with regional ischemia (decreased regional pH and shortening). Regional ischemia was also demonstrated in two of nine dogs even under O2CS conditions. Among our major conclusions: (1) decreased Pa during PUO is due to decreased CO; (2) LV afterload does not increase during PUO; (3) with limited coronary flow reserve (CS), PUO can lead to myocardial ischemia. This is mostly but not solely due to hypoxia.