Pathology-related changes in cardiac energy metabolites, inflammatory response and reperfusion injury following cardioplegic arrest in patients undergoing open-heart surgery

Abstract

Introduction: Changes in cardiac metabolites in adult patients undergoing open-heart surgery using ischemic cardioplegic arrest have largely been reported for non-ventricular tissue or diseased left ventricular tissue, with few studies attempting to assess such changes in both ventricular chambers. It is also unknown whether such changes are altered in different pathologies or linked to the degree of reperfusion injury and inflammatory response. The aim of the present work was to address these issues by monitoring myocardial metabolites in both ventricles and to establish whether these changes are linked to reperfusion injury and inflammatory/stress response in patients undergoing surgery using cold blood cardioplegia for either coronary artery bypass graft (CABG, n = 25) or aortic valve replacement (AVR, n = 16).

Methods: Ventricular biopsies from both left (LV) and right (RV) ventricles were collected before ischemic cardioplegic arrest and 20 min after reperfusion. The biopsies were processed for measuring selected metabolites (adenine nucleotides, purines, and amino acids) using HPLC. Blood markers of cardiac injury (Troponin I, cTnI), inflammation (IL- 6, IL-8, Il-10, and TNFα, measured using Multiplex) and oxidative stress (Myeloperoxidase, MPO) were measured pre- and up to 72 hours post-operatively.

Results: The CABG group had a significantly shorter ischemic cardioplegic arrest time (38.6 ± 2.3 min) compared to AVR group (63.0 ± 4.9 min, p = 2 x 10^-6). Cardiac injury (cTnI release) was similar for both CABG and AVR groups. The inflammatory markers IL-6 and Il-8 were significantly higher in CABG patients compared to AVR patients. Metabolic markers of cardiac ischemic stress were relatively and significantly more altered in the LV of CABG patients. Comparing diabetic and non-diabetic CABG patients shows that only the RV of diabetic patients sustained major ischemic stress during reperfusion and that diabetic patients had a significantly higher inflammatory response.

Discussion: CABG patients sustain relatively more ischemic stress, systemic inflammatory response and similar injury and oxidative stress compared to AVR patients despite having significantly shorter cross-clamp time. The higher inflammatory response in CABG patients appears to be at least partly driven by a higher incidence of diabetes amongst CABG patients. In addition to pathology, the use of cold blood cardioplegic arrest may underlie these differences.

Keywords: aortic valve replacement (AVR); cardioplegia; coronary artery bypass graft (CABG); ischaemic reperfusion injury; metabolites.

Figure 1

Metabolic ischemic stress in CABG and AVR patients. Values are mean ± SEM for ATP/ADP (A), ATP/AMP (B), Ala/Glu (C), and Energy charge (D) in left (LV) and right (RV) ventricles of patients pre- (white) and post- (black) cardioplegic arrest in CABG or AVR surgery. ^*Represents a significant difference vs. corresponding pre samples (unpaired two-tailed student's t-test or Mann-Whitney U-test as appropriate).

Figure 2

Diabetes and metabolic ischemic stress during surgery in CABG patients. Values are mean ± SEM for ATP/ADP (A), ATP/AMP (B), Ala/Glu (C), and Energy charge (D) in left (LV) and right (RV) ventricles of patients Pre- (white) and Post- (black) CABG surgery who are non-diabetic or diabetic. *Represents a significant difference vs. corresponding Pre samples (unpaired two-tailed student's t-test or Mann-Whitney U-test as appropriate).

Figure 3

Cardiac injury and systemic oxidative stress in CABG and AVR patients. Pre- and post-operative levels of (A) troponin I (ng/L) and (B) MPO (ng/ml) in patients undergoing CABG (white) or AVR (black) surgery. Values are mean ± SEM for CABG or AVR. Two-way mixed model ANOVA for (A) revealed a significant interaction between time and operation type but no significance differences from post-hoc testing and for (B) revealed no significant differences. One-way ANOVAs with post-hoc Dunnett's test where appropriate were also performed individually for each surgery type; + represents a significant difference compared to basal levels within the same group. No statistical significance was found for the AUC (area under the curve) analyses (unpaired two-tailed student's t-test or Mann-Whitney U-test as appropriate).

Figure 4

Cardiac injury and oxidative stress in diabetic and non-diabetic CABG patients. Values are mean ± SEM for 'levels of (A) troponin I (ng/L) and (B) MPO (ng/ml) in patients undergoing CABG surgery who are non-diabetic (ND, white) or diabetic (D, black). No significant differences were revealed by two-way mixed model ANOVA. One-way ANOVAs with post-hoc Dunnett's test where appropriate were also performed individually for each surgery type; + represents a significant difference compared to basal levels. No statistical significance was found for the AUC (area under the curve) analyses (unpaired two-tailed student's t-test or Mann-Whitney U-test as appropriate).

Figure 5

Postoperative changes in inflammatory markers in CABG and AVR patients. Values (pg/ml) are mean ± SEM for levels of IL-10 (A), IL-6 (B), IL-8 (C), and TNF-α (D), in patients undergoing CABG (white) or AVR (black) surgery. Analysis by two-way mixed model ANOVA did not reveal any significant differences for (A) or (D), whilst in (B), and (C) a significant interaction was found between time and operation type; * represents a significant effect of operation type (CABG vs. AVR) at individual timepoints. One-way ANOVAs with post-hoc Dunnett's test where appropriate were also performed individually for each surgery type; + represents a significant difference compared to basal levels. AUC (area under the curve) was analyzed using unpaired two-tailed student's t-test or Mann-Whitney U-test as appropriate; *Represents a significant difference between groups.

Figure 6

Effect of diabetes on postoperative changes in inflammatory markers. Values (pg/ml) are mean ± SEM for levels of IL-10 (A), IL-6 (B), IL-8 (C), and TNF-α (D), in patients undergoing CABG surgery who are non-diabetic (ND, white, n = 12) or diabetic (D, black, n = 12). Analysis by two-way mixed model ANOVA did not reveal any significant differences for (A) or (B), whilst the horizontal bracket in (C) and (D) represents a significant “between subjects effect” over all timepoints. One-way ANOVAs with post-hoc Dunnett's test were appropriate were also performed individually for non-diabetic and diabetic patients; + represents a significant difference compared to basal levels. AUC (area under the curve) was analyzed using unpaired two-tailed student's t-test or Mann-Whitney U-test as appropriate; *Represents a significant difference between groups.