Discussion:
To the best of our knowledge, this is the first study presenting reduced graft blood flow results in obese patients which also correlate with increased NLR and PLR. Medium 2-year results (897 +/- 123 days) were satisfactory in obese group despite significant differences in arterial grafts flow.
According to our study, obesity was not a significant risk factor for higher perioperative mortality after coronary artery bypass grafting which is consistent with previous with previous reports [13.14]. Our results of OPCAB suggest an underestimated value of low blood flow velocity in obesity-related grafts. The mean values of arterial grafts blood flow in obese and non-obese patients were significantly different in our study with mean values of 6 mL/min (4-13) vs 15 mL/min (8-27) and 10 mL/min (3-13) vs 18mL/min (9-25) in RIMA and LIMA, respectively. The differences in grafts’ blood flow were not related to maximum values of postoperative Troponin-I serum levels 3.62 (1.01 – 25.25) mcg/L vs 3.37 (2.37 – 9.16) mcg/L in obese and non-obese patients, respectively (p=0.07414).
We showed statistically significant difference between blood flow measurements between overweight and non-overweight patients. Coronary blood flow measurements can be regarded as one of the significant risk factors for cardiovascular complications in obese patients since coronary microvascular dysfunction is superior to BMI in risk prediction [15]. Coronary arteries diameter and flow velocity are two determinants of myocardial oxygen supply requirements [16]. Both the blood flow and troponin serum levels are believed to be strong indicators of future major adverse cardiovascular events [17-19]. There was no case of periprocedural myocardial infarction in our study group. We revealed a reduced graft flow in obese patients which was not related to periprocedural ischemia/injury.
During off-pump surgery, the intraluminal shunts are used to facilitate performance of anastomosis. The non-significant difference in diameters of shunts used allow to conclude that the results obtained in graft blood flow measurement are not related to diameters or wall quality of coronary arteries. The mean values of shunts applied during anastomoses presented in Table 2 confirm the hypothesis that not a coronary artery diameter is responsible for diminished blood flow but chronic inflammatory processes presented by NLR and PLR. Obese patients presented higher NLR with mean values of 3.5 +/- 1.3 vs 2.7 +/- 1 (p=0.0312). The PLR results, second indirect marker of inflammation, were also significantly different between obese and normal weight patients with mean values of 221 +/- 81 vs 142 +/- 60 (p=0.0003), respectively. The unique nature of the inflammatory response to obesity was already postulated sharing some similarities with other chronic inflammatory processes. This trigger provoked by energy homeostasis disruption over time leads to maladaptive response [20].
Osadnik et al compared NLR and PLR results as significant factors of chronic inflammation between obese and non-obese patients [21]. The increased NLR and PLR were characteristic for obese patients in present study. The reduced blood flow reserve in chronic inflammatory states have already been observed [22.23].
Our study results present the blood flow significant differences in coronary grafts between obese and non-obese patients. Analysis based on patients who underwent arterial revascularization as possible best option with satisfactory long-term graft patency rates though recent studies indicate more further studies [24]. The significant difference noted can be explained with a correlation between BMI and increased inflammatory parameters as a sign of inflammatory state. BMI results were correlated with PLR and NLR ratios. There was as inverse correlation observed between PLR (chronic inflammatory marker) and mean diameters of the anastomosed coronary artery.
Previous reports suggested that the increased level of serum CRP (C-reactive protein) was a possible trigger for intimal hyperplasia and risk for calcification in grafts applied during coronary artery bypass grafting procedures [24]. Subclinical atherosclerosis estimated by intimal thickening of arteries is related to serum adiponectin levels in obese patients [25]. These reports are presenting a possible explanation of our results and confirm our hypothesis of chronic inflammation as a causative agent. In a multicenter analysis, Schwann confirmed the correlation between higher mortality and morbid obesity in early and long-term periods and a partial protective role of “the obesity paradox” in the early and intermediate postoperative periods in overweight and mildly obese patients [26]. The poorer long-term results following coronary artery bypass grafting (increased 5-year and 10-year mortality rates) in obese patients were also observed despite the immediate good survival rates [27].
There is a considerable body of evidence suggesting that endothelial signals modulate the blood flow [27] and may therefore be responsible for the discrepancy between obese and non-obese patients presented in our results.
Study limitation is related to retrospective analysis of small sample group who underwent arterial coronary artery bypass grafting performed as single center study related to midterm results.