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.