SYNTAX Score I is an anatomical scoring system that used for assessment of the complexity of coronary arteries and estimation of long-term mortality and MACCE post PCI; SSII combines both SSI and 8 clinical variables, for estimation of 4 years mortality following both CABG and PCI for individual patient and gives its recommendation about the best revascularization strategy for the patient (PCI, CABG, or both). The impact of these scores on the short-term results following CABG is still unclear.
We prospectively studied 150 patients with MVD, performed elective primary isolated CABG, to assess the impact of preoperative SYNTAX Scores on the short-term outcome. We followed up our patients for 90 days postoperatively (in hospital, visits, and phone calls), for onset of mortality, MI, stroke, mediastinitis, and need for RRT, then correlated the results obtained with the preoperatively calculated SYNTAX Scores and the preoperative clinical data. Table 2 summarizes the incidence of mortality and each of the studied complications in our study in 90-day follow-up period.
Does SSI, which reflects the anatomical complexity of the coronary arteries, affect the short-term outcome of CABG? This was the first question to be answered in our study. By reviewing the published studies in this topic, we found a little available data on the effect of SSI on the short-term results. Birim [10] and his colleagues searched the outcome of CABG in relation to SSI in 148 patients with LM disease, within 30 days and 1-year follow-up durations and found that the higher SSI was associated with greater incidence of mortality and MACCE within 30 days. Also, Alcazar [13] and his colleagues, when studied 716 patients with 3-vessel and/or LM disease, performed primary off pump CABG to evaluate the influence of SSI on both short- and long-term outcomes concluded that higher SSI is associated with higher in-hospital and long-term onset of MACCE but not with mortality.
In our study, we found a significant impact of SSI on short-term outcome, by founding a significant association between increased preoperative SSI and total 90 days mortality (mean ± SD = 30.75 ± 2.9) (P < 0.001), in-hospital mortality (mean ± SD = 31.63 ± 1.87) (P < 0.001), MI within 90-day follow-up (mean ± SD = 30.55 ± 4.79) (P = 0.015), and mediastinitis (mean ± SD = 27.70 ± 1.10) (P = 0.045).
Melina [14] and associates had another opinion, when they studied 191 patients with left ventricular dysfunction undergoing CABG with mean SSI was 32 ± 13, to assess the relation between the complexity of coronary arteries with short- and long-term outcome. They did not find a significant impact of SSI on the outcome in first 12-month follow-up but found that the greater complexity was associated with increased incidence of mortality and MACCE in 6-year follow-up duration. Moher [14] and his colleagues also found no impact of SSI on the postoperative outcome, within 2-year follow-up of SYNTAX cohort, who performed CABG in the original SYNTAX trial, and the outcome was related mainly to the completeness of revascularization, that was also, the main factor affected post CABG outcome in the study performed by Kato [15] and his working group, for the same purpose. These differences with our work may be due to the differences in study design, number of enrolled patients, associated comorbidities in each cohort, mean SSI for the study cohort, duration of the follow-up, and differences in the graft material and revascularization techniques.
The importance of SSII arises from its ability to individualize the decision making, by respecting the special patient-related clinical parameters that affect the outcome of surgery; Esper [11] and his colleagues performed a subgroup analysis of the patients enrolled in FREEDOM trial who received CABG and correlated their incidence of MACCE with preoperative SSI. They found a great impact of other factors, rather than SSI on the outcome of CABG in diabetic patients with MVD, as age and associated comorbidities. Finally, they recommended that SSI should not be used as the sole guiding tool, in choosing the revascularization strategy in diabetic patients and MVD.
In a multicenter trial conducted on 2961 patient performed isolated primary CABG, Gonzales [9] and his colleagues tried to assess the performance of STS Score, EuroSCORE II, and SSII in the prediction of both 30 days and 4 years mortalities. They found a better performance of EuroSCORE II and STS Score in prediction of 30 days mortality, while SSII was the most powerful predictor of long-term mortality.
Misumida [16] and his associates tested the prognostic value of SSII, when they retrospectively reviewed the data of 286 American Veterans with 3-vessel and/or LM disease performed either CABG or PCI. They compared the predicted 4 years mortality from SSII calculations with the observed 4 years mortality for the study population and found a well performance of SSII in estimation of 4 years mortality following both CABG and PCI at low and intermediate scores and underestimation of mortality in PCI group only with high scores.
In our study, we also found a prognostic value of preoperative SSII in evaluating the post CABG short-term outcome, as we found a significant association between increased preoperative SSII and in-hospital mortality (mean ± SD = 36.92 ± 6.63) (P = 0.007), total 90 days mortality (mean ± SD = 33.64 ± 9.07) (P = 0.043), and need for RRT (mean ± SD = 42.40 ± 13.50) (P = 0.012).
Should we respect SSII recommendations? Modolo [17] and his colleagues answered this question, when they reviewed SSII recommendations for the patients involved in EXCEL trial, and compared it with the actual treatment received, expected, and observed all causes mortality within 4 years. They found a higher observed mortality in the patients randomly assigned to PCI with SSII CABG recommendation, in comparison with their expected post CABG mortality, and reach the conclusion that non respect SSII CABG treatment recommendation was associated with higher mortalities. In our study, all patients were assigned to CABG with 14 of them had SSII PCI recommendation; among these patients, we had one in-hospital mortality from perioperative MI (7.1%).
Analysis of mortality in our study showed that we had 5.3% in-hospital mortality and 6.7% total 90 days mortality. Our incidence was near to the results of Alberto [18] and his colleges, when they investigated the risk factors of mortality in their series of 1628 CABG patients within 30-day follow-up. They had 30 days mortality rate 8.7%, with dialysis and neurological dysfunction were the main associated risk factors, while in our study MI was the main associated complication.
Also, our total mortality showed a significant association with SSI and SSII (P values were 0.014 and 0.048 respectively) in the results of its univariable analysis with the preoperative clinical data, while SSI appeared to be independent risk factor for mortality in the multivariable analysis (OR 1.192, 95% CI 1.018–1.396).
Diagnosis of MI in the perioperative period is challenging, with a wide range of incidence in the literatures, according to the methods and definitions used in its diagnosis. This point in particular, approved by Belly-Cote [19] and his colleges, when they used different biomarkers (CKMB, Troponins), to study the differences in both incidence and prognosis of post CABG MI, when different definitions based on different biomarkers used in its diagnosis; they found that not only the incidence was different, but also, the prognosis according to the biomarker that used for definition of MI.
Diagnosis of perioperative MI does not depend on a single parameter; a combination of ECG changes (ST elevation, new Q wave, new LBBB) with hemodynamic instability, ventricular arrhythmias, elevated biomarkers, and/or new RWMA in the echo, is diagnostic. In these cases, early coronary angiography is very important to confirm the diagnosis, detect the etiology (graft or non-graft related causes), and provide treatment (ad hoc PCI) [19,20,21].
In our study, we used CKMB/total CK ratio > 10%, as the biomarker for diagnosis of perioperative MI; this biomarker used also by Rupperchet [21] and his working group, when they retrospectively studied 108 patients, suffered from post CABG ischemia and performed early postoperative coronary angiography, to evaluate the impact of early coronary angiography in improving the outcome in the cases associated with post CABG ischemia.
We had a total incidence of MI in 90-day follow-up 6.7% and 4.6% in the perioperative period. In PREVENT IV study which included a total number of 3014 patients performed CABG, the investigators studied the incidence, mechanisms, and prognosis of MI in both perioperative period and 2-year follow-up; they found the incidence of perioperative MI in their series 9.8% [22].
All the previously mentioned studies and the recent guidelines on myocardial revascularization emphasize on the importance of coronary angiography, in cases with post CABG ischemia to improve the outcome. In our study, we relied only on the clinical, biochemical, and echo changes in diagnosis of MI in the perioperative period (lacking the facility of intraoperative or early postoperative angiography in our institute) and coronary angiography done for the patients who presented with late onset MI after hospital discharge. This issue demonstrates high incidence of mortalities, among the patients with MI in our series [3, 19,20,21,22].
Univariable analysis of MI incidence in relation to the preoperative clinical data showed a significant association with SSI (mean ± SD = 30.55 ± 4.79) (P = 0.020) that also appeared to be an independent risk factor for MI in the results of multivariable analysis (OR 1.182, 95% CI 1.016–1.375) (P = 0.030).
We did not find recent papers that discuss the association between SSI and perioperative MI as a separate entity, but many authors included MI as one of the components of MACCE in their studies of the relation between SSI and post CABG outcome as Birim [10], Alcazar [13], Melina [23], Mohr [14], and their colleagues. Their results already compared with our results in a previous part of discussion.
Lack of studies that investigate the relation between perioperative MI as a separate entity and SSI is considered as a point of strength in our study.
We had 3.3% of our patients stroked in 90-day follow-up period and 2.6% in the perioperative period; these numbers are near to the incidence in the literatures. We did not find a significant association between stroke incidence in our study population and any of the preoperative clinical factors included in the analysis [24].
The need for RRT in our study occurred in 2% of cases (3 patients), with no mortality among them. Ivert [25] and colleagues, on their series of 28,220 patients with primary isolated CABG, 0.6% of their patients needed a postoperative dialysis with 30 days mortality rate, among them was 26%. Ranucci [26] and his working group, during their analysis of 7675 adult patient undergoing on pump cardiac surgery, showed that 1.7% of their patients needed dialysis with mortality rate, among them was 46.9%. Absence of RRT associated mortality among our patients may be explained by the low number of cases, with a little chance for mortality to appear and/or early initiation of RRT in these patients that proved to be a very important factor in the reduction of mortality and improving the outcome, which is approved by a recently published meta-analysis on this topic [27].
Preoperative creatinine clearance, EuroSCORE II, and SSII of our study population showed a significant association with need for RRT (P values = 0.045, 0.006, 0.027 respectively) when the univariable analysis of RRT with the preoperative clinical data was done, but none of them appeared as independent risk factor for RRT in the result of multivariable analysis.
Incidence of mediastinitis among our patients was 3.3%; this incidence coincides with the results of Oliviera group [28] when they studied 1322 cases undergoing CABG and found the incidence of mediastinitis among their patients was 4.2%.
The results of univariable analysis of mediastinitis incidence with the preoperative clinical data showed a significant association between mediastinitis with age and EuroSCORE II (P = 0.019, 0.006 respectively), but none of them could be considered as independent risk factor of mediastinitis.
The strong relation between SSI and short-term outcome especially mortality and MI in our study may be explained by increased anatomical complexity of CAD is associated with technical difficulties as increased procedure time, number of grafts, and need for endarterectomy with target vessel reconstruction; all these are associated with increased mortality and morbidity. Also, increased SSI is always associated with poor distal run off in the native coronaries that contributes to a subsequent graft occlusion. These factors explain the higher incidence of mortalities and MI associated with high SSI (short-term complications that related mainly to anatomical complexity and technical factors).
Despite increased SSII is associated with significant increase in the mortality, it is less powerful than SSI in prediction of short-term post CABG outcome. We explained it by the fact that SSII value is affected by both SSI and the clinical situation of the patient. For example, a patient with high SSI and few comorbidities will have low SSII, while those with low SSI and multiple comorbidities will have high SSII. On the other hand, increased SSI is associated with more technical difficulties and procedure time with their impact on short-term outcome and vice versa.
