Abstract
Purpose
There has been debate whether off pump coronary artery bypass surgery (OPCAB) has results comparable to conventional on pump bypass surgery. This has led to the low uptake of OPCAB in the West. In India, OPCAB is the default mode of coronary revascularization. However, there is scarce data on mid-term outcomes of OPCAB in our patients. This study aims to evaluate both short and mid-term mortality and analyze factors associated with mortality.
Methods
This is a single center study of all consecutive patients undergoing isolated OPCAB from October 2014 to December 2019. Patient data was collected from hospital records and follow-up was from the hospital electronic medical records and telephone interviews. Mortality and factors contributing to survival were analyzed.
Results
Operative mortality was 2.3%. Mid-term mortality was 5.5%. Preoperative renal dysfunction, post-operative renal failure, use of the intra-aortic balloon pump (IABP), re-exploration for bleeding, postoperative stroke, ventilation > 24 h, and postoperative atrial fibrillation were associated with operative mortality. Factors associated with mid-term mortality were age > 62 years, postoperative renal failure, IABP usage, ventilation time > 24 h, and postoperative atrial fibrillation. The mean survival time was 2343.55 + / − 15.27 days and 6-year survival was 88.7%.
Conclusion
OPCAB can safely be performed with satisfactory short and mid-term outcomes. Further corroborative studies from different regions of the country or a multi-center study will help to establish the suitability of the technique in Indian patients.
Keywords: Off pump coronary artery bypass surgery, Mid-term outcomes, Survival
Introduction
Coronary artery bypass graft surgery (CABG) remains the gold standard for coronary artery revascularization, especially in patients with left main disease, diabetes and left ventricular (LV) dysfunction. With the development of cardiac stabilizers, off-pump coronary artery bypass surgery (OPCAB) was taken up in larger numbers as a means to avoid the deleterious effects of extracorporeal circulation [1]. However, the increased technical challenge of the procedure when compared to conventional on pump CABG and the failure of robust data to show any significant benefit of OPCAB are the main reasons for its low adoption worldwide [2–4]. Moreover, the conflicting results of OPCAB in the literature led to suggestions that it should be abandoned [5]. But most of the literature for substantiating this claim were based on data from western patients which may not be relevant in the Indian context.
OPCAB is the default technique of CABG in India and Japan [6]. Coronary artery disease in Indian patients is different from western patients due to the smaller size of the coronaries, an increased incidence of diffuse disease, higher incidence of diabetes, and the tendency for early calcification of atheromatous plaques and more incidence of acute coronary syndrome prior to revascularization and higher prevalence of ischemic cardiomyopathy [7]. These factors make the performance of CABG, especially OPCAB more challenging with the potential for suboptimal results in short and long-term. But the data on outcomes of OPCAB in India is sparse and is mainly restricted to early outcomes of surgery [8–10]. It is obvious that there is a need for data on longer term follow-up of OPCAB patients to establish the appropriateness of the technique in Indian patients. Hence, this study was undertaken to fill the existing gap in knowledge regarding the outcomes of OPCAB in a large cohort of patients.
The primary objective of the study was to assess the early and mid-term outcomes of OPCAB. The secondary outcome was assessment of factors associated with early and late mortality.
Materials and methods
This is a retrospective study with prospective collection of data of 1789 consecutive patients who underwent isolated OPCAB from October 2014 to December 2019 at a single tertiary level cardiac surgical center situated at a university hospital in South India. Inclusion criteria for the study was all adult patients age > 18 years who underwent isolated OPCAB surgery in our institution during the study period. Patients having associated procedures and patients who had an intraoperative OPCAB conversion to on pump CABG were excluded from the study.
Retrospective part
Data was retrieved from the department database and from the hospital electronic medical records (EMR). Operative mortality was calculated and factors potentially contributing to the mortality were analyzed.
Prospective part
Follow-up survival was done by means of outpatient follow-up records in the EMR and if no recent follow-up (< 3 months) was present in the EMR, then telephone interviews were done to determine the overall survival. The study was conducted during the months of April and May 2022 and the cut-off date for follow-up was set as May 31, 2022. Follow-up time was defined from the date of surgery to death or the cut-off date of follow-up. One hundred twenty-four (6.9%) patients were lost to follow-up. Lost to follow-up patients’ data from the hospital records were gathered up to their last follow-up and were included in the study. Factors contributing to survival were also analyzed.
The study was conducted in full conformance with the principles of the “Declaration of Helsinki” (as amended at the 56th World Medical Association General Assembly, Tokyo, Japan, 2008). The hospital Institutional Review Board approved the study and the need for individual patient consent was waived off.
Definition of variables
Operative mortality was defined as 30-day or in hospital mortality. Mid-term mortality was defined as death during a mean follow-up period of 3.9 ± 1.58 years (0.1–6.9 years). Preoperative renal dysfunction was defined as a creatinine clearance of < 60 ml/min/1.73 m2 or chronic kidney disease (stages 3, 4, or 5) based on the National Kidney Foundation Classification [11]. Postoperative renal dysfunction was defined as a rise of serum creatinine of 0.3 mg/dl in the first 48 h as per The Kidney Disease: Improving Global Outcomes (KDIGO) definition of acute kidney injury [11]. Postoperative renal failure was defined as the need for dialysis postoperatively in a patient not previously on dialysis. Timing of surgery was classified as elective or urgent as per the EuroSCORE II definition [12]. Carotid stenosis was defined as narrowing of vessel by greater than 50% on the preoperative duplex scan.
Anesthetic and surgical techniques
Anesthesia followed a standard protocol of induction and maintenance. Anticoagulation was achieved with heparin at a dose of 2 mg/kg targeting an activated clotting time > 300 s. Intraoperatively, transesophageal echocardiography and pulmonary artery catheters were used in all patients as standard protocol. All the procedures were performed through median sternotomy. Conduits used were the internal mammary artery, radial artery, and saphenous vein. A suction-type stabilizer (Octopus 4.3; Medtronic, Minneapolis, MN, USA) was used to facilitate the surgery. Intracoronary shunts and carbon dioxide blower were used in all patients.
Statistical analysis
Data were compiled by using Microsoft Excel 2010 version and analyzed with IBM SPSS 20.0 version (SPSS Inc, Chicago, USA). The results are either given in mean ± SD for continuous variables or as a percentage for categorical variables. To analyze the association of each variable with 30-day mortality and mid-term mortality, the chi-square test/Fisher’s exact test (wherever applicable) for categorical variables and the independent t-test for continuous variables were applied. To determine the pre-operative and post-operative risk factors for mortality, univariate analysis and binary logistic regression analysis were used. To find the survival probability of overall survival and event free survival, Kaplan–Meier test was used and the Cox proportional hazard regression was used to calculate the adjusted hazard ratio with 95% confidence interval. A p value of < 0.05 was considered statistically significant.
Results
A total of 1789 patients underwent isolated OPCAB surgery during the above time period. The overall OPCAB rate in the department during this study period was 96.8% and 33 patients (1.8%) had an intraoperative conversion to on-pump CABG.
The mean EuroSCORE II of the study group was 1.97 ± 2.26. Operative mortality was 2.3% (41 patients). The mid-term mortality was 5.5% (100 patients). Tables 1 and 2 show the demographic profile and the association of pre and postoperative variables with operative mortality by univariate analysis. In multivariate analysis, preoperative renal dysfunction (HR 4.17 95% CI 1.23–14.11), post-operative renal failure (HR 29.43 95% CI 7.35–117.92), use of the intra-aortic balloon pump (IABP) (HR 6.30 95% CI 1.97–20.10), re-exploration for bleeding (HR 9.27 95% CI 2.57–33.42), postoperative stroke (HR 6.23 95% CI 1.35–28.65), ventilation > 24 h (HR 3.99 95% CI 1.48–10.77), and postoperative atrial fibrillation (HR 3.60 95% CI 1.43–9.06) were found to be the significant factors associated with operative mortality (Table 3).
Table 1.
Association of pre-operative variables with 30-day mortality
| Variables | n = 1789 | Alive n (%) |
Dead n (%) |
p value |
|---|---|---|---|---|
| Age > 62 years | 859 | 830 (96.6) | 29 (3.4) | 0.001* |
| Female | 331 | 322 (97.3) | 9 (2.7) | 0.565 |
| Emergency | 399 | 382 (95.7) | 17 (4.3) | 0.003* |
| EuroSCORE II (%) | ||||
| < 3 | 1400 | 1383 (98.8) | 17 (1.2) | < 0.001* |
| 3–6 | 178 | 166 (93.3) | 12 (6.7) | < 0.001* |
| > 6 | 46 | 38 (82.6) | 8 (17.4) | < 0.001* |
| Diabetes mellitus | 1194 | 1164 (97.5) | 30 (2.5) | 0.377 |
| Hypertension | 1286 | 1254 (97.5) | 32 (2.5) | 0.374 |
| Dyslipidemia | 763 | 743 (97.4) | 20 (2.6) | 0.422 |
| COPD | 127 | 121 (95.3) | 6 (4.7) | 0.057 |
| PVD | 51 | 46 (90.2) | 5 (9.8) | < 0.001* |
| Carotid stenosis | 50 | 49 (98.0) | 1 (2.0) | 1.000 |
| Renal dysfunction | 867 | 833 (96.1) | 34 (3.9) | < 0.001* |
| Renal failure | 10 | 6 (60.0) | 4 (40.0) | < 0.001* |
| Stroke | 54 | 51 (94.4) | 3 (5.6) | 0.124 |
| Myocardial infarction | 745 | 723 (97.0) | 22 (3.0) | 0.148 |
| NSR | 1772 | 1732 (97.7) | 40 (2.3) | 0.327 |
| Good LVEF (> 60%) | 1143 | 1131 (99.0) | 12 (1.0) | < 0.001* |
| Mild LVEF(45–60%) | 315 | 305 (96.8) | 10 (3.2) | 0.249 |
| Moderate LVEF (35–45%) | 222 | 214 (96.4) | 8 (3.6) | 0.163 |
| Severe LVEF(< 35%) | 109 | 98 (89.9) | 11 (10.1) | < 0.001* |
Significant p value < 0.05*. n, number of patients; COPD, chronic obstructive pulmonary disease; PVD, peripheral vascular disease; NSR, normal sinus rhythm; LVEF, left ventricular ejection fraction
Table 2.
Association of post-operative variables with 30-day mortality
| Variables | n = 1789 | Alive n (%) |
Dead n (%) |
p value |
|---|---|---|---|---|
| ICU stay (> 3 days) | 443 | 417 (94.1) | 26 (5.9) | < 0.001* |
| Hospital stay (> 7 days) | 712 | 693 (97.3) | 19 (2.7) | 0.387 |
| Inotropic support (> 24 h) | 695 | 660 (95.0) | 35 (5.0) | < 0.001* |
| LIMA graft | 1764 | 1724 (97.7) | 40 (2.3) | 0.442 |
| Second artery graft | 149 | 148 (99.3) | 1 (0.7) | 0.251 |
| Ventilation hours (> 24 h) | 127 | 100 (78.7) | 27 (21.3) | < 0.001* |
| Reexploration | 52 | 42 (80.8) | 10 (19.2) | < 0.001* |
| Renal dysfunction | 166 | 151 (91.0) | 15 (9.0) | 0.001* |
| Renal failure | 21 | 8 (38.1) | 13 (61.9) | < 0.001* |
| Stroke | 22 | 17 (77.3) | 5 (22.7) | < 0.001* |
| IABP usage | 30 | 17 (56.7) | 13 (43.3) | < 0.001* |
| PoAF | 311 | 283 (91.0) | 28 (9.0) | < 0.001* |
| Mediastinitis | 28 | 25 (89.3) | 3 (10.7) | 0.025* |
| Surgical site infection | 127 | 132 (96.4) | 5 (3.6) | 0.269 |
| Blood stream infection | 34 | 30 (88.2) | 4 (11.8) | 0.007* |
| Therapeutic antibiotics | 192 | 169 (88.0) | 23 (11.8) | < 0.001* |
Significant p value < 0.05*. n, number of patients; ICU, intensive care unit; LIMA, left internal mammary artery; RIMA, right internal mammary artery; IABP, intra-aortic balloon pump; PoAF, post-operative atrial fibrillation
Table 3.
Multivariate analysis — risk factors for 30-day mortality
| Variables | B | Wald | Multivariate analysis | |
|---|---|---|---|---|
| HR (95% of CI) | p value | |||
| Post-operative renal failure | 3.38 | 22.81 | 29.43 (7.35–117.92) | < 0.001* |
| Re-exploration | 2.23 | 11.59 | 9.27 (2.57–33.42) | < 0.001* |
| IABP usage | 1.84 | 9.66 | 6.30 (1.97–20.10) | < 0.001* |
| Post-operative stroke | 1.83 | 5.52 | 6.23 (1.35–28.65) | 0.02* |
| Pre-operative renal dysfunction | 1.43 | 5.25 | 4.17 (1.23–14.11) | 0.02* |
| Ventilation > 24 h | 1.38 | 7.44 | 3.99 (1.48–10.77) | 0.01* |
| PoAF | 1.28 | 7.42 | 3.60 (1.43–9.06) | 0.01* |
Significant p value < 0.05*. HR, hazard ratio; CI, confidence interval; IABP, intra-aortic balloon pump; PoAF, post-operative atrial fibrillation
The association of preoperative and postoperative variables with mid-term mortality is shown in Tables 4 and 5. Multivariate analysis showed age > 62 years (HR 3.59 95% CI 1.14–11.29), postoperative renal failure (HR 30.81 95% CI 6.25–151.96), IABP usage (HR 13.24 95% CI 3.92–44.71), ventilation time > 24 h (HR 6.40 95% CI 2.49–16.44), and postoperative atrial fibrillation (HR 3.02 95% CI 1.22–7.51) to be the factors significant for mid-term mortality (Table 6).
Table 4.
Association of pre-operative variables with mid-term mortality
| Variables | n = 1624 | Alive n (%) |
Dead n (%) |
p value |
|---|---|---|---|---|
| Age > 62 years | 767 | 701 (91.4) | 66 (8.6) | 0.002* |
| Female | 295 | 277 (93.9) | 18 (6.1) | 0.926 |
| Emergency | 363 | 348 (95.9) | 15 (4.1) | 0.062 |
| EuroSCORE II (%) | ||||
| < 3 | 1290 | 1244 (96.4) | 46 (3.6) | < 0.001* |
| 3–6 | 153 | 123 (80.4) | 30 (19.6) | < 0.001* |
| > 6 | 30 | 22 (73.3) | 8 (26.7) | < 0.001* |
| Diabetes mellitus | 1084 | 1013 (93.5) | 71 (6.5) | 0.434 |
| Hypertension | 1169 | 1094 (93.6) | 75 (6.4) | 0.599 |
| Dyslipidemia | 694 | 654 (94.2) | 40 (5.8) | 0.511 |
| COPD | 113 | 102 (90.3) | 11 (9.7) | 0.109 |
| PVD | 43 | 38 (88.4) | 5 (11.6) | 0.137 |
| Carotid stenosis | 46 | 43 (93.5) | 3 (6.5) | 0.761 |
| Renal dysfunction | 763 | 684 (89.6) | 79 (10.4) | < 0.001* |
| Renal failure | 5 | 3 (60.0) | 2 (40.0) | 0.034* |
| Stroke | 43 | 38 (88.4) | 5 (11.6) | 0.137 |
| Myocardial infarction | 669 | 620 (92.7) | 49 (7.3) | 0.123 |
| NSR | 1609 | 1510 (93.8) | 99 (6.2) | 0.238 |
| Good LVEF (> 60%) | 1051 | 1013 (96.4) | 38 (3.6) | < 0.001* |
| Mild LVEF(45–60%) | 286 | 260 (90.9) | 26 (9.1) | 0.027* |
| Moderate LVEF (35–45%) | 195 | 175 (98.7) | 20 (10.3) | 0.013* |
| Severe LVEF(< 35%) | 92 | 75 (81.5) | 17 (18.5) | < 0.001* |
Significant p value < 0.05*. n, number of patients; COPD, chronic obstructive pulmonary disease; PVD, peripheral vascular disease; NSR, normal sinus rhythm; LVEF, left ventricular ejection fraction
Table 5.
Association of post-operative variables with mid-term mortality
| Variables | n = 1624 | Alive n (%) |
Dead n (%) |
p value |
|---|---|---|---|---|
| ICU stay (> 3 days) | 383 | 335 (87.5) | 48 (12.5) | < 0.001* |
| Hospital stay (> 7 days) | 636 | 577 (90.7) | 59 (9.3) | < 0.001* |
| Inotropic support (> 24 h) | 607 | 548 (90.3) | 59 (9.7) | < 0.001* |
| LIMA graft | 1604 | 1511 (94.2) | 93 (5.8) | < 0.001* |
| Second artery graft | 137 | 134 (97.8) | 3 (2.2) | 0.041* |
| Ventilation hours (> 24 h) | 90 | 73 (81.1) | 17 (18.9) | < 0.001* |
| Reexploration | 39 | 35 (89.7) | 4 (10.3) | 0.300 |
| Renal dysfunction | 140 | 120 (85.7) | 20 (14.3) | < 0.001* |
| Renal failure | 6 | 4 (66.7) | 2 (33.3) | 0.049* |
| Stroke | 1610 | 1511 (93.9) | 99 (6.1) | 0.215 |
| IABP usage | 15 | 11 (73.3) | 4 (26.7) | 0.011* |
| PoAF | 263 | 234 (89.0) | 29 (11.0) | < 0.001* |
| Mediastinitis | 22 | 16 (72.7) | 6 (27.3) | < 0.001* |
| Surgical site infection | 120 | 102 (85.0) | 18 (15.0) | < 0.001* |
| Blood stream infection | 30 | 24 (80.0) | 6 (40.0) | 0.002* |
| Therapeutic antibiotics | 154 | 130 (84.4) | 24 (15.6) | < 0.001* |
Significant p value < 0.05*. n, number of patients; ICU, intensive care unit; LIMA, left internal mammary artery; IABP, intra-aortic balloon pump; PoAF, post-operative atrial fibrillation
Table 6.
Multivariate analysis — risk factors for mid-term mortality
| Variables | B | Wald | Multivariate analysis | |
|---|---|---|---|---|
| HR (95% of CI) | p value | |||
| Postoperative renal failure | 3.43 | 17.72 | 30.81 (6.25–151.96) | < 0.001* |
| IABP usage | 2.58 | 17.30 | 13.24 (3.92–44.71) | < 0.001* |
| Ventilation > 24 h | 1.86 | 14.90 | 6.40 (2.49–16.44) | < 0.001* |
| Age > 62 years | 1.28 | 4.79 | 3.59 (1.14–11.29) | 0.029* |
| PoAF | 1.11 | 5.68 | 3.02 (1.22–7.51) | 0.017* |
Significant p value < 0.05*. HR, hazard ratio; CI, confidence interval; IABP, intra-aortic balloon pump; LIMA, left internal mammary artery; PoAF, post-operative atrial fibrillation
The mean number of grafts received for all patients during the study period was 3.54 ± 0.8. The patients who were alive received 3.54 ± 0.81 grafts compared to 3.56 ± 0.67 grafts for patients who died (p value 0.852). At mid-term follow-up, patients who were alive received 3.54 ± 0.81 grafts while patients who had died received 3.46 ± 0.75 grafts which was also not statistically significant (p value 0.26).
The mean follow-up period of the study was 3.9 ± 1.58 years. Follow-up of the 1624 patients is shown in Table 7. Two hundred fifty-seven (15.8%) patients had a readmission after surgery and 39 (2.4%) patients underwent a repeat revascularisation. Analysis of follow-up outcomes with mid-term mortality showed heart failure, myocardial infarction, renal dysfunction, stroke, and readmission to be associated with mortality. Analysis of the effect of age on operative and mid-term mortality showed that the transition in mortality occurred in the 60–69 age group and the mortality significantly increased in patients above 80 years of age.
Table 7.
Association of follow-up outcomes with mid-term mortality
| Variables | n = 1624 | Alive n (%) |
Dead n (%) |
p value |
|---|---|---|---|---|
| Heart failure | 20 | 14 (70.0) | 6 (30.0) | < 0.001* |
| Angina | 38 | 38 (100.0) | 0 (0) | 0.167 |
| Myocardial infarction | 39 | 9 (23.1) | 30 (76.9) | < 0.001* |
| Renal dysfunction | 35 | 27 (77.1) | 8 (22.9) | < 0.001* |
| Renal failure | 9 | 8 (88.9) | 1 (11.1) | 0.440 |
| Stroke | 25 | 16 (64.0) | 9 (36.0) | < 0.001* |
| Revascularization | 39 | 38 (97.4) | 1 (2.6) | 0.510 |
| Readmission | 257 | 212 (82.5) | 45 (17.5) | < 0.001* |
Significant p value < 0.05*. n, number of patients
The mean survival time was 2343.55 + / − 15.27 days. One-year survival was 96.2%, 2-year survival 94.8%, 3-year survival was 93.8%, 4-year survival was 91.8%, 5-year survival was 90.4%, and 6-year survival was 88.7% (Fig. 1). In event free survival analysis, mean survival time was 1952.28 + / − 25.08 days and 1-year survival was 84.3%, 2-year survival was 80.6%, 3-year survival was 78.1%, 4-year survival was 75.3%, 5-year survival was 73.5%, and 6-year survival was 70.8% (Fig. 2).
Fig. 1.
Overall survival analysis
Fig. 2.
Event-free analysis
Discussion
The main finding of our study was that OPCAB was associated with acceptable early results with good midterm overall survival and event free survival. The average age of patients in our series was 61.68 years and 81.5% were male. The predominance of males undergoing CABG is similar in the literature, with a large cohort of patients followed at the Cleveland Clinic showing a male predominance of 81% in their series and a recent STS database analysis showed that 75% of patients undergoing isolated CABG were males [8, 9, 13, 14]. The incidence of diabetes in patients in our study was 66.7% and is much higher than what is reported in the literature. In China which has the highest prevalence of diabetes in the world, the incidence of diabetes in a patient cohort undergoing CABG was only 31.8% whereas in North America the proportion of CABG patients who are diabetic had increased from 40.4 to 47.8% over the last decade [14–16].
The left internal mammary artery (LIMA) graft was used in 98.6% of the patients which compares favorably with what is reported from the STS database at 96.7% [14]. A second arterial graft was used in only 8.3% of the patients. Post-operative new onset atrial fibrillation (POAF) in our study was 21% which was much lower than the Society of Thoracic Surgery (STS) reported incidence of 27.4% [17]. We had earlier reported about this lower incidence of POAF in our population of patients undergoing OPCAB [10]. But the incidence of POAF in our study group was higher than reported by other studies in Indian patients [17]. The exact reasons for this are unclear and probably may be related to the higher mean age of our patients compared to other studies in Indian patients. The incidence of postoperative stroke was 1.2% which is lower than the reported incidence of postoperative stroke in the STS database at 1.45 [18].
Factors found to be associated with operative mortality on multivariate analysis were preoperative renal dysfunction, re-exploration, usage of IABP, postoperative stroke, postoperative renal dysfunction, ventilation > 24 h, and post-operative atrial fibrillation. Dialysis dependent renal failure, severe LV dysfunction and mediastinitis though significantly associated with operative mortality on univariate analysis did not find significance on multivariate analysis.
The association of preoperative renal dysfunction with operative mortality has been reported earlier. Lv et al. had concluded that the presence of occult preoperative renal dysfunction defined as a creatinine clearance < 60 ml/min/1.73 m2 had a higher operative mortality with an OR of 2.884; (95% CI 1.293–6.432) [19, 20].
The incidence of re-exploration in our study was 2.9%. This compares with the 3.7% incidence reported in the STS database. The lower incidence of re-exploration for OPCAB as compared to conventional CABG and its incremental risk on operative mortality has been described [21, 22].
The lower incidence of stroke in our study as compared to what is often quoted in the literature may be related to the younger age of our population when compared with the western population and also due to OPCAB technique. Stroke is often quoted as one of the Achilles heels of CABG surgery. Whether OPCAB leads to a lower risk of stroke has been often debated [6, 23, 24]. The association of postoperative atrial fibrillation with operative mortality has been described earlier with Lewicki et al. reporting an incidence of operative mortality of 3.1% vs 1.2% in patients developing POAF as compared to patients remaining in sinus rhythm [25, 26].
The benefit of LIMA on mid-term survival was gratifying to see in our study. There was also benefit of a second arterial graft (right internal mammary artery or radial) on mid-term mortality by univariate analysis, but it did not reach statistical significance in multivariate analysis probably due to the low utilization of second arterial graft. Though the overall use of second arterial graft was low during the study period, the findings of our study and results from the literature have led to an increase in the use of second arterial graft in our current practice.
The incidence of mediastinitis was 1.5% in our study. This is similar to what has been reported in the literature which varies from 1.3 to 2.4% [27]. Mediastinitis was a significant factor for mortality on univariate analysis both on short- and mid-term but did not reach statistical significance on multivariate analysis probably due to the lower incidence. Previous studies have reported that mediastinitis is associated with decreased long-term survival after cardiac surgery [28, 29]. Long-term follow-up will be required to establish the relation of mediastinitis with late mortality.
Post-operative new onset atrial fibrillation was found to be a risk factor for mid-term mortality. Our finding was similar to other studies that had previously described the association of POAF with long-term mortality after CABG [30, 31].
The impact of age on mid-term survival was significant in our study, with patients > 62 years having an increased risk of mortality with a hazard ratio of 3.59 (95% CI 1.14–11.29). This risk of mortality increased in each decade and mid-term mortality was 36.3% in patients above 80 years.
Postoperative renal failure occurred in 21 patients (1.1%) in our study. It was a significant predictor of both short-term and mid-term mortality. Postoperative renal failure had the highest hazard ratio for mid-term mortality on our study at 30.81 (95% CI 6.25–151.96). The association of postoperative renal failure with reduced long-term survival after cardiac surgery was reported by other studies also [32, 33].
IABP usage was associated with increased mortality both at short-term and mid-term. This increased mortality probably reflects the sicker subset of patients who required IABP. However, other studies had reported that the use of IABP did not impact the long-term survival after CABG [34].
Readmission after discharge occurred in 15% of patients. This was associated with increased risk of mortality at mid-term follow-up. Readmission after cardiac surgery is common and associated with increased risk of mortality and is a focus of healthcare delivery with an aim at improving the quality of care and containing healthcare costs [35]. We did not separately analyze the reasons for readmission in our study.
The 5-year survival in our study was 90.4% which is comparable to other studies. The 5-year survival after OPCAB was 84.8% in the Randomized On/Off Bypass – Follow-up Study (ROOBY-FS) and 85.4% in the CABG Off or On Pump Revascularisation Study (CORONARY) trial [36, 37]. A recent meta-analysis of on versus off-pump CABG showed a 5-year survival of 86.1% [38]. Event free survival at 5 years in our study was 73.5% which was comparable with the 69% in the ROOBY-FS and 76.9% in the CORONARY trial.
Limitations
This study on mid-term follow-up of patients undergoing OPCAB surgery has some limitations. One major limitation was that the patients were from a single center that caters to one regional area. So, this study highlights the factors associated with mortality in this particular patient profile and geographic area but whether it can be generalized to the whole country is questionable. Another limitation of the study is the relatively small sample size and event rates. As the event rates were low, the possibility of missing significant associations is present. To avoid these errors, a larger study population and possible multi-center collaboration will be needed.
Conclusion
Off pump coronary bypass surgery is the default mode of surgical coronary revascularization in India. The results of OPCAB surgery are good both in the short-term and at mid-term with very satisfactory event-free survival. Longer follow-up and corroborative data from other centers in India will help to establish the suitability of OPCAB surgery in the Indian population.
Author contribution
All authors contributed to the study conception and design. Material preparation, data collection, and analysis was done by Kirun Gopal, Prashanth Vytla, Neethu Krishna, and Greeshma Ravindran. Review of the analysis was done by Rajesh Jose, Rohik Micka, and Praveen Kerala Varma. The first draft of the manuscript was written by Kirun Gopal. Review and editing of the manuscript was done by Rohik Micka, Rajesh Jose, and Praveen Kerala Varma. All versions of the manuscript were reviewed by all the authors and the final manuscript was approved by all authors.
Funding
No funding was received for conducting this study.
Data Availability
Data can be made available on request by direct correspondence.
Declarations
The authors have no relevant financial or non-financial interests to disclose.
Ethical approval
Institutional Review Board (IRB) approval was obtained for the study and the board waived individual written patient consent for the study. (IRB number IRB-AIMS-2019–089 dated 16/4/2019).
Conflict of interest
The authors declare no conflict of interest in relation to this manuscript.
Statement of human and animal rights
All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Footnotes
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References
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Associated Data
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Data Availability Statement
Data can be made available on request by direct correspondence.