Introduction

CABG is the gold standard for revascularization in coronary artery disease. Patients with left main disease, multivessel disease, and left ventricular (LV) dysfunction benefit from CABG rather than percutaneous coronary intervention (PCI) or medical therapy [1]. CABG is commonly performed with the use of cardiopulmonary bypass (CPB) and cardioplegic arrest. With this approach, the composite outcome of perioperative mortality and major adverse cardiac and cerebral events is less than 10% [1]. The development of cardiac stabilizers in the late 1990s allowed widespread application of alternative technique of coronary revascularization that does not require CPB [2]. Many studies reported reduced operative morbidity with OPCAB relative to on-pump CABG. OPCAB patients had less transfusion requirement, less inotropic support, shorter ventilation time, lower stroke rate, lower incidence of acute kidney injury, and shorter intensive care unit stay [3]. Routine patients may achieve an excellent outcome irrespective of the type of procedure; however, it was thought that OPCAB gave substantial benefit to high-risk and elderly patients [4].

However, there is a decline of interest in OPCAB worldwide [5]. Only 13% of CABG were performed by OPCAB technique in the latest Society of Thoracic Surgeons (STS) database [6]. Besides being technically more demanding and concerns about the quality of anastomosis, many studies had shown a tendency to incomplete revascularization, lower graft patency, and increased need for repeat revascularization with reduced long-term survival in patients undergoing OPCAB technique [7, 8]. Moreover, OPCAB has not shown any substantial benefit in high-risk groups, e.g., patients with depressed LV function, patients with renal dysfunction, and elderly subjects [9, 10]. Even though a newer randomized trial showed similar results in both on-pump and off-pump in early and 5-year outcomes, need for repeat revascularization remained higher in the off-pump group [11]. These factors led to even an opinion to abandon off-pump revascularization altogether [12, 13]. Most of these data and studies were based on western patients. Hence, this data may not be applicable in Indian context.

CABG is difficult in Indian patients because of smaller caliber of coronary vessels, diffuse nature of disease, and tendency to early calcification of atheromatous plaque [14]. In India, currently OPCAB surgery is performed in more than 60% of patients undergoing CABG; mainly because of shorter operative time and reduced procedure cost. However, there is a paucity of published data on outcomes of OPCAB in Indian patients [15,16,17]. Hence, we designed a prospective study to evaluate the early outcomes of OPCAB patients in our institute.

Patients and methods

Study design and data collection

A prospective observational study of early outcomes in patients undergoing off-pump coronary artery bypass grafting was conducted at the Department of Cardiovascular and Thoracic Surgery. Eight hundred consecutive patients who underwent OPCAB from August 2015 to October 2017 were included in the study. Three consultant cardiothoracic surgeons performed all the procedures. Eight hundred twenty-three patients were planned for OPCAB procedure, of which 23 patients underwent elective conversion to on-pump CABG. Patients who required emergency intraoperative conversion were included in the analysis and were reported as an outcome. The variables collected are included in Table 1. Follow-up at 30 days was carried out by direct follow-up of patients in outpatient department.

Table 1 Distribution of preoperative variables
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Ethics committee approval

The study was approved by the hospital ethics committee. The need for informed consent was waived off. All personal identifying data was removed from the study database so that individuals could not be identified.

OPCAB technique

All patients underwent median sternotomy. Heparin was administered to achieve a target activated clotting time of more than 400 s. Left internal mammary artery (LIMA) was the preferred conduit to bypass left anterior descending artery (LAD). Ninety-five percent of patients received saphenous vein grafts to bypass the other systems. Proximal anastomoses were constructed in ascending aorta using partial occlusion clamp. Our strategy was to perform all proximal anastomoses separately whenever possible. Sequential grafts and vein to vein anastomosis were performed only if the vein length was inadequate. Heparin was fully reversed with protamine after the procedure. Patients were shifted to dedicated intensive care unit (ICU) for postoperative monitoring.

Perioperative care

Angiotensin-converting enzyme (ACE) inhibitors, β-blocker therapy, and aspirin were continued to the day of surgery. Clopidogrel was withdrawn 2 days prior to operation. Aspirin was started within 6 h after CABG. β-Blocker was started on postoperative day 1, if the patients were not on inotropes and vasopressor agents. All patients received atorvastatin 20 mg on the first postoperative day. Patients were monitored with continuous cardiac output with pulmonary artery flotation catheter (Edwards Lifesciences, USA) during perioperative period. Patients were treated with dual antiplatelet therapy (aspirin 150 mg + clopidogrel 75 mg) for 1 year post-CABG; thereafter, only aspirin was prescribed.

Definition of variables

Early mortality was defined as “death due to any cause within 30 days of surgery or during hospitalization.” Emergency surgery was defined as patients requiring immediate surgery due to ongoing chest pain or cardiogenic shock. Recent myocardial infarction (MI) was defined as MI occurring within 30 days prior to surgical intervention. Chronic kidney disease (CKD) was defined as glomerular filtrate rate (GFR) < 60 ml/min/1.73 m2. Cerebrovascular disease was defined to include those patients who had asymptomatic internal carotid artery stenosis with luminal narrowing of < 69%. Patients with symptomatic carotid occlusion or with > 70% luminal narrowing were excluded as they underwent concomitant carotid end arterectomy. Peripheral vascular disease was defined to include those patients who had asymptomatic luminal narrowing of lower limb arteries on Doppler analysis.

Statistical analysis

Based on the mortality rate among the patients undergoing OPCAB observed in the earlier publications, minimum sample size comes to 1200 patients. However, this study included a total of 800 cases, making it slightly underpowered. Statistical analysis was done using IBM SPSS 20.0 version (SPSS Inc., Chicago, USA). For all the continuous variables, the results are given in mean ± SD or median with interquartile range where appropriate and for categorical variables as percentage. To compare the mean difference of numerical variables between groups, independent two-sample “t” test was applied. To study the association of categorical variables with mortality, chi-square test was applied. P value < 0.05 was considered as statistically significant. Those variables with p value of less than 0.2 were used for multivariate logistic regression analysis for association with mortality.

Results

Early outcomes are reported in Table 2. Mean age of the study group was 61.75 ± 8.78 years. Eighteen percent were female patients; however, there was no difference in their mortality compared to male patients (p value 0.227). In univariate analysis, chronic kidney disease (p value 0.027), emergency surgery (p value < 0.001) development of postoperative atrial fibrillation (PoAF) (p value < 0.001), dialysis-dependent renal failure (p value < 0.001), and severe LV dysfunction (p value < 0.001) were associated with mortality. On multivariate analysis, emergency surgery (HR 9.72; CI 1.96–48.21, p value 0.005), severe LV dysfunction (HR 2.28; CI 1.25–4.76, p value 0.026), PoAF (HR 9.95; CI 3.12–32.01, p value 0.05), and dialysis-dependent renal failure (HR 29.7, CI 10.02–87.99, p value 0.006) were the factors associated with mortality (Tables 3 and 4). Nine patients (1.2%) required emergency conversion to on-pump due to hemodynamic instability. Seven (53.89%) patients died due to ventricular arrhythmia, two (15.3%) patients died from septic shock, and four (30.7%) died from low cardiac output and multiorgan dysfunction in the postoperative period. The observed mortality was 1.6% (13/800); the expected mortality by EuroSCORE II was 2.6% [18]. The median EuroSCORE II of expired patients was 3.03 and of entire cohort was 1.54 (p value 0.001). Stroke rate was 0.9%. Deep sternal wound infection occurred in 0.9%, and 4% patients were readmitted to the hospital after discharge. PoAF occurred in 18.7% patients.

Table 2 Thirty-day/in-house outcomes
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Table 3 Association of preoperative variables with mortality
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Table 4 Association of postoperative variables with mortality
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Discussion

Our study showed that emergency surgery, severe LV dysfunction, POAF, and dialysis-dependent renal failure were the factors associated with early mortality. Emergency surgery, severe LV dysfunction, and dialysis-dependent renal failure are well-known risk factors for early mortality in cardiac surgery [19]. We also found that PoAF was significant risk factor for mortality. In the past, PoAF was considered as a self-limiting and benign arrhythmia [20]; however, multiple studies [21,22,23] have shown that PoAF increases the postoperative morbidity and mortality in short and long term. PoAF can lead to low cardiac output and hemodynamic instability and potentially increases the risk for early mortality in patients with diastolic and systolic dysfunction. It may also be a surrogate marker for a sicker patient [24].

EuroSCORE II is a robust risk model for predicting early mortality after cardiac surgery. Risk scoring systems are most reliable when the patient characteristics and quality of healthcare delivery are comparable with those on which the system originated [25]. Even though it is still not very well validated in Indian patients, it is important to measure risk-adjusted mortality to ensure the quality of the performance of the hospital, unit, or surgeon. In the absence of central registry, database, or public reporting of results in India, we relied on EuroSCORE II for measuring risk-adjusted mortality. Our observed mortality was less than the expected mortality by EuroSCORE II, which was reassuring. The median EUROSCORE II of expired patients was 3.03, meaning those patients had increased risk for cardiac surgery.

The data reveal significant difference from the population undergoing CABG in developed countries. The incidence of DM was 66% in our study which is much higher than 49% reported in STS database [7]. The study group seemed to have lower incidence of PoAF than reported in Western literature [26, 27]. Younger age group, racial differences, and lower body mass index are the likely reasons for this phenomenon. Continuous ECG monitoring of patients occurred only during ICU stay. More systematic ECG monitoring could result in a better identification and a higher detected incidence of PoAF. The very low incidence of intraoperative conversion to on-pump, reexploration for bleeding, new requirement of dialysis, and blood stream infection are noteworthy.

Stroke is a devastating complication after cardiac surgery. It increases the morbidity, affects the quality of life, and increases the period of hospital stay and hospital expenses. The stroke rate in this study group was 0.9% which is slightly lower than most reported series [28]. Younger age at the time of CABG and OPCAB technique could explain the lower stroke rate reported in this study compared to studies published from Western patients. Even though debatable [12, 28], OPCAB has been suggested to decrease the risk of stroke [29].

Patients requiring conversion to on-pump on emergency basis have increased morbidity and worse composite outcomes [30, 31]. Our conversion rates are lower than reported in most literature [1, 32]. The mean numbers of grafts placed were high, and LIMA usage was close to 98%. Very low usage of second arterial graft (< 5%), increased ventilator hours, and readmission rates remain a major concern and are potential areas for quality improvement.

There are several limitations in our study. India is a vast country with significant regional differences in the racial profile, socioeconomic factors, literacy rates, and healthcare delivery. Hence, outcome reported from single center may not be applicable to the entire population. Our study was also underpowered; hence, the results should be interpreted with caution. Perioperative myocardial infarction rates were not captured in the data collection. Hence, 30-day composite outcome could not be reported. We were also not able to show any data on completeness of revascularization since we did not collect information on the observed versus expected number of grafts in any patient. Outcomes of CABG have historically been measured in terms of mortality and morbidity; however, outcomes after CABG are a multidimensional phenomenon. They include long-term event-free survival, quality of life, cognitive function, and physical activity. We do not have any data on these important outcome variables.

Conclusions

Early outcome of off-pump CABG was excellent in this study. Very low usage of second arterial graft, increased ventilator hours, and readmission rates remain a major concern and are potential areas for quality improvement. Multicenter study with a larger sample size is required for a precise and dependable evaluation of the efficacy of off-pump CABG in Indian population.