Short –term outcome of off pump versus on pump coronary artery bypass grafting

INTRODUCTION

The most frequent adult cardiac surgery procedure implemented worldwide is coronary artery bypass grafting (CABG), which is also the cornerstone of our profession.¹

One of the most controversial topics in cardiac surgery is whether coronary artery bypass grafting achieved without cardiopulmonary bypass or cardioplegia is preferable to bypass grafting conducted when the heart in a chemical-arrest state with the use of the heart-lung machine.²

 Off-pump coronary artery bypass grafting surgery (conducted on a beating heart) was designed to reduce perioperative problems associated with cardiopulmonary bypass and aortic cross clamping.³

The current widely used procedure of surgical coronary artery revascularization was developed and adopted around 40 years ago, and it has since become the standard of care. The success of this method in comparison to percutaneous coronary procedures has grasped the attention of many publications in recent years.⁴

 Hemodynamic instability complicates off-pump coronary artery bypass grafting (OPCABG), which may lead to many organ dysfunctions, especially in patients with a low LV ejection fraction (LVEF 35 < %).⁵

PATIENTS AND METHODS

This prospective randomized trial was pursued with a sample of 120 patients with stable coronary artery disease who received elective CABG without any concomitant surgical interventions at El Hussein and MKH Hospitals between August 2017 and September 2019.

Patients were divided to two equal groups: Off-pump and On-pump.

After receiving informed consent from each patient, as well as confirmation from our Department Council and Local Ethical Committees, the study was carried out.

Inclusion criteria: adult patients of both gender undergoing an elective coronary artery bypass graft whomCABG was justified by coronary angiographic investigations and preoperative echocardiography.

 Exclusion criteria:

• Re-do patients.
• Recent myocardial infarction < 6 weeks
• Patients with associated coronary and other pathology requiring combined procedure.
• Patients exhibited significant carotid artery stenosis that needs surgery.
• Patients refusing to participate in the study.

In all patients, a comprehensive history was taken, with asking about previous MI, or PCI and determination of patient's NYHA classification. After thorough physical examination, comprehensive laboratory testing, chest x-ray, ECG, and echocardiogram were reviewed.

Simpson's approach was used to calculate ejection fraction using 2D transthoracic echocardiography.

In Off-pump group: standard midline sternotomy incision was deployed for heart exposure; left internal mammary artery and right great saphenous vein were harvested simultaneously, and deep pericardial sutures were performed after incision of the pericardium. Anticoagulation was achieved using heparin, the activated clotting time was conserved above 250 seconds and the heart stabilization was secured using stabilizer (octopus). LIMA was anastomosed to LAD initially in most cases according to collateralized and collateralizing artery, then saphenous vein grafts were anastomosed to obtuse marginal branches, diagonals, and the RCA territory. This was followed by finishing proximal anastomosis, assessment of graft patency by TTFM flow and pressure, good hemostasis, and finally closure of the layers after insertion of chest tubes.

In On-pump group: standard midline sternotomy incision was deployed for heart exposure; left internal mammary artery and right great saphenous vein harvested; heparin was utilized for achieving anticoagulation; the activated clotting time was conserved above 480 seconds. CPB was instituted with a single right atrial cannula and ascending aorta cannula; moreover, myocardial protection via cardioplegia was fulfilled either by ante-grade warm blood or ante-grade cold crystalloid. Saphenous vein grafts were anastomosed to obtuse marginal branches, diagonals, RCA territory. Finally, LIMA was anastomosed to LAD and coming off CPB. This was followed by proximal anastomosis, assessment of graft patency by TTFM flow and pressure, removal of venous and arterial cannula, good hemostasis, and finally closure of the layers after insertion of chest tubes.

Anesthetic management procedures were the same in both groups — induction and maintenance of general anesthesia with endotracheal intubation. 

The following intra-operative data were collected: operative time in minutes, number of distal grafts as total and per each patient, type and number of proximal anastomosis, graft distribution territory, need for cardiac inotropes, need for IABP, transfusion of blood components, bleeding, use of D/C shock and graft patency assessment by TTFM.

Dramatic conversion to on-pump in off-pump group was assessed; meanwhile, specific parameters (aortic cross clamp time, bypass time, types of preservation cardioplegia) were assessed in on-pump group   .

Echocardiography was done 1 day prior to surgery then rechecked six months postoperatively to measure the ejection fraction, degree of mitral valve regurgitation, and regional wall motion abnormality.

Total CK, CKMB and cardiac troponin I levels were measured for each patient 6 hours, 12 hours, and 24 hours post-surgery.

The primary end point was early outcome including the success rate, morbidity follow-up of (MI, Arrhythmia, and Cerebrovascular stroke, renal failure requiring dialysis, Hepatic impairment, and wound infection), while secondary end points were ICU stay, ventilation time in hours and hospital stays.

Patients’ follows-up was conducted after six months post operatively by NYHA, ECG, ECHO and MSCT angiography for assessment of graft patency.

Statistical analysis

IBM Statistical Package for the Social Sciences (SPSS) software (SPSS Inc., Chicago, IL, USA) was adopted for the statistical analysis. Presentation of quantitative data included mean and range, while the data were compared by independent t-test or Mann-Whitney test. Qualitative data are expressed as number and percentage; they were compared by Chi‑square test or Fisher’s exact test. P < 0.05 was deemed statistically significant.

RESULTS

The analyzed groups' demographic data, risk factors for heart diseases, and cardiac parameters revealed no significant differences. (Table 1).

Cardiac functions were assessed by echocardiography (ejection fraction (EF %), degree of mitral regurgitation, and regional wall motion abnormality. SWMA significantly improved postoperatively after six months in both groups. In off-pump group, the patients had an EF% with a mean of 61(55-69), while in on-pump group displayed a mean of 62.5(54-71) (p < 0.001) as show in (Figure 1, Table 2).

Fig 1: Box-plot diagram compares pre and post operative range of EF percentage; each box have upper and the bottom line to reflect the 75th & 25th percentile respectively; the line across each box denotes the median. Whiskers represent the range between the minimum and maximum values with exclusion of both outliers (rounded markers) and extreme observations (asterisks).

Intraoperative parameters: operative time, need for cardiac inotropes, use of D/C shock and blood transfusion (packed RBCs, other blood components), and graft patency assessment by TTFM were recorded. Patients who underwent off-pump CABG had less mean operative time (p < 0.01), while the need for cardiac inotropes, use of D/C shock, blood transfusion were significantly large in on-pump group unlike Off-pump group (p < 0.01) (Table 3).

On the other hand, the off-pump group considerably required more TTFM than the on-pump group (p 0.01), whereas TTFM values were substantially lower in the on-pump groups in comparison to the off-pump group (p < 0.01) (Table 4).

TTFM flow readings showed statistically significant difference in favor of the off-pump group compared to on-pump group as the following: LIMA to LAD, SVG to OM, SVG to RCA, and SVG to PDA. Likewise, TTFM flow readings of SVG to D were deemed significant hence it was higher in off-pump group compared to on-pump group (p 0.017).

On the other hand, the following TTFM pressure index readings were significantly low in off-pump group compared to on-pump group: in LIMA to LAD (p < 0.01), SVG to D, (p 0.002), SVG to OM (p 0.001) (Table 4).

Table 1: Clinical-demographic data in both groups, Quantitative data were expressed as Median (range) and compared using Mann Whitney test, while qualitative data were expressed as numbers and percentages and compared using Chi-square X2 test.

Table 2: Echocardiographic parameters of studied cases. Quantitative data were expressed as Median (range) and compared using Mann Whitney test, while categorized data were expressed as numbers and percentages and compared using Chi-square X2 test, EF= Ejection fraction, MVR=Mitral valve regurgitation, and SWMA=Systolic regional wall motion abnormality.

Table 3: Intraoperative parameters of studied cases. Quantitative data were denoted as Median (range) and underwent comparison using Mann Whitney test, while qualitative data were expressed as numbers and percentages and compared using Chi-square X2 test.

Table 4: graft patency assessment by TTFM among studied cases. Quantitative data were expressed as Median (range) and compared using Mann Whitney test, while qualitative data were expressed as numbers and percentages and compared using Chi-square X2 test.

In terms of myocardial damage markers (CK, CK-MB, and troponin I), the off-pump group's troponin I levels were considerably lower at 6, 12, and 24 hours following the surgery than the on-pump group (p 0.002).

Mechanical ventilation duration and elevated liver enzymes were significantly greater in the on-pump group compared to the off-pump group (p < 0.01).

The length of ICU stay was also significantly longer in the on-pump group compared to the off-pump group.

Accordingly, the mean ICU stay in the on-pump group was 60(37-90) hours, compared to 36(32-80) hours in the off-pump group (p<0.001).

In terms of postoperative MI, stroke, arrhythmia, and renal failure that requires dialysis, there were no statistically significant differences between the two groups.

In the current study, no patient needed examination owing to bleeding (Table 5).

Regardingto the follow-up of NYHA Score and comparing it with baseline NYHA Score, the difference was statistically significant between the two groups (P-value < 0.001) (Figure 2, Table 6).

Fig 2: Pre and Post-operative NYHA score in both groups

The total number of performed grafts in on-pump group was 185 grafts: two grafts revealed significant stenosis, three grafts showed occlusion. However, off-pump group number of grafts was 177: two grafts showed significant stenosis, three grafts exhibited occlusion. The difference was not statistically significant in revascularization between the two groups after comparing them with multi assessments as the following: number of diseased coronary arteries, number of distal grafts, graft distribution, and postoperative checking of the graft patency after six months using MSCT coronary angiography (Table 7).

Table 5: major postoperative adverse events among studied groups. Quantitative data were expressed as Median (range) and compared using Mann Whitney test, while qualitative data were expressed as numbers and percentages and compared using Chi-square X2 test.

Table 6: Postoperative outcomes of studied groups.

Table 7: post-operative follow up of graft patency by MSCT Angiography after 6 months. Quantitative data were expressed as Median (range) and compared using Mann Whitney test, while qualitative data were expressed as numbers and percentages and compared using Chi-square X2 test, N=not done, P= patent, O=occlusion, S=significant stenosis > 50%.