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Improvement of Ejection Fraction in Patients undergoing Coronary Artery Bypass Grafting with Impaired Left Ventricular Function

Background Myocardial revascularization surgery has shown better long term survival expectancy compared to medical therapy in patient with impaired left ventricular function. Objective To evaluate the change in ejection fraction after 90 days in patients who underwent coronary artery bypass surgery and had preoperative left ventricular ejection fraction of less than and equal to 45% in a single cardiac center of Nepal over the period of 2 years. Method Out of 82 eligible patients during 2 years, 3 patients expired in immediate postoperatively and 24 patients had loss of 90 days’ follow up. So, they were excluded from the study. Total 55 patients were taken for the study for whom statistical analysis was done to compare preoperative ejection fraction with post-operative 90 days’ ejection fraction. Single present patients, double vessel disease in 7(12.7%) patients and triple vessel disease in 46(83.6%) of the patients. In 2(3.6%) patients 2 grafts, in 18(32.7%) patients 3 grafts, in 33(60%) patients grafts and in 2(3.6%) patients 5 grafts were placed for revascularization. The mean left ventricular EF in preoperative patients was 37.12±5.69% which improved to 45.80±10.00% in postoperative follow up at 90 days which was statistically significant (p=0.000). Conclusion Surgical revascularization of myocardium in preoperatively impaired left ventricular function patients helps improve left ventricular ejection fraction postoperatively. So we suggest surgical revascularization in patient with low ejection fraction for improvement of myocardial function. Hence improve survival rate in these patients.


INTRODUCTION
Impaired left ventricular function has been considered to be associated with increased risk of hospital stay and mortality after coronary artery bypass grafting (CABG) since long. 1 However improvement in surgical technique, myocardial protection and postoperative care has shown that patients have improved ejection fraction (EF) and have better long term survival expectancy after coronary surgery than with continuous medical therapy. [2][3][4] Medical management in patient with coronary artery disease with impaired left ventricular ejection fraction have poor outcome with a two year survival rate of only 20 to 30%. 5 Most of this group of patient has shown to benefit from myocardial revascularization surgery. 6 The aim of this study is to evaluate the change in ejection fraction after 90 days in patients who underwent CABG and had preoperative EF of less than and equal to 45% in a single cardiac center of Nepal over the period of 2 years. The outcome of this study can be useful as future reference in choosing the surgical treatment option in this impaired left ventricular function patients.

METHODS
After obtaining institutional review board approval the patient with ejection fraction of less than or equal to 45% who underwent isolated CABG surgery from January 2018 to December 2019 were taken from hospital record book for this study.
This was a retrospective observational study performed at Shahid Gangalal National Heart Center of Nepal. All adult cardiac surgical patients more than 18 years of age who underwent elective isolated onpump CABG surgery with EF of less than and equal to 45% from January 2018 to December 2019 were included in this study. Out of 82 eligible patients during the time frame 3 patients expired in post-operative period and 24 patients had loss of 90 days' follow up. So, they were excluded from the study ( fig. 1).
Total 55 patients were taken for the study and demographic details of the patients like age, sex, height and weight were recorded. Total number of diseased vessel preoperatively and number of grafts used in the patients were also recorded. Preoperative left ventricular EF and postoperative left ventricular EF after 90 days was recorded by transthoracic echocardiography in all of these patients and these data were recorded from hospital record book. The objective of the study was to evaluate the effect of CABG surgery in patient with preoperative impaired left ventricular function on improvement of EF after 90 days follow up postoperatively.
Collected data were analysed by means of statistical software SPSS22. Statistical analysis for demographic variables was done by chi-square test and student's paired t test was applied to compare the ejection fraction pre and post operatively. P-value of < 0.05 was considered to be significant.

RESULTS
Out of the 55 patients eligible for the study, 43(78.3%) were male and 12(21.8%) were female. The demographic data of patients is shown in Table 1. Single vessel disease was present in 2(3.6%) patients, double vessel disease was present in 7(12.7%) patients and triple vessel disease was present in 46(83.6%) of the patients ( fig. 2). In 2(3.6%) patients 2 grafts were placed, in 18(32.7%) patients 3 grafts were placed, in 33(60%) patients 4 grafts were placed and in 2(3.6%) patients 5 grafts were placed for revascularization ( fig. 3). The mean left ventricular EF in preoperative patients was 37.12±5.69% which improved to 45.80±10.00% in postoperative follow up at 90 days which was statistically significant (p=0.000).

DISCUSSION
The management of patients with impaired left ventricular function is challenging and is often thought to be associated with significant morbidity and mortality after coronary artery bypass grafting since long.  12 The decrease in EF post-operatively after CABG surgery could be due to various factors like presence and extent of viable tissue preoperatively, significant intraoperative global ischemia, myocardial stunning or early postoperative graft failure. [13][14][15] Our study also showed in-hospital mortality of 3.65% in the patients with EF of less than or equal to 45% after CABG surgery which is acceptable with other currently published data. 16,17 Various factors are shown to contribute to mortality like presence of diabetes or use of intra or post-operative intra-aortic balloon pump. 18,19 On-pump surgery on arrested heart has shown to cause more myocardial edema and ischemia compared to on-pump beating heart surgery. 20 Moreover off-pump CABG surgery has shown to have more improved outcomes and less mortality compared to conventional technique. 21 The limitations of this study is that it is a retrospective study with a small sample size and we couldn't get the information of all the cases in that time frame due to loss of follow up. These could be the major confounding factors for the result of our study. Besides, all the cases were on pump CABG surgeries. So we recommend to do a comparative study between on pump and off pump CABG with a larger sample size and longer follow up in future.

CONCLUSION
Surgical revascularization of myocardium in preoperatively impaired left ventricular function patients help to improve their left ventricular ejection fraction postoperatively. So, we suggest surgical revascularization in patients with low ejection fraction for improvement of myocardial function and hence improve the overall survival rate in these patients.