Pakistan Journal of Medical Sciences

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ISSN 1681-715X

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ORIGINAL ARTICLE

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Volume 25

July - September 2009

Number  4


 

Abstract
PDF of this Article

Outcome and factors associated with hospital mortality in
patients with impaired left ventricular function undergoing
coronary artery bypass grafting: where do we stand?

Mubashir Zareen Khan1, Perveen S2, Ansari JA3, Sami SA4, Furnaz S5, Fatimi SH6

ABSTRACT

Objective: Impaired ventricular function is a known risk factor for mortality after coronary artery bypass grafting however increasingly more patients with impaired ventricular function are referred for surgery. Currently no large data is available from Pakistan regarding this aspect of coronary surgery. Our objectives were to find out the hospital mortality and mid term functional improvement in patients with impaired ventricular function undergoing coronary artery by pass grafting and identify the risk factors for mortality.

Methodology: Retrospective analysis of preoperative, operative and postoperative variables of patients with impaired ventricular function who were operated for isolated first time coronary artery bypass between October 2006 to April 2009.

Results: Total 190 patients with impaired ventricular function underwent isolated first time coronary artery bypass grafting during this period with a male predominance (82.6%). Mean ejection fraction of the group was 25.4±5.3%. Mean predicted mortality on logistic Euro score was 10.9±2.7%. Actual in hospital mortality of the group was 4.7% which is comparable to contemporary published results. Multivariate analysis identified use of intra aortic balloon pump, non use of internal mammary artery and preoperative NYHA functional class as factors associated with mortality.

Conclusion: Coronary artery bypass grafting can be performed in patients with impaired ventricular function with acceptable hospital mortality and mid term functional improvement.

KEY WORDS: Out come, Factors, Mortality, CABG, Impaired ventricular function.

Pak J Med Sci    July - September 2009    Vol. 25 No. 4    526-532

How to cite this article:

Khan MZ, Perveen S, Ansari JA, Sami SA, Furnaz S, Fatimi SH. Outcome and factors associated with hospital mortality in patients with impaired left ventricular function undergoing coronary artery bypass grafting: where do we stand?. Pak J Med Sci 2009;25(4):526-532.


1. Khan MZ,
2. Perveen S,
3. Ansari JA
Karachi Institute of Heart Diseases,
Karachi - Pakistan.
4 Sami SA,
5 Furnaz S,
6 Fatimi SH,
1-2, 4-6: Division of Cardiothoracic Surgery,
Aga Khan University Hospital,
Karachi - Pakistan.

Correspondence

Dr Mubashir Zareen Khan
Division of Cardiothoracic Surgery,
Aga Khan University Hospital
Stadium Road,
PO. Box 3500,
Karachi 74800, Pakistan
E Mail: mubashir.khan@aku.edu

* Received for Publication: July 7, 2009
* Revision Received: July 28, 2009
* Revision Accepted: July 29th 2009


INTRODUCTION

Balancing the risks and benefits has remained the cornerstone of decision making in surgery and this fact features prominently in offering the surgery for coronary artery bypass grafting to a patient with impaired left ventricular function. Traditionally impaired ventricular function has been a risk factor for mortality associated with CABG, however major randomized series have shown a survival benefit for patients with impaired LV function undergoing CABG as compared to medical treatment alone.1,2 Presently the available literature has addressed the hospital outcome in these patients and identified peripheral artery disease, COPD, female sex, reoperation, renal failure, advanced age and serially decreasing EF as risk factors for mortality and one and five year survival being 88% and 75% respectively.3-5 However no data is available from Pakistan making it pertinent to study this aspect of coronary artery disease in our country.

With improvements in thrombolytic therapy and PCI the proportion of patients with impaired LV function presenting for revascularization will increase. There is a requirement that we look into the outcome of CABG in this relatively high risk group and know the factors associated with mortality as well as midterm out come so that patients who would benefit more from the procedure are identified.

The objectives of this study were to know the hospital mortality and mid term functional improvement in patients with EF<or equal to 30% who had undergone isolated first time co-ronary artery bypass grafting as well as to find the factors associated with early mortality.

METHODOLOGY

Retrospective analysis of prospectively collected preoperative, operative and post operative data of patients with EF less than or equal to 30% undergoing isolated first time CABG at our institution between 2006 - 2009.

Inclusion criteria: Patients undergoing first time elective or urgent isolated CABG with an EF of 30% or less.

Exclusion criteria: Those undergoing an emergency procedure or in cardiogenic shock preoperatively.

Data collection and interpretation: All preoperative, intraoperative and postoperative variables were taken from a common data base form maintained for every cardiac patient, this includes telephonic interviews at one month and one year intervals after surgery. Additional information was taken from patient’s record files if required.

Definitions: The definition of low EF or impaired ventricular function is an EF of less than or equal to 30% as assessed by 2D and color echo.

Outcome as defined in our study included hospital mortality and functional status (NYHA class) at follow up the maximum duration being one year after surgery. Logistic EURO score was used for risk stratification of patients with those falling below 9% categorized as low to moderate risk and those above 9% as high risk group.

Emergency procedures were situations requiring immediate surgical intervention like cardiogenic shock, ongoing ST segment changes and failed or complicated PCI. Urgent procedures were situations where surgery was required as a priority during next few days eg. left main stenosis, unstable angina requiring IV nitrates or heparin.

Preoperative renal failure was defined as serum creatinine level more than two gm/dl. Post operatively creatinine going above 2gm/dl or more than one gm/dl of the base line level was taken as renal failure. Prolonged ventilation was defined as more than 72 hours.

Surgical Strategy: The surgical strategy included approach through median sternotomy and establishment of cardiopulmonary bypass. Ante grade blood cardioplegia was used and if required combined with graft or retrograde cardioplegia. Ionotropic support was started before coming off by pass. The patients were shifted to CICU ventilated where they were gradually weaned off from mechanical ventilatory support. After extubation and discontinuation of ionotropic, IABP support patients were assessed and shifted to step down unit from where they are started on a rehabilitation programme.

Statistical Analysis: Data was analyzed on Statistical Package for the Social Sciences (SPSS) version 16. Discrete variables were expressed in frequency and percentage. Continuous variables were presented in mean (± standard deviation) for normally distributed data while median (inter-quartile range) was used for non-normal distribution. Their Scale analysis was done. Collinearity was checked for all the independent variables. Univariate p-values of <0 .25 were determined by Exact and t-tests. Multivariable logistic regression was applied to estimate odds ratios for in-hospital mortality adjusting for other variables. Independent variables including age, cross clamped time, BMI, gender, CVA, PVD,CLD, Previous CV intervention, PCI, MI, CHF, NYHA, Angina, left main Disease >50%, Ejection Fraction, Operative Status, IABP, Internal mammary artery graft and distal anastomosis with venous conduit were scanned at P value of <0.05. Confounding effect at 15% and interaction at 10% were examined. Final model was built on Wald P value and verified by likelihood ratio test. Its fit was assessed by Deviance/ Pearson Chi square. Additionally, Survival plot was plotted for one month and one year follow up by using Kaplan Meier method and compared with Log-rank test.

RESULTS

All preoperative variables are shown in Table-I the study population comprised of total 190 patients with males being 82.6%. Mean age was 58.44±9.55 years .The incidence of important risk factors is shown here, important features are preop MI documented in 148(77.9%) patients and prior PCI seen in 11 (5.45%) patients. Overall EF of the group was 25.4± 5.3% and 18 (9.5%) patients had an EF of 20% or less. Mean logistic euroscore was 10.9± 2.7%.

Operative variables are shown in Table-II. Majority (94.7%) of the patients underwent conventional on pump CABG. Mean cross clamp time was 100.2 ±33.1mins and mean cross clamp time was 61 ± 23.4 mins. Mean number of grafts was 3.3±0.8 for on pump and 1.5±0.5 for off pump cases.

Post operative data is shown in Table-III. Over all incidence of complications was 26.3% (50 complications), post operative respiratory problems being the most frequent complication seen in 14.8 % patients. Over all mortality was 4.7 % (9/190).

An analysis of hospital mortality showed that out of 190 patients the intra aortic balloon pump was used only in 34 (17.9%) patients and not used in 156 (82.1%). Out of those who got an IABP there were 7 inhospital deaths so the mortality of patients with an IABP was 20.6% (7 out of 34) and mortality of those in which IABP was not used was 1.3% (two out of 156). As shown in table II internal mammary artery (IMA)was used in 85.7% (163) patients and not used in 14.2% (27) patients, out of those who got an IMA there were 2 hospital deaths, mortality being 1.22% and in the group where IMA was not used the hospital mortality was 25.9%. Based on preoperative NYHA functional class there were no hospital deaths in patients in class II, three out of a total 98 in class III(3.1%) and six out of a total 44 patients in class IV (13.6%). There were no patients in NYHA class I before surgery.

Post op follow up data was recorded at one month and one year intervals. Of the 181 patients discharged alive from the hospital there were three deaths at one month interval (1.65%) while six patients (3.3%) were lost to follow up. The cause of death shown in the table included two cardiac deaths and one due to infection. There were 22 (12.1%) readmissions during one month of discharge. This left 172 patients out of initial 190 for one year follow up. Out of those 124 completed one year time from operation and 48 were at various stages of one year time. There were six deaths (4.8%) at one year interval and 19 (15.3%) patients were lost to follow up. The patients who had not completed one year follow up time (n 48) were contacted on telephone. There were two deaths (4.1%) in this group, so in total eight documented deaths occurred between one month and one year following surgery. The cause of death at one year interval is shown in Table-IV.

Functional class improvement is shown in Table-V. It is evident that majority of the patients were in class III or IV preoperatively, however at one month and one year follow-up the proportion of patients in class I and II increased.

Multivariate analysis performed showed use of intra aortic balloon pump, non use of internal mammary artery and preoperative NYHA functional class as factors significantly associated with hospital mortality.

First two variables shows strong positive association (OR=11.47 and 95%CI=2.00, 65.65) and (OR=14.27 and 95%CI=2.36, 87.76) while third one shows protective to positive association (OR=5.38 and 95%CI=0.99, 28.95) with outcome (Table-VI).

When stratification was done on NYHA, Survival curve at both one month and one year follow up showed significant association with P value of 0.034 and <0.001 respectively. Both intervals showed better survival of Low Ejection Fraction CABG in functional class I as compared to class II, III and IV (Fig IA & IB). Furthermore, improved outcome in terms of NYHA functional class (Table-V) even with huge missing data in lost to follow up (6 at one month follow up and 19 at one year follow up) was also evident.

DISCUSSION

In this retrospective study we have analyzed the out come of CABG in low EF group. Main findings of the study are an acceptable hospital mortality and functional improvement at one month and one year interval. These results reflect improving results of surgery in this high risk group. The reported incidence of patients with EF less than 30% presenting for CABG is up to 15%,6 at our institution the incidence of CABG for patients with a low ejection fraction is about 12% of all the coronary artery revascularization procedures performed which compares with a range of 3.4-15% in literature5,6 and this number is expected to increase in future.7

Post operative out come in these patients is worse as compared to those with normal EF,9 however major randomized controlled series have shown a survival benefit for surgically treated patients in this group8,9 and CABG is frequently performed in this group.10

The hospital mortality in our study is 4.75% whereas predicted mortality by logistic euro score was 10.9%. This observation has been made in other contemporary studies.11 In Canadian registry data base the reported mortality for CABG in patients with an EF of less than 30% was 4.6% between 1996 and 2001.12 The improvement in operative results is probably attributed to better myocardial protection, improved perioperative care as well as better patient selection involving myocardial viability studies.11

Although our data is deficient in terms of follow up however of the 190 patients 172 were seen at one month interval (9 in hospital deaths, three deaths during one month and six were lost to follow up). Of these remaining patients 124 completed one year after surgery but there were another 19 patients missing in follow up and six more deaths were recorded so 99 patients were living out of 124 at one year interval with an actual survival rate of 79.8%. The survival data in similar group of patients ranges from 81 – 92% at one year and 68 – 875 at three years interval.5,14 Similarly as shown in results there was a significant improvement in the functional status of the patients both at one month and one year interval a fact that must carry an equal weight while balancing risks and benefits of surgery.

We have shown that use of intra aortic balloon pump, non use of internal mammary artery and preoperative worse functional class were the risk factors associated with in hospital mortality. Out of these first two factors reflect the criticality of patient (only more sick patients are likely to get an intra aortic balloon pump or would not be a candidate for internal mammary artery use) rather than having a direct bearing on the mortality. These factors have been quoted in other studies as well as being associated with the perioperative mortality.10,11 Additional risk factors found in New York state department of Health data such as advanced age, female sex, hepatic failure, renal failure and emergent procedures were not confirmed in our study.

The fact that significant number of patients were lost to follow up is a potential weakness in our study however it should be noted that some of the patients were from out side Karachi from areas as far as Skardu (a common referral base for AKU) and did not have an access to even a phone. Similarly a few would contact on phone without any formal documentation or would follow up with their family doctor after surgery so their record does not show in our medical documents.

Strength: The importance of this study is that it is from a developing country, provides detailed view of pre-operative co-morbidities and associated factors. It also shows improved outcome which justified CABG surgery in this high risk group

Limitation: It has the following limitations:

* sparse data with very small number of outcome which is reflected with large CI

* Retrospective data analysis

* Huge number of missing data in lost to follow up

* Lack of data about post operative co-morbidity, complications, and cost-benefit analysis

CONCLUSION

CABG can be performed in patients with low ejection fraction with acceptable hospital mortality and improvement in functional status. Careful patient selection for revascularization would confer maximum benefit to the patients in this relatively high risk group.

REFERENCES

1. Topkara VK, Cheema FH, Kesavaramanujam S. Coronary artery bypass grafting in patients with low ejection fraction. Circulation 2005;112(9 suppl):1-344-50.

2. Antunes PE, de Oliveira JM, Antunes MJ. Coronary surgery with non cardioplegic methods in patients with advanced left ventricular dysfunction: immediate and long term results. Heart 2003;89:427-31.

3. Scott SM, Deupree RH, Sharma GV, Luchi RJ. A study of unstable angina: 10 year study shows duration of surgical advantage for patients with impaired ejection fraction. Circulation 1994;90(suppl):II-120-3.

4. Passamani E, Davis KB, Gillespie MJ, Killip T. A randomized trail of coronary artery bypass surgery. Survival of patients with low EF. N Eng J Med 1985;312:1665-71.

5. Filsoufi F, Rahmanian PB, Castillo GJ, Chikwe J, Kini AS, Adams DH. Results and predictors of early and late outcome of coronary artery bypass grafting in patients with severely depressed left ventricular function. Ann Thorac Surg 2007;84:808-16.

6. Hillis GS, Zehr K, Williams AW, Schaff HV, Orzulak TA, Daly RC, et al. Out come of patients with low ejection fraction undergoing coronary artery bypass grafting. Renal function and mortality after 3.8 years. Circulation 2006;114(suppl I): I-414-419.

7. Ascione R, Narayan P, Rogers CA, Lim KH, Capoun R, Angelini GD. Early and mid term out come in patients with severe left ventricular dysfunction undergoing coronary artery surgery. Ann Thorac Surg 2003;76:793-799.

8. Ferguson TB, Hammil BG, Peterson ED, Delong ER, grover FL. A decade of change- risk profiles and out comes for isolated coronary artery bypass grafting procedures, 1990- 1999: a report from the STS national database committee and the Duke clinical research institutwe. Ann Thorac Surg 2002;73:480-90.

9. Eagle KA, Guyton RA, Davidoff R. ACC/AHA 2004 guidelines update for coronary artery bypass surgery. Circulation 2004;110:e 340-437.

10. CASS principal investigators and their associates. Coronary artery surgery study (CASS): a randomized trial of coronary artery bypass surgery. Survival data. Corculation 1983;68:939-950.

11. The veteran administration coronary artery bypass surgery cooperative study group. Eleven year survival in the veteran administration randomized trial of coronary bypass for stable angina. N Eng J Med 1984;311:1333-1339.

12. Rich MW. Heart failure in older adults. Med Clin North Am 2006;90:863-85,xi.

13. Appoo J, Norris C, merali S. Long term out come of isolated coronary artery bypass surgery in patients with severe left ventricular dysfunction. Circulation 2004;110(11 suppl 1):II-13-7.

14. DeRose JJ, Toumpoulis IK, Balaram SK. Preoperative prediction of long term survival after coronary artery bypass grafting in patients with low left ventricular ejection fraction. J Thorac Surg 2005;129:314-21.


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