INTRA-AORTIC BALLOON PUMP IN CORONARY ARTERY BYPASS GRAFT - FACTORS AFFECTING OUTCOME

Okonta KE, *Kanagarajan N, Anbarasu M.
Department of Cardiac Surgery &
Department of Cardiac Anesthesia*
Institute of Cardiovascular Diseases Madras Medical Mission, Chennai, India
E- mail: okontakelechi@yahoo.com

*Correspondence: Okonta KE.
Grant support: None
Subvention: Aucun
Conflict of Interest: None

Abstract

Background: The management of coronary artery bypass graft (CABG) patients, especially in high risk patients ,can be challenging as the postoperative periods may be characterized by a low cardiac output state. Inotropes used in the perioperative periods to increase cardiac output may be detrimental thus making the use of mechanical devices like intra-aortic Balloon pump (IABP) for circulatory assistance desirable.

Aims & Objectives: To study the use of intra-aortic balloon pump in coronary artery bypass patients in preoperative and post operative settings and factors that affect morbidity and mortality.

Setting: Madras Medical Mission, Chennai, India.

Methods: A retrospective study of 3974 consecutive patients who had CABG done between March 2007 and February 2011 with or without additional procedures. One hundred and seven (2.7%) patients had IABP instituted either pre-operatively or postoperatively when it was obvious the patient will need cardiac assistance. The demographic data, clinical features, the indications for insertion, management offered and outcome , the creatinine levels, the duration of intraarortic balloon pump, the intensive care unit(ICU) and Hospital stay were analyzed for means and standard deviations and Pearsons Chi-square test using SPSS 10.0 window soft ware version with significant value of p-value<0.005.

Results: The mean age of all the patients was 59.7 + SD 10.7, 85(79.4%) patients were males,22(20.6%) were females .Out of the 107 patient who had IABP insertion, 59(55.1%) patients had IABP inserted preoperatively and 48(44.9%) postoperatively. The creatinine levels after the insertion of IABP in 68 patients was<1.5mg/dl and in 39 patients was>1.5mg/dl with mortality of 15.0% for the preoperative insertion group versus 29.0% for the postoperative group respectively (p=0.005). The preoperative and postoperative insertion ICU stay were 8.3+4.7 days and 5.7+1.6days respectively (p=0.005) and mortality were16.8% and 27.1 %( p=0.005) respectively

Conclusion

Early institution of intra-aortic balloon pump gives a better outcome even in high risk coronary artery bypass graft patients as it reduces ICU stay and mortality, and elevated post-insertion creatinine levels has been shown to be an indicator of impending mortality and so an early warning for putting in place mitigating protocols.

Key words: Intra-aortic balloon pump, Coronary artery bypass graft, Maximum inotropic dose, Creatinine levels, Low Cardiac Output Syndrome.

INTRODUCTION

The management of patients with coronary vascular disease can be challenging especially in patients with severe left ventricular dysfunction and critical left main or severe triple vessel disease [1]. Postoperative periods may also be characterised by low output cardiac state [2] with attendant morbidity and mortality and thus action needs to be intensified to forestall these.

Inotropes used in the perioperative or critical care periods to increase cardiac output can, in addition to increasing myocardial contractility, have other effects which may be detrimental on preload, after-load, heart rhythm, ventricular relaxation and myocardial oxygen demand. This may make the use of inotropes counterproductive [3] and the need for mechanical devices like intra-aortic balloon pump (IABP) for circulatory assistance desirable. This pump does not only decrease myocardial oxygen demand but increases its supply, improves ventricular after-load and subsequently improve the perfusion to the other vital organs. This pump serves these functions especially in coronary bypass graft (CABG) patients. CABG is the commonest cardiac surgery done in this institution as shown in a recent review [4]

The use of the IABP with some pharmacological agents may influence the eventual size of the infarcted segment of the myocardium by preventing the extension of the myocardial infarction as a result of improved coronary blood flow [5].The insertion of IABP is an invasive procedure with several potential complications; as a result, its usage should be accurately tailored to high risk patients with persistent low cardiac output state in order to prevent the attendant high mortality and morbidity. The concept of using IABP to produce diastolic augmentation of the coronary and systematic blood flow was first illustrated by Moulopoulos et al [6] and the first indication 5 years afterward was for cardiogenic shock in a 48 year old woman who was unresponsive to the traditional therapy [7]

We therefore set out study the outcome of using intra-aortic balloon pump in coronary artery bypass graft patients in the preoperative and post operative periods over a 4-year period at Madras Medical Mission.

PATIENTS & METHODS

Out of the 3974 consecutive patients managed at Madras Medical Mission,Chennai,India from March 2007 to February 2011 who had had coronary artery Bypass graft (CABG) 107(2.9%) needed intra-aortic balloon pump insertion to support their cardiac function. Theses 107 patients form the subject of this retrospectively study. The demographic data, the indications for surgery and insertion, the left ventricular ejection fraction(LVEF),the premorbid state, the creatinine levels, the duration of cardiopulmonary bypass(CPB) and IABP, Intensive care unit(ICU) and hospital stay and 30 day in-hospital mortality were analyzed using SPSS 10.0 window soft ware version. The mean, standard deviation (SD)and Pearsons Chi-square testing were applied where necessary ,and significant if p value<0.005.

Surgical Techniques

The catheter was inserted in patients who were haemodynamically unstable with the mean arterial pressure persistently lower than 70mmhg and cardiac index less than 2.0 l/min/m2 irrespective of maximum dose inotropic support with any of the following 2 or 3 inotropes (Dopamine 20microgram/kg/min or adrenaline0.1microgram/kg/min or Noradrenaline 0.1microgram/kg/min) The device has two major components: (i) a double-lumen 8.0-9.5 French catheter with a 25-50 ml balloon attached at its distal end; (ii) a console with a pump to drive the balloon. The balloon is made of polyethylene and is inflated with helium gas driven by the pump. Helium is often used because its low density facilitates rapid transfer of gas from console to the balloon. It is also easily absorbed into the blood stream in case of rupture of the balloon.

It was inserted percutaneously into the right common femoral artery with or without introducer sheath using the modified Seldinger technique. Once vascular access was obtained, the balloon catheter was inserted and advanced into the descending thoracic aorta, with its tip 2 to 3 cm distal to the origin of the left subclavian artery which was confirmed with a chest radiograph and fluoroscopy after insertion.

The outer lumen of the catheter was used for delivery of gas to the balloon and the inner lumen is be used for monitoring systemic arterial pressure. The console is programmed to identify a trigger for balloon inflation and deflation. The most commonly used triggers are the ECG waveform and the systemic arterial pressure waveform on the cardiac monitor console. The balloon is inflated at the onset of diastole, which corresponds to the middle of the T-wave. The balloon deflated at the onset of Left Ventricular systole, and that corresponds to the peak of the R-wave. Though automated, poor ECG quality, electrical interference, and cardiac arrhythmias could result in erratic balloon inflation hence the need for vigilance during the procedure.

The balloon was set to inflate after the aortic valve closure (which corresponds to the dicrotic notch on the arterial waveform) and deflate immediately before the opening of the aortic valve (which corresponded to the point just before the upstroke on the arterial pressure waveform). Intra-aortic balloon pump(IABP) timing refers to inflation and deflation of the IABP in relation to the cardiac cycle. Depending upon the patient's haemodynamic status, the balloon was programmed to assist every beat (1:1). With haemodynamic improvement, the device was 'weaned' to less frequent cycling.

When the catheter was about to be removed, the area below the arteriotomy was compressed to allow the blood from the proximal portion to flush out any clots before compressing the area for about 30 minutes while observing the limb for any evidence of compromised perfusion.

RESULTS

The mean age of all the patient was 59.7+10.7 years, 85(79.4%) patients were males, 22(20.5%) were females. The institution of IABP in 59(55.1%) patients was preoperatively and in 48(44.9%) patients it was perioperative. The mean height was162.0+9.7cm.The height of 52(48.6%) patients in the study participants was <162cm, in 55(51.4%) patients it was ranged between 162 and 185cm .The left ventricular ejection factor in 58(54.2%) was <35%, while 29(27.1%) ranged between 35-55% while in 20(18.7%) patients it was >55 %. The premorbid status of the patients was as follows : 23(21.5%) patients were diabetic, 9(8.4%) were hypertensive, 14 (13.1%)were hypertensive and diabetic, 5(4.7%) had chronic renal diseases and the remaining 56(52.3%) had no premorbid factors. The New York Heart Association (NYHA) in 6(5.6%) patients was Class I, 58(54.2%) class II, 43(40.2%) class III and none in class IV. The indications for the surgery were as follows: 11(10.3%) patients for failed percutaneous transluminal coronary angioplasty( PTCA) , 49(45.8%) with symptomatic Triple vessel disease with severe left ventricular dysfuction,21(19.6%) had recent acute myocardial infarction and mechanical defects(such as Ventricular septal defect-VSD, papillary muscle rupture) ,21(19.6%) for CABG and valve replacements,3(2.8%) for critical left main stenosis (Table 2).The indications for insertion of IABP were as follows: 19(17.8%) had acute myocardial infarction and mechanical complications(such as VSD, papillary muscle rupture etc), 44(41.1%) had low cardiac output syndrome, 32(30.8%) had recent acute myocardial infarction with low cardiac output(post infarction unstable angina) and 12(11.2%) had unsuccessful/difficult weaning off cardiopulmonary bypass ( Table 3). The complications were as follows:36(33.6%) patient had acute renal failure which necessitated peritoneal dialysis, 11(10.3%) patients had mild limb ischaemia(reduction in the pulse volume which resolved with discontinuation), 3(2.8%) had Compartment syndrome which necessitated discontinuation and fasciotomy. The creatinine level in 68(63.6%) was< 1.5mg/dl and in 39 was >1.5mg/dl(p value <0.005)(Table 4).The CPB time was 146.1+84.6min,the IABP time was 84.4+6.5 hr, the ICU stay8.3+4.2 day, the Hospital stay 18.4+10.5 day and the 30 day in-hospital mortality was 47(43.9%)(Table1). The cause of death in 42 (89.4%) patients was persistent low cardiac output, in 2(4.3%) patients was multiple organ failure, in 2(4.3%) patients was overwhelming sepsis, while in1patient it was respiratory failure. Thirty one (86.1%) patients with renal failure died and the cause of death was persistent low cardiac output in 29(93.5%) and overwhelming sepsis in 2(6.5%) patients. The mortality in preoperative insertion and postoperative insertion were 16.8% and 27.1% respectively (p value<0.005).The mortality for patients with creatinine level after insertion<1.5mg/dl was 15.0% and for patients with creatinine levels >1.5mg/dl was 29.0 %( p value< 0.005).

Discussion

The indications for the insertion of IABP have been evolving and increasing since its first use 5,7, 8 . However, not too many new indications have emerged (Table 3).The commonest indication remains low cardiac output syndrome (either preoperatively or postoperatively)5. This was also observed in 88(82%) of the patients reviewed in our study.

The findings from our study showed that the morbidity and mortality was higher in patients whose heights were 162cm and below (Table5). This is in tandem with previous findings which noted that small body surface area (BSA) was a predictor of increased complications [10] and that commensurately smaller IABP catheter size contributed to the decreased morbidity9-11.

Instituting IABP preoperatively yielded better outcome than postoperatively because the our finding showed that morbidity and mortality were less (Table 1). Similarly, other studies corroborated with this finding12, 13. The reason was that the perfusion of end organs was tackled earlier before irreversible damage could occur as a result of the delayed insertion.

While some authors stated that there was improved renal status as a result of increased perfusion from reduced ventricular afterload after insertion of the pump, others reported deterioration of renal status10-14. However,there was increased mortality when there was post insertion increase in creatinine levels ; the operative mortality of IABP institution was 29.0% when there was progressive increase in creatinine levels to greater than 1.5mg/dl after the insertion of IABP (Table3). Progressive increase in creatinine levels after the institution of IABP is an important prognostic factor that depict poor outcome as previously documented12, 15.We observed an increase in creatinine levels of >1.5mg/dl, as a marker of poor prognosis.(p value<0.005) Again, the progressive deterioration renal function following the insertion of IABP as evidenced by decreasing in urinary output or increasing creatinine should raise the suspicion of the presence of the balloon or clot at the juxta-renal area, or the possible effects of iatrogenic aortic dissections in this region10-14 besides the progression of the clinical state of low cardiac output. Several literatures are awash with the advantage of timely institution of IABP as a way of improving the clinical outcome of patients11-16.This is evident in our studies as most of all the favourable parameters where better for patients who had IABP instituted preoperatively.

Conclusion: Early institution of intra-operative balloon pump gives a better outcome even in high risk coronary artery bypass graft patients as it reduces ICU stay and mortality; elevated post insertion creatinine levels has been shown to be an indicator of impending mortality and so an early warning for putting in place mitigating protocols

Acknowledgement

We are grateful to Mr M.Theodore for data collection and Ms S. Kumari and Ms G. Jeeva for statistical analyses of the data.

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