Intraaortic balloon pump boon for off-pump coronary artery bypass grafting

Introduction

Off-pump coronary artery bypass (OPCAB) techniques have continued to evolve over the years, but one area of concern for the surgeon remains hemodynamic decompensation during coronary anastomosis. Hemodynamic decompensation during OPCAB has been traditionally treated by institution of cardiopulmonary bypass. Emergency conversion of OPCAB to an on-pump procedure is associated with increased morbidity and mortality, and hence is undesirable. ¹ Hemodynamic decompensation during OPCAB can be due to either decreased preload resulting from hypovolemia or myocardial dysfunction resulting from ischemia. Hypovolemia can be easily treated using volume resuscitation. Hypotension due to myocardial ischemia can be treated using inotropic support. For hypotension refractory to inotrope therapy, an intraaortic balloon pump (IABP), which is routinely used to treat cardiogenic shock, has been used. There have been reports of use of ventricular assist device to prevent conversions, however, IABP use during OPCAB to prevent conversion has not been reported before. ² Various studies have suggested that preoperative IABP insertion in high-risk patients may facilitate OPCAB. ³ We perform OPCAB routinely in all isolated coronary artery bypass cases, and use an IABP to treat hemodynamic compromise rather than for preoperative prophylactic use. The objective of this study was to assess the effectiveness of IABP in preventing OPCAB conversions to cardiopulmonary bypass.

Patients and methods

All 529 cases of consecutive unselected isolated coronary artery bypass grafting operated on by the first author were included in this retrospective study of prospectively collected data and operation notes. The operation records of all patients were analyzed.

OPCAB was performed routinely in all patients. Complete revascularization was attempted in every case. An IABP was kept on standby with electrocardiogram leads connected. Each patient had femoral artery access and a central venous line (central line or pulmonary artery catheter) inserted under local anesthesia before induction of general anesthesia. We followed a standard protocol for OPCAB in all patients. After pericardiotomy, cardiac manipulation was avoided and only the left anterior descending artery (LAD) was inspected and palpated. We did not use a deep pericardial stay suture. Warm saline-soaked gauze pads were used to position the heart. A suction type of stabilizer and mister bower were used for OPCAB. Grafting of the LAD can be easily performed with minimal cardiac manipulation. We used maximum number of arterial grafts and both internal mammary arteries (IMA) when possible. Vein grafts were used when arterial grafts were not suitable for use, or to supplement the length of arterial grafts. Aortic clamping was avoided when possible. Both IMA were used in situ. The left IMA was used most frequently to graft the LAD, and sometimes the right IMA was used for LAD grafting; the other IMA was used as a composite graft with radial artery or saphenous vein. After grafting the LAD, the heart was lifted and the other target vessels were assessed. A composite graft between the other IMA and radial artery was created, ⁴ and the remaining grafts were constructed.

In every patient, an inotropic infusion was kept connected so it could be started without delay. Any ventricular arrhythmia considered to be of ischemic origin was treated by medical therapy initially, and by IABP insertion if refractory. Ventricular arrhythmia was treated by direct current shock and an intravenous lidocaine bolus. Intravenous amiodarone infusion was started. Hypokalemia and acidosis were corrected. If hemodynamics were satisfactory after the restoration of normal rhythm, off-pump grafting was continued. However, if ventricular arrhythmia recurred, myocardial contractility was poor, and/or hemodynamics remained unsatisfactory, IABP was inserted.

If systolic arterial blood pressure was less than 100 mm Hg in spite of inotropic support, IABP insertion was considered. If systolic pressure was less than 100 mm Hg, we assessed the cardiac filling pressure. The central venous pressure or pulmonary artery diastolic pressure indicates cardiac filling. In the presence of low cardiac filling, temporary lowering of head end to increase systolic pressure and volume resuscitation were initiated. However, in the presence of increased filling pressure, elevation of the head end will improve hemodynamics. In such situations, inotropic support with dobutamine (up to 10 µg kg⁻¹) and norepinephrine (up to 0.1 µg kg⁻¹) were used. If blood pressure remained refractory and/or myocardial contraction appeared sluggish, IABP was inserted.

After IABP insertion and a functioning graft to the LAD was achieved, if the patient continued to require high doses of inotropics, we revascularized the right coronary artery or posterior descending artery, which can be performed without too much cardiac manipulation. The IABP was removed in the postoperative intensive care unit, depending on the clinical condition of the patient.

Results

Table 1 shows the distribution of patients according to left ventricular ejection fraction. An IABP was inserted in 33 (6.2%) patients during grafting to treat ischemia-induced hemodynamic instability and arrhythmia. Table 2 shows the various indications for IABP insertion; intraoperative hemodynamic compromise was the commonest indication. In patients with hemodynamic compromise, after IABP insertion, systolic blood pressure improved and cardiac filling pressure decreased. These favorable changes in hemodynamics allowed us to complete OPCAB without conversion to cardiopulmonary bypass. Often in these patients, performing the distal coronary anastomosis and reestablishing blood flow in the coronary artery resulted in further improvement in hemodynamics (increased systemic blood pressure and decreased cardiac filling pressure). In patients with arrhythmia, after IABP insertion normal rhythm was restored and hemodynamics improved. In these patients, an improvement in hemodynamics was also noted after distal coronary anastomosis. OPCAB conversion was avoided in all 529 patients. Complete revascularization was achieved in all patients. There was no IABP-related complication in the patients who required IABP insertion. Table 3 shows the distribution of arterial and venous grafts. A total of 2256 grafts were created (range 1–9). Table 4 shows the distribution of patients according to the number of grafts they received; 406/529 (76.7%) patients received 4 or more grafts. Forty-seven patients who received 1 or 2 grafts had single-vessel disease of the LAD and received a graft to either the LAD alone (7 patients) or the LAD and diagonal.

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Table 1.

Use of an intraaortic balloon pump in 529 patients undergoing off-pump coronary artery bypass.

IABP insertion	Total	EF ≤ 30%	EF 31%–49%	EF ≥ 50%
No. of patients	529	153	198	178
No IABP	486	119	195	172
IABP	43 (8.1%)	34 (22.2%)	3 (1.5%)	6 (3.4%)
Preoperative	6	6	0	0
Intraoperative	33	25	3	5
Postoperative	4	3	0	1

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Table 2.

Indications for intraaortic balloon pump insertion.

Indication	Preoperative	Intraoperative	Postoperative
Hemodynamic instability	1	29	1
Arrhythmia	0	4	3
Left ventricular failure	2	0	0
Unstable angina	3	0	0
Total	6	33	4

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Table 3.

Distribution of grafts in 529 patients.

Grafts	No. of patients
Bilateral IMA grafts	484 (91.5%)
Total grafts per patient	4.2
Arterial grafts per patient	3.8
Vein grafts per patient	0.4

IMA: internal mammary artery.

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Table 4.

Distribution of patients according to number of grafts received.

No. of grafts	No. of patients
9	1 (0.2%)
8	4 (0.8%)
7	14 (2.6%)
6	56 (10.6%)
5	142 (26.8%)
4	189 (35.7%)
3	76 (14.4%)
2	40 (7.6%)
1	7 (1.3%)

Discussion

OPCAB technique continues to evolve, particularly in India and other Asian countries. ⁵ There are some concerns about short and long term results of OPCAB compared to conventional on-pump coronary bypass grafting which was previously considered the gold standard for surgical revascularization. We tried to address the two key issues associated with OPCAB skepticism in this study: conversion to cardiopulmonary bypass, and completeness of revascularization. ⁵ To prevent OPCAB conversion, we followed a standardized protocol in every patient. Using this protocol, we were able to treat 529 consecutive unselected cases of OPCAB with no conversions to cardiopulmonary bypass. It has been well established that the rate of conversion decreases with operator experience.^1,6 It can be argued that many of the conversions are the result of a panic reaction by the surgeon or anesthetist or both. In view of the adverse outcomes of such conversions, the rate of conversion may be considered a surrogate performance indicator in OPCAB. ¹

Management of hemodynamic instability during OPCAB is not as complex as touted. Hypotension due to hypovolemia is easily treated by volume resuscitation. Just as hypotension due to myocardial infarction in cardiogenic shock is treated using IABP support, ischemic myocardial dysfunction-induced hypotension during OPCAB can also be managed by IABP, and thus avoid conversion. Ischemia-induced arrhythmias refractory to pharmacological agents can also be successfully treated with an IABP. There are reports of the use of a ventricular assist device to prevent OPCAB conversion. ⁷ Many articles describe the use of prophylactic IABP in high-risk patients during OPCAB. ⁸ We feel that with established femoral access, proper training and motivation of team members, and keeping an IABP on standby, IABP support can be started at very short notice. We feel routine prophylactic use of preoperative an IABP to facilitate OPCAB is unnecessary even in high-risk patients because we often observe an increase in systemic blood pressure and a decrease in cardiac filling pressure after graft flow is established to ischemic coronary artery. Preoperative IABP insertion should be reserved for patients with unstable angina refractory to medical therapy, left ventricular failure, or cardiogenic shock.

What constitutes complete revascularization remains controversial. It is often observed that the requirement of more than 3 grafts is considered an indication for an on-pump procedure rather than OPCAB. ⁹ In our series, the average number of grafts per patient was more than 4, and 76% received 4 or more grafts. No diseased artery was left without a bypass graft because of a technical difficulty. Earlier revascularization of the posterolateral and inferior vessels used to be considered difficult during OPCAB, but with refinement of the technique, these vessels are being routinely grafted during OPCAB without any hemodynamic instability. Actually, we find grafting these vessels easier during OPCAB because no assistance is required to retract the heart as in on-pump grafting. We successfully performed 9 grafts in a patient with diffuse coronary artery disease. We feel that without the stress imposed by prolonged aortic crossclamp time or cardiopulmonary bypass time, complete revascularization can be performed more often than not. This is particularly true in patients with small vessels and diffuse coronary artery disease, which are prevalent in our part of the world. We sometimes even have to cut across a severely diseased segment and perform a long anastomosis using innovative techniques such as onlay patch plasty. It is obvious that such a long anastomosis will increase the cardiopulmonary bypass and clamp time and deter surgeons from performing complete revascularization. With OPCAB, our threshold for sequentially grafting the LAD has become low; for distal LAD disease, we use sequential left IMA grafts to the mid and distal LAD, whereas in on-pump coronary artery bypass, surgeons might be inclined to leave the distal LAD disease to medical management.

Several limitations of our study should be recognized. The study was retrospective in nature. Moreover, it is the experience of a single surgeon with a strong bias for OPCAB. There was no control group of patients who required conversion to cardiopulmonary bypass. Further study on the use of IABP insertion to prevent OPCAB conversion is warranted.

We concluded that complete revascularization and OPCAB conversion are interrelated. Apprehension of OPCAB conversion and its sequelae will always be in the mind of a surgeon while performing lateral wall revascularization. This is particularly true for a beginner in a low-volume center. The apprehension of OPCAB conversion can lead to incomplete revascularization. This may be the reason for the widespread reports of incomplete revascularization in OPCAB. ⁵ The detrimental effects of conversion and incomplete revascularization are well highlighted in the literature, but there are very few articles that provide a framework for prevention of emergency conversion in OPCAB. In our large series, we found that conversion can be avoided and complete revascularization in OPCAB is possible by timely and effective use of an IABP.