Perioperative Use of Impella 5.0/5.5 in High-Risk Coronary Artery Bypass Grafting

Abstract

Coronary artery bypass grafting in patients with low ejection fraction is a high-risk operation because of high incidence of postoperative low cardiac output syndrome. Impella 5.0/5.5 is a surgically implanted left ventricular assist device that can unload the left ventricle. It is capable of full circulatory support. A perioperative use of Impella 5.0/5.5 can potentially improve the surgical outcomes of high-risk coronary artery bypass grafting by avoiding postoperative low cardiac output syndrome. However, the outcomes of Impella 5.0/5.5-supported coronary artery bypass grafting have not been reported frequently. In this chapter, the most recent evidence and the pros and cons of the Impella 5.0/5.5 use at the time of high-risk coronary artery bypass grafting are discussed.

1. Introduction

Coronary artery bypass grafting for patients with severely reduced cardiac function is challenging because of the high incidence of postoperative low cardiac output syndrome [1]. A study that investigated 55,515 patients in New York State database reported that patients with low ejection fraction had >4 times higher mortality than patients with high ejection fraction [2].

Low cardiac output syndrome is defined by an inadequate cardiac pump function resulting in impaired oxygen delivery and tissue hypoxia. The incidence of postoperative low cardiac output syndrome has been reported to be 2–27%, and it carries high hospital mortality of 25–50% [3, 4, 5, 6]. Preoperative systolic heart failure, especially left ventricular ejection fraction less than 30%, is known to be a major risk factor for postoperative low cardiac output syndrome.

Since the occurrence of low cardiac output syndrome is associated with other morbidities such as renal and pulmonary failure, stroke, myocardial infarction, sepsis, and prolonged hospital stay, it would increase the health care costs. A study that reviewed 59,810 patients having cardiac surgery from 164 hospitals in the United States showed that hospital costs elevated to $64,041 in patients with low cardiac output syndrome versus $48,086 in patients without the same [4].

Therefore, it is crucial for healthcare providers to understand how to avoid and manage postoperative low cardiac output syndrome after a high-risk coronary artery bypass grafting.

2. Mechanical circulatory support for low cardiac output syndrome

In the setting of postoperative low cardiac output syndrome, there has been an overall increase in the use of temporary mechanical circulatory support.

Intra-aortic balloon pump has been widely used for postoperative circulatory support in patients with reduced cardiac function [7, 8]. However, it usually requires bed rest, which adversely affects patients’ recovery and mobility. In addition, intra-aortic balloon pump may not provide adequate circulatory support for a profound cardiogenic shock.

Impella 2.5 and Impella CP have been widely used in the field of percutaneous coronary intervention. They can be percutaneously inserted through the femoral artery or axillary artery. The benefit of prophylactic use of Impella 2.5 or CP in high-risk percutaneous coronary interventions was reported in several studies [9, 10, 11, 12]; however, prophylactic use of Impella in high-risk cardiac surgery has been scarcely reported.

Veno-arterial extracorporeal membrane oxygenation is the most advanced mechanical circulatory support device; however, it is associated with high incidence of complications, such as bleeding, thrombosis, vascular complications, acute renal failure, stroke, and infections. Another disadvantage includes patient immobility.

3. Introduction of Impella 5.0/5.5

Impella 5.0/5.5 with SmartAssist (Abiomed, Danvers, Massachusetts, United States of America) is a surgically implanted heart pump that unloads the left ventricle and therefore can reduce ventricular work. It is composed of 19 Fr microaxial pump and 21 Fr cannula mounted on a 9 Fr drive-line/bearing purge delivery catheter (Figure 1). The tip of the Impella is equipped with optical sensor technology, which can be detected by echocardiography so that the proper positioning of the device can be facilitated.

Figure 1.

A scheme of Impella 5.5.

Impella 5.5 is capable of full circulatory support, delivering up to 6.2 L/min. The indication of Impella 5.5 is short-term (14 days) use for the treatment of ongoing cardiogenic shock that occurs immediately (< 48 hours) following acute myocardial infarction or open-heart surgery or in the setting of cardiomyopathy, including peripartum cardiomyopathy, or myocarditis as a result of isolated left ventricular failure that is not responsive to optimal medical management and conventional treatment measures (including volume loading and use of vasopressors and inotropes, with or without intra-aortic balloon pump). The use of Impella 5.5 was approved by the Food and Drug Administration in 2019, and since then, more than 10,000 implants have been performed. In recent years, Impella 5.0/5.5 has been used as a perioperative hemodynamic support at the time of high-risk cardiac surgery. In addition to providing the adequate circulatory support, Impella 5.0/5.5 enables patients to ambulate, and it could optimize recovery.

A first multicenter prospective study of Impella 5/0/LD for patients developing cardiogenic shock or low cardiac output syndrome after weaning of cardiopulmonary bypass (RECOVER I) was reported in 2013 [13]. Sixteen patients were enrolled; all patients provided informed consent. The Impella 5.0/LD was inserted via the femoral artery or directly to the ascending aorta. The mean preoperative ejection fraction was 23+/−7%, and the patients had multiple comorbidities with high predicted risk of mortality. Despite that, the surgical outcomes were very good; 30-day, 6-month, and 1-year survival was 94, 81, and 75%, respectively.

4. Physiologic change after Impella placement

The most important physiologic effect of Impella is unloading the left ventricle, reducing left ventricular end diastolic pressure and left ventricular wall tension, and consequently decreasing left ventricular work and myocardial oxygen demand.

Secondary, Impella could result in an increase in mean arterial pressure, diastolic pressure, cardiac output, and consequently cardiac power output (calculated by mean arterial pressure x cardiac output/451). It could improve coronary perfusion and systemic perfusion.

Third, Impella could decrease pulmonary capillary pressure and reduce the right ventricular afterload.

The automated Impella Controller displays a real-time hemodynamic and catheter position information (Figure 2). This includes the mean arterial pressure, a left ventricular end diastolic pressure, total cardiac output, native cardiac output, and cardiac power output. These numbers can be utilized for patient management and during the weaning process. The Impella Controller can be accessible from any internet-connected device.

Figure 2.

Automated Impella controlled home screen.

Impella technology is load-dependent but not rhythm-dependent like intra-aortic balloon pump, which leads to a number of physiologic implications. The flow of Impella is afterload-sensitive in that forward flow through the pump decreases with increasing ventriculo-aortic pressure gradient. This sensitivity accounts for the characteristic phasic motor current fluctuations during the cardiac cycle with the highest pump flow and motor current achieved during systole when the gradient between left ventricle and aorta is minimal. This characteristic phasic flow pattern is reported as maximum and minimum flows on the Automated Impella Controller. The phasic motor current is also used in the positioning monitoring algorithm and allows for precise flow calculation. Furthermore, pump flow is preload-dependent because the pump needs sufficient inflow for normal pump output. In patients with acute hemodynamic distress due to left ventricular failure, preload is normally sufficient for normal pump action. Yet extremely impaired inflow may be observed in situations where left ventricular filling pressure is low, the left ventricular cavity is small, or severe right ventricular function impairment is present [14].

5. Implantation technique of Impella 5.0/5.5

The Impella 5.0/5.5 can be implanted via the axillary or subclavian artery [15], innominate artery [16, 17], and the ascending aorta (Figure 3) [18, 19, 20]. Since sternotomy is usually performed at the time of coronary artery bypass grafting, our favorite approach is through the ascending aorta. One of the advantages of the ascending aorta route is the nonnecessity of intraoperative fluoroscopy, which is usually required in the axillary or subclavian artery insertion.

Figure 3.

A scheme of Impella 5.5 insertion via the right axillary artery (left) and innominate artery (right).

The indications for use of Impella 5.0/5.5 are (a) severe left ventricular dysfunction (left ventricular ejection fraction <30%); (b) estimated prolonged use of cardiopulmonary bypass; (c) comorbidities such as liver disease, chronic kidney disease, chronic obstructive pulmonary disease, and peripheral vascular disease; (d) poor-quality targets, and a combination of these. The contraindications for use of Impella 5.0/5.5 are (a) mechanical aortic valve prosthesis, (b) aortic valve stenosis (equivalent to an orifice area of 0.6 cm² or less), (c) moderate to severe aortic insufficiency, (d) severe right heart failure, (e) combined cardiorespiratory failure, and (f) left ventricular thrombus.

We prefer to place Impella 5.5 prophylactically in high-risk cases, rather than placing it emergently after failing to wean cardiopulmonary bypass.

Our technique for Impella 5.5 placement via the ascending aorta is (a) initiation of the cardiopulmonary bypass with a distal ascending aorta cannulation; (b) a partial aortic clamp on the ascending aorta and aortotomy with adequate length; (c) a beveled 10-mm graft anastomosis to the ascending aorta in a side-to-end fashion at least 7 cm above the aortic valve; (d) a small incision is made in the left neck, and the 10 mm graft is tunneled above the skin; (e) aortic cross clamp and completion of coronary artery bypass grafting as usual; (f) insertion of Impella sheath through the 10-mm graft; (g) advancement of J-wire and pig-tail catheter into the left ventricle under a transesophageal echo guidance; (h) advancement of Impella guidewire into the left ventricle under a transesophageal echo guidance; (i) advancement of Impella 5.5 pump through the guidewire, the tip of Impella should be placed about 5 cm below the aortic valve and it should point toward the cardiac apex and away from the septal wall and mitral valve; (j) initiation of Impella 5.5 device; (h) removal of the Impella sheath and trim the graft to the neck incision; and (i) weaning of cardiopulmonary bypass and chest closure. The intraoperative picture is shown in Figure 4.

Figure 4.

An intraoperative picture of Impella 5.5 insertion into the ascending aorta via a prosthetic graft.

The tips and tricks for this technique are (a) make an adequate length of aortotomy, (b) bevel the graft so that anastomosis can be bigger than the circle area of 10-mm graft, (c) a transesophageal echo guidance (fluoroscopy is not usually necessary), (d) manual manipulation can be used when the Impella pump is passed through the graft anastomosis site, (e) the advancement of Impella could be easier if the blood is returned to the patient from the cardiopulmonary bypass circuit, and (f) do not make the graft length too short, because that would make the future Impella removal difficult.

6. Perioperative management of Impella 5.0/5.5

After the insertion of the Impella, the position of the device should be confirmed routinely with at least two views of transthoracic echocardiography such as parasternal long axis and apical four chamber views. Impella 5.5 does not have a pigtail in the tip as opposed to Impella 5.0. The malposition of the device could easily happen. The device could attach or push the ventricular septum if it is rotated away from the mitral valve and that could cause suction events. The Impella pump needs to be away from the ventricular septal wall. Functional mitral stenosis caused by the dislocation of the device shaft on the anterior mitral leaflet was reported [21]. A big benefit of Impella system through the direct aorta approach is that patients can be extubated and are able to ambulate with Impella system. That can promote patients’ quick recovery.

Balthazar and colleagues reviewed the management of mechanical circulatory support [22]. The weaning of Impella should be managed by a multidisciplinary team including cardiac surgeons, cardiologists, intensivists, and perfusionists. Before starting weaning, the patients should have normal lactated levels and on low pressors or inotropes. A daily turndown of the Impella flow with a cautious hemodynamic evaluation should be attempted. When the increase in native cardiac output after weaning of Impella meets the patients’ metabolic needs and does not result in significant increases in ventricular pressures, Impella could be removed.

The removal of Impella 5.0/5.5 can be done even with local anesthesia in the intensive care unit. No repeat sternotomy is required. After the Impella is weaned off, the device is pulled out from the graft. The graft is clamped and tied off with heavy silk string or oversewn with monofilament polypropylene sutures. The graft can be closed with surgical staplers. The stump of the graft is put back into the neck incision, and the incision is closed.

7. Postoperative outcomes

The postoperative outcomes of coronary artery bypass grafting with a support of Impella 5.0/5.5 have not been reported frequently. The postoperative outcomes of Impella supported CABG are summarized in Table 1. Overall, the reported outcomes have been excellent in consideration of high-risk patients’ population.

	Number of cases	Operation	30-day mortality	Duration of Impella
Benke et al. [23]	14	10 coronary artery bypass grafting, 2 aortic valve surgery, and 2 coronary artery bypass grafting and valvular surgery	7.2%	4 days
Ranganath et al. [24]	13	All coronary artery bypass grafting	0%	5.7 days
Sabra et al. [25]	9	5 isolated coronary artery bypass grafting, 4 coronary artery bypass grafting, and valvular surgery	11%	Not reported
Akay et al. [26]	1	Off-pump coronary artery bypass grafting	100%	2 days
Tavilla et al. [27]	1	Off-pump coronary artery bypass grafting	0%	Not reported
Smith et al. [28]	4	All coronary artery bypass grafting	25%	0–500 hours
Ramzy et al. [29]	12	7 postcardiotomy cardiogenic shock, 5 coronary artery bypass grafting	16.4%	Not reported
Funamoto et al. [30]	12	7 isolated coronary artery bypass grafting, and 5 valve or combined valve/coronary/aortic procedure	0%	6.3 days
Marin-Cuartas et al. [31]	19	Postcardiotomy cardiogenic shock	15.8%	Not reported

Table 1.

Surgical outcomes of Impella-supported coronary artery bypass grafting.

8. Complications of Impella 5.0/5.5 use

There are some complications that are specifically related to Impella 5.0/5.5 use. Ghannam and colleagues reported a case of aortic valve injury related to the Impella 5.5 use [32]. The Impella 5.5 was removed on postoperative day 8, and the patient went into cardiogenic shock due to aortic valve leaflet injury, which required aortic valve replacement.

Pump thrombosis is a rare complication, but it has been reported [33]. Systemic anticoagulation with heparin is suggested; however, it can increase the risk of bleeding [34, 35]. Currently, there are no clear data in terms of optimal anticoagulation regimen [36].

Left ventricular perforation could also happen because of the manipulation of the guidewire and cannula into the left ventricle. There were multiple case reports for that [37, 38, 39, 40, 41]. Surgeons should suspect left ventricular perforation when there is a newly discovered pericardial effusion, change in waveform on the Impella controller placement signal, or patients’ rapid deterioration.

Debenham and colleagues reported adverse events related to Impella 5.0/5.5 in the American College of Cardiology meeting, using the manufacturer and user facility device experience database (the abstract is available at https://www.jacc.org/doi/epdf/10.1016/S0735-1097%2822%2901478-4). Compared with Impella 5.0, the Impella 5.5 had a higher incidence of pump stoppage (51.7% vs. 10.9%, p < 0.001) and LV perforation (13.3% vs. 1.7%, p < 0.001) with a lower incidence of stroke (0% vs. 8.4%, p < 0.021), mitral valve regurgitation (1.6% vs. 11.8%, p < 0.02), hemorrhage (8.3% vs. 21.8%, p < 0.024), and sepsis (0% vs. 6.7%, p < 0.04). There was no difference in the incidence of vascular injury, limb ischemia, aortic valve damage, pump thrombosis, or hemolysis between the two devices.

The other complications include bleeding, infection, stroke, and acute kidney injury, which are accompanied with usual coronary artery bypass grafting. Since the patient population is sicker than regular patients, the occurrence of complications was reported to be higher than normal.

9. Conclusions

The Impella 5.0/5.5 can be easily inserted into the ascending aorta via a prosthetic graft and can provide a tremendous hemodynamic support during and after high-risk coronary artery bypass grafting. It could improve surgical outcomes by avoiding a postoperative low cardiac output syndrome, which is associated with high operative mortality. Direct insertion of an Impella 5.0/5.5 to the ascending aorta allows the patients to ambulate and recover until heart function improves. The explanation of the device is easy and does not require a repeat sternotomy.