**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% [3–6]. 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, intraaortic 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 [9–12]; 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.

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.

*Perioperative Use of Impella 5.0/5.5 in High-Risk Coronary Artery Bypass Grafting DOI: http://dx.doi.org/10.5772/intechopen.113370*

**Figure 1.** *A scheme of Impella 5.5.*

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].
