Indication
Device
Reason of implantation
Bridge-to-decision
vaECMO, Impella, TandemHeart
Cardiogenic shock (INTERMACS Level 1); need for further evaluation before implantation of a long-term device (e.g., evaluation of neurological outcome after cardiopulmonary resuscitation)
Bridge-to-recovery
vaECMO, Impella, TandemHeart
Postcardiotomy syndrome, reperfusion syndrome after heart transplantation, acute myocardial infarction or myocarditis
Bridge-to-transplantation
VAD
Hemodynamic instability with secondary organ failure (e.g., renal insufficiency) despite inotropic therapy
Cave: Device-associated sensitization by preformed antibodies increases risk of antibody-mediated rejection after heart transplantation
Destination therapy
VAD
End-stage heart failure (NYHA state IV, ejection fraction < 30 %) with recurrent cardiac decompensation despite best medical therapy and presence of contraindications for heart transplantation
20.1 Percutaneous Assist Device Support
In the emergency setting of cardiogenic shock, acute decompensated heart failure and large myocardial infarctions, percutaneously implantable short-term devices are used frequently in the cardiac catheterization laboratory. The ease of use of modern devices suggests a benefit in high-risk percutaneous coronary intervention and other procedures. But evidence on meaningfully improved outcomes is limited [3].
The intra-aortic balloon pump (IABP) has long been the only representative of this group with a broad range of indications of its adjunctive use in heart failure and cardiogenic shock. Recently, the 2013 STEMI guidelines have downgraded the IABP from a I to a IIa recommendation [4], because of no mortality benefit with or without IABP at 30 days after myocardial infarction induced cardiogenic shock in the Intra-aortic Balloon Support for Myocardial Infarction with Cardiogenic Shock (IABP-SHOCK II) trial [5]. The IABP is increasingly replaced by the veno-arterial extracorporeal membrane oxygenation (vaECMO), the Impella pump (Abiomed) or the Tandem Heart (CardiacAssist). The cannulas of the vaECMO are implanted through the femoral artery and vein. An extracorporeal centrifugal pump generates high blood flow rates without load relieve of the left ventricle. An external oxygenator ensures gas exchange. Complications are severe bleeding, hemorrhagic stroke, peripheral and central embolisms and infections [6]. Until now, there are no recommendations from the ACC/AHA concerning timing of implantation [4].
The TandemHeart device has, comparable to the vaECMO, an external centrifugal pump. The inflow cannula is placed transseptally in the left atrium and the outflow cannula in the femoral artery. A flow of 3.5–4.5 l/min can be generated. Complications include pericardial tamponade, major bleeding, aortic regurgitation, critical limb ischemia, arrhythmias and iatrogenic atrial septal defect [7]. The TandemHeart can be a good option in patients with severe aortic stenosis. A higher cardiac index but no mortality benefit at 30 days was shown after randomization to IABP or TandemHeart [8]. The Impella pump is introduced via the femoral artery and directed via the aortic valve. The axial flow pump delivers non-pulsatile blood flow to the ascending aorta, which results in load relieve of the left ventricle. Currently, three Impella systems (Impella 2.5, 5.0 and CP) with different maximum flow rates are used. The Impella–EUROSHOCK-registry evaluates the Impella 2.5 device in patients with cardiogenic shock after acute myocardial infarction. Men tended to have a higher 30-day mortality, which did not reach statistical significance [9]. Due to the wide flow range and the possibility of fast and atraumatic implantation, the Impella is also used for hemodynamic stabilization in elective high-risk coronary procedures despite convincing evidence of a net benefit [10]. The most commonly reported complications are limb ischemia, vascular injury, bleeding and hemolysis [11]. The Impella LP 2.5 versus IABP in Cardiogenic Shock (ISAR-SHOCK) trial found a slightly higher cardiac index at 30 min in the Impella group compared to the IABP group, but no differences in mortality rates at 30 days were seen [12].
Despite the hemodynamic improvement seen with Impella and TandemHeart in comparison to IABP, no study has shown a survival benefit yet. Therefore, there is actually only a class IIb recommendation for alternative left ventricular assist devices in patients with severe cardiogenic shock [4]. The majority of individuals, in whom percutaneous ventricular assist devices are used, are male. The distribution of generally two-thirds or more male patients, however, most likely only mirrors the underlying disease distribution since it resembles coronary artery disease and acute heart failure samples [8, 13]. Data considering gender aspects in percutaneous assist device support are almost non-existent although increasing numbers of patients are supplied with percutaneous circulatory support.
20.2 Historical Development of Surgical Mechanical Circulatory Support
20.2.1 From the First Heart-Lung Machine to the Total Artificial Heart
The first heart-lung machine (HLM) was developed by John H. Gibbon in 1953. In 1966, Michael E. DeBakey implanted a left VAD (LVAD) successfully for the first time, even before the first heart transplantation was performed. The first total artificial heart was implanted by Domingo Liotta and Denton A. Cooley in 1969. Significant advances in the development of VAD systems were seen in the late 1980s: The assist devices of the first generation were pulsatile-flow devices. The systems of the second generation (1990s) were characterized by continuous flow. Similar to the third generation devices, they had a longer half-life and the possibility of intracorporeal implantation.
20.2.2 From Paracorporeal to Intracorporeal Systems
The main representative of the paracorporeal systems is the Thoratec VAD system. Both its ventricles and cannulas are placed on the anterior abdominal wall. Still of importance is the Berlin Heart EXCOR VAD paracorporeal system. To date, it is the only lifesaving opportunity for children with cardiac decompensation. The first representative of the intracorporeal systems, the HeartMate I, is a pulsatile device and only of historical interest today. The modern pumps (e.g., HeartMate II, HVAD) are continuous-flow systems with a higher energy efficiency and a lower wastage. However, a higher rotation speed is needed, which increases the risk of hemolysis. In addition, as complete ventricular unloading by continuous flow devices prevents blood flow via the aortic valve, its loss of function leads to remodeling processes and aortic regurgitation.
20.2.3 Technical Issues of an Intracorporeal VAD Implantation Using the HVAD (HeartWare) Pump
The implantation rates of the HVAD continue to rise because of the small pump size, the technically easy handling and the improved adverse event rates. Surgery can be performed with or without HLM via conventional sternotomy or minimally invasive via two thoracotomies. Apical purse-string sutures are placed at the optimal HVAD inflow site at the apex of the left ventricle. The HVAD sewing ring is attached, the apex is cored and the HVAD pump secured (Fig. 20.1). The outflow graft is anastomosed to the ascending aorta and the patient is weaned from the HLM. Minimally invasive implantation technique is supposed to reduce perioperative right ventricular failure associated with reduced outcomes and may prevent scar and adhesion formation making subsequent heart transplantation easier.
Fig. 20.1
Implanted HVAD pump: The HVAD sewing ring is attached at the apex of the left ventricle and the HVAD pump is secured. The outflow graft is anastomosed to the ascending aorta (Photo courtesy of HeartWare International, Inc. Framingham, MA)
20.3 Contraindications and Adverse Events Under Ventricular Assist Device Support
Contraindications for VAD support are multi-organ failure, sepsis, malignancies with a life expectancy under 2 years, impossibility of therapeutic anticoagulation (e.g., active cerebral or gastrointestinal bleeding), severe vascular disease (e.g., abdominal aortic aneurysm over 5 cm, peripheral artery occlusive disease), patient incompliance and a severe precapillary pulmonary hypertension.
Frequent adverse events after VAD implantation are bleeding, thromboembolic complications, right ventricular failure, infections and arrhythmias. Bleeding complications are often localized in the gastrointestinal tract or nasal mucosa and occur either perioperatively or late in the postoperative course. Right heart failure or acquired von Willebrand disease are often responsible for late bleeding complications. Thromboembolic complications are caused by activation of plasmatic coagulation and thrombocyte aggregation triggered by the contact of the blood with the VAD surface. To minimize the risk of right ventricular failure, preoperative evaluation of the right ventricle is necessary and temporary (about 3–4 weeks) right VAD (RVAD) implantation must be discussed. Beside the perioperative infections as pneumonia and urinary tract infection, device-associated infections (mainly driveline infections) caused by Staphylococcus species, rarely Pseudomonas species and Candida or Aspergillus species must be considered. Ventricular arrhythmias are due to the underlying disease, but can also be induced mechanically by the pump. The implantation of an implantable cardioverter defibrillator (ICD), if not already performed, must be discussed.
20.4 Epidemiology of MCS
Most of the current evidence is derived from large registries. The 2011 founded INTERMACS registry is a National Heart, Lung and Blood Institute (NHLBI) sponsored database. The latest 2014 published sixth INTERMACS report [1] summarizes demographical data, survival, adverse event rates and risk factors of over 10,000 patients of about 141 participating centers in the first 8 years (June 2006 to June 2013) of patient enrolment. In patients with continuous-flow assist devices, the current 1-year survival is 80 %, the 2-year survival 70 % [1]. Since 2010, all patients with destination therapy are supported with a continuous-flow system. The destination therapy has increased from 14.7 % in 2006/2007 up to 41.6 % in 2012/2013 and thus represents one of the main indications. Adverse event rates with continuous-flow pumps are significantly lower than for previous pulsatile technology [14]. Multi-organ failure is the main complication in the first four postoperative months, whereas neurological adverse events dominate after 3 months. The risk for multi-organ failure and infections rises after 4–5 years. The overall survival is higher with continuous-flow systems.
20.5 Gender Differences in VAD Support
20.5.1 Imbalance of VAD Implantation to the Disadvantage of Women
Despite the similar prevalence in both sexes, women are hospitalized more frequently and die more often from the consequences of heart failure than men [15]. Nevertheless, VAD placement is far less likely used in women than in men. Women are underrepresented in large multicenter heart failure or mechanical circulatory support studies [16, 17]. In the use of VADs for bridge-to-transplantation (BTT), women comprise only 22 % of individuals in the HeartMate II BTT trial and 28 % in the HVAD ADVANCE trial [18]. This may be explained by anatomical reasons, as women cannot accommodate the huge pumps of the early VAD types because of their smaller intrathoracic volume. Topkara et al. analysed the outcome of heart transplanted patients bridged to transplantation with both HVAD (HeartWare) and HeartMate II (Thoratec) devices [19]. It was shown that HVAD patients had smaller body surface areas and lower body weight and that the HVAD system was implanted significantly more often in women. The preferred use of HVAD pumps in women is also confirmed by European data [20]. The smaller pump size of the HVAD pump and the possibility of intrapericardial implantation enable VAD implantation in individuals with small body surface area. This may also facilitate VAD support in children in the future.
20.5.2 Gender Specific Characteristics in the Perioperative Course
Similar to previous published studies [17, 21], data derived from the European Registry for Patients with Mechanical Circulatory Support (EUROMACS) showed that significantly more male patients received mechanical circulatory support (N = 967, 151 women) [20]. As expected, women and men differed in height, weight and body surface area and women were reported to have less ischemic but more dilated and restrictive cardiomyopathy (Fig. 20.2). Female patients bridged to transplantation with continuous-flow systems were shown to present with more advanced states of heart failure [22], having more severe mitral and tricuspid regurgitation and a significantly lower cardiac output [20]. Postoperatively, they needed longer inotropic medication, required longer intensive care therapy and needed more additional right ventricular support. Bogaev et al. showed that fewer women underwent heart transplantation and thus continued longer on assist device support [16]. Gender-specific higher levels of class I panel reactive antibodies were made responsible for the lower transplantation rates, because they are associated with a higher risk for antibody-mediated rejection after heart transplantation.
Fig. 20.2
Female specific therapeutic course in VAD support
20.5.3 Gender Differences Concerning Adverse Events and Survival
In several studies, women were described to have more adverse events and a worse outcome after VAD implantation [23, 24]. Adverse events such as bleeding, neurological complications, right heart failure, infections and arrhythmias are different in both genders (Fig. 20.3). In women, more re-operations for bleeding complications were recorded, whereas the prevalence of pump thrombosis or cerebral bleeding was similar [20]. A first gender-specific analysis of the INTERMACS data 2012 revealed no gender differences in time to first infection, bleeding or device dysfunction [21]. Nevertheless, women suffered earlier than men from neurological complications. Female gender alone was described as a significant risk factor for stroke [25]. Bogaev et al. showed a higher rate of hemorrhagic stroke although there were no differences in INR, partial thromboplastin time and thrombocyte count [16]. If the higher rate of neurological complications in women is due to gender differences in pharmacokinetics and pharmacodynamics of the anticoagulation therapy or due to gender-specific differences in thrombotic risk is unknown. Ochiai et al. demonstrated that female gender was a significant risk factor for right heart failure after implantation of a pulsatile-flow system [26]. Data from the EUROMACS registry showed that women more often experienced right heart failure, although the preoperative right heart function was not different in both genders [20]. Additionally, a higher prevalence of arrhythmias and peripheral arterial embolisms and a slightly higher rate of driveline infections were seen in women.
