The inlet cannula is also made of titanium and is inserted into the left ventricular apex. As mentioned previously, HA5 has optimized the design of the DeBakey-Noon LVAD especially in the impeller. Similarly to other axial LVADs, it has a flow straightener with three blades at inflow which also contribute to be a front bearing for the inducer-impeller with six blades and a flow diffuser with other six blades for the outlet, which function as rear bearing support for the impeller. The diffuser also helps to increase outflow pressure by directing the flow in the axial direction. Other main feature of the HA5 LVAD is the spinning direction of the impeller that is clockwise and differs from other devices available on the market. The wide stator was upgraded too with a new special arrangement of electromagnets. From the previous version with 5 magnets, the new version was upgraded with 8 magnets stator without changes in volume occupied. This also led a reduction in power consumption.
Numerical simulation and measurement of platelet activation rates in recirculation flow loops have showed that platelets are exposed to a lower stress accumulation and lower thrombus formation [10–13]. Early on during the development of what became MicroMed, Dr. Michael DeBakey directed the engineering team to design a pump that could drain a swimming pool full of water balloons without breaking a single balloon. Careful study of computational fluid dynamics and proprietary testing systems has allowed to refine the technology of the impeller, working with the flow straightener and diffuser, and draws blood more smoothly through the LVAD with the intended result of less damage to the blood’s fragile components, including less platelet activation.
Moreover, this design study have made a device small enough to be implanted within the pericardium beside the heart and, unlike many LVADs today, implants above the diaphragm. An LVAD implanted in the abdomen can cause additional complications. Patients may feel prematurely full when they eat because an implant below the diaphragm can cause pressure on the stomach. Moreover, implantation of LVAD in the abdomen has a significantly larger blood path along nonhuman surfaces. The HA5 size can help to avoid many of the complications caused by nonhuman surface contact and by the stresses caused by cavitation as the blood flows through a larger device. In the second half of 2015, a new version of HA5 named first HA5 direct (HA5D) and then aVAD was released and entered clinical trials (◘ Table 54.1). This recent version differs from the standard HA5 for the taper inflow adaptor that allows the VAD to be inserted directly into the left apex (◘ Figs. 54.1 and 54.2). The aVAD has the same pump characteristics of HA5 allowing the same VAD performance and hemodynamics. The possibility of being inserted directly in the left apex allows the aVAD to be more similar to other pumps [2, 3] than standard HA5 allowing even a minimally invasive surgical implantation. Currently this novel device is still under investigation in trial centers in terms of FDA transplant eligible (short) and FDA destination (long) approval. Recently, on Tuesday, August 2, 2016, the company received CE mark approval for the aVAD usage (◘ Table 54.1).
Fig. 54.1
aVAD (ReliantHeart Inc., TX) support system
Fig. 54.2
aVAD (ReliantHeart Inc., TX) inflow cannula
In terms of outflow, the HA5 has a pre-embroidered Vascutek Gelweave (Terumo Cardiovascular System Corp., Ann Arbor, MI) vascular graft with another unique characteristic of an ultrasonic-flow probe placed around the outflow graft that provides real-time flow measurement, and data collected by the probe are continuously sent to the external controller. This graft together with all blood contacting surfaces are now Carmeda® BioActive (Carmeda AB, Sweden) biocompatible thus limiting the rate of thrombus formation which was commonly reported during the early experience with the device. The flow probe could accurately measure the flow inside the outflow graft, and this technology has been called “true flow.” Also Frazier [14] and colleagues have demonstrated that HA5 is more “pulsatile” than other LVADs and previews MicroMed DeBakey VAD; in detail the HA5 could automatically adjust the pump flow rate on small changes in pump preload. The probe is connected with the device and could measure the aortic opening and mitral valve closure to ensure a more physiologic support for the left ventricle; this is a functional and capable option to better estimate and adapt the pump flow to the patient [14]. This information is useful when a patient is stable, but can prove vital if a patient is experiencing complications. This is an extremely reliable tool for the detection of cardiac arrhythmias such is atrial fibrillation in which is clearly viewable a modification in waveform and wave intervals.
Other LVADs rely on estimates by their software providings or they do not have flow data at all, which can leave the clinician flying blind whenever this information is the most needed. Flow measurement is unaffected by changes in blood or fibrin deposition, the ultrasonic flow probe has been proven highly accurate measuring real-time blood flow, and it is correctly positioned on the outflow graft to measure blood pumped from the HA5 as it moves into the aorta.
In addition to flow data, the HA5 tracks speed and electrical current usage by the pump motor, providing valuable information both about the volume of blood flow and its fluidity. All patients have specific characteristics which are continuously recorded by HA5; changes to this data can clearly indicate problems ranging from minor dehydration to more significant side effects.
Finally, all data are recorded by HA5 controller. The controller displays device main parameters such as pump flow (L/min), power consumption (watts), pump speed (rpm), and battery charge. The controller has a cellphone radio which automatically connects to vadlink.com. All data were constantly updated to the main server, and if Internet resource is absent, the data is stored in the controller and updated once network is available. Two rechargeable batteries serve as energy supply to the pump and the controller too. It is also used to connect the pump to the portable console, the HeartAttendant (HA). All data collected by the controller and the HA are stored in a remote sever at vadlink.com where the patients together with the physician could control remotely the all the information.
54.4 Indications for Implant
The pump comes in both adult and pediatric versions (◘ Fig. 54.3), which differ in terms of inflow angle (140° for children and 115° for adults) and length of the outflow graft (60 mm for children and 90 mm for adults). The constant shortage of suitable donor hearts for transplantation has created the drive for more LVAD. For that reason, newer continuous-flow LVAD utilizing magnetic levitation technologies has proven to be more durable than previous-generation pulsatile-flow devices allowing them to be also used as a destination therapy [2, 15].
Fig. 54.3
Anatomical fit options according to inflow cannula angle of HeartAssist5 (HA5)
The development of HA5 in both adult and pediatric versions was approved as bridge to transplant (BTT) for the first time in 2010 and bridge to recovery and destination therapy (DT) in Europe, whereas FDA has approved the device only for humanitarian exemption from 2005 in children 5–16 years of age with end-stage heart failure and refractory to medical therapy while they are waitlisted for cardiac transplantation. The adult version is currently being tested in several centers across the USA as a BTT [16].
Current indication for LVAD implant from ESC is reported in the Guidelines of 2012 in which patients with severe heart failure (HF) with low LVEF (<25%) with frequent hospital admission for HF (>3), inotropic support, end-organ dysfunction due to low cardiac output and right-side deteriorating are candidate for LVAD implantation [17].
Anticoagulation management for patients with HA5 requires an INR value of 2.5–3.5 with a standard therapy with warfarin. From 2001 all devices are coated with Carmeda® BioActive and preliminary data report encouraging result on preventions of thromboembolic events; however, new data on this issue are still needed. HA5 together with Roche has incorporated in their remote database the INR information of the CoaguChek® device to improve safety of the device and monitoring of patients’ therapy. Together with the anticoagulation therapy should be introduced an antiplatelet therapy; this has been proved to reduce risk of stroke and pump thrombosis [18]. In case of pediatric patients, this should be administered in the first 48–72 h from LVAD implant.
54.5 Surgical Technique
Traditionally, a complete median sternotomy is performed (◘ Figs. 54.4, 54.5, 54.6, and 54.7). The skin incision is prolonged 5 cm below the xiphoid process. Central cardiopulmonary bypass is installed and the heart is arrested by usage of a cardioplegic solution. A pump holder ring is sewed with 8–12 U pledgeted stitches on the left ventricular apex. A star incision is performed with a surgical knife, and a coring device is utilized. The surgeon must pay attention during this procedure to ensure a full-thickness incision and detaching of the muscle in the apex to allow a perfect fit of the inflow cannula and the absence of chordae or myocardial trabeculae in front of the inflow cannula too.
Fig. 54.4
HeartAssist5 (HA5) surgical implantation in adolescents. Panel a, apical coring and sewing ring placement. Panel b, inflow cannula placement. Panel c, device in place. Panel d, X-chest ray postoperative view
Fig. 54.5
aVAD (ReliantHeart Inc., TX) surgical implantation. Panels a1–a2, apical sewing ring and fast connect device placement. Panels b1–b2, apical coring by usage of aVAD core device
Fig. 54.6
aVAD (ReliantHeart Inc., TX) surgical implantation. Panel a, handle temporary fixation of apical sewing ring and fast connect device. Panel b, aVAD inflow cannula introduction. Panel c, left ventricular aVAD placement surgical view
Fig. 54.7
Fast connect device adjustable depth (1 cm) for aVAD inflow cannula placement
Then the wire connector is tunnelized under the muscular fascia 3–5 cm above the iliac crest. The inflow cannula is then secured by sewing the inflow cannula ring to the previous apical fixation ring. The device is now tested and partial deairing is performed by filling the left ventricle. Finally, a connection between the embroidered graft and the ascending aorta is performed. This final suture could be performed also on beating heart. After a careful deairing of the device and graft, the cardiopulmonary bypass can be stopped, and the chest can be closed (◘ Figs. 54.4, 54.5, 54.6, and 54.7). This is the only surgical approach suitable in childhood patients. Other approaches (left thoracotomy or multiple mini-incisions) are not appropriate for the tiniest size of the thorax and might lead to a complex operation without benefits for the patient, and in some cases, this might only increase the number of perioperative complications. Nevertheless, in adult patients, the left thoracotomy (4th–5th intercostal space) allows the surgeon to a better view of the left apex, and the outflow graft can be anastomosed to the descending aorta. Another feasible choice for HA5 implant in adult patients is through multiple small incisions. A left mini-thoracotomy (4th–5th intercostal space) may be performed for left ventricle apex exposure. The outflow cannula anastomosis is instead performed through a right mini-thoracotomy or a J-shaped upper mini-sternotomy. In case of planned minimally invasive surgery, an CT angiography scan may be helpful to focus on preoperative anatomic features. Surely, in the near future, the novel aVAD (◘ Figs. 54.1, 54.2, 54.5, 54.6, and 54.7) will get more facilities for minimally invasive surgical approaches.
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