Novel Left Ventricular Assist System® II

Abstract

The pump's outflow connector of the Novel Left Ventricular Assist System® I (Novel LVAS® I) has been redesigned to be sutured to the infrarenal abdominal aorta either as a procedure of choice (due to its simplicity) or as an alternative in the presence of an unhealthy descending thoracic aorta.

The implantation of the Novel Left Ventricular Assist System® II (Novel LVAS® II) requires only a single passage of the pump's inflow connector through the diaphragm. Of still greater importance, the Novel LVAS II enables a considerably shorter (20- or 22-mm) Dacron vascular graft as the outflow connector to the abdominal infrarenal aorta.

The electrocardiogram-synchronized Novel LVAS II possibly ensures the most effective approach to the perfusion of visceral organs and kidneys, while avoiding both excessive mechanical stress on the blood and anatomical and functional damage to the native left ventricle.

The Novel Left Ventricular Assist System® I (Novel LVAS® I),^* an electrocardiogram-synchronized LVAS that avoids both ventricular and atrial cannulation, has been previously reported.¹ The new physiology of the proposed LVAS, which combines the unloading of the heart with counterpulsation, provides a sound approach to functional heart recovery. Patients would be placed on β-adrenergic blocker therapy that would help adjust heart rate to the pump, and they might also be on antiarrhythmic drugs (amiodarone). The pump should be able to serve in its most effective role, that of a true left ventricular assist device, such as we had conceived it back in 1962.^2–4 The Novel Left Ventricular Assist System® II (Novel LVAS® II) adopts the basic characteristics of the Novel LVAS I and its most outstanding features—the atriostomy technique for the pump's input, which creates an opening in the left atrial wall larger than the patient's mitral valve area (Figs. 1 and 2), and the safety of the driver unit.¹

Fig. 1 A) The key to the success of the Novel LVAS® I and II is in the atriostomy technique. The endocardium of the left atrium must coapt with the Dacron fabric underneath the planar component of the atrial cuff, when the inner circle of the cuff is sutured. The inlet of the atrial cuff should remain 1 to 2 mm inside the left atrial chamber. B) The atrial cuff as seen from the left atrium. The notched circle indicates the suture line of the left atrial wall to the atrial cuff.

Fig. 2 The patient is under extracorporeal circulation (ECC). The ascending aorta is clamped and the heart arrested with a cardioplegic solution. After the inner circle of the atrial cuff has been sutured, a balloon-tipped catheter is introduced into the lumen of the prosthesis. The patient is then placed under partial ECC, and suturing of the cuff's outer circle can be performed without rushing. The visceral pericardium over the left pulmonary veins can be included in the suturing of the atrial cuff's outer circle.

The present report of the Novel LVAS II concerns the redesign of the pump's outflow connector, in such a manner that it can be sutured to the abdominal aorta below the renal arteries, instead of to the descending thoracic aorta. This approach can be viewed as a procedure of choice (due to its simplicity) or as an alternative in the presence of an unhealthy descending thoracic aorta.

The procedure for inserting the LVAS II is both simple and quick. Speed is essential to achieve optimal clinical outcomes in chronic heart failure patients whose functional status is New York Heart Association class IV. The prospect of functional myocardial recovery, including myoangiogenesis via cell-based strategies, will be a primary criterion in patient selection. In regard to the durability of Novel LVAS I and II components, the only relevant remaining question is that of durability in the bloodstream, because in the laboratory they can pump water indefinitely.

Description of the System

The Novel LVAS II provides a pump output in the range of 3.4 to 6 L/min under a mean arterial pressure (afterload) of 110 mmHg, with a minimum atrial pressure (preload) of 9 mmHg and a pneumatic pressure (systolic compression in the blood pump chamber) of 180 to 220 mmHg. The pump's outflow connector is rotated 180° in the body of the pump, in relation to the inflow connector of the Novel LVAS I. The inflow connectors of the LVAS I and II are unchanged. When contrast material is injected into the inflow connector during pump filling, it displays a perfect clockwise vortex that washes the periphery of the blood chamber (Fig. 3).

Fig. 3 A) Photograph of the Novel LVAS® II. B) The drawing shows the clockwise direction of the blood during the filling of the blood pump's chamber.

LA = left atrium

The pump of the Novel LVAS II is implanted through the 4th space of a left anterolateral thoracotomy to gain access to the left atrial wall; access to the abdominal aorta is gained through a left vertical incision lateral to the rectus muscle or through a linea alba incision. The pump is positioned in the left hypochondriac region. The 20-mm Dacron graft reaches the infrarenal aorta through the greater omentum and through the transverse mesocolon via a pre-pancreatic passage.

It is well known that the vulnerable percutaneous connection of a left ventricular assist system carries a significant risk of infection. In the Novel LVAS I and II, the driveline exit site is at the right hypocondrium and the tunnel is at least 25 cm (10 in) long. A localized infection of the driveline is less likely to track a long, well-healed tunnel and thereby infect the intra-abdominal pump. However, as soon as the patient starts to move about, the driveline may begin to loosen around the skin incision and become contaminated. The 6-mm (outside diameter) driveline of the Novel LVAS I and II is cushioned at the circular skin-exit site by a Dacron-velour–covered balloon of approximately 25 mm in length, which is filled with either dextran solution or medical silicone. The area of the balloon that opposes the deep dermis is greatly increased (Fig. 4). The ingrowth of connective tissue into the Dacronvelour fabric on the outside surface of the polyurethane driveline and the polyurethane balloon chamber is greatly enhanced.⁵

Fig. 4 Schematic cross-section shows the Dacron velour fabric that covers both the 6-mm (external diameter) driveline and the polyurethane balloon; this last is filled with either dextran solution or medical silicone at the percutaneous exit site. Transcutaneous surgical placement of the balloon is simple: A) The surgeon gently pulls the driveline until he sees a distinctive mark at the distal end of the balloon. B) The mark remains 2 mm outside the epidermis. Then the extra-long driveline is sectioned to join the rotational system that will reach the driver.

1 = skin section; 2 = polyurethane balloon filled with either dextran solution or medical silicone; 3 = distinctive mark at the balloon's distal end; 4 = coaptation of the Dacron fabric to the deep dermis; 5 = the intersection of the epidermis and the driveline's external Dacron fabric must be sealed. We use Dermabond® (Ethicon, Inc.; Somerville, NJ; a Johnson & Johnson company) for that purpose.

Discussion

Implantation of the Novel LVAS II requires only a single opening through the diaphragm, which simplifies the surgical procedure. Long-term left ventricular assist device (LVAD) support with pumps having long blood connectors—such as the pulsatile Novacor® LVAS and the TCI HeartMate® VE LVAS, or the nonpulsatile MicroMed DeBakey VAD® and the Jarvik 2000 FlowMaker—carry a small risk of kinking. The Novel LVAS I and II have been designed with the shortest possible inflow and outflow connectors (Fig. 5).

Fig. 5 A) Sketch shows the left atrium–descending thoracic aorta configuration of the Novel LVAS® I. B) Sketch shows the left atrium–infrarenal aorta configuration of the Novel LVAS® II.

Unidirectional blood flow is obtained in the implantable Novel LVAS II. The pump's inflow connector, the clockwise vortex into the pump's blood chamber, and the pump's outflow connector become hemodynamically aligned.

Long-term infrarenal bypass is perfectly feasible, as illustrated by the following example. Twenty-eight years ago, a patient of ours underwent resection for coarctation of the aorta. Six months later, he developed a huge mycotic pseudoaneurysm and underwent an ascending aorta–infrarenal aorta bypass, with resection of the descending thoracic aorta from the left subclavian artery to near the diaphragm.⁶ Recent computed tomographic angiography of this patient (Fig. 6) shows normal perfusion of visceral organs, kidneys, and lower extremities. The lower spinal cord must have good perfusion; fortunately, a large volume of blood can be bypassed to the infrarenal aorta. This patient is doing well at his 28-year follow-up.⁷

Fig. 6 Computed tomography with gadolinium chelates in frontal (A), left (B), and right (C) projections, and transverse section (D) shows ascending aorta–abdominal aorta bypass consequential to resection of the descending thoracic aorta, due to a massive mycotic pseudoaneurysm. This patient had undergone surgery 28 years earlier. Curved arrows indicate absence of the descending thoracic aorta; short arrows indicate the bypass from the ascending aorta to the abdominal aorta (see text).

The function of the LVAS II must be optimized to enable good aortic valve opening, which will avoid clotting at the outflow tract of the left ventricle. An anticoagulation regimen with a target INR of 2.0 to 2.5 is proposed for the Novel LVAS I and II.

To prevent hypoxia from right-to-left shunting and an eventual stroke, it is crucial to close a patent (or probe-patent) foramen ovale. Formation of thrombi in the right atrial appendage is not uncommon in chronic heart failure, and dislodged thombi can result in cerebral, systemic, or renal embolism through a patent foramen ovale. The ascending aorta is exposed through the left anterolateral thoracotomy. The aorta is clamped, and the heart is arrested with cardioplegic solution. The atrial septal wall is well exposed through the left atriostomy, and the left ventricle is decompressed through the left atriostomy, too.

An electrocardiogram-synchronized LVAS that ejects blood into the infrarenal aorta during diastole might ensure the greatest perfusion to visceral organs and kidneys.

In sum, the Novel LVAS II, with its inflow from an atriostomy and its outflow to the infrarenal aor-ta, may provide high perfusion to vital organs while avoiding excessive mechanical stress to the blood. In addition, it avoids anatomic and functional damage to the native left ventricle, because it does not require cannulation of the ventricle.

We have done extensive work in calves with the Novel LVAS I, starting in 1998. Currently, we are removing the pump after an average of 30 days of hemodynamic study. Human studies must await approval of a protocol by the Argentine Federal Agency (similar to the Food and Drug Administration of the United States).