- Email: [email protected]
Intraperitoneal pocket for left ventricular assist device placement
MECHANICAL CIRCULATORY SUPPORT
Intraperitoneal Pocket for Left Ventricular Assist Device Placement Tim Icenogle, MD,a,b David Sandler, MD,a Mark Puhlman, MSN, RN,a Steve Himley, MSME,a David J. Sato, MSBE, CCE,a and Stacy Schaefer, RN, CCRNa Background: Implantation of the HeartMate Implanted Pneumatic or Vented Electric Ventricular Assist Device requires that the pump be implanted either in the peritoneal cavity or in the abdominal wall. Both sites have been problematic. Methods: We describe a new technique in which an intraperitoneal pocket is created, using Gore-Tex Dual Mesh Plus Biomaterial with Holes, to contain the ventricular assist device. This shields the ventricular assist device from the peritoneal contents and avoids abdominal wall dissection. Thirty consecutive patients who underwent implantation using this technique were compared with 16 patients who underwent implantation before this technique was in use. Results: Thirty consecutive patients underwent implantation, and 2 of those patients underwent re-implantation because of device failure (16/30 HeartMate Implanted Pneumatic, 14/30 HeartMate Vented Electric, and 2/14 HeartMate Vented Electric replaced with the HeartMate Implanted Pneumatic). Twenty-five patients have undergone explantation. Pocket infections in patients who have had implanted devices for ⬎1 month decreased from 4 of 13 before the pockets were used to 1 of 25 with the intraperitoneal pockets (Fisher’s exact test p ⫽ 0.038). Two hernia repairs were required after explantation when the biomaterial pocket was used. A decrease in return to surgery for bleeding was noted after the pocket was used (7/16 without the pocket and 3/32 with the pocket; Fisher’s exact test, p ⫽ 0.010). Conclusions: Bleeding complications and pocket infections decreased in this early experience. Further study is necessary to confirm the apparent decrease in complication rate by using this new technique in this small cohort of patients. J Heart Lung Transplant 2003;22:818 – 821.
T
he number of donors available limits heart transplantation, and there is increasing need for left ventricular assist device (LVAD) support as a bridge to transplantation. The HeartMate Implanted Pneu-
matic (IP) and HeartMate Vented Electric (VE) (Thoratec; Pleasanton, CA) may be implanted in either the peritoneal cavity1 or the abdominal wall.2 Both sites are associated with significant complica-
From the aInland Northwest Thoracic Organ Transplant Program, Heart Institute of Spokane, Sacred Heart Medical Center, Spokane, Washington; and bInternational Heart Institute of Montana, Missoula, Montana. Submitted April 4, 2002; revised July 16, 2002; accepted August 13, 2002. Reprint requests: Timothy Icenogle, MD, Northwest Cardiothoracic and Transplant Surgeons, Suite 532, West 105 Eighth
Avenue, Spokane, Washington 99204. Telephone: 509-6237575. Fax: 509-623-7578. E-mail: [email protected] Copyright © 2003 by the International Society for Heart and Lung Transplantation. 1053-2498/03/$–see front matter doi:10.1016/S1053-2498(02)00644-7
818
The Journal of Heart and Lung Transplantation Volume 22, Number 7
Icenogle et al.
819
tions.1 Intraperitoneal placement has been associated with erosion into the bowel,3 bowel obstruction, and injury to abdominal viscera during explantation. Abdominal wall implantation requires dissection in the pre-peritoneal plane or between the transversus abdominus and internal oblique muscles. This dissection creates a large surface area for bleeding during implantation and explantation.4 This patient population is prone to coagulopathies, and with HeartMate implantation, there is a 39% incidence of return to surgery for bleeding.5 Controlling bleeding in the pocket consumes considerable operating room time. There is also a significant incidence of bleeding and infection with the abdominal pocket.4 In an effort to decrease the complications associated with the current techniques for LVAD placement, we sought to create a simple technique for intraperitoneal placement of the LVAD with an inert material to shield the abdominal contents from the VAD.
METHODS Patient Selection From November 1998 to February 2002, a total of 30 consecutive patients underwent implantation with either the HeartMate IP (16 patients) or the HeartMate VE (14 patients) LVAD using a peritoneal pocket. Two patients subsequently underwent reimplantation with the HeartMate IP LVAD because of failure of their HeartMate VE LVADs (32 implants total). Twenty-eight patients were transplant candidates and 2 were destination therapy patients. This group is compared with 16 patients who underwent implantation before November 1998, of whom 2 had intraperitoneal implants and 14 had abdominal wall implants.
Implant Surgical Technique The operating room is terminally cleaned and prepped per our protocol for prosthetic device implantation of mechanical hearts. Surgical personnel wear the Stackhouse Freedom Aire System (Stackhouse; Riverside, CA), and entry into the operating room is restricted. All patients undergo intra-operative transesophageal echocardiography and pulmonary artery catheter placement after induction of anesthesia. After prepping and draping, a midline incision is made from the sternal notch to 5 cm to 6 cm. above the umbilicus. The sternum is divided and the peritoneal cavity entered. The falciform and round ligaments of the liver are divided, and then the coronary ligament of the liver is divided to expose the inferior surface of the dia-
FIGURE 1 The Gore-Tex Dual Mesh Plus Biomaterial with Holes before implantation.
phragm. A HeartMate fit trial conforming to the general size of the HeartMate is introduced into the peritoneal cavity, and the left lateral-most point on the diaphragm is determined for the pocket. A 26⫻34-cm sheet of Gore-Tex Dual Mesh Plus Biomaterial with Holes (Item 1DLMCPH08, WL Gore and Associates; Flagstaff, AZ), Figure 1, is placed in the abdomen with care to ensure that the smooth side is toward the bowel and that the roughened side is toward the abdominal wall. The Biomaterial comes in an oval shape, so one end is trimmed to be straight. The Biomaterial is sewn to the diaphragm from left to right about 4 cm to 6 cm below the junction between the diaphragm and the anterior abdominal wall, allowing adequate placement of inflow and outflow conduits from the device. An Auto Suture ProTack, (Auto Suture; Norwalk, CT), using 5-mm tacks (Item 174006), or an Auto Suture Endo Universal 65o 12-mm stapler (Item 173052), using 4.8-mm staples, is used to attach the Biomaterial to the anterior abdominal wall. The inferior portion is attached with 1-0 prolene. Gore-Tex recommends using
820
Icenogle et al.
The Journal of Heart and Lung Transplantation July 2003
FIGURE 2 The pocket in the abdominal cavity after the Gore-Tex is implanted.
suture to reinforce the tacks and staple attachment to the abdominal wall. The sheet of Biomaterial is of sufficient size to cross the midline and to allow complete isolation of the device and the driveline from the abdominal contents, Figure 2. The diaphragm is divided, with a GIA stapler (item TLC 75, Ethicon Endo-Surgery; Cincinnati, OH) using Gore-Tex Seam Guards (item ASGS002), from the midline to the proposed site for exit of the inflow valve conduit, with care not to injure the phrenic nerve. The device is fired, and cautery is used to ensure hemostasis along the cut edge of the diaphragm. The patient is placed on cardiopulmonary bypass, and without cross-clamping the aorta, a left ventriculotomy is made and the suture ring of the HeartMate is secured. The HeartMate IP or VE is placed into the newly created abdominal pocket, and the site for the driveline exit from the peritoneal cavity is determined. A pursestring suture is placed in the peritoneum around the site for the driveline exit, and then a driveline tunnel is made from the intended exit site on the skin to the center of the pursestring suture on the peritoneum. The driveline tunnel through the subcutaneous tissue is made as long as possible to ensure tissue in-growth. The driveline is then brought through the tunnel. The pursestring suture is not secured until the abdomen is ready to close. The pursestring suture
is intended to decrease the flow of any fluid from the pocket into the driveline tunnel. The outflow graft is sutured to the aorta and connected to the outflow valve housing. The HeartMate is de-aired, and the graft nut secured according to the HeartMate Implant Protocol. After weaning the patient from bypass, chest tubes are placed in the mediastinum and the left chest, but the pocket is not drained. A Blake drain (item 2190, Ethicon; Sommerville, NJ) is placed in the left thorax, laterally and posterior, to drain the pleural fluid that collects there secondary to the holes in the GoreTex biomaterial. A Gore-Tex Pericardial patch (item 1PCM103) is used to close the pericardium so that it covers the heart and outflow graft.
Surgical Explant Procedure The previous incision is opened down to the sternum, over the chest and onto the HeartMate in the abdomen. The femoral vessels are dissected in case of emergency, the sternum opened, the Gore-Tex pericardial patch removed, the heart dissected, and the patient placed on bypass. After cross-clamping, the aortic outflow graft is divided and the outflow valve housing is unscrewed and removed. The heart is divided across the ventricles and then dissected in the usual fashion for transplantation. The left ven-
The Journal of Heart and Lung Transplantation Volume 22, Number 7
tricular remnant is cut away from the inflow of the HeartMate, and then the inflow valve housing is unscrewed and removed. The donor heart is implanted in the usual fashion. After the patient is weaned from bypass, the HeartMate is pulled from the pocket, the driveline divided, and passed from the field. The driveline is then dissected from the peritoneal side and pulled under the drapes by an assistant. The Gore-Tex Biomaterial is left in place to prevent hernias.
RESULTS Thirty consecutive patients underwent implantation with the above technique. Two patients with HeartMate VEs underwent re-implantation with HeartMate IPs, which replaced the old devices while leaving the Biomaterial in place. Return to surgery for bleeding after implantation decreased from 7 of 16 implants before the pockets were in use to 3 of 32 implants after the Biomaterial pockets were used (Fisher’s exact test, p ⫽ 0.010). Removing those patients from consideration who had implant devices for ⬍1 month, there were 4 pocket infections of 13 implants before the pocket was used and 1 pocket infection of 25 implants after the pocket was employed (p ⫽ 0.038). The 1 patient with infection had undergone a contaminated procedure in that the surgeon’s sleeve tore during implantation. Both HeartMate devices were easy to remove from their pockets at the time of transplantation, and the Biomaterial was left in place to prevent the development of abdominal hernias. Two hernias have occurred in 30 patients since the use of the pocket. Of the 16 patients without the pockets, 3 experienced abdominal dehiscences after implantation and 4 experienced hernias in the post-transplant period. We observed no injuries to abdominal viscera using this technique. Two of 16 patients who underwent implantation before the pockets were used had intraperitoneal placement of the devices. One of these patients died after the HeartMate eroded into the bowel causing hemorrhage, and the other patient had a splenic tear during device explantation that required repair.
DISCUSSION This preliminary report describes a simplified technique for implanting the HeartMate IP or VE. Use
Icenogle et al.
821
of the technique is meant to avoid the bleeding complications associated with abdominal wall implantation, to avoid complications of bowel and viscera attachment or erosion secondary to intraperitoneal placement, and to decrease infection. This small series did demonstrate fewer bleeding complications manifested by fewer returns to surgery for bleeding. Pocket infections also decreased compared with our previous experience. The one pocket infection in the series occurred early in the experience and was associated with a mechanical failure of the surgeon’s gown. Our team switched to the full hood and gown suit from Stackhouse after this event. We have observed no further pocket infections since this change. This technique should avoid most secondary hernias after transplantation. The Biomaterial is Food and Drug Administration approved as a hernia repair prosthesis. The cost to the hospital of the Gore-Tex Dual Mesh Plus Biomaterial with Holes is $2,549.00. We feel this cost is more than offset by the savings achieved by avoiding re-operations for bleeding and by the costs and morbidity of pocket and device infections. Patients with previous abdominal surgery who have extensive adhesions may not be candidates for this technique and may be better served with an abdominal wall implant. Experience with this technique is limited, but our initial impression is positive. Confirmatory experience at other centers is necessary to assure the value of this technique.
REFERENCES 1. Wasler A, Springer W, Radovancevic B, et al. A comparison between intraperitoneal and extraperitoneal left ventricular assist device system placement. ASAIO J 1996;42:M573– 6. 2. McCarthy PM, Wang N, Vargo R. Preperitoneal insertion of the HeartMate 1000 IP implantable left ventricular assist device. Ann Thorac Surg 1994;57(3):634 –7. 3. Phillips WS, Burton NA, Macmanus Q, Lefrak EA. Surgical complications in bridging to transplantation: the Thermo Cardiosystems LVAD. Ann Thorac Surg 1992;53:482–5. 4. Goldstein D, Oz M, Rose E. Implantable left ventricular assist devices. N Engl J Med 1998;339:1522–33. 5. Frazier OH, Rose EA, Macmanus Q, et al. Multicenter evaluation of the HeartMate 1000 IP left ventricular assist device. Ann Thorac Surg 1992;53:1080 –90.
Intraperitoneal Pocket for Left Ventricular Assist Device Placement Tim Icenogle, MD,a,b David Sandler, MD,a Mark Puhlman, MSN, RN,a Steve Himley, MSME,a David J. Sato, MSBE, CCE,a and Stacy Schaefer, RN, CCRNa Background: Implantation of the HeartMate Implanted Pneumatic or Vented Electric Ventricular Assist Device requires that the pump be implanted either in the peritoneal cavity or in the abdominal wall. Both sites have been problematic. Methods: We describe a new technique in which an intraperitoneal pocket is created, using Gore-Tex Dual Mesh Plus Biomaterial with Holes, to contain the ventricular assist device. This shields the ventricular assist device from the peritoneal contents and avoids abdominal wall dissection. Thirty consecutive patients who underwent implantation using this technique were compared with 16 patients who underwent implantation before this technique was in use. Results: Thirty consecutive patients underwent implantation, and 2 of those patients underwent re-implantation because of device failure (16/30 HeartMate Implanted Pneumatic, 14/30 HeartMate Vented Electric, and 2/14 HeartMate Vented Electric replaced with the HeartMate Implanted Pneumatic). Twenty-five patients have undergone explantation. Pocket infections in patients who have had implanted devices for ⬎1 month decreased from 4 of 13 before the pockets were used to 1 of 25 with the intraperitoneal pockets (Fisher’s exact test p ⫽ 0.038). Two hernia repairs were required after explantation when the biomaterial pocket was used. A decrease in return to surgery for bleeding was noted after the pocket was used (7/16 without the pocket and 3/32 with the pocket; Fisher’s exact test, p ⫽ 0.010). Conclusions: Bleeding complications and pocket infections decreased in this early experience. Further study is necessary to confirm the apparent decrease in complication rate by using this new technique in this small cohort of patients. J Heart Lung Transplant 2003;22:818 – 821.
T
he number of donors available limits heart transplantation, and there is increasing need for left ventricular assist device (LVAD) support as a bridge to transplantation. The HeartMate Implanted Pneu-
matic (IP) and HeartMate Vented Electric (VE) (Thoratec; Pleasanton, CA) may be implanted in either the peritoneal cavity1 or the abdominal wall.2 Both sites are associated with significant complica-
From the aInland Northwest Thoracic Organ Transplant Program, Heart Institute of Spokane, Sacred Heart Medical Center, Spokane, Washington; and bInternational Heart Institute of Montana, Missoula, Montana. Submitted April 4, 2002; revised July 16, 2002; accepted August 13, 2002. Reprint requests: Timothy Icenogle, MD, Northwest Cardiothoracic and Transplant Surgeons, Suite 532, West 105 Eighth
Avenue, Spokane, Washington 99204. Telephone: 509-6237575. Fax: 509-623-7578. E-mail: [email protected] Copyright © 2003 by the International Society for Heart and Lung Transplantation. 1053-2498/03/$–see front matter doi:10.1016/S1053-2498(02)00644-7
818
The Journal of Heart and Lung Transplantation Volume 22, Number 7
Icenogle et al.
819
tions.1 Intraperitoneal placement has been associated with erosion into the bowel,3 bowel obstruction, and injury to abdominal viscera during explantation. Abdominal wall implantation requires dissection in the pre-peritoneal plane or between the transversus abdominus and internal oblique muscles. This dissection creates a large surface area for bleeding during implantation and explantation.4 This patient population is prone to coagulopathies, and with HeartMate implantation, there is a 39% incidence of return to surgery for bleeding.5 Controlling bleeding in the pocket consumes considerable operating room time. There is also a significant incidence of bleeding and infection with the abdominal pocket.4 In an effort to decrease the complications associated with the current techniques for LVAD placement, we sought to create a simple technique for intraperitoneal placement of the LVAD with an inert material to shield the abdominal contents from the VAD.
METHODS Patient Selection From November 1998 to February 2002, a total of 30 consecutive patients underwent implantation with either the HeartMate IP (16 patients) or the HeartMate VE (14 patients) LVAD using a peritoneal pocket. Two patients subsequently underwent reimplantation with the HeartMate IP LVAD because of failure of their HeartMate VE LVADs (32 implants total). Twenty-eight patients were transplant candidates and 2 were destination therapy patients. This group is compared with 16 patients who underwent implantation before November 1998, of whom 2 had intraperitoneal implants and 14 had abdominal wall implants.
Implant Surgical Technique The operating room is terminally cleaned and prepped per our protocol for prosthetic device implantation of mechanical hearts. Surgical personnel wear the Stackhouse Freedom Aire System (Stackhouse; Riverside, CA), and entry into the operating room is restricted. All patients undergo intra-operative transesophageal echocardiography and pulmonary artery catheter placement after induction of anesthesia. After prepping and draping, a midline incision is made from the sternal notch to 5 cm to 6 cm. above the umbilicus. The sternum is divided and the peritoneal cavity entered. The falciform and round ligaments of the liver are divided, and then the coronary ligament of the liver is divided to expose the inferior surface of the dia-
FIGURE 1 The Gore-Tex Dual Mesh Plus Biomaterial with Holes before implantation.
phragm. A HeartMate fit trial conforming to the general size of the HeartMate is introduced into the peritoneal cavity, and the left lateral-most point on the diaphragm is determined for the pocket. A 26⫻34-cm sheet of Gore-Tex Dual Mesh Plus Biomaterial with Holes (Item 1DLMCPH08, WL Gore and Associates; Flagstaff, AZ), Figure 1, is placed in the abdomen with care to ensure that the smooth side is toward the bowel and that the roughened side is toward the abdominal wall. The Biomaterial comes in an oval shape, so one end is trimmed to be straight. The Biomaterial is sewn to the diaphragm from left to right about 4 cm to 6 cm below the junction between the diaphragm and the anterior abdominal wall, allowing adequate placement of inflow and outflow conduits from the device. An Auto Suture ProTack, (Auto Suture; Norwalk, CT), using 5-mm tacks (Item 174006), or an Auto Suture Endo Universal 65o 12-mm stapler (Item 173052), using 4.8-mm staples, is used to attach the Biomaterial to the anterior abdominal wall. The inferior portion is attached with 1-0 prolene. Gore-Tex recommends using
820
Icenogle et al.
The Journal of Heart and Lung Transplantation July 2003
FIGURE 2 The pocket in the abdominal cavity after the Gore-Tex is implanted.
suture to reinforce the tacks and staple attachment to the abdominal wall. The sheet of Biomaterial is of sufficient size to cross the midline and to allow complete isolation of the device and the driveline from the abdominal contents, Figure 2. The diaphragm is divided, with a GIA stapler (item TLC 75, Ethicon Endo-Surgery; Cincinnati, OH) using Gore-Tex Seam Guards (item ASGS002), from the midline to the proposed site for exit of the inflow valve conduit, with care not to injure the phrenic nerve. The device is fired, and cautery is used to ensure hemostasis along the cut edge of the diaphragm. The patient is placed on cardiopulmonary bypass, and without cross-clamping the aorta, a left ventriculotomy is made and the suture ring of the HeartMate is secured. The HeartMate IP or VE is placed into the newly created abdominal pocket, and the site for the driveline exit from the peritoneal cavity is determined. A pursestring suture is placed in the peritoneum around the site for the driveline exit, and then a driveline tunnel is made from the intended exit site on the skin to the center of the pursestring suture on the peritoneum. The driveline tunnel through the subcutaneous tissue is made as long as possible to ensure tissue in-growth. The driveline is then brought through the tunnel. The pursestring suture is not secured until the abdomen is ready to close. The pursestring suture
is intended to decrease the flow of any fluid from the pocket into the driveline tunnel. The outflow graft is sutured to the aorta and connected to the outflow valve housing. The HeartMate is de-aired, and the graft nut secured according to the HeartMate Implant Protocol. After weaning the patient from bypass, chest tubes are placed in the mediastinum and the left chest, but the pocket is not drained. A Blake drain (item 2190, Ethicon; Sommerville, NJ) is placed in the left thorax, laterally and posterior, to drain the pleural fluid that collects there secondary to the holes in the GoreTex biomaterial. A Gore-Tex Pericardial patch (item 1PCM103) is used to close the pericardium so that it covers the heart and outflow graft.
Surgical Explant Procedure The previous incision is opened down to the sternum, over the chest and onto the HeartMate in the abdomen. The femoral vessels are dissected in case of emergency, the sternum opened, the Gore-Tex pericardial patch removed, the heart dissected, and the patient placed on bypass. After cross-clamping, the aortic outflow graft is divided and the outflow valve housing is unscrewed and removed. The heart is divided across the ventricles and then dissected in the usual fashion for transplantation. The left ven-
The Journal of Heart and Lung Transplantation Volume 22, Number 7
tricular remnant is cut away from the inflow of the HeartMate, and then the inflow valve housing is unscrewed and removed. The donor heart is implanted in the usual fashion. After the patient is weaned from bypass, the HeartMate is pulled from the pocket, the driveline divided, and passed from the field. The driveline is then dissected from the peritoneal side and pulled under the drapes by an assistant. The Gore-Tex Biomaterial is left in place to prevent hernias.
RESULTS Thirty consecutive patients underwent implantation with the above technique. Two patients with HeartMate VEs underwent re-implantation with HeartMate IPs, which replaced the old devices while leaving the Biomaterial in place. Return to surgery for bleeding after implantation decreased from 7 of 16 implants before the pockets were in use to 3 of 32 implants after the Biomaterial pockets were used (Fisher’s exact test, p ⫽ 0.010). Removing those patients from consideration who had implant devices for ⬍1 month, there were 4 pocket infections of 13 implants before the pocket was used and 1 pocket infection of 25 implants after the pocket was employed (p ⫽ 0.038). The 1 patient with infection had undergone a contaminated procedure in that the surgeon’s sleeve tore during implantation. Both HeartMate devices were easy to remove from their pockets at the time of transplantation, and the Biomaterial was left in place to prevent the development of abdominal hernias. Two hernias have occurred in 30 patients since the use of the pocket. Of the 16 patients without the pockets, 3 experienced abdominal dehiscences after implantation and 4 experienced hernias in the post-transplant period. We observed no injuries to abdominal viscera using this technique. Two of 16 patients who underwent implantation before the pockets were used had intraperitoneal placement of the devices. One of these patients died after the HeartMate eroded into the bowel causing hemorrhage, and the other patient had a splenic tear during device explantation that required repair.
DISCUSSION This preliminary report describes a simplified technique for implanting the HeartMate IP or VE. Use
Icenogle et al.
821
of the technique is meant to avoid the bleeding complications associated with abdominal wall implantation, to avoid complications of bowel and viscera attachment or erosion secondary to intraperitoneal placement, and to decrease infection. This small series did demonstrate fewer bleeding complications manifested by fewer returns to surgery for bleeding. Pocket infections also decreased compared with our previous experience. The one pocket infection in the series occurred early in the experience and was associated with a mechanical failure of the surgeon’s gown. Our team switched to the full hood and gown suit from Stackhouse after this event. We have observed no further pocket infections since this change. This technique should avoid most secondary hernias after transplantation. The Biomaterial is Food and Drug Administration approved as a hernia repair prosthesis. The cost to the hospital of the Gore-Tex Dual Mesh Plus Biomaterial with Holes is $2,549.00. We feel this cost is more than offset by the savings achieved by avoiding re-operations for bleeding and by the costs and morbidity of pocket and device infections. Patients with previous abdominal surgery who have extensive adhesions may not be candidates for this technique and may be better served with an abdominal wall implant. Experience with this technique is limited, but our initial impression is positive. Confirmatory experience at other centers is necessary to assure the value of this technique.
REFERENCES 1. Wasler A, Springer W, Radovancevic B, et al. A comparison between intraperitoneal and extraperitoneal left ventricular assist device system placement. ASAIO J 1996;42:M573– 6. 2. McCarthy PM, Wang N, Vargo R. Preperitoneal insertion of the HeartMate 1000 IP implantable left ventricular assist device. Ann Thorac Surg 1994;57(3):634 –7. 3. Phillips WS, Burton NA, Macmanus Q, Lefrak EA. Surgical complications in bridging to transplantation: the Thermo Cardiosystems LVAD. Ann Thorac Surg 1992;53:482–5. 4. Goldstein D, Oz M, Rose E. Implantable left ventricular assist devices. N Engl J Med 1998;339:1522–33. 5. Frazier OH, Rose EA, Macmanus Q, et al. Multicenter evaluation of the HeartMate 1000 IP left ventricular assist device. Ann Thorac Surg 1992;53:1080 –90.