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The Journal of Heart and Lung Transplantation, Vol 34, No 7, July 2015
Figure 2
Accepting aggressive therapy in context of varied risks of major complications.
medical decision such as DT LVAD. These findings should be validated further in a heart failure population offered DT LVAD. Until then, clinicians should assume that accurate and thoughtful presentation of risks and benefits is essential to high-quality decision making regarding DT LVAD.
Disclosure statement There are no relevant conflicts of interest to disclose. The study was conducted with support from the University of Colorado Department of Medicine Early Career Scholars Program. D.D.M. is supported by the National Institutes on Aging (Grant No. K23AG040696). L.A.A. is supported by the National Heart, Lung, and Blood Institute (Grant No. K23HL105896). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
Percutaneous withdrawal of HeartWare HVAD left ventricular assist device support Stephen J. Pettit, PhD, MRCP,a Leonard M. Shapiro, MD, FRCP,b Clive Lewis, PhD, FRCP,a Jayan K. Parameshwar, MD, FRCP,a and Steven S.L. Tsui, MD, FRCS(C-Th)a From the aTransplant Unit; and the b Cardiology Unit, Papworth Hospital NHS Foundation Trust, Papworth Everard, Cambridge, UK.
Recovery of heart function during support with a left ventricular assist device (LVAD) is unusual. Of 1,309 transplant-listed patients who received a continuous-flow LVAD in the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS), only 1% of patients recovered sufficiently to enable explant of their
References 1. Allen LA, Stevenson LW, Grady KL, et al. Decision making in advanced heart failure: a scientific statement from the American Heart Association. Circulation 2012;125:1928-52. 2. Iacovetto M, Matlock DD, McIlvennan CK, et al. Educational resources for patients considering a left ventricular assist device: a cross-sectional review of internet, print, and multimedia materials. Circ Cardiovasc Qual Outcomes 2014;7:905-11. 3. McIlvennan CK, Magid KH, Ambardekar AV, Thompson JS, Matlock DD, Allen LA. Clinical outcomes following continuous-flow left ventricular assist device: a systematic review. Circ Heart Fail 2014;7: 1003-13. 4. Mason W, Suri W. Conducting behavioral research on Amazon’s Mechanical Turk. Behav Res Methods 2012;44:1-23. 5. McIlvennan CK, Allen LA, Nowels C, Brieke A, Cleveland JC, Matlock DD. Decision making for destination therapy left ventricular assist devices: “There was no choice” versus “I thought about it an awful lot.” Circ Cardiovasc Qual Outcomes 2014;7:374-80.
LVAD by 12 months.1 Outcomes after LVAD explant are uncertain. In the largest observational study of recovery from LVAD support, 10 patients survived 430 ⫾ 337 days (mean ⫾ standard deviation) after explant, but 2 patients died of post-operative complications within 30 days, despite re-institution of mechanical circulatory support.2 There are several risks associated with LVAD explantation. Dense adhesions form around the device and there is a risk of trauma during dissection. Use of blood products may increase pulmonary vascular resistance and risk of right heart failure. Cardiopulmonary bypass may lead to a systemic inflammatory response and vasoplegia.3 Furthermore, in the event of future deterioration necessitating heart transplantation, each additional sternotomy will confer a risk of increased post-transplant mortality.4 For these reasons, a strategy for minimally invasive withdrawal of LVAD support is attractive. We report the case of a 17-year-old male with a dilated cardiomyopathy who received a HeartWare HVAD (HeartWare, Inc., Framingham, MA). Over the first 6 months, he
Research Correspondence had a dramatic reduction in cardiothoracic ratio. After 22 months of support, when tests were performed with the HVAD pump speed reduced to 2,400 revolutions per minute (rpm), the patient had mild impairment of left ventricular systolic function by echocardiography, a peak oxygen consumption of 23 ml/min/m2 and a cardiac output of 6.92 liters/min measured at right heart catheterization. A decision was made to withdraw LVAD support by placement of vascular plugs in the proximal and distal end of the outflow graft, followed by burial of the subcutaneous drive-line. Warfarin was stopped and low-molecular-weight heparin was started when the prothrombin time fell beneath the target range. The procedure was performed in a cardiac catheterization laboratory. An 8-French sheath was placed in the right femoral artery. The HVAD outflow graft was cannulated with a multi-purpose catheter. Contrast injection into the outflow graft showed normal HVAD function (see Video Loop 1 in Supplementary Material online). The HVAD speed was reduced to 1,800 rpm and invasive measurements of cardiac function remained satisfactory. The HVAD was turned off. Repeated contrast injection into the outflow graft showed reflux of contrast through the LVAD into the LV cavity (see Video Loop 2 online). Vascular plugs were deployed at each end of the outflow graft. To ensure complete closure, a 14-mm vascular plug (Amplatzer; St Jude Medical, Inc., St Paul, MN) that was over-sized respective to the 10-mm outflow graft was selected. The first vascular plug was deployed at the proximal end of the outflow graft, immediately adjacent to the HVAD, in order to minimize the risk of migration due to retrograde flow when the pump was switched off (Figure 1, and Video Loop 3 online). Contrast was injected into the outflow graft distal to the device at regular intervals to monitor flow. Within 5 minutes, there was complete occlusion of the
Figure 1 Fluoroscopic image captured during deployment of an Amplatzer vascular plug within the proximal portion of an HVAD outflow graft.
991
Figure 2 Fluoroscopic image captured 5 minutes after deployment of an Amplatzer vascular plug with contrast injection in the outflow graft, showing complete occlusion of outflow graft and absence of retrograde flow through the HVAD.
outflow graft (Figure 2, and Video Loop 4 online). The second vascular plug was deployed in the distal end of the outflow graft flush with the ascending aorta, in order to avoid leaving a blind-ended graft open to the aorta (Video Loop 5 online). The drive-line was disconnected from the system controller. The patient was taken to the operating room on the following day. A subcutaneous segment of the drive-line was exposed with a 3-cm skin incision approximately 10 cm from the drive-line exit site. This was divided and the distal end was mobilized all the way to the skin exit site and removed. The proximal cut end of the drive-line was covered with an 8-mm Hemashield graft (Maquet, Rastatt, Germany) and buried in the subcutaneous space. The patient has been free of LVAD support for 24 months and remains in New York Heart Association (NYHA) Class I. There have been no problems with the deactivated HVAD or buried drive-line. He remains anti-coagulated and takes ramipril, carvedilol and spironolactone. Echocardiography shows mild left ventricular dilation (end-diastolic dimension 5.9 cm) and mild left ventricular systolic dysfunction. Functional testing is unchanged (peak VO2 ¼ 23 ml/min/m2) and natriuretic peptide levels are not elevated (N-terminal proB-type natriuretic peptide o500 pg/ml). There are no plans to remove the deactivated HVAD, unless a complication arises due to the redundant system or anti-coagulation. Several strategies for minimally invasive LVAD explantation have been described. The HeartMate II LVAD (Thoratec Corp., Pleasanton, CA) has been removed via 2 mini-thoracotomies and an epigastric incision, but cardiopulmonary bypass was required.5,6 In later reports, the HeartMate II LVAD and HeartWare HVAD were explanted without cardiopulmonary bypass and using a plug in the left ventricular apex and leaving a portion of the outflow graft in situ.7,8 Outcomes are reasonable, although infection in the remaining limb of the
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The Journal of Heart and Lung Transplantation, Vol 34, No 7, July 2015
outflow graft has been reported.5 A less invasive approach has been described with the Jarvik 2000 LVAD and HeartMate II LVAD. In each case, the outflow graft was ligated close to the aorta and the pump was left within the left ventricle.9,10 This avoided the need for sternotomy and cardiopulmonary bypass and eliminated the risk of trauma during pump removal. The least invasive approach is to simply turn off the device. This has been described in 3 patients with biventricular support using HeartWare HVAD devices. In each case, recovery of right ventricular (RV) function permitted withdrawal of the RVAD.11 Device thrombosis and cessation of retrograde flow were observed within 48 hours. This approach is unattractive in an LVAD because the pressure drop across the pump would lead to significant retrograde flow though the LVAD and pose a high risk of systemic thromboembolism. In conclusion, we have described a technique for percutaneous withdrawal of LVAD support. This strategy is attractive for patients who have recovered LV function during HeartWare HVAD support and may be applicable for patients with other types of implantable LVAD.
Disclosure statement The authors have no conflicts of interest to disclose.
Supplementary data Supplementary data associated with this article can be found in the online version at www.jhltonline.org.
Defining the impact of intraaortic balloon pump setting on ventricular assist device flow Christian Swinney, BA, Akinobu Itoh, MD, PhD, Angela Keith, MS, Keki Balsara, MD, Susan Joseph, MD, and Scott Silvestry, MD From the Department of Surgery, Washington University School of Medicine, St. Louis, Missouri.
Intraaortic balloon pumps (IABPs) are increasingly used to optimize patients with chronic heart failure to receive continuous-flow left ventricular assist devices (LVADs).1 Traditional use of IABPs centered on augmenting coronary blood flow and decreasing afterload,2–4 whereas LVAD optimization is focused on improving right ventricular function and pre-operative renal and splanchnic blood flow.5 After LVAD implantation, the IABP and LVAD are used together in the immediate post-operative period. The mechanism of the IABP predictably causes transient obstruction to flow in continuous-flow LVADs. To minimize this effect, lower augmentation and frequency settings have been suggested when an IABP is used with a continuous-flow LVAD. However, the impact of the IABP
References 1. Kirklin JK, Naftel DC, Pagani FD, et al. Sixth INTERMACS annual report: a 10,000-patient database. J Heart Lung Transplant 2014; 33:555-64. 2. Birks EJ, George RS, Hedger M, et al. Reversal of severe heart failure with a continuous-flow left ventricular assist device and pharmacological therapy: a prospective study. Circulation 2011;123: 381-90. 3. Licker M, Diaper J, Cartier V, et al. Clinical review: management of weaning from cardiopulmonary bypass after cardiac surgery. Ann Card Anaesth 2012;15:206-23. 4. Schulze PC, Jiang J, Yang J, et al. Preoperative assessment of high-risk candidates to predict survival after heart transplantation. Circ Heart Fail 2013;6:527-34. 5. Cohn WE, Gregoric ID, Radovancevic B, et al. A felt plug simplifies left ventricular assist device removal after successful bridge to recovery. J Heart Lung Transplant 2007;26:1209-11. 6. Haj-Yahia S, Birks EJ, Dreyfus G, et al. Limited surgical approach for explanting the HeartMate II left ventricular assist device after myocardial recovery. J Thorac Cardiovasc Surg 2008;135:453-4. 7. Cheung A, Bashir J, Kaan A, et al. Minimally invasive, off-pump explant of a continuous-flow left ventricular assist device. J Heart Lung Transplant 2010;29:808-10. 8. Schweiger M, Potapov E, Vierecke J, et al. Expeditious and less traumatic explantation of a HeartWare LVAD after myocardial recovery. ASAIO J 2012;58:542-4. 9. George RS, Khaghani C, Bowles CT, et al. Sustained myocardial recovery 5 years after in situ disconnection of a Jarvik 2000 device. J Heart Lung Transplant 2010;29:587-8. 10. Khvilivitzky K, Mountis MM, Gonzalez-Stawinski GV. HeartMate II outflow graft ligation and driveline excision without pump removal for left ventricular recovery. Proc Bayl Univ Med Cent 2012;25:344-5. 11. Potapov E, Schweiger M, Vierecke J, et al. Discontinuation of HeartWare RVAD support without device removal in chronic BIVAD patients. ASAIO J 2012;58:15-8.
on LVAD flow is undefined. We hypothesized that inflation of the IABP would not impair the mean LVAD flow rate, but would have an impact on the other flow characteristics, such as the maximum and minimum flow rate. A series of 51 LVAD flow tracings from 15 patients was retrospectively reviewed. Institutional review board approval was obtained from Washington University in St. Louis. Flow measurements were obtained using a flow probe (Transonic Systems, Inc, Ithaca, NY) on the LVAD outflow graft before chest closure. Measurements included 16 flow tracings with the IABP in the off setting, 17 flow tracings with IABP at 1:1, 11 flow tracings with the IABP at 1:2, and 7 flow tracings with the IABP at 1:3. In 2 instances, a single patient contributed independent sets of flow tracings at different RPM settings. Extracted data included maximum, minimum, and mean LVAD flow (ml/ min); direct pulsatility index from the flow probe; beat interval of the IABP; augmentation setting; LVAD RPM setting; and mean arterial pressure. Flow values were obtained using automated algorithms from the flow printout for each measurement. Patients had either the HVAD (HeartWare, Framingham, MA) or the HeartMate II (Thoratec Corp, Pleasanton, CA) ventricular assist device. Statistical analysis was performed using Microsoft Excel 2010 to conduct a paired t-test.
The Journal of Heart and Lung Transplantation, Vol 34, No 7, July 2015
Figure 2
Accepting aggressive therapy in context of varied risks of major complications.
medical decision such as DT LVAD. These findings should be validated further in a heart failure population offered DT LVAD. Until then, clinicians should assume that accurate and thoughtful presentation of risks and benefits is essential to high-quality decision making regarding DT LVAD.
Disclosure statement There are no relevant conflicts of interest to disclose. The study was conducted with support from the University of Colorado Department of Medicine Early Career Scholars Program. D.D.M. is supported by the National Institutes on Aging (Grant No. K23AG040696). L.A.A. is supported by the National Heart, Lung, and Blood Institute (Grant No. K23HL105896). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
Percutaneous withdrawal of HeartWare HVAD left ventricular assist device support Stephen J. Pettit, PhD, MRCP,a Leonard M. Shapiro, MD, FRCP,b Clive Lewis, PhD, FRCP,a Jayan K. Parameshwar, MD, FRCP,a and Steven S.L. Tsui, MD, FRCS(C-Th)a From the aTransplant Unit; and the b Cardiology Unit, Papworth Hospital NHS Foundation Trust, Papworth Everard, Cambridge, UK.
Recovery of heart function during support with a left ventricular assist device (LVAD) is unusual. Of 1,309 transplant-listed patients who received a continuous-flow LVAD in the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS), only 1% of patients recovered sufficiently to enable explant of their
References 1. Allen LA, Stevenson LW, Grady KL, et al. Decision making in advanced heart failure: a scientific statement from the American Heart Association. Circulation 2012;125:1928-52. 2. Iacovetto M, Matlock DD, McIlvennan CK, et al. Educational resources for patients considering a left ventricular assist device: a cross-sectional review of internet, print, and multimedia materials. Circ Cardiovasc Qual Outcomes 2014;7:905-11. 3. McIlvennan CK, Magid KH, Ambardekar AV, Thompson JS, Matlock DD, Allen LA. Clinical outcomes following continuous-flow left ventricular assist device: a systematic review. Circ Heart Fail 2014;7: 1003-13. 4. Mason W, Suri W. Conducting behavioral research on Amazon’s Mechanical Turk. Behav Res Methods 2012;44:1-23. 5. McIlvennan CK, Allen LA, Nowels C, Brieke A, Cleveland JC, Matlock DD. Decision making for destination therapy left ventricular assist devices: “There was no choice” versus “I thought about it an awful lot.” Circ Cardiovasc Qual Outcomes 2014;7:374-80.
LVAD by 12 months.1 Outcomes after LVAD explant are uncertain. In the largest observational study of recovery from LVAD support, 10 patients survived 430 ⫾ 337 days (mean ⫾ standard deviation) after explant, but 2 patients died of post-operative complications within 30 days, despite re-institution of mechanical circulatory support.2 There are several risks associated with LVAD explantation. Dense adhesions form around the device and there is a risk of trauma during dissection. Use of blood products may increase pulmonary vascular resistance and risk of right heart failure. Cardiopulmonary bypass may lead to a systemic inflammatory response and vasoplegia.3 Furthermore, in the event of future deterioration necessitating heart transplantation, each additional sternotomy will confer a risk of increased post-transplant mortality.4 For these reasons, a strategy for minimally invasive withdrawal of LVAD support is attractive. We report the case of a 17-year-old male with a dilated cardiomyopathy who received a HeartWare HVAD (HeartWare, Inc., Framingham, MA). Over the first 6 months, he
Research Correspondence had a dramatic reduction in cardiothoracic ratio. After 22 months of support, when tests were performed with the HVAD pump speed reduced to 2,400 revolutions per minute (rpm), the patient had mild impairment of left ventricular systolic function by echocardiography, a peak oxygen consumption of 23 ml/min/m2 and a cardiac output of 6.92 liters/min measured at right heart catheterization. A decision was made to withdraw LVAD support by placement of vascular plugs in the proximal and distal end of the outflow graft, followed by burial of the subcutaneous drive-line. Warfarin was stopped and low-molecular-weight heparin was started when the prothrombin time fell beneath the target range. The procedure was performed in a cardiac catheterization laboratory. An 8-French sheath was placed in the right femoral artery. The HVAD outflow graft was cannulated with a multi-purpose catheter. Contrast injection into the outflow graft showed normal HVAD function (see Video Loop 1 in Supplementary Material online). The HVAD speed was reduced to 1,800 rpm and invasive measurements of cardiac function remained satisfactory. The HVAD was turned off. Repeated contrast injection into the outflow graft showed reflux of contrast through the LVAD into the LV cavity (see Video Loop 2 online). Vascular plugs were deployed at each end of the outflow graft. To ensure complete closure, a 14-mm vascular plug (Amplatzer; St Jude Medical, Inc., St Paul, MN) that was over-sized respective to the 10-mm outflow graft was selected. The first vascular plug was deployed at the proximal end of the outflow graft, immediately adjacent to the HVAD, in order to minimize the risk of migration due to retrograde flow when the pump was switched off (Figure 1, and Video Loop 3 online). Contrast was injected into the outflow graft distal to the device at regular intervals to monitor flow. Within 5 minutes, there was complete occlusion of the
Figure 1 Fluoroscopic image captured during deployment of an Amplatzer vascular plug within the proximal portion of an HVAD outflow graft.
991
Figure 2 Fluoroscopic image captured 5 minutes after deployment of an Amplatzer vascular plug with contrast injection in the outflow graft, showing complete occlusion of outflow graft and absence of retrograde flow through the HVAD.
outflow graft (Figure 2, and Video Loop 4 online). The second vascular plug was deployed in the distal end of the outflow graft flush with the ascending aorta, in order to avoid leaving a blind-ended graft open to the aorta (Video Loop 5 online). The drive-line was disconnected from the system controller. The patient was taken to the operating room on the following day. A subcutaneous segment of the drive-line was exposed with a 3-cm skin incision approximately 10 cm from the drive-line exit site. This was divided and the distal end was mobilized all the way to the skin exit site and removed. The proximal cut end of the drive-line was covered with an 8-mm Hemashield graft (Maquet, Rastatt, Germany) and buried in the subcutaneous space. The patient has been free of LVAD support for 24 months and remains in New York Heart Association (NYHA) Class I. There have been no problems with the deactivated HVAD or buried drive-line. He remains anti-coagulated and takes ramipril, carvedilol and spironolactone. Echocardiography shows mild left ventricular dilation (end-diastolic dimension 5.9 cm) and mild left ventricular systolic dysfunction. Functional testing is unchanged (peak VO2 ¼ 23 ml/min/m2) and natriuretic peptide levels are not elevated (N-terminal proB-type natriuretic peptide o500 pg/ml). There are no plans to remove the deactivated HVAD, unless a complication arises due to the redundant system or anti-coagulation. Several strategies for minimally invasive LVAD explantation have been described. The HeartMate II LVAD (Thoratec Corp., Pleasanton, CA) has been removed via 2 mini-thoracotomies and an epigastric incision, but cardiopulmonary bypass was required.5,6 In later reports, the HeartMate II LVAD and HeartWare HVAD were explanted without cardiopulmonary bypass and using a plug in the left ventricular apex and leaving a portion of the outflow graft in situ.7,8 Outcomes are reasonable, although infection in the remaining limb of the
992
The Journal of Heart and Lung Transplantation, Vol 34, No 7, July 2015
outflow graft has been reported.5 A less invasive approach has been described with the Jarvik 2000 LVAD and HeartMate II LVAD. In each case, the outflow graft was ligated close to the aorta and the pump was left within the left ventricle.9,10 This avoided the need for sternotomy and cardiopulmonary bypass and eliminated the risk of trauma during pump removal. The least invasive approach is to simply turn off the device. This has been described in 3 patients with biventricular support using HeartWare HVAD devices. In each case, recovery of right ventricular (RV) function permitted withdrawal of the RVAD.11 Device thrombosis and cessation of retrograde flow were observed within 48 hours. This approach is unattractive in an LVAD because the pressure drop across the pump would lead to significant retrograde flow though the LVAD and pose a high risk of systemic thromboembolism. In conclusion, we have described a technique for percutaneous withdrawal of LVAD support. This strategy is attractive for patients who have recovered LV function during HeartWare HVAD support and may be applicable for patients with other types of implantable LVAD.
Disclosure statement The authors have no conflicts of interest to disclose.
Supplementary data Supplementary data associated with this article can be found in the online version at www.jhltonline.org.
Defining the impact of intraaortic balloon pump setting on ventricular assist device flow Christian Swinney, BA, Akinobu Itoh, MD, PhD, Angela Keith, MS, Keki Balsara, MD, Susan Joseph, MD, and Scott Silvestry, MD From the Department of Surgery, Washington University School of Medicine, St. Louis, Missouri.
Intraaortic balloon pumps (IABPs) are increasingly used to optimize patients with chronic heart failure to receive continuous-flow left ventricular assist devices (LVADs).1 Traditional use of IABPs centered on augmenting coronary blood flow and decreasing afterload,2–4 whereas LVAD optimization is focused on improving right ventricular function and pre-operative renal and splanchnic blood flow.5 After LVAD implantation, the IABP and LVAD are used together in the immediate post-operative period. The mechanism of the IABP predictably causes transient obstruction to flow in continuous-flow LVADs. To minimize this effect, lower augmentation and frequency settings have been suggested when an IABP is used with a continuous-flow LVAD. However, the impact of the IABP
References 1. Kirklin JK, Naftel DC, Pagani FD, et al. Sixth INTERMACS annual report: a 10,000-patient database. J Heart Lung Transplant 2014; 33:555-64. 2. Birks EJ, George RS, Hedger M, et al. Reversal of severe heart failure with a continuous-flow left ventricular assist device and pharmacological therapy: a prospective study. Circulation 2011;123: 381-90. 3. Licker M, Diaper J, Cartier V, et al. Clinical review: management of weaning from cardiopulmonary bypass after cardiac surgery. Ann Card Anaesth 2012;15:206-23. 4. Schulze PC, Jiang J, Yang J, et al. Preoperative assessment of high-risk candidates to predict survival after heart transplantation. Circ Heart Fail 2013;6:527-34. 5. Cohn WE, Gregoric ID, Radovancevic B, et al. A felt plug simplifies left ventricular assist device removal after successful bridge to recovery. J Heart Lung Transplant 2007;26:1209-11. 6. Haj-Yahia S, Birks EJ, Dreyfus G, et al. Limited surgical approach for explanting the HeartMate II left ventricular assist device after myocardial recovery. J Thorac Cardiovasc Surg 2008;135:453-4. 7. Cheung A, Bashir J, Kaan A, et al. Minimally invasive, off-pump explant of a continuous-flow left ventricular assist device. J Heart Lung Transplant 2010;29:808-10. 8. Schweiger M, Potapov E, Vierecke J, et al. Expeditious and less traumatic explantation of a HeartWare LVAD after myocardial recovery. ASAIO J 2012;58:542-4. 9. George RS, Khaghani C, Bowles CT, et al. Sustained myocardial recovery 5 years after in situ disconnection of a Jarvik 2000 device. J Heart Lung Transplant 2010;29:587-8. 10. Khvilivitzky K, Mountis MM, Gonzalez-Stawinski GV. HeartMate II outflow graft ligation and driveline excision without pump removal for left ventricular recovery. Proc Bayl Univ Med Cent 2012;25:344-5. 11. Potapov E, Schweiger M, Vierecke J, et al. Discontinuation of HeartWare RVAD support without device removal in chronic BIVAD patients. ASAIO J 2012;58:15-8.
on LVAD flow is undefined. We hypothesized that inflation of the IABP would not impair the mean LVAD flow rate, but would have an impact on the other flow characteristics, such as the maximum and minimum flow rate. A series of 51 LVAD flow tracings from 15 patients was retrospectively reviewed. Institutional review board approval was obtained from Washington University in St. Louis. Flow measurements were obtained using a flow probe (Transonic Systems, Inc, Ithaca, NY) on the LVAD outflow graft before chest closure. Measurements included 16 flow tracings with the IABP in the off setting, 17 flow tracings with IABP at 1:1, 11 flow tracings with the IABP at 1:2, and 7 flow tracings with the IABP at 1:3. In 2 instances, a single patient contributed independent sets of flow tracings at different RPM settings. Extracted data included maximum, minimum, and mean LVAD flow (ml/ min); direct pulsatility index from the flow probe; beat interval of the IABP; augmentation setting; LVAD RPM setting; and mean arterial pressure. Flow values were obtained using automated algorithms from the flow printout for each measurement. Patients had either the HVAD (HeartWare, Framingham, MA) or the HeartMate II (Thoratec Corp, Pleasanton, CA) ventricular assist device. Statistical analysis was performed using Microsoft Excel 2010 to conduct a paired t-test.
