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Echocardiographic Evaluation of LVAD Flow During Intra-Aortic Balloon Pump Support
CASE REPORT
Echocardiographic Evaluation of LVAD Flow During Intra-Aortic Balloon Pump Support Giulio Melisurgo, MD,* Silvia Ajello, MD,† and Federico Pappalardo, MD*
P
ATIENTS UNDERGOING LEFT VENTRICULAR assist device (LVAD) implantation often are supported preoperatively with an intra-aortic balloon pump (IABP), but no clear guideline addresses the management of this device after surgery.1 The 3 major aims of IABP use are to increase coronary perfusion, reduce left ventricular afterload, and increase cardiac output. The precise hemodynamic changes during LVAD support and IABP have not been described clearly. The case description of the management of an IABP after HeartWare LVAD centrifugal flow pump implantation is reported here. CASE REPORT A 56-year-old man suffering from ischemic dilated cardiomyopathy received a HeartWare LVAD. The patient required 2 weeks of preoperative inotropic and IABP (40 mL) support for the optimization of his right ventricular function. After the implantation, the patient was admitted to the intensive care unit with the LVAD running at 2,500 rotations per minute (rpm), epinephrine (0.2 μg/kg/min), and inhaled nitric oxide (20 ppm) and the IABP was left in situ with a ratio of 1:2. Transesophageal echocardiography was performed with optimal visualization of the outflow graft anastomosed to the ascending aorta, in the midesophageal ascending aorta long-axis view, with the flow being aligned perfectly with the transducer. The outflow graft flow velocity with IABP ratio 1:2 was sampled with pulsed-wave Doppler (Fig 1A). During diastolic balloon inflation the graft flow velocity drops to near zero, whereas during an unassisted cardiac cycle this phenomenon is not observed. This phenomenon can be systematically observed with an IABP ratio 1:1 (Fig 1B) and disappears when the pump is turned off (Fig 1C). Right ventricular function was assessed simultaneously with tissue Doppler imaging by the evaluation of S wave sampled at lateral tricuspid annulus during IABP 1:1 (Fig 2A) and IABP turned-off (Fig 2B); no change in such parameter was observed: A reduced S-wave velocity (6 cm/sec- normal value above 11 cm/sec) was recorded either during IABP 1:1 or IABP turned-off (Fig 2). The flow-time chart of the LVAD monitor showed abrupt reduction of flow during the counterpulsed diastole. DISCUSSION
LVADs are mechanical circulatory support devices intended for long-term treatment of advanced-stage heart failure patients. The HeartWare Ventricular Assist System (HeartWare System, Miami Lakes, FL) is a type of LVAD that consists of an implantable centrifugal flow pump, an external controller, and external power sources. A wideblade impeller with a hybrid suspension system uses passive magnetic and hydrodynamic thrust bearings to create a contact-free rotation of the impeller. The pump is positioned
surgically in the pericardial space with the integrated inflow cannula in the left ventricle. Blood from the left ventricle enters the pump through the inflow cannula and exits through a 10-mm outflow graft attached to the ascending aorta. The maximum flow rate is 10 L/min. The pump is connected to external system components by a driveline that is tunnelled subcutaneously and exits the patient’s abdominal wall.2 The use of the IABP assistance, prior to the LVAD implantation, is driven by the physiologic effect on the coronary circulation to actively optimize the right ventricular function.3 The intra-aortic balloon exerts its effect by volume displacement and pressure changes caused by rapidly shuttling helium gas in and out of the balloon chamber.4 During diastole, because the volume in the aorta suddenly is increased, the intraaortic pressure increases sharply. The amount of blood flow through the LVAD at a constant impeller rotational speed is determined by the differential pressure across the pump. The difference between preload (left ventricular pressure) and afterload (aortic pressure) is the hemodynamic parameter mainly affecting blood flow through the pump. Head pressure and flow curve correlate with the amount of blood flow that can be generated by the pump at any rpm across a wide range of pressures (Fig 3). As with all rotary blood pumps, higher flow rates are achieved with lower pressure differentials across the pump. A higher preload and lower afterload will result in higher flow rates at any given impeller speed. Actual flow through a pump will vary with changes in pressure during a cardiac cycle. As the differential pressure changes, motor current also changes.2 In this patient, the authors observed that during IABP counterpulsation, the diastolic balloon inflation caused an increase in pressure in the ascending aorta, an increase of differential pressure across the pump, and subsequent lower flow.
From the *Department of Cardiovascular Anesthesia and Intensive Care; and †Department of Cardiology, San Raffaele University Hospital, Milan, Italy. Address reprint requests to Silvia Ajello, MD, Department of Cardiology, San Raffaele University Hospital, Via Olgettina, 60, 20132 Milano, Italy. E-mail: [email protected] © 2014 Elsevier Inc. All rights reserved. 1053-0770/2602-0033$36.00/0 http://dx.doi.org/10.1053/j.jvca.2014.08.019 Key words: ventricular assist device, intra-aortic balloon pump, cardiomyopathy
Journal of Cardiothoracic and Vascular Anesthesia, Vol ], No ] (Month), 2014: pp ]]]–]]]
1
2
MELISURGO ET AL
Fig 1. Doppler flow velocity profile sampled with pulsed-wave Doppler at the outflow graft anastomosis in the ascending aorta. (A) IABP ratio 1:2, (B) IABP 1:1, (C) normal flow velocity pattern without IABP (IABP turned off). Flow velocity drops near zero during diastolic balloon inflation (white arrow).
Fig 2. Tissue Doppler Imaging of right ventricle (RV) as direct measurement of intrinsic RV contractility or RV myocardial performance (not influenced by asymmetric shape of the RV and is not load-dependent). S-wave sampled at lateral tricuspid annulus during (A) IABP 1:1 and (B) IABP turned-off.
Fig 3. Flow-pressure (HQ) curve for the pump at a constant blood viscosity of 2.5 cP during the entire range of operating speeds. This HQ curve is used to estimate blood flow.
During the onset of systole, the deflation of the balloon should cause a fall in pressure in the aorta and higher pump flow rates, but no changes in Doppler flow velocity were observed (Fig 1) and no benefit was observed on the right ventricular function.
Further studies are required to address this phenomenon at different pump speeds and with axial flow pumps. According to the authors’ experience, the IABP support should be removed promptly after the LVAD implantation.
3
ECHOCARDIOGRAPHIC EVALUATION OF LVAD FLOW
REFERENCES 1. Slaughter MS, Pagani FD, Rogers JG, et al: Clinical management of continuous-flow left ventricular assist devices in advanced heart failure. J Heart Lung Transplant 29(suppl):S1-39, 2010 2. Larose JA, Tamez D, Ashenuga M, et al: Design concepts and principle of operation of the HeartWare ventricular assist system. ASAIO J 56:285-289, 2010
3. Arafa OE, Geiran OR, Andersen K, et al: Intraaortic balloon pumping for predominantly right ventricular failure after heart transplantation. Ann Thorac Surg 70:1587-1593, 2000 4. Counterpulsation applied. An introduction to intra-Aortic balloon pumping. 2005 Arrow International. Available at http://www.arrowintl. com/documents/pdf/education/abt-tg0605.pdf. Accessed July 26, 2014.
Echocardiographic Evaluation of LVAD Flow During Intra-Aortic Balloon Pump Support Giulio Melisurgo, MD,* Silvia Ajello, MD,† and Federico Pappalardo, MD*
P
ATIENTS UNDERGOING LEFT VENTRICULAR assist device (LVAD) implantation often are supported preoperatively with an intra-aortic balloon pump (IABP), but no clear guideline addresses the management of this device after surgery.1 The 3 major aims of IABP use are to increase coronary perfusion, reduce left ventricular afterload, and increase cardiac output. The precise hemodynamic changes during LVAD support and IABP have not been described clearly. The case description of the management of an IABP after HeartWare LVAD centrifugal flow pump implantation is reported here. CASE REPORT A 56-year-old man suffering from ischemic dilated cardiomyopathy received a HeartWare LVAD. The patient required 2 weeks of preoperative inotropic and IABP (40 mL) support for the optimization of his right ventricular function. After the implantation, the patient was admitted to the intensive care unit with the LVAD running at 2,500 rotations per minute (rpm), epinephrine (0.2 μg/kg/min), and inhaled nitric oxide (20 ppm) and the IABP was left in situ with a ratio of 1:2. Transesophageal echocardiography was performed with optimal visualization of the outflow graft anastomosed to the ascending aorta, in the midesophageal ascending aorta long-axis view, with the flow being aligned perfectly with the transducer. The outflow graft flow velocity with IABP ratio 1:2 was sampled with pulsed-wave Doppler (Fig 1A). During diastolic balloon inflation the graft flow velocity drops to near zero, whereas during an unassisted cardiac cycle this phenomenon is not observed. This phenomenon can be systematically observed with an IABP ratio 1:1 (Fig 1B) and disappears when the pump is turned off (Fig 1C). Right ventricular function was assessed simultaneously with tissue Doppler imaging by the evaluation of S wave sampled at lateral tricuspid annulus during IABP 1:1 (Fig 2A) and IABP turned-off (Fig 2B); no change in such parameter was observed: A reduced S-wave velocity (6 cm/sec- normal value above 11 cm/sec) was recorded either during IABP 1:1 or IABP turned-off (Fig 2). The flow-time chart of the LVAD monitor showed abrupt reduction of flow during the counterpulsed diastole. DISCUSSION
LVADs are mechanical circulatory support devices intended for long-term treatment of advanced-stage heart failure patients. The HeartWare Ventricular Assist System (HeartWare System, Miami Lakes, FL) is a type of LVAD that consists of an implantable centrifugal flow pump, an external controller, and external power sources. A wideblade impeller with a hybrid suspension system uses passive magnetic and hydrodynamic thrust bearings to create a contact-free rotation of the impeller. The pump is positioned
surgically in the pericardial space with the integrated inflow cannula in the left ventricle. Blood from the left ventricle enters the pump through the inflow cannula and exits through a 10-mm outflow graft attached to the ascending aorta. The maximum flow rate is 10 L/min. The pump is connected to external system components by a driveline that is tunnelled subcutaneously and exits the patient’s abdominal wall.2 The use of the IABP assistance, prior to the LVAD implantation, is driven by the physiologic effect on the coronary circulation to actively optimize the right ventricular function.3 The intra-aortic balloon exerts its effect by volume displacement and pressure changes caused by rapidly shuttling helium gas in and out of the balloon chamber.4 During diastole, because the volume in the aorta suddenly is increased, the intraaortic pressure increases sharply. The amount of blood flow through the LVAD at a constant impeller rotational speed is determined by the differential pressure across the pump. The difference between preload (left ventricular pressure) and afterload (aortic pressure) is the hemodynamic parameter mainly affecting blood flow through the pump. Head pressure and flow curve correlate with the amount of blood flow that can be generated by the pump at any rpm across a wide range of pressures (Fig 3). As with all rotary blood pumps, higher flow rates are achieved with lower pressure differentials across the pump. A higher preload and lower afterload will result in higher flow rates at any given impeller speed. Actual flow through a pump will vary with changes in pressure during a cardiac cycle. As the differential pressure changes, motor current also changes.2 In this patient, the authors observed that during IABP counterpulsation, the diastolic balloon inflation caused an increase in pressure in the ascending aorta, an increase of differential pressure across the pump, and subsequent lower flow.
From the *Department of Cardiovascular Anesthesia and Intensive Care; and †Department of Cardiology, San Raffaele University Hospital, Milan, Italy. Address reprint requests to Silvia Ajello, MD, Department of Cardiology, San Raffaele University Hospital, Via Olgettina, 60, 20132 Milano, Italy. E-mail: [email protected] © 2014 Elsevier Inc. All rights reserved. 1053-0770/2602-0033$36.00/0 http://dx.doi.org/10.1053/j.jvca.2014.08.019 Key words: ventricular assist device, intra-aortic balloon pump, cardiomyopathy
Journal of Cardiothoracic and Vascular Anesthesia, Vol ], No ] (Month), 2014: pp ]]]–]]]
1
2
MELISURGO ET AL
Fig 1. Doppler flow velocity profile sampled with pulsed-wave Doppler at the outflow graft anastomosis in the ascending aorta. (A) IABP ratio 1:2, (B) IABP 1:1, (C) normal flow velocity pattern without IABP (IABP turned off). Flow velocity drops near zero during diastolic balloon inflation (white arrow).
Fig 2. Tissue Doppler Imaging of right ventricle (RV) as direct measurement of intrinsic RV contractility or RV myocardial performance (not influenced by asymmetric shape of the RV and is not load-dependent). S-wave sampled at lateral tricuspid annulus during (A) IABP 1:1 and (B) IABP turned-off.
Fig 3. Flow-pressure (HQ) curve for the pump at a constant blood viscosity of 2.5 cP during the entire range of operating speeds. This HQ curve is used to estimate blood flow.
During the onset of systole, the deflation of the balloon should cause a fall in pressure in the aorta and higher pump flow rates, but no changes in Doppler flow velocity were observed (Fig 1) and no benefit was observed on the right ventricular function.
Further studies are required to address this phenomenon at different pump speeds and with axial flow pumps. According to the authors’ experience, the IABP support should be removed promptly after the LVAD implantation.
3
ECHOCARDIOGRAPHIC EVALUATION OF LVAD FLOW
REFERENCES 1. Slaughter MS, Pagani FD, Rogers JG, et al: Clinical management of continuous-flow left ventricular assist devices in advanced heart failure. J Heart Lung Transplant 29(suppl):S1-39, 2010 2. Larose JA, Tamez D, Ashenuga M, et al: Design concepts and principle of operation of the HeartWare ventricular assist system. ASAIO J 56:285-289, 2010
3. Arafa OE, Geiran OR, Andersen K, et al: Intraaortic balloon pumping for predominantly right ventricular failure after heart transplantation. Ann Thorac Surg 70:1587-1593, 2000 4. Counterpulsation applied. An introduction to intra-Aortic balloon pumping. 2005 Arrow International. Available at http://www.arrowintl. com/documents/pdf/education/abt-tg0605.pdf. Accessed July 26, 2014.