Research Correspondence Echocardiographic markers of left ventricular unloading using a centrifugal-flow rotary pump Andrew J. Sauer, MD,a Karen Meehan, ACNS-BC,b Robert Gordon, MD,a Travis Abicht, MD,b Jonathan D. Rich, MD,a Allen S. Anderson, MD,a Clyde Yancy, MD,a and Edwin C. McGee Jr, MDb From the aCardiology; and the bCardiac Surgery, Northwestern University Feinberg School of Medicine, Chicago, Illinois
Optimizing the rotary left ventricular (LV) assist device (LVAD) speed remains an important pursuit of all clinicians caring for LVAD-supported patients. In an effort to attenuate the consequences of excessive ventricular unloading and non-pulsatile flow, recent guidelines have suggested the routine use of echocardiography in the nonintensive care unit post-operative period as one tool for measuring LV unloading to help select the appropriate LVAD speed.1 Furthermore, novel echocardiographic speed ramp algorithms involving patients with an axialflow rotary pump have been proposed to quantify the degree of LV unloading by measuring the slope of serial changes in LV end-diastolic dimension (LVEDD) at varying LVAD speeds.2 Thus, echocardiographic ramp study protocols, which are inherently center-specific and not yet standardized, have become variably adopted despite limited evidence for their appropriate use. Furthermore, LVEDD as a marker of LV unloading has not been well validated in patients with durable centrifugal-flow devices. Therefore, we reviewed speed ramp optimization studies performed at our center for patients with the recently approved centrifugal-flow HeartWare LVAD (HVAD; HeartWare International Inc, Framingham, MA) to describe conventional echocardiographic markers of ventricular unloading; specifically, LVEDD, frequency of aortic valve opening, and the degree of mitral regurgitation. We retrospectively analyzed all HVAD speed ramp optimizations performed for clinical purposes at the Bluhm Cardiovascular Institute of Northwestern Memorial Hospital from January 1, 2013, to August 1, 2013. We excluded from our analysis all ramp tests performed on patients with a surgically or percutaneously closed aortic valve or when performed to evaluate for suspected pump thrombus. The retrospective analysis of data involving our HVAD patients was approved by the Northwestern University Feinberg School of Medicine Institutional Review Board. Once all baseline echocardiographic data had been recorded, the speed was decreased every minute by 200 revolutions per minute (rpm) until the speed was settled at 2,200 to 2,400 rpm, which is the initial lower limit determined by the speed that allowed for aortic valve opening on every beat. At this point, the device was allowed to equilibrate at the new speed for 2 minutes. The following echocardiographic measurements were obtained: LVEDD, LV end-systolic dimension (LVESD),
449 frequency of aortic valve opening, degree of aortic regurgitation, degree of mitral regurgitation, estimated pulmonary arterial systolic pressure, estimated mitral inflow E wave velocity, and the position of the interventricular septum (method details are provided in the Supplementary materials, available on the jhltonline.org Web site). In addition, Doppler-measured mean arterial pressure, pump power (watts), and pump estimated flow (liters/min) were recorded for each speed. After the described parameters were measured, the pump speed was increased by an increment of 200 rpm and all measurements were repeated after 2 minutes of equilibration. The ramp protocol was continued until the speed at which point the aortic valve remained closed on every beat and the speed was 200 rpm higher than the speed at which the aortic valve was first noted to be persistently closed. Data were collected using Excel 2010 software (Microsoft Corp, Redmond, WA). Continuous variables are summarized as mean ⫾ standard deviation. The Student’s t-test for independent samples was used to determine differences in the normally distributed data. For each patient, the LVEDD (cm) was plotted against device speed (rpm). The slope for each line was generated by fitting a linear slope function. Finally, a scatterplot was generated to visually represent the raw data and avoid introducing any statistical confounding in representing the relationship between pump speed and LVEDD.
Table 1
Ramp Study Characteristics
Ramp study parameters Initial lowest speed MAP, mm Hg Final highest speed MAP, mm Hg Initial lowest speed power, W Final highest speed power, W Initial lowest speed estimated pump flow, liters/min Final highest speed estimated pump flow, liters/min Initial lowest speed LVESD, cm Final highest speed LVESD, cm LVESD slope Initial lowest speed LVEDD, cm Final highest speed LVEDD, cm LVEDD slope Highest speed for intermittent AV opening, rpm Lowest speed for persistent AV closure, rpm Initial lowest speed degree of MRa Final highest speed degree of MRa Initial lowest speed degree of ARa Final highest speed degree of ARa
All patients (N ¼ 15) (Mean ⫾ SD) 71 79 2.6 5.7 4.2
⫾ ⫾ ⫾ ⫾ ⫾
11 9 0.8 0.9 0.7
6.0 ⫾ 0.9 5.4 5.3 –0.0003 6.1 5.8 –0.0004 2,700
⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾
1.2 0.8 0.0003 0.8 0.7 0.0003 239
2,881 ⫾ 229 2.2 1.9 1.3 1.4
⫾ ⫾ ⫾ ⫾
1.3 1.0 0.6 0.6
AR, aortic regurgitation; AV, aortic valve; LVEDD, left ventricular end-diastolic dimension; LVESD, left ventricular end-systolic dimension; MAP, mean arterial pressure; MR, mitral regurgitation; rpm ¼ revolutions per min; SD, standard deviation. a See numerical grading in Supplementary materials, available on the jhltonline.org Web site, to correlate regurgitation degree.
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The Journal of Heart and Lung Transplantation, Vol 33, No 4, April 2014
Figure 1 Scatterplot of raw data points demonstrates the relationship between left ventricular end-diastolic dimension (LVEDD) and the HeartWare LVAD speed (HeartWare International Inc, Framingham, MA) and is notable for the general lack of change in LVEDD (shown on the y-axis) despite an increasing pump speed (shown on the x-axis), ranging from 2,200 to 3,200 rpm. The black line represents the LVEDD slope.
Of the 15 ramp studies analyzed, the mean patient age was 54 ⫾ 18 years, and approximately 50% of the patients had an ischemic etiology of heart failure (Supplementary Table 1, available on the jhltonline.org Web site). Ramp testing results (Table 1) generally encompassed the working range of speeds used with the HVAD (2,200–3,200 rpm). The mean LVEDD slope for all of the ramp studies (–0.0004 ⫾ 0.0003) was consistent with the raw data scatterplot and linear representation of a minimal decrease in LVEDD with increasing pump speed (Figure 1). In a sample of 15 consecutive retrospectively analyzed echocardiographic speed ramp studies performed clinically for HVAD optimization, we observed a minimal decrease in the LVEDD slope (–0.0004 ⫾ 0.0003) with increasing pump speed within the normal operating range of 2,200 to 3,200 rpm. Only15% of the patients had a decrease in LVEDD by more than 0.6 cm (while an equal proportion of patients had essentially no change in LVEDD) despite achieving a speed at which the aortic valve remained persistently closed. To put this into perspective, in a similarly protocoled ramp study involving an axial-flow LVAD cohort,2 the LVEDD slope was –0.29 ⫾ 0.11 for patients thought to have normal axial-flow parameters and was –0.08 ⫾ 0.04 for patients with confirmed pump thrombosis, a setting in which unloading of the LV is markedly diminished. In addition, the degree of mitral regurgitation remained largely unchanged regardless of HVAD speed. In effect, our findings appear to raise an exception to the existing literature regarding continuous-flow LVADs recommending the serial measurement of LVEDD as a surrogate marker for quantifying the degree of LV unloading.1–3 Although there are obvious limitations that should be considered when interpreting our study (see Supplementary
materials, available on the jhltonline.org Web site), the implications of our findings should not be understated: using LVEDD as a surrogate measure of LV unloading for HVAD patients may be a misguided practice.
Disclosure statement This study was supported by endowments to the Bluhm Cardiovascular Institute. Dr McGee reports a consultant preceptor agreement with HeartWare International Inc, Framingham, MA. None of the other authors has a financial relationship with a commercial entity that has an interest in the subject of the presented manuscript or other conflicts of interest to disclose.
Supplementary data Supplementary data are available in the online version of this article at jhltonline.org.
References 1. Feldman D, Pamboukian SV, Teuteberg JJ, et al. The 2013 International Society for Heart and Lung Transplantation guidelines for mechanical circulatory support: executive summary. J Heart Lung Transplant 2013;32:157-87. 2. Uriel N, Morrison KA, Garan AR, et al. Development of a novel echocardiography ramp test for speed optimization and diagnosis of device thrombosis in continuous-flow left ventricular assist devices: the Columbia ramp study. J Am Coll Cardiol 2012;60:1764-75. 3. Estep JD, Stainback RF, Little SH, Torre G, Zoghbi WA. The role of echocardiography and other imaging modalities in patients with left ventricular assist devices. JACC Cardiovasc Imaging 2010;3: 1049-64.
Optimizing the rotary left ventricular (LV) assist device (LVAD) speed remains an important pursuit of all clinicians caring for LVAD-supported patients. In an effort to attenuate the consequences of excessive ventricular unloading and non-pulsatile flow, recent guidelines have suggested the routine use of echocardiography in the nonintensive care unit post-operative period as one tool for measuring LV unloading to help select the appropriate LVAD speed.1 Furthermore, novel echocardiographic speed ramp algorithms involving patients with an axialflow rotary pump have been proposed to quantify the degree of LV unloading by measuring the slope of serial changes in LV end-diastolic dimension (LVEDD) at varying LVAD speeds.2 Thus, echocardiographic ramp study protocols, which are inherently center-specific and not yet standardized, have become variably adopted despite limited evidence for their appropriate use. Furthermore, LVEDD as a marker of LV unloading has not been well validated in patients with durable centrifugal-flow devices. Therefore, we reviewed speed ramp optimization studies performed at our center for patients with the recently approved centrifugal-flow HeartWare LVAD (HVAD; HeartWare International Inc, Framingham, MA) to describe conventional echocardiographic markers of ventricular unloading; specifically, LVEDD, frequency of aortic valve opening, and the degree of mitral regurgitation. We retrospectively analyzed all HVAD speed ramp optimizations performed for clinical purposes at the Bluhm Cardiovascular Institute of Northwestern Memorial Hospital from January 1, 2013, to August 1, 2013. We excluded from our analysis all ramp tests performed on patients with a surgically or percutaneously closed aortic valve or when performed to evaluate for suspected pump thrombus. The retrospective analysis of data involving our HVAD patients was approved by the Northwestern University Feinberg School of Medicine Institutional Review Board. Once all baseline echocardiographic data had been recorded, the speed was decreased every minute by 200 revolutions per minute (rpm) until the speed was settled at 2,200 to 2,400 rpm, which is the initial lower limit determined by the speed that allowed for aortic valve opening on every beat. At this point, the device was allowed to equilibrate at the new speed for 2 minutes. The following echocardiographic measurements were obtained: LVEDD, LV end-systolic dimension (LVESD),
449 frequency of aortic valve opening, degree of aortic regurgitation, degree of mitral regurgitation, estimated pulmonary arterial systolic pressure, estimated mitral inflow E wave velocity, and the position of the interventricular septum (method details are provided in the Supplementary materials, available on the jhltonline.org Web site). In addition, Doppler-measured mean arterial pressure, pump power (watts), and pump estimated flow (liters/min) were recorded for each speed. After the described parameters were measured, the pump speed was increased by an increment of 200 rpm and all measurements were repeated after 2 minutes of equilibration. The ramp protocol was continued until the speed at which point the aortic valve remained closed on every beat and the speed was 200 rpm higher than the speed at which the aortic valve was first noted to be persistently closed. Data were collected using Excel 2010 software (Microsoft Corp, Redmond, WA). Continuous variables are summarized as mean ⫾ standard deviation. The Student’s t-test for independent samples was used to determine differences in the normally distributed data. For each patient, the LVEDD (cm) was plotted against device speed (rpm). The slope for each line was generated by fitting a linear slope function. Finally, a scatterplot was generated to visually represent the raw data and avoid introducing any statistical confounding in representing the relationship between pump speed and LVEDD.
Table 1
Ramp Study Characteristics
Ramp study parameters Initial lowest speed MAP, mm Hg Final highest speed MAP, mm Hg Initial lowest speed power, W Final highest speed power, W Initial lowest speed estimated pump flow, liters/min Final highest speed estimated pump flow, liters/min Initial lowest speed LVESD, cm Final highest speed LVESD, cm LVESD slope Initial lowest speed LVEDD, cm Final highest speed LVEDD, cm LVEDD slope Highest speed for intermittent AV opening, rpm Lowest speed for persistent AV closure, rpm Initial lowest speed degree of MRa Final highest speed degree of MRa Initial lowest speed degree of ARa Final highest speed degree of ARa
All patients (N ¼ 15) (Mean ⫾ SD) 71 79 2.6 5.7 4.2
⫾ ⫾ ⫾ ⫾ ⫾
11 9 0.8 0.9 0.7
6.0 ⫾ 0.9 5.4 5.3 –0.0003 6.1 5.8 –0.0004 2,700
⫾ ⫾ ⫾ ⫾ ⫾ ⫾ ⫾
1.2 0.8 0.0003 0.8 0.7 0.0003 239
2,881 ⫾ 229 2.2 1.9 1.3 1.4
⫾ ⫾ ⫾ ⫾
1.3 1.0 0.6 0.6
AR, aortic regurgitation; AV, aortic valve; LVEDD, left ventricular end-diastolic dimension; LVESD, left ventricular end-systolic dimension; MAP, mean arterial pressure; MR, mitral regurgitation; rpm ¼ revolutions per min; SD, standard deviation. a See numerical grading in Supplementary materials, available on the jhltonline.org Web site, to correlate regurgitation degree.
450
The Journal of Heart and Lung Transplantation, Vol 33, No 4, April 2014
Figure 1 Scatterplot of raw data points demonstrates the relationship between left ventricular end-diastolic dimension (LVEDD) and the HeartWare LVAD speed (HeartWare International Inc, Framingham, MA) and is notable for the general lack of change in LVEDD (shown on the y-axis) despite an increasing pump speed (shown on the x-axis), ranging from 2,200 to 3,200 rpm. The black line represents the LVEDD slope.
Of the 15 ramp studies analyzed, the mean patient age was 54 ⫾ 18 years, and approximately 50% of the patients had an ischemic etiology of heart failure (Supplementary Table 1, available on the jhltonline.org Web site). Ramp testing results (Table 1) generally encompassed the working range of speeds used with the HVAD (2,200–3,200 rpm). The mean LVEDD slope for all of the ramp studies (–0.0004 ⫾ 0.0003) was consistent with the raw data scatterplot and linear representation of a minimal decrease in LVEDD with increasing pump speed (Figure 1). In a sample of 15 consecutive retrospectively analyzed echocardiographic speed ramp studies performed clinically for HVAD optimization, we observed a minimal decrease in the LVEDD slope (–0.0004 ⫾ 0.0003) with increasing pump speed within the normal operating range of 2,200 to 3,200 rpm. Only15% of the patients had a decrease in LVEDD by more than 0.6 cm (while an equal proportion of patients had essentially no change in LVEDD) despite achieving a speed at which the aortic valve remained persistently closed. To put this into perspective, in a similarly protocoled ramp study involving an axial-flow LVAD cohort,2 the LVEDD slope was –0.29 ⫾ 0.11 for patients thought to have normal axial-flow parameters and was –0.08 ⫾ 0.04 for patients with confirmed pump thrombosis, a setting in which unloading of the LV is markedly diminished. In addition, the degree of mitral regurgitation remained largely unchanged regardless of HVAD speed. In effect, our findings appear to raise an exception to the existing literature regarding continuous-flow LVADs recommending the serial measurement of LVEDD as a surrogate marker for quantifying the degree of LV unloading.1–3 Although there are obvious limitations that should be considered when interpreting our study (see Supplementary
materials, available on the jhltonline.org Web site), the implications of our findings should not be understated: using LVEDD as a surrogate measure of LV unloading for HVAD patients may be a misguided practice.
Disclosure statement This study was supported by endowments to the Bluhm Cardiovascular Institute. Dr McGee reports a consultant preceptor agreement with HeartWare International Inc, Framingham, MA. None of the other authors has a financial relationship with a commercial entity that has an interest in the subject of the presented manuscript or other conflicts of interest to disclose.
Supplementary data Supplementary data are available in the online version of this article at jhltonline.org.
References 1. Feldman D, Pamboukian SV, Teuteberg JJ, et al. The 2013 International Society for Heart and Lung Transplantation guidelines for mechanical circulatory support: executive summary. J Heart Lung Transplant 2013;32:157-87. 2. Uriel N, Morrison KA, Garan AR, et al. Development of a novel echocardiography ramp test for speed optimization and diagnosis of device thrombosis in continuous-flow left ventricular assist devices: the Columbia ramp study. J Am Coll Cardiol 2012;60:1764-75. 3. Estep JD, Stainback RF, Little SH, Torre G, Zoghbi WA. The role of echocardiography and other imaging modalities in patients with left ventricular assist devices. JACC Cardiovasc Imaging 2010;3: 1049-64.
