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
Can echocardiography be used to help optimize speed or detect thrombosis in patients supported with continuous flow left ventricular assist devices (LVADs)?
This was a single-center study of patients supported with HeartMate II LVADs who underwent echocardiography with a standardized ramp protocol. Ramp protocols were used for speed optimization (for goal LViDd, aortic valve opening, and mitral regurgitation), or to assess the presence or absence of device thrombosis (suspected based on elevated LDH, power elevation, or heart failure symptoms). The ramp study started at 8000 rpm with measurement of LV end-diastolic dimension (LViDd), mitral regurgitation severity, and frequency of aortic valve opening. LVAD speed was then increased in 400 rpm increments with repeat echocardiography measurement in 2-minute intervals until a peak speed of 12,000 rpm was reached or there was evidence of suction. LVAD speed was plotted againt LVAD pulsatility index, power, and LViDd measured on echo and slopes were measured.
Thirty-nine patients underwent 52 ramp studies. Of these studies, 28 were performed in 22 patients for speed optimization (54% of studies) and 24 (46% of studies) were done in 17 patients to assess for LVAD thrombosis. In the speed optimization group, 17 (61%) tests resulted in device speed changes of a mean absolute value of 424 ± 211 rpm. In those with suspected device thrombosis, 10 had minimal reduction in LViDd on ramp study. Of these 10 patients, 9 underwent LVAD exchange due to concerns for thrombosis, and 8 of these patients had confirmed clot on device analysis after explant. Patients with a confirmed device thrombosis had a lower mean LViDd slope (-0.08 ± 0.11) than those without confirmed clot (-0.29 ± 0.11, p < 0.001), suggesting less rate of reduction in LV dimensions with increase in LVAD speed. A slope of >-0.16 was considered “diagnostic” of flow obstruction.
The authors concluded that echo ramp testing can be used for LVAD speed optimization and for detection of device malfunction.
The LVAD community certainly benefits from studies aimed at detecting device complications and improving device performance. At this time, however, no standard definition for ‘device optimization’ exists in the field of mechanical circulatory support (MCS), and data on morbidity or mortality are lacking to support intermittent aortic valve opening or speed adjustments used herein to guide LVAD speed adjustment. Likewise, there really is no standard definition for device thrombosis, aside from INTERMACS definitions of serum hemoglobin and definitive diagnosis in the form of pathology and device review at the time of LVAD explant. Diagnosis reliant on device confirmation of clot is fraught with bias, and many argue serum-free hemoglobin and/or LDH are insensitive or nonspecific. These issues aside, this analysis is a good foundation for using echocardiography to understand LVAD function and LVAD complications. Independent assessment, inter- and intra-observer variability of the above measurements, and positive and negative predictive values of the ‘optimal slope’ need to be examined in further study. Importantly, we need to know what defines optimal device function.
Clinical Topics: Cardiac Surgery, Heart Failure and Cardiomyopathies, Noninvasive Imaging, Cardiac Surgery and Heart Failure, Acute Heart Failure, Mechanical Circulatory Support, Echocardiography/Ultrasound
Keywords: Thrombosis, Heart-Assist Devices, Heart Failure, Echocardiography
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