Echocardiography is a valuable tool for assessing left ventricular assist devices (LVADs), both prior to implantation to screen for potential complications and after the procedure to manage patient outcomes. As practice evolves, understanding which echo measurements are most useful is growing, as is the role of echo in optimizing LVAD pump settings long-term.
LVADs have changed the outlook for patients with advanced heart failure. The devices have been shown to improve survival over medical therapy and offer recipients a chance at a normal, active life. Earlier this year, the University of Michigan Health System in Ann Arbor celebrated the life of Joe Ann Bivins, 68, who represented an example of what LVADs offer. She received her LVAD in 2005, and lived longer on a single device than any other U.S. patient before passing away in January, according to the university. “It’s certainly something special to be given a second chance,” Bivins was quoted as saying, “and it’s even more of a blessing to know that my story can give others with heart failure the same hope.”
LVADs achieve these results by unloading the LV in patients with severe congestive heart failure secondary to LV systolic dysfunction. Sometimes used as a bridge to a heart transplant, the devices also are growing in use as the destination therapy for those who are not candidates for transplantation.
Screening for problems
Before implanting an LVAD, physicians must identify risk factors for adverse outcomes to predict patient response and make any necessary practice modifications, with transthoracic echocardiography used as the go-to noninvasive modality for assessing cardiac structure and function in the context of LVAD implantation.
Preoperative echo adds “off-axis” imaging to the standard transthoracic echocardiography study to focus on the LVAD graft sites. Prior to implanting the LVAD, aortic root aneurysms and LV apical aneurysms must be addressed.
Echo also is used preoperatively to screen for potential right ventricular (RV) failure following implantation, according to Jerry D. Estep, MD, of the Methodist DeBakey Heart and Vascular Center in Houston. Estep says his institution combines clinical models in addition to echo surrogates of RV failure to assess risk. “Echo is robust and there’s no one echo parameter that equates to a higher preoperative risk of RV failure, but it’s a combination of parameters, left and right.”
Specifically, Estep and colleagues have found that measuring RV-to-LV size ratio is useful, as concern for RV failure grows when this ratio is greater than 0.75 and gets worse closer to a 1:1 ratio. It’s also important to have an understanding of a patient’s aortic insufficiency severity and to screen out patients with intracardiac shunts and interatrial septal defects, adds Estep.
Researchers from the Mayo Clinic in Rochester, Minn., who studied echocardiographic predictors of adverse outcomes in the context of LVAD implantation, confirmed that a relatively small LV (less than 63 mm) and early systolic equalization of RV and right atrial pressure were associated with increased 30-day morbidity and mortality (J Am Coll Cardiol Img 2011;4:211–222).
Postoperative echo is focused on identifying any significant deviation from normal cardiac function since the LV is being continuously unloaded by LVAD pump flow. Following the operation, however, a number of challenges present themselves when trying to use echo to evaluate LVADs, says Ravi Rasalingam, MD, of Washington University School of Medicine in St. Louis. Patients will have significant bandaging and tubing, and will be in a post-inflammatory state in the intensive care unit (ICU). Since air is the enemy of ultrasound, patients must be positioned so the ultrasound beam can interact with cardiac tissue without being obscured by the lungs. Even though utilizing echo is more cumbersome in the ICU, Rasalingam says it can still be used immediately after the operation to see if the LVAD is unloading the heart effectively and whether the patient has developed a hematoma around the heart.
After leaving the ICU, it becomes easier to obtain flow measurements. Doppler echo is utilized to measure blood flow as it exits the heart into the LVAD and remeasured as it exits the device through the outflow graft. “We can tell [physicians] if the velocities are in the expected range, or—if the velocities are very high, for example—we may be worried about some type of obstruction, such as could be caused by a blood clot or something like that,” says Rasalingam.
3D echocardiography has been shown to be highly accurate in assessing RV size and function, though no studies have been performed to show it offers significantly more useful information in the context of LVAD implantation compared with standard transthoracic echo. Estep adds that since CT with contrast offers better visualization of the inflow and outflow cannulas, it can be useful as an additional modality in patients with inflow cannula malposition or suspected kinking in the outflow cannula.
Estep is working with colleagues to write a consensus document for the American Society of Echocardiography, to be published later this year, which will contain a checklist of items to screen for prior to LVAD implantation and outline the role of echo postoperatively. A hot topic is tailoring pump speed to the aortic valve opening, or pulsatility, to minimize aortic valve fusion and aortic insufficiency on the back end of the implantation process.
Traditionally, the optimization of pump settings has not been very scientific, notes Rasalingam, with the process being mostly trial and error based on clinical evaluation of the patient’s response at various settings. Echo is improving this process, starting in the operating room. Once the LVAD is switched on, transesophageal echocardiography can detect whether the septum is being dragged over to the LV—a sign the pump settings are too high—or if the LV is not being unloaded properly.
What’s needed now is a growing understanding of how echo can be used to regulate pump settings long after patients leave the operating room or ICU, as inotropic medications administered in the hospital will affect the patient’s physiology differently from discharge medications, explains Rasalingam. A ramp study—in which an LVAD’s pump speed is systematically increased over a certain range—can be conducted to optimize echocardiographic measurements. With that data, physicians can determine a recommended outpatient pump speed. This setting can be reviewed later in the clinic with subsequent echocardiograms, offering a more tailored, patient-centered approach.
“Echocardiography, a very readily available tool, without any radiation can image the heart real-time and is important in providing information about how the VAD interacts with the heart. Studies are ongoing as to which paramenters are most critical for monitoring these patients as they go on to lead longer, more active lives,” says Rasalingam.
Think of the Children
Based on success in adults, left ventricular assist devices (LVADs) increasingly are being utilized in pediatric patients, though this population is more complicated because of a wider range in patient sizes, the presence of congenital heart disease and a more frequent need for biventricular assist devices, used when both ventricles are unable to function.
Ritu Sachdeva, MD, of Arkansas Children’s Hospital and University of Arkansas for Medical Sciences in Little Rock, and colleagues looked at the role of echo in managing children supported by VADs in a study of 32 patients, and found it could successfully screen for complications such as:
- Device malfunction
- Intracardiac thrombi
- Pericardial effusions
Source: (J Am Soc Echocardiogr 2013;26:41-49.)