Despite other quality of life improvements, heart patients supported by left ventricular assist devices (LVADs) face “severely impaired” exercise capacity, according to a study published online in JACC: Heart Failure.
Since they were first introduced in the 60s, LVADs have afforded advanced heart failure patients more time to live, Noah Moss, MD, of the Icahn School of Medicine at Mount Sinai, and colleagues wrote in the journal—and it’s better-quality time. Still, studies continue to report lower-than-normal peak oxygen consumption (VO2) during exercise for LVAD-supported patients, suggesting impaired functional capacity.
Current-generation LVADs use continuous flow technology with axial and centrifugal flow mechanics with either partial or fully magnetically levitated rotors, the authors explained, but none have the ability to modify rotational speed based on workload. Right now, the output of an LVAD is dependent on the pressure difference between a patient’s mean arterial pressure and left-ventricular end-diastolic pressure or the difference between their mean arterial pressure and pulmonary capillary wedge.
“During normal exercise, there is an increase in preload and a variable change in afterload,” Moss et al. wrote. “In patients on LVAD support, these changes may not occur to the same extent. How hemodynamic parameters change in response to exercise and then correlate with VO2 is poorly understood.”
The team studied 45 LVAD-supported patients who were referred for post-VAD hemodynamic optimization between December 2017 and June 2019. Patients were fitted with Swan Ganz catheters before undergoing upright incremental bicycle ergometry and respiratory gas analysis, and every 3 minutes during exercise Moss and colleagues recorded hemodynamic measurements, mixed venous saturation and arterial blood pressure.
Twelve of the authors’ patients were supported by axial flow pumps, while the remaining 33 had been implanted with centrifugal flow pumps. At baseline, most participants were around age 60, and peak VO2 averaged 10.6 ml/kg/min.
Moss and co-authors reported that, after performing linear correlations between peak VO2 and a host of measures of peak exercise performance, the Fick measure of cardiac output (CO) was the most accurate. Fick CO showed the greatest correlation with peak VO2 (r=0.73), followed by intrinsic CO (r=0.67).
The multivariate model that best predicted peak VO2 included the difference between Fick CO and peak arterial venous oxygen. The authors said Fick CO seems to be augmented “primarily by the patient’s own native cardiac capacity.”
“Attention to correction of anemia and conditioning status could potentially improve aerobic function of these patients,” they wrote. “Whether biomechanical enhancements with activity, volume and pressure sensors embedded in the LVAD can enable the device to respond to increased workload of exercise and to improve functional capacity in LVAD-supported patients remains to be investigated.”