Limiting factors of peak and submaximal exercise capacity in LVAD patients

Abstract

Aims Although patients supported with a Continuous-Flow Left Ventricular Assist Device (CF-LVAD) are hemodynamically stable, their exercise capacity is limited. Hence, the aim of this work was to investigate the underlying factors that lead to peak and submaximal exercise intolerance of CF-LVAD supported patients. Methods Seven months after CF-LVAD implantation, eighty three patients performed a maximal cardiopulmonary exercise test and a six minute walk test. Peak oxygen uptake and the distance walked were measured and expressed as a percentage of the predicted value (%VO2p and %6MWD, respectively). Preoperative conditions, echocardiography, laboratory results and pharmacological therapy data were collected and a correlation analysis against %VO2p and %6MWD was performed. Results CF-LVAD patients showed a relatively higher submaximal exercise capacity (%6MWD = 64 ±16%) compared to their peak exertion (%VO2p = 51±14%). The variables that correlated with %VO2p were CF-LVAD parameters, chronotropic response, opening of the aortic valve at rest, tricuspid insufficiency, NT-proBNP and the presence of a cardiac implantable electronic device. On the other hand, the variables that correlated with %6MWD were diabetes, creatinine, urea, ventilation efficiency and CF-LVAD pulsatility index. Additionally, both % 6MWD and %VO2p were influenced by the CF-LVAD implantation timing, calculated from the occurrence of the cardiac disease. Conclusion Overall, both %6MWD and %VO2p depend on the duration of heart failure prior to CF-LVAD implantation. %6MWD is primarily determined by parameters underlying the patient's general condition, while %VO2p mostly relies on the residual function and chronotropic

Exercise physiology in left ventricular assist device patients: insights from hemodynamic simulations

“…Furthermore, as opposed to stable HF patients where pVO 2 s are clinically interpreted based on beta blockers, in LVAD patients treatment with beta blockers showed no clear trend of influencing pVO 2 s, nor did atrial fibrillation, noradrenaline levels or HF etiology (18,32,33,35). Contradictory results compared to the aforementioned studies were in regards to device type, chronotropic incompetence as well as determinants of right heart function (18,31,32,34,35).…”

“…Predicted values, calculated by percentage to averages of gender and age-matched healthy controls, showed higher values for submaximal than maximal exercise capacity (18,29,36). This might imply that the stress generated by submaximal exercise, where regulatory mechanisms are not involved to their maximum, might be better tolerated for LVAD patients.…”

“…Higher age and weight, deconditioning and HF with reduced ejection fraction are associated with lower pVO 2 , to name a few of the general impairments involved (17). Confounding factors for pVO 2 are possibly implied in "LVAD implantation timing" or "HF time course" (18). Despite the success of normalizing hemodynamics at rest and improvements in survival after LVAD implantation, patients' pVO 2 remain severely impaired at approximately 50% compared to age and gender matched controls (19).…”

“…In general, the following parameters have been reported to show associations with pVO 2 : age, total CO, flow through the aortic valve, peak arterial venous oxygen difference, chronotropic incompetence (HR reserve), hemoglobin levels, PCWP, NT-pro BNP, valve pathology or status, absolute LVAD parameters and timing of LVAD implant (18,(31)(32)(33)(34). Furthermore, as opposed to stable HF patients where pVO 2 s are clinically interpreted based on beta blockers, in LVAD patients treatment with beta blockers showed no clear trend of influencing pVO 2 s, nor did atrial fibrillation, noradrenaline levels or HF etiology (18,32,33,35). Contradictory results compared to the aforementioned studies were in regards to device type, chronotropic incompetence as well as determinants of right heart function (18,31,32,34,35).…”

The left ventricular assist device as a patient monitoring system

“…Heart rate recovery, in particular, has been shown to be a predictor of clinical outcome and mortality (50,51). While exercise capacity of LVAD patients has been extensively investigated (52)(53)(54) less is known about daily patient activity and how this could be utilized to better understand the impact of AE on patient well-being or even to anticipate/predict them. In Figure 7, two exemplary cases show the amount of steps/day from patients over the course of about one year after LVAD implantation.…”