Changes in Total Cardiac Output and Oxygen Extraction During Exercise in Patients Supported With an HVAD Left Ventricular Assist Device.

Following implantation of a left ventricular assist device (LVAD), acceptable functional performance is now being achieved; however, peak VO2 and peak work load (watts) remain considerably limited. Maximum physical capacity is essentially dependent on generated cardiac output (CO) and arteriovenous oxygen difference (avDO2 ). We investigated the changes in CO and avDO2 during exercise in LVAD patients with an HVAD pump (HeartWare Inc., Framingham, MA, USA). Approximately 6 weeks after implantation, 20 patients (100% male, 60.8 ± 7.3 years old, BMI 25.7 ± 3.3) underwent a six-minute walk test (6MWT), a cardiopulmonary exercise test (CPET), and noninvasive hemodynamic measurement. The mean six-minute walking distance (6MWD) was 403 m (68% of predicted), and mean peak VO2 was 10.9 mL/kg/min (39% of predicted). Mean total CO improved from 3.8 L at rest to 7.0 L at maximum exercise. The mean avDO2 increased from 7.4 mL/dL (44% of oxygen content) at rest to 13.2 mL/dL (75% of oxygen content) at maximum exercise. There was a significant increase in both total CO (P < 0.01) and avDO2 (P < 0.05) between rest and sub-maximum exercise. As exercise levels increased, however, no further significant changes were achieved. Long-term studies, especially in combination with exercise programs, would be desirable in order to observe the development of these parameters.

Inert gas rebreathing - helpful tool in the management of left ventricular assist device patients.

In patients with left ventricular assist devices (LVAD), exercise capacity is a decisive factor regarding the quality of life. When evaluating exercise capacity, precise information about the total cardiac output generated is crucial. To date, complex measurements using a right-heart catheter were necessary in order to determine total cardiac output. The inert gas rebreathing method facilitates non-invasive, direct and valid measurement of total cardiac output as well as associated parameters, like the difference in arteriovenous oxygen saturation, both at rest and during exercise. It is the aim of this paper to focus on this conclusive method which is, despite its simplicity and low-risk reproducibility, rarely used within the framework of LVAD patient treatment at the present time. The test protocol used at our hospital is presented to facilitate the implementation of this helpful tool in other interested institutions.

Development of exercise-related values in heart failure patients supported with a left ventricular assist device.

Following implantation of a left ventricular assist device, the build-up and long-term maintenance of adequate exercise capacity and functional performance become crucial. The aim of this study was to observe the development of exercise-related values at different times, as well as to detect possible influencing factors. We performed a prospective single-centre study: 10 patients (63 years, 100% male, body mass index = 27.5, 100% HeartWare) underwent the following diagnostic tests during cardiac rehabilitation and during two subsequent ambulatory visits: 6-min walking test, handgrip strength test, cardiopulmonary exercise test and Minnesota Living with Heart Failure questionnaire. Mean follow-up was 482 days after left ventricular assist device implantation. Significant improvements could be observed between the end of cardiac rehabilitation and ambulatory visit 1; 6-min walking distance increased from 367 to 449 m (p < 0.01), peak VO2 from 10.0 to 11.9 mL/kg/min (p < 0.05) and peak load from 62.4 to 83.0 W (p < 0.01). However, there were no further improvements between ambulatory visit 1 and ambulatory visit 2. In the long term, a significant mean weight gain of more than 10 kg could be observed (p < 0.01). A negative linear correlation between weight gain and absolute improvement in peak load (r = -0.77, p < 0.01) and peak VO2 (r = -0.75, p < 0.05) could be demonstrated. In conclusion, exercise-related values following left ventricular assist device implantation initially improve significantly. Later, however, no further improvements can be observed. In the long term, pronounced weight gain is conspicuous, concomitant with a significantly lower increase in exercise values of the patients. In the future, both dietary and structured physical activity follow-up interventions should be integrated in patient routines.