Effect of Heart Rate Reserve on Exercise Capacity in Patients Treated with a Continuous Left Ventricular Assist Device.

We hypothesized that an inadequate increase in heart rate (HR) during exercise was associated with low peak oxygen uptake (VO2 peak) seen in left ventricular assist device (LVAD) recipients and aimed to analyze the potential relation between HR and VO2 peak and use of drugs with negative chronotropic effect. Sixty-eight LVAD recipients (44 Heartmate 2 and 24 HeartWare Ventricular Assist Device) with support duration >1 month and a VO2 peak were included from two centers. Patients were 57 ± 13 years at time of VO2 peak and LVAD support duration was 483 ± 545 days. Peak oxygen uptake was 12 ± 4 ml/kg/min (40% ± 13% of predicted). Heart rate reserve (HRR = maximal HR - resting HR) was 59 ± 22 min (75% ± 15% of predicted for age, %HRR) and was significantly associated with VO2 peak (r = 0.244, p = 0.045). Predicted heart rate reserve was associated with %Predicted VO2 peak (P = 0.011). Chronotropic incompetence (CI) was observed in 44% and VO2 peak was clearly lower in patients with CI (10 ± 2.7 vs. 13 ± 4.6 ml/kg/min, p = 0.005). Beta-blockers (BB) were prescribed to 85% and adjusting for being on target BB-dose did not affect the correlation between %predicted VO2 peak and %HRR (r = 0.33, p = 0.024). In conclusion, almost half of LVAD recipients suffer from CI which is associated with lower VO2 peak. This relation did not seem to be affected by BB therapy.

Computed Tomography-Estimated Right Ventricular Function and Exercise Capacity in Patients with Continuous-Flow Left Ventricular Assist Devices.

Using four-dimensional (4D) cardiac computed tomography (CCT) scans at rest and immediately after exercise, we examined the right heart chamber sizes and systolic function and its association with exercise capacity in left ventricular assist device (LVAD) recipients. Fifteen patients with HeartMate (HM) II or 3 underwent echocardiography and maximal cardiopulmonary exercise test. Subsequently, contrast-enhanced CCT scans were performed at rest and immediately after two minutes of supine 25 Watt ergometer bike exercise. Patients were (60 ± 12 years of age) 377 ± 347 days postimplant. Peak oxygen uptake (pVO2) was 15 ± 5 ml/kg/min. LV ejection fraction measured by echocardiography was 15 ± 9%. Pump speed was 9500 ± 258 in HM II and 5518 ± 388 rpm in HM 3 recipients. Resting right atrial ejection fraction (RAEF) was 18 ± 9%, and right ventricular ejection fraction (RVEF) was 36 ± 8%. During stress, RAEF was 19 ± 10%, and RVEF was 37 ± 8%. RAEF and RVEF did not correlate significantly with pVO2 at rest or during stress. Resting-RAEF and stress RAEF correlated significantly: r = 0.87, p < 0.01 as did resting RVEF and stress RVEF: r = 0.76, p < 0.01. In conclusion, resting-EF predicted stress-EF for both RA and RV in patients with an LVAD. Neither RVEF nor RAEF correlated with pVO2.

Ramp Study Hemodynamics, Functional Capacity, and Outcome in Heart Failure Patients with Continuous-Flow Left Ventricular Assist Devices.

Ramp studies-measuring changes in cardiac parameters as a function of serial pump speed changes (revolutions per minute [rpm])-are increasingly used to evaluate function and malfunction of continuous-flow left ventricular assist devices (CF-LVADs). We hypothesized that ramp studies can predict functional capacity, quality of life (QOL), and survival in CF-LVAD patients. Hemodynamic changes per Δrpm were measured at a minimum of CF-LVAD support, at baseline pump speed, and at maximal tolerable pump speed. Subsequently functional capacity and QOL were assessed. Eighty ramp tests were performed in 44 patients (HeartMate II, Thoratec Corporation, Pleasanton, CA). Functional status was evaluated in 70% (31/44); average 6 minute walk test (6MWT) was 312 ± 220 min, New York Heart Association (NYHA) I-II/III-IV (70/30%) and activity scores very low-low/moderate-very high (55/45%). Decrease in pulmonary capillary wedge pressure per Δrpm was related to better NYHA classification; NYHA I-II vs. III-IV, -0.29 ± 0.15 vs. -0.09 ± 0.16 mm Hg/rpm * 10 (p = 0.007) as well as to activity score; very low-low vs. moderate-very high, -0.16 ± 0.16 vs. -0.31 ± 0.16 mm Hg/rpm * 10 (p = 0.02). Cardiac output change per Δrpm was correlated to measures of QOL. Ramp tests did not predict survival. In conclusion, hemodynamic changes during ramp studies are associated with measures of functional capacity and QOL. Hence, such tests could potentially identify patients in risk of failure to thrive during CF-LVAD support.

Relation between pressure and volume unloading during ramp testing in patients supported with a continuous-flow left ventricular assist device.

Pulmonary capillary wedge pressure (PCWP) is the key to describing left ventricular (LV) unloading; however, the relation between pressure and the echocardiography-derived surrogate of LV volume (LV end-diastolic diameter [LVEDD]) as a function of pump speed (revolutions per minute [RPM]) in continuous-flow LV assist device (CF-LVAD) patients is unknown. In this study, the pressure-volume relation as a function of RPM during ramp testing was investigated by simultaneously measuring PCWP by Swan-Ganz catheter and LVEDD by echocardiography. The ramp protocol started at usual pump setting (ramp-base) and then went from 8,000 RPM (ramp-low) increasing by 400 RPM/5 minutes until reaching 12,000 RPM or suction/arrhythmic event (ramp-high). The study was finalized by a 25 Watt exercise test at two ramp steps. Ten patients with ramp-base of 9,300 ± 241 RPM (at which 3 of 10 had aortic valve opening) were examined. At ramp-low, ramp-base, and ramp-high, PCWP was 20 ± 4, 14 ± 4, and 7 ± 3 mm Hg (p < 0.001 for all comparisons) and LVEDD 6.6 ± 1.0, 6.7 ± 0.9, and 5.5 ± 1.7 cm (p < 0.05 for all comparisons but ramp-low versus ramp-base). Correlation between PCWP and LVEDD slopes; R = 0.53 (p = 0.02). In conclusion, PCWP as a function of RPM is weakly correlated with changes in LVEDD. Thus, LVEDD is not an accurate measure of unloading in CF-LVAD patients.