Editorials
A Classical But Useful Predictor of Future Left Ventricular Assist Device Explantation
– Possible Significant Role of Cardiopulmonary Exercise Testing –
2015 年 79 巻 3 号 p. 505-507
詳細
2015 年 79 巻 3 号 p. 505-507
Left ventricular assist devices (LVADs) are increasingly being implanted in stage D heart failure patients. Recent innovations in device technology and improvements in peri- and postoperative management have been changing the long-term survival of patients with LVADs for the better. Although their principal use to date has been as a bridge-to-heart transplant (BTT), longer survival expectancy and better quality of life with LVAD support are making possible other clinical uses, such as destination therapy (DT).
Article p 560
There are increasing reports of cardiac functional recovery after maximum optimal medical therapy under mechanical circulatory support and finally, LVAD explantation in some patients.1–3 This LVAD treatment strategy as a bridge to recovery (BTR) may be very important in the current era of donor shortage. We might be able to change the current concept of LVADs as the final therapeutic strategy before heart transplantation, to that of a powerful temporary device enabling medical therapy for severe heart failure before LVAD removal. The strategy of BTR may be a paradigm shift in the treatment of severe heart failure. However, in some cases, the extent of improvement of native cardiac function may be insufficient4 and the decision to explant becomes challenging, considering the risks of long-term LVAD support and the benefits of device removal. There are some reports concerning the predictors of cardiac functional recovery, but there is not any definitive evidence. If the precise predictors for future removal of LVAD are elucidated, optimal candidate selection for LVAD explantation becomes possible.
In Japan, because of the severe shortage of cardiac donors, many patients with LVADs have a protracted wait for a heart transplant. However, there are some strict limitations to the indication for an implantable continuous flow (I-CF) LVAD. Consequently, there is still a proportion of patients with extracorporeal pulsatile flow (E-PF) LVADs. In these patients, considering the possible major complications with long-term E-PF LVAD support, we need to make the challenging decision of whether to try weaning off the E-PF LVAD or conversion to I-CF LVAD as a bridge to bridge (BTB).
To assess the possibility of explantation, the LVAD off/weaning test seems to be the most reliable method to date.1,2 Although there are some small differences in the explantation criteria, patients are considered for LVAD explantation if they demonstrate the following after the LVAD is switched off for 15 min: left ventricular end-diastolic diameter (LVDd) <55–60 mm; left ventricular ejection fraction (LVEF) >45%; pulmonary capillary wedge pressure (PCWP) <12–13 mmHg; and resting cardiac index >2.6–2.8 L·min–1·kg–1. There is another report suggesting the efficiency of dobutamine stress echocardiography during a LVAD weaning test,5 and another of the significance of hemodynamic change after volume loading during the LVAD off test.6
However, during this test, there are some possible serious adverse events such as hemodynamic deterioration and thrombosis. So not all patients with LVADs, only carefully selected candidates, are eligible for this test. In this regard, there is an increasing need for another method of selecting suitable candidates for the LVAD off test.
In this issue of the Journal, Imamura et al7 use cardiopulmonary exercise (CPX) testing to predict explantation of LVADs. They propose a new “explantation score” to predict future explantation using 3 simple parameters derived from symptom-limited CPX testing at 3 months after E-PF LVAD implantation. In their study, 8 of 33 enrolled patients achieved LVAD explantation following LVAD off test accompanied by volume loading6 within 2 years. Their explantation score, which includes higher maximum load, lower V̇E/V̇CO2 slope, and higher PV̇O2, was associated with success following explantation of the LVAD.
Although LVAD explantation is mainly affected by the physician’s decision based on the results of the LVAD off test, this result is very suggestive from the point of view that the parameters of exercise capacity derived from CPX testing under LVAD support performed in a relatively early phase after surgery may predict the future candidacy for the LVAD off test, and LVAD explantation. This suggests that exercise capacity with continued LVAD support is a promising tool for selection of patients for future explantation. In their report, neither echocardiographic parameters nor neurohumoral factors revealed sufficient recovery at the first CPX testing, and even during the LVAD off test, LVDd or LVEF did not satisfy the explantation criteria proposed previously.1,2 Furthermore, exercise capacity in the early phase may be critically important when considering the possible need for conversion to I-CF LVAD before complications such as exit site infection and thromboembolic episodes emerge. Otherwise, considering the risk of re-surgery, it may be acceptable to choose a BTR strategy and continue to manage with maximum medical therapy under E-PF LVAD support.
Determinants of the exercise capacity of chronic heart failure patients are mainly noncardiac, such as peripheral skeletal muscle or respiratory muscle strength, regulation of endothelium-mediated blood flow of skeletal muscle, mitochondrial metabolism, and so on;8–10 low cardiac output plays only a partial role in exercise intolerance.11 The situation seems to be the same for patients with LVADs, especially in the early phase after implantation. Imamura et al7 report greater improvement in exercise capacity after 3 months of the LVAD surgery in the 8 patients who would achieve LVAD explantation compared with the remaining patients. In several reports on the effect of exercise training on exercise capacity in patients with LVADs, it was suggested that training primarily enhances submaximal exercise tolerance rather than PV̇O2.8,9 This effect may be related to the fact that maximum cardiac output and flow generated by a LVAD are limited and probably insufficient to meet the metabolic demands of higher workloads. The mechanism of this difference remains unclear, but the native cardiac functional reserve in those 8 patients may have improved more than in the others after LV unloading with a LVAD and optimal medical therapy.
Interestingly, PV̇O2 ≥12.8 ml·kg–1·min–1 and V̇E/V̇CO2 slope ≤34 as cutoff values for predicting future LVAD explantation are comparable with their well-known predictive value of prognosis in chronic heart failure patients.10–13 In fact, the 8 patients who underwent LVAD explantation continued to show improvement in their exercise capacity until the LVAD off test. There have been no studies demonstrating a convincing cutoff level of CPX parameters to predict LVAD explantation, and further studies are needed.
There are still some issues to be solved concerning the prognostic value of exercise capacity in LVAD patients. (1) If exercise capacity has a significant correlation with the prognosis of LVAD patients, does exercise training improve the exercise capacity and prognosis of LVAD patients? (2) Are there any differences in the effect of exercise capacity among the different type of LVAD? (3) How can we know the ideal setting of LVAD to obtain better exercise capacity? (4) How can we define the optimal exercise prescription for LVAD patient? (5) Is the acquired exercise capacity maintained after LVAD explantation?
If the current era of long-term LVAD support is durable and inevitable, further investigations are needed to improve the treatment strategy of LVAD patients. CPX testing may have a potent and significant role in evaluating native cardiac function reserve and predicting prognosis, and could be useful in selecting the treatment strategy from BTT, BTB, BTR or DT (Figure).
Proposed algorithm for choosing the treatment strategy with a left ventricular assist device (LVAD).7 ACEI, angiotensin-converting enzyme inhibitor; ARB, angiotensin-receptor blocker; CI, cardiac index; LVEF, left ventricular ejection fraction; mRAP, mean right atrial pressure; PCWP, pulmonary capillary wedge pressure.
