Ann Thorac Surg 2004;77:1808-1810
© 2004 The Society of Thoracic Surgeons
Case report
Monitoring weaning from BIVAD thoratec with peak oxygen consumption
Pascal H. Colson, MDa*,
Frederique Ryckwaert, MDa,
Max Saussine, MDa,
Marc Ferrière, MDb,
Bernard Albat, MDc
a Department of Anesthesiology and Intensive Care, Hôpital Arnaud de Villeneuve, CHU Montpellier, Montpellier, France
b Department of Cardiology, Hôpital Arnaud de Villeneuve, CHU Montpellier, Montpellier, France
c Department of Cardiothoracic and Vascular Surgery, Hôpital Arnaud de Villeneuve, CHU Montpellier, Montpellier, France
Accepted for publication June 6, 2003.
* Address reprint requests to Dr Colson, Départment D'Anesthésie-Réanimation D, Hôpital Arnaud de Villeneuve, 291 Avenue du Doyen Giraud, 34295 Montpellier Cedex 5, France
e-mail: p-colson{at}chu-montpellier.fr
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Abstract
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A biventricular assistance device has been implanted in a young woman for a peripartum cardiac failure. An intended weaning consisted of gradual reloading and exercise training monitored with peak oxygen consumption (VO2) and radionuclide-left ventricle ejection fraction. Progressive increase in peak VO2 during partial assistance occurred more than 2 months, from 10.3 to 19 mL · kg–1 · min–1. Successful explantation was realized when peak VO2 exceeded 15 mL · kg–1 · min–1 and radionuclide-left ventricle ejection fraction was more than 40% during off-pump testing.
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Introduction
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The use of mechanical assist device has become an accepted means to support refractory heart failure. Improvement of indices of cardiac metabolism and function has been observed in some patients allowing weaning from mechanical support rather than transplantation [1, 2]. We report a case of successful weaning from a biventricular assistance device (BIVAD) implanted for a peripartum cardiac failure monitored with peak oxygen consumption.
A 28-year-old African woman, gravida III, para III, presented with complaints of fatigue and hepatitis symptoms 2 months after her last delivery. The patient was thought to have hepatitis; her symptoms were severe enough to warrant admission for observation in a medical unit. Two days after admission, the patient began to complain of weakness and shortness of breath and was transferred to the cardiology unit in an unstable condition.
Transthoracic echocardiography showed depressed global cardiac function with dilation of both ventricles (estimated left ventricular ejection fraction [LVEF], 10%). She was unresponsive, hypotensive, tachycardic, and oliguric, and her condition did not improve with the administration of dobutamine.
It was thought that the only chance the patient had for survival was immediate total cardiac support as could be provided by a mechanical assistance, possibly as a bridge to transplantation. A BIVAD (Thoratec, Pleasanton, CA) was implanted (with a right atrial and pulmonary artery cannulas for right ventricular assist device [VAD] and a left ventricle and aorta cannulas for left VAD). The patient awoke gradually over the next 24 hours and was extubated on the second postimplantation day (PID). Two episodes of bleeding occurred on the fifth and sixth PID that required reoperation. Clinical status then improved with renal function normalized within 3 weeks; bilirubin levels returned to normal within 1 month.
The possibility of weaning from assistance had been tested fortnightly. Reduced assistance using brief episodes of the asynchronous mode set at 50% of the automatic values was evaluated under general anesthesia and transesophageal echocardiography. Our first evaluations showed an inefficient left ventricle with dilatation while the right ventricle was doing well. However, left ventricle contractility improved by the 45th PID.
An exercise training program and progressive ventricle reloading were then scheduled while heart failure treatment was carefully titrated to a maximal dose (converting enzyme inhibitor, ß-blocker, and Aldactone). The exercise was performed on a cycle ergometer. The patient was asked to do a 20-minute exercise and keep her heart rate below the 75% theoretical maximum heart rate. She was able to do a 50-W exercise twice daily after 2 months' training. Progressive reloading consisted of gradually decreasing the assistance using asynchronous mode and manipulation of the rate and percent of systole. The left VAD rate was progressively reduced to 50 bpm; then a high rate was preferred because this mode allows to decrease flow of the device by reducing filling of the external ventricle but avoiding blood stagnation. Device support was reduced up to a rate of 140 bpm and 70% of systole within 2 months. Asynchronous mode was set for both VADs; right VAD was set at 10% to 20% less than left VAD. Transesophageal echocardiography was used repeatedly to confirm opening of the native aortic valve and a lack of ventricular enlargement.
Monitoring was ensured by peak oxygen consumption (VO2) (Brainware Metasys TR version W98) and radionuclide-LVEF. Five VO2 tests had been performed under various assistance modes (full, partial, or no assistance) (Table 1).
Radionuclide-LVEF was 35% and 44% during off-pump periods on PID 140 and PID 170, respectively.
Removal of the BIVAD was performed on PID 182 and was uneventful. Long-term follow-up has confirmed successful weaning: radionuclide-LVEF was 48% 2 weeks after explantation, VO2 was 21.5 mL · kg–1 · min–1 6 months later.
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Comment
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Peripartum cardiomyopathy is a disorder of unknown etiology occurring between the last trimester of pregnancy up to the first 6 months postpartum. A high mortality rate has been reported, and overall outcome remains poor despite treatment with an angiotensin-converting enzyme inhibitor and ß-blockers; the main predictor of poor outcome is low LVEF [3]. The patient in this case presented with severe symptoms and very low LVEF, in the context of postpartum without any evidence of other causes of acute myocardiopathy. Mechanical assistance was mandatory and provided us the opportunity to introduce an angiotensin-converting enzyme inhibitor and ß-blockers. Left ventricular assistance explantation has been performed in some cases of peripartum myocardiopathy when dictated by intercurrent infection [4]. In this case we used biventricular assistance with intended weaning and training protocols.
In case of assistance weaning, monitoring myocardial recovery is critical [1, 2]. Cardiac function can be assessed by echocardiography using left ventricle dimensions and ejection fraction. An assist device can be explanted when the internal diastolic diameter of the left ventricle is less than 55 mm and LVEF is more than 40% to 45% while off-pump [1]. Radionuclide ventriculography is a more sensitive method than echocardiography to measure LVEF and should be preferred when available. Besides cardiac systolic function, an evaluation of cardiovascular reserve has been used through exercise performance and peak VO2. Peak VO2 improves sensitivity of recovery assessment and is a good predictor of survival [5]. A peak VO2 more than 15 mL · kg–1 · min–1 during off-pump test could be a good end point to achieve successful explantation.
Most studies assessed cardiac recovery after repeated off-pump tests without progressive cardiac reloading [1, 2]. However, the on/off technique exposes the heart to acute changes from total unloading to full loading. Dramatic changes in cardiac status may lead to unsuccessful recovery [6]. Slaughter and colleagues [5] have suggested that gradual reloading of the ventricle would avoid sudden increase in wall stress and stretching of the myocyte.
Peak VO2 during partial assistance or short periods of off-pump measures actual exercise capacity. On the 100th PID in this case, VO2 was 23 mL · kg–1 · min–1 during full assistance, and only 13.7 mL · kg–1 · min–1 during partial assistance, a change that might predict unsuccessful explantation [6]. However, performance improved over time, and the VO2 increased markedly within 2 months as an effect of training or myocardial recovery, or both. VO2 improvement may be more sensitive than an arbitrary cut-off VO2 value to predict successful weaning.
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References
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- Young J.B. Healing the heart with ventricular assist device therapy: mechanisms of cardiac recovery. Ann Thorac Surg 2001;71(Suppl):S210-219.[Abstract/Free Full Text]
- Sliwa K., Skudicky D., Bergemann A., Candy G., Puren A., Sareli P. Peripartum cardiomyopathy: analysis of clinical outcome, left ventricular function, plasma levels of cytokines and Fas/APO-1. J Am Coll Cardiol 2000;3:701-705.
- Frazier O.H., Myers T.J. Left ventricular assist system as a bridge to myocardial recovery. Ann Thorac Surg 1999;68:734-741.[Abstract/Free Full Text]
- Slaughter M.S., Silver M.A., Farrar D.J., Tatooles A.J., Pappas P.S. A new method of monitoring recovery and weaning the Thoratec left ventricular assist device. Ann Thorac Surg 2001;71:215-218.[Abstract/Free Full Text]
- Mancini D.M., Beniaminovitz A., Levin H., et al. Low incidence of myocardial recovery after left ventricular assist device implantation in patients with chronic heart failure. Circulation 1998;98:2383-2389.[Abstract/Free Full Text]
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Abstract
Introduction
