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Ann Thorac Surg 2000;69:1146-1151
© 2000 The Society of Thoracic Surgeons
a Division of Cardiovascular and Thoracic Surgery, University of Minnesota Hospital and Clinic, Minneapolis, Minnesota, USA
Address reprint requests to Dr Park, Division of Cardiovascular and Thoracic Surgery, University of Minnesota, Box 207, 420 Delaware St SE, Minneapolis, MN 55455
e-mail: parkx021{at}maroon.tc.umn.edu
| Abstract |
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Methods. From April 1995 to March 1998, 7 patients were identified as having AMI associated with cardiogenic shock. All received intraaortic balloon pump assistance, in addition to maximal inotropic support.
Results. The mean preoperative cardiac index was 2.0 ± 0.3 L/min/m2 and pulmonary capillary wedge pressure was 23 ± 6 mm Hg. Three patients received thrombolytic therapy and 4 patients underwent percutaneous transluminal coronary angioplasty without success. Left ventricular assist devices (LVADs) were implanted as bridge therapy to heart transplantation. One patient died from recurrence of a ventricular septal defect during LVAD support. Six patients were transplanted successfully after mean LVAD support of 59 ± 33 days. Five patients are alive and well at a mean follow-up of 898 ± 447 days. One patient died 3 days after transplantation from acute allograft dysfunction.
Conclusions. Timely application of LVADs as bridge therapy to heart transplantation in these critically ill patients can be lifesaving, and should be investigated further.
| Introduction |
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| Patients and methods |
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All 7 patients with cardiogenic shock (2 women, 5 men) were referred from outlying community hospitals. Tables 1 and 2 list the patient characteristics. The mean (± standard deviation) age was 53 ± 9 years (range 37 to 63). Mean body surface area was 1.9 ± 0.3 m2 (range 1.4 to 2.2). Before LVAD implantation, all patients received two or more inotropic agents and intraaortic balloon pump (IABP) assistance in an attempt to maintain a cardiac output compatible with life. Their mean preoperative cardiac index while on IABP support was 2.0 ± 0.3 L/min/m2 (range 1.6 to 2.5), and the average pulmonary capillary wedge pressure was 23 ± 6 mm Hg (range 12 to 33). The mean pulmonary artery pressure was 32 ± 4 mm Hg and the mean right atrial pressure was 14 ± 2 mm Hg. Three patients had had previous myocardial infarctions in addition to coronary artery bypass grafting (CABG) operation before AMI presentation. Six underwent diagnostic cardiac catheterization at the time of AMI. One had a recent catheterization, which demonstrated nonoperable coronary vasculature a few weeks before admission. Four patients had emergent percutaneous transluminal coronary angioplasty (PTCA), and 3 received thrombolytic therapy without success. Three patients suffered one or more episodes of cardiac arrest, but were successfully resuscitated. All of the patients required mechanical ventilation for hypoxia and/or respiratory distress. One patient required extracorporeal membrane oxygenation (ECMO) support before LVAD implantation.
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LVAD implantation was performed within 3.9 ± 2.6 days (range 1 to 9) of the initial AMI. Transesophageal echocardiography was performed routinely at LVAD implantation. Routine perioperative antibiotic prophylaxis was given. Inotropic support was weaned approximately during the postoperative period. The anticoagulation regimen included one aspirin per day. The patients underwent progressive cardiac rehabilitation before being relisted for heart transplantation.
The Heartmate LVAD was implanted in an intraperitoneal location in 6 and in an extraperitoneal position in 1 patient. Surgical techniques have been described elsewhere [2]. We made some modifications in techniques to deal with the friable nature of the acutely infarcted myocardium. In all patients presenting with AMI, we electively arrested the heart with cardioplegia. Often it was difficult to identify the extent of infarcted tissue. The left ventricular apex was chosen as the site of inflow cannula insertion. A large donut-shaped strip of Teflon (Impra Inc, subsidiary of L.R. Bard, Tempe, AZ) felt (2 cm) was used to reinforce the suture line. Horizontal mattress sutures of 2-0 nonabsorbable material were placed through both the Teflon felt and the full thickness of the left ventricular wall. This approach allowed for distribution of tension over a large area of the suture line, thus avoiding tearing of the friable myocardium.
The outflow conduit was anastomosed end-to-side to the ascending aorta while the aortic cross-clamp was still in place. Care was taken to avoid damage to patent coronary artery grafts. Three of our patients had previous CABG operations. In these cases it was possible to anastomose the outflow conduit to the aorta without having to reposition the proximal anastomoses of the previous coronary bypass grafts.
| Results |
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The complications associated with LVAD implantation are listed in Table 3. These included urinary tract infections in 2, pneumonias in 2, and central line infection in 1 patient. One of the patient suffered from Staphylococcus epidermis bacteremia, which was due to a peri-LVAD abscess noted at the time of LVAD explanation for heart transplant. This occurred in a patient who had the device implanted extraperitoneally. The infection was eradicated with long-term intravenous antibiotic treatment after device removal and heart transplantation. Cerebrovascular accident on postoperative day 1 was noted in 1 patient. She suffered a cardiac arrest prior to LVAD implantation. Currently, she has mild residual impairment in speech. One patient developed acute renal failure and required hemodialysis. This patient required ECMO support prior to LVAD implantation for profound hypoxia and metabolic acidosis. He also experienced a malignant ventricular arrhythmia on postoperative day 2, necessitating electrical cardioversion. One patient had a mild episode of pancreatitis, documented by elevation of serum amylase and lipase. Mediastinal reexploration for postoperative bleeding was required in 1 patient who received thrombolytic agents, angioplasty, and abciximab (ReoPro). This same patient also required thromboembolectomy of the right lower extremity for ischemia, a complication of IABP placement.
| Comment |
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Many circulatory assist devices are now available. These include the HeartMate 1000 LVAD, Norvacor Left Ventricular Assist System (Baxter Healthcare Corp, Oakland, CA), Thoratec Ventricular Assist Device (Thoratec Lab Co, Berkeley, CA), centrifugal pumps, and the total artificial heart. These devices are available for various indications such as postcardiotomy ventricular failure, cardiac transplant rejection or primary graft failure, myocarditis, postpartum cardiomyopathy, and idiopathic hypertrophic subaortic stenosis. The most common indication for the implantable LVAD is bridge therapy to heart transplantation in chronic heart failure patients. The experience is expanding rapidly, and favorable outcomes are noted in patients with IDCM and end-stage ischemic cardiomyopathy. The success rates for bridge therapy to heart transplantation are 65% to 91%, and the subsequent discharge rates after transplantation are 72% to 93% [36, 11].
In light of such success with LVAD in patients with chronic cardiomyopathy, we hypothesized that the outcome of patients with AMI in cardiogenic shock could be improved with timely implantation of LVAD as a bridge-to-heart transplantation. The first reported use of a LVAD as a bridge-to-heart transplantation in a patient with an AMI in cardiogenic shock was with a Thoratec Pierce-Donachy device [12]. The patient underwent successful heart transplantation after 2 days of systemic mechanical circulatory support. Other authors have included their experiences with AMI patients as small parts of a larger body of experience, as shown in Table 4 [5, 11, 1320].
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The HeartMate IP LVAD was employed in our experience. According to the HeartMate Data Registry [G. Heatley, 1998], from 1986 to 1998, 41 patients (5% of the total number of Heartmate IP patients) were supported with this implantable pneumatic device for AMI. It is unclear, however, what proportion of these patients was in cardiogenic shock. Twenty-five (61%) were successfully bridged to heart transplantation. Our success rate with LVAD implantation was 86% in 7 patients with AMI in cardiogenic shock. This result is comparable to those reported in patients with chronic cardiomyopathy who underwent bridge therapy. With timely application of the LVAD, normal hemodynamic status was restored early, and none of the patients suffered irreversible failure of other organs due to persistent cardiogenic shock. After the implantation of the LVAD, patients underwent extensive cardiac rehabilitation and were not placed on active heart transplantation status until they demonstrated good functional capacity on a treadmill.
Early in the experience of the HeartMate, AMI was considered an exclusion criteria for LVAD implantation for fear of left ventricular disruption upon insertion of the inflow cannula and poor filling from the small acutely infarcted left ventricle [5]. We have not had a problem with left ventricular cannulation, despite the friable nature of the acutely infarcted myocardium. Recently, the Thoratec biventricular assist device has become available at our institution. In a situation where cannulation of the left ventricle cannot be accomplished, left atrial cannulation can be performed instead using the Thoratec device.
Several small, nonrandomized series have demonstrated reasonable survival rates, ranging from 45% to 91%, for patients with AMI in cardiogenic shock who undergo emergent surgical revascularization [7, 8]. Because of severely diseased native coronary vessels or previous bypass grafts, only 1 of the 7 patients in our series underwent a one-vessel coronary bypass graft to the right coronary system, in addition to LVAD placement.
Left ventricular assist devices have been shown to improve the cardiac function of the native heart [21]. A few series reported on successful LVAD explantation in patients with chronic heart failure. Müller and colleagues reported a 29% explantation rate (5 out of 17 patients) with dilated cardiomyopathy [22]. Only one patient (4%) underwent successful LVAD explantation in the series reported by Chen and associates [20]. Mancini and colleagues also reported a significantly lower rate of weaning from LVAD (5 out of 111 patients) [23]. Our experience with LVAD weaning is similar to that of Mancini. We have performed only one successful explantation in a patient with dilated cardiomyopathy. The patient subsequently died of a malignant arrhythmia several weeks after explantation. Myocardial recovery seems to occur in a subgroup of patients during LVAD support. However, a small fraction of the patients with AMI may tolerate LVAD explantation. No patient in our current series tolerated LVAD weaning when judged by vital signs and by echocardiographic evaluation of the native left ventricular function during a prolonged period of LVAD venting.
The incidence of right ventricular dysfunction following LVAD implantation has been reported in the range of 11% to 23% [6, 24]. Right ventricular failure during LVAD support is correlated with increased morbidity and mortality. Nakatani and colleagues reported on three predictors of right ventricular dysfunction (mean right arterial pressure
20 mm Hg and transpulmonary gradient
16 mm Hg before LVAD implantation and an acute decrease in mean pulmonary artery pressure
10 mm Hg after LVAD placement) [25]. In the series by Chen and associates, the incidence of RVAD implantation in AMI patients was 12% [20]. In our study population, none of the patients suffered from post-LVAD right ventricular failure, which we defined as the need for RVAD implantation. This is not unexpected however, because the myocardial infarctions involved mostly the left ventricle. Right ventricular function was spared in this group of patients once left ventricular function was supported with the LVAD. None of our patients met any of the criteria set forth by Nakatani and colleagues. The patient population studied by that group of investigators included patients with dilated cardiomyopathy and end-stage ischemic cardiomyopathy. Whether those criteria can be applied to patients with AMI is unclear.
The optimal timing for LVAD implantation following the AMI has not been well-defined. Chen and colleagues compared early (< 2 weeks) against late (> 2 weeks) LVAD implantation following AMI [20]. In that series, patients who had early LVAD implantation appeared to have a lower mortality rate. The patients in our series underwent LVAD implantation within 1 to 9 days of AMI presentation. We believe that the LVAD should be implanted before the development of irreversible end-organ failure.
The 1 patient in our series who did not survive LVAD implantation suffered from a massive AMI that was complicated by ventricular septal rupture. This patient underwent successful LVAD implantation and velour patch closure of the VSD. However, he subsequently expired from a high-flow, right-to-left shunt after recurrence of the VSD. This is a difficult problem, and clinical experience regarding the use of LVAD in this scenario is lacking. Noda and colleagues reported on 3 patients whose AMIs were complicated by ventricular septal perforations. Following LVAD support, 2 patients could be weaned and were discharged from the hospital [16]. Caution should be exercised if LVAD bridge therapy is contemplated for a patient with AMI and a concurrent VSD.
Patients in cardiogenic shock due to AMI who do not respond to optimal conventional therapy may be candidates for LVAD bridge therapy to heart transplantation. The LVAD can be safely implanted into the friable acutely infarcted myocardium. Right ventricular function is often spared in this group of patients once left ventricular function is supported by the LVAD. Further studies need to be done to evaluate the efficacy of LVAD weaning in patients with AMI. Timely application of LVADs as bridge therapy to heart transplantation in patients in cardiogenic shock due to AMI, before the development of irreversible end-organ failure, can be lifesaving.
| References |
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