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Ann Thorac Surg 1999;68:2181-2184
© 1999 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

Preoperative risk factors for right ventricular failure after implantable left ventricular assist device insertion

^a Departments of Biomedical Engineering, Cleveland, Ohio, USA
^b Thoracic and Cardiovascular Surgery, Cleveland, Ohio, USA
^c Cardiology, The Kaufman Center for Heart Failure, The Cleveland Clinic Foundation, Cleveland, Ohio, USA

Address reprint requests to Dr Fukamachi, Department of Biomedical Engineering/ND20, The Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, OH 44195
e-mail: fukamach{at}bme.ri.ccf.org

	Abstract

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Background. Implantable left ventricular assist device (LVAD) insertion complicated by early right ventricular (RV) failure has a poor prognosis and is generally unpredictable.

Methods. To determine preoperative risk factors for perioperative RV failure after LVAD insertion, patient characteristics and preoperative hemodynamics were analyzed in 100 patients with the HeartMate LVAD (Thermo Cardiosystems, Inc, Woburn, MA) at the Cleveland Clinic.

Results. RV assist device support was required for 11 patients (RVAD group). RVAD use was significantly higher in younger patients, female patients, smaller patients, and myocarditis patients. There was no significant difference in the cardiac index, RV ejection fraction, or right atrial pressure between the two groups preoperatively. The preoperative mean pulmonary arterial pressure (PAP) and RV stroke work index (RV SWI) were significantly lower in the RVAD group (p = 0.015 and p = 0.011, respectively). Survival to transplant was poor in the RVAD group (27%) and was 83% in the no-RVAD group.

Conclusions. The need for perioperative RVAD support was low, only 11%. Preoperative low PAP and low RV SWI were significant risk factors for RVAD use.

	Introduction

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An implantable left ventricular assist device (LVAD) has been successfully used for the treatment of end-stage heart failure, mainly as a bridge-to-heart transplant [1–7]. With a portable electric LVAD, permanent use as an alternative to heart transplant has become a realistic, ultimate goal of LVAD use. However, there are several potential complications during LVAD support, which have to be avoided to achieve this goal. These include right ventricular (RV) failure, bleeding, air embolism, multiple organ failure, thromboembolism, infection, and device failure. Among these, RV failure is one of the most serious complications because severe RV failure necessitates the use of a right ventricular assist device (RVAD) to sustain LVAD output. Even if these patients receive an RVAD, high mortality is still common. Moreover, because the mechanisms for RV failure are not known, its occurrence is generally unpredictable [1, 2].

The purpose of this study was to determine preoperative risk factors for RV failure after implantable LVAD insertion. Patient characteristics and preoperative hemodynamics were analyzed in a total of 100 patients with a HeartMate LVAD (Thermo Cardiosystems, Inc, Woburn, MA) at the Cleveland Clinic.

	Material and methods

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Device
The implantable TCI HeartMate LVAD (Thermo Cardiosystems, Inc) used in this study was either the pneumatic air-driven system (1000 IP) or the vented-electric system (V-E). The pump uses a pusher-plate mechanism with a maximum stroke of 85 mL and a maximum pump output of approximately 11 L/min. Patient selection criteria, description of the device, implantation technique, management, and indications for transplantation were published previously [1, 3].

Patients
From December 1991 to December 1996, HeartMate LVADs were implanted in a total of 100 patients at the Cleveland Clinic. A detailed description of these 100 patients was published elsewhere [8]. Briefly, the 1000 IP was used in 64 patients and the V-E was used in 36 patients. The device was used as a bridge-to-heart transplant in 97 patients, as a bridge to recovery in 2 patients, and as a permanent device in 1 patient. There were 86 males and 14 females with a mean age of 52.5 years, ranging from 27 to 70 years. The underlying diseases were ischemic cardiomyopathy in 70 patients, dilated cardiomyopathy in 25 patients, myocarditis in 3 patients, and valvular disease in 2 patients. We did not exclude any patients from LVAD implantation due to high pulmonary arterial pressure or high pulmonary vascular resistance.

To determine the preoperative risk factors for RV failure during LVAD support, we divided these 100 patients into two groups. The RVAD group consisted of the 11 patients who required additional RVAD support after LVAD insertion. The remaining 89 patients who did not require an RVAD were classified as the no-RVAD group.

Hemodynamic measurements and statistical analysis
Hemodynamics were measured with patients anesthetized for LVAD insertion. The mean pulmonary arterial pressure (PAP), the right atrial pressure (RAP), the cardiac output (CO), and the RV ejection fraction (EF) were obtained by a rapid-response thermistor pulmonary artery catheter (Swan-Ganz catheter, Baxter Healthcare Corp, Irvine, CA). The left atrial pressure (LAP) was measured by a fluid-filled catheter inserted into the LA. Transpulmonary gradient (TPG) was calculated as the difference between the PAP and the LAP. Pulmonary vascular resistance (PVR) was calculated by dividing the TPG by the CO. Pulmonary vascular resistance index (PVRI) was calculated by dividing the TPG by the cardiac index (CI). Right ventricular stroke work index (RV SWI) was calculated by the following equation:

where stroke volume index (SVI) was calculated by the CI divided by the heart rate.

Several clinical factors, that have been reported to be important in predicting RVAD use, were also evaluated. These included: presence of preoperative fever, preoperative laboratory tests for liver and renal function, and incidence of reoperation for postoperative bleeding.

Data were expressed as the mean ± the standard deviation. Statistical analysis was performed by ² test or unpaired Student’s t test. Differences were considered significant at the level of p less than 0.05.

	Results

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Table 1 summarizes the patients’ preoperative characteristics and laboratory data in each group. RVAD use was significantly higher in female patients, younger patients, and smaller patients. All 3 patients diagnosed with myocarditis fell into the RVAD group. The need for a preoperative intraaortic balloon pump (IABP), ventilator, or extracorporeal membrane oxygenation (ECMO) support were not risk factors for RVAD use. Only 10 patients did not require any mechanical or ventilatory support preoperatively, and none required RVAD insertion (p = 0.52, not significant). There was no significant difference in the preoperative body temperature between the two groups. Among the laboratory tests for liver and renal function, only aspartate aminotransferase (AST) was significantly different between the two groups.

View larger version (10K): [in this window] [in a new window]   Fig 1. The preoperative mean pulmonary arterial pressure in each group. Small triangles are individual patient data points. The closed circle and bars show the mean and standard deviation in each group. (PAP = pulmonary arterial pressure; RVAD = right ventricular assist device.)

View larger version (11K): [in this window] [in a new window]   Fig 2. The preoperative right ventricular stroke work index in each group. Small triangles are individual patient data points. The closed circle and bars show the mean and standard deviation in each group. (RV SWI = right ventricular stroke work index; RVAD = right ventricular assist device.)

	Comment

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Pulmonary hypertension with elevated PVR has been considered to be a contraindication for LVAD use because of the high risk for RV failure after LVAD insertion [3]. Our study, however, indicated that a preoperative low PAP was a significant risk factor for RVAD use. Although the mean PAP was greater than 40 mm Hg in 36% of the patients in the no-RVAD group, none of the patients in the RVAD group had a mean PAP greater than 40 mm Hg. This finding suggests that RV contractility was not strong enough in the patients in the RVAD group to elevate the PAP in the presence of a high PVR. The RV SWI data also demonstrated that if the preoperative RV SWI was greater than 300 mm Hg mL/m², none of the patients required RVAD support. There was, however, no significant difference in the RV EF between the two groups. If the RV contractility had been the same between the two groups, the RV EF should have been higher in the RVAD group, which had a significantly lower PAP, due to afterload dependence of the EF as an index of contractility. Therefore, this finding also suggests that the RV contractility was lower in the RVAD group. These findings agree with our previous report in the first 63 patients with the HeartMate LVAD [9]. In that study, the patients were divided into two groups: with or without pulmonary hypertension. We demonstrated that pulmonary hypertension was not a risk factor for RVAD use after LVAD support and that a significantly larger number of patients without pulmonary hypertension died while on support (14% versus 44%, p = 0.01). In an abstract, Levin and associates also presented that a higher RAP and lower mean PAP were associated with an increased need for RVAD support in 92 patients with the HeartMate LVAD [10].

There was no significant difference in the TPG, PVR, or PVRI between the two groups. These data indicate that the RV afterload was less crucial than intrinsic RV contractility for RV performance in patients supported by an LVAD. This may be attributable to a beneficial effect of LVAD support on RV afterload reduction [11]. In our patients series, none of the patients were treated with nitric oxide to decrease PVR, because it was not available. In fact, the PVR decreased to 2.1 ± 1.1 wood units (p < 0.0001 compared with preoperative values) at the time of heart transplantation in these patients. These findings agree with a report by Levin and associates that the preoperative PVR was not a determinant of postoperative RV failure [10].

RVAD use was also significantly higher in younger patients, female patients, and smaller patients. Interestingly, all 3 patients diagnosed with myocarditis fell into the RVAD group. The RV in these 3 patients was necrotic with very poor contraction. Since these 3 patients were female, young, and small, these factors might be biased in a data set of only 11 patients.

Although the need for perioperative RVAD support was low (11%) in our series of 100 patients, this is one of the most serious complications during LVAD support, because the survival to heart transplant was significantly lower in the RVAD group (27%) when compared with that in the no-RVAD group (83%). Frazier and associates reported clinical results for 34 patients who received the HeartMate LVAD as a bridge-to-heart transplantation [4]. Although RV function was found to improve with the HeartMate LVAD, approximately 20% of the patients experienced severe RV dysfunction after implantation. All 4 of these patients, who required right-heart assistance, ultimately died. Among the adverse effects analyzed, RV failure was the only complication that had a significantly negative correlation with the outcome. Goldstein and associates also reported that 21 of the 22 patients (95%) who required an RVAD with the HeartMate LVAD ultimately died [7]. Kormos and associates reported their successful experience with the Novacor LVAD (Baxter Healthcare Corp, Oakland, CA) as a bridge-to-heart transplantation [2]. Five (21%) out of 23 patients required mechanical RV support; 2 patients died of multiple-organ failure while on the device, and 3 others required only temporary (2–4 days) RV support and were successfully transplanted. The investigators described that there were no differences in preimplant hemodynamics or type of cardiomyopathy, which could have distinguished between those who required maximal versus those who required minimal support for the RV after LVAD implantation.

Because the reported mortality is very high with the patients who required additional RVAD support, the prediction of RV failure is very important for the selection of patients. This will be especially true when both permanent LVADs and permanent total artificial hearts (TAHs) become available as alternatives to heart transplantation in the future. Although several authors have attempted to identify risk factors for RV failure after LVAD insertion, few data are available to predict RV failure before the operation [10, 12, 13]. We have previously reported that a dilated RV with increased RV preload and afterload predisposed to RV dysfunction after LVAD implantation in our first 28 patients with the HeartMate LVAD [13]. Since the number of patients who required additional RVAD support was only 3 in that study, the patients (n = 8) who had an RAP greater than 15 mm Hg at the time of transplantation or death were also included in the RV dysfunction group. Kormos and associates recently reported that fever in the absence of infection, an increased number of perioperative blood transfusions, and an increased need for preimplant inotropic support were more predictive of the need for additional right-ventricular support than preimplantation measures of right-ventricular function or hemodynamic variables [12]. In our current study, fever was not found to be an important factor in predicting RVAD use. Among the laboratory tests for liver and renal function, only AST had a significant difference between the two groups. Although the incidence of reoperation for bleeding was significantly higher in the RVAD group in our study and others [7, 12], this is not a preoperative risk factor because bleeding happens perioperatively, postoperatively, or both.

There are several limitations in this study. Although the lower PAP and lower RV SWI in the RVAD group suggested that the RV contractility was lower in that group, we failed to demonstrate this objectively. Since the EF is known to be easily influenced by loading conditions, it would not properly evaluate the RV contractility. The slope (E_max) of the end-systolic pressure-volume relation (ESPVR) has been reported to be sensitive to the contractile state and relatively independent of the preload as well as afterload in both the LV and RV [14–16]. However, measurement of the in situ RV volume, which is necessary to obtain a pressure-volume loop, is difficult, and no ideal standard exists, due to RV complicated geometry. End-systolic pressure-area relation with echocardiographic automated border-detected RV area may be useful for clinical assessment of RV contractility [17]. A further limitation is that we did not assess the compliance of the RV, which is another important determinant for the RV performance. We have previously reported in normal dogs that LVAD support improved RV compliance due to unloading of the LV through diastolic ventricular interdependence [11].

In conclusion, the need for perioperative RVAD support was low, only 11%. Preoperative low PAP and low RV SWI were significant risk factors for RVAD use, indicating poor intrinsic RV contractility. Additional risk factors for RVAD use included being female, young, and small and having myocarditis, high AST, and low cardiac output.

	References

Top Abstract Introduction Material and methods Results Comment References

 

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Patrick M. McCarthy Nicholas G. Smedira James B. Young Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Fukamachi, K. Articles by Young, J. B. Search for Related Content PubMed PubMed Citation Articles by Fukamachi, K. Articles by Young, J. B.