Eur J Cardiothorac Surg 2008;34:262-267. doi:10.1016/j.ejcts.2008.03.057
Copyright © 2008, European Association for Cardio-thoracic Surgery. Published by Elsevier. All rights reserved.
Impact of preoperative hemodynamic support on early outcome in patients assisted with paracorporeal Thoratec® ventricular assist device
Matthias Kirscha,*,
Emmanuelle Vermesa,
Costin Radua,
Birgit Streichb,
Kuniki Nakashimaa,
Armand Mekontso-Dessapc,
Daniel Loisancea
a Service de Chirurgie Thoracique et Cardiovasculaire, Pr. Loisance, AP-HP, Hôpital Henri Mondor, Créteil, France
b Service de Réanimation Chirurgicale, Pr. Marty, AP-HP, Hôpital Henri Mondor, Créteil, France
c Service de Réanimation Médicale, Pr. Brun-Buisson, AP-HP, Hôpital Henri Mondor, Créteil, France
Received 8 November 2007;
received in revised form 25 March 2008;
accepted 27 March 2008.
* Corresponding author. Address: 51 Avenue du Maréchal de Lattre de Tassigny, 94 000 Créteil Cédex, France. Tel.: +33 1 49 81 21 72; fax: +33 149 81 21 52. (Email: matthias.kirsch{at}hmn.aphp.fr).
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Abstract
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Background: Mechanical circulatory support has become a well-established procedure for some patients with cardiogenic shock. However, patient selection and timing of implantation remains critical. This retrospective study was undertaken to identify preoperative predictors of survival in ICU of patients requiring mechanical circulatory support. Methods: Between 1996 and 2006, 71 patients (61 men, 10 women, aged 41.6 ± 12.2 years) with primary cardiogenic shock were assisted using the paracorporeal Thoratec® VAD. Twenty-seven (38%) patients needed preoperative mechanical ventilation. Preoperative IV hemodynamic drug support included dobutamine in 63 (89%), vasopressors (adrenaline, noradrenaline or dopamine 
5 µg/kg min) in 47 (66%), and intraaortic balloon counter-pulsation in 22 (31%) patients. Mean preoperative blood creatinine and total bilirubin levels were 162.2 ± 72.4 µmol/l and 36.4 ± 53.9 µmol/l, respectively. Results: Fifty-six (79%) patients required biventricular and 15 (21%) left ventricular support. Patients were assisted for a mean duration of 73.1 ± 93.6 days (extremes, 1–480 days). Twenty-five patients (35%) died while on support. Among these, 18 patients (25%) never recovered sufficiently to allow dismissal from ICU, and died after a mean of 15.4 ± 14.3 days. Logistic regression identified preoperative IV adrenaline as sole predictor for ICU death (OR, 5.48; 95% CI, 1.45–20.7, p
=
0.012). Conclusions: The need for preoperative IV adrenaline therapy appeared to be the sole independent risk factor for death in ICU in patients assisted with the Thoratec® paracorporeal VAD. This suggests that, besides hemodynamic and metabolic consequences of cardiogenic shock, preoperative activation of the inflammatory cascade could influence the prognosis of patients undergoing mechanical circulatory support.
Key Words: Mechanical circulatory support • Cardiogenic shock • Survival • Adrenaline
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1. Introduction
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Mechanical circulatory support as a bridge to transplantation or myocardial recovery has evolved to become a well-established procedure for some patients with cardiogenic shock. Adequate patient selection and timing of implantation are among the most important factors influencing success, but remain at the same time the most difficult aspects of the procedure [1]. Thus, early postoperative death related to multiple organ dysfunction syndrome despite adequate mechanical support remains an all too common scenario.
Several studies have identified preimplantation risk factors for adverse outcome under support and screening scales to help the decision process have been proposed [2,3]. However, some of these studies are limited by the fact that they used overall mortality under support as primary end-point, irrespective of the time of occurrence of death, early in the intensive care unit (ICU) or late, after ICU discharge. Indeed, we feel that late deaths, defined as those which occur once the patients are dismissed from ICU, are not as directly related to patient selection and timing of implantation as early deaths, occurring during the initial ICU stay.
Therefore, we undertook the present study to evaluate preimplant demographic, hemodynamic and blood chemistry variables in 71 patients before mechanical assist device insertion as potential risk factors for death during postoperative ICU stay. We analyzed a relatively homogenous population of patients with primary cardiogenic shock assisted using the Thoratec® ventricular assist device (Thoratec Laboratories Corp.) at one single institution.
1.1 Patients
Between September 1996 and September 2006, 71 consecutive patients with primary cardiogenic shock were assisted using the Thoratec® paracorporeal VAD in our department. Patients with postcardiotomy shock, early cardiac allograft failure, right ventricular dysfunction after LVAD implantation or other indications were not included. The series comprised 61 men and 10 women, aged 41.6 ± 12.2 (extremes, 13.9–59.4) years. The average body surface area calculated according to the Mosteller formula [BSA (m2) = (height (cm) x weight (kg)/3600)1/2] was 1.83 ± 0.24 m2. Causes of heart failure are listed in Table 1
. Three (4%) patients had a history of previous CABG which was associated with a left ventricular restoration procedure in one patient.
1.2 Status at admission
Sixteen (23%) patients had experienced cardiac arrest within 24 h of implantation. The type and level of hemodynamic monitoring at admission varied widely between patients depending on the severity of the cardiac decompensation and local logistic issues. Thus, preoperative cardiac index values (n
= 40) were gathered from echocardiographic or pulmonary artery catheter estimations and are reported in Table 2
. Mean values of preoperative laboratory tests are provided in Table 2.
1.3 Preimplantation support
Twenty-seven (38%) patients needed preoperative mechanical ventilation initiated a mean of 2.2 ± 6.1 (extremes, 0–30) days before MCS implantation.
Preoperative intravenous hemodynamic drug support (Table 3
) was used in 70 (99%) patients. One patient suffered major ventricular arrhythmias and did not tolerate any inotropic support. Twenty-four (34%) patients were treated with a single drug, 40 (56%) patients with a combination of two drugs, and six patients (9%) received a combination of three drugs. Intravenous drugs included dobutamine in 63 (89%, mean dose 12.5 ± 5.5 µg/kg min), adrenaline in 35 (49%, mean dose 4.4 ± 5.0 mg/h), dopamine in 16 (23%, mean dose 7.6 ± 4.2 µg/kg min), phosphodiesterase inhibitors in 5 (7%), and norepinephrine in 3 (4%) patients. When used, dopamine was administered at infusion rates 5 µg/kg min in most cases (14/16 patients). Inodilator therapy was defined by administration of dobutamine and/or phosphodiesterase inhibitors (milrinone), and was used in 66 (93%) of patients. Vasopressor therapy, defined by administration of adrenaline and/or dopamine 5 µg/kg min [4,5] and/or norepinephrine, and was noted in 47 (66%) patients.
Twenty-two (31%) patients had preoperative intraaortic balloon counter-pulsation (IABC) that was initiated at a mean of 1.2 ± 1.3 (extremes, 0–5) days before MCS. However, no patient had previous hemodynamic support with a different system such as centrifugal pump or extracorporeal membrane oxygenation. In addition, no patient had hemofiltration or dialysis prior to VAD implantation.
1.4 Surgical technique
Fifty-six (79%) patients received biventricular, and 15 (21%) patients left ventricular support. This high rate of biventricular support is related to our preference for rapid biventricular support using paracorporeal volume displacement pumps in cardiogenic shock patients with end-organ failure in order to achieve complete biventricular unloading and pulsatile perfusion for optimal end-organ recovery. Thus, our indications for biventricular support included overt right ventricular dysfunction at operation and/or associated end-organ dysfunction as indicated by elevated liver enzymes and renal failure.
All devices were implanted through median sternotomy and using cardiopulmonary bypass (CPB). Mean CPB duration was 153.8 ± 61.4 min (extremes, 58–362 min). Aortic cross-clamp was used according to the operating surgeon's preference in 43 patients (61%) and averaged 64.3 ± 29.5 min (extremes, 24–175 min). In the latter patients, myocardial protection was achieved using cold crystalloid cardioplegia. Concomitant CABG was performed in three (4%) patients.
Left VADs were implanted between the left ventricular apex and the ascending aorta in all instances. Right VAD (n
= 56) inflow cannulas were placed either in the right atrium (n
= 34, 61%) or the right ventricle (n
= 22, 39%). Mean LVAD flow upon arrival in postoperative ICU was 4.9 ± 0.57 l/min. Mean LVAD flow upon arrival in ICU was significantly lower in BiVAD patients in whom right VAD inflow was placed in the right atrium than in those in whom it was placed in the right ventricle (4.6 ± 0.42 l/min vs 5.2 ± 0.51 l/min, respectively, p
< 0.001). However, this difference between both cannulation techniques (right atrium vs right ventricle) amended progressively during the immediate postoperative period (postoperative day 1, 4.9 ± 0.43 vs 5.1 ± 0.41, p
= 0.13; postoperative day 5, 5.3 ± 0.58 vs 5.3 ± 0.46, p
= 0.94, respectively).
1.5 Anticoagulation protocol
After surgery, anticoagulation was started within 8–12 h using intravenous heparin to achieve an anti-Xa activity between 0.3 and 0.4 UI/l.
Aspirin was started 24 h after surgery at a daily dose of 250 mg. Aspirin doses were subsequently adjusted to in vitro platelet function tests as reported previously [6].
Oral antivitamine K therapy was started after removal of all chest drains and extubation to maintain an international normalized ratio between 3 and 4. In the last 13 patients however, antivitamine K therapy was not introduced and replaced by subcutaneous low molecular weight heparin (enoxaparin) in order to achieve an anti-Xa activity between 0.5 and 0.6 UI/l.
1.6 Data collection
Since 2004, patient data are collected prospectively in the Henri Mondor Mechanical Circulatory Support Devices Registry. For patients implanted before this date, hospital records were reviewed and entered retrospectively into the registry. The present study was approved by our local medical ethics committee.
The primary end-point retained in the present study was death of any cause occurring during the initial ICU stay following device implantation.
Other definitions used were those of the ISHLT MCSD Database and are available at http://www.ishlt.org/mcsd.
1.7 Statistical analysis
Statistical analysis was performed using SPSS Base 12.0 statistical software (SPSS Inc, Chicago, IL). Categorical variables were expressed as percentages and continuous variables were expressed as the mean ± 1 standard deviation. Survival data were analyzed with standard Kaplan–Meier actuarial techniques for estimation of survival probabilities. Patients were censored at the time of device explantation because of weaning or transplantation.
To identify risk factors for ICU death, univariate analysis of preoperative variables was performed by comparing patients who died during their initial ICU stay with those who survived after ICU dismissal. Categorical variables were compared using the 
2 test or Fisher's exact test for small numbers (n
5). Continuous variables were compared using the Mann–Whitney test for unpaired groups in order to avoid the assumption of normality. To evaluate independent risk factors for ICU death, significant and marginally significant (p
0.1) preoperative variables were examined using backward stepwise logistic regression [7]. A subsequent, more restricted analysis was performed using only significant and marginally significant preoperative hemodynamic support variables, in order to evaluate more specifically their impact on patient outcome. Coefficients were computed by the method of maximum likelihood ratio.
A two-tailed p value of less than 0.05 was taken to indicate statistical significance.
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2. Results
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2.1 Overall survival
Patients were assisted for a total of 5193 patients-days. Mean duration of support averaged 73.1 ± 93.6 days (extremes, 1–480 days). Forty-six patients (65%) were successfully bridged to transplantation (n
= 41, 58%) or recovery (n
= 5, 7%). Actuarial estimates of survival under MCS were 76 ± 5%, 68 ± 6% and 62 ± 7% at 1–3 months after implantation, respectively.
2.2 Causes of death
Twenty-five (35%) patients died during MCS after a mean of 52.2 ± 101.9 days of support. Among these, 18 (25%) patients never recovered sufficiently to allow ICU dismissal and died after 15.4 ± 14.3 days (extremes, from 2 to 43 days). The other seven patients died after ICU dismissal at a mean of 146.7 ± 162.7 (extremes, from 30 to 480 days). Causes of death in both groups are listed in Table 4
. During the initial ICU stay, death was mainly related to MODS. After ICU dismissal, deaths were mostly related to infection and bleeding complications.
2.3 Postimplantation hemodynamics and end-organ function
Mean flow rates achieved by the left VAD and postoperative central venous pressure (CVP) on postoperative days 1, 5 and 10 were similar in patients who died in ICU and those who survived until ICU dismissal (Fig. 1
). In contrast, while renal and hepatic function progressively returned to normal in ICU survivors, end-organ function continued to deteriorate despite adequate hemodynamic support in patients who finally died in ICU (Fig. 2
).
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Fig. 1. Perioperative hemodynamics. Systemic blood flow (l/min) achieved preoperatively by the native heart or postoperatively by the left ventricular assist device (squares); and central venous pressure (CVP, mmHg, circles) in patients who survived ICU (empty symbols) and those who died in ICU (filled symbols). Error bars represent ±1SEM.
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Fig. 2. Perioperative changes in serum total bilirubin levels (µmol/l, squares) and creatinine levels (µmol/l, circles) in patients who survived ICU (empty symbols) and those who died in ICU (filled symbols). Error bars represent ±1SEM.
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2.4 Preimplantation risk factors for ICU death
Univariate analysis (Tables 2 and 3) showed that patients who died in ICU significantly differed from ICU survivors only in the type of preoperative pharmacological hemodynamic support. Patients who died in ICU were significantly more frequently supported with IV adrenaline [14/18 (78%) vs 21/53 (40%), p
= 0.007] and received less frequently IV dobutamine [13/18 (72%) vs 50/53 (94%), p
= 0.021] than those who survived ICU. Preimplantation vasopressor therapy appeared to be significantly related to ICU death [31/53 (59%) in ICU survivors vs 16/18 (89%) in patient who died in ICU, p
= 0.022].
Logistic regression performed on preoperative significant or marginally significant variables (p
0.1, Table 5
) revealed that IV adrenaline therapy was the only significant and independent predictor of death in ICU (OR for ICU death, 5.48; 95% CI, 1.45–20.70, p
=
0.012). Our subsequent analysis, restricted to preoperative hemodynamic support variables (Table 3), similarly identified preoperative IV adrenaline administration as sole independent predictor for ICU death (results not shown).
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3. Discussion
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In the present study we have analyzed preimplantation risk factors for death in ICU of patients suffering primary cardiogenic shock and undergoing MCS using the paracorporeal Thoratec® VAD. Previously identified risk factors were not found to be prognostic of adverse outcome in ICU. However, preoperative hemodynamic support using IV adrenaline appeared as the sole significant and independent risk factor for death in ICU.
Overall survival to transplantation or weaning in our patient population was similar to that reported by other groups using the same device [8–11] or to published registry data [12]. Most of the deaths in our series occurred early after implantation and before ICU dismissal, and were related to MODS. In the present study we have focused our analysis on these early ICU deaths making the assumption that they are more directly related to immediate preoperative patient status than late deaths, occurring after ICU dismissal. Although some of these ICU deaths might be considered as device-related, making a precise distinction between death strictly related to preoperative patient status, or to surgery with cardiopulmonary bypass, or to the circulatory support device, appears extremely difficult. Indeed, all three causes blend into a complex critical state and any attempt to unravel these different causes would probably lead to major selection bias. Therefore, we have chosen as primary end-point death of any cause occurring during the initial ICU stay.
Interestingly, patients aggravated and died in ICU despite adequate hemodynamics achieved under mechanical circulatory support. Indeed, LVAD flow and CVP values were similar in patients who died in ICU and ICU survivors. Furthermore, ICU survival was not influenced by uni- or biventricular support. Similarly, Masai et al. [13] have reported a group of patients under LVAD and who died from MODS after severe hepatic failure despite adequate hemodynamic support. We [14] have previously shown that some patients under mechanical circulatory support develop a drop in systemic vascular resistances in the absence of obvious infection which might be related to an ongoing systemic inflammatory response syndrome (SIRS). Indeed, patients undergoing MCS present a SIRS [15] which appears to be more pronounced at least initially, than that observed in patients undergoing conventional cardiac procedures under cardiopulmonary bypass [16]. The immediate postoperative SIRS observed in MCS recipients is the result of a complex interaction between patient-related variables (cardiogenic shock, end-stage heart failure), acute blood–biomaterial interactions on the cardiopulmonary bypass and mechanical circulatory assist device surfaces, and a multitude of biomaterial-independent variables (anesthesia, surgical procedures, hypothermia, non-pulsatile perfusion during cardiopulmonary bypass, ischemia-reperfusion injury, drugs, and blood products) [15]. Ongoing SIRS in these patients might contribute to the development of MODS [17]. Thus, patients under MCS who evolve towards MODS have been shown to have increased plasma CRP, IL-6 and IL-8 levels [13]. Moreover, increased plasma levels of IL-6 and IL-8 during support have been shown to be prognostic of death in patients undergoing MCS as a bridge to transplantation [18]. However, in patients undergoing MCS, it remains to be determined whether preoperative plasma levels of pro-inflammatory cytokines such as IL-6 are prognostic of postoperative outcome as has been shown in non-assisted patients [19,20].
In the present study, previously identified risk factors for death in patients assisted with the Thoratec® paracorporeal VAD such as older patient age [11], pre-implant mechanical ventilation [11], higher total bilirubin levels [9,11] and higher BUN [8] were not found to be significant. This might be related to the fact that our selection process takes these variables into account at least to some degree. In contrast, our study shows that ICU death was dependent on the type of hemodynamic support received before implantation. Thus, multivariate analysis revealed that the need for preoperative adrenaline therapy was the only significant and independent predictor of death in ICU. Our study being retrospective in nature, we cannot exclude the possibility that a severe unmeasured bias against patients who received adrenaline was present and which accounted for the increase in mortality in this group. Furthermore, preoperative drug administration did not follow a predetermined algorithm and might therefore be flawed by a lack of standardization in the use of catecholamines as shown by a recent French survey [21]. However, evidence from the SHOCK registry has shown that hypotensive cardiogenic shock requiring vasopressor support has also a worse prognosis than non-hypotensive cardiogenic shock [22].
The need for vasopressor support in cardiogenic shock patients might be the reflection of a more advanced and critical shock, where the classic paradigm is complicated by the occurrence of a systemic inflammatory response with inappropriate vasodilation [23]. Thus, one might reasonably expect this pre-existing inflammation to add up to the unavoidable postoperative SIRS related to VAD implantation, and to worsen patient prognosis. Furthermore, use of adrenaline might by itself have deleterious effects. Indeed, vasoconstriction induced by sympathomimetics can lead to organ perfusion mismatch, more particularly in the splanchnic area [24]. Moreover, adrenaline use is associated with several metabolic effects such as increased lactate levels, decreased arterial pH and higher blood glucose levels which might contribute to adverse outcome in these patients [24]. Finally, some studies provide evidence that the use of sympathomimetics can directly lead to enhanced systemic inflammatory response due to an increased IL-6 expression [25].
Whatever the precise mechanisms involved, the need for vasopressors in cardiogenic shock patients should be considered as a marker of disease severity. Therefore, in our opinion, these patients justify pulmonary artery catheterization to adequately assess their hemodynamic profile and the surgical team should be put on alert for an eventual device implantation. As recommended by the 2004 AHA/ACC guidelines for cardiogenic shock in ST-elevation myocardial infarction [26], first line vasopressor therapy should be dopamine followed by, if necessary, norepinephrine. The potential harmful effects of adrenaline should restrain its use to life-threatening hypotension. Moreover, the finding in our study that cardiogenic shock patients requiring vasopressor support evolve more frequently an adverse outcome despite adequate hemodynamic support, suggests that a mechanistic approach aimed at simply re-establishing perfusion is insufficient. Future research will have to evaluate more precisely the role of SIRS in the development of MODS in these patients, and develop specific therapeutic strategies.
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Abstract
1. Introduction
