European Heart Journal Advance Access originally published online on May 17, 2006
European Heart Journal 2006 27(13):1550-1557; doi:10.1093/eurheartj/ehl006
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Clinical impact of direct referral to primary percutaneous coronary intervention following pre-hospital diagnosis of ST-elevation myocardial infarction
1 Institute of Cardiology, Azienda Ospedaliera S. Orsola-Malpighi Hospital, University of Bologna, Via Massarenti 9, 40138 Bologna, Italy
2 118 Emergency Medical Service, Maggiore Hospital, Bologna, Italy
Received 23 November 2005; revised 27 March 2006; accepted 6 April 2006; online publish-ahead-of-print 17 May 2006.
* Corresponding author. Tel: +39 (0) 516364477; fax: +39 (0) 51344859. E-mail address: paortol{at}tin.it
See page 1515 for the editorial comment on this article (doi:10.1093/eurheartj/ehl064)
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Abstract |
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Aims Treatment delay is a powerful predictor of survival in ST-elevation myocardial infarction (STEMI) patients undergoing primary percutaneous coronary intervention (PCI). We investigated effectiveness of pre-hospital diagnosis of STEMI with direct referral to PCI, alongside more conventional referral strategies.
Methods and results From January 2003 to December 2004, 658 STEMI patients were referred for primary PCI at our intervention laboratory. Three predefined referral routes were compared: (1) for patients within 90 min drive of the PCI centre, pre-hospital diagnosis and direct transportation (n=166), (2) diagnosis at the interventional hospital emergency department (n=316), (3) diagnosis at local hospitals before transportation (n=176). Pre-hospital diagnosis was associated with more than 45 min reduction in treatment delay (P=0.001). No significant difference in in-hospital mortality was apparent in the overall study population. In the cardiogenic shock subgroup (n=80), pre-hospital diagnosis was associated with a two-thirds reduction in in-hospital mortality (P=0.019); mortality was only 6.2% in shock patients who underwent PCI in <2 h.
Conclusion This study shows that pre-hospital diagnosis can provide a reduction in primary PCI treatment delay, and suggests the hypothesis that this referral strategy might provide survival benefits to patients with cardiogenic shock.
Key Words: Myocardial infarction • Angioplasty • Transluminal • Percutaneous coronary • Shock
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Introduction |
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Percutaneous coronary intervention (PCI) is an effective procedure for re-establishing coronary artery perfusion in ST-elevation myocardial infarction (STEMI). A metanalysis of 23 randomized trials supports the superiority of PCI over thrombolysis for treatment of STEMI.1 In 2003, the European Society of Cardiology Task Force on the Management of Acute Myocardial Infarction stated that PCI is the preferred therapeutic option when it can be performed by an experienced team within 90 min of the first medical contact.2 Time from onset of symptoms to balloon inflation seems to correlate directly with 1-year mortality rates.3 Furthermore, the survival benefits associated with PCI may be lost if door-to-balloon time is delayed for more than 1 h with respect to tissue plasminogen activator therapy door-to-needle time.4 These and other5 findings underline the importance of reducing the treatment time in order to maximize the clinical effectiveness of primary PCI. A pre-hospital diagnosis strategy could help reduce treatment delay. Herein, we investigate the impact of ambulance-based pre-hospital diagnosis of STEMI followed by direct referral to the PCI intervention laboratory on in-hospital mortality rates and treatment delay, as compared with more conventional referral strategies.
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Methods |
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Setting and referral routes
The Italian province of Bologna (3702 Km2) contains about 915 200 inhabitants. Systematic use of PCI for STEMI patients began in January 2003 in the context of the PRIMA RER project set up by the Regione Emilia Romagna (http//:www.regione.emilia-romagna.it/agenziasan/index.htm, accessed September 27, 2005). The province contains two centrally located PCI intervention laboratories (one at S.Orsola-Malpighi hospital), which are available at short notice on a 24 h basis, in addition to nine local hospitals without PCI facilities. Each intervention laboratory has a distinct hub-and-spoke catchment zone. Since June 2003, an innovative referral system has been implemented, whereby all STEMI patients who call the ‘118 Emergency Medical Service’ from a location within about 90 min drive from a PCI centre are directly transported to the intervention laboratory after pre-hospital, ambulance-telemedicine diagnosis (previously, patients were transported to the nearest hospital for diagnosis). In particular, ambulance personnel (one physician and two paramedics) first perform the diagnostic ECG at patient's home (LIFE-PAK 12, Medtronic Physio-control, Redmond, WA, USA). The trace is then transmitted via GSM network to a dedicated computer at the appropriate intensive care unit, where a cardiologist is on-hand to provide confirmation of the diagnosis. In cases of confirmed diagnosis of STEMI, the patient is immediately transferred to the intervention laboratory. Outside normal hours, if interventional staff were not ready in the catheterization laboratory at the ambulance arrival, patient monitoring and pharmacological treatments were performed by physicians and nurses of the intensive care unit.
For the remaining patients, referral to PCI continues to be based on more conventional strategies. In particular, patients who spontaneously present at the emergency department (ED) of a PCI centre are transferred to the intervention laboratory on diagnosis of STEMI. Patients who spontaneously present at local hospitals are transported to the nearest intervention laboratory on diagnosis of high-risk STEMI;6 non-high risk patients generally receive thrombolytic treatment, but some may also be directly referred to PCI at clinicians' discretion. Finally, patients who call the emergency service from distant locations (>90 min drive from the intervention laboratory) receive pre-hospital thrombolytic treatment and are then referred to a PCI centre for further evaluation. These referral strategies all received prior approval from the regional Ethics Committee.
Study design and selection criteria
This registry study was based on a prospectively assembled database dedicated to the contribution of S. Orsola-Malpighi hospital to the PRIMA RER project. This database contains demographic information and comprehensive clinical, ECG, and procedural data (including treatment delay); institutional follow-up data are systematically updated. The study period comprises the years 2003 and 2004. This analysis regards all patients directly referred to primary PCI at the S. Orsola-Malpighi intervention laboratory due to STEMI either (1) within 12 h of self-reported onset of symptoms, or (2) beyond this time limit in the presence of symptomatic/ECG evidence of continuing ischaemia with onset prior to hospital admission (patients who developed STEMI after hospital admission were excluded). No restriction based on age, sex, or clinical status was applied. Informed consent (for PCI, participation in the study protocol and anonymous publication of scientific data) was systematically sought whenever possible; in line with national practice, patients in coma or cardiogenic shock were treated and are anonymously reported in the study (no patient was excluded due to lack of informed consent).
Analysis was based on comparison of the outcomes associated with the three possible referral routes (Figure 1): i.e. (1) following pre-hospital, ambulance-telemedicine diagnosis; (2) via the institutional ED; (3) via a local hospital. Main outcome measures were (1) treatment delay, define as time to PCI from self-reported onset of symptoms, (2) all-cause in-hospital mortality (from any cause, either in the hospital where the patient was treated or after transferral). A decision to perform a subgroup analysis of patients with cardiogenic shock was taken before the protocol was implemented.
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STEMI diagnosis
STEMI was defined as significant ST-elevation (in two adjacent leads and
0.1 mV in leads I–III, aVF, aVL, V4–V6, and 0.2 mV in leads V1–V3), as recorded in a pre-hospital ECG or the first ECG obtained at the hospital of admission.2 PCI was performed within 12 h of self-reported onset of symptoms, or later in the presence of symptomatic/ECG evidence of continuing ischaemia.
PCI protocol
No restriction based on age, sex, or clinical status was applied. Before PCI execution, all patients received aspirin (250 mg iv) and heparin (5000 IU iv) and use of platelet Gp IIb/IIIa inhibitors, ß-adrenergic blocking agents, and nitrates was strongly encouraged; heparin administration was continued for 24 h after PCI in any patients who did not receive Gp IIb/IIIa inhibitors. For practical reasons, the timing of medication varied between the different routes. All patients arriving via the ED route received heparin and aspirin before transfer to the catheterization laboratory. In the pre-hospital diagnosis route, patients only received aspirin during transportation (due to lack of ambulance refrigeration facilities at the time of the study). At local hospitals, most patients were treated with a more complete therapy constituted by aspirin, heparin, and Gp IIb/IIIa inhibitors before transportation. When not previously administered, heparin (and Gp IIb/IIIa inhibitors when not contraindicated) was always given in the interventional laboratory before PCI. After PCI, ticlopidine or clopidogrel was administered to patients receiving stents. Creatinine kinase level and myocardial band isoenzyme were measured every 8 h for the first 24 h after the STEMI onset.
Angiography and diagnostic definitions
All angiograms were independently reviewed by three experienced investigators (P.O., S.S., and F.B.) who were blinded to all data apart from the coronary angiogram; differences were resolved by group discussion. Culprit vessel TIMI (Thrombolysis In Myocardial Infarction) flow grades were assessed before and after the PCI procedure.7 TIMI risk index8 was calculated using the equation: [heart ratex(age/10)2]/systolic blood pressure.
Presence of one or more of the main risk profile criteria proposed by TIMI investigators (age 70, anterior STEMI, heart rate 100 beats/min on admission) was used for stratification of patients into ‘low-risk’ and ‘non-low-risk’ subsets.9 In all three groups of patients, diagnosis of cardiogenic shock was made in the catheterization laboratory before PCI or implantation of the aortic balloon pump. Cardiogenic shock was defined as persistent systolic blood pressure <90 mmHg, unresponsive to iv fluid administration (or need for vasopressor agents to maintain systolic pressure 90 mmHg), secondary to left or right ventricular dysfunction.10 Treatment delay (ischaemic time) was defined as the time interval (minutes) between the onset of symptoms and first balloon dilatation. All patients received two-dimensional echocardiographic evaluation within the first 24 h after PCI to assess the left (LVEF) and right ventricular ejection fractions (RVEF) and to exclude any mechanical complication.
In-hospital mortality data collection
Mortality data within the intervention hospital were available from the main database, which also provided systematic information on dismissals and transferral to patients' local hospitals. Data regarding mortality in patients' local hospitals were systematically collected by telephone (from May 2005).
Statistical analysis
Categorical data were expressed as numbers (percentages), continuous variables as median (25–75th percentiles). For group comparisons, analysis of Kruscal–Wallis was used for continuous variables and the 
2 test for categorical variables. Multivariable logistic regression analysis was performed to determine predictors of in-hospital all-cause mortality in the whole study population. A separate logistic regression analysis was tentatively performed for the subgroup of patients with cardiogenic shock. In both cases, the following variables were examined at univariate analysis: age (continuous variable); male gender; heart rate (continuous variable); smoking history; family history of cardiovascular accident (stroke/MI/cardiovascular death); diabetes; hypertension; dyslipidaemia; previous MI; previous PCI; previous CABG; anterior MI site; cardiogenic shock; post-PCI LVEF 
35%; multivessel disease; TIMI risk index (continuous variable); ‘non-low’ patient risk; treatment delay (continuous variable); pre- and post-procedural culprit vessel TIMI flow grades (for both variables 2–3 vs. 0–1); culprit vessel treated; multivessel treatment; administration of Gp IIb/IIIa platelet inhibitors; administration of ß-blockers; PCI referral route (ED or local hospitals vs. pre-hospital-diagnosis). Correlations among variables were determined by Spearman's correlation test. No correlated variables reaching P<0.05 at univariate analyses were included in the multivariable logistic regression analysis. Model discrimination was assessed with the c-statistic, and model calibration was assessed with the Hosmer–Lemeshow statistic. To assess linearity, we categorized continuous variables as intervals and performed the score test for trend of odds on the proportions of death at each interval (using STATA 7.0). All statistical analyses were performed using SPSS for Windows, release 12.0 (SPSS Inc, Chicago, IL, USA). All P-values refer to two-tailed tests of significance; P<0.05 was considered significant.
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Results |
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Characteristics of the study population
In the study period (January 2003 to December 2004), a total of 730 patients with STEMI within 12 h from onset of symptoms (or longer in the presence of persisting ischaemia) underwent PCI at our Institute. Of these, 658 patients satisfied the eligibility criteria (after exclusion of 39 patients who underwent rescue PCI and 33 who developed STEMI after hospital admission). Table 1 reports the basal clinical characteristics and risk factors of the 658 eligible patients according to PCI referral route (pre-hospital, ambulance-telemedicine diagnosis, n=166; via ED of PCI centre, n=316; via local hospitals, n=176). The recommendation to local hospitals to preferentially send high-risk patients to the PCI centres can explain the higher incidence of anterior myocardial infarction in this referral route. In other respects, the clinical characteristics of patients referred via the pre-hospital diagnosis route appeared to be similar or worse (in terms of frequency of cardiogenic shock) than those in the other two groups. As regards angiographic and procedural characteristics (Table 2), the main difference between the three groups regarded pre-procedural TIMI flow: the pre-hospital-diagnosis route was associated with a high frequency of unfavourable TIMI flow (probably due to both the shorter treatment delay and the unavailability of heparin and Gp IIb/IIIa platelet inhibitors in ambulances during the study period). Analogous data regarding the subgroup of patients with cardiogenic shock (n=80) are reported in Table 3: the only factors that appeared to be more favourable for patients referred by the pre-hospital-diagnosis route were a higher proportion of men, a lower proportion of patients with post-PCI LVEF
35%, and a somewhat lower TIMI risk index.
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Treatment delay
In the overall study population, treatment delay was different among the three referral routes, with the pre-hospital diagnosis route showing the shortest time: 146 (108.2–214.5) vs. 191 (135–318.7) min for ED route and 236 (163.7–363.2) min for referral via local hospitals (P=0.001) (Table 1). These treatment delay differences were broadly reflected within the subgroup of patients with cardiogenic shock: 155 (117.5–216) vs. 216 (154–300) min for ED route vs. 230.5 (185–308) min for referral via local hospitals (P=0.01)(Table 3).
In-hospital mortality
Figure 2 summarizes in-hospital mortality according to referral route in the overall study population and in the subgroups of patients with and without laboratory diagnosed cardiogenic shock. Overall, the in-hospital all-cause mortality associated with the pre-hospital diagnosis route was about 35% lower than those recorded for either of the other two routes, but this difference was not statistically significant (8/166, 4.8% for pre-hospital route vs. 23/316, 7.3% for ED route vs. 13/176, 7.4% for local hospitals route; P=0.537). The number needed to treat (NNT) to prevent a death using the pre-hospital diagnosis route was 40 when compared with the ED route and 39 in comparison with the local hospitals route. Within the subgroup of patients with cardiogenic shock, those referred by pre-hospital diagnosis showed about 65% lower in-hospital mortality with respect to either of the other two routes (4/29, 13.8% for pre-hospital route vs. 13/27, 48.1% for ED route vs. 9/24, 37.5% for local hospitals route; P=0.019). This translates into a NNT to prevent a death of three when compared with the ED route and four in comparison with the local hospitals route. As expected, treatment delay was longer in patients from the overall study population who died during hospitalization (n=44) as compared with patients who reached discharge (n=614) (347±50.6 min vs. 264±9.5 min, P=0.03). Figure 3 depicts in-hospital mortality within the cardiogenic shock subgroup after stratification by 2 h intervals in treatment delay (the differences almost reached significance). Of note, the cardiogenic shock patients treated within the first 2 h showed remarkably low in-hospital mortality (6.2%).
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Analysis of predictors of in-hospital mortality
Factors associated with in-hospital mortality at univariate analysis of the entire study population are shown in Table 4. Of note, no association with in-hospital mortality was apparent for either anterior site of STEMI (P=0.59) or referral route (P=0.54). Independent predictors of in-hospital all-cause mortality in the entire population were age, cardiogenic shock, post-procedure TIMI flow 2–3, and lack of administration of Gp IIb/IIIa inhibitors (Table 4). The predictive accuracy of the model correlated well with the observed events (94.7% correct classification; c-statistics =0.853; Hosmer–Lemeshow goodness-of-fit, P=0.515).
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A tentative analysis was also performed in patients with cardiogenic shock (Table 5): independent predictors of death were treatment delay
120 min, post-PCI LVEF 35%, multivessel disease, and lack of administration of Gp IIb/IIIa inhibitors (PCI referral route was not entered in the multivariable model because of co-linearity with treatment delay). The predictive accuracy of the model correlated well with the observed events (87.8% of correct classification, c-statistics=0.892, Hosmer–Lemeshow goodness-of-fit P=0.798). Of note, treatment delay turned out to be a very strong predictor of in-hospital mortality within the cardiogenic subgroup (OR 30.11; 95% CI, 1.18–767.06; P=0.04).
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Discussion |
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This study provides suggestive evidence that implementation of an ambulance-based (telemedicine) strategy for pre-hospital diagnosis of STEMI followed by direct transportation to a regional intervention laboratory (within a 90 min drive) can lead to a significant reduction in PCI treatment delay in a real-world setting. Previous studies indicate that an innovative strategy of pre-hospital diagnosis and direct referral to the intervention laboratory can reduce treatment delay with respect to either the ED route 11 or referral via local hospitals,12 and the findings from this larger study support these concepts. Average reductions in treatment delay appeared to be about 45 min as compared with the ED route (within the interventional hospital setting) or, in line with previously reported data,12 as much as 90 min with respect to local hospital admission and inter-hospital transportation. Some of these time savings can likely be attributed to quicker reaction times among patients who tend to call the emergency services12 (unfortunately our database is not informative on this point). Patients admitted to local hospitals experienced longer delays (median, 97 min) between ECG and first balloon dilatation than those recommended by American and European guidelines 2,13 or recorded during randomized trials.14 This frustrating finding can almost certainly be attributed to the intrinsic difficulty to reduce delays in a real-world inter-hospital transportation strategy. In our province (with a network organization strategy) the average delay was less than in the large NRMI (National Registry of Myocardial Infarction)-3/4 study, where the median total door-to-balloon time for transfer patients undergoing primary PCI was 180 min and only 4% were treated within 90 min.15
To our knowledge, the present report provides the first analysis of possible impact of pre-hospital diagnosis on in-hospital outcome. In the overall study population, we were unable to provide statistical demonstration of any effect of referral route or treatment delay on early mortality at logistic regression analysis. The lack of significance for these variables is unsurprising: in the literature, associations between treatment delay and mortality have emerged after a longer (1-year) follow-up,3,16 among non-low-risk patients,9,16 and especially in studies devoted to patients with cardiogenic shock.10,17–19
The evidence that reduced treatment delay is associated with important clinical benefits in patients with cardiogenic shock provided the rationale for our subgroup analysis (which was decided before the protocol was implemented). Nevertheless, we were surprised by the magnitude of the differences shown in Figure 2, which occurred despite broadly comparable values of pre-treatment clinical/angiographic variables within the cardiogenic shock subgroup for each of the three referral routes. Although this subgroup analysis can only generate hypotheses that need to be tested in specifically designed studies, it is reasonable to suppose that the survival differences within the cardiogenic shock subgroup might have been related to the much lower prevalence of depressed LVEF (35%) at completion of PCI among patients who followed the pre-hospital diagnosis route. This finding could in turn be attributed to the over 60 min average time saving associated with pre-hospital diagnosis. Remarkably, the proportion of cardiogenic shock patients who died after receiving PCI within 2 h was very low (6%). In contrast, the in-hospital mortality rate of those patients who were treated later (via any referral route) was several times higher (Figure 3) and broadly in line with rates reported in other studies.10,17–19 Moreover, in our tentative logistic regression analysis of the cardiogenic shock subgroup, 2 h treatment delay appeared to be the most powerful independent predictor of in-hospital mortality. Taken together, these observations are broadly in line with all available clinical evidence from studies focusing on this dramatic complication of STEMI.10,17–19 For example, analysis of registry data for STEMI patients with cardiogenic shock who received primary PCI indicated that ischaemic time seems to be a predictor of early and late mortality.18 Furthermore, in the SHOCK trial19 most of the benefit occurred in patients randomized to revascularization within the first 6 h from STEMI onset. On pathophysiological grounds, duration of ischaemia appears a major determinant of microvascular injury in STEMI patients20 and significant recovery of LV function after primary PCI seems to occur only in patients with very early (<2 h) coronary reperfusion.21 Of note, in our series, patients with cardiogenic shock who reached the intervention laboratory within 2 h showed a remarkably good outcome (Figure 3).
In a primary PCI setting, <2 h treatment delays can be regularly achieved only by taking advantage of the possibilities of pre-hospital diagnosis. Technically, such a referral strategy should be possible in any zone covered by a mobile phone network and an adequate territorial distribution of emergency vehicles. The major initial challenge is to set up and coordinate an effective organizational network, and clearly different geographic and infrastructure settings are likely to require different logistic solutions. As well as feasibility and cost-effectiveness, other important issues need to be confronted. Patients' contact behaviour patterns are likely to represent a major limiting factor to the global effectiveness of a pre-hospital diagnosis strategy. Most STEMI patients telephone too late (the mean delay from symptoms onset to ambulance call was 2.3 h in the GRACE registry22). Furthermore, only a minority of patients (10–48% in the REACT study23) choose to contact the ambulance service. No immediate solution to these problems may exist, as use of emergency medical systems increased sub-optimally even after public education on warning signs of STEMI.23,24
Study limitations
The results of this single-centre registry study may be influenced by several selection (referral) biases. The recommendation to local hospitals to refer high-risk patients to PCI is reflected by higher prevalence of anterior STEMI in this group (no other adverse difference in clinical and angiographic characteristics was discernible when compared with the other two groups). However, the clinical relevance of this bias is attenuated by the finding that in the overall study population, anterior site of STEMI did not appear to predict in-hospital mortality. Moreover, a further logistic regression analysis performed in the subgroup of patients with anterior STEMI (data not shown) confirmed the same set of predictors of in-hospital mortality apparent in Table 4. Another bias regards the lack of ambulance administration of heparin and Gp IIb/IIIa inhibitors, which explains the higher frequency of unfavourable pre-PCI TIMI flow in the pre-hospital group and also suggests opportunities for clinical improvements in the presence of more timely pre-treatment. A further bias regards the known tendency of sicker patients to call ambulance services, a factor that explains the high prevalence of cardiogenic shock in the pre-hospital diagnosis route. Both these findings represent negative biases potentially decreasing the favourable effect on mortality of the pre-hospital diagnosis strategy that consequently in more comparable patient groups could still turn out more effective.
The striking results regarding patients with laboratory diagnosed cardiogenic shock were generated by a numerically limited subgroup analysis (that may limit the validity of the multivariable analysis), however, the decision to perform this analysis was taken before the protocol was implemented. Therefore, the potentially relevant hypothesis that direct referral may provide major clinical benefits for patients with cardiogenic shock, needs to be tested in more adequately powered dedicated studies.
A concern regarding the pre-hospital diagnosis strategy potentially regards the potential for false-positive and false-negative initial ECG diagnosis. Although our study provides no data on this point, it should be noted that each telemedicine transmitted ECG was independently analysed both by an Emergency Medical Service physician and a cardiologist in the Intensive Care Unit before a decision for direct transfer to the intervention laboratory.
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Conclusions |
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This study indicates that pre-hospital diagnosis with direct transportation to the intervention laboratory is associated with greatly reduced treatment delay. This approach could provide a way of increasing the number of STEMI patients who can be treated with primary PCI within the accepted time delay of 90 min from the first medical contact. As regards clinical outcome, the results of the study suggest the hypothesis that a direct referral strategy might provide survival benefits to patients with cardiogenic shock. Appropriately designed and adequately powered follow-up studies are required to test this relevant hypothesis.
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Acknowledgement |
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This study was supported by the Fanti Melloni Foundation.
Conflict of interest: none declared.
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