Introduction
Cardiogenic shock (CS) is characterized by a clinical presentation of end-organ hypoperfusion, requiring intervention with vasoactive medication or mechanical circulatory support (MCS) [
1,
2]. Although CS complicates only 3–13% of acute myocardial infarction cases (AMI), it remains the leading cause of death [
2‐
6]. Despite multiple attempts to improve treatment strategies, mortality rates in acute myocardial cardiogenic shock (AMI-CS) have remained persistently around the 40–50% for years [
4,
5,
7‐
9]. Two decades ago, the SHOCK trial demonstrated lower 6-month mortality after immediate revascularization in AMI-CS patients [
10]. Recently, the DANGER shock trial reported a significant survival benefit with the microaxial flow pump, in a highly selected cohort of non-comatose AMI-CS patients with ST-elevation myocardial infarction (STEMI) [
11].
Nevertheless, vasopressors and inotropes remain the cornerstone of treatment for CS. Both the European and the American guidelines recommend noradrenaline as the first-line vasopressor, based on two randomized controlled trials (RCTs). comparing noradrenaline to both dopamine and epinephrine, but no recommendation is made on the inotrope of choice [
1,
12‐
14].
Dobutamine and milrinone are both frequently used as inotropes in the treatment of CS. Dobutamine is a synthesized catecholamine, stimulating mainly β1 receptors, exhibiting mild vasodilatory effects from β2 stimulation and α1 antagonism at low doses. Milrinone, on the other hand, a phosphodiesterase inhibitor, has inotropic and lusitropic effects, causing more pronounced hypotension due to increased vasodilation. Unlike dobutamine, milrinone does not stimulate β-receptors, lowering the risk for tachycardia and the accompanying increase of myocardial oxygen consumption [
15,
16]. This offers a theoretical advantage in preventing myocardial ischemia and arrhythmias, particularly of importance in AMI-CS patients.
The DOREMI trial (
n = 192) is the only RCT comparing the effects of dobutamine and milrinone in a CS population and reported no significant difference in primary or secondary clinical outcomes [
17]. However, since the DOREMI trial included all-comers with CS, with only a third of the participants (
n = 65) being AMI-CS patients, the effects of these two inotropes on outcomes in AMI-CS remain unclear. Therefore, we aimed to identify patient characteristics associated with treatment with milrinone and dobutamine and to assess their effects on 30-day mortality in a large real-world cohort of AMI-CS patients.
Discussion
In this observational, real-world cohort — to our knowledge the largest available cohort comparing milrinone and dobutamine treatment in patients with AMI-CS undergoing PCI — we identified baseline characteristics associated with treatment with milrinone and dobutamine and investigated their effects on 30-day mortality using propensity-score matching methods.
In the unmatched cohort (n = 739), baseline, admission and catheterization laboratory characteristics differed significantly between the milrinone group (n = 247) and dobutamine group (n = 492). Upon admission, the milrinone patients presented with significantly higher heart rates, were more likely to present with NSTEMI and a consequently longer duration of symptoms before presentation, had higher levels of creatinine and more often experienced an IHCA. In the catheterization laboratory, they were more frequently intubated prior to CCU/ICU admission. Importantly, 30-day mortality (50.6% vs. 41.5%, p = 0.018), concomitant noradrenaline and MCS usage, and the ACCS-risk scores were higher in the milrinone group, indicating that these patients were more severely ill.
After PSM on 25 variables available at the catheterization laboratory, resulting in 198 patients per group, baseline, admission and catheterization laboratory characteristics became comparable. Also, 30-day mortality rates were now similar between the groups (46.5% vs. 41.9%, p = 0.362).
Both the European and American guidelines do not recommend a specific inotrope in AMI-CS treatment [
1,
14]. The European guidelines recommend inotropes when needed to overcome the increased afterload often associated with noradrenaline use, and in patients with left ventricular systolic dysfunction, low cardiac output and low systolic blood pressure (e.g., < 90 mmHg) (14). The American guidelines suggest the addition of an inotropic agent in several CS subtypes [
1]. This latter recommendation is based on a PSM analysis, comparing CS patients who received a vasopressor alone (noradrenaline, epinephrine, and dopamine) to those receiving a combination of a vasopressor and an inotrope, in which a lower short-term mortality was observed in the combination group [
23]. The guidelines additionally recommend making the choice of inotrope based on the cause or presentation of CS; further considerations may include heart rate, systemic vascular resistance, renal function, prior β-blockade treatment and inotrope half-life [
1].
Current evidence on the selection of inotrope is limited. The DOREMI trial is the only RCT (
n = 192) comparing the effects of milrinone and dobutamine in CS patients, showing no significant differences in primary and secondary endpoints, including mortality [
17]. However, only 65 patients (33.8%) of their cohort concerned AMI-CS patients [
24]. Our study cohort and even the matched groups were substantially larger. Studies comparing milrinone to dobutamine have also been conducted in other patient populations, including a small RCT in patients awaiting cardiac transplant and an observational study of heart failure patients on chronic milrinone and dobutamine infusions [
25,
26]. Both studies reported no difference in mortality. A meta-analysis on patients with CS or a low cardiac output state, including both the DOREMI trial in CS patients and the RCT on cardiac transplant patients, along with 9 observational studies, found no survival benefit for either inotrope in the combined RCT data [
27]. However, a reduction in all-cause in-hospital mortality with milrinone was observed in the pooled data of the observational studies, most of which were of low methodologic quality. Moreover, a cohort study of patients with CS due to acute decompensated heart failure (ADHF-CS) showed a benefit of milrinone after PSM [
28]. However, AMI-CS patients were excluded from this analysis and two-thirds of those included had long-standing heart failure before admission. This type of acute-on-chronic DHF-CS involves a subacute problem with a more gradual decline and chronic compensation mechanisms, contrasting the acute presentation of AMI-CS.
Inotrope selection in AMI-CS patients remains variable in clinical practice due to limited evidence. Theoretically, milrinone is often preferred in patients with pulmonary hypertension due to its potential lusitropic effects, which reduce pulmonary artery and central venous pressures more effectively than dobutamine [
16,
29]. Milrinone may also be favored in patients at risk of tachyarrhythmias and myocardial ischemia, as it does not affect β-receptors and reduces myocardial oxygen consumption [
15,
16,
30‐
32]. Milrinone also has a more pronounced vasodilatory effect, underscored by the higher use of noradrenaline in both the unmatched and matched cohorts, though no differentiation can be made whether noradrenaline had been started before or after milrinone or dobutamine initiation. Accordingly, in bradycardic and severely hypotensive patients, dobutamine may be the preferred inotrope. Also, in cases of acute kidney injury (AKI), where milrinone accumulation is a potential concern, dobutamine may be preferred agent [
33]. A substudy of the DOREMI trial reported that milrinone was associated with lower risk of death in patients without AKI but not in those with AKI [
34].
Of note, as a result of the PSM method, the milrinone patients were matched to the sicker dobutamine patients. Among dobutamine patients in the matched cohort, this is evident by the increase in heart rate, incidence of OHCA, and number of mechanically ventilated patients. As a result, 30-day mortality is higher in the dobutamine group within the matched cohort, whereas it remains unchanged in the milrinone group.
In the matched cohort, no association was found between treatment and mortality in any of the subgroups. Even among patients who underwent PCI of the right coronary artery (RCA), who might be expected to benefit most from milrinone, no difference was observed. However, RCA infarctions can also cause both severe hypotension and atrioventricular node block, in which case dobutamine may be preferred. These nuanced distinctions cannot be assessed with the existing data in this study. In the DOREMI trial, no mortality differences were observed in a small subgroup of patients with right ventricular involvement as well [
17]. Importantly, in a sensitivity analysis excluding OHCA and IHCA patients, outcomes remained unchanged, suggesting that cardiac arrest did not drive the overall findings.
Lastly, although differences between Impella and ECMO devices in terms of hemodynamic profiles, complications and effectiveness might have influenced the comparison between milrinone and dobutamine, no significant differences in 30-day mortality were observed between devices in either the unmatched or matched cohorts. However, these findings are hypothesis generating due to low numbers of patients.
In this large national cohort of AMI-CS patients, no significant differences were found in 30-day mortality in a PSM cohort of milrinone and dobutamine patients. This is consistent with previously published small-sized data on patients with CS from various etiologies, heart failure patients, and patients awaiting cardiac transplant [
17,
25‐
27]. These findings suggest that the choice of inotrope may continue to be tailored to individual patient characteristics at the discretion of the treating physician. Additionally, in our cohort lower unadjusted mortality was reported for patients who did not receive any inotrope. Accordingly, we await the results of the DOREMI-II trial, comparing milrinone and dobutamine to placebo, revising the foundational question whether inotropes are indicated at all in the CS population, as this has never been properly established [
35].
Limitations
Our study has several limitations inherent to observational cohort studies. One limitation is that we only had access to data on whether inotropes were administered during the period prior to PCI to 24 h post PCI. Therefore, this analysis lacks data on dosages, infusion rates, and duration. Another limitation is that, despite PSM, confounding by indication cannot be eliminated, as treatment decisions were made by treating physicians based on individual patient characteristics. Additionally, data on hemodynamic measurements and arrhythmic complications were missing. Furthermore, numbers in our subgroup and device comparison analyses were small and 95% CIs were not adjusted for multiple comparisons; therefore, these results should be considered hypothesis-generating rather than conclusive regarding treatment effects. Baseline characteristics and Kaplan–Meier curves of patients treated with both milrinone and dobutamine, and no inotrope, were exploratory; no conclusions should be drawn. Moreover, a center effect, with a specific preference for one inotrope over the other, could not be identified in this cohort. Lastly, data on LVEF, RVEF, and CKMB levels were incomplete.
Acknowledgements
Members of the PCI Registration Committee of the Netherlands Heart Registration (NHR): Dr. J. M. Cheng (Albert Schweitzer ziekenhuis), Dr. M. Meuwissen (Amphia Ziekenhuis), Dr. M. Grundeken (Amsterdam UMC), Dr. R. Al Hashimi (Canisius Wilhelmina Ziekenhuis), Dr. K. Teeuwen (Catharina Ziekenhuis), Dr. M. Magro (Elisabeth-TweeStedenZiekenhuis), Dr. R. Diletti (Erasmus Medisch Centrum), Dhr. B. J. Sorgdrager (Haaglanden Medisch Centrum), Dhr. C. E. Schotborgh (HagaZiekenhuis), Dr. R. J. R. Snijder (Isala), Dr. J. Polad (Jeroen Bosch Ziekenhuis), Dr. R. Scherptong (Leids Universitair Medisch Centrum), Dr. E. Bakker (Maasstad Ziekenhuis), Prof. dr. A.J.W. van’'t Hof (Maastricht UMC+, Zuyderland Medisch Centrum), Dhr. F. Spano (Meander Medisch Centrum), Dhr. J. Brouwer (Medisch Centrum Leeuwarden), Dhr. K. G. van Houwelingen (Medisch Spectrum Twente), Dr. J. van Ramshorst (Noordwest Ziekenhuisgroep), Dr. G. Amoroso (Onze Lieve Vrouwe Gasthuis), Dhr. C. Camaro (Radboudumc), Dr. P. W. Danse (Rijnstate), Dr. K. Sjauw (St. Antonius Ziekenhuis), Dr. E. K. Arkenbout (Tergooi), Dhr. W. T. Ruifrok (Treant Zorggroep), Dr. A. O. Kraaijeveld (UMC Utrecht), Dr. E. Lipsic (Universitair Medisch Centrum Groningen), Dr. L. Hoebers (Viecuri Medisch Centrum), Dhr. R. Erdem (ZorgSaam Ziekenhuis).
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