Myocardial infarction (MI) complicated by cardiogenic shock (MI-CS) remains a major problem in cardiovascular medicine. Although outcomes have improved over the last 2 decades with early revascularization and modern intensive care, morbidity and mortality remain high. This review will summarize currently available evidence on the factors that influence or predict outcomes in MI-CS. A wide range of clinical, laboratory, radiologic, and angiographic variables and therapeutic approaches have been evaluated.
A comprehensive understanding of the most relevant factors may better identify an individual patient trajectory and assist in the development of management strategies, including timing, techniques, and mode of revascularization, the transfer to tertiary centers, the institution of more aggressive mechanical or pharmacological support, appropriate resource utilization, or compassionate palliative care in futile situations. This information may also facilitate discussions of prognosis with family members, provide a framework for risk stratification for future clinical trials, and be valuable for quality assessment and targeted efforts for institutions.
Studies were identified through a systematic search of the PubMed database, clinicaltrials.gov, and Cochrane database of Systematic Reviews. No limits were set on language, publication status, and start date. Randomized and nonrandomized studies were included. The literature search was performed until October 31, 2017. Titles and abstracts were screened for potentially relevant articles. All articles that reported on mortality and predictors of outcomes were reviewed. Full-length manuscripts and online appendices of relevant articles were evaluated.
Clinical History and Risk Factors
Prior MI can lead to worse outcomes in those who develop CS, presumably because of a lower reserve to tolerate additional injury. Diabetes mellitus (DM) has been identified as an independent risk factor in some studies but not in others. Anoxic brain injury, higher body mass index, cerebrovascular disease, stroke, peripheral vascular disease, history of angina, prior percutaneous coronary intervention (PCI), dialysis, and white race are other risk factors for mortality in individual studies. Different studies have shown contradictory results regarding a protective effect of either sex on mortality. Cardiac arrest, as expected, is a significant risk factor for mortality.
Echocardiographic and Other Radiologic Predictors
The Multicenter Investigation of Limitation of Infarct Size (MILIS) study, started in 1976, identified LVEF by radionucleotide ventriculogram as an independent predictor of mortality in CS. A substudy of the SHOCK trial showed that LVEF < 28% and mitral regurgitation (MR) severity (2+ or more) were the only independent echocardiographic predictors of 30-day and 1-year mortality, and there was benefit to early revascularization at all levels of LVEF and MR. In the CREATE trial, LVEF < 40% was associated with an odds ratio of 3.78 for 30-day mortality. In another study of 147 patients, patients with no, mild, moderate, and severe MR had 1-year mortality of 8%, 23%, 30%, and 58%, and each grade increase in MR was independently associated with a 71% increase in mortality after accounting for LVEF, multivessel disease, no reflow, age, gender, and prior MI.
STEMI Versus Non-STEMI
Cardiogenic shock occurs in a smaller proportion of patients with non-STEMI (NSTEMI) compared to those with STEMI, but mortality is high in either condition once shock develops. In the Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries (GUSTO) IIb trial which enrolled patients between 1994 and 1995, those with NSTEMI who developed CS were older, had a higher prevalence of diabetes and 3-vessel coronary artery disease, and less TIMI 0 flow on angiography than STEMI patients who developed shock. Shock developed at a median of 76.2 hours in the NSTEMI group compared with 9.6 hours in the STEMI group. The 30-day mortality was 10% higher in the NSTEMI shock group, and NSTEMI was an independent predictor of mortality in multivariable analysis. A report from the SHOCK trial registry revealed similar differences in baseline characteristics and also found that NSTEMI patients were less likely to undergo angiography.
Metabolic and Laboratory Derangements
Hyperlactatemia can reflect impaired tissue perfusion, intracellular metabolic derangements, and hepatic dysfunction. In one study, lactate > 6.5 mmol/L was a powerful independent predictor of 30-day mortality. In another study, each mmol increase in lactate was associated with an odds ratio of 1.14 for mortality, and fewer than 30% of patients with peak lactate >10 μmol/L survived to discharge. Lactate clearance <10% can also predict intensive care unit and 90-day mortality. Based on the available evidence, hyperlactatemia or impaired clearance with standard therapies are easily available measures that could be utilized as triage variables for more aggressive measures.
The ability to successfully restore perfusion in the infarct-related artery has been consistently shown to be a crucial determinant of in-hospital, 30-day, and long-term survival. In the SHOCK trial, 30-day survival was 65% with successful PCI and 20% with unsuccessful PCI. TIMI score ≤ 2 post-PCI had an odds ratio of 19.5 for 30-day mortality in a study of 45 patients with STEMI and CS.
Systems Of Care
Given the complexity of decision-making, the lack of an evidence base for standardized society guidelines, and multiple management approaches in MI-CS, there exists the possibility for significant heterogeneity in patient management and delays in care. Therefore, in-hospital multidisciplinary shock teams, protocol-driven management, care bundles, shock centers, and regional systems of care with clear predefined algorithms and channels of communication have been proposed as strategies to improve outcomes associated with CS. The few small studies that have evaluated these strategies have included acute MI and nonacute MI patients and have demonstrated that shock teams can decrease time to intervention and may improve mortality.
Several findings are consistently observed across many studies. Revascularization has benefit at all risk levels. Hemodynamic parameters and measures of end-organ perfusion, including lactate and creatinine, are important predictors of outcomes. Mechanical circulatory support has a role in improving outcomes, but defining appropriate population and best mode of support has been difficult. Earlier MCS appears to be beneficial, but when is too early and when is too late has not been conclusively determined and needs further study. Emerging concepts of “door-to-unloading” time and well-defined bundles of management approaches await large multicenter clinical trials.
Despite high clinical acuity at presentation, many MI-CS patients can have excellent long-term outcomes with some recovery of contractile function and physiologic accommodation. Therefore, a focus on improvement in early mortality via the thorough understanding of the inflammatory response and prevention or early reversal of end-organ dysfunction may provide these critically ill patients with improved quality and longer duration of life.